JP2008225100A - Electrophoretic display device, driving method of electrophoretic display device, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a contrast characteristic of an electrophoretic display device. <P>SOLUTION: The electrophoretic display device includes a display part which has a plurality of pixel parts containing electrophoretic elements having electrophoretic layers interposed between pixel electrodes and a common electrode, and a control part connected to the common electrode and pixel electrodes. The control part performs control of periodically repeating a plurality of times (a) one or more first voltage writings which make potentials of pixel electrodes relatively higher than the potential of the common electrode, and one or more second voltage writings which makes potentials of pixel electrodes relatively lower than the potential of the common electrode, and (b) a third voltage writing according to image data after (a). A total value T1 of periods of the first voltage writings and a total value T2 of periods of the second voltage writings are regulated to satisfy 1.5×T2>T1>0.8×T2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophoretic display device, a driving method thereof, and an electronic apparatus including the electrophoretic display device.

  In an active matrix electrophoretic display device, a driving method has been proposed in which the driving voltage is not increased more than necessary and no erroneous rewriting occurs (see Patent Document 1). According to this driving method, when changing the display contents, first, the pixel electrodes are all set to the same potential (second voltage) with the common electrode set to the first voltage, and the common electrode is placed between the common electrode and the pixel electrode. A potential difference is applied and the display content is erased over the entire display area. The gradation at this time is defined as the first gradation. Next, with the common electrode at the second voltage, the first voltage is applied to the desired pixel electrode, and the second voltage is applied to the other pixel electrodes. In the pixel in which the first voltage is applied to the pixel electrode, a potential difference is generated between the pixel electrode and the common electrode, and the display changes from the first gradation to the second gradation. In the pixel to which the second voltage is applied, no potential difference is generated between the pixel and the common electrode, so the display remains at the first gradation.

  However, in the conventional electrophoretic display device as described above, when the image writing is repeatedly performed at a relatively short cycle (for example, about several seconds to several tens of seconds), the contrast characteristics are reduced with the passage of time. There was a case where the trouble of doing. Such a defect is remarkable in an electrophoretic display device in which a display image needs to be switched relatively frequently, such as an electrophoretic display device incorporated in an electronic book, and improvement has been desired.

JP 2002-149115 A

  Accordingly, an object of the present invention is to provide an electrophoretic display device capable of obtaining good contrast characteristics even when image writing is periodically repeated.

An electrophoretic display device according to the present invention includes:
A display unit having a plurality of pixel units each including an electrophoretic element having an electrophoretic layer interposed between the pixel electrode and the common electrode, and a capacitor whose one terminal is connected to the pixel electrode;
A control unit connected to each of the common electrode and the pixel electrode;
Wherein the electrophoretic layer is disposed between the common electrode and the pixel electrode and has a capsule having a diameter in the range of 30 μm to 60 μm, and an average particle size in the range of 0.1 μm to 0.8 μm The first particles in the first charged state and included in the capsule, and the second particles are in the second charged state and included in the capsule in an average particle size in the range of 0.02 to 0.1 μm. Second particles.
Then, the control unit (a) first voltage writing in which the potential of the pixel electrode is relatively higher than the potential of the common electrode, and the potential of the pixel electrode is higher than the potential of the common electrode. The second voltage writing to be in a relatively low state is performed at least once or more. (B) Next, a reference potential is applied to the common electrode, and each of the pixel electrodes is larger than the reference potential. The control of repeating the third voltage writing for applying either the potential or the potential equal to or lower than the reference potential is performed periodically and a plurality of times, and the total time T1 for performing the first voltage writing at this time And the total time T2 of the second voltage writing is defined as 1.5 × T2>T1> 0.8 × T2.

