JPS6131851B2 - - Google Patents

Description

[Detailed Description of the Invention] <Summary> The present invention comprises two substrates, at least one of which is transparent, an electrode, at least one of which is transparent, provided on opposing surfaces of the substrates, and an electric current applied to these electrodes. A display device (so-called electrochromic display, hereinafter abbreviated as "ECD") consisting of a substance whose visible light absorption characteristics change reversibly with voltage or current (so-called electrochromic material, hereinafter abbreviated as "EC material"). The present invention relates to a driving method. More specifically, the counter electrode is grounded, and a segment is to be changed from a decolored state to a colored state (when a plurality of display electrodes are appropriately selected and a display is performed by a combination thereof, each display electrode is called a segment). ) is driven for a certain period of time with a negative constant voltage source (this is called writing), and the segment to be changed from the colored state to the uncolored state is driven for a certain period of time with a positive constant voltage source (this is called erasing). ), writing and erasing are started at the same time to reduce the time required to update display information.

With this method, by increasing the erasing time, photochromism (a phenomenon in which EC materials are colored by irradiation with light) and "remaining erasing" (if the erasing driving conditions are inappropriate, erasing is not completed completely, resulting in discoloration) This method aims to prevent the deterioration of display quality due to the phenomenon in which a large number of particles are accumulated, and to obtain a good display condition over a long period of time by using the "refresh method" in combination.

<Prior Art> First, an overview of ECD will be described below. The following types of systems are attracting attention as ECD.

The first type is one in which an electrochromic substance (hereinafter abbreviated as EC substance) in a solution is electrochemically oxidized or reduced, and a reaction product is deposited on an electrode for display. A typical example is a system using heptyl viologen described in JP-A-47-1562. In this system, by energizing the display electrode as a cathode, a reddish-purple insoluble film is formed on the electrode, which is separated from the drive circuit.
If it is electrically open, its coloring is maintained (memory function), and it disappears when it is energized as an anode. This reaction formula is shown below.

A reaction that goes to the right colors it, and a reaction that goes to the left decolors it.

In the second type, a solid EC material is formed into a thin film and placed on the display electrode, and is electrochemically oxidized or reduced in an electrolytic solution to change the visible light absorption characteristics of the EC material. Transition metal compounds (particularly oxides and sulfides) are known as this type of EC substance, and among them, a vapor-deposited film of tungsten trioxide is detailed in RCA Review 36 177 (1975). The most likely theory is that the coloring mechanism in this system is that tungsten bronze is formed by simultaneous injection of protons from the electrolyte and electrons from the electrode. The reaction formula is as follows.

Even in this system, when current is applied to the display electrode as a cathode, the reaction proceeds to the right and the color becomes blue, and when electricity is applied to the display electrode as an anode, the reaction proceeds to the left and the color disappears. The same goes for the memory function. Furthermore, there is a report that coloring occurs when Li ions are injected using an electrolyte prepared by dissolving LiClO ₄ in propylene carbonate instead of protons (SID 75 digest P.50).
It has also been confirmed by the inventor of the present invention using various organic solvents. For example, Japanese Patent Application No. 51-22969
105586) "Electrochromic display device", Japanese Patent Application No. 51-45227 (Japanese Unexamined Patent Publication No. 52-127486) "Electrochromic display device" There is a "Tsuku display device".

Figure 1 shows a schematic diagram of the structure of this type of ECD cell. In the figure, 1 is a transparent insulator substrate, 2 is a display electrode, 3 is a counter electrode, 4 is a reference electrode, 5 is a spacer, 6 is an electrolyte, 7 is a display electrode 2 and a counter electrode 3
The EC material film 8 provided above is an insulating film for protecting the display electrodes 2.

The third type uses the same EC material as the second type, but uses a solid electrolyte (a material that is an insulator for electron conduction and has ion conductivity) instead of an electrolyte. A typical example is a US patent
Described in No. 3521941. There are two explanations for the coloring mechanism in this case: one is that the adsorbed water acts as an electrolyte and is essentially the same as the second type, and the other is that the color center is caused by oxygen vacancies.

