JP5034291B2 - Electro-optical device, driving method of electro-optical device, and electronic apparatus - Google Patents

Description

The present invention relates to an electro-optical device including a dispersion system containing electrophoretic particles that migrate when an electric field is applied, a driving method of the electro-optical device, and an electronic apparatus.

2. Description of the Related Art Conventionally, an electrophoretic display device using an electrophoretic phenomenon is known as a non-light-emitting electro-optical device (see, for example, Patent Document 1). Electrophoresis is caused by fine particles (in the dispersion medium)
A phenomenon in which, when an electric field is applied to a dispersion system in which (electrophoretic particles) are dispersed, the fine particles migrate by Coulomb force.

Here, a schematic configuration of the electrophoretic display device will be briefly described. The electrophoretic display device has one electrode and the other electrode facing each other at a predetermined interval, and a large number of dispersion systems as pixels, which are display units of an image, are arranged in a matrix therebetween. The electrophoretic display device includes a peripheral circuit for applying an electric field to the dispersion system.

FIG. 7 is an exploded perspective view showing a mechanical configuration of the electrophoretic display device, and FIG. 8 is a cross-sectional view of a main part of the display panel showing a dispersion system corresponding to one pixel. A dispersion system 61 serving as a pixel includes a partition wall 66 between an element substrate 63 provided with a pixel electrode 62 and the like and a counter substrate 65 provided with a common electrode 64 and the like.
And a liquid (dispersion medium) 68 in which electrophoretic particles 67 are dispersed is filled in a space 69 formed by both electrodes 62 and 64 and partition walls 66. As the common electrode 64 and the counter substrate 65, a material having transparency is used. Here, for example, when realizing binary display, the dispersion medium 68 is dyed black, and the electrophoretic particles 67 are white particles such as titanium oxide. The electrophoretic particles 67 are charged so as to have either a positive or negative charge.

In addition to the pixel electrode 62 described above, a thin film transistor (hereinafter referred to as TFT) functioning as a scanning line, a data line, and a switching element is formed on the element substrate 63 (this is not shown in FIG. 8). is doing).

FIG. 9 is an explanatory diagram for explaining an equivalent circuit corresponding to one pixel. That is, the scanning lines 71 and the data lines 72 are provided on the element substrate 63 of the display panel along directions orthogonal to each other, and the TFTs 73 are provided corresponding to the intersections thereof. The TFT 73 has a gate electrode connected to the scanning line 71, a source electrode connected to the data line 72, and a drain electrode connected to one pixel electrode 62 sandwiching the dispersion system 61. A common voltage Vcom (generally a ground voltage) is applied to the other common electrode 64 sandwiching the dispersion system 61.

In such a configuration, the scanning line 71 is activated by a scanning line signal supplied from a scanning line driving circuit (not shown), and during this active period (selection period), T
The FT 73 is turned on. A voltage is applied to the pixel electrode 62 by supplying a data signal from a data line driving circuit (not shown) via the data line 72 and the turned on TFT 73.

When a potential difference is applied between the pixel electrode 62 and the common electrode 64, the electrophoretic particles 67 are attracted to either the pixel electrode 62 or the common electrode 64 by Coulomb force. At this time, when the electrophoretic particles 67 are drawn toward the transparent common electrode 64, the light incident from the common electrode 64 is reflected by the electrophoretic particles 67, and the color (white) of the electrophoretic particles 67 can be seen. . On the other hand, when the electrophoretic particles 67 are attracted to the pixel electrode 62 side, the incident light and the reflected light described above are absorbed by the dispersion medium 68, and the color (black) stained by the dispersion medium 68 can be seen. That is, the electrophoretic display device forms images by individually controlling the movement positions of the electrophoretic particles 67 of the dispersion system 61 for each of the dispersion systems 61 arranged in a matrix on the display panel.

JP 2002-116734 A

However, in Patent Document 1, for example, when the TFT 73 is a Pch TFT, the scanning line 71
To the gate electrode of the TFT 73 is a voltage for turning on the TFT 73 (0V
) And the voltage for turning off the TFT 73 (power supply voltage), the voltage between the pixel electrode 62 and the common electrode 64 sandwiching the dispersion system 61 is sufficiently obtained by subtracting the threshold voltage of the TFT 73 from the power supply voltage. Can not get the correct voltage. Therefore, by measuring the threshold voltage of the TFT 73 and subtracting the threshold voltage from the voltage to be turned off and applying it to the gate terminal, the power supply voltage can be made between the pixel electrode 62 and the common electrode 64. When the threshold voltage of the TFT 73 fluctuates due to external factors or changes over time due to the passage of energization time, an overvoltage is applied to the gate terminal when the threshold voltage is reduced, causing gate breakdown of the TFT 73, or a voltage shortage when the threshold voltage is increased. There is a problem that an accurate image cannot be formed.

