KR100846588B1 - Apparatus for driving electrophoretic display comprising organic thin film transistor - Google Patents

Abstract

The present invention discloses an electrophoretic display device comprising an organic thin film transistor (OTFT). The disclosed electrophoretic display device includes an electrophoretic light emitting device that emits light in response to an applied data signal, an organic thin film transistor that switches a data signal to the electrophoretic light emitting device, and a data signal of the organic thin film transistor. A capacitor for storing a voltage, and a leakage current blocking unit connected to the organic thin film transistor, the capacitor, and the electrophoretic light emitting device, and configured to block a current leaking from the capacitor when the organic thin film transistor is turned off.

Description

Electrophoretic display comprising an organic thin film transistor {Apparatus for driving electrophoretic display comprising organic thin film transistor}

1 is a circuit diagram illustrating a unit pixel of a conventional electrophoretic display.

2a to 2c are views for explaining the principle of the electrophoretic light emitting device of FIG.

3 is a circuit diagram illustrating an electrophoretic display unit pixel including an organic thin film transistor according to an exemplary embodiment of the present invention.

4 is a circuit diagram illustrating an electrophoretic display device including an organic thin film transistor according to an exemplary embodiment of the present invention.

** Brief description of symbols for the main parts of the drawing **

50: driver 60: scan driver

70: data driver 100: pixel portion

150: module pixel

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophoretic display, and more particularly, to an apparatus for driving an electrophoretic display having an organic thin film transistor (OTFT).

FIG. 1 is a circuit diagram illustrating a unit pixel of a conventional electrophoretic display (EPD) driving device as a flexible display device.

The unit pixel of the electrophoretic display shown in FIG. 1 is selected by the nth scan signal applied through the scan line Scan [n] and transmits a data signal applied through the data line Data [m]. And an organic thin film transistor M, a storage capacitor Cst, and an electrophoretic light emitting device Ceq.

One organic thin film transistor M is provided as a switching element. The organic thin film transistor M includes an organic semiconductor layer made of an organic material on a plastic substrate. The organic semiconductor layer may be formed on a plastic substrate because it is processed under a low temperature process. Therefore, it can be used as a switching element in manufacturing a flexible display device. However, such an organic thin film transistor does not effectively perform a switching element function due to the characteristics of the organic semiconductor. The organic thin film transistor M does not block the flow of current well even when turned off, so that a leakage current is generated from the storage capacitor Cst to the organic thin film transistor M. FIG. Therefore, the storage capacitor Cst does not occupy the charge corresponding to the data signal and thus cannot apply the data signal to the electrophoretic light emitting device Ceq. This causes a fatal problem in which a desired picture cannot be realized in a flexible display.

On the other hand, the electrophoretic light emitting device is a display device that emits reflected light according to the position of the charged particles in the fluid.

Hereinafter, the principle of the electrophoretic light emitting device will be described with reference to FIGS. 2A to 2C. 2A, in the electrophoretic light emitting device Ceq, an upper electrode 3 and a lower electrode 4 are formed between the front substrate 1 and the rear substrate 2. The dispersion medium 5 filled between the upper and lower electrodes 3 and 4 and the charged particles 6 dispersed in the dispersion medium 5 are disposed.

When the charged particles 6 have a white color, when a predetermined electric field V1 is applied to the electrophoretic light emitting device Ceq, as shown in FIG. 2B, the charged particles 6 are formed on the front substrate 1. The white light reflected by the charged particles 6 may be emitted by moving in the () direction. The white light can be sensed by the viewer through the front substrate 1.

2C illustrates a case in which a reverse electric field V2 is applied to the electrophoretic light emitting device Ceq, and the charged particles 6 move to the rear substrate 2. Therefore, the observer cannot observe the white light reflected by the charged particle 6 through the front substrate 1.

Since the electrophoretic light emitting device Ceq must move the charged particles 6 in the dispersion medium 5 in order to emit reflected light, a data signal capable of moving the charged particles 6 should be appropriately applied. However, as described above, when the data signal to be maintained by the storage capacitor Cst leaks through the organic thin film transistor M, an appropriate data signal cannot be applied to the electrophoretic light emitting device Ceq. Therefore, the charged particles 6 remain in a dispersed state in the dispersion medium 5 without being completely aggregated into the front substrate 1 or the back substrate 2, and thus cannot emit light of a desired degree. Therefore, various attempts have been made to develop a flexible display having no problem in realizing an image by applying a desired data signal to the electrophoretic light emitting device Ceq.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophoretic display device capable of realizing an image corresponding to a predetermined data signal by preventing leakage current from a storage capacitor to a switch element in developing a flexible display.

