JP4347253B2 - Light emitting device - Google Patents

Description

  The present invention relates to a light-emitting device that excites a phosphor with light emitted from an electron emission source.

  In recent years, compared to conventional light emitting devices such as incandescent bulbs and fluorescent lamps, cold cathode field emission type that excites and emits phosphors by colliding the electrons emitted from the electron emission source in vacuum with the phosphors at high speed. Light emitting devices have been developed. This type of light emitting device is a field emission device in which electrons are drawn out by a grid electrode applied with a positive potential with respect to the cathode electrode, and are further made to emit fluorescent light by colliding electrons with a fluorescent plate electrode applied with a positive high voltage. Applications are expected as a field illumination lamp (FEL) and a field emission display (FED).

  For example, Patent Document 1 discloses a technique related to FEL in which a grid electrode having a structure in which holes are formed in a substantially flat plate substantially parallel to the surface of the cathode electrode and the ends of the holes protrude toward the cathode electrode side is disclosed. Yes. According to the technique of this Patent Document 1, the electric field at the hole end can be made higher than the electric field in the substantially flat region, and invalid electrons jumping from the cathode electrode to the grid electrode can be suppressed.

  Similarly, Patent Document 2 discloses a technique related to FEL in which a semicylindrical grid electrode partially having an opening surrounds a rectangular parallelepiped cathode electrode with a gap. According to the technique of Patent Document 2, it is possible to suppress positive ions struck by the electrons entering the fluorescent plate electrode from entering the cathode electrode, thereby preventing discharge breakdown.

  By the way, an electron emission source of a cold cathode formed by a general method does not have a constant field emission characteristic for each part where the film is formed. There is a problem that unevenness occurs in the light emission luminance of the body. This light emission unevenness will be described by taking the structure of the cathode electrode of a typical FEL shown in FIG. 3 as an example.

In the example of FIG. 3, an emitter material such as carbon nanotube is formed on the cathode electrode 101 formed on the glass substrate 100 to form the cold cathode electron emission source 102. A grid electrode 103 is disposed opposite to the cathode electrode 101 with a predetermined distance. The distance A between the cathode electrode 101 and the grid electrode 103 is, for example, 100 μm, and the electric field strength for emitting certain electrons (for example, a current density of 100 μA / cm ² ) from the electron emission source 102 is 1 V / μm. Then, if the cathode electrode 101 is grounded to 0 V and a direct current of 100 V is applied to the grid electrode 103, 100 μA / cm ² of electrons are arranged opposite to the grid electrode 103 and the cathode electrode 101 (FIG. 3). In this case, the light is emitted toward a plane seen from above.

  Therefore, if a DC voltage of, for example, 5 kV is applied to the phosphor plate electrode, electrons accelerated at 5 ekV collide with the phosphor of the phosphor plate electrode 104 and the phosphor emits light. At this time, as shown in FIG. Assuming that the field emission characteristic of the AA part of the electron emission source 102 is 0.8 V / μm and the field emission characteristic of the BB part is 1.2 V / μm, the light emission when viewed from above the fluorescent plate is very high in the AA part. And the BB part becomes dark. As a result, uneven light emission occurs.

  Patent Document 3 discloses a technique for dealing with such light emission unevenness caused by variations in the field emission characteristics of the electron emission source. The technique of Patent Document 3 is a technique related to FED, in which a flat cold cathode made of carbon nanotubes is formed on a cathode substrate, a transparent anode substrate is striped on a transparent anode strip, and a stripe shape intersecting this is formed. The selected grid strip and the grid-like electronic lead-out grid are formed.

According to the technique of Patent Document 3, electrons emitted from the cold cathode are retained in an electron retention region between the cold cathode and the electron extraction grid to form an electron cloud. Then, when a voltage is applied to any selected grid strip and any anode strip, the electron flow from the electron cloud passes through the opening of the electron extraction grid and the opening of the selected grid strip and then on the anode strip. Collides with phosphor. Thereby, the uneven distribution of electrons due to cold cathode field emission can be averaged, and the uneven emission of the phosphor can be eliminated.
JP 2004-207066 A JP 2004-220896 A JP 2004-335385 A

  However, the technique disclosed in Patent Document 3 is premised on a display device that emits a phosphor for each pixel by dividing an anode (phosphor electrode) into a matrix. For this reason, brightness much higher than that of the display device is required, and it is difficult to apply the technique of Patent Document 3 when considering an application for illumination that emits light from the entire surface of the planar phosphor electrode. However, the structure becomes complicated and the cost increases.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a light emitting device that can reduce unevenness in light emission due to variations in field emission characteristics of an electron emission source without requiring a complicated structure. Yes.

