JP3432991B2 - Reflective liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reflection type liquid crystal display device.

[0002]

2. Description of the Related Art In general, a liquid crystal display element comprises a pair of substrates arranged opposite to each other at a fixed distance, electrodes formed on surfaces of the substrates facing each other, and an alignment formed on the electrodes. It is mainly composed of a film and a liquid crystal material sealed between a pair of substrates. In such a liquid crystal display element, a transparent or non-transparent electrode is laminated on a substrate in a pixel portion, and an alignment film is formed on the electrode. A voltage for driving liquid crystal is applied by the electrode.

In recent years, as an active matrix type liquid crystal display element, a liquid crystal display element having a driving element such as a thin film transistor (TFT) mounted on one substrate of a pixel portion has been developed and put into practical use. In particular, a reflective liquid crystal display element that reflects light incident from one side of the substrate on the other side does not require a backlight component that consumes a large amount of power, and thus requires lower power consumption than a transmissive liquid crystal display element. Can,
Application to portable display elements is expected.

Among the constituent materials of the liquid crystal display element, the liquid crystal material functions as an optical switching element by changing its alignment / arrangement state by an externally applied electric field / magnetic field or the like and changing optical properties. are doing. Generally, a twisted nematic liquid crystal display (TN), a surface stabilized ferroelectric liquid crystal display (SSFLC), and a light component controlled by a polarizing plate are controlled by a liquid crystal arrangement to show a bright state and a dark state. Antiferroelectric liquid crystal display (AFLC)
Etc. are used. However, in these methods, the use efficiency of light is up to 50 due to the use of a polarizing plate.
%.

As a liquid crystal display element that does not require a polarizing plate, a nematic liquid crystal display element (G
HLC, GHHeilmeier and LAZanoni: Appl.Phys.Let
t.Vol.13 (1968) 91), nematic-cholesteric phase transition type liquid crystal display device added with dichroic dye (PCG
H, DLWhite and GNTaylor: Appl.Phys.Lett.Vol.45
(1974) 4718), and a polymer dispersed liquid crystal display element (PDLC, see JP-A-61-83519) that performs optical switching based on the scattering state of a liquid crystal material dispersed in a polymer material has been proposed and put into practical use. It is aimed at becoming. Further, as a display system having a higher light use efficiency than the above-mentioned liquid crystal display device, a polymer stable cholesteric liquid crystal display system (PS) in which a small amount of a polymer material is dispersed in a cholesteric liquid crystal material.
CT) has recently been announced (Japanese Unexamined Patent Publication No. 6-507505), and has attracted attention.

Among the above liquid crystal display devices, GHLC and PCGH are display devices based on light absorption (dark) / non-absorption (bright), and PDLC is light scattering (bright) / non-scattering (dark) or light scattering. The display device is based on (dark) / reflection (bright), and the PSCT is a display device based on light reflection (bright) / non-reflection (dark) or light scattering (bright) / non-scattering (dark).
In these devices, a light component that is not absorbed, scattered or reflected may exist in a single liquid crystal layer, so that the device has a multilayer structure in which another liquid crystal layer for absorbing, scattering or reflecting this light is provided. As a result, the light use efficiency can be further improved.

As a measure for improving the light use efficiency, an attempt can be made to make the ratio (aperture ratio) occupied by the display pixel electrodes on the element display surface close to 1. For example, with respect to a normal structure in which a display pixel electrode and a driving TFT thereof are juxtaposed in a substrate surface, as disclosed in JP-A-56-132387 or JP-A-56-67884,
With the structure in which the display surface element electrode covers a part or all of the driving TFT via the green layer, all the element surfaces other than the region separating the individual electrodes can be used for display. In the above-mentioned multi-layer liquid crystal display device, an electrode may be provided on the separation film separating the individual layers, and the electrode on the separation film is also provided so as to cover a part or the whole of the driving TFT. A similar effect can be expected.

[0008]

However, in the case of a structure in which a driving TFT is usually put into practical use, that is, a structure in which a control gate electrode is located below a semiconductor (channel) portion, the entire upper surface thereof is used for display. If covered with electrodes, there is a risk of malfunction. More specifically, since the channel portion of the TFT is sandwiched between the gate electrode and the display electrode, even if the gate electrode is in a low-potential state in order to maintain a pixel potential at a predetermined value, the gate electrode and the display electrode are connected to each other. If the potential difference between the display electrode and the display electrode is large, an electric field acts on the channel portion in a simulated manner, causing the TFT to conduct, causing a phenomenon that the surface element potential changes to an unexpected value.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and simultaneously increases the driving efficiency while increasing the light use efficiency to the utmost.
It is an object of the present invention to provide a reflection type liquid crystal display element by active matrix driving in which an FT malfunction does not occur.

[0010]

Means for Solving the Problems A first invention of the present invention is:
First substrate with pixel electrodes and interconnected on both sides
An intermediate separation layer having an intermediate electrode, and a second separation layer having a counter electrode.
And a thin film transistor formed on the first substrate.
And one of the pixel electrode and the intermediate electrode faces
Between the first substrate and the intermediate separation layer
Held first liquid crystal layer, and the other and pair of the intermediate electrodes.
The intermediate separation layer disposed so that the facing electrodes face each other;
A second liquid crystal layer sandwiched between second substrates.
The thin film transistor is formed on the first substrate.
A gate electrode, and a gate insulating film interposed on the gate electrode;
And a semiconductor layer formed on both sides of the semiconductor layer.
A source electrode and a drain electrode,
The body layer is covered with a protective insulating film,
An alignment film is formed on the surface of the electrode and the counter electrode.
A reflective liquid crystal display device characterized by satisfying the following expression (1 ). {(Dg / εg) + (Dch / εch)} / {(Dg / εg) + (Dch / εch) + (Dbg / εbg) + (Dlc / εlc) + (Dal / εal)} ≦ (Vth−Vg ) / (in Vbg-Vg) · · · formula 1 (wherein, Dg is the distance between the semiconductor layer and the gate electrode, Ipushirong
Is the average dielectric constant of the material of the gate insulating film, and Dch is the average dielectric constant of the semiconductor layer.
Thickness, εch is the dielectric constant of the material of the semiconductor layer, Dbg is the semiconductor layer
The thickness of the protective insulating film provided above, εbg is the thickness of the protective insulating film.
The average dielectric constant of the material, Dlc is the thickness of the first liquid crystal layer, and εlc is
The minimum value of the dielectric constant of the liquid crystal material of the first liquid crystal layer, Dal is the first dielectric constant.
The thickness of the alignment film in contact with the liquid crystal layer, εal, is in contact with the first liquid crystal layer.
The average dielectric constant, Vbg, of the material of the alignment film to be taken is taken by the intermediate electrode.
The maximum voltage to be obtained, Vth is the threshold value of the thin film transistor, and Vg is
Gate electrode voltage when the thin film transistor is turned off
Pressure. )

A second aspect of the present invention has a pixel electrode.
Having a first substrate and interconnected intermediate electrodes on both sides
An intermediate separation layer, a second substrate having a counter electrode,
A thin film transistor formed on one substrate and the pixel
Before placing one of the electrodes and the intermediate electrode facing each other
A first liquid sandwiched between the first substrate and the intermediate separation layer;
Crystal layer, the other of the intermediate electrodes and the counter electrode face each other
Between the intermediate separation layer and the second substrate arranged as described above.
A second liquid crystal layer carried by the thin film transistor.
A gate electrode formed on the first substrate;
The semiconductor formed on the gate electrode via the gate insulating film
And a source electrode and a source electrode provided on both sides of the semiconductor layer.
And a drain electrode, wherein the semiconductor layer is a protective insulating film.
And the pixel electrode, the intermediate electrode and the counter electrode.
An alignment film is formed on the surface of the pole, and one of the intermediate electrodes
The portion facing the thin film transistor is removed and
The intermediate separation layer is in contact with the first liquid crystal layer, and the following formula 1
And a reflection type liquid crystal display element characterized by satisfying the following.

