JPH0360099B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrochromic display (ECD) using electrochemical redox reactions.
For more details, see
Concerning the configuration of ECD.

As is well known, ECD can provide a clearer display than LCD and is independent of viewing angle. However, it is inferior to liquid crystals in terms of display functionality and power consumption. In particular, for multi-functional displays, multiplexing cannot be applied to the drive method, which is disadvantageous for multi-digit displays, character displays, and matrix displays. The reason for this is that current crosstalk occurs due to the highly conductive electrolyte filled between the display electrode and counter electrode of the ECD.

FIG. 1 shows the simplest matrix type display consisting of four pixels. Display electrodes A to D consist of a transparent electrode patterned on a transparent glass substrate and an EC thin film laminated thereon. Counter electrodes a to d are printed and coated with a mixture of carbon and redox substance. The display electrode and counter electrode are wired as shown in the figure to enable multiplex driving.
Further, an electrolytic solution or a solid electrolyte is filled between the display electrode and the counter electrode, and conduction of electrons and ions occurs. Now, in this display, on the opposite side (X ₁ ,
Assuming that X ₂ ) is scanned line-sequentially and the display poles (Y ₁ , Y ₂ ) are turned on and off in synchronization with this,
In order to light up the pixel A, the display electrode may be set to -V (to cause a reduction reaction) with respect to the counter electrode a.
In other words, the X ₁ row is selected sequentially at 0 potential, and the Y ₁ column is selected sequentially.
Set the ON potential to -V. Then, a potential difference -V is generated between the display electrode A and the counter electrode a, which are the intersections of the _X1 row and the _Y1 column, so that the pixel A lights up in color. However, at this time, since the display electrode and the counter electrode are a good conductor due to the electrolyte, a similar potential difference -V is generated between the display electrode B and the counter electrode a, and the pixel B is also turned on. Y ₁
If there are many display poles in a row other than A and B, all of them light up with the _X1 row as the opposite pole. The same situation applies when erasing the display.

In this way, the usual matrix driving method (multiplexing) that has been applied to EL and LCD cannot fundamentally be used with ECD. In other words, the driving method of selecting the intersection of rows and columns and turning them on and off is completely unsuitable for field-effect elements.

Therefore, in order to eliminate such crosstalk, it is absolutely essential to make each pixel electrically independent.

However, a method of integrating ECD small cells by providing partition walls between each pixel is difficult in terms of manufacturing. Therefore, we came up with the idea of using an active matrix.
This is ECD multiplexing.

Figure 2 is a diagram of the principle when an active matrix is applied to ECD. The parts corresponding to pixels in the matrix are ECD cells numbered 1 to 6 (common counter electrodes), and coloring and erasing of the display is done by field effect transistors 7 to 12 installed at each intersection of the matrix. Control. Now, if you want to light up a point (i, i) on the matrix, you can apply a voltage that turns on the transistor to the Xi row, and in synchronization with that, apply a write voltage -V to the Yi column. At that time, the transistors in other rows such as Xj are OFF,
Also, it is assumed that no voltage is applied to the Yj, Yk columns, etc. Then, a voltage of -V is applied to cell 1, and the other cells 2 to 8 are placed in an electrically floating state. That is, only cell 1 is independently selected and colored. The same is true for erasing the display, and the opposite voltage V may be applied. Therefore, with the help of such an active matrix
In ECD, if the X rows are line-sequentially scanned and ON/OFF signals are sent to the Y columns in synchronization with this, multiplex driving can be performed without causing the aforementioned crosstalk.

In order to apply this driving principle, thin film transistors made by vapor deposition or silicon substrates are used.
It is necessary to form a MOS transistor, in particular,
In the latter case, since the substrate is opaque and the pixel electrode for display must be formed on the same silicon substrate as the transistor, restrictions are placed on the installation location of the counter electrode. That is, the silicon substrate must be located at the rear of the display panel, and therefore, the pixels are necessarily colored on the rear substrate side, so it is desirable that the counter electrode is transparent and can be formed on the front glass substrate. However, with the existing technology, it is not possible to form the counter electrode transparently. That is, in ECD using tungsten oxide, a black electrode material made of carbon, or a mixture of carbon and metal powder, or carbon and a redox substance is used as the counter electrode. The present invention takes this point into consideration and provides a counter electrode that meets the conditions of ECD using an active matrix.