In order to achieve the above object, a light emitting device according to the present invention is a light emitting device in which at least a cathode electrode having an electron emission source and a fluorescent plate electrode having a phosphor are arranged opposite to each other in a vacuum, and the field emission in the electron emission source. And a voltage control means for periodically applying a control voltage at which the current density is equal to or higher than a current density at which light emission from the phosphor reaches a saturated state .

  Further, in a light emitting device having a three-pole structure in which a grid electrode is disposed between a cathode electrode and a fluorescent plate electrode, a control voltage is periodically applied between the grid electrode and the cathode electrode, and the control voltage is applied. In synchronization, it is desirable to apply a voltage higher than the control voltage between the fluorescent plate electrode and the cathode electrode.

  The voltage control means of the light-emitting device having a three-pole structure can be configured using a transformer circuit in which a cathode electrode, a grid electrode, and a fluorescent plate electrode are connected to the secondary side, and a periodic voltage signal is provided on the primary side of the transformer circuit. Is applied periodically in synchronization with the control voltage between the grid electrode and the cathode electrode and the voltage between the fluorescent plate electrode and the cathode electrode.

  The application of the control voltage to the cathode electrode is preferably performed at a repetition period of 60 Hz or more, and the period of applying the control voltage to the cathode electrode is at least 10 times the period of applying the control voltage to the cathode electrode. It is desirable.

  The light emitting device according to the present invention can reduce light emission unevenness due to variations in field emission characteristics of the electron emission source without requiring a complicated structure.

  Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 relate to an embodiment of the present invention, FIG. 1 is a basic configuration diagram of a light emitting device, and FIG. 2 is an explanatory diagram of a drive circuit.

  As shown in FIG. 1, the light-emitting device 1 in this Embodiment is a light-emitting device used as a planar field emission illumination lamp, for example, and the inside of the glass base materials 2 and 3 opposingly arranged by the predetermined space | interval Is maintained in a vacuum state, and in this vacuum state, the cathode electrode 5, the grid electrode 10, and the fluorescent plate electrode 15 are arranged in this order. In FIG. 1, a three-pole structure including the cathode electrode 5, the grid electrode 10, and the fluorescent plate electrode 15 is illustrated, but a two-pole structure that does not use the grid electrode 10 may be used.

  The cathode electrode 5 is made of a conductive material formed on the glass substrate 2 serving as a base. For example, a metal such as aluminum or nickel is deposited by vapor deposition or sputtering, or a silver paste material is applied and dried. It is formed by firing. On the surface of the cathode electrode 5, an electron emission source 6 is formed by applying an emitter material such as a carbon nanotube, a carbon nanowall, a spint type micro cone, or a metal oxide whisker in a film shape.

  The grid electrode 10 is disposed to face the cathode electrode 5 and applies an electric field to the electron emission source 6 according to a potential difference (gate voltage) with the cathode electrode 5 to emit electrons. The grid electrode 10 has a large number of fine openings through which electrons emitted from the electron emission source 6 pass, and is formed by etching or punching a conductive thin plate such as stainless steel, nickel, or amber. Etc., a large number of openings such as a circle and a rectangle are formed.

  The fluorescent plate electrode 15 is made of a transparent conductive film (for example, ITO film) disposed on the back surface side of the glass substrate 3 serving as a light projecting surface, and has an electron emission source on the surface facing the grid electrode 10 (cathode electrode 5). A phosphor 16 that is excited and emitted by electrons emitted from 6 is applied. The phosphor 16 is formed on the phosphor plate electrode 15 by using an ink jet method, a photolithography method, a precipitation method, an electrodeposition method or the like using, for example, a zinc oxide-based material.

  In the light emitting device 1 described above, the anode electrode 17 made of the fluorescent plate electrode 15 and the phosphor 16 on the glass substrate 3 is provided with respect to the cathode electrode 7 made of the cathode electrode 5 and the electron emission source 6 on the glass substrate 2. While maintaining a predetermined positive high potential, a predetermined gate voltage is applied between the cathode 7 and the grid electrode 10 to cause electrons to be emitted from the electron emission source 6 into the vacuum. The electrons emitted from the field are accelerated toward the anode electrode 17, and the electrons passing through the openings of the grid electrode 10 collide with the phosphor 16 to emit light.