An electrophoretic display device driving method according to the present invention includes:
A display unit having a plurality of pixel units each including an electrophoretic element having an electrophoretic layer interposed between the pixel electrode and the common electrode, and a capacitor having one terminal connected to the pixel electrode; The electrophoretic layer includes a capsule having a diameter in the range of 30 μm to 60 μm disposed between the common electrode and the pixel electrode, and an average particle diameter in the range of 0.1 μm to 0.8 μm. The first particles contained in the capsule and in the charged state, and the second particles in the second charged state and contained in the capsule having an average particle diameter in the range of 0.02 to 0.1 μm. And an electrophoretic display device including particles.
(A) First voltage writing in which the potential of the pixel electrode is relatively higher than the potential of the common electrode, and a state in which the potential of the pixel electrode is relatively lower than the potential of the common electrode (B) A reference potential is applied to the common electrode, and each of the pixel electrodes has a potential greater than or less than the reference potential. The third voltage writing for applying any one of the potentials is periodically repeated a plurality of times, and the total time T1 for performing the first voltage writing at this time and the second voltage writing are performed. The relationship with the total value T2 of the time for performing is defined as 1.5 × T2>T1> 0.8 × T2.

  In the present invention, the relationship between the total time of the first voltage writing and the total time of the second voltage writing is defined as described above based on the knowledge obtained by the experiment, and each voltage writing is performed at least once or more. After that, the third voltage writing (corresponding to image writing) is performed. This provides an electrophoretic display device or a driving method thereof that can obtain good contrast characteristics even when image writing is periodically repeated.

  As the first particle, for example, titanium oxide particles can be adopted. At this time, the first charged state is, for example, a negatively charged state. For example, carbon black particles can be adopted as the second particles. At this time, the second charged state is, for example, a positively charged state.

  The period when the above (a) and (b) are periodically repeated can be defined as, for example, 10 seconds.

  In the above (a), the number of times of performing the first voltage writing and the second voltage writing can be set to, for example, 4 times.

  An electronic apparatus according to the present invention includes the above-described electrophoretic display device as a display unit. Examples of the electronic device include a display device, a television device, an electronic book, an electronic paper, a clock, a calculator, a mobile phone, a portable information terminal, and the like. In addition, for example, a flexible paper / film object, an object belonging to a real estate such as a wall surface to which these objects are attached, an object belonging to a moving object such as a vehicle, a flying object, and a ship are also used in this specification. It shall be included in the concept of “electronic equipment”.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing the overall configuration of the electrophoretic display device. The electrophoretic display device 100 illustrated in FIG. 1 includes a panel unit 110, a scanning line driving circuit 130, a data line driving circuit 140, and a common electrode control circuit 150. The panel unit 110 is arranged corresponding to each of the scanning lines 101 of m rows, the data lines 102 of n columns arranged so as to intersect the scanning lines 101, and the intersections of the scanning lines 101 and 102. And a pixel portion 109. Each pixel portion 109 includes a transistor 103, an electrophoretic element 104, and a capacitor element 108. Each pixel unit 109 is arranged in a matrix. The electrophoretic display device 100 is connected with a controller 190 as a peripheral circuit. The controller 190 includes an image signal processing circuit and a timing generator. Here, the image signal processing circuit generates image data and common electrode control data, and inputs them to the data line driving circuit 140 and the common electrode control circuit 150, respectively. The common electrode control circuit 150 supplies a common electrode signal COM to the common electrode of the electrophoretic element 104. The timing generator generates various timing signals for controlling the scanning line driving circuit 130 and the data line driving circuit 140 when reset settings and image data are output from the image signal processing circuit. Note that the transistor 103, the scanning line driving circuit 130, the data line driving circuit 140, and the common electrode control circuit 150 described above correspond to the “control unit” in the present invention.

  FIG. 2 is a schematic cross-sectional view illustrating the structure of the electrophoretic display device. The electrophoretic element 104 includes a pixel electrode 105, a common electrode 106, and an electrophoretic layer (electrophoretic material) 107 disposed therebetween. A common electrode signal COM is given to the common electrode 106 shared between the pixel portions. The common electrode 106 may be separated for each electrophoretic element 104. In the present embodiment, it is assumed that the state of the electrophoretic layer 107 (in other words, the display state) is viewed from the common electrode 106 side, and the common electrode 106 is a transparent conductive material such as an ITO (Indium Tin Oxide) film. A membrane is used.

  The electrophoretic layer 107 includes a large number of capsules (microcapsules) containing white particles and black particles. Each capsule is disposed between the pixel electrode 105 and the common electrode 106 as shown, and has a diameter in the range of 30 μm to 60 μm. The white particles (first particles) are, for example, titanium oxide particles and have an average particle diameter in the range of 0.1 μm to 0.8 μm and are negatively charged (first charged state). The black particles (second particles) are, for example, carbon black particles having an average particle diameter in the range of 0.02 to 0.1 μm and being positively charged (second charged state). The state of the electrophoretic layer 107 is schematically shown in FIG. As shown in the figure, in this embodiment, when the potential of the pixel electrode 105 is relatively higher than the potential of the common electrode 106 (HI), the positively charged black particles move to the common electrode 106 side and become negative. The charged white particles move to the pixel electrode 105 side. When the pixel portion in this state is viewed from the common electrode 106 side, it is recognized as black. In addition, when the potential of the pixel electrode 105 is relatively lower than the potential of the common electrode 106 (LO), the positively charged black particles move to the pixel electrode 105 side, and the negatively charged white particles become the common electrode. Move to the 106 side. When the pixel portion in this state is viewed from the common electrode 106 side, it is recognized as white. That is, the electrophoretic display device 100 of the present embodiment basically performs black and white binary display, but can also perform gradation display by combining a plurality of neighboring pixel portions. Note that the color tone applied to each particle of the electrophoretic layer 107 is not limited to the combination of black and white, and the charged state of each particle is not limited to the above. Further, it may be configured to be viewed from either side of the pixel electrode 105 and the common electrode 106. That is, these conditions can be changed as appropriate.

  FIG. 3 is a circuit diagram illustrating a detailed configuration of each pixel unit. The transistor 103 as a switching element has a gate connected to the scanning line 101, a source connected to the data line 102, and a drain connected to the pixel electrode 105. The capacitor 108 has one terminal connected to the pixel electrode 105 and the other terminal connected to the ground terminal (ground potential) GND. The scanning signal Y1 is given to the scanning line 101. The scanning signal Y1 represents a scanning signal corresponding to the scanning line 101 in the first row. Scan signals are sequentially supplied to the scanning lines 101 in the second row,. A data signal D1 is applied to the data line 102. The potential of the data signal D1 is held by the capacitor element (holding capacitor) 108. The data signal D1 represents a data signal corresponding to the data 102 in the first column. A data signal is also supplied to the data line 102 in the second column to the nth column. The electrophoretic element 104 is configured by disposing an electrophoretic layer 107 between the pixel electrode 105 and the common electrode 106. The panel unit 110 is configured by arranging the electrophoretic elements 104 in a matrix. Between the pixel electrode 105 and the common electrode 106, an electrostatic capacitance having a size corresponding to the electrode area of the pixel electrode 105, the distance between the pixel electrode 105 and the common electrode 106, and the dielectric constant of the electrophoretic layer 107. A capacitance is formed. The common electrode 106 is shared by the plurality of electrophoretic elements 104 and is connected to the common electrode control circuit 150 via the wiring 201 (see FIG. 1). A common electrode signal COM is supplied to the wiring 201. As the common electrode signal COM, for example, either a reference potential that is a relatively low potential or a relatively high potential is applied.

  In such an electrophoretic display device 100, first, when all scanning line signals become active at a predetermined timing, the transistor 103 connected to the jth scanning line 101 is also turned on. At this time, all data signals are set to a white or black level, and a signal of a predetermined level is applied to the common electrode 106 from the counter electrode modulation circuit 150 to set all the electrophoretic elements to white or black display. Thereafter, the scanning lines 101 are sequentially selected and image writing is performed. When the transistor 103 connected to the jth scanning line 101 is turned on, a data signal (image signal) supplied from the data line driver circuit 140 is written to the pixel electrode 105 in synchronization with the scanning line selection. At this time, the capacitor block 08 is also charged at the voltage level of the data signal, and even after the transistor 103 is cut off, the charge of the pixel (pixel electrode and common electrode) is maintained, and the image is maintained by the electrophoretic particles 104. Each pixel performs display in accordance with the voltage level of the data signal, thereby displaying an image.

  The configuration of the electrophoretic display device 100 according to the present embodiment is as described above. Next, the operation thereof will be described in detail.

