FR2467454A1 - ELECTROCHROMIC DISPLAY DEVICE - Google Patents

Abstract

The invention relates to display devices. An electrochromic display device comprises two substrates 1, 4 separated by an electrolyte 7, a group of display electrodes 3a-3g, several fictitious display electrodes 1D-3D, a counter electrode 5 and means which apply a voltage between the counter electrode and several of the dummy display electrodes. Application to electronic watches with digital display. (CF DRAWING IN BOPI)

Description

The present invention relates to a display device which

  uses an electrochromic substance.

  More particularly, the invention relates to a regeneration device which is intended to compensate for a decrease in the color density in an electrochromic display attacked by the etching process which is termed the "electric charge transfer etching method". . According to this method, a voltage is applied between a group of electrochromic display electrodes in a colored state and a group of electrochromic display electrodes in a bleached state, in order to transfer to the group of electrodes in the state. discolored an electrical charge of staining that is preserved in the

  group of electrodes in the colored state.

  The electric charge transfer etching method for an electrochromic display device has the advantages of requiring only a single power source for etching, ensuring uniform coloration and having a characteristic

  fast response. FIG. 1 schematically represents a device

  electrochromic display to facilitate understanding of

  operation of the attack by transfer of electric charges.

  In the electrochromic display device, electro-

  transparencies 2a to 2c are formed on a flat face of a

  transparent substrate 1 by evaporation of In203 or an analyte substance

  this side being in contact with an electrolyte 7. In the group of transparent electrodes, electrochromic layers 3a to 3c are formed with a configuration of display elements, by

evaporation of W03 or MoO3.

  TiO2 powder is mixed with the electrolyte 7 to

form a white back screen.

  To avoid current leakage, an insulating layer is formed on the conductive electrodes of the display element configuration region, i.e. on the portion of the transparent electrodes 2a2c other than that corresponding to the layers.

  electrochromic 3a-3c. However, the insulating layer is not re-

  shown in Figure 1. The generic term is

  pressure "display electrodes A-C" transparent electrodes

  2a-2c and the electrochromic layers 3a-3c.

  A spacer 6 is placed between the substrates 1 and 4 so as to maintain the electrolyte between them. A counter-electrode 5 in

  AuVa i surace substrate that is in contact with the electrolyte 7.

  We will now describe a circuit element. Interactions

  staining switches 8a-8c are connected to connect each transparent electrode 2a-2c to a negative electrode of a DC voltage source 11. Discoloration switches 9a-9c are connected to connect each transparent electrode 2a-2c at

  a positive electrode of the DC voltage source 11. The reference

  10 denotes a switch which is intended to inject a coloring electric charge and the switch 10 is connected so as to connect the counterelectrode 5 to the positive electrode of the

DC voltage source 11.

  We will now describe the operation of the device

  electrochromic recording which is constituted in the manner described above.

  above. Firstly, an electric charge of coloration is injected into the electrochromic display device. Assuming that the electrode to which the electric charge is initially injected is the display electrode A, when the switches 8-a and 10 are closed, the current flows from the counter-electrode 5 to the display electrode A. As a result, the electrochromic layer 3a is reduced and becomes colored. Even if switches 8a and 10 are opened after the color density has

  reaches a predetermined value, the reduced state of the electro-

  chromic 3a is maintained. This condition is what is called

  a memory action and the colored display state is maintained.

  We will now describe the transfer of electrical charges.

  When the switches 9a and 8c are closed to connect the positive electrode of the DC voltage source to the display electrode A and to connect the negative electrode of the DC voltage source to the display electrode C, a coloring electric charge which is stored in the display electrode A is transferred to the display electrode C. At this moment, the coloring electric charge which is emitted by the display electrode A is transferred by the electrolyte 7 and is injected into the display electrode C. As a result, the display electrode A changes state

  color from a colored state to a faded state, for coloring

  Now, the display electrode C, and the display state is changed. Although the principle of charge transfer attack

  electrical power corresponds to what has just been described, in the function-

  In practice, the number of display electrodes that must change from a colored state to a bleached state is not always equal to the number of display electrodes that must pass from

  discolored state in a colored state. So we can not perform simple-

  the operation indicated above.

  Thus, when performing the electric charge transfer etching operation in practice, it is necessary to further add a dummy display electrode to equalize the number of display electrodes that must pass from one colorful state to a

  discolored state and the number of display electrodes that must not-

  be from a faded state to a colored state. In Figure 2, the combination

  The state of the colored / faded states is shown in the case of the addition of the dummy display electrode. Figure 2 shows a combination in which numbers are displayed using seven

  display electrodes A to G which are arranged in a configura-

  in ', -ii. The dummy display electrode consists of three kinds of dummy electrodes, namely a dummy electrode 1, a dummy electrode 2 and a dummy electrode 3. Assuming that the area of each display electrode A to G is equal at 1, the

  fictitious electrodes are designed to have display areas

  chage in 1: 2: 2 ratios. The constituent material for the three kinds of dummy display electrodes (dummy electrode 1 with dummy electrode 3) is the same as that of the display electrodes

A to G.

  Under the conditions in which the electrode of

  fictitious record which consists of such a material and which pre-

  such an area, the display electrodes which take the colored state are indicated by the symbol "O", the display electrodes which take the discolored state are indicated by the symbol "X" 'and the electrodes of unchanged display is not indicated by any symbol. In all the display states shown in FIG. 2, the number of display electrodes that take on the colored state

  is equal to the number of display electrodes that take the decoded state

  Lore. As a result, the electric charge transfer operation can

to be accomplished perfectly.

  FIG. 3 represents an electrochromic display device

  with a dummy display electrode. In the elements which are represented in FIG. 3, the parts identical to those of FIG. 2 are designated by the same references, and these parts

are not described again.

  A dummy display electrode D is formed so that a 2D transparent electrode is formed by evaporation on the surface of a substrate 4 which is in contact with an electrolyte 7 and so that a 3D electrochromic layer is formed by evaporation on the 2D transparent electrode. An 8D staining switch is connected to connect the 2D transparent electrode to the electrode

  negative of the DC voltage source. A decolor switch

  9D is plugged in to connect the transparent electrode

  2D to the positive electrode of the DC voltage source.

  Since in the electrochromic display device shown in FIG. 3, the dummy display electrode D is masked by the TiO2 white powder mixed with the electrolyte-7, the dummy electrode D does not appear. on the surface, so that

  the display operation can be performed clearly.

  However, there is a slight loss of charge transfer

  in the practical operation of transferring electric charges.

  cudgels. As a result, the color density decreases when the number

  transfer operations increases. Experience has shown that

  staining capacity is significantly reduced when the number of

  transfers is greater than 103. Thus, there is a disadvantage

  which consists of the appearance of a difference in color density

  between the display electrode group in which the number of transfer operations is higher, and the display electrode group in which the number of transfer operations is lower. Thus, it appears a lack of color uniformity and the

  Overall color density gradually decreases.

  The invention makes it possible to eliminate the drawbacks mentioned above and one of its aims is to achieve a regeneration avoiding

  the decrease in the color density.

  The invention also aims to accomplish independently

  temperature changes the regeneration operation which

  holds a constant color density.

  The object of the invention is also to provide an electrochromic display device which comprises two substrates, an electrolyte and a white powder between the two substrates, a group of display electrodes which comprise a layer of material

  electrochromic and which are formed on the surface of a first sub-

  stratum which is in contact with the electrolyte, a plurality of dummy display electrodes, a counter electrode which is formed on a surface of a second substrate, and means which apply a voltage between the counter electrode and a plurality of electrodes which part of

  group of fictitious display electrodes.