  In this case, since the field emission characteristics of the electron emission source 6 are not necessarily constant, the current density of the electron emission differs depending on the region of the electron emission source 6 in the electric field intensity generated at a normal gate voltage. When viewed, uneven brightness may occur. Therefore, the light emitting device 1 is provided with voltage control means (described later) for periodically applying the control voltage Vg at which the field emission current density in the electron emission source 6 is equal to or higher than a set value to the cathode electrode 5 as a gate voltage. By this control voltage Vg, an electric field strength that gives a current density that causes the entire phosphor 16 to emit light with high luminance is given to the entire cathode electrode 7.

  That is, in general, the current density of field emission increases gradually as the electric field strength increases when the applied electric field strength is relatively small, but when the electric field strength exceeds a certain electric field strength, the current density increases. Increases rapidly. On the other hand, the phosphor has higher emission luminance as the current density increases. However, the emission luminance is saturated at a predetermined current density or higher, and the emission luminance does not increase even if the current density is increased further. Accordingly, the electric field intensity applied to the cathode electrode 7 is greatly increased than usual so that the phosphor 16 emits light in a saturated state or at a high brightness close to the saturated state, thereby causing a region due to variations in the field emission characteristics of the electron emission source 6. It is possible to reduce a difference in light emission luminance for each light emission and to reduce light emission unevenness.

In the present embodiment, the current density setting value corresponding to the control voltage Vg applied to the cathode electrode 7 is defined as the current density at which the light emission from the phosphor 16 reaches a saturated state, and the field emission current in the electron emission source 6 is determined. A control voltage Vg for generating an electric field strength at which the density is equal to or higher than a set value (current density at which light emission from the phosphor 16 reaches a saturated state) is applied to the cathode electrode 7. For example, assuming that the distance A between the grid electrode 10 and the cathode electrode 15 is 100 μm, the electric field strength required to obtain the electron emission of 100 μA / cm ^{2 at} the cathode electrode 7 is 0.8 V / μm at the AA portion and at BB portion. When the voltage is 1.2 V / μm, the control voltage Vg for generating an electric field of 2 V / μm is applied to the entire cathode electrode 7, thereby causing the entire phosphor 16 to emit light with high brightness in a saturated state.

  The control voltage Vg for causing the phosphor 16 to emit light with high brightness is applied only for a short time in order to prevent burning of the phosphor 16 and wasteful power consumption. Recognize as continuous light emission using visual afterimage phenomenon. Except for the period of high-luminance light emission in which the control voltage Vg is applied as the gate voltage, in this embodiment, the gate voltage is set to zero and the rest period in which no cathode current flows is set.

  Specifically, the function as voltage control means for applying the control voltage Vg to the cathode electrode 5 can be realized by the transformer circuit 20 including a transformer shown in FIG. The transformer circuit 20 has a pulse generation source (not shown) connected to the primary side, the fluorescent plate electrode 15 (anode electrode 17) on the secondary high voltage first tap TP1, and the secondary low voltage second tap TP2. The grid electrode 10 is connected to the cathode electrode 5 (cathode electrode 7) and the third tap TP3 between the high and low pressures on the secondary side. The first tap TP1 and the second tap TP2 are provided in the secondary winding that generates a positive high voltage (anode voltage) Va applied from the fluorescent plate electrode 15 to the cathode electrode 5, and the third tap TP3 and the second tap TP2 are provided. TP2 is provided in a secondary winding that generates a control voltage Vg applied from the grid electrode 10 to the cathode electrode 5.

  The pulse generation source outputs a pulse signal having an ON (high level) period of T2 and an ON (high level) and OFF (low level) period of T1, and this pulse signal is applied to the primary side of the transformer circuit 20. As a result, the control voltage Vg generated between the third tap TP3 and the second tap TP2 on the secondary side in the period T2 is periodically applied from the grid electrode 10 to the cathode electrode 5, and the phosphor 16 is saturated. Periodically emits high-intensity light. As described above, if the current that the phosphor 16 reaches the saturation state is continuously supplied, the phosphor 16 is burned out and the power is wasted. Therefore, the (T1-T2) period is provided as a sufficient pause period in which the gate voltage is zero and no cathode current flows, in contrast to the T2 period in which the control voltage Vg is applied. In order to ensure this sufficient rest period, for example, it is desirable to set the repetition period T1 to at least 10 times the T2 period during which the phosphor 16 emits light with high brightness in a saturated state.

  Note that in the (T1-T2) period, which is a pause period, the gate voltage may be set to a voltage at which weak light emission is possible without being completely zero. Of course, in this state, even if light is emitted slightly at the position facing the AA portion of the phosphor 16, light is hardly emitted at the position facing the BB portion and unevenness in light emission luminance occurs. If high-intensity light emission in the period remains as an afterimage and the frequency of the period T1 is approximately 60 Hz or more, it is recognized as continuous light emission.

