JP2007114622A - Particle movement type display and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To heighten reproducibility of display surface unobstructed display and memory properties of display by collecting charged particles onto partitions with high reproducibility with no relation to display gradation directly before the display surface unobstructed display is performed. <P>SOLUTION: A dispersion liquid 3 in which black charged particles 4 are dispersed is packed in a movement space 16 enclosed by the partitions 6. A transparent colored layer 10a having insulation properties is formed on a white display electrode 12 and a resistance layer 9 is formed covering the whole surfaces of partition electrodes 7 and the colored layer 10a. White display is performed by applying an AC voltage and then applying a DC voltage between the partition electrodes 7 and the display electrode 12 to collect the charged particles 4 onto the partitions 6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a particle movement type display device such as an electrophoretic display device that performs display by moving charged particles between a display surface and an upright surface of a partition wall, and more specifically, charged particles from a display surface to an upright surface of a partition wall. The present invention relates to a voltage driving method for movement.

  As a non-light emitting display device, a particle movement type display device is known that performs display by moving charged particles by the action of an electric field. The particle movement type display device is an image display device that performs pixel display by moving charged particles between a pair of electrodes arranged facing a moving space of charged particles. The particle movement type display device does not require a polarizing plate that impairs the light source light by 50% or more, enables high-contrast pixel display with colored charged particles, has a simple structure and operation, etc., and has been conventionally used as an image display device. It has many advantages over An electrophoretic display device, which is a kind of particle movement display device, has a display memory property that can maintain pixel display for a while after the electric field is released, and thus low power consumption that does not require power to maintain gradation display of pixels. It is also attracting attention as an image display device.

  Patent Document 1 discloses an electrophoretic display device in which a partition wall is formed surrounding a display surface on which display electrodes are arranged. Here, a DC voltage is applied between the partition electrode disposed on the rising surface of the partition wall and the display electrode to move the charged particles between the display surface and the rising surface of the partition wall.

  Patent Document 2 discloses an electrophoretic display device in which a transparent electrode is arranged with a number of capsules each enclosing charged particles interposed therebetween. Here, prior to writing in which a DC voltage is applied to the transparent electrode, a reset is performed in which a DC voltage having a polarity opposite to that of writing is performed, so that an afterimage of the previous display state does not remain. The display state is shaken (loosened) by applying a high-frequency AC voltage prior to the application of the reset and write DC voltages.

  Patent Document 3 discloses an electrophoretic display device in which light-shielding charged particles are enclosed in a moving space surrounded by a partition wall. Here, by applying an alternating electric field to the moving space, the charged particles are dispersed in the moving space, and the light shielding state of the pixels, that is, black display is performed.

JP 9-2111499 A International Patent Publication WO-2003-1000075 JP-A-4-221990

  In the electrophoretic display device disclosed in Patent Document 1, when a voltage signal having the same polarity as the charged particles is applied to the display electrode, the charged particles repel the display surface at the center and jump out in the normal direction. Since the detour travels along the opposite transparent substrate surface (see FIG. 11), the charged particles are unevenly distributed on the upper part of the partition wall (see FIG. 10) when they are collected on the partition wall electrode. As a result, the charged particles that protrude to the center narrow the field of view, and it becomes impossible to display the gradation as expected in a display that collects the charged particles on the partition wall electrodes and sees through the display surface. In other words, when black charged particles and a white display surface are used, the white display becomes gray.

  Since the charged particles deposited thickly on the partition wall do not have a binding force on the partition wall surface, when the application of the voltage signal collected to the partition electrode is canceled, the charged particles diffuse from the partition wall and ooze out to the center side. In other words, the memory performance of pixel display is insufficient.

  In addition, when there is no charged particles in the center of the display surface (gray display, etc.) in the display state immediately before displaying the display surface, the charged charge is unevenly distributed on the upper part of the partition wall when the charged particles are collected on the partition wall. The amount of particles is reduced. As a result, the gradation of the display allowing the display surface to be seen differs depending on whether or not there is a charged particle in the center of the display surface in the previous display state.

  The present invention collects charged particles on a partition wall with high reproducibility and displays reproducibility that allows the display surface to be seen, regardless of the display gradation immediately before performing display that allows the display surface to be seen, and display memory performance. The purpose is to increase.

  The particle movement type display device of the present invention includes a display electrode disposed for each display surface, a partition electrode disposed on a rising surface of a partition wall surrounding the display surface, and disposed on the display surface and connected to the display electrode. And a control means for collecting a charged particle on the rising surface by applying a DC voltage having a predetermined polarity between the display electrode and the partition wall electrode. The means applies the DC voltage after applying an AC voltage between the display electrode and the partition wall electrode.

  In the particle movement type display device of the present invention, the charged particles are swept to the portion near the partition wall while reciprocating between the rising surface of the partition wall and the display surface by the AC voltage, so that the center of the display surface is moved to the upper part of the partition wall. The charged particles that move and stagnate are reduced, and variations in the charged particles in the height direction of the rising surfaces of the partition walls are eliminated.

  In other words, by applying an alternating voltage, a stacked state of charged particles uniformly distributed in the vertical direction with high reproducibility is formed on the rising surface of the partition wall without being affected by the display state before the application.

  Accordingly, there is no possibility that the gradation of the display for allowing the charged particles to stay in the upper part of the partition and seeing through the display surface is different. In addition, the gradation after the voltage is released is less likely to change due to the diffusion of the staying charged particles having no binding force, and the memory performance of the display is improved.

  Hereinafter, electrophoretic display devices 100, 200, and 300, which are embodiments of the present invention, will be described in detail with reference to the drawings. The electrophoretic display devices 100, 200, and 300 are of a reflective type that does not have a backlight. However, in the present invention, a transmissive type in which a backlight is provided adjacent to the rear substrate 1 or a combination of a backlight and a reflective electrode is used. The transflective type may be implemented. In addition, the electrophoretic display devices 100, 200, and 300 are active matrix types in which thin film transistor elements formed for each display cell 15 are dynamically controlled by a large number of write signal lines and a large number of scanning signal lines arranged in a lattice pattern. However, the present invention may employ a display cell driving system other than the active matrix type.

  The electrophoretic display device 100 is an image display element in which a large number of display cells 15 are arranged in a lattice pattern, but in FIG. 1, a single display cell (unit display) 15 is representatively illustrated. In addition, the general structure, the general manufacturing method, the surface treatment, and the like of the electrophoretic display devices disclosed in Patent Document 1 and Patent Document 2 are different from the gist of the present invention. Detailed illustrations are also omitted.

  Further, the particle movement type display device of the present invention can be implemented both when a charged particle is interposed between a pair of substrates and when a charged particle dispersed in an insulating dispersion liquid is interposed. Since the essence of these embodiments is the same, a typical embodiment of the latter electrophoretic display device will be described below.

<First Embodiment>
1 is an explanatory diagram of a cross-sectional configuration of a display cell in the electrophoretic display device of the first embodiment, FIG. 2 is an explanatory diagram of a drive circuit for the display cell, FIG. 3 is an explanatory diagram of a circuit configuration of the electrophoretic display device, and FIG. Is an explanatory diagram of voltage signals in white display, and FIG. 5 is an explanatory diagram of behavior of charged particles in white display control. In FIG. 5, (a) is before resetting, (b) is the first positive voltage, (c) is the subsequent negative voltage, and (d) is the second positive voltage. In FIG. 1, an electric signal applying circuit (driver, wiring) for applying an electric signal between the electrodes, a thin film transistor element arranged with respect to the display cell 15 and the like are not shown.

  As shown in FIG. 1, the electrophoretic display device 100 according to the first embodiment forms a partition 6 on a rear substrate 1 to form a moving space 16, and a dispersion liquid 3 in which black charged particles 4 are dispersed. The transparent substrate 2 is overlaid on the partition wall 6 so as to fill the moving space 16, and the display surface surrounded by the partition wall 6 is observed from the transparent substrate 2 side. On the rear substrate 1, a display electrode 12 that also serves as a reflective surface is disposed. On the display electrode 12, colored layers 10a, 10b, and 10c as color filters are disposed.

  The partition 6 keeps the rear substrate 1 and the transparent substrate 2 at a predetermined interval, and separates the display unit 15 from the adjacent display unit. The transparent substrate 2 is composed of a light transmissive plate such as transparent glass or a transparent film. On the other hand, the rear substrate 1 does not necessarily need to be transparent, and may be formed of a film substrate, a metal substrate, or the like.

  As the partition wall 6, a generally used resist material, thermoplastic material, ultraviolet curable material, or the like can be used. The thickness of the partition wall 6 is usually about 5 μm to 30 μm. A partition electrode 7 common to all display cells 15 is formed on the surface of the partition 6. The partition wall electrode 7 may be composed of not only an Al or Ti metal film but also an ITO film.

  The display electrode 12 is formed by laminating a metal thin film having a high reflectance on an uneven layer 13 having a fine surface uneven shape. The uneven layer 13 can be formed, for example, by applying a photosensitive resin and then performing exposure and wet development. Moreover, you may employ | adopt the method of making a fine unevenness | corrugation in glass.

  As a material of the display electrode 12 formed on the concavo-convex layer 13, a material having high reflectivity such as aluminum or silver is desirable. With this configuration, the display electrode 12 can have a function of diffusing light. Then, by controlling the distribution of the inclination angle of the surface irregularity shape, the viewing angle can be expanded and the external light can be reflected efficiently, so that a brighter and better display can be obtained.

  In the electrophoretic display device 100 of the first embodiment, red (R), green (G), and blue (B) are assigned to three adjacent display units 15, and one display pixel 15 is configured by the three display units 15. . A total of eight colors including white and black can be displayed by combining 100% light-shielding state and 100% transmission state of the display electrode 12 with three display units 15 and combining them.

  In addition, it is also possible to perform intermediate gradation display individually in the three display units 15 and perform full color display of one pixel by the gradation balance of the three display units 15. On the display electrode 12, colored layers 10a (G), 10b (R), and 10c (B) as color filters are formed. The colored layers 10a, 10b, and 10c are made of, for example, an ultraviolet curable acrylic resin resist in which a red, green, or blue pigment is dispersed. The film thickness of the colored layers 10a, 10b, and 10c is usually about 0.1 μm to 4 μm, and an opening of the contact hole 11 reaching the display electrode 12 is formed at the center of the display unit 15.

  The surfaces of the colored layers 10a, 10b, and 10c surrounded on all sides by the partition walls 6 constitute a display surface, and the resistance layer 9 is formed by covering the display surface and the surface of the partition wall electrodes 7 together. The resistance layer 9 is connected to the display electrode 12 through a contact hole 11. The resistance layer 9 is a light transmissive material, such as an organic film such as polysilane, polysiloxane, or polyacetylene, or a composite or copolymer thereof, or a carbon-containing film, indium-tin oxide (ITO), or the like. An inorganic film, a semiconductor film such as silicon, or a conductive filler (filler), for example, a conductive resin film obtained by blending metal powder, carbon particles, or the like with an epoxy resin, a polypropylene resin, or the like can be used. Furthermore, a laminated film of these films may be used as the interface member. The sheet resistance of the resistance layer 9 is desirably 104Ω / □ to 1018Ω / □.

  When a DC voltage is applied to the display electrode 12, a voltage gradient connecting the potential of the partition wall electrode 7 and the potential of the contact hole 11 is formed in the resistance layer 9 on the display surface through a transient state immediately after the application. As a result, a spatial potential gradient (see FIG. 8) toward the partition wall 6 is also formed at the center of the moving space 16, and compared with the electrophoretic display device disclosed in Patent Document 1, the display surface is separated from the partition wall 6. Thus, the reciprocating movement of the charged particles 4 becomes smooth and fast.

  The moving space 16 of the charged particles 4 is surrounded by the transparent substrate 2 and the resistance layer 9. In the dispersion liquid 3 filled in the moving space 16, charged black charged particles 4 that are the main body of display are dispersed. The dispersion liquid 3 may be an interface with water, methanol, ethanol, acetone, hexane, toluene, aromatic hydrocarbons such as benzenes having a long-chain alkyl group, or other various oils alone or a mixture thereof. An activator etc. can be mix | blended and used.

  The charged particles 4 are organic or inorganic particles having a property of moving by electrophoresis due to a potential difference in the dispersion liquid 3. As the charged particles 4, for example, black pigments such as aniline black and carbon black can be used. In addition, 1 type, or 2 or more types, such as white pigments, such as titanium dioxide and an antimony trioxide, an azo pigment, and another coloring pigment, can also be used.

  Furthermore, these pigments include electrolytes, surfactants, resins, rubbers, oil-based charge control agents, titanium-based coupling agents, aluminum-based coupling agents, silane-based coupling agents, etc., as necessary. A dispersant, a lubricant, a stabilizer and the like can be added.

  A drive circuit (see FIG. 2) that generates a drive voltage is connected between the display electrode 12 and the partition wall electrode 7. On the rear substrate 1 below the display electrode 12, driving wiring and a thin film transistor element (46: FIG. 2) for each display cell 15 described later are formed, and an output terminal of the thin film transistor element is connected to the display electrode 12.

  Next, the operation will be described. In the following description, a case where the charged particles 4 are positively charged will be described as an example. However, even when the charged particles 4 are negatively charged, the same explanation will be given in consideration of the fact that the moving direction of the charged particles 4 is reversed. be able to.

  In the electrophoretic display device 100 of the first embodiment, the surface of the resistance layer 9 on the colored layer 10a (10b, 10c: hereinafter omitted) is the display surface of the display cell 15. When an electric signal is applied so that the display electrode 12 has a negative potential with respect to the partition wall electrode 7, the charged particles 4 are moved to the display surface by the electric field formed in the moving space 16. Thus, when the display surface is covered with the black charged particles 4, the display cell 15 is displayed in black.

  On the other hand, when an electric signal is applied so that the display electrode 12 has a positive potential with respect to the partition electrode 7, the charged particles 4 are collected on the partition electrode 7 side, and the charged particles 4 are removed from the display surface. Can be seen from the transparent substrate 2 side. Thereby, the reflected light from the display electrode 12 is transmitted through the colored layer 10a and a bright green display is made.

  In such an intermediate state between black display and bright green display, that is, in a display state in which the charged particles 4 are stacked in the peripheral portion of the display surface and the charged particles 4 do not reach the central portion, the display cell 15 Are observed in a light to dark green color with a middle gradation.

  By the way, in the electrophoretic display device 100, the display electrode 12 and the partition wall electrode 7 are connected to each other by the resistance layer 9, so that when the current supply to the display electrode 12 is interrupted, the voltage of the display electrode 12 rapidly decreases. . However, since the write voltage signal applied to the display electrode 12 is supplied only to the display cell 15 at a scan signal input timing, the write voltage signal is applied to the display electrode 12 as it is after the scan signal is input. As a result, the voltage of the display electrode 12 quickly decreases.

  Therefore, as shown in FIG. 2, by holding the write voltage signal read from the write signal line 48 in the auxiliary capacitor 50 and controlling the voltage control TFT 53, the write voltage signal is reproduced from the drive power supply voltage Vdd to display the display electrode. 12 continues to be applied.

  On the rear substrate 1, write signal lines 48 and scanning signal lines 47 arranged in a three-dimensional cross in a lattice shape are arranged, and each display cell 15 is associated with each intersection of the write signal line 48 and the scanning signal line 47. The pixel TFT (Thin Film Transistor) 46, the voltage control TFT 53, and the auxiliary capacitor 50 are arranged. On the rear substrate 1, an auxiliary capacitance line 51, a drive power supply line 52, and a common electrode 49 common to the display cells on the rear substrate 1 are also arranged. The drive power supply line 52 is applied with + Vdd and -Vdd alternately. The partition electrode 7 of the display cell 15 is connected to the common electrode 49 having the voltage Vcom, and 0 V is always applied thereto.

  The pixel TFT 46 and the voltage control TFT 53 are switching elements for active matrix drive display composed of n-type transistors, and are covered with an interlayer insulating layer (not shown) formed on the rear substrate 1. A storage capacitor 50 is connected between the drain electrode of the pixel TFT 46 and the storage capacitor line 51, and a gate electrode of the voltage control TFT 53 is also connected. The drive power line 52 and the display electrode 12 of the display cell 15 are connected to the source electrode and the drain electrode of the voltage control TFT 53, respectively.

  The scanning signal line 47 that is a trigger line is connected to the gate electrode of the pixel TFT 46, and the write signal line 48 that is a data line is connected to the source electrode of the pixel TFT 46.

  In the drive circuit configured as described above, when a scanning signal is input to the scanning signal line 47, a writing voltage signal is read from the writing signal line 48 to the auxiliary capacitor 50 through the pixel TFT 46. Then, the voltage control TFT 53 is controlled by the write voltage signal held in the auxiliary capacitor 50 until the next scanning signal is input, so that the write voltage signal formed from the drive power supply voltage Vdd is continuously applied to the display electrode 12.

  Then, an AC voltage can be applied between the display electrode 12 and the partition wall electrode 7 by inverting the supply voltage to the drive power supply line 52 in a state where a predetermined write voltage signal is held in the auxiliary capacitor 50. . Note that the write voltage accumulated in the auxiliary capacitor 50 is reset by writing a negative reset signal through the write signal line 48.

  As shown in FIG. 3, a large number of display cells 15 are arranged in a grid pattern on the display unit 44 of the rear substrate 1, and a panel controller 41, a source driver 43, and a gate driver 42 are arranged outside the display unit 44. Has been. The panel controller 41 generates control signals such as a field synchronization signal, a horizontal synchronization signal, a data capture clock, and display data based on the input image data, and transfers them to the source driver 43 and the gate driver 42.