{(Dg / εg) + (Dch / εch)} / {(Dg / εg) + (Dch / εch) + (Dbg / εbg) + (Dlc / εlc) + (Dal / εal)} ≦ ( Vth-Vg) / (Vbg- Vg) ··· formula 1 (wherein, Dg is the distance between the semiconductor layer and the gate electrode, Ipushirong
Is the average dielectric constant of the material of the gate insulating film, Dch is the thickness of the semiconductor layer, εch is the dielectric constant of the material of the semiconductor layer, Dbg is the thickness of the protective insulating film provided on the semiconductor layer, and εbg is the protective insulating film. Dlc is the thickness of the first liquid crystal layer, εlc is
The minimum value of the dielectric constant of the liquid crystal material of the first liquid crystal layer, Dal is the thickness of the alignment film and the intermediate separation layer in contact with the first liquid crystal layer, and εal is
The average dielectric constant of the material of the alignment film and the intermediate separation layer in contact with the first liquid crystal layer , Vbg is the maximum voltage that the intermediate electrode can take, Vth
Is a threshold value of the thin film transistor, and Vg is a gate electrode voltage when the thin film transistor is in a cutoff state. Here, the average dielectric constant is defined as the thickness of the layer / {the sum of (single thickness / dielectric constant) of the constituent material} when the layer is composed of a plurality of materials. A thing.

A third aspect of the present invention has a pixel electrode.
Having a first substrate and interconnected intermediate electrodes on both sides
An intermediate separation layer, a second substrate having a counter electrode,
A thin film transistor formed on one substrate and the pixel
Before placing one of the electrodes and the intermediate electrode facing each other
A first liquid sandwiched between the first substrate and the intermediate separation layer;
Crystal layer, the other of the intermediate electrodes and the counter electrode face each other
Between the intermediate separation layer and the second substrate arranged as described above.
A second liquid crystal layer carried by the thin film transistor.
A gate electrode formed on the first substrate;
The semiconductor formed on the gate electrode via the gate insulating film
And a source electrode and a source electrode provided on both sides of the semiconductor layer.
And a drain electrode, wherein the semiconductor layer is a protective insulating film.
And the pixel electrode, the intermediate electrode and the counter electrode.
An alignment film is formed on the surface of the pole, and the following formulas 2 to 4 are used.
And a reflection type liquid crystal display element characterized by satisfying the following. ΔV = Vbg-Vs-Vth ··· formula 2 ΔV ≧ 0 ··· Equation ^{3 W (ΔV) 2 · Tf} / [L {Dbg / εbg) + (Dlc / εlc) + (Dal / εal)} · Ctotal ] ≦ 0.1Vbg ··· formula 4 (wherein, L is the current direction during conduction in the semiconductor layer activity
(Channel) region length, W is the direction perpendicular to the current direction
Direction width, Tf is the pixel selection period, and Dbg is on the semiconductor layer.
The thickness of the protective insulating film provided in bg is the material of the protective insulating film
Dlc is the thickness of the first liquid crystal layer, and εlc is the
The minimum value of the dielectric constant of the liquid crystal material of the first liquid crystal layer, Dal is the first liquid
The thickness of the alignment film in contact with the crystal layer, εal is in contact with the first liquid crystal layer.
The average dielectric constant and Vbg of the alignment film material can be taken by the intermediate electrode.
The maximum voltage Vs is the drive signal electrode of the thin film transistor.
The minimum voltage that can be taken, Vth is the threshold of the thin film transistor, C
total is the total connected to the pixel electrode side of the thin film transistor
Capacity. ) Fourth aspect of the present invention, having a pixel electrode
With a first substrate and interconnected intermediate electrodes on both sides
An intermediate separation layer, a second substrate having a counter electrode,
A thin film transistor formed on a first substrate;
It is arranged so that one of the elementary electrode and the intermediate electrode faces
A first substrate sandwiched between the first substrate and an intermediate separation layer;
The liquid crystal layer faces the other of the intermediate electrodes and the counter electrode.
Between the intermediate separation layer and the second substrate arranged in such a manner that
A second liquid crystal layer sandwiched between the thin film transistors.
A gate; a gate electrode formed on the first substrate;
A half formed on the gate electrode via a gate insulating film
A conductor layer and source electrodes provided on both sides of the semiconductor layer
And a drain electrode, wherein the semiconductor layer is a protective insulation
Covered with a film, the pixel electrode, the intermediate electrode and the facing
An alignment film is formed on the surface of the electrode, and one of the intermediate electrodes
The portion facing the thin film transistor is removed,
The intermediate separation layer is in contact with the first liquid crystal layer, and has the following formula:
A reflective liquid crystal display, characterized by satisfying the following criteria:
An indicator element is provided.

ΔV = Vbg−Vs−Vth Equation 2 ΔV ≧ 0 Equation 3 W (ΔV) ² · Tf / [L ｛Dbg / εbg) + (Dlc / εlc) + (Dal / εal) ｝ · C total] ≦ 0.1 Vbg Equation 4 (where L is the length of an activation (channel) region in the current direction in the semiconductor layer during conduction, W is the region width in the direction perpendicular to the current direction, Tf is the pixel selection period, Dbg is the thickness of the protective insulating film provided on the semiconductor layer, εbg is the average dielectric constant of the material of the protective insulating film, Dlc is the thickness of the first liquid crystal layer, and εlc is the thickness of the first liquid crystal layer .
1 is the minimum dielectric constant of the liquid crystal material of the liquid crystal layer, Dal is the thickness of the alignment film and the intermediate separation layer in contact with the first liquid crystal layer, and εal is the
1, the average dielectric constant of the material of the alignment film and the intermediate separation layer in contact with the liquid crystal layer , Vbg is the maximum voltage that the intermediate electrode can take, Vs is the minimum voltage that the drive signal electrode of the thin film transistor can take,
Vth is the threshold value of the thin film transistor, and Ctotal is the total capacitance connected to the pixel electrode side of the thin film transistor. )

[0015]

Embodiments of the present invention will be specifically described below with reference to the drawings. The present invention has been made based on the following findings. That is, usually, TFT
Is evaluated by the dependence of the drain current (Id) on the gate-source potential (Vgs) (Id-Vgs curve). In an active matrix type liquid crystal display element, a signal electrode is located on a source side, and a pixel electrode and a storage capacitor electrode usually provided as an auxiliary are located on a drain side. FIG. 1 shows a typical Id-Vgs curve in an active matrix type liquid crystal display device.