For example, a pulse signal input to the primary side of the transformer circuit 20 is a signal having a period T1 = 10 ms (frequency 100 Hz) and a period T2 = 1 ms in which the control voltage Vg is applied, and is 300 μA / cm ² from the AA unit in a 1 ms period. electron emission is obtained, also with those of the electron emission obtained 200 .mu.A / cm ² from the BB unit, further, assuming that light emitted from the phosphor 16 reaches saturation at a current density of 200 .mu.A / cm ^2, the control The AA portion and the BB portion have substantially the same emission luminance in 1 ms when the voltage Vg is applied, and it is recognized as uniform light emission without continuous luminance unevenness due to the afterimage in 9 ms of the rest period (T1-T2).

  In the present embodiment, a high voltage anode voltage Va is applied from the fluorescent plate electrode 15 to the cathode electrode 5 in synchronization with the application of the control voltage Vg. That is, during the T2 period of the pulse signal, the control voltage Vg that enables high-luminance light emission in the saturation state of the phosphor 16 is applied from the grid electrode 10 to the cathode electrode 5, and T2 is applied to this control voltage Vg. Only during the period, a high anode voltage Va is applied from the fluorescent plate electrode 15 to the cathode electrode 5.

  This makes it possible to prevent unnecessary power consumption by setting the voltages from the fluorescent plate electrode 15 and the grid electrode 10 to zero except during the T2 period in which the phosphor 16 emits light with high brightness in a saturated state. In addition, the anode voltage and the gate voltage can be simultaneously applied only during a period necessary for light emission only by inputting a pulse signal to the transformer circuit 20, and a rectifier circuit for applying the anode voltage and the gate voltage as in the prior art. Etc., and it is not necessary to generate a high DC voltage, and the cost can be reduced with a simple configuration.

  In the actual device design, the type and thickness of the phosphor 16 applied to the phosphor plate electrode 15, the voltage applied to the phosphor plate electrode 15 and the grid electrode 10, and the pulse signal so as to obtain the desired emission luminance and emission uniformity. The period T1 and the time period T2 during which the control voltage Vg is applied are optimally adjusted.

  In the light emission method of the present invention, the emission luminance can be freely adjusted by changing the frequency of the pulse signal from, for example, about 60 Hz to 200 Hz. Furthermore, if the average or effective current flowing through the cathode electrode is detected and the period of the pulse signal is automatically adjusted so that a constant cathode current continues to flow at all times, the decrease in emission luminance associated with changes over time in the cathode is automatically performed. It is also possible to correct automatically.

Basic configuration diagram of light emitting device Configuration diagram of transformer circuit Explanatory drawing which shows the light emission nonuniformity in the conventional light-emitting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light-emitting device 5 Cathode electrode 6 Electron emission source 10 Grid electrode 15 Phosphor plate electrode 16 Phosphor 20 Transformer circuit (voltage control means)
Vg control voltage

Claims (5)

At least in a light emitting device in which a cathode electrode having an electron emission source and a fluorescent plate electrode having a phosphor are arranged opposite to each other in a vacuum,
A voltage control means is provided for periodically applying a control voltage at which the current density of field emission in the electron emission source is equal to or higher than a current density at which light emission from the phosphor reaches a saturated state to the cathode electrode. Light-emitting device. The light emitting device
A grid electrode is disposed between the cathode electrode and the fluorescent plate electrode,
The voltage control means is
The control voltage is periodically applied between the grid electrode and the cathode electrode, and a voltage higher than the control voltage is synchronously applied between the fluorescent plate electrode and the cathode electrode. The light-emitting device according to claim 1 . The voltage control means is configured using a transformer circuit in which the cathode electrode, the grid electrode, and the fluorescent plate electrode are connected to the secondary side,
By applying a periodic voltage signal to the primary side of the transformer circuit, the control voltage is applied between the grid electrode and the cathode electrode, and the control is performed between the fluorescent plate electrode and the cathode electrode. 3. The light emitting device according to claim 2 , wherein a voltage higher than the voltage is applied synchronously. The light-emitting device according to claim 1 , wherein the control voltage is applied to the cathode electrode at a repetition period of 60 Hz or more. 5. The light-emitting device according to claim 1 , wherein a period in which the control voltage is applied to the cathode electrode is at least 10 times longer than a period in which the control voltage is applied to the cathode electrode. .

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