  FIG. 4 is a diagram for explaining a driving method of the electrophoretic display device according to this embodiment. Specifically, FIG. 4A is a waveform diagram showing the potential of the common electrode 106, FIG. 4B is a waveform diagram showing the potential of the pixel electrode 105 of one pixel portion 109, and FIG. FIG. 10 is a waveform diagram showing a potential of a pixel electrode 105 of another pixel portion 109. FIG. 5 is a diagram schematically showing the state of each particle in the capsule of the electrophoretic display device 100 during driving. As described above, the drive control described below is performed by the “control unit” including the transistor 103, the scan line drive circuit 130, the data line drive circuit 140, and the common electrode control circuit 150. This is realized by appropriately setting and supplying electrode signals.

  As shown in FIGS. 4A to 4C, first voltage writing is performed in which the potential of each pixel electrode 105 is relatively higher than the potential of the common electrode 106. In the present embodiment, this first voltage writing corresponds to the case where the visual recognition state of the pixel portion 109 is controlled to black (see FIG. 2). Here, since all the pixels are controlled to be black, this first voltage writing is indicated by the abbreviation “all black” in FIG. 4. This state is shown in FIG. Here, the potential of the common electrode 106 is set to +1.5 V (reference potential) as an example, and the potential of each pixel electrode 105 is set to +10 V as an example.

  Next, as shown in FIGS. 4A to 4C, second voltage writing is performed in which the potential of each pixel electrode 105 is relatively lower than the potential of the common electrode 106. In the present embodiment, the second voltage writing corresponds to a case where the visual recognition state of the pixel unit 109 is controlled to be white (see FIG. 2). Here, since all the pixels are controlled to be white, this second voltage writing is indicated by an abbreviation “all white” in FIG. 4. This state is shown in FIG. Here, the potential of the common electrode 106 is set to +10 V as an example, and the potential of each pixel electrode 105 is set to +1.5 V as an example.

  Such first voltage writing (all black) and subsequent second voltage writing (all white) are performed at least once. In the present embodiment, the first voltage writing and the second voltage writing are repeated four times as illustrated. This drive control can also be regarded as a process (erasing process) for resetting the state of each of the white and black particles (see FIG. 5A) due to the previous data writing. At this time, in the present embodiment, the relationship between the total value T1 of the first voltage writing time and the total time T2 of the second voltage writing time is 1.5 × T2> T1> 0.8 × T2. Specified within the scope of In the example shown in FIG. 4, the total value (total time) T1 = t1 + t3 + t5 + t7, and the total value (total time) T2 = t2 + t4 + t6 + t8. Numerical examples of the times T1, T2, and t1 to t8 will be described later.

  Next, as shown in FIGS. 4A to 4C, the common electrode 106 is supplied with a reference potential (for example, +1.5 V), and each pixel electrode 105 is supplied with a potential higher than the reference potential ( For example, either +10 V) or a potential equal to or lower than the reference potential (for example, +1.5 V. A potential lower than that, for example, 0 V may be applied). This third voltage writing is to control each pixel portion 109 to be either white or black according to the image data, and is indicated by an abbreviation “data writing” in the drawing. This state is shown in FIG. t9 is appropriately set.

  Thereafter, the potentials of the pixel electrodes 105 and the common electrode 106 are both controlled to a common low potential, and the image written by the third voltage writing is held. This state is shown in FIG.

  Although one image writing control is completed as described above, in this embodiment, this image writing control is periodically repeated a plurality of times as shown in FIG. Specifically, FIG. 6A is a waveform diagram showing the potential of the common electrode 106, FIG. 6B is a waveform diagram showing the potential of the pixel electrode 105 of one pixel portion 109, and FIG. FIG. 10 is a waveform diagram showing a potential of a pixel electrode 105 of another pixel portion 109. At this time, the period t10 when the image writing control of each time is periodically repeated is defined as about 10 seconds as an example.

  FIG. 7 is a graph showing a result of measuring a change in reflectance with elapsed time when the electrophoretic display device 100 is driven by the driving method according to the present embodiment. This reflectance characteristic is measured by setting the relationship between the total time T1 of the first voltage writing and the total time T2 of the second voltage writing to the following five conditions. The detailed conditions of the electrophoretic display device 100 used are as described above. In the following conditions 1 to 3, the first first voltage write (full black) time is two orders of magnitude longer than the first voltage write time thereafter, and the last second voltage write The (all white) time is set two orders of magnitude larger than the second voltage writing time before that time.