This curve defines the threshold value (threshold voltage Vth) of Vgs that separates the insulated state and the conductive state in the TFT. That is, the threshold value Vth is defined as a gate-source potential having a predetermined Id reference value Idstd. Idstd
The specific value depends on the structural dimensions and driving specifications of the liquid crystal display element to be manufactured. For example, according to the findings found by the inventors, the display method described above is PSCT.
The method (the thickness of the liquid crystal layer is about 1.5 μm) is set as follows. In the case of a liquid crystal display element in which a pixel electrode and a TFT are set with a pixel structure dimension of about 100 μm on a side and a driving voltage is about 15 V, Idstd is about 10 pA or less. Then, a display operation without practical problems was possible.

However, in order to improve the light use efficiency, only the pixel structure was changed and the pixel electrode was extended just above the TFT, but the liquid crystal layer almost did not operate. The following experiment was performed to identify the cause. That is, the Id-Vgs curve of the TFT was measured in a state where the connection between the pixel electrode and the TFT was cut off and a specific voltage was supplied from the outside (the change range of Vgs was -15 V to +25 V).
As a result, the dependency of the obtained Id minimum value on the pixel potential is shown in FIG.
Shown in

Thus, the following interpretation of the above problem becomes possible. Between the TFT channel in the above structure and the pixel electrode immediately above it, Si nitride of the same material as the TFT channel-gate electrode insulating film is used, and its thickness is almost the same as that of the TFT channel-gate insulating film. Common 4
00 nm. Further, the potential between the pixel electrode and the source at the time of non-selection (which can be 15 V-(− 15 V) = 30 V at the maximum) reaches a value equivalent to Vgs at the time of pixel selection. At this time, between the TFT channel and the pixel electrode, the TFT channel
By generating a comparable strong electric field between the gate electrodes,
TF in a form where the pixel electrode acts as a pseudo gate electrode
A situation occurred in which a portion of the T-channel region on the pixel electrode side became conductive, which led to a remarkable increase in Id in the negative Vgs region of FIG.

That is, even if the non-selection state (that is, the charge holding state) of the pixel is set to Vgs equal to or lower than Vth defined by the normal specification to realize the insulation state, in practice, it is several thousand times the assumed reference value. It was strongly suggested that a current flowed, which made it impossible to hold display charges on the pixel electrodes.

Further, in the element having the above-mentioned structural conditions,
It has also been found that this phenomenon is more remarkable than in the past, in that the problem of the instantaneous drop in pixel potential that occurs at the moment when the gate electrode switches from the high potential state to the low potential state after the pixel selection period ends. This phenomenon is caused by the overlapping area between the source electrode and the gate electrode connected to the display electrode, that is, the presence of a capacitance between these electrodes. It is known that a part of the electric charge written in the capacitance (and the storage capacitance) of the layer is derived from a phenomenon that is distributed to the capacitance component. In the above-described structure, it is considered that the phenomenon was conspicuous because the capacitance component was increased by the overlap between the newly appearing display electrode and the gate electrode.

In the liquid crystal display device according to the reference example of the present invention,
A thin film transistor (TFT) includes a source electrode and a drain electrode formed over one substrate, and a gate electrode arranged above a channel region formed by the source electrode and the drain electrode (top gate structure). The distance from the region to the electrode layer immediately above the gate electrode is 2 μm or less, and the device is driven by a driving voltage of 10 V or more. Here, if the distance to the electrode layer immediately above the gate electrode exceeds 3 μm, in the case where the electrode layer is an electrode placed directly above the insulating film (and the flattening film) on the TFT (below the liquid crystal layer), This is not preferable because it becomes difficult to ensure conduction between the source electrode adjacent to the semiconductor layer (channel) portion of the TFT and the electrode. Also,
It is not preferable that the electrode is provided directly above the liquid crystal layer because the electric field for driving the liquid crystal layer is excessively reduced. If the driving voltage is less than 10 V, the liquid crystal driving electric field is undesirably lowered.

According to the structure of the reference example of the present invention, the closest conductor covering the semiconductor (channel) portion of the TFT is the gate electrode. In this case, due to the electrostatic shielding effect, the electric field distribution between the channel portion and the gate electrode is defined only by the gate electrode potential, and is not affected by (change in) the electric field distribution in a region outside the gate electrode potential. Thus, even if the display electrode group is provided so as to cover the entire TFT in order to improve the aperture ratio, malfunction of the TFT is avoided. The structure of the reference example exhibits an effect even in a single-layer structure, but exhibits a particularly remarkable effect in a multilayer structure.

FIG. 3 is a sectional view showing a liquid crystal display device having a two-layered liquid crystal layer according to a reference example of the present invention. In the figure, reference numeral 1 denotes an upper transparent substrate. On the transparent substrate 1, a transparent electrode (counter electrode) 2 is formed. On the surface of the counter electrode 2 in contact with the first liquid crystal layer 5, a liquid crystal alignment film (not shown) for further stabilizing the adsorption of liquid crystal molecules is usually provided.
The first liquid crystal layer 5 and the second liquid crystal layer 16 are
Has a constant thickness. As a method of forming the spacers 3, a method of spraying resin spheres (spacer balls) (in this case, the density of spacer balls is preferably 100 or less per 1 mm 2), or more preferably printing or photosensitivity In this case, a method of forming a resin column by a photo-etching process of a conductive material is used (in this case, it is desirable that the column material and the liquid crystal alignment film material are common and both are formed collectively).

An intermediate separation layer 13 is provided between the first liquid crystal layer 5 and the second liquid crystal layer 16. Intermediate separation layer 1
The two transparent electrodes provided on the upper and lower surfaces of 3 are guaranteed to be conductive through the through holes 15, and constitute one intermediate electrode 14 as a whole. The intermediate electrode 14 is a floating electrode that is insulated from the voltage supply source, and has a role of minimizing the amount of voltage drop in the intermediate separation layer 13 that occurs when driving the liquid crystal.

On the other hand, on the lower substrate 4, the pixel electrodes 6, T
The FT and the flattening layer 7 are formed. Specifically, the source electrodes 11 are provided on the lower substrate 4 at predetermined intervals.
And a drain electrode 12, and a semiconductor layer (channel) 9 is formed between the two.
A gate electrode 8 is formed thereon with an insulator layer 12 interposed therebetween. Further, a flattening layer 7 is provided so as to bury the TFT. The gate electrode group is arranged linearly in the direction penetrating the plane of the paper, and the signal electrode group is arranged linearly in a direction perpendicular thereto, thereby forming a pixel matrix. On the lower substrate 4, an auxiliary capacitance electrode (not shown) is usually provided to help maintain the pixel potential. Pixel electrode 6
On the surface in contact with the second liquid crystal layer 16, a liquid crystal alignment film is arranged as in the case of the counter electrode 2.

In the liquid crystal display device having such a configuration, in the case of a display system in which the first and second liquid crystal layers 5 and 16 are dark when the transmittance is high, the pixel electrode 6 is made of a transparent electrode material. The flattening layer 7 is formed using a light absorbing material. In the case of a display system in which bright display is performed when the transmittance of the first and second liquid crystal layers 5 and 16 is high, the pixel electrode 6
Is formed using a light reflecting material or is coated with a light reflecting material layer. Since the pixel electrode 6 is formed so as to cover the entire TFT, the entire area other than the spacer area can be used for display. At the same time, since the semiconductor layer 9 of the TFT is covered with the gate electrode 8, normal operation is possible irrespective of the potential value of the pixel electrode 6 located above the TFT by the above-described action.