The present invention provides an electrophoretic light emitting device that emits light in response to an applied data signal; An organic thin film transistor for switching a data signal to the electrophoretic light emitting device; A capacitor configured to store a voltage corresponding to a data signal of the organic thin film transistor; And a leakage current blocking unit connected to the organic thin film transistor, the capacitor, and the electrophoretic light emitting device, and configured to block a current leaking from the capacitor when the organic thin film transistor is turned off.

An electrophoretic display of the present invention includes a plurality of unit pixels arranged in an n × m matrix, and a driver for controlling the plurality of unit pixels, wherein the unit pixels emit light in response to an applied data signal. Electrophoretic light emitting device; An organic thin film transistor selected according to an n th scan signal and switching an m th data signal to the electrophoretic light emitting device; A capacitor configured to store a voltage corresponding to an m th data signal of the organic thin film transistor; And blocking current flowing from the storage capacitor to the organic thin film transistor when the organic thin film transistor is turned off because the scan signal is not applied to the organic thin film transistor, the capacitor, and the electrophoretic light emitting device. Provide leakage current interruption.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a circuit diagram illustrating a unit pixel of an electrophoretic display device according to an exemplary embodiment of the present invention. In the present embodiment, an electrophoretic display including an organic thin film transistor and at least one diode as a leakage current blocking unit is illustrated. However, the present invention is not limited thereto, and the electrophoretic display device of the present invention may arrange two or more diodes in series according to the characteristics of the electrophoretic display device such as the degree of integration and the aperture ratio.

Referring to FIG. 3, an n−1 th scan line Scan [n−1] and an n th scan line Scan [n] are disposed adjacent to and parallel to each other, and the m th data line crosses the scan lines. (Data [m]) is disposed. The unit pixels of the electrophoretic display are defined by the scan lines and the data lines.

The unit pixel includes an organic thin film transistor M1 as a switching element and a diode D1 as a leakage current blocking element. The first organic thin film transistor M1 and the diode D1 are connected in series. The organic thin film transistor M1 selected by the nth scan line serves as a switching element for transmitting a data signal, and the diode D1 stores the data signal switched and transmitted by the organic thin film transistor M1. To pass). In addition, when the organic thin film transistor M1 is turned off, the diode D1 serves as a leakage current blocking unit to prevent leakage of charges accumulated in the storage capacitor Cst.

In addition, the unit pixel includes a storage capacitor Cst that maintains a data signal transmitted through the diode D1 for a predetermined time when the organic thin film transistor M1 is selected.

In addition, the unit pixel includes an electrophoretic light emitting device Ceq that emits reflected light corresponding to the data signal. In the electrophoretic light emitting device Ceq, charged particles are dispersed in a dispersion medium between upper and lower electrodes and upper and lower electrodes. The charged particles have a white color, for example, so that the viewer can see the light reflected by the charged particles through the front substrate according to the position of the charged particles in the dispersion medium. Alternatively, the electrophoretic light emitting device Ceq may include a plurality of charged particles having a plurality of colors, for example, first charged particles having a white color and second charged particles having a black color and charged with a different charge from the first charged particles. When a predetermined electric field is applied and the first charged particles are agglomerated in the front substrate direction, the viewer can see the reflected light of white color, and a black screen is displayed when the reverse electric field is applied and the second charged particles are agglomerated in the front substrate direction. It may be a device that an observer can identify.

The connection relationship and driving method of the electrophoretic display device as described above will be described in detail below. Hereinafter, each signal is exemplified to be applied at a voltage level.

When a first level, for example, a high level voltage is applied to the main electrode of the organic thin film transistor M1 along the nth scan line Scan [n], the organic thin film transistor M1 is turned on. do. The diode D1 is also turned on by applying the voltage of the first level along the nth scan line Scan [n]. When the organic thin film transistor M1 is selected, a data voltage is transferred to the first electrode of the organic thin film transistor M1 and is transferred from the second electrode of the organic thin film transistor M1 to the anode electrode of the diode D1. . The data voltage is transferred from the cathode electrode of the diode D1 to one terminal of the storage capacitor Cst.

The storage capacitor Cst accumulates charge by a difference between the data voltage transferred to one terminal and the voltage of the other terminal of the storage capacitor Cst, and maintains the accumulated charge for a predetermined time. After a voltage of a first level, for example, a high level, is applied to the main electrode of the organic thin film transistor M1 for a predetermined time and the data voltage is transferred to the storage capacitor Cst, a second level, for example, a low voltage is applied. Since the organic thin film transistor M1 is turned off by being applied to the main electrode, the storage capacitor Cst must maintain the data voltage while the electrophoretic light emitting device Ceq is operating. In this case, the storage capacitor Cst should maintain the charged charge well, but leakage current may be generated from the electrophoretic light emitting device Ceq to the switching device. However, in the present invention, the diode D1 may be included as the leakage current blocking device between the storage capacitor Cst and the switching device to prevent the leakage current from being continuously generated.

One terminal of the electrophoretic light emitting device Ceq is connected to the cathode electrode of the diode D1 and one terminal of the storage capacitor Cst. The organic thin film transistor M1 is turned off after transferring the data voltage, but since the data voltage is applied to and maintained at one terminal of the storage capacitor Cst, the electrophoretic light emitting device connected to one terminal of the storage capacitor Cst. The data voltage is applied to one terminal of (Ceq). Accordingly, the electrophoretic light emitting device Ceq moves charged particles by a difference between the data voltage applied to the one terminal and the voltage across the other terminal of the electrophoretic light emitting device Ceq to emit the corresponding reflected light.

4 is a circuit diagram illustrating an electrophoretic display device according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the electrophoretic display device according to the present invention includes a processor 50, a scan driver 60, a data driver 70, and a pixel unit 100.

The processor 50 processes a scan signal and a data signal input from an external power source and transmits the scan signal and the data signal to the scan driver 60 and the data driver 70, respectively.

The data signal input from the processor 50 is applied to the corresponding data line by the data driver 70, and the scan signal is continuously applied to the scan line by the scan driver 60.

The pixel unit 100 includes a plurality of unit pixels arranged in an n × m matrix, n scan lines arranged in a row direction, and m data lines arranged in a column direction. As shown in FIG. 3, the unit pixel 150 includes an organic thin film transistor as a switching element that is selected by a scan signal applied through a scan line and transmits a data voltage applied through a data line, and includes a scan signal. By the organic thin film transistor is turned off by the diode (D1) as a leakage current blocking element to block the leakage of current from the storage capacitor (Cst) to the switching element. And a storage capacitor Cst and an electrophoretic light emitting device Ceq connected to the diode D1.

Hereinafter, the driving method in which one unit pixel 150 of the plurality of unit pixels emits light will be described. In this embodiment, each of the signals is applied to the voltage level.

When a first level, for example, a high level voltage is applied through the previous scan line Scan [1], the storage capacitor Cst connected to Scan [1] may be discharged and initialized. In this embodiment, the storage capacitor Cst is connected to the scan line to reduce the number of wires. However, the discharge line for applying a separate signal for discharging may be connected to the storage capacitor Cst separately.

A voltage of a second level, for example a low level, is applied to Scan [1], and a voltage of a first level, for example, a high level, is applied to the first organic thin film transistor M1 through a current scan line Scan [2]. When applied to the main electrode, the organic thin film transistor M1 is turned on. While the organic thin film transistor M1 is turned on and selected, a data voltage is transferred to one terminal of the organic thin film transistor M1 through the data line Data [1]. The data voltage is provided to one terminal of the storage capacitor Cst through the diode D1 connected in series with the organic thin film transistor M1. The other terminal of the storage capacitor Cst is connected to a previous scan line Scan [1], and a first level, for example, a high level, is applied through the previous scan line Scan [1], and one terminal of the storage capacitor Cst is provided. In the current scan line Scan [2], when a second level, for example, a low level voltage is applied, a voltage difference opposite to a voltage difference between one terminal of the charged storage capacitor Cst and the other terminal may be discharged. have.

A second level, for example, a low level voltage, is applied to the main electrode of the organic thin film transistor M1 through the current scan line Scan [2] so that the organic thin film transistor is turned off and one of the storage capacitors Cst is turned on. The terminal is loaded with the data voltage already delivered. Therefore, the storage capacitor Cst occupies and maintains a charge by a difference between the data voltage transferred to one terminal of the storage capacitor Cst and the voltage applied to the other terminal.