(Condition 1) T1 = 0.8 × T2
Breakdown;
T1 = t1 + t3 + t5 + t7 = 1100 + 45 + 45 + 10 = 1200 (milliseconds)
T2 = t2 + t4 + t6 + t8 = 10 + 45 + 45 + 1400 = 1500 (milliseconds)

(Condition 2) T1 = 1.5 × T2
Breakdown;
T1 = t1 + t3 + t5 + t7 = 2150 + 45 + 45 + 10 = 2250 (milliseconds)
T2 = t2 + t4 + t6 + t8 = 10 + 45 + 45 + 1400 = 1500 (milliseconds)

(Condition 3) T1 = T2
Breakdown;
T1 = t1 + t3 + t5 + t7 = 1400 + 45 + 45 + 10 = 1500 (milliseconds)
T2 = t2 + t4 + t6 + t8 = 10 + 45 + 45 + 1400 = 1500 (milliseconds)

(Condition 4) T1 = 0.5 × T2
Breakdown;
T1 = t1 + t3 + t5 + t7 = 350 + 350 + 20 + 400 = 1120 (milliseconds)
T2 = t2 + t4 + t6 + t8 = 700 + 700 + 40 + 800 = 1500 (milliseconds)

(Condition 5) T1 = 2 × T2
Breakdown;
T1 = t1 + t3 + t5 + t7 = 700 + 700 + 40 + 800 = 2240 (milliseconds)
T2 = t2 + t4 + t6 + t8 = 350 + 350 + 20 + 400 = 1120 (milliseconds)

  According to FIG. 7, when the total time T2 of the second voltage writing (all white) is twice the total time T1 of the first voltage writing (all black) (condition 4), the white display reflection It can be seen that the rate decreases with time. According to FIG. 7, when the total time T2 of the second voltage writing (all white) is 0.5 times the total time T1 of the first voltage writing (all black) (condition 5), It can be seen that the reflectance of the black display increases with time. Therefore, in the conditions 4 and 5, the contrast determined by the relative relationship between the white display and the black display is lowered. On the other hand, in the conditions 1 to 3, there is no inconvenience as described above, and the contrast is maintained even after a lapse of time. FIG. 8 shows the contrast characteristics after 2 hours under each condition. In FIG. 8, in order to define the relationship between T1 and T2, the number multiplied by T2 is taken as the horizontal axis, and the contrast (arbitrary unit) is taken as the vertical axis. From FIG. 8, it can be seen that the contrast is maintained in a high state between the conditions 1 and 3, but the contrast is lowered when the condition is removed.

  As described above, according to the present embodiment, the relationship between the total time T1 of the first voltage writing and the total time T2 of the second voltage writing is appropriately defined as described above, and each voltage writing is performed at least 1 times. After that, the third voltage writing (corresponding to image writing) is performed. This provides an electrophoretic display device or a driving method thereof that can obtain good contrast characteristics even when image writing is periodically repeated.

  FIG. 9 is a perspective view illustrating a specific example of an electronic apparatus to which the electrophoretic display device of the present invention is applied. FIG. 9A is a perspective view illustrating an electronic book that is an example of the electronic apparatus. The electronic book 1000 includes a book-shaped frame 1001, a cover 1002 that can be rotated (openable and closable) with respect to the frame 1001, an operation unit 1003, and the electrophoretic display device of the present embodiment. The display unit 1004 is provided. FIG. 9B is a perspective view illustrating electronic paper which is an example of the electronic apparatus. The electronic paper 1200 includes a main body 1201 formed of a rewritable sheet having the same texture and flexibility as paper, and a display unit 1202 configured by the electrophoretic display device of the present embodiment. By configuring the display unit using the electrophoretic display device of the present embodiment, an electronic apparatus capable of obtaining good display without deterioration of contrast characteristics even when time passes during use is realized.