The present invention has been made in view of such circumstances, and an electro-optical device that can be turned on / off even when the threshold voltage of the switching element fluctuates with the passage of energization time, a driving method of the electro-optical device, and an electronic apparatus Is intended to provide.

In order to solve the above problems, the electro-optical device driving method of the present invention includes a dispersion system in which electrophoretic particles that migrate by an electric field applied through a common electrode and a plurality of pixel electrodes are dispersed in a dispersion medium. In addition, the electro-optical device includes a storage unit and a time measuring unit that obtains an elapsed time for energization of the electro-optical device, and the electro-optical device corresponds to the elapsed time for energization of the electro-optical device. , A result of previously measuring a threshold voltage of a switching element connected to each of the plurality of pixel electrodes is stored in the storage unit, and a voltage applied to a gate terminal of the switching element to turn on the switching element Is applied until a first time point at which the voltage value of the pixel electrode is saturated, and after the first time point, a current energization elapsed time is obtained from the timing unit, and the energization progress is obtained. A threshold voltage of the switching element with respect to the gap is obtained from the storage unit, and one or more kinds of voltages lower than the first voltage and higher than a voltage obtained by subtracting the threshold voltage from the first voltage are applied to the gate terminal. The gist is to apply.

According to this configuration, even when the threshold voltage of the switching element fluctuates with the passage of energization time, the gate of the switching element can be prevented and the power supply voltage can be set between the pixel electrode and the common electrode, thereby forming an accurate image. be able to.

In the driving method of the electro-optical device according to the aspect of the invention, the one or more types of voltages are voltages obtained by subtracting the threshold voltage from the first voltage.

According to this configuration, even when the threshold voltage of the switching element fluctuates with the passage of energization time, the gate of the switching element can be prevented and the power supply voltage can be set between the pixel electrode and the common electrode, thereby forming an accurate image. be able to.

In the driving method of the electro-optical device according to the aspect of the invention, the one or more types of voltages may be a predetermined voltage that is lower than the first voltage and higher than a voltage obtained by subtracting the threshold voltage from the first voltage. And a third voltage that is a voltage obtained by subtracting the threshold voltage from the first voltage. After applying the second voltage to the gate terminal, the third voltage is Applied to the gate terminal.

According to this configuration, even when the threshold voltage of the switching element fluctuates with the passage of energization time, the gate of the switching element can be prevented and the power supply voltage can be set between the pixel electrode and the common electrode, thereby forming an accurate image. be able to.

In the electro-optical device according to the aspect of the invention, the one or more types of voltages include the first voltage and a plurality of voltages obtained by linearly interpolating a voltage obtained by subtracting the threshold voltage from the first voltage. Are sequentially applied to the gate terminals.

According to this configuration, even when the threshold voltage of the switching element fluctuates with the passage of energization time, the gate of the switching element can be prevented and the power supply voltage can be set between the pixel electrode and the common electrode, thereby forming an accurate image. be able to.

  The electro-optical device of the present invention is driven by the above-described driving method of the electro-optical device.

According to this configuration, even when the threshold voltage of the switching element fluctuates with the passage of energization time, the gate of the switching element can be prevented and the power supply voltage can be set between the pixel electrode and the common electrode, thereby forming an accurate image. be able to.

In the electro-optical device according to the aspect of the invention, the electro-optical device includes a scanning line driving circuit that applies a voltage to the gate terminal, and the voltage output unit of the scanning line driving circuit includes a transfer gate. .

According to this configuration, even when the threshold voltage of the switching element fluctuates with the passage of energization time, the gate of the switching element can be prevented and the power supply voltage can be set between the pixel electrode and the common electrode, thereby forming an accurate image. be able to.

Next, an electronic apparatus according to the present invention includes the above-described electro-optical device, and corresponds to, for example, a personal computer, a mobile phone, and a portable information terminal.

The electro-optical device according to the present invention is a method for driving an electro-optical device including electrophoretic particles dispersed in a dispersion medium that migrates by applying a voltage through the first electrode and the second electrode. And after electrically connecting the data line and the first electrode through the switching transistor by applying a first voltage to the gate terminal of the switching transistor connected to the first electrode, By applying a second voltage having a voltage level different from the first voltage to the gate terminal of the switching transistor, the data line and the first electrode are electrically connected through the switching transistor. This is the gist.

According to this configuration, even when the threshold voltage of the switching element fluctuates with the passage of energization time, the gate of the switching element can be prevented and the power supply voltage can be set between the pixel electrode and the common electrode, thereby forming an accurate image. be able to.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.
(First embodiment)

<Configuration of electro-optical device>
First, a configuration of an electrophoretic display device that is an electro-optical device according to the first embodiment will be described with reference to FIG.
Will be described with reference to FIG.

FIG. 1 is a block diagram showing the configuration of the electrophoretic display device according to the first embodiment of the present invention. As shown in FIG. 1, the electrophoretic display device 1 includes a display area A1 and a peripheral area A2 shown in FIG.
In the display area A1, the dispersion system 61 shown in FIGS. 8 and 9 is arranged in m rows and n columns (m and n are arbitrary natural numbers).

The peripheral area A2 (see FIG. 7) includes a data line driving circuit 100 and a scanning line driving circuit 200.
A control circuit 300, a storage unit 310, a timer unit 320, and a common voltage output circuit 400 are arranged.

The data line driving circuit 100 supplies data signals X1 to Xn to the source terminal of the TFT 73 via the n data lines 72. The scanning line driving circuit 200 passes through the m scanning lines 71, and T
Scan signals Y1 to Ym are supplied to the gate terminal of FT73.

The control circuit 300 includes a control signal from an external device (not shown), a storage unit 310 and a timer unit 3.
Based on the information from 20, the voltage supplied to the scanning signals Y1 to Ym is determined, and the data line driving circuit 100, the scanning line driving circuit 200, and the common voltage output circuit 400 are controlled.

The storage unit 310 is an EEPROM (Electronically Erasable and Programmable Read On
ly Memory) and the like, and stores information from an external device (not shown). The timer unit 320 counts the elapsed time from the time when the electrophoretic display device 1 is turned on. The common voltage output circuit 400 supplies a common voltage Vcom to the common electrode 64 of all the distributed systems 61.
Supply.

<Operation configuration of TFT controlling dispersion system>
Next, the operation of the TFT for controlling the dispersion system will be described with reference to FIG. FIG. 2 is a timing chart for explaining the operation of the TFT 73 that controls the dispersion system 61. In the present embodiment, it is assumed that the conductivity type of the TFT 73 is a p-channel type and is composed of an organic TFT.

FIG. 2A is a timing chart for explaining an operation (data writing) for attracting the electrophoretic particles 67 of each dispersion system 61 to the common electrode 64 side, and FIG.
It is a timing diagram explaining the operation | movement (data clear) drawn near.

At the time of data writing, the common voltage Vcom is set to the ground potential (0 V) as shown in FIG.
, The data signal Xi (1 ≦ i ≦ n) is supplied from the power supply potential (VDD, for example, 40 V), and the scanning signal Yj (
1 ≦ j ≦ m) is set to the ground potential (0 V) which is the first voltage. In this state, VDD is applied to the source terminal of the TFT 73 and 0 V is applied to the gate terminal.
Is turned on, and the drain terminal of the TFT 73 has a period t (first time during which the dispersion system 61 is charged.
After that, it becomes VDD.

On the other hand, at the time of data clear, as shown in FIG. 2B, the common voltage Vcom is set to VDD, the data signal Xi is set to 0V, and the scanning signal Yj is set to 0V. TFT in this state
Since 0V is applied to the source terminal of 73 and 0V to the gate terminal, the TFT 73 is turned on. However, the drain terminal of the TFT 73 does not change to 0V even after the period t during which the dispersion system 61 is charged. The threshold voltage Vth remains. For this reason, since the potential difference between the pixel electrode 62 and the common electrode 64 of the dispersion system 61 is VDD−Vth, the operation of attracting the electrophoretic particles 67 toward the pixel electrode 62 becomes slow or not sufficiently attracted. It was.

In order to solve this problem, a potential of −Vth may be applied to the gate terminal of the TFT 73. For example, a so-called organic TFT in which a semiconductor layer is formed of an organic material or an amorphous structure in which a semiconductor layer is formed of amorphous silicon. Since a so-called threshold voltage shift in which a threshold voltage changes with an increase in energization time is remarkable in a silicon TFT, it is difficult to set a voltage to be applied to the gate terminal as -Vth. For example, if −Vth is uniformly applied to the gate terminal, the gate breakdown may occur if the threshold voltage becomes lower than the initial Vth.

FIG. 3A is a graph illustrating the transition of the threshold voltage with respect to the energization elapsed time of the TFT 73. Note that the values in the graph of FIG. 3A are prepared for simplifying the explanation, and are not based on actual values.