  The source driver 43 supplies the display cell 15 with a write signal voltage through the write signal line 48 and a drive power supply voltage Vdd through the drive power supply line 52. The gate driver 42 supplies a scanning signal to the display cell 15 through the scanning signal line 47. The source driver 43 and the gate driver 42 perform image display for each scanning line on the display cell 15 of the display unit 44 according to the control signal and display data received from the panel controller 41. In addition, after a predetermined write voltage signal is held in all the display cells 15 of the display unit 44, the drive power supply voltage Vdd is inverted between positive and negative so that the display electrodes 12 and the partition wall electrodes 7 of all the display cells 15 are connected. It is also possible to apply an alternating voltage collectively.

  In the electrophoretic display device 100 of the first embodiment, a white display (green display of maximum brightness) is performed by applying a positive DC voltage after applying an AC voltage to the display electrode 12. As shown in FIG. 4 with reference to FIG. 2, in the period T1, the voltage polarity between the signal line 48 and the common electrode 49 is reversed while the auxiliary capacitor 50 holds a predetermined write voltage signal. Then, an alternating voltage is applied to the display electrode 12. The period of the AC voltage is set to the time + α in which the charged particles 4 reciprocate between the partition wall 6 and the display surface. After the AC voltage is applied, in the period T2, the brightest gradation display is maintained by applying the DC voltage.

  Note that after the end of the period T2, the drive power supply voltage Vdd of the drive power supply line 52 is made negative, and an intermediate gradation write voltage signal for each display cell 15 is written to the auxiliary capacitor 50, so that the intermediate gradation of each display cell 15 You may write. Thus, full color display of one pixel is performed by changing the gradation balance of the three adjacent display cells 15 in which the colored layers 10a (G), 10b (R), and 10c (B) shown in FIG. 1 are formed. Is possible. As described above, the gradation writing can be controlled by the voltage of the DC voltage, the number of pulses, the application time, and the like.

  Also, the drain electrode of the pixel TFT 46 in the drive circuit of FIG. 2 is directly connected to the display electrode 12, and the display electrode 12 is AC connected using a normal voltage control type drive circuit that eliminates the drive power supply line 52 and the voltage control TFT 53. A voltage may be applied. In this case, positive and negative voltages are applied to the write signal line 48 at the timing of the scanning signal supplied to the scanning signal line 47, and an alternating voltage is applied to the display electrode 12. And the voltage drop by the resistance layer 9 can be reduced by performing writing of the same polarity a plurality of times in a half cycle of the AC voltage.

  The behavior of the charged particles 4 when an AC voltage is applied during the period T1 in FIG. 4 is shown in FIGS. FIG. 5A shows a black display state before voltage application. Here, when an alternating voltage such as period T1 in FIG. 4 is applied, the distribution state of the charged particles 4 changes from (b) in FIG. 5 to (d) in FIG. 5 through (c) in FIG. .

  Since the half cycle of the AC voltage is set to about 10 ms to 500 ms corresponding to the migration speed of the charged particles 4, the bias of the charged particles 4 on the rising surface of the partition wall 6 is leveled for each reciprocation, and the display surface The charged particles 4 gradually disappear near the center. After that, when a DC voltage for the brightest gradation display is applied in the period T2 in FIG. 4, a group of charged particles 4 unevenly distributed along the transparent substrate 2 on the partition wall 6 as shown in FIG. As a result, the charged particles 4 are distributed almost uniformly covering the rising surfaces of the partition walls 6 as shown in FIG.

  Therefore, by applying the AC voltage before applying the DC voltage, the charged particles 4 that gather on the partition walls 6 and lower the gradation during white display (green display of maximum brightness) can be reduced, and the brightest gradation is achieved. The reflectance at can be improved. Further, since the charged particles 4 covering the upright surface almost uniformly can be effectively restrained by the intermolecular attractive force, affinity, chargeability in the dispersion liquid 3, etc. on the upright surface of the partition wall 6, the brightest gradation can be maintained. The characteristics can be remarkably improved. Further, since the amount of the charged particles 4 collected near the boundary between the upper part of the partition wall 6 and the transparent substrate 2 does not depend on the gradation state before white display (green display of maximum brightness), the afterimage can be greatly reduced. it can.

  Further, each time the AC voltage is inverted, the resistance layer 9 on the display surface is subjected to a transient state during a period in which the voltage accumulated in the resistance layer 9 is discharged through the resistance layer 9, and the potential of the partition wall electrode 7 and the contact hole 11. A voltage gradient connecting the potentials is formed.

  Since the charged particles 4 are moved in the direction along the display surface by this voltage gradient, the half period of the AC voltage is obtained by adding the time when the transient state disappears. This is because if the half cycle of the AC voltage is made shorter than the time constant of this discharge, the potential gradient is generated in the resistance layer 9 and the polarity of the applied voltage is reversed before the charged particles 4 have sufficiently moved. Because does not function effectively.

  On the other hand, in order to form a potential gradient in the resistance layer 9 on the display surface, it is determined by the capacitance formed between the display electrode 12 sandwiching the colored layer 10 a and the resistance layer 9 and the resistance value of the resistance layer 9. More than the time constant is required. It is also possible to set the sheet resistance of the resistance layer 9 high so that the half cycle of the AC voltage is shorter than its time constant. In this case, since the polarity of the AC voltage changes before the potential gradient is generated in the resistance layer 9, no potential gradient is generated. Therefore, a stable electric field distribution can be obtained even if there is resistance unevenness of the resistance layer 9 or misalignment between the contact hole 11 and the partition wall electrode 7, and regardless of the final potential gradient formation state, FIG. It is also possible to obtain symmetrical behavior of the charged particles 4 as shown in (a) to (d).

Second Embodiment
FIG. 6 is an explanatory diagram of a cross-sectional configuration of a display cell in the electrophoretic display device of the second embodiment. The electrophoretic display device 200 of the second embodiment is configured and driven in the same manner as the electrophoretic display device 100 of the first embodiment except that the resistive layer 9a on the display surface and the resistive layer 9b of the partition wall 6 are separated. Has been. Therefore, in FIG. 6, the same components as those in FIG.