The liquid crystal display device according to the embodiment of the present invention comprises:
A thin film transistor includes a gate electrode formed over the one substrate, a semiconductor layer formed over the gate electrode with a gate insulating film interposed therebetween, and a source electrode and a drain electrode provided on both sides of the semiconductor layer. Equation 2 below
~ Expression 4 is satisfied. These relations 2
Nos. To 4 were obtained by considering current / voltage characteristics in the semiconductor layer of the thin film transistor.

ΔV = Vbg−Vs−Vth Equation 2 ΔV ≧ 0 Equation 3 W (ΔV) ² · Tf / [L ｛(Dbg / εbg) + (Dlc / εlc) + (Dal / εal) ｝ · C total] ≦ 0.1 Vbg Equation 4 (where L is the length of a region in the semiconductor layer in the current direction during conduction, W is the region width in the direction perpendicular to the current direction, Tf is the pixel selection period, Dbg is the thickness of the insulating film provided on the semiconductor layer, εbg is the average dielectric constant of the material of the insulating film, Dlc is the thickness of the liquid crystal layer adjacent to the thin film transistor, and εlc is the minimum dielectric constant of the liquid crystal material of the liquid crystal layer. Value, Dal is the thickness of the insulating member in contact with the liquid crystal layer, εal is the average dielectric constant of the material of the insulating member, Vbg is the maximum voltage that can be taken by the nearest pixel electrode located immediately above the semiconductor layer, and Vs is the thickness of the thin film transistor. The minimum voltage that the drive signal electrode can take, Vth is the threshold value of the thin film transistor, and Ctotal is the thin film transistor. This condition is a holding period (non-selection period) that occurs because a TFT that should be in an insulated state becomes partially conductive due to the potential difference between the pixel electrode and the source electrode. During this period, the reduction of the pixel potential is limited to such an extent that the display operation can be performed practically.

In equation 4, W (ΔV) ² · Tf / [L ｛Db
g / εbg) + (Dlc / εlc) + (Dal / εal)} is an approximate expression in the positive region (region of Vgs ≧ Vth) of the Id-Vgs curve. In the case where the pixel electrode is regarded as a pseudo gate electrode, the maximum value of the amount of current leak generated according to the electrode potential is estimated in the above-described portion. At this time,
The left side of Equation 4 represents a variation amount of the pixel electrode potential resulting from the charge leakage phenomenon during the holding period, and Equation 4 indicates that the variation amount is allowed to be up to 10% of the entirety. In the above-described study examples, the inventors have found that the display operation can be performed by providing the same offset value in the drive voltage waveform when the fluctuation amount is about 1 to 2 V.

The liquid crystal display element according to the embodiment of the present invention
In the semiconductor device, the thin film transistor includes a gate electrode formed over the one substrate, a semiconductor layer formed over the gate electrode with a gate insulating film interposed therebetween, and a source electrode provided on both sides of the semiconductor layer. And a drain electrode, which satisfies the following expression (1). Note that this relational expression 1 is obtained by considering the electric field distribution in the semiconductor layer of the thin film transistor.

{(Dg / εg) + (Dch / εch)} / {(Dg / εg) + (Dch / εch) + (Dbg / εbg) + (Dlc / εlc) + (Dal / εal)} ≦ ( Vth−Vg) / (Vbg−Vg) Equation 1 (where Dg is the distance between the semiconductor layer and the gate electrode, ε
g is the average dielectric constant of the material of the gate insulating film, Dch is the thickness of the semiconductor layer, εch is the dielectric constant of the material of the semiconductor layer, Dbg is the thickness of the insulating film provided on the semiconductor layer, and εbg is the thickness of the insulating film. The average dielectric constant of the material, Dlc is the thickness of the liquid crystal layer adjacent to the thin film transistor, εlc is the minimum dielectric constant of the liquid crystal material of the liquid crystal layer,
Dal is the thickness of the insulating member in contact with the liquid crystal layer, εal is the average dielectric constant of the material of the insulating member, Vbg is the maximum voltage that the nearest pixel electrode located immediately above the semiconductor layer can take, Vth is the threshold of the thin film transistor, Vg is the gate electrode voltage when the thin film transistor is in the cut-off state.) This condition can avoid the problem more reliably than the above condition. That is, when the connected pixel is in the non-selected state, the effective voltage applied to the TFT channel layer acting as a dielectric located between the gate electrode and the display pixel electrode group exceeds the threshold value Vth defined above. Is not specified. In the conventional typical Id-Vgs curve, Id slightly increases with a decrease in Vgs in the region of Vgs <Vth. However, the display pixel electrode studied in this case acts as a pseudo gate electrode. In a potential device, this curve often has a general shape that is shifted to the left with respect to Vgs, in which case Id decreases monotonically due to the decrease in Vgs in the potential difference region. The potential holding characteristics of the pixel electrode are surely improved. As a result, if Expression 1 is satisfied, even if a high voltage is applied to the display pixel electrode group during a period in which the gate electrode is at a low potential and the TFT is expected to be in a cutoff state,
This operation of the FT can be avoided.

Further, when the liquid crystal display element according to the embodiment of the present invention has a liquid crystal layer having a multilayer structure, the electrode area of the electrode surface corresponding to one pixel of the intermediate electrode group is in contact with the first liquid crystal layer. Where S1 is the area of the electrode in contact with the second liquid crystal layer, S1 is the thickness of the first liquid crystal layer, and d2 is the thickness of the second liquid crystal layer. The display quality can be further improved. Equation 5 shows a condition for keeping the effective capacitance of the first liquid crystal layer and the effective capacitance of the second liquid crystal layer approximately constant. Thereby, even if the intermediate display electrode is formed in an independent pattern on the upper and lower surfaces, a uniform voltage is applied to both liquid crystal layers, and a desired display quality can always be achieved.

(Absolute value of S1 / d1−S2 / d2) / (S1 / d1) ≦ 0.1 Equation 5 As described above, in the liquid crystal display element having a structure optimized according to the driving method, Regarding the instantaneous variation of the pixel potential at the time of the gate potential switching described above, the design is also made in a direction to reduce the capacitance between the pixel line and the signal line. Can be.

FIG. 7 is a sectional view showing a liquid crystal display device having a liquid crystal layer having a two-layer structure according to an embodiment of the present invention. FIG.
3, the same reference numerals as in FIG. 3 denote the same parts as in FIG. 3, and a detailed description thereof will be omitted.

In FIG. 7, on the lower substrate 4, a pixel electrode 6, a TFT, and a flattening layer 7 are formed. Specifically, a gate electrode 8 is formed on the lower substrate 4, and a semiconductor layer (channel) 9 is formed on the gate electrode 8 via an insulator layer 12. Drain electrode 10 and pixel electrode 6 connected to signal electrode
Is formed. further,
A flattening layer 7 is provided so as to bury the TFT. The TFT, in particular, the semiconductor layer (channel) 9 is covered with an insulating film (not shown) made of a dielectric. As a dielectric covering this channel, silicon nitride (SiN
x) is used. If a material having a higher dielectric constant, for example, tantalum oxide (Ta ₂ O ₅ ) or bismuth-strontium-tin oxide (Bi-Sr-Ti-O) is used,
This is effective in reducing the local electric field immediately above the channel.