In this way, the common characteristics of the various types of ECD are listed.

(1) Driving voltage is low. (Several volts or less) (2) The display state continues for several hours or several days even after the applied voltage is removed (open state). (Memory function) (3) Low power consumption. (The energy required for one writing or erasing is several mJ/cm ² to several tens of mJ/cm ^2. ) (4) Coloring density is uniquely determined by the density of charges flowing per unit area of the display electrode. It is decided.

(5) Good contrast and no viewing angle dependence.

(6) Passive display makes it easy to see even in bright surroundings.

(7) The flatness of the display is good, and the degree of freedom in the shape of the display pattern is large.

(8) Due to the features 1 and 3, it is easy to drive with a semiconductor element.

Next, we will discuss the ECD driving method. There are three main types of driving methods:

(1) Constant potential driving method This driving method uses the constant potential electrolysis method used for electrode reaction analysis as is for ECD driving.In addition to the display electrode and the counter electrode, a reference electrode is provided, which allows the display electrode to The potential is detected and negative feedback is applied to the counter electrode voltage to keep it constant. In this method, even if the voltage drop caused by the reaction at the counter electrode changes, the potential of the display electrode is kept constant. Another advantage is that side reactions are unlikely to occur.

On the other hand, since a linear amplifier is required, it is difficult to integrate an ECD drive circuit including a digital circuit into a single chip IC using current technology. Furthermore, as a power source for the linear amplifier, two positive and negative power supplies of about ±4.5 V are required, which is higher than the drive voltage of the ECD itself, so the utilization rate of the power supply voltage is low, which is disadvantageous in terms of power consumption.

(2) Constant current driving method The color density of ECD is uniquely determined by the charge density per unit area. Therefore, by flowing a constant current corresponding to the display area for a certain period of time, it is possible to maintain a constant charge density and to maintain a constant coloring density. According to this method, temperature dependence of color density can be eliminated. However, when considering mass production of drive circuits, the following points arise. The first is that the set value of the current varies widely, and the second is that the current value must be changed depending on the display area to be driven. Therefore, if the shapes and sizes of characters differ, they become incompatible. Further, in order to perform constant current driving, it is necessary to use, for example, a transistor in an active region, which lowers the power supply voltage utilization rate compared to constant voltage driving which can be used in a saturated region.

(3) Constant voltage driving method This driving method applies a constant voltage between the display electrode and the counter electrode for a certain period of time. In this method, the drive circuit can be constructed of only digital circuits, and compared to the two types of drive methods described above, it is easier to implement a single-chip IC including a logic circuit. Also, since there is no need to use transistors in the active region,
Highest power supply voltage utilization rate. However, unlike other driving methods, it is directly affected by the voltage drop caused by the reaction at the opposing electrode, and therefore requires the following characteristics.

The potential (starting force) of the counter electrode is stable, and changes due to the number of colored segments are small.

The overvoltage of the reaction at the counter electrode is small.

The resistance of the lead part of the segment is small, and its value is inversely proportional to the display area of the segment.

If these conditions are not met, the coloring density will fluctuate and the response speed will vary between segments. The present inventors were able to obtain an ECD cell with practically acceptable characteristics even when using a constant voltage drive method using the construction method shown in the Examples below.

Now, as mentioned above, ECD has a memory function, and the coloring density is proportional to the charge density, so
When one segment is written many times, the coloring density becomes darker accordingly, resulting in a difference in density from a segment written only once. Therefore, it is necessary to prevent duplicate writing. There are two specific methods for this:

[A] A method in which every time display information is changed, all the previous display is erased, and only the necessary segments are selected and written. This method has the disadvantage that it consumes more power than the method [B] described below. Also, the times required for writing and erasing are τW and τE, respectively.
Then, changing the display information requires a time of τW+τE.