  As shown in FIG. 6, the electrophoretic display device 200 according to the second embodiment includes a barrier layer electrode 7 and a colored layer 10 a (10 b, 10 c: hereinafter omitted) integrally formed with a resistive layer 9. A band-like region that goes around the base of the film 6 is selectively removed by photolithography. Therefore, the resistance layer 9 a on the colored layer 10 a is patterned separately from the resistance layer 9 b of the partition wall 6. In other words, the resistance layer 9a is electrically connected to the display electrode 12 by the contact hole 11, while the connection resistance between the resistance layer 9a and the partition wall electrode 7 is from the display electrode 12 to the end of the resistance layer 9a. The resistance is higher than the resistance.

  In such a configuration, the potential gradient formed in the resistance layer 9a and its transient change are greatly different from those of the electrophoretic display device 100 of the first embodiment. That is, immediately after the voltage is applied to the display electrode 12, the potential of each part of the resistance layer 9a is determined by the capacitive partial pressure between the display electrode 12 and the partition wall electrode 7 to form a potential gradient, and then through the resistance layer 9a. The potential gradient disappears due to charge transfer. For example, immediately after application of a voltage signal having a negative potential, a potential gradient is formed in the resistance layer 9a. The potential of the resistance layer 9a is low at the center of the display surface and becomes higher as the barrier electrode 7 is approached. Accordingly, the electric field vector in the lateral direction that pushes the positively charged particles into the center becomes strong, and during this period, the charged particles 4 migrate toward the center of the display surface. Thereafter, charges are injected from the display electrode 12 into the resistance layer 9a, and the potential of the resistance layer 9a is made uniform.

  Even in such a configuration, as shown in FIG. 4, by applying an AC electric field before applying a DC voltage, the brightest gradation is displayed at the top of the partition wall 6 and near the boundary with the transparent substrate 2. The charged particles 4 (see FIG. 5B) can be reduced, and the same effect as in the first embodiment can be obtained.

<Third Embodiment>
FIG. 7 is an explanatory diagram of a cross-sectional configuration of the display cell in the electrophoretic display device of the third embodiment, and FIG. 8 is an explanatory diagram of an electric field profile in the liquid layer when a voltage is applied. The electrophoretic display device 300 according to the third embodiment is the same as the electrophoretic display according to the first embodiment except that the display electrode 5 is disposed at the center of the display surface and is integrally covered with the colored layer 10 by the resistance layer 9. The configuration is the same as that of the device 100. Therefore, in FIG. 7 and FIG. 8, the same reference numerals are given to the components common to FIG.

  As shown in FIG. 7, the electrophoretic display device 300 of the third embodiment has a substantially square display surface in which a colored layer 10 constituting a white reflective surface on the rear substrate 1 is formed and surrounded by a partition wall 6. The display electrode 5 formed at 2% or less of the area of the display surface is disposed in the center of the display. A resistance layer 9 is formed so as to integrally cover the display electrode 5, the colored layer 10, and the partition wall electrode 7.

  In the electrophoretic display device 300 configured in this way, a positive voltage signal is applied to the display electrode 5 and the charged particles 4 are collected on the partition wall 6 so that the white colored layer 10 can be seen from the transparent substrate 2 side. White display. Further, a black voltage is displayed by applying a negative voltage signal to the display electrode 5 to cover the display surface with the charged particles 4.

  Then, when a DC voltage is applied to the display electrode 5, as shown in FIG. 8, the horizontal electric field toward the center becomes strong, so that the charged particles 4 reach the center of the display surface. Therefore, it is possible to display a black gradation more quickly than the electrophoretic display device disclosed in Patent Document 1. However, although the electric field in the lateral direction becomes stronger, the application of a simple DC voltage alone does not provide an effect of improving the particle trajectory at the time of white display, and the charge stays in the boundary region between the upper part of the partition wall 6 and the transparent electrode 2. Various problems caused by the particles 4 are not solved. That is, the gray level viewed from the transparent substrate 2 side is reduced and the white reflectance loss is high, the amount of stagnation of the charged particles 4 is changed due to the gray level before the white display, and the white display varies. Each problem is diffused and lacks memory.

  However, also in the electrophoretic display device 300 of the third embodiment, as shown in FIG. 4, by applying an AC electric field before applying a DC voltage, near the boundary between the upper part of the partition wall 6 and the transparent substrate 2. Since the stagnant charged particles 4 (see FIG. 5B) can be eliminated, these problems can be solved as in the first embodiment.

<Electrophoretic display device of comparative example>
With the development of various portable information devices such as wearable PCs and electronic notebooks, the need for low power consumption and thin display devices is increasing, and research and development of display devices that meet these needs is actively conducted. Yes. Since portable information devices are often used outdoors, and low power consumption and space saving are desired, for example, a display function and a coordinate input process using a thin display such as a liquid crystal display are integrated and displayed on the display. Products that can be directly input by pressing the content with a pen or a finger have been commercialized.

  However, since many liquid crystals do not have so-called memory properties, it is necessary to continue voltage application to the liquid crystals during the display period. On the other hand, a liquid crystal having a memory property has not been put into practical use because it is difficult to ensure reliability when it is assumed to be used in various environments such as a wearable PC.

  Therefore, an electrophoretic display device disclosed in Patent Document 1 has attracted attention as one of thin and light display systems having memory properties. 9 is an explanatory diagram of a cross-sectional configuration of a display cell in an electrophoretic display device of a comparative example shown in Patent Document 1, FIG. 10 is an explanatory diagram of problems in the electrophoretic display device of a comparative example, and FIG. FIG. 12 is an explanatory diagram of an electric field state in the moving space when a voltage is applied.

  As shown in FIG. 9, the electrophoretic display device 500 of the comparative example is arranged with a transparent substrate 101 and a rear substrate 102 in a state where a predetermined gap is opened with a conductive partition wall 106 also serving as a common electrode interposed therebetween. A gap between the substrate 101 and the rear substrate 102 is filled with a dispersion liquid 103 in which charged particles 104 are dispersed. A display electrode 105 is formed on a display surface in which the surface of the rear substrate 102 is surrounded by a partition wall 106, and the display electrode 105 and the partition wall 106 are covered with dielectric layers 105 and 108, respectively. The dielectric layers 105 and 108 adsorb the charged particles 104 by forming a charged surface with a reverse polarity in response to the charged particles 104 that are close to each other.