In the liquid crystal display device having such a configuration, in the case of a display system in which the first and second liquid crystal layers 5 and 16 perform dark display when the transmittance is high, the pixel electrode 6 is made of a transparent electrode material. It is preferable to use a light absorbing material for the flattening layer 7 or to provide a black plate on the back surface. In the case of a display system in which a bright display is performed when the transmittance of the first and second liquid crystal layers 5 and 16 is high, the pixel electrode 6 should be formed using a light reflecting material or covered with a light reflecting material layer. Is preferred.

The lower surfaces of the pixel electrode 6 and the intermediate electrode 14
In the region directly above the TFT, it is removed in an island shape by etching. The ratio (S2 / S1) of the area of the electrode in contact with the second liquid crystal layer to the area of the electrode in contact with the first liquid crystal layer and the first liquid crystal layer with respect to the thickness of the first liquid crystal layer are set such that Equation 5 is satisfied. Of the liquid crystal layer (D2 / D1).

As a result of examining the TFT characteristics used for the liquid crystal display device according to the second aspect of the present invention, the value of the threshold voltage Vth was about -5V. The liquid crystal layer thickness D1 is 2 μm.
In the case of a liquid crystal display device having a ratio of about:
The value of (Vth-Vg) / (Vbg-Vg) (in this case, Vbg
By selecting a driving method such that the voltage applied to the intermediate electrode 14 becomes about 1/3, the potential of the TFT channel layer is kept below a threshold voltage at which no malfunction occurs.

In the above embodiment of the present invention , any of the existing reflective display modes can be used for the structure of the first and second liquid crystal layers 5 and 16.
It is preferable to use the CT mode. That is, a chiral nematic liquid crystal, which is a mixture of a cholesteric liquid crystal and a nematic liquid crystal, is used as a liquid crystal material (in order to stabilize the liquid crystal molecule alignment, a perfluoroalkyl compound-based material is further mixed at 1% to 3%. It is also effective to use a liquid crystal material). Further, for the first liquid crystal layer 5, a twisted structure between liquid crystal molecules is used in a right-handed material.
For the second liquid crystal layer 16, a left-handed material is used. According to this configuration, when natural light including various polarized light components is incident, the right circularly polarized light component having a predetermined reflection wavelength width determined by the period of the twisted structure is reflected and scattered in the first liquid crystal layer 5, and furthermore, In this transmitted light, a left circularly polarized light component having a predetermined reflection wavelength width determined by the same mechanism as that of the first liquid crystal layer 5 is reflected and scattered in the second liquid crystal layer 16, so that bright display with high luminance can be performed without a voltage mark. Obtained upon addition. When a voltage of 10 to several tens of volts is applied, the liquid crystal molecules of both layers dissolve the twisted structure and are arranged in the direction of the electric field, and both layers are in a transparent state. The display is obtained.

Next, a description will be given of an embodiment performed to clarify the effects of the present invention. In addition, these examples are:
It is described for the purpose of facilitating the understanding of the present invention, and can be variously changed and used without changing the gist of the present invention. Reference Example 1 FIG. 3 is a sectional view showing a reflective liquid crystal display device according to a first reference example of the present invention. This reflective liquid crystal display element
It is produced as follows.

On the glass substrate as the upper substrate 1, ITO as the counter electrode 2 was deposited to a thickness of 150 nm. A through hole 15 is formed in a predetermined position of the glass substrate as an intermediate separation layer 13 by etching, and a bump alloy is melt-filled in the through hole 15 to establish electrical continuity between the front and back surfaces. The thickness 150n
m, and this was etched in an island shape to form an intermediate electrode 14 corresponding to each pixel.

On a glass substrate as the lower substrate 4, SiOx as an undercoat layer was deposited to a thickness of 500 nm. Further, a Mo-W alloy was deposited thereon to a thickness of 300 nm, and this was patterned to form a signal electrode, and a drain electrode 10 and a source electrode 11 connected to the signal electrode. A-Si as an active layer is formed thereon to a thickness of 100 nm.
The semiconductor layer (channel) 9 was formed by patterning in an island shape using the light shielding layer as a mask.

Next, SiNx is deposited thereon as a gate insulating film 12 to a thickness of 350 nm, and Al and Mo are deposited as a gate electrode 8 in a thickness of 300 nm and 50 nm as a gate electrode 8 on the channel corresponding region, respectively. did. Thereafter, n + a-Si as an ohmic contact layer was formed around the gate electrode 8 by an ion doping operation. Further, SiNx having a thickness of 20
Deposition was performed at 0 nm, and SiNx on the end pad electrode and the source electrode of the matrix electrode group was removed by etching.

Next, a photosensitive acrylic resin CK-S201 (Fuji Hunt Technology Co., Ltd.) in which a black pigment is dispersed as
(Trade name) was deposited to a thickness of 1.8 μm, and was patterned to form a contact hole, and the contact hole was melt-filled with a bump alloy. An ITO as the pixel electrode 6 was deposited thereon with a thickness of 100 nm and patterned.

Next, a polyimide optomer AL-3046 (trade name, manufactured by Nippon Synthetic Rubber Co., Ltd.) having a thickness of 70 nm was formed as an alignment film on the surface of the counter electrode 2, the pixel electrode 6 in contact with the liquid crystal material, and on both surfaces of the intermediate electrode 14. It was formed by spin coating. Further, an epoxy adhesive for bonding was applied to predetermined positions on the upper and lower substrate surfaces by a conventional method. A resin spacer ball having a diameter of 2 μm is placed on the substrate surface at a density of 100.
Pieces / mm ² or less, and the three substrates were combined so that the pixel electrodes overlap.

Finally, a nematic liquid crystal material E48 (ME
RCK, trade name) 59 parts, chiral substance CB15
A first liquid crystal material mixed with 41 parts (trade name, manufactured by MERCK) was injected into the gap on the upper substrate side to form a first liquid crystal layer 5. Next, a second liquid crystal material in which 61 parts of nematic liquid crystal E486 and 39 parts of chiral substance C15 were mixed was injected into the gap on the lower substrate side to form a second liquid crystal layer 16.

The reflection type liquid crystal display device shown in FIG. 3 was manufactured as described above. In this reflective liquid crystal display device,
The maximum distance between the channel region and the electrode layer immediately above the gate electrode was about 1.7 μm. The aperture ratio, the reflectance, and the contrast of this reflective liquid crystal display element were adjusted to a driving voltage of 14 V.
As a result, the aperture ratio was 80%, the reflectance was 65%, and the contrast was 80. Reference Example 2 FIG. 4 is a cross-sectional view showing a reflective liquid crystal display device according to a second reference example of the present invention. In this structure, a so-called mortar-shaped contact hole in which the source electrode 11 is exposed at the center is formed in the planarization layer 7.

As a resin substrate as the intermediate separation layer 13,
Using a resin material capable of shifting the phases of the ordinary light component and the extraordinary light component of the light belonging to the selective reflection wavelength range (wavelength centered at 570 nm) of the second liquid crystal material by approximately 1/2 wavelength; A reflective liquid crystal display device shown in FIG. 4 was produced in the same manner as in Reference Example 1 except that a mortar-shaped contact hole was formed in the layer 7.