Figure 3 shows ECD using active matrix
FIG. 13 is a silicon substrate, on which there are
MOS field effect transistor 14 and pixel electrode 1
5 are being made. The pixel electrode 15 is directly connected to the drain electrode of the transistor 14 and has Al wiring. A thin tungsten oxide layer 16 is laminated on the pixel electrode 15, and this layer changes color and fades. Reference numeral 17 is transparent glass, and on its inner surface, the counter electrode material 18, which is mainly composed of carbon, is printed and coated in a grid or striped pattern. The present invention is characterized by the method of making this counter electrode. 19 is an electrolyte sealed in the cell, 1M-LiClO ₄
of propylene carbonate solution. 20 is an insulating film which also serves as a protective coat for the transistor and wiring.

FIG. 4 is a diagram showing the overall shape of the counter electrode 18 provided within the windshield. As is clear from this figure, in the present invention, counter electrodes are formed at locations corresponding to between rows or columns of a matrix type display, in other words, at locations corresponding to spaces between display pixels. Therefore, as a method for forming it, vapor deposition using a shadow mask, sputtering method, etching method using photolithography, or screen printing method can be applied. The former two methods may be advantageous for counter electrodes using noble metals or redox substances. Furthermore, the printing method is simple for the current counter electrode using carbon powder. In other words, a suitable binder is mixed with a powder such as graphite or activated carbon, or with a metal or a redox substance to form a viscous liquid, which is then applied to a screen printing machine that forms a pattern. Therefore, the binder may be coated on a glass substrate, and the binder may be dried and solidified by heat treatment, or carbonized or vaporized by sintering.

In this example, an attempt was made to use activated carbon and graphite as the carbon and Berlin blue, an iron complex, as the redox substance. Sodium carboxymethyl cellulose was used as the binder, and the viscosity was adjusted by adjusting the amount of water added. The electrode pattern was formed by printing using a stencil screen, and the electrode pattern was shaped like a lattice as shown in FIG. The heat treatment after printing was performed at 100°C for 1 hour to solidify the binder. As a result, an electrode was obtained that had no cracks after printing, had good conductivity, and also functioned smoothly in oxidation-reduction reactions as a counter electrode. Although the area ratio of the opposing electrodes between the display pixels was about 20%, there was little visual resistance to the display. However, with future improvements in printing technology and the development of counter electrode materials that work effectively with a small area ratio, it will be necessary to improve this lattice-shaped counter electrode to the point where it is no longer noticeable.

As described above, the present invention relates to a method for forming a counter electrode of an ECD using an active matrix, and the usefulness of the present invention can be exhibited particularly when a Si substrate is used. Although the present invention uses inorganic solid tungsten oxide as the EC material, this method may also be applied to organic thin film ECDs in which an EC material is bonded to a polymer film. Moreover, various modifications are possible for the shape of the counter electrode. For example, in a character display, counter electrodes may be provided between the lines of characters to make the display easier to read and to perform the necessary function as an electrode. Furthermore, it may also have a decorative effect.

As described above, in the present invention, an electrolytic solution is sandwiched between a pair of substrates, and signal electrode lines and scanning electrode lines are formed in a matrix on one of the pair of substrates, and the signal electrode lines and scanning electrode lines are formed in a matrix. At the intersection of and the scanning electrode line,
A MOS transistor and a pixel electrode are formed,
In an electrochromic display in which _three WO layers are formed on a pixel electrode and a counter electrode is formed on the other substrate, the counter electrode is an opaque electrode and overlaps the pixel electrode. By arranging them so that they do not overlap, the pixel electrode does not overlap with the opaque counter electrode, and the change in color tone of the WO ₃ layer on the pixel electrode is not blocked by the opaque counter electrode, so the luminance changes. A display body with bright and clear display quality can be obtained. Furthermore, since the transistor is covered with an opaque electrode, it is completely unaffected by light, and malfunctions due to the influence of light are completely eliminated.

[Brief explanation of drawings]

Figure 1 shows a conventional matrix type ECD.
Figure 2 is a diagram showing a conventional active matrix type ECD. FIG. 3 is a sectional view showing the ECD of the present invention.
FIGS. 4a and 4b are diagrams showing the shape of the counter electrode used in the present invention.

Claims (1)

[Claims] 1. An electrolytic solution is sandwiched between a pair of substrates, a signal electrode line and a scanning electrode line are formed in a matrix on one of the pair of substrates, and the signal electrode line and the scanning electrode line are formed in a matrix. In an electrochromic display body, a MOS transistor and a pixel electrode are formed at the intersection with the pixel electrode, _three WO layers are formed on the pixel electrode, and a counter electrode is formed on the other substrate. An electrochromic display characterized in that the counter electrode is an opaque electrode and is arranged so as not to overlap the pixel electrode.