[B] Compare the previous display content with the new display content, keep the common parts as they are (memory state), and drive only the segments that need to change from the colored state to the erased state or vice versa. (hereinafter referred to as "partial erasure method"). For example, when changing the display from ``2'' to ``3'' in a 7-segment pattern as shown in Figure 2, each of a, b, d, e, and g is colored in the ``2'' state. segment, and in the state of "3", a,
Since each segment is b, c, d, and g,
All that is required is to erase the e-segment and color the c-segment.

If the numbers 0 to 9 are displayed sequentially using this method, the number of drives is 3/10 compared to the method [A], and power consumption can be significantly reduced.

This method was proposed by the inventors of the present invention in a patent application filed in 1973.
No. 152354 (Japanese Unexamined Patent Publication No. 52-75292) (December 19, 1950)
(Japanese) The application is currently being filed as a "method for driving a display device."

This shows an example in which a data flip-flop stores whether a segment was previously colored. It is also possible to detect the potential of each segment and determine whether or not that segment is colored. An example of this method is
No. 53545 (Utility Model Application No. 52-145783) "Electrochromic Display Device" (filed on April 28, 1975), and a further improved example
No. 154768 (Unexamined Japanese Patent Publication No. 53-76850) "Integration drive circuit and vehicle display device" and its divisional application, Japanese Patent Application No. 52-20494 (Unexamined Japanese Patent Publication No. 53-76700)
This is shown in "Driving device for electrochromic display device" (filed on February 25, 1978). In addition, in devices such as clocks and counters where the order in which the displayed numbers change is determined, the output becomes "1" only when each segment changes from non-selected to selected, or vice versa. Alternatively, a decoder may be configured and the drive control may be performed based on the output signal thereof. Third
The figure shows an example of a decoder in which the value becomes "1" only when writing is to be performed when the value is incremented by 1 from 0.

<Object of the present invention> By the way, by combining the above-mentioned "partial erase method" with a constant current driving method or a constant voltage driving method, and by grounding the opposing electrode, it is possible to erase the b segment while writing the a segment, for example. becomes.
(Hereinafter referred to as "simultaneous writing and erasing.") According to this method, the time required to change display information is shortened. In other words, the display change is completed in the time which is the larger of τW and τE. In this case, the sum of the write voltage and erase voltage is applied between the write segment and the erase segment, but the response characteristics are poor.
In order to drive the ECD element at a practical speed (for example, 500 msec), the sum of these voltages must exceed 3.5V. When such a high voltage is applied, defects such as deterioration of the EC material, decomposition of the electrolyte, and reduction of the transparent conductive film occur, which significantly shortens the life of the element.
However, the inventors of the present invention were able to obtain an element with good response characteristics and a long life (thus, it can be driven at a low voltage) using the element manufacturing method shown in the following examples.
This has characteristics suitable for the driving method according to the invention.

Furthermore, the present invention attempts to prevent deterioration of display quality due to "photochromism" and "remaining erasure" by providing a sufficient time for applying the erase voltage. This idea was published in Japanese Patent Application No. 51-111381 (Japanese Patent Application No. 53-37050).
"Display device drive method" (filed on September 16, 1975)
It is also described in Japanese Patent Application No. 52-46097 (Japanese Unexamined Patent Publication No. 53-130996) entitled "Driving System for Display Device" (filed on April 20, 1978).

Furthermore, the present invention attempts to "refresh" the colored segments, which gradually fade during the memory period and the display quality deteriorates. Discoloration is caused by dissolved oxygen in the electrolyte,
Possible causes include leakage current when the drive circuit is in the memory state. This "refresh method" is based on the aforementioned Japanese Patent Application No. 50-152354 (Japanese Unexamined Patent Publication No. 52-75292) and its improved invention is published in Japanese Patent Application No. 50-89342 (Unexamined Japanese Patent Application No. 52-89342).
13341) The present inventors are currently filing an application as "Memory regeneration method for electrochromic display device." The idea of the present invention has been explained above.