In this reflection type liquid crystal display device, the maximum distance between the channel region and the electrode layer immediately above the gate electrode was about 1.7 μm. When the aperture ratio, the reflectance, and the contrast of this reflective liquid crystal display element were examined by driving at a driving voltage of 14 V, the aperture ratio was 80%, and the reflectance was 6%.
5% and the contrast was 75. Reference Example 3 FIG. 5 is a sectional view showing a reflective liquid crystal display device according to a third reference example of the present invention. In this structure, the source electrode 11 is also used as the pixel electrode 6, whereby the planarizing layer 7 is formed.
Is omitted.

The reflection type liquid crystal display device having this structure is:
It was produced as follows. First, the upper substrate with electrode 1 and the intermediate separation layer 13 were produced in the same manner as in Example 1. Next, SiOx as an undercoat layer was deposited to a thickness of 500 nm on a glass substrate as the lower substrate 4. A Mo-W alloy is deposited thereon with a thickness of 200 nm, and is patterned to form an auxiliary signal electrode 17. After that, ITO is deposited thereon with a thickness of 100 nm, and this is patterned. The pixel electrode 6 integrated with the signal electrode and the drain electrode 10 and the source electrode connected to the signal electrode was formed. Next, n ⁺ a as an ohmic contact layer
-Si having a thickness of 50 nm and a-Si having a thickness of 3 as an active layer.
Semiconductor layers (channels) 9 were formed by depositing 0 nm each and patterning them in an island shape.

Then, a 300 nm-thick SiNx is formed thereon as the gate insulating film 12 and A is formed as the gate electrode 8.
1 and Mo were deposited to a thickness of 300 nm and 50 nm, respectively, and this was patterned. Next, Si
Nx was deposited to a thickness of 200 nm, and the end pad electrodes of the matrix electrode group were removed by etching.

Lastly, when combining the three substrates, the first and second liquid crystal layers are formed in the same manner as in Reference Example 1 except that the black plate 18 is simultaneously bonded to the outside of the lower substrate 4. went.

Thus, the reflection type liquid crystal display device shown in FIG. 5 was manufactured. In this reflective liquid crystal display device,
The maximum distance between the channel region and the electrode layer immediately above the gate electrode was about 2 μm. When the aperture ratio, the reflectance, and the contrast of this reflective liquid crystal display element were examined by driving at a driving voltage of 15 V, the aperture ratio was 60%, the reflectance was 55%, and the contrast was 60. Comparative Example 1 FIG. 6 is a sectional view showing a reflective liquid crystal display device according to Comparative Example 1. This reflective liquid crystal display element
It is produced as follows.

First, the upper substrate with electrode 1 and the intermediate separation layer 13 were produced in the same manner as in Example 1. Next, the lower substrate 4
A Mo-Ta alloy having a thickness of 250
The gate electrode 8 was formed by patterning. After depositing SiOx as a gate insulating film 12 thereon to a thickness of 300 nm and SiNx to a thickness of 50 nm, a-Si is continuously formed as an active layer to a thickness of 50 n.
m, SiNx was deposited to a thickness of 200 nm as a channel protective film. After the channel protective film is formed in an island shape by etching, n ⁺ a-S is formed as an ohmic contact layer.
i with a thickness of 50 nm, a-Si and n ⁺ a-S
The semiconductor layer (channel) 9 was formed by etching i in an island shape. Further, the gate insulating film at the portion where the gate electrode was taken out was removed.

Next, Cr and Al were deposited thereon to a thickness of 50 nm and 300 nm, respectively, and were patterned to form a signal electrode and a drain electrode 10 and a source electrode 11 connected to the signal electrode. Using the signal electrode as a mask, n ⁺ a-Si between the source and the drain was selectively removed by etching together with the channel protective film. This whole surface is SiNx
Was deposited to a thickness of 200 nm, and SiNx on the end pad electrode and the source electrode of the matrix electrode group were removed by etching.

Next, a photosensitive acrylic resin CK-S201 (trade name, manufactured by Fuji Hunt Technology Co., Ltd.) in which a black pigment was dispersed was deposited to a thickness of 1.8 μm as a flattening layer 7.
This was patterned to expose the source electrode. ITO was deposited thereon as a pixel electrode 6 to a thickness of 100 nm and patterned.

Finally, the first and second liquid crystal layers were formed in the same manner as in Reference Example 1 to produce the conventional reflection type liquid crystal display device shown in FIG. In this reflective liquid crystal display device,
The maximum distance between the channel region and the electrode layer immediately above the gate electrode was about 1.2 μm. The aperture ratio, the reflectance, and the contrast of this reflective liquid crystal display element were adjusted to a driving voltage of 14 V.
The aperture ratio was 80% when examined by driving with
Due to the influence of the electrode above the gate electrode, stable display cannot be performed by ordinary active matrix driving. Example 1 FIG. 7 is a cross-sectional view showing a reflective liquid crystal display device according to Example 1 of the present invention. This reflective liquid crystal display element
It is produced as follows.

On the glass substrate as the upper electrode 1, ITO as the counter electrode 2 was deposited to a thickness of 150 nm. A through hole 15 is formed in a predetermined position of the glass substrate as an intermediate separation layer 13 by etching, and a bump alloy is melt-filled in the through hole 15 to establish electrical continuity between the front and back surfaces. The thickness 150n
deposited by m, and forms the shape of the intermediate electrode 14 corresponding to each pixel by etching it into an island shape.

On a glass substrate as the lower substrate 4, Mo
A -Ta alloy was deposited to a thickness of 250 nm, and this was patterned to form a gate electrode 8. After depositing SiOx to a thickness of 300 nm and SiNx to a thickness of 50 nm as a gate insulating film 12 thereon, a-Si is continuously formed as an active layer to a thickness of 50 nm and Si is used as a channel protection film.
Nx was deposited in a thickness of 200 nm each. After etching the channel protective film into an island shape, n ⁺ a-Si as an ohmic contact layer is deposited to a thickness of 50 nm,
The semiconductor layer (channel) 9 was formed by etching a-Si and n ⁺ a-Si into an island shape. Note that the gate insulating film at the gate electrode take-out portion was removed.

Next, Cr and Al were deposited thereon with a thickness of 50 nm and 300 nm, respectively, and were patterned to form a signal electrode and a drain electrode 10 and a source electrode 11 connected to the signal electrode. Using the signal electrode as a mask, n ⁺ a-Si between the source and the drain was selectively removed by etching together with the channel protective film. Further, SiNx is deposited to a thickness of 200 nm on the entire surface, and SiNx is deposited on the end pad electrode and the source electrode of the matrix electrode group.
Nx was removed by etching.

Next, a photosensitive acrylic resin CK-S201 (trade name, manufactured by Fuji Hunt Technology Co., Ltd.) in which a black pigment is dispersed is 2.6 μm thick as a flattening layer 7 thereon.
This was patterned, and this was patterned to form a mortar-shaped contact hole in which the source electrode 11 was exposed at the center. On top of this, ITO is formed as a pixel electrode 6 with a thickness of 100 nm.
And deposited. At this time, the pixel electrode 6
It was formed by removing the portion immediately above the position where the gate electrode 8 located below the FT was formed by etching.