  The invention will be better understood on reading the description

  which will follow embodiments, and with reference to the accompanying drawings in which:

  FIG. 1 is a diagram of an electronic display device

  chromic which is intended to facilitate the understanding of the fundamental principle of electric charge transfer;

  Figure 2 is a table showing the combinations of trans-

electric charges;

  FIG. 3 is a diagram of an electronic display device

  chromic which comprises a fictitious display electrode; FIG. 4 represents an embodiment of a device

  electrochromic display which is intended to facilitate the comprehension

  regeneration process corresponding to the invention; Figure 5 is a graph that shows the relationship between

  duration of injection of an electrical charge of coloring and the temperature

  according to the regeneration method of the invention; and

  FIG. 6 represents another embodiment of the invention.

  vention. FIG. 4, which represents an embodiment of an electrochromic display device intended to

  to facilitate the understanding of a regeneration process

  corresponds to the invention. In the elements shown in FIG. 4, the parts identical to those of FIGS. 1 and 3 are

  designated by the same references and will not be repeated

  scription. References 2a-2g designate transparent electrodes, and display electrodes A-G are formed by evaporation of

  electrochromic layers 3a-3g on each transparent electrode.

  Each transparent electrode 2a-2g is connected to the negative electrode

  of the DC voltage source 11 via inter-

  switches 8a-8g and the positive electrode of the voltage source

  continue 11 via switches 9a-9g.

  References 21D to 23D denote transparent electrodes and imaginary ID display electrodes to 3D are formed by evaporation of electrochromic layers 31D to 33D on each transparent electrode. Each transparent electrode 21B to 23D is connected to

  the negative electrode of the DC voltage source

  Switches 81D to 83D and the positive electrode of the DC voltage source are connected via switches 91D to 93D. We will now describe the regeneration operation which is performed in the electrochromic display device having

the structure described above.

  Before beginning the explanation, it will be assumed that the duration of the regeneration operation corresponds to a period that starts just after the display has transitioned to the state rlj and ends just

  before the display changes to state r2.

  G After switching from the display to r1J, the 2D and 3D dummy display electrodes are in the colored state and these states

are stored.

  E The electric charge injection switch 10 and the

  switches 82D and 83D are closed while the other interrup-

  shown in Figure 4 are open. At this moment, an electric charge is only injected into the fictitious display electrodes

  2D and 3D, from the counter electrode 5.

  O Once the predetermined injection time has elapsed

  10, the switch 10 and the switches 82D and 83D are open. At this time, all the display electrodes A to G and the electrodes

  fictitious display 1D to 3D go into the storage state.

  The switches 8a, 8d, 8e and 8g and the switches 9c, 91D and 92D are closed to switch the display to the state. In accordance with the electric charge transfer combinations shown in FIG. are opened or closed in turn to periodically change the display state. The color density is always maintained at the predetermined value by performing the operation corresponding to the items

  O to O described above. The reasons are given below.

after.

  The value of the electric charge that is injected from the counter

  electrode 5 to the 2D and 3D dummy display electrodes in the aforementioned regeneration operation which corresponds to the

  fy is determined by fixing the duration during which the

  switch 117 'and switches 82D and 83D are closed (i.e. the injection time; so that this value is equal to the value

  of the electrical charge that is lost in all the electrodes of

  the display electrodes A to G and the dummy display electrodes 1D to 3D) until the regeneration operation is completed. Thus, the total value of the coloring electric charge which is stored in the electrochromic display device is always kept constant at the moment when the regeneration operation

the topic is complete.

  Then, because the electric charge in the 2D dummy display electrode is transferred to the display electrodes A, D, E and G, along with the electrical charge which is stored in the electrode. 1D dummy display and in the display electrode C, during the regeneration operation of the item O, the electric charge that is injected during the regeneration operation of the item t is also distributed to the display electrodes A, D, E and G. In addition, the electric charge that is injected into the 3D dummy display electrode is also transferred and distributed to the dummy display electrode 1D and

  the display electrode E in the display state 6.

  The injected electric charge that is distributed in the state

  r and 36, is distributed to other electrodes of

  records whenever the display state is changed, according to the combination of electric charge transfer. The value of the electric charge that is stored in each display electrode is

  equalized and the regeneration operation is carried out with a densi-

stain of constant color.

  Figure 5 shows an example of data showing the relationship between

  between the injection time and the temperature in accordance with the regeneration process. The characteristic of FIG. 5 corresponds to the conditions in which the applied voltage is 1.5 volts and the total area of the dummy display electrodes is equal to the sum of the area of 9 display electrodes. For example, when considering a digital display electric watch in which the information consists of digits, with a four-digit display for hours and minutes, it is necessary to use nine display electrodes fictive, or a dummy display electrode whose area corresponds to the area of the seventeen segments of the electrodes

  display. In view of this fact, the experimental curve was

  which is shown in FIG.