<Preferred Embodiment> Next, an embodiment of the present invention will be described. First, the method for creating an ECD cell is as follows.

In ₂ O ₃ is deposited as a transparent conductive film on a glass substrate to a thickness of 2000 Å by electron beam heating vacuum evaporation to form display electrodes 2 . The sheet resistance of this film is
It was 20Ω/sq. Next, WO ₃ is vacuum-deposited as an EC substance by resistance heating. Vapor deposition conditions are substrate temperature
350℃, film thickness 5000Å, deposition rate 10Å/sec, pressure 5
×10 ^-4 Torr (O ₂ partial pressure), and vapor deposition was performed only on the display area using a metal mask. Next, the display electrode was divided into segments by photoetching. For etching In ₂ O ₃ , FeCl ₃ dissolved in HCl was used. Furthermore, SiO is vacuum-deposited to a thickness of 5000 Å on the lead-out portion of the display electrode for protection. This will be the front board. Meanwhile, on another glass substrate
A counter electrode 3 was formed by vapor depositing Ni to a thickness of 2000 Å. The sheet resistance of this film was 2Ω/sq or less. In the case of the present invention, the reference electrode 4 is required in order to judge whether to color or decolorize the segment by detecting the potential in the above-mentioned "partial erasure method", so the Ni film is divided and used as the reference electrode 4. use This operation is not necessary if other methods are used. Next, WO ₃ was deposited on the counter electrode 3. The deposition conditions were as described above. In this way, the two substrates provided with each electrode were bonded together using a 1 mm square glass rod as a spacer 5. At this time, a porous white ceramic plate was enclosed inside to make the background of the display white. The purpose of this is to hide the counter electrode. By providing a background material close to the display electrode, parallax is eliminated, and since the incident hole is observed twice through the EC material film, the contrast ratio at the same charge density (coloring state and Two points are that the ratio of light transmittance or light reflectance to the decolorized state is improved. An electrolytic solution was injected into the ECD cell thus prepared, and after permeating into the porous white ceramic plate, the injection port was sealed. The electrolyte used was LiClO ₄ dissolved in γ-butyrolactone at a concentration of 1.0 mol/.

Next, the drive circuit will be explained. First, a drive determination circuit determines whether or not to drive. As mentioned above, this can be done by providing a dedicated decoder (Fig. 3), by storing the previous state in the data flip-flop 40 (Fig. 4), or by detecting the segment potential (Fig. 4). Figure 5). Figure 6 shows the segment potential and contrast ratio when Ni was used as a reference electrode. The contrast ratio also changes depending on the film thickness of the EC material and the wavelength of the measurement light source, but the contrast ratio of the cell mentioned above is
When the potential is -500mV when measured at 590nm, 10:
It was about 1. Vcomp is set to a potential corresponding to an appropriate contrast ratio. In this example, -0.4 to -0.2V was appropriate. If the color is lighter than this, it is considered to be in a decolored state, and new writing is performed. The output write signals Sw in FIGS. 3, 4, and 5 all indicate the previous display state as S' (the colored state is "1" and the uncolored state is "0"), and the new display If the state is S, it is expressed as Sw='·S, and becomes "1" only when new writing is necessary. Furthermore, S
is the output of a normal "BCD to 7 segment decoder", and the waveforms corresponding to each segment are shown in Figure 2c. Here we have described the circuit that determines whether or not to write, but the erase signal
Se=S′・ can also be constructed in the same way. Furthermore, since it does not matter how many times the erase voltage is applied, Se= may be used. Since almost no current flows after color erasure is completed, the increase in power consumption is very small even if this is done.

In addition to the signals Sw and Se obtained in this way, the pulses W and E that determine the write time τw and the erase time τe are used to generate the logical product Sw・E of these and the signals Sw and Se.
The semiconductor switches provided in each segment are opened/closed and driven by Se/E.

