JPS61277929A - Electrochromic display element - Google Patents

Abstract

PURPOSE:To connect surely the drain electrode of the 1st transistor and the gate electrode of the 2nd transistor so that the sure insulation is made possible by forming the title element in such a manner that the positional relation of the source electrode and drain electrode with a gate electrode viewed from a substrate varies with the 1st thin film transistor and the 2nd thin film transistor. CONSTITUTION:The drain electrode 31 of the 1st TR is connected electrically to the 2nd gate electrode of the 2nd TR. The drain electrode 25 of the 2nd TR is connected electrically to a display picture electride 5. The 1st TR is made into the reverse stagger structure in which the gate electrode 23 exists on the lower side of the source electrode 30 and the drain electrode 31. The 2nd TR is made into the co-planar structure in which the gate electrode 32 exists on the side upper than the source electrode 24 and the drain electrode 25. The direct electrical connection of the drain electrode of the 1st TR and the gate electrode of the 2nd TR is thus made possible without using contact through-holes and the reliability is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrochromic display element that exhibits one-color/discoloration by an electrochemical redox reaction, and more specifically relates to an electrochromic display element that exhibits one-color/discoloration by an electrochemical redox reaction. The present invention relates to a matrix-driven electrochromic display element.

[Prior art 1] An electrochromic display element 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 l made of glass, plastic, etc., and a recessed portion. glass or plastic, consisting of an electrode 5 and a counter electrode 6 formed on a substrate 4 having a

A counter electrode substrate made of ceramic, metal, etc. is placed facing each other,
It is obtained by sealing an electrolyte 7 and, if necessary, a background plate 8 between these two substrates.

Such display - non-response to the counter electrode.

When the display electrode is made negative (or positive) and a voltage is applied, the electrochromic substance is reduced (or oxidized) and becomes colored. On the contrary, if a voltage is applied to the counter electrode by making the display electrode positive (or negative), the 1 display returns to the erased state.

FIG. 3 shows the relationship between the response time of coloring and decoloring of a display element using an amorphous tungsten oxide thin film, which is an electrochromic substance, and the applied voltage. 8m C/
-1,0V to -2 for colored charge density of ctn'
, by applying a negative voltage of 2V.

The speed at which an amorphous tungsten oxide thin film changes from a transparent state to a blue color is usually 500 sec to 50 m5 ec.
is within the range of Also, the speed when erasing this by applying a voltage from -0.2V to +1.0V is usually 300ma.
Values range from ec to 50s+sac.

Here, the voltage VOO at which the response time becomes infinite during coloring is determined by the electromotive force of the amorphous tungsten oxide thin film in the 1-colored state, which is caused by the voltage V(X) applied from the outside and the electromagnetic fan display element. This corresponds to a state in which the back electromotive force shown in FIG.

This electromotive force that electrochromic materials generally exhibit is 1
Increases with degree of coloration. This electromotive force is a major hindrance when performing one-hour side drive using an electrochromic display element. In other words, when a display pixel in a colored state and a display pixel in a decolored state are connected to each other in an XY matrix type electrode arrangement, the display pixel in a colored state goes from a display pixel in a decolored state to a display pixel in a decolored state. A charge movement occurs, and both change to an intermediate colored state.

As a method of compensating for these basic drawbacks of electrochromic display elements and obtaining a dot matrix type display device by time-division driving, a method of adding a TRS dynamic element such as a transistor to each display pixel is known. In FIG. 4, 11 is a row electrode, 12 is a column electrode,
13 indicates a display pixel, and 14 indicates a transistor. To drive such display pixels, the row electrodes are driven every 19 inches, and at this time, the corresponding column electrodes of the display pixels on the selected line are simultaneously A signal corresponding to coloring or decoloring the pixel is applied.

On the other hand, if one transistor is added to each pixel and writing or erasing is performed by line sequential scanning, the response of the electrochromic material becomes slower as the number of scanning lines increases.

It takes time to display all pixels. In order to overcome this, two transistors are added to each pixel as shown in FIG. 5, the drain electrode of the first transistor 15 is connected to the gate electrode of the second transistor 1B, and the first transistor address at high speed.

Controls the gate potential of the transistor tJIJ2.

After deciding whether to turn on or off the second transistor, connect the power line 1B connected to the power path line 17.
A so-called screen sequential drive has been devised in which the entire screen is displayed simultaneously by applying a voltage to the screen. In this method, as you can see from the way it works, ditto! It cannot be colored or erased.

In any case, when performing a dot matrix display with a large display capacity using an electrochromic display element, at least one transistor is required for each display pixel. This transistor is formed on a single crystal or glass substrate, but in many cases it is formed on a glass substrate, which has no size restrictions and is advantageous in terms of cost. Silicon or reduced pressure CV
Polycrystalline silicon made by the D method is used.

