Patent Application
20080143426
This application claims all benefits accruing under 35 U.S.C. §119 from Taiwan Patent Application No. 95147248, filed on 2006/12/15 in the Taiwan Intellectual Property Office, the disclosure of which is incorporated herein by reference.
The present invention relates to methods for reducing leakage current of thin film transistors (TFTs) of a TFT array substrate of a liquid crystal display (LCD), and particularly to a method for reducing leakage current of TFTs by applying static bias voltages to the TFTs.
A typical liquid crystal display (LCD) is capable of displaying a clear and sharp image through thousands or even millions of pixels that make up the complete image. The LCD has thus been applied to various electronic equipment in which messages or pictures need to be displayed, such as mobile phones and notebook computers. A liquid crystal panel is a major component of the LCD, and generally includes a thin film transistor (TFT) array substrate, a color filter substrate parallel to the TFT array substrate, and a liquid crystal layer sandwiched between the two substrates. The TFT array substrate includes a plurality of TFTs, which function as switching elements.
Referring to
When the TFT 150 works, a negative voltage is applied between the gate electrode 153 and the source portion 154. A strong electric field is generated in the insulating layer 152, and the electric field repulses electrons and attracts holes in the channel portion 156 adjacent to the insulating layer 152. Thereby, a conductive channel is generated in the channel portion 156. Thus, the source portion 154 and the drain portion 155 are connected via the conductive channel, so that the TFT 150 is turned on. On the contrary, when a positive voltage is applied between the gate electrode 153 and the source portion 154, the TFT 150 is turned off.
During a process of manufacturing the TFTs 150, some defects may be generated. The defects are particularly liable to occur at or near the junction between the drain portion 155 and the channel portion 156 of a TFT 150, and at or near the junction between the source portion 154 and the channel portion 156 of a TFT 150. Such defects include disordered atoms and broken bonds. Thus, when the TFT 150 is turned off, a leakage current is liable to occur. As a result, the TFT array substrate 100 has impaired performance.
What is needed, