JPS614030A - Electrochromic display device - Google Patents

Abstract

PURPOSE:To improve the responsibility of the electrochromic display device by forming plural electrochromic display picture elements, two thin-film transistors (TR), and one capacitor on a substrate, and using polycrystalline Si formed in the semiconductor layer of a thin-film TR for driving by a beam annealing method. CONSTITUTION:Row electrodes 25 are driven, line by line, and capacitors 23 provided corresponding to picture elements on the lines 25 are applied with a 0 or negative voltage from row electrodes 26 simultaneously through thin-film TRs 21 in an ON state according to coloring/decoloring states of picture elements. Feeding electrodes 27 applies a negative voltage to a counter electrode after the charging/discharging states of the capacitors 23 are determined. Consequently, a TR22 turns on to supply an electron to a picture element 24, and an ion is supplied from an electrolyte side at the same time to color the picture element. The polycrystalline Si obtained by annealing amorphous or fine crystal Si with an electron beam or laser beam is used for the thin-film TR for driving to form a semiconductor layer, improving the responsiveness.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrochromic display device that exhibits coloring and decoloring through an electrochemical redox reaction. The present invention relates to an active matrix drive type electrochromic display device including a capacitor of the present invention.

[Conventional technology]

The electrochromic display has the configuration shown in FIG. 2, and includes a display electrode substrate consisting of a transparent electrode (2) and an electrochromic substance (3) formed on a transparent substrate (1), and a substrate ( 4) Electrode (5) formed on
) and a counter electrode substrate consisting of a counter electrode (6) are arranged to face each other, and an electrolytic solution (7) and, if necessary, a background plate (8) are sealed between these two substrates.

In such a display body, the display electrode is placed in a negative (
When the voltage is turned off (or positive) and the voltage is turned off, the electrochromic substance is reduced (or oxidized) and becomes colored. On the contrary, if the display electrode is made positive (or negative) with respect to the counter electrode and a voltage is applied, the display returns to the erased state.

FIG. 3 shows the relationship between the response time and applied voltage during coloring and decoloring of a display using an amorphous tungsten oxide thin film as an electrochromic material. By applying a voltage of -1,0"i' to -2,2v to a colored charge of 5mc/-, the amorphous tungsten oxide thin film changes from transparent to blue, and its response time changes from 500mθθC to 5Q m
It changes between 5ec. Also, from -0.2V to +1. O
The color is erased by applying a voltage of v, but the response time is 30
It takes values ranging from 0 m5ec to 5 Q m5ec.

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ω corresponds to a state in which the externally applied voltage and the back electromotive force of the electrochromic display are balanced by the action of the electromotive force of the amorphous tungsten oxide in the colored state.

This electromotive force exhibited by electrochromic materials increases with increasing amount of coloration.

When time-division driving is performed using an electrochromic display, this electromotive force exhibited by the electrochromic material becomes a major obstacle. In other words, when a display pixel in a colored state and a display pixel in a decolored state are connected to each other by a common line in an xY matrix type, electric charge moves from the display pixel in a colored state to a display pixel in a decolored state. occurs, and both change to an intermediate colored state.

As a method of eliminating the basic drawbacks of such electrochromic display bodies and obtaining a dot matrix type display device using time-division driving, a method of adding an active element such as a transistor to each display pixel is known. Fourth
In the figure, (11) is a row electrode, (12) is a column electrode, (1
3) indicates a display pixel, and (14) indicates a thin film transistor.

Driving such a display device is achieved by driving the row electrodes line by line and simultaneously applying a coloring or decoloring signal to the column electrodes corresponding to the display pixels existing on the selected line. be done.

[Problem to be solved by the invention]

However, in the display device having the configuration shown in FIG. 4, since writing or erasing is performed in each pixel while sequentially selecting row electrodes, the time required to display the entire screen is considerably long, making it impractical. It was ringing. This is especially true when using an electrochromic material such as amorphous tungsten oxide, which has a relatively slow response speed.In a dot matrix type display with N row electrodes, the response time is 5QxN (msθC). If N is 1000, it will take 50 seconds.

[Failure to solve the problem]

The present invention has been made to improve these drawbacks,
First and second thin film transistors and one capacitor are provided for each of the plurality of display pixels formed on the substrate, and the drain electrode of the first thin film transistor is connected to the gate electrode of the second thin film transistor and the capacitor. the other end of the capacitor is connected to a source or drain electrode of a second thin film transistor, the drain electrode of the second thin film transistor is connected to an electrochromic display pixel; By using polycrystalline silicon obtained by a beam annealing method using a laser beam, an electron beam, etc. as the semiconductor layer for this second thin film transistor, which directly supplies charge, an active matrix drive type electrochromic transistor with improved response characteristics is realized. The present invention provides a fixed-touch display device.