As shown in FIG. 3A, the threshold voltage of the TFT 73, which was 5 V when measured before energization, linearly decreases from 4 hours to 4 V after 5 hours. Organic TF
The reason why the threshold voltage of T changes as the energization time elapses is that electron donation / electron acceptance is caused by adsorption of water molecules, ions, etc. on the semiconductor interface (underlayer to semiconductor interface, or gate insulating layer to semiconductor interface). It is possible that sex is manifested.

In this embodiment, the threshold voltage value for the energization elapsed time of the TFT 73 is measured in advance, and a table in which the threshold voltage for the energization elapsed time is stored in the storage unit 310 as shown in FIG. Thus, the control circuit 300 is configured to set the voltage to be applied to the gate terminal of the TFT 73 based on the current threshold voltage value.

FIG. 4 is a flowchart for explaining the operation of the control circuit 300. The control circuit 300 performs processing when the data in the distributed system 61 is cleared.

First, in step S <b> 100, the control circuit 300 acquires the current elapsed time from the time measuring unit 320.

Next, in step S102, the threshold voltage value Vth of the TFT 73 with respect to the elapsed time is acquired with reference to a table storing the threshold voltage with respect to the elapsed time of energization in the storage unit 310.

Next, in step S104, the TFT is detected by the scanning signal Yj from the scanning line driving circuit 200.
A voltage of −Vth is applied to the gate terminal 73 after 0V is applied for a period t.

FIG. 5A shows the voltage applied to the gate terminal of the TFT 73 and the TFT in the first embodiment.
FIG. 73 is a timing diagram showing changes in voltage at 73 drain terminals. As shown in FIG.
When 0V is applied to the gate terminal of the TFT 73 for a period t, the potential of the drain terminal of the TFT 73 shifts from VDD to Vth. After that, since the potential of −Vth is applied to the gate terminal of the TFT 73, the potential of the drain terminal of the TFT 73 shifts from Vth to 0V.

FIG. 6 is a circuit diagram illustrating the configuration of the scanning line driving circuit 200. Scanning line driving circuit 200
Is for the shift register 210 and each scanning line 71 that outputs the scanning signals Y1-Ym.
A level shifter 220, an inverter 230, and a transfer gate 240 are included.

  According to the embodiment described above, the following effects can be obtained.

In the present embodiment, since the potential difference between the pixel electrode and the common electrode can be set to a predetermined value that does not depend on the threshold voltage of the changing TFT 73, an accurate image can be displayed. If the predetermined value is appropriately set, the gate breakdown of the TFT 73 can be prevented even if the threshold voltage of the TFT 73 serving as a switching element varies with the passage of energization time.

(Second Embodiment)
Next, application of an electronic apparatus equipped with the electrophoretic display device 1 described in the first embodiment will be described with reference to FIG. FIG. 10 is a perspective view showing a configuration of a mobile personal computer. In the figure, a personal computer 2000 includes a keyboard 2002.
And a display unit 2001 using the electrophoretic display device 1. Even in this case, the display unit 2001 using the electrophoretic display device 1 is the first unit.
The same effect as the embodiment is exhibited. As a result, the personal computer 2000 can realize a high-quality image.

As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, In the range which does not deviate from the meaning of this invention, it can be implemented with various forms. Hereinafter, a modification will be described.

(Modification 1) A first modification of the electro-optical device according to the invention will be described. In the first embodiment, as shown in FIG. 5A, the voltage applied to the gate terminal of the TFT 73 after the period t is a potential of −Vth. However, as shown in FIG. A potential between 0 V and −Vth (for example, −½ × Vth) may be applied before applying the potential of −Vth. Moreover, you may apply in multiple steps not only in two steps.

(Modification 2) A second modification of the electro-optical device according to the invention will be described. In the first embodiment, as shown in FIG. 5A, the voltage applied to the gate terminal of the TFT 73 after the period t is a potential of −Vth. However, as shown in FIG. Linear interpolation may be performed between 0V and -Vth, and the voltage may be sequentially changed from 0V to -Vth.

(Modification 3) A third modification of the electro-optical device according to the invention will be described. In the first embodiment, as shown in FIG. 1, the case where the electrophoretic display device 1 includes the storage unit 310 and the time measuring unit 320 has been described. However, the electrophoretic display device 1 includes the storage unit 310 and the time measuring unit 320. The storage unit 310 and the time measuring unit 320 may be included in an external device that controls the electrophoretic display device 1 without including the storage unit 310.