  In the electrophoretic display device 500 of the comparative example configured as described above, the position of the charged particles 104 can be controlled by applying an appropriate voltage between the display electrode 105 and the partition wall 6, as shown in FIG. In addition, when the display electrode 105 is covered with the charged particles 104, coloring of the charged particles 104 is observed through the transparent substrate 101. On the other hand, when a voltage having a reverse polarity is applied to drive off the charged particles 104 from the display electrode 105, the display electrode 105 can be seen through the transparent substrate 101 as shown in FIG.

  By using the display electrode 105 as a transparent electrode and the rear substrate 102 as a transparent substrate, a reflective surface and a backlight are disposed behind the rear substrate 102, so that the brightest gradation can be displayed. Of course, as described in the first embodiment, the same brightest gradation can be displayed by using the display electrode 105 as a white reflective surface.

  Further, if the display electrode 105 is black while the charged particles 104 are white particles, white display is performed by collecting the charged particles 104 on the display electrode 105, and black particles are obtained by driving away the charged particles 104 from the display electrode 105. It is also possible to display.

  In the electrophoretic display device 500 of the comparative example configured as described above, as shown in FIG. 9, a black display state in which the white display electrode 105 is covered 100% with the black charged particles 104, and as shown in FIG. Further, it is possible to display a white display in which 100% of the black charged particles 104 are collected on the partition wall 106 and the white display electrode 105 is exposed. Further, by forming a partial covering state of the display electrode 105 with the charged particles 104, various intermediate gradations can be displayed. However, the electrophoretic display device 500 of the comparative example has the following four problems.

  The first problem is that the white reflectance loss due to the uneven vertical distribution of the charged particles 104 is large. If the charged particles 104 are collected on the partition 106 during white display, the charged particles 104 are collected near the boundary between the partition 106 and the transparent substrate 101 as shown in FIG. That is, there is a decrease in the aperture ratio due to the charged particles 104.

  The reason why the charged particles 104 gather near the boundary between the partition wall 106 and the transparent substrate 101 is that the point A at the center of the display electrode 105 is applied when a positive DC voltage is applied to the display electrode 105 as shown in FIG. This is because the charged particle 104 repels the display electrode 105 and collides with the transparent substrate 101 at the point B and then moves toward the partition wall 106.

  The second problem is an afterimage. The amount of the charged particles 104 collected near the boundary between the partition 106 and the transparent substrate 101 depends on the covering state of the display electrode 105 before the charged particles 104 are collected on the partition 106, which causes the afterimage. For example, when the intermediate gray level has been displayed before, the amount of the charged particles 104 collected near the boundary between the partition wall 106 and the transparent substrate 101 is reduced, and the reflectance is higher than that in the case of displaying black. A difference in reflectance will occur.

  In general, the distribution state of charged particles in an electrophoretic display device tends to depend on the history of applied voltage, and has a drawback that the previous display state remains. This afterimage problem is known to be improved by applying an alternating electric field, and Patent Document 2 discloses a driving method for reducing afterimages of a microcapsule type electrophoretic display device. Yes. The content is that an AC electric field is applied before or after the voltage pulse for resetting the standby position of the charged particles.

  A third problem is that when black is displayed, the charged particles 104 do not easily reach the center of the display surface, and sufficient black cannot be displayed. FIG. 12 shows equipotential lines when a DC voltage is applied between the display electrode 105 and the partition wall 106 of the electrophoretic display device 500 of the comparative example. As shown in FIG. 12, the equipotential lines are dense where the distance between the partition 106 at the base of the partition 106 and the display electrode 105 is narrow, and the electric field is strong. On the other hand, the equipotential lines are sparse in the center of the display surface. It turns out that an electric field becomes weak.

  In the case of black display, when a negative voltage is applied to the display electrode 105 to collect the charged particles 104 on the display electrode 105, as shown in FIG. It moves to point D, and then reaches point A by a horizontal electric field. However, as shown in FIG. 12, since the electric field toward the center of the display surface is very weak, the charged particles 104 do not reach the center of the display surface. For this reason, the display electrode 105 cannot be reliably covered with the charged particles 104, and there is a problem that sufficient contrast cannot be obtained or the display response speed is remarkably slow.

  A fourth problem is white retention failure. As shown in FIG. 11, in consideration of the trajectory of the charged particles 104, a material that hardly adheres the charged particles 104 is generally selected as a characteristic of the transparent substrate 102. As described above, when white display is performed, the charged particles 104 gather near the boundary between the partition wall 106 and the transparent substrate 101. Since these charged particles 104 do not interact with the transparent substrate 101 and do not adsorb, the memory property cannot be obtained.

  Of these, the third problem can be improved by forming the resistance layer 9 (FIG. 7) shown in the third embodiment. For the remaining first, second, and fourth problems, the white reset operation shown in the first to third embodiments, that is, drive control that applies an alternating voltage of a predetermined period prior to white display. What is solved is as described above. The vertical distribution of the charged particles 104 on the rising surface of the partition wall 106 can be made uniform and dense, and the charged particles 104 can be prevented from collecting near the boundary between the partition wall 106 and the transparent substrate 101.

  According to such a driving method, as shown in FIG. 9, also in the electrophoretic display device 500 of the comparative example, the charged particles 104 that gather near the boundary between the partition wall 106 and the transparent substrate 101 at the time of white display can be reduced. The rate and white retention characteristics can be significantly improved. Since the amount of the charged particles 104 collected near the boundary between the partition wall 106 and the transparent substrate 101 does not depend on the immediately preceding display state, the afterimage can be reduced.

  Further, as shown in FIG. 1, in the electrophoretic display device 100 of the first embodiment, the colored layer 10 a is formed on the display electrode 12, and the resistance layer 9 and the display electrode 12 are connected via the contact hole 11. The display electrode 12 and the resistance layer 9 are superimposed. Here, the period of the alternating electric field prior to the white display is made shorter than the time constant determined by the capacitance between the display electrode 12 and the resistance layer 9 and the resistance of the resistance layer 9, thereby causing the resistance layer 9 to have a potential. Since the polarity of the applied voltage changes before the gradient is generated, the potential gradient does not occur, and the charged particles 4 are attracted to the strong electric field portion below the partition wall 6, and more effectively near the boundary between the partition wall 6 and the transparent substrate 2. It is possible to reduce the charged particles 4 gathered in the.