The electrochromic substance used in the display pixel of the present invention is a solid electrochromic substance that changes color in the visible light range by applying a voltage, such as a transition metal compound such as tungsten oxide, iridium oxide, or molybdenum oxide.

Examples include rare earth diphthalocyanine compounds such as ruthenium siphthalocyanine.

The counter electrode may be any material that can smoothly color and erase the electrochromic material of the display pixel, and usually a mixture of a transition metal compound such as carbon, manganese dioxide, tungsten oxide, and an adhesive, or a single electrochromic material may be used. good.

An electrolytic solution disposed between a display pixel and a counter electrode in which a timing electrolyte such as lithium perchlorate is dissolved in an organic solvent is preferable from the viewpoint of response speed, but an electrolytic solution in which a gelling agent such as a resin is added to these is preferable. A gel electrolyte, a porous film impregnated with the electrolyte, or a sheet-like solid electrolyte can also be used, as long as it can color or erase the electrochromic substance on the display screen.

-Of course, in addition to these basic configurations, there are also applications such as background plates, color printing on substrates, transfer between substrates, metal leads, non-110 part insulation overcoats, lighting devices, and combinations with other display elements. It is also possible to provide display pixels and a counter electrode on the same substrate side, or to form a third electrode such as a reference electrode.

[For production]

The first transistor (21), second transistor (22), capacitor (23), display pixel (
24), row electrodes (25), column electrodes (26), and supply electrodes (27) for supplying charges necessary for coloring/decoloring electrochromic display pixels.
Figures (a) and (b) show an example in which the capacitor is provided between the drain electrode of the first thin film transistor and the drain electrode of the second thin film transistor, and (b) The container is the drain electrode of the first ON film transistor and the source t of the second thin film transistor.
r: This is an example provided between the pole.

An example of operation with respect to FIG. 1(,) is explained as follows.

The row electrodes are sequentially driven line by line, and a capacitor provided for each display pixel on this line has a first thin film transistor (
21) from the column electrodes (26), respectively, are simultaneously applied with O or negative voltages. After all row electrodes have been driven and the charging or discharging state of each capacitor has been determined, a negative voltage is applied to the feed electrode (27) with respect to the counter electrode. By applying this voltage, the second thin film transistor corresponding to the display pixel whose capacitor is in the discharged state is turned on, and the electrochromic display pixel (24) is connected to the second thin film transistor.
Electrons are supplied through the thin film transistor (22) of
At the same time, light is supplied from the electrolyte side 7, and the display pixels become colored.

On the other hand, if the capacitor is negatively charged and therefore the potential of the gate electrode of the second thin film transistor is equal to the voltage applied to the source electrode, the second thin film transistor will not be in the ON state and the drain electrode will be Connected display pixels exhibit no coloration.

The coloring time T of the electrochromic display body carried out in this way is T=T1 x where the number of row electrodes is N.
It is expressed as N+T1. Here, T1 is the time required to drive one of the row electrodes (25) connected to the gate electrode of the first thin film transistor'),'r! is the time to drive the power supply & (27) connected to the source electrode of the second thin film transistor in order to color the electrochromic material or the response time of the electrochromic material.

Here, several tens of microseconds is sufficient for T1,
T again! is several tens to several hundreds of milliseconds, so if the number of row electrodes N is 1000, T is several tens of milliseconds to several tens of milliseconds.
It can take values in the range 0 milliseconds. Thus, it can be seen that the response time is significantly improved compared to the conventional example.

However, in order to supply the necessary charge to the electrochromic material in a short time, it is important that the current in the ON state of the second thin film transistor be sufficiently large. When using a tungsten oxide thin film as an electrochromic material,
It is necessary to determine this current value in consideration of the area of each display pixel.

Thin film transistors whose semiconductor layer is an amorphous silicon thin film are being considered as active matrix components for image display devices, especially in combination with liquid crystal display elements, but when considering combination with electrochromic display elements, , it is difficult to obtain a sufficiently large current value,
Therefore, sufficient current cannot be supplied to achieve the response speed unique to such electrochromic materials.