  FIG. 5 shows that the duration of injection is con-

  aunt in the temperature range from 00C to 500C. This fact shows that since one can perform a constant regeneration operation

  regardless of the temperature, no compensating element or circuit

  temperature is not necessary.

  FIG. 6 represents another embodiment of the invention.

vention.

  In an electrochromic display device which is

  shown in FIG. 6, several ID and 2D dummy display electrodes are placed on the same surface of a substrate 1 as display electrodes A to F. and a masking plate 15 is placed on the surface of the substrate 1 which is opposed to the surface on which the dummy display electrodes 1D and 2D are located. The plate 15 is placed just above the dummy display electrodes 1D and 2D so as to cover these electrodes. The switches are not

  represented to avoid complicating the figure.

  In the case of FIG. 6, the regeneration operation is performed in a similar manner between the fictitious display electrodes

and the counter-electrode.

  In the preceding description, the electrolyte used is

  liquid (electrolyte 7), but the goals of

  the invention using a solid electrolyte.

  In addition, both the colored display electrode group and the fictitious display electrode group in the colored state can be used to perform the regeneration, although the electrochromic display device uses nine electrodes

  fictitious display in the description above. The number of

  trodes used for regeneration may also be set to an arbitrary value less than the number of all electrodes

are in the colored state.

  The invention makes it possible to obtain the following characteristics (1) Because the duration of electric charge injection

  which is necessary to compensate for the color density is approximately

  constant in the range of 00C to 500C, the electrochromic display device can be operated with a density

  constant color without any temperature compensation.

  (2) Because multiple display electrodes are used

  fictitious as color compensation electrodes

  no new electrode configuration is required for the regeneration operation. As a result, there are many

  place for the realization of the display device and for the con-

  reception. (3) Because multiple display electrodes are used

  fictive for the compensation of the color density, it does not appear

  there is no momentary increase in the color density at the display surface during the regeneration operation, so that

  the display quality is never reduced.

  Since the decrease of the color density in the electrochromic display device resulting from the electric charge transfer attack can be fully compensated, as well as

  the lack of uniformity of the coloring between the different electro-

  display, resulting from a difference in the number of transactions

  of transfer, it is possible to produce an electrochromic display device

  with good display quality.

  It goes without saying that many changes can be made

  to the device described and shown without departing from the

vention.

Claims (5)

  1. Electrochromic display device comprising two   substrates, an electrolyte and a white powder between the two sub-   strats, a group of display electrodes having a layer of electrochromic material, the group of display electrodes being formed on a surface of a first substrate which is in contact with the electrolyte, and a counter electrode which is formed on a   surface of one of the two substrates-which is in contact with the electro-   lyte, characterized in that it comprises a plurality of dummy display electrodes which are formed on a surface of one of the two substrates which is in contact with the electrolyte, and means which apply a voltage between the counter-electrode and at least one of the electrodes fictitious display.   2. Electrochromic display device according to claim 1, characterized in that the fictitious display electrode or electrodes   to which a voltage is applied are in the colored state.   Electrochromic display device according to the claim   1, characterized in that the means which applies a voltage established   a voltage not exceeding 1.5 volts between the counter-electrode   and at least one dummy display electrodes.   4. Electrochromic display device according to claim   1, characterized in that the means applying a voltage applied to   positive electrode voltage and negative voltage   at least one of the dummy display electrodes.   5. Electrochromic display device comprising two sub-   strats, an electrolyte and a white powder between the two substrates, a display electrode group having a layer of electrochromic material, the display electrode group being formed on a surface of a first substrate which is in contact with the electrolyte, and a counter electrode which is formed on a surface of one of the two substrates which is in contact with the electrolyte, characterized in that   it includes several fictitious display electrodes that are   on one surface of one of the two substrates that is in contact with the electrolyte, and means that apply a voltage between the   against the electrode, on the one hand, and at least one of the electrode electrodes   fictitious display as well as at least one of the electrodes of the group   of display electrodes, on the other hand.