  Since the electric field profile in such a transient state does not depend on the state of the potential gradient of the resistance layer 9, even if misalignment between the contact hole 11 and the partition wall electrode 7 occurs, a uniform distribution of the charged particles 4 is formed. can do.

<Correspondence with Invention>
The electrophoretic display device 100 according to the first embodiment includes a display electrode 12 disposed for each display surface, a partition electrode 7 disposed on an upright surface of the partition 6 surrounding the display surface, the display electrode 12 and the partition electrode 7. And a panel controller 41 that collects the charged particles 4 on the upright surface by applying a DC voltage of a predetermined polarity. The panel controller 41 applies a DC voltage between the display electrode 12 and the partition wall electrode 7 after applying an AC voltage.

  Therefore, the charged particles 4 are swept to a portion close to the partition wall 6 while reciprocating between the rising surface of the partition wall 6 and the display surface by the AC voltage, so that the charged particles 4 move from the center of the display surface to the upper part of the partition wall 6 and stagnate. The number of charged particles 4 to be reduced is reduced, and the variation of the charged particles 4 in the height direction of the rising surfaces of the partition walls 6 is eliminated.

  In other words, by applying the AC voltage, a stacked state of the charged particles 4 uniformly and regularly distributed in the vertical direction with high reproducibility is formed on the rising surface of the partition wall 6 without being affected by the display state before the application. . As a result, it is possible to prevent the charged gradation 4 from staying in the upper part of the partition wall 6 and changing the gradation of the display through which the display surface can be seen. In addition, the gradation after the voltage is released is less likely to change due to the diffusion of the staying charged particles 4 having no binding force, and the memory performance of the display is improved.

  The electrophoretic display device 100 according to the first embodiment is disposed so as to cover the colored layer 10a and the translucent colored layer 10a disposed on the display electrode 12, and is connected to the display electrode 12 at the center side of the display surface. The planar resistive layer 9 is provided.

  Therefore, due to the potential gradient formed in the resistance layer 9, the electric field density can be increased even in the central portion of the display electrode 12, and sufficient acceleration in the direction along the display surface with respect to the charged particles 4 can be ensured. Thereby, the response speed and the gradation writing speed of the charged particles 4 at the time of voltage application are increased. In addition, the reproducibility of gradation writing is improved and variation in display gradation with respect to application of the same signal voltage is reduced, so that image display and color display with high reproducibility are possible.

  In the electrophoretic display device 300 according to the third embodiment, the display electrode 5 includes a resistance layer 9 that is disposed on the center side of the display surface at a distance from the standing surface and is connected to the display electrode 5 to cover the display surface.

  In the electrophoretic display device 100 according to the first embodiment, the period of the alternating voltage is determined based on the time during which the charged particles 4 move from the display surface to the standing surface by the alternating voltage. Further, the cycle of the AC voltage is corrected based on a time constant when the AC voltage stored in the resistance layer 9 is discharged through the resistance layer 9.

  The white display in the first embodiment includes a display electrode 12 disposed on the display surface and a partition electrode 7 disposed on an upright surface of the partition wall 6 surrounding the display surface, and between the display electrode and the partition electrode 7. By applying a DC voltage having a predetermined polarity to the charged particles 4 and moving the charged particles 4 to the upright surfaces of the partition walls 6, the display surface can be viewed. And after applying the alternating voltage of the period defined based on the time which the charged particle 4 moves to the standing surface of the partition 6 from a display surface between the display electrode 12 and the partition electrode 7, the voltage of predetermined polarity is applied. . Thereby, the standing surface of the partition wall 6 can be uniformly covered with the charged particle 4 without causing the charged particle 4 to stay in the boundary region between the partition wall 6 and the transparent substrate 2.

  The electrophoretic display device 100 according to the first embodiment includes a display electrode 12 disposed on a display surface and a partition electrode 7 disposed on a standing surface of a partition wall 6 surrounding the display surface. Subsequent to the reset operation for collecting on the standing surface, a gradation writing operation for moving the charged particles 4 to the display surface can be performed. At this time, the reset operation can be performed by white display, and the white display voltage is set to a predetermined value following application of an alternating voltage with a period determined based on the time for the charged particles 4 to move from the display surface to the rising surface of the partition wall 6. Hold for hours. As a result, the rising surface of the partition wall 6 is uniformly covered with the charged particles 4 without causing the charged particles 4 to stagnate in the boundary region between the partition walls 6 and the transparent substrate 2 regardless of the display state before the reset operation. Tonal writing can be executed with high reproducibility.

  By the way, as already described with reference to FIGS. 9 to 12, in the electrophoretic display device 500 of the comparative example, the display surface is covered with the charged particles 104, and the charged particles 104 are transferred to the partition walls 106. An intermediate gradation (dark gray to light gray) can be displayed between two gradations that display the 100% transmissive state in which the display surface is exposed and collected. In such halftone display, the coverage of the display surface by the charged particles 104 is adjusted by changing the voltage of the voltage signal for collecting the charged particles 104 on the display surface, the application time, the number of pulses, and the like.

  When displaying the intermediate gradation, the charged particles 104 are once collected on the partition wall 106 and reset to a display state in which the display surface can be seen, and then a predetermined voltage signal for collecting the charged particles 104 on the display surface is applied. It has been proposed to perform gradation writing on the display surface. This is because even if the same DC voltage is applied for the same time, if the starting point has a different gradation, the written result will have a different gradation, and even if the starting point has the same gradation, This is because the reproducibility of gradation writing cannot be ensured, for example, the gradation of the result written by time difference is different.

  However, in practice, when such a reset is performed, if the gradation displayed before the reset is different, the reset gradation is different, and thereafter, the gradation after the same writing is also different. This is because when charged particles 104 are collected on the partition 106 by applying a DC voltage, the charged particles 104 are likely to stay excessively on the partition 106 as described above, and the amount of stagnation displayed before the reset is displayed. This is because it changes depending on the key.