When used in an electronic timepiece, signals with appropriate pulse widths can be selected from the middle of the frequency dividing circuit and used for the pulses W and E. If the display changes are non-periodic, a one-shot multivibrator can be used. When the "refresh signal R" is input, all the segments that were colored last time must be erased and only the necessary segments must be written again, so pulse E should be applied first.
Then the pulse W must begin. Therefore, the writing semiconductor switch is (Sw+
It is closed by R.S).W, and the erase semiconductor switch is closed by (Se+R).E. Further, when performing "continuous erasing", it may be performed by +R/E. FIG. 7 shows a block diagram of the latter. In the figure, 11 and 12 are one-shot multivibrators for generating write pulses and erase pulses, respectively, which are triggered by falling edge.
3 and 14 are constant voltage sources for writing and erasing, respectively. Figure 8 shows a time chart. V is a voltage applied to the segment, and the broken line portion represents a state where the impedance is maintained at high impedance. I is the current,
The erasing direction was set as positive. C and R represent contrast ratio. Note that the refresh signal R may be input manually, and in the case of a clock or the like, the refresh signal R may be input at fixed time intervals, or in the case of a counter or the like, each time a suitable digit is incremented. You can also do it. Note that the refresh signal R must be synchronized with the clock pulse Cl so that it does not start or end in the middle of the W pulse or the E pulse.

Now, using such a drive circuit, the above-mentioned
Driven ECD cell. Preferred driving conditions were a write voltage of about 0.5V and an erase voltage of about 2.0 to 2.5V when the write time was 500 msec. The actual erasing time was 200 msec or less. During coloring, a charge of 5mC/ ^cm2 or more flows, and the contrast ratio is 3:
1 (reflectance ratio at 590 nm) or more was obtained, and for erasing, almost the same amount of charge flowed in the opposite direction, resulting in complete erasure. In addition, almost no change in coloring density was observed even when the film was left in a memory state at room temperature for 24 hours. Under these driving conditions, aging was carried out by sequentially displaying 0 to 9 every 2 seconds, and it continued to operate well even after more than 10 ⁶ times.

[Brief explanation of the drawing]

Figure 1 is a schematic structural cross-sectional view of an ECD cell, Figure 2 a is a segment type display pattern, and Figure 2 b is a 1
~0 display state diagram, Figure 2c is a time chart of each segment selection signal (normal decoder output), Figure 3a is a circuit diagram of the decoder for ECD writing, Figure 3b is 1 ~ 0 display state diagram, Figure 3c
is the time chart of the output waveform, and Figure 4 is the data
FIG. 5 is a circuit diagram for determining a write segment using a flip-flop; FIG. 5 is a circuit diagram for determining a write segment by detecting the potential of a segment; FIG. 6 is a diagram showing the voltage dependence of contrast ratio; FIG. 7 is a drive circuit according to the present invention; FIG. 7 shows a circuit diagram, and FIG. 8 shows a time chart. 11... One shot multivibrator for generating write pulses, 12... One shot multivibrator for generating erase pulses, 13... Constant voltage source for writing, 14... Constant voltage source for erasing, Sw... Write signal , Se...Elimination signal.

Claims (1)

[Claims] 1. A pair of substrates, at least one of which is transparent, and electrodes, at least one of which is transparent, are provided on mutually opposing surfaces of the substrates, and the electrodes are reversibly reversible by a voltage or current applied between the electrodes. In an electrochromic display device comprising a material whose visible light absorption characteristics change, at least one of the electrodes is divided into a plurality of segments, and a common segment between the previous display pattern and the changed display pattern is used to store a memory state. In addition to holding
When coloring only the erasing segments that are not common to the previous display pattern and the changed display pattern, or erasing only the colored segments that are not common, the coloring and erasing drives are started at the same time, and the erasing drive time is longer than the coloring drive time. 1. A method for driving an electrochromic display device characterized by increasing the size of the electrochromic display device.