One terminal of the storage capacitor Cst to which the data voltage is transmitted is connected to one terminal of the electrophoretic light emitting device Ceq. Therefore, the data voltage maintained by the storage capacitor Cst is transferred to the electrophoretic light emitting device Ceq, and the electrophoretic light emitting device Ceq is connected between the data voltage and the voltage applied to the other terminal of the electrophoretic light emitting device Ceq. As long as the difference, the reflected light can be emitted. The other terminal of the electrophoretic light emitting device Ceq may be connected in common to the other terminals of the electrophoretic light emitting device Ceq of another unit pixel, or may be commonly grounded to apply the same signal. In addition, the number of wirings can be reduced compared to the case of wiring for applying a predetermined voltage to the other terminals of the electrophoretic light emitting devices of each of the plurality of unit pixels.

The electrophoretic display of the present invention includes an organic thin film transistor as a switching element, and includes one or more organic thin film transistors as a leakage current blocking element between the switching element and the storage capacitor to prevent leakage current from the storage capacitor to the switching element. You can prevent it. Therefore, the storage capacitor can effectively maintain the data signal initially input to implement an image corresponding to the data signal in a flexible display using an organic thin film transistor and an electrophoretic light emitting device.

Although the present invention has been described with reference to the embodiments shown in the drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (8)

An electrophoretic light emitting device which emits light in response to an applied data signal; An organic thin film transistor for switching a data signal to the electrophoretic light emitting device; A capacitor configured to store a voltage corresponding to a data signal of the organic thin film transistor; And A leakage current blocking unit connected to the organic thin film transistor, the capacitor and the electrophoretic light emitting device, and configured to block a current leaking from the capacitor when the organic thin film transistor is turned off; The first electrode of the organic thin film transistor is connected to a data line applying the data signal, One electrode of the leakage current blocking unit is connected to a second electrode of the organic thin film transistor, And the other electrode of the leakage current blocking unit is connected to one terminal of the capacitor and one terminal of the electrophoretic light emitting device. The electrophoretic display of claim 1, wherein the leakage current blocking unit comprises at least one diode. The method of claim 2, The first electrode of the organic thin film transistor is connected to a data line applying the data signal, And an anode electrode of the diode is connected to a second electrode of the organic thin film transistor, and a cathode electrode of the diode is connected to one terminal of the capacitor and one terminal of the electrophoretic light emitting device. The method of claim 3, wherein the leakage current blocking unit comprises at least two diodes, The diodes are electrophoretic display device connected in series. a plurality of unit pixels arranged in an n × m matrix, and A driving unit controlling the plurality of unit pixels, The unit pixel, An electrophoretic light emitting device which emits light in response to an applied data signal; An organic thin film transistor selected according to an n th scan signal and switching an m th data signal to the electrophoretic light emitting device; A capacitor configured to store a voltage corresponding to an m th data signal of the organic thin film transistor; And A leakage current connected to the organic thin film transistor, the capacitor and the electrophoretic light emitting device, and blocking a current leaking from the storage capacitor to the organic thin film transistor when the organic thin film transistor is turned off because the scan signal is not applied. A blocking part, The first electrode of the organic thin film transistor is connected to the m-th data line applying the m-th data signal, One electrode of the leakage current blocking unit is connected to a second electrode of the organic thin film transistor, The other electrode of the leakage current blocking unit is connected to one terminal of the capacitor and one terminal of the electrophoretic light emitting device, The other terminal of the capacitor is connected to an n-1th scan line which transmits an nth-1th scan signal that is before the nth scan signal. And the other terminal of the electrophoretic light emitting device is connected in common with the electrophoretic light emitting elements of the plurality of unit pixel units. The electrophoretic display of claim 5, wherein the leakage current blocking unit comprises at least one diode. The method of claim 6, The first electrode of the organic thin film transistor is connected to the m-th data line applying the m-th data signal, An anode electrode of the diode is connected to a second electrode of the organic thin film transistor, The cathode electrode of the diode is connected to one terminal of the capacitor and one terminal of the electrophoretic light emitting device, The other terminal of the capacitor is connected to an n-1th scan line which transmits an nth-1th scan signal that is before the nth scan signal. And the other terminal of the electrophoretic light emitting device is connected in common with the electrophoretic light emitting elements of the plurality of unit pixel units. 8. The electrophoretic display of claim 7, wherein the capacitor is discharged and initialized by the n-th scan signal.

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