When using amorphous tungsten oxide, which is a typical electrochromic material, a charge of about 8 mC/- is required to obtain sufficient contrast, which is
A current of 80 mA/- is required to inject with Q m5ec . Dot matrix type light where each dot has an area of 1- (in order to realize this in a display device, the driving thin film transistor must have a power supply capacity of 0.8 mA with a 1-gauge pixel; It is extremely difficult to realize thin film transistors with such power supply capability using amorphous silicon.On the other hand, amorphous or microcrystalline silicon obtained by various methods can be processed using electron beams, lasers, etc. When manufacturing a thin film transistor using polycrystalline silicon obtained by beam annealing, the above current value can be obtained relatively easily.Here, the reason for using beam annealing is the above-mentioned 2. This is because only one of the thin film transistors is selectively made of polycrystalline silicon.
The other first thin film transistor is not subjected to beam annealing and is used as a high-resistance semiconductor thin film as it is to obtain a more preferable result. This increases the resistance of the first thin film transistor when it is OFF and also increases the ON10 FF ratio, thereby reducing the size of the capacitor to be added for each pixel and minimizing the effective display area. It can be made louder.

FIG. 5 shows a cross-sectional view of one display pixel of an active matrix driven electrochromic display device according to the present invention.

(31) is a transparent substrate, and on this is a 20th thin group transistor whose semiconductor layer (32) is a silicon thin film crystallized by a laser beam, and a transistor whose semiconductor layer (33) is made of amorphous silicon. a first thin film transistor;
The drain electrode (34) of the second thin film transistor is connected to the gate electrode (35) of the second thin film transistor. Further, a capacitor is formed between the gate electrode (35) and the drain electrode (36) of the second thin film transistor. The solid drain electrode (36) is further connected to a transparent conductive film (37) formed on the substrate (31), and an amorphous tungsten oxide thin film (38) is formed on this transparent electrode.

The other substrate (39) is a substrate with a concave groove formed by etching, and an electrode (40) is formed on the inner surface of the substrate.
is formed. A plate-shaped counter electrode (41) made of carbon and a depolarizing material is fixed on this electrode with a conductive adhesive, and a background plate (42) made of a porous polymer containing a white material is further placed on top of this. Placed.

The space between the side substrates is filled with propylene carbonate electrolytic i (43) in which Li0104 of IM is dissolved to complete the display device.

FIG. 6 is a plan view showing the display-side electrode substrate obtained in this manner.

〔Effect of the invention〕

As described above, the present invention solves the problem of electrolytic displays that are difficult to drive in a time-division manner and have a relatively slow response speed. By arranging two thin film transistors and one capacitor, which have a higher power supply capability to electrochromic display pixels than K, using the method already shown, we have created a practical dot matrix type electrochromic display with even higher response speed. This makes it possible to manufacture chromic display devices.

This makes it possible to provide a display device that can display characters, numbers, figures, etc. with excellent visibility.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the arrangement of two thin film transistors, a capacitor, and an electrochromic display pixel of a display device of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the structure of an electrochromic display. FIG. 3 is a diagram showing the relationship between the response time and applied voltage of the display shown in FIG. 2. FIG. 4 is a diagram showing a conventional example of an electrochromic display in which one thin film transistor is provided for each display pixel. FIG. 5 is a schematic cross-sectional view showing one display pixel of the display device of the present invention. FIG. 6 is a schematic plan view of the display pixel shown in FIG. 5. 1.31...Transparent substrate, 2.37・Curve・Transparent electrode 3.38...Electrochromic material layer 4
．． 39... Substrate having a recess, 5.40...
... Electrode 4 6.41 ... Counter electrode, 7,43 ... Electrolyte 8.42 ...
・Background plate, 11.25...Row electrode 12.2
6...Column electrode, 13.24...Display pixel, 14...Thin film transistor, 15,2...
... Common counter electrode, 21 ... First thin film transistor, 22 ... Second thin film transistor, 23 ... Capacitor, 27 ... Power supply Electrode, 28... Source electrode of first thin film transistor, 29. 34... Drain electrode of first thin film transistor, 30... Source electrode of second thin film transistor, 32 ...Polycrystalline silicon, 33...Amorphous silicon, 35...
・Gate electrode of second thin film transistor, 36...
...Drain electrode of second thin film transistor (Figure 1, Figure 2, applied voltage) Figure 3, Figure 4, Figure 6, Figure 5

Claims (1)

[Claims] 1. A display device comprising a plurality of electrochromic display pixels formed on a substrate, two thin film transistors, first and second, and one capacitor added to each display pixel. , the drain electrode of the first thin film transistor is connected to the gate electrode of the second thin film transistor and one end of a capacitor, the other end of the capacitor is connected to the source or drain electrode of the second thin film transistor, and the second thin film transistor is connected to the drain electrode of the first thin film transistor. The drain electrode of the thin film transistor is connected to the electrochromic display pixel,
An electrochromic display device characterized in that the semiconductor layer constituting the second thin film transistor is polycrystalline silicon formed by a beam annealing method. 2. The electrochromic display device according to claim 1, wherein the electrochromic substance is amorphous tungsten oxide.