  In addition, this invention is not limited to the content of embodiment mentioned above, In the range of the summary of this invention, it can change and implement variously. For example, in the above-described embodiment, an electrophoretic display device including pixel units arranged in a matrix has been described. However, the present invention can be applied to an electrophoretic display device (for example, a segment display type) other than this. It is possible to apply.

It is a block diagram which shows the whole structure of an electrophoretic display device. It is a schematic cross section explaining the structure of the electrophoretic display device. It is a circuit diagram which shows the detailed structure of each pixel part. It is a figure for demonstrating the drive method of an electrophoretic display device. It is a figure which shows typically the mode of each particle | grain in the capsule of an electrophoretic display device. It is a figure for demonstrating the drive method of an electrophoretic display device. It is a graph which shows the result of having measured the change of the reflectance of an electrophoretic display device. It is the figure which showed the contrast characteristic of the electrophoretic display device. It is a perspective view explaining the specific example of the electronic device to which the electrophoretic display apparatus is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Electrophoretic display device 101 ... Scan line, 102 ... Data line, 103 ... Transistor, 104 ... Electrophoretic element, 105 ... Pixel electrode, 106 ... Common electrode, 107 ... Electrophoretic layer, 108 ... Capacitor element, 109 ... Pixel unit 110... Panel unit 130 Scanning line drive circuit 140 Data line drive circuit 150 Common electrode control circuit 190 Controller

Claims (5)

A display unit having a plurality of pixel units each including an electrophoretic element having an electrophoretic layer interposed between the pixel electrode and the common electrode, and a capacitor having one terminal connected to the common electrode;
A control unit connected to each of the common electrode and the pixel electrode;
With
The electrophoretic layer is
A capsule having a diameter in the range of 30 μm to 60 μm disposed between the common electrode and the pixel electrode, and having an average particle diameter in the range of 0.1 μm to 0.8 μm and being in the first charged state. First particles included in the capsule, and second particles included in the capsule in a second charged state having an average particle diameter in the range of 0.02 to 0.1 μm;
Including
The controller is
(A) First voltage writing in which the potential of the pixel electrode is relatively higher than the potential of the common electrode, and a state in which the potential of the pixel electrode is relatively lower than the potential of the common electrode Performing the second voltage writing at least once,
(B) Next, a third voltage writing is performed in which a reference potential is applied to the common electrode, and each of the pixel electrodes is applied with either a potential higher than the reference potential or a potential lower than the reference potential. ,
Is repeated periodically several times,
The relationship between the total time T1 for performing the first voltage writing and the total time T2 for performing the second voltage writing in the control is 1.5 × T2>T1> 0.8 × T2. Prescribed,
Electrophoretic display device. The first particles are titanium oxide particles and the first charged state is negatively charged;
The second particles are carbon black particles and the second charged state is a positively charged state;
The electrophoretic display device according to claim 1. The cycle when repeating (a) and (b) periodically was defined as 10 seconds,
The electrophoretic display device according to claim 1. An electrophoretic element having an electrophoretic layer interposed between the pixel electrode and the common electrode, and a display unit having a plurality of pixel units each including a capacitor element having one terminal connected to the pixel electrode, The electrophoretic layer includes a capsule having a diameter in a range of 30 μm to 60 μm disposed between the common electrode and the pixel electrode, and an average particle diameter in a range of 0.1 μm to 0.8 μm. First particles contained in the capsule and in an average particle diameter in the range of 0.02 to 0.1 μm and second charged state and contained in the capsule. A method of driving an electrophoretic display device including particles,
(A) First voltage writing in which the potential of the pixel electrode is relatively higher than the potential of the common electrode, and a state in which the potential of the pixel electrode is relatively lower than the potential of the common electrode Performing the second voltage writing at least once,
(B) performing a third voltage writing in which a reference potential is applied to the common electrode and each of the pixel electrodes is applied with either a potential higher than the reference potential or a potential lower than the reference potential;
Is periodically repeated a plurality of times, and the relationship between the total time T1 for performing the first voltage writing and the total time T2 for performing the second voltage writing is 1.5 × T1. >T2> 0.8 × T1
Driving method of electrophoretic display device.   An electronic device comprising the electrophoretic display device according to claim 1 as a display unit.

Images