The source, gate, and drain electrodes of transistors are mainly made of aluminum, which has low resistance and is easy to etch.0Display pixel electrodes are usually made of indium oxide (ITO) doped with tin, and Si3N.
An electrochromic material such as tungsten oxide or molybdenum oxide is formed on the 0 display pixel electrode which is connected to the drain electrode through a contact hole made in an insulating film such as 4.5i02 or 5iON.

A display electrode substrate incorporating such a thin film transistor in each pixel and a counter electrode substrate incorporating a counter electrode were placed facing each other and sealed, and then a lithium salt such as lithium perchlorate was dissolved in a nonaqueous solvent such as propylene carbonate. An electrochromic display element capable of displaying a dot matrix is produced by injecting an electrolytic solution.

[Dark problem to be solved by the invention] There are two methods for producing a dot matrix type electrochromic display: a static method in which each display pixel is operated individually, and an active method in which switching elements such as thin film transistors are used. be. The former has a limit in terms of display capacity because the number of leads to be taken out is large. The latter method has no problem with regard to display capacity, but with electrochromic display elements, which are charge-controlled elements, it takes time to color or erase one pixel, so one transistor per pixel requires a large number of operating lines. In some cases, there is a problem in that it takes a long time to display the entire screen.For this reason, a method has been devised in which two transistors are added to each pixel and the pixels are sequentially driven.

In the double transistor method in which two transistors are added to each pixel, it is necessary to electrically connect the drain electrode of the first transistor and the gate electrode of the second transistor, as shown in FIG. In order to do this, contact holes must be made in the interlayer insulating film, but pinholes are generated in the interlayer insulating film during this process, and the wiring that will be deposited afterwards and the wiring that has already been formed under the insulating film are the cause of this. The problem was that short circuits frequently occurred between the two.

The probability of short-circuit defects per unit area is 1 to 3 orders of magnitude higher than the probability of defects due to pinholes in the interlayer insulating film.
It has been confirmed that it is several orders of magnitude larger. Therefore, it is believed that the large number of short-circuit defects is caused by defects in the photoresist. In any case, there is a strong demand for a structure and manufacturing method that reliably connects the drain electrode of the first transistor and the gate electrode of the second transistor, and that provides solid insulation without short circuits between layers.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems.
It has a plurality of electrochromic display pixels formed on an insulating substrate, and two thin film transistors added to each display pixel, and the drain electrode of the first thin film transistor and the second thin film transistor of the two thin film transistors are provided. In an electrochromic display element, the gate electrodes of the second thin film transistor are electrically connected to each other, and the drain electrode of the second thin film transistor is connected to the electrochromic display pixel. The present invention provides an electrochromic display element characterized in that a first thin film transistor and a second S film transistor have different positional relationships when viewed from above.

There are four types of structures for thin film transistors, as shown in Figures 6(a) to (d), depending on the positional relationship of gate electrodes: (a) coplanar type, (b) staggered type, and their inverted structure. (C) inverse coplanar type, (d)
There is a reverse stagger type. In these figures, 39 is a gate electrode, 40 is a source electrode, 41 is a drain electrode, and 42 is a semiconductor layer.

In the present invention, since the drain electrode of the first thin film transistor and the gate electrode of the second Viv transistor are electrically connected, the positional relationship between the source electrode and the drain electrode with respect to the gate electrode of these two transistors is Specifically, the combinations of thin film transistors are (a) and (C), (a) and (d), (b) and (C), and (b) and (d). There are several types of thin film transistors, which can be selected appropriately in consideration of other process conditions, and any of them may be used as the first thin film transistor.For example, if the first thin film transistor is a coplanar type, the second thin film transistor If the first vis transistor is a coplanar type or an inverted stagger type, and the first vis transistor is an inverted stagger type, the second thin film transistor may be a coplanar type or a stagger type.

Note that when amorphous silicon is used for the semiconductor layer and one semiconductor layer, especially the semiconductor layer of the second run shifter, is recrystallized by a laser or the like and used as polycrystalline silicon, recrystallization is required. It is advantageous in terms of the manufacturing process to form a thin film transistor having a semiconductor layer of a coplanar type.

Figures t51 (a) to (C) are an enlarged plan view (a) of one pixel of a typical example of the electrochromic display element of the present invention, its AA' cross-sectional view (b), and its BB' cross-sectional view (C). show.