Next, a polyimide optomer AL-3046 (trade name, manufactured by Nippon Synthetic Rubber Co., Ltd.) having a thickness of 70 nm was formed as an alignment film on the surface of the counter electrode 2, the pixel electrode 6 in contact with the liquid crystal material, and on both surfaces of the intermediate electrode 14. It was formed by spin coating. Further, an epoxy adhesive for bonding was applied to predetermined positions on the upper and lower substrate surfaces by a conventional method. A resin spacer ball having a diameter of 2 μm is placed on the substrate surface at a density of 100.
Pieces / mm ² or less, and the three substrates were combined so that the pixel electrodes overlap.

Finally, the nematic liquid crystal material E48 59
, A first liquid crystal material mixed with 41 parts of a chiral substance CB15 was injected into the gap on the upper substrate side to form a first liquid crystal layer 5. Next, a second liquid crystal material in which 61 parts of nematic liquid crystal E486 and 39 parts of chiral substance C15 were mixed was injected into the gap on the lower substrate side to form a second liquid crystal layer 16.

As described above, the reflection type liquid crystal display device shown in FIG. 7 was manufactured. This reflection type liquid crystal display element satisfied the above-mentioned expressions 1 to 5. When the aperture ratio, the reflectance, and the contrast of this reflective liquid crystal display element were examined by driving at a driving voltage of 14 V, the aperture ratio was 70%, the reflectance was 65%, and the contrast was 75. Example 2 FIG. 8 is a sectional view showing a reflective liquid crystal display device according to Example 2 of the present invention. In this structure, the pixel electrode 6 is connected to the source electrode 11 in the same plane, and the flattening layer 7 is omitted. In this structure, the intermediate electrode 14 immediately above the TFT is removed.

As a resin substrate as the intermediate separation layer 13,
Using a resin material capable of shifting the phase of the ordinary light component and the extraordinary light component of the light belonging to the selective reflection wavelength range (wavelength centered at 570 nm) of the second liquid crystal material by approximately 波長 wavelength; The upper substrate 1 and the intermediate isolation layer 13 were formed in the same manner as in Example 1 except that the intermediate electrode on the lower surface of the intermediate isolation layer 13 immediately above the gate electrode was removed by etching and the flattening layer 7 was not provided. , And the lower substrate 4.

Finally, when combining the three substrates, the first and second liquid crystal layers are formed in the same manner as in Example 1 except that the black plate 18 is simultaneously bonded to the outside of the lower substrate 4. went. Thus, the reflective liquid crystal display device shown in FIG. 8 was manufactured. This reflection type liquid crystal display element satisfied the above-mentioned expressions 1 to 5.

The reflection type liquid crystal display element has an aperture ratio,
When the reflectance and the contrast were examined by driving at a driving voltage of 14 V, the aperture ratio was 70%, the reflectance was 60%, and the contrast was 65. Comparative Example 2 FIG. 9 is a sectional view showing a reflective liquid crystal display device according to Comparative Example 2. This reflective liquid crystal display element
It is produced as follows.

T at the pixel electrode 6 and the intermediate electrode 14
The same procedure as in Example 1 was carried out except that the FT and the position immediately above the matrix electrode group were not etched.
The upper substrate 1 with an electrode, the intermediate separation layer 13 with an intermediate electrode 14, and the lower substrate 4 with a TFT and an electrode were produced.

Next, the first and second liquid crystal layers were formed in the same manner as in Example 1 , except that the diameter of each of the resin-made spacer balls sprayed on the upper and lower substrate surfaces was 2 μm. Thus, the conventional reflective liquid crystal display device shown in FIG. 9 was manufactured. In this reflection type liquid crystal display device, the above-mentioned formulas 1 and 4 were not satisfied.

The reflection type liquid crystal display device has an aperture ratio,
When the reflectivity and contrast were examined by driving at a driving voltage of 14 V, the aperture ratio was 80%. However, due to the influence of the electrode above the gate electrode, stable display could not be performed by ordinary active matrix driving. It was possible.

[0071]

[0072]

As described above, according to the reflection type liquid crystal display device of the present invention, the amount of leakage current in the TFT insulating state is suppressed to a level that does not cause a practical problem, or more strictly, the TFT
By adopting a structure in which a potential exceeding the threshold voltage is not applied to the channel layer, both the aperture ratio and the reflection luminance are high while suppressing the malfunction of the TFT and the instantaneous fluctuation of the pixel potential. Further, by providing a constant relationship between the display electrode area and the liquid crystal layer pressure, an appropriate voltage distribution can be always applied to each of the multilayer liquid crystal layers.

[Brief description of the drawings]

FIG. 1 shows an Id of an active matrix type liquid crystal display device.
Vgs curve.

FIG. 2 is a characteristic diagram showing a pixel potential dependency of a minimum value of Id of an active matrix type liquid crystal display element.

FIG. 3 is a sectional view showing a reflective liquid crystal display device according to a first reference example of the present invention.

FIG. 4 is a sectional view showing a reflective liquid crystal display device according to a second reference example of the present invention.

FIG. 5 is a sectional view showing a reflective liquid crystal display device according to a third reference example of the present invention.

FIG. 6 is a sectional view showing a reflective liquid crystal display element according to Comparative Example 1.

FIG. 7 is a sectional view showing a reflective liquid crystal display device according to the first embodiment of the present invention.

Sectional view showing such a reflective liquid crystal display device in the second embodiment of the present invention; FIG.

FIG. 9 is a sectional view showing a reflective liquid crystal display element according to Comparative Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Upper substrate, 2 ... Counter electrode, 3 ... Spacer, 4 ... Lower substrate, 5 ... First liquid crystal layer, 6 ... Pixel electrode, 7 ... Flattening layer, 8 ... Gate electrode, 9 ... Semiconductor layer, 10 ... Drain electrode, 11 ... Source electrode, 12 ... Gate insulating layer, 13 ... Intermediate separation layer, 14 ... Intermediate electrode, 15 ... Through hole, 16
... second liquid crystal layer, 17 ... auxiliary signal electrode, 18 ... black plate.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-150532 (JP, A) JP-A-7-302912 (JP, A) JP-A-9-90424 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G02F 1/1368

Claims (4)