  In other words, in the display of the intermediate gradation, the charged particles 104 are unevenly distributed in the peripheral part of the display surface, and the display part looks through the central part of the display surface. This is different from the case where the vertical distribution of the charged particles 104 gathered in the partition wall 106 is reset from the cut-off state of 100%. When writing is performed from a reset state in which the vertical distribution of the charged particles 104 is different, the gradation of the written result is different even when the same voltage signal is applied.

  In other words, as a result, as disclosed in Patent Document 2, there is a problem that “the reproducibility of writing is impaired due to the display gradation before resetting”. This is a problem inherent to the structure shown, “the reproducibility of the vertical distribution of the charged particles in the partition cannot be obtained due to the influence of the display gradation before resetting”.

  In the electrophoretic display device 500 in which the partition electrode (106) is disposed on the rising surface of the partition wall 106 surrounding the display surface and the charged particles 106 are moved between the rising surface of the partition wall 106 and the display surface, a patent document is disclosed. 2 is not an AC voltage for loosening the fixing state of the display surface and the charged particles, but positively between the rising surface and the display surface as shown in FIGS. Thus, a uniform vertical distribution of the charged particles 104 in the partition wall 106 can be achieved by an alternating voltage that causes the charged particles 106 to reciprocate.

  And after resetting, by applying a predetermined write signal voltage (voltage, application time, number of pulses, etc.) without applying a second AC voltage (relaxing adhesion) as shown in Patent Document 2 Thus, it is possible to perform half-tone writing with high reproducibility according to the writing signal voltage and with little variation for each display cell.

  And as above-mentioned, the resistance layer 9 (FIG. 1 etc.) in 1st Embodiment-3rd Embodiment raises the moving speed of the charged particle 4 of the direction along a display surface, Therefore The alternating voltage of the time of reset is set. The period is made shorter than when the resistance layer 9 is not provided, thereby shortening the reset time. As a result, the total time required for resetting and writing is shortened, and the frequency of rewriting the image display is increased so that a moving image can be displayed.

  In the electrophoretic display device disclosed in Patent Document 3, a white display that allows a display cell to be seen by applying a DC electric field to a display cell, and a black display that shields the display surface by applying an AC electric field are performed. Therefore, when white control → black display → white display is added, if a new control requirement such as optimizing the frequency of the AC electric field is added, the second white display becomes brighter than the first white display. However, this is contrary to the object of the present invention to obtain a reproducible white display with a uniform gradation on the screen. In addition, since the resistive layer itself is not provided, the effect of the alternating electric field cooperating with the resistive layer on the display surface to increase the moving speed of the charged particles to the partition wall surface There is no expectation that charged particles will be collected.

It is explanatory drawing of the cross-sectional structure of the display cell in the electrophoretic display device of 1st Embodiment. It is explanatory drawing of the drive circuit of a display cell. It is explanatory drawing of the circuit structure of an electrophoretic display apparatus. It is explanatory drawing of the voltage signal in white display. It is explanatory drawing of the behavior of the charged particle in control of white display. It is explanatory drawing of the cross-sectional structure of the display cell in the electrophoretic display device of 2nd Embodiment. It is explanatory drawing of the cross-sectional structure of the display cell in the electrophoretic display device of 3rd Embodiment. It is explanatory drawing of the electric field profile in the liquid layer at the time of a voltage application. It is explanatory drawing of the cross-sectional structure of the display cell in the electrophoretic display apparatus of a comparative example. It is explanatory drawing of the problem in the electrophoretic display apparatus of a comparative example. It is explanatory drawing of the movement path | route of the charged particle with respect to voltage application. It is explanatory drawing of the electric field state in the movement space at the time of applying a voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Back substrate 2 Transparent substrate 3 Dispersed liquid 4 Charged particle 5, 12 Display electrode 6 Partition 7 Partition electrode 9 Resistance layer 10a, 10b, 10c Colored layer 11 Contact hole

Claims (7)

Display electrodes arranged for each display surface;
A partition electrode disposed on an upstanding surface of the partition wall surrounding the display surface;
A resistance layer disposed on the display surface and connected to the display electrode;
In a particle movement type display device comprising: a control means for applying a DC voltage of a predetermined polarity between the display electrode and the partition wall electrode and collecting charged particles on the rising surface,
The particle moving display device, wherein the control means applies the DC voltage after applying the AC voltage between the display electrode and the partition wall electrode. A translucent insulating layer disposed on the display electrode;
2. The particle movement type display device according to claim 1, wherein the resistance layer is disposed so as to cover the insulating layer, and is connected to the display electrode at a center side of the display surface. The display electrode is disposed on the center side of the display surface at a distance from the standing surface,
The particle movement type display device according to claim 1, wherein the resistance layer is connected to the display electrode and covers the display surface.   4. The particle according to claim 1, wherein the period of the AC voltage is determined based on a time during which the charged particles move from the display surface to the standing surface by the AC voltage. Mobile display device.   5. The particle movement type display device according to claim 4, wherein the period of the AC voltage is corrected based on a time constant when the AC voltage stored in the resistance layer is discharged through the resistance layer. . A display electrode disposed on the display surface, and a partition electrode disposed on an upright surface surrounding the display surface, and a DC voltage having a predetermined polarity is applied between the display electrode and the partition electrode, In the driving method of the particle movement type display device for performing the display through which the display surface can be seen by moving the charged particles to the standing surface,
Applying a DC voltage having a predetermined polarity after applying an AC voltage having a period determined based on a time required for the charged particles to move from the display surface to the standing surface between the display electrode and the partition wall electrode; A method for driving a particle movement type display device. A display electrode disposed on the display surface; and a partition electrode disposed on an upstanding surface surrounding the display surface; and following the reset operation for collecting charged particles on the upstanding surface, the charged particles are applied to the display surface. In the driving method of the particle movement type display device for performing the gradation writing operation to move,
The method of driving a particle movement type display device, wherein the resetting operation includes application of an alternating voltage with a period determined based on a time for which the charged particles move from the display surface to the standing surface.

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