In the figure, 21 is the semiconductor layer of the second transistor;
2 is a gate line, 23 is a gate electrode of the first transistor, 24 is a source electrode of the second transistor, 25 is a drain electrode of the second transistor, 28 is a power line, 27 is an interlayer insulating film, and 28 is a first transistor. 28 is a source line, 30 is a source electrode of the first transistor, 31 is a drain electrode of the first transistor, 32 is a gate electrode of the second transistor, 33
3 is a contact hole between the drain electrode of the second transistor and the display pixel electrode; 34 is a contact hole between the power line and the power pass line; 35 is the display pixel electrode;
Reference numeral B indicates a contact portion between the power line and the power pass line, 37 indicates a purge film, and 38 indicates an electrochromic material.

As is clear from the figure, the drain electrode 31 of the first transistor is electrically connected to the gate electrode of the second transistor, and the drain electrode 25 of the second transistor is electrically connected to the display pixel electrode 35. is connected to
In addition, in this example, the first transistor has an inverted staggered structure, the gate electrode 23 is located below the source electrode 30 and the drain electrode 31, the second transistor has a coplanar structure, and the gate electrode 32 is located below the source electrode 30 and the drain electrode 31. It is located above the source electrode 24 and drain electrode 25.

In this way, by reversing the positional relationship of the source electrode and drain electrode with respect to the gate electrode of the transistor il to the positional relationship of the source electrode and drain electrode with respect to the gate electrode of the second transistor, the drain of the first transistor The electrode and the gate electrode of the second transistor can be directly electrically connected without using a contact hole, improving reliability.

Although not particularly limited as a semiconductor layer of a thin film transistor, amorphous silicon, polycrystalline silicon, CdSe, etc. are mainly used as an insulating film between 0M and 5i02.5.
ii4.5iON etc., but the wiring material is AI, C
Metals such as r, Ni, No, and Ta are used.

The electrochromic substance of the present invention is not particularly limited, but includes oxides such as amorphous tungsten, molybdenum oxide, vanadium oxide, titanium oxide, niobium oxide, and iridium oxide, and macroscopic composites. or organic viologen compounds,
Rare earth sifthalodianine, mixed valence complexes of transition metals such as Prussian blue, and conductive polymer materials such as polythiophene and polypyrrole are used.

The electrolyte can be used as either a solid electrolyte or an electrolytic solution, and can be used depending on the purpose. Examples of solid electrolytes include:
Sin, 5i02. CaF2. MgF2゜Zr
β-A1203, a thin film consisting of a porous body of an inorganic insulating material such as O2, ChA205, and moisture occluded therein. R
bAg41s, Li3N, etc. tL Lou'! H
IM ion conductor materials and ion conductive polymers are mentioned, and the electrolyte includes various Ja-free acids, organic acids,
LiCl0a, LiBFa, LiAlCl4. L
iPF6. A nonaqueous electrolyte obtained by dissolving a salt such as LiAsF6 in propylene carbonate, γ-butyrolactone, acetonitrile, or the like may be used.

For the counter electrode, background plate, counter electrode substrate, etc., known materials and shapes can be used.

As the counter electrode, MnO on carbon or carbon
A porous ceramic plate is used as the background plate, and glass, ceramics, plastic, etc. are used as the counter electrode.

[Function] The present invention specifically provides a coplanar type electrochromic display element by appropriately selecting a combination of structures of a first transistor and a second transistor in a double transistor type electrochromic display element having two transistors in one pixel. By combining combinations such as and reverse stagger type, coplanar type and reverse coplanar type, stagger type and reverse stagger type, and stagger type and reverse coplanar type, the drain electrode of the first transistor and the gate type of the second transistor can be connected at the same time. As is clear from FIG. 6, in the transistor structure that is characterized by the fact that it can be formed in zero combinations, the stacking order of the gate electrode, source electrode, and drain electrode is different with respect to the substrate. Therefore, it is possible to form the drain electrode of the first transistor and the gate electrode of the second transistor at the same time and to connect them to each other. By doing this, it is not necessary to make a contact hole for connection in the living room insulating film, and as a result, short-circuit defects caused in this process are eliminated, and reliability is improved.

[Example] 510,211 g of amorphous silicon film was deposited on a glass substrate, and then 1,000 g of each amorphous silicon film was sequentially deposited on a glass substrate by plasma CVD.
After depositing 2,000 people, the amorphous silicon was deposited in Figure 1 and 2.
1 was patterned to form the semiconductor layer of the second transistor. 8 Next, 3000 layers of AI were deposited by EB evaporation and patterned to form the gate line 22 and the gate electrode of the first thin film transistor (hereinafter abbreviated as TFT 1). 2
3. A source electrode 24 of a second thin film transistor (hereinafter abbreviated as TF2), a drain electrode 25 of TFT2, and a power line 2B were formed.