1 is a block diagram illustrating a configuration of an electrophoretic display device. (A) is a timing chart explaining the movement of each signal at the time of data writing, (B) is a timing chart explaining the movement of each signal at the time of data clear. FIG. 5A is a graph for explaining a change in threshold voltage with respect to the elapsed time of energization of a TFT, and FIG. The flowchart figure explaining operation | movement of a control circuit. (A) is a timing chart showing changes in the voltage applied to the gate terminal of the TFT and the voltage at the drain terminal of the TFT in the first embodiment, and (B) is a voltage applied to the gate terminal of the TFT in Modification 1 and the TFT. FIG. 9C is a timing diagram showing changes in the voltage at the drain terminal, and FIG. 6C is a timing diagram showing changes in the voltage applied to the gate terminal of the TFT and the voltage at the drain terminal of the TFT in Modification 2. FIG. 10 is a circuit diagram illustrating a structure of a scan line driver circuit. The disassembled perspective view which shows the mechanical structure of an electrophoretic display apparatus. The principal part sectional drawing of the display panel which shows the dispersion system corresponding to 1 pixel. Explanatory drawing explaining the equivalent circuit corresponding to 1 pixel. FIG. 6 is an overview perspective view illustrating a configuration of a personal computer according to a second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrophoretic display apparatus, 61 ... Dispersion system, 62 ... Pixel electrode, 63 ... Element substrate, 64 ... Common electrode, 65 ... Opposite substrate, 66 ... Partition, 67 ... Electrophoretic particle, 68 ... Dispersion medium, 69 ... Space ,
71 ... Scanning line, 72 ... Data line, 73 ... TFT, 100 ... Data line driving circuit, 200 ... Scanning line driving circuit, 210 ... Shift register, 220 ... Level shifter, 230 ... Inverter,
240 ... transfer gate, 300 ... control circuit, 310 ... storage unit, 320 ... timer,
400: Common voltage output circuit.

Claims (8)

A driving method of an electro-optical device including a dispersion system in which electrophoretic particles that migrate by an electric field applied through a common electrode and a plurality of pixel electrodes are dispersed in a dispersion medium,
The electro-optical device includes a storage unit, and a time measuring unit that calculates an elapsed time of energization to the electro-optical device,
The result of measuring in advance the threshold voltage of the switching element connected to each of the plurality of pixel electrodes with respect to the energization elapsed time to the electro-optical device is stored in the storage unit,
Applying a first voltage, which is a voltage applied to a gate terminal of the switching element to turn on the switching element, until a first time point when a voltage value of the pixel electrode is saturated;
After the first time point, a current energization elapsed time is obtained from the timing unit, a threshold voltage of the switching element with respect to the energization elapsed time is obtained from the storage unit, and is lower than the first voltage and the first Applying one or more types of voltages in a range equal to or higher than a voltage obtained by subtracting the threshold voltage from a voltage to the gate terminal;
A driving method for an electro-optical device.   2. The electro-optical device driving method according to claim 1, wherein the one or more types of voltages are voltages obtained by subtracting the threshold voltage from the first voltage. 3. The method of driving an electro-optical device according to claim 1, wherein the one or more types of voltages are lower than the first voltage and higher than a voltage obtained by subtracting the threshold voltage from the first voltage. And a third voltage that is a voltage obtained by subtracting the threshold voltage from the first voltage, and after applying the second voltage to the gate terminal, the third voltage Is applied to the gate terminal, and the electro-optical device is driven.   4. The electro-optical device driving method according to claim 1, wherein the one or more types of voltages are linearly obtained by subtracting the threshold voltage from the first voltage and the first voltage. 5. An electro-optical device driving method comprising: a plurality of interpolated voltages, wherein the plurality of voltages are sequentially applied to the gate terminal.   An electro-optical device that is driven by the driving method of the electro-optical device according to claim 1.   6. The electro-optical device according to claim 5, wherein the electro-optical device includes a scanning line driving circuit that applies a voltage to the gate terminal, and a voltage output unit of the scanning line driving circuit is configured by a transfer gate. An electro-optical device.   An electronic apparatus comprising the electro-optical device according to claim 5. A method for driving an electro-optical device including electrophoretic particles dispersed in a dispersion medium, which migrates by applying a voltage through a first electrode and a second electrode,
After electrically connecting the data line and the first electrode through the switching transistor by applying a first voltage to the gate terminal of the switching transistor connected to the first electrode, the switching transistor By applying a second voltage having a voltage level lower than the first voltage and in a range equal to or higher than a voltage obtained by subtracting the threshold voltage from the first voltage to the gate terminal of the gate terminal via the switching transistor. Electrically connecting the data line and the first electrode;
A method for driving an electro-optical device.

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