(57) [Claims] A first substrate having a pixel electrode; an intermediate separation layer having an intermediate electrode interconnected on both sides; a second substrate having a counter electrode; and a first substrate formed on the first substrate. A thin film transistor, a first liquid crystal layer sandwiched between the first substrate and an intermediate separation layer arranged so that one of the pixel electrode and the intermediate electrode faces each other, and the other of the intermediate electrodes and a counter electrode face each other. A second liquid crystal layer sandwiched between the intermediate separation layer and a second substrate, wherein the thin film transistor has a gate electrode formed on the first substrate, and a thin film transistor on the gate electrode. A semiconductor layer formed with a gate insulating film interposed therebetween, and a source electrode and a drain electrode provided on both sides of the semiconductor layer; the semiconductor layer is covered with a protective insulating film; An alignment film is formed on the surface of the counter electrode, and the following formula 1 is satisfied. {(Dg / εg) + (Dch / εch)} / {(Dg / εg) + (Dch / εch) + (Dbg / εbg) + (Dlc / εlc) + (Dal / εal)} ≦ (Vth−Vg ) / (Vbg−Vg) Equation 1 (where Dg is the distance between the semiconductor layer and the gate electrode, εg
Is the average dielectric constant of the material of the gate insulating film, Dch is the thickness of the semiconductor layer, εch is the dielectric constant of the material of the semiconductor layer, Dbg is the thickness of the protective insulating film provided on the semiconductor layer, and εbg is the protective insulating film. Dlc is the thickness of the first liquid crystal layer , εlc is
The minimum value of the dielectric constant of the liquid crystal material of the first liquid crystal layer , Dal is the thickness of the alignment film in contact with the first liquid crystal layer, εal is the average dielectric constant of the material of the alignment film in contact with the first liquid crystal layer, and Vbg is the intermediate value. Vth is the threshold voltage of the thin film transistor, and Vg is the gate electrode voltage when the thin film transistor is in a cutoff state. ) 2. A first substrate having a pixel electrode, an intermediate separation layer having an intermediate electrode interconnected on both sides, a second substrate having a counter electrode, and a second substrate formed on the first substrate. A thin film transistor, a first liquid crystal layer sandwiched between the first substrate and an intermediate separation layer arranged so that one of the pixel electrode and the intermediate electrode faces each other, and the other of the intermediate electrodes and a counter electrode face each other. A second liquid crystal layer sandwiched between the intermediate separation layer and a second substrate, wherein the thin film transistor has a gate electrode formed on the first substrate, and a thin film transistor on the gate electrode. A semiconductor layer formed with a gate insulating film interposed therebetween, and a source electrode and a drain electrode provided on both sides of the semiconductor layer; the semiconductor layer is covered with a protective insulating film; And an alignment film is formed on the surface of the counter electrode, a portion of the intermediate electrode facing the thin film transistor is removed, and the intermediate separation layer is in contact with the first liquid crystal layer. A reflective liquid crystal display element characterized by satisfying. {(Dg / εg) + (Dch / εch)} / {(Dg / εg) + (Dch / εch) + (Dbg / εbg) + (Dlc / εlc) + (Dal / εal)} ≦ (Vth−Vg ) / (Vbg−Vg) Equation 1 (where Dg is the distance between the semiconductor layer and the gate electrode, εg
Is the average dielectric constant of the material of the gate insulating film, Dch is the thickness of the semiconductor layer, εch is the dielectric constant of the material of the semiconductor layer, Dbg is the thickness of the protective insulating film provided on the semiconductor layer, and εbg is the protective insulating film. Dlc is the thickness of the first liquid crystal layer , εlc is
The minimum dielectric constant of the liquid crystal material of the first liquid crystal layer , Dal is the thickness of the alignment film and the intermediate separation layer in contact with the first liquid crystal layer, and εal is the material of the alignment film and the intermediate separation layer in contact with the first liquid crystal layer. Vbg is the maximum voltage that the intermediate electrode can take, Vth
Is a threshold value of the thin film transistor, and Vg is a gate electrode voltage when the thin film transistor is in a cutoff state. ) 3. A first substrate having a pixel electrode, an intermediate separation layer having an intermediate electrode interconnected on both surfaces, a second substrate having a counter electrode, and a first substrate formed on the first substrate. A thin film transistor, a first liquid crystal layer sandwiched between the first substrate and an intermediate separation layer arranged so that one of the pixel electrode and the intermediate electrode faces each other, and the other of the intermediate electrodes and a counter electrode face each other. A second liquid crystal layer sandwiched between the intermediate separation layer and a second substrate, wherein the thin film transistor has a gate electrode formed on the first substrate, and a thin film transistor on the gate electrode. A semiconductor layer formed with a gate insulating film interposed therebetween, and a source electrode and a drain electrode provided on both sides of the semiconductor layer; the semiconductor layer is covered with a protective insulating film; And a reflection type liquid crystal display device, wherein an alignment film is formed on the surface of the counter electrode, and the following Expressions 2 to 4 are satisfied. ΔV = Vbg−Vs−Vth Equation 2 ΔV ≧ 0 Equation 3 W (ΔV) ² · Tf / [L ｛Dbg / εbg) + (Dlc / εlc) + (Dal / εal)｝ · Ctotal ≦ 0.1 Vbg Equation 4 (where L is the length of an activation (channel) region in the semiconductor layer in the current direction during conduction, W is the region width in the direction perpendicular to the current direction, and Tf is the pixel. Where Dbg is the thickness of the protective insulating film provided on the semiconductor layer, εbg is the average dielectric constant of the material of the protective insulating film, Dlc is the thickness of the first liquid crystal layer, and εlc is the first liquid crystal layer. , Dal is the thickness of the alignment film in contact with the first liquid crystal layer, εal is the average dielectric constant of the material of the alignment film in contact with the first liquid crystal layer, and Vbg is the maximum possible value of the intermediate electrode. Voltage, Vs is the minimum voltage that the drive signal electrode of the thin film transistor can take, Vth is the threshold value of the thin film transistor, C
total is the total capacitance connected to the pixel electrode side of the thin film transistor. ) 4. A first substrate having a pixel electrode, an intermediate separation layer having an intermediate electrode interconnected on both surfaces, a second substrate having a counter electrode, and a first substrate formed on the first substrate. A thin film transistor, a first liquid crystal layer sandwiched between the first substrate and an intermediate separation layer arranged so that one of the pixel electrode and the intermediate electrode faces each other, and the other of the intermediate electrodes and a counter electrode face each other. A second liquid crystal layer sandwiched between the intermediate separation layer and a second substrate, wherein the thin film transistor has a gate electrode formed on the first substrate, and a thin film transistor on the gate electrode. A semiconductor layer formed with a gate insulating film interposed therebetween, and a source electrode and a drain electrode provided on both sides of the semiconductor layer; the semiconductor layer is covered with a protective insulating film; And the surface of the counter electrode alignment film is formed, said one opposed portions to said thin film transistor of the intermediate electrode is removed, the intermediate separation layer is in contact with the first liquid crystal layer, the formulas 2 to below A reflection-type liquid crystal display device, which satisfies Expression 4 . ΔV = Vbg−Vs−Vth Equation 2 ΔV ≧ 0 Equation 3 W (ΔV) ² · Tf / [L ｛Dbg / εbg) + (Dlc / εlc) + (Dal / εal)｝ · Ctotal ≦ 0.1 Vbg Equation 4 (where L is the length of an activation (channel) region in the semiconductor layer in the current direction during conduction, W is the region width in the direction perpendicular to the current direction, and Tf is the pixel. Where Dbg is the thickness of the protective insulating film provided on the semiconductor layer, εbg is the average dielectric constant of the material of the protective insulating film, Dlc is the thickness of the first liquid crystal layer, and εlc is the first liquid crystal layer. dielectric constant minimum value of the liquid crystal material, Dal thickness of the alignment film and the intermediate separating layer in contact with the first liquid crystal layer, Ipushironal the average dielectric constant of the alignment layer and the intermediate separation layer material in contact with the first liquid crystal layer, Vbg is the maximum voltage that the intermediate electrode can take, Vs is the minimum voltage that the drive signal electrode of the thin film transistor can take,
Vth is the threshold value of the thin film transistor, and Ctotal is the total capacitance connected to the pixel electrode side of the thin film transistor. )