Next, 3000 layers of interlayer crystal 5iON film 2''7 were deposited, and then amorphous silicon was deposited and patterned to form the semiconductor layer 28 of the first transistor.
After depositing 3,000 layers, patterning was performed to form the source line 29, the source electrode 30 of TFT 1, the drain electrode 31 of 7FT 1, and the gate electrode 32 of TFT 2. Zero-order contact holes 33, 34 and peripheral leads were formed. After removing the insulating film at the extraction portion, the display pixel electrode 35
A contact portion 36 between the power line and the power line was formed by a lift-off method.

A passivation film 37 was formed by using photosensitive polyimide to cover the area other than the display pixel electrode and the peripheral lead extraction portion.

Finally, an electrochromic material 38 made of tungsten oxide was formed in the display pixel portion to create an electrochromic display element substrate with thin film transistors.

The incidence of short-circuit defects in the substrate thus prepared was the same as that of the insulating film itself, and was very small. This defect level is considered to be within the range that can be eliminated by improving the thickness of the interlayer insulating film and improving the process.

In the examples, a photosensitive polyimide of 5i02. There is no problem with Sin or 5iON, and although an example of a combination of a coplanar and an inverted stagger structure has been given, it is clear that the structure is not limited to this.

[Effect of the invention] gjI8 for each pixel! Conventionally, in an electrochromic display element that includes two transistors and performs so-called field sequential driving, a contact hole is formed in an interlayer insulating film to connect a first transistor and a second transistor. However, the number of short-circuit defects has increased significantly due to pinholes caused by this drilling process. For this reason, even if a display element was actually manufactured and driven, there were many short circuits and the display element was not suitable for practical use.

In the present invention, by appropriately selecting the structures of the first transistor and the second transistor, the drain electrode of TFT 1 and the gate of TFT 2 are formed. is no longer necessary, and it is now possible to eliminate short-circuit defects caused by pinholes that occur during the drilling process of the living room insulation film, making it possible to maintain the original performance of the single-layer insulation film.

[Brief explanation of the drawing]

FIG. 1(a): A plan view of a display pixel to which the thin film transistor of the present invention is added. FIG. 1(b): A sectional view taken along line AA' in FIG. 1 (second transistor) FIG. 1(C): BB cross-sectional view in Figure 1 (first transistor) Figure 2: Cross-sectional view of electrochromic display element
4 Figure 3: A graph showing the relationship between the response time and applied voltage of an electrochromic display element. Figure 4: A circuit diagram of an active matrix spider tree with one thin film transistor added to each pixel. Figure 5: A graph showing the relationship between the response time and applied voltage of an electrochromic display element. Circuit diagram of active matrix type with two transistors added Figure 6(a): Cross-sectional view of coplanar type transistor Figure 6(b) Cross-sectional view of Nystagger type transistor'
6 Figure (c): Cross-sectional view of an inverted coplanar transistor Figure 6 (d): Cross-sectional view of an inverted staggered transistor 1 Transparent substrate 2 Transparent electrode 3.38 Electrochromic (EC) material 4
Substrate 5 having a recessed part Electrode 6 Counter electrode 7 Electrolyte 8 Background plate 12.29 Source (electrode) line 13, Display pixel 14 Transistor 15 First transistor 1B Second transistor 17 Power pass line 18.28 Power line 21 Semiconductor layer 23 of the second transistor 23 Gate electrode 24 of the first transistor Source electrode 25 of the second transistor Drain electrode 27.43 of the second transistor Interlayer insulating film 28 Semiconductor layer 30 of the Ml transistor
Source electrode 31 of the first transistor Drain electrode 32 of the second transistor Gate electrode 33 Contact hole 34 between the drain electrode of the transistor wS2 and the display pixel Contact hole 35 between the power line and the power pass line Display pixel electrode 3B Contact part 37 between power line and power pass line Passivation film 38 Gate electrode 40 Source electrode 41 Drain electrode 42 Semiconductor layer 1 1 n (rut in yl) Fig. 4 Fig. 6 (α) (b) (C)
td) Seven Procedures IE Book July 4, 1985

Claims (2)

[Claims] (1) A plurality of electrochromic display pixels formed on an insulating substrate, and 2 pixels added to each display pixel.
of the two thin film transistors, the drain electrode of the first thin film transistor and the gate electrode of the second thin film transistor are electrically connected to each other, and the drain electrode of the second thin film transistor is electrically connected to each other. is an electrochromic display element connected to an electrochromic display pixel, characterized in that the positional relationship of the source electrode and the drain electrode with respect to the gate electrode as seen from the substrate is different between a first thin film transistor and a second thin film transistor. display element. (2) The electrochromic display element according to claim 1, wherein the electrochromic substance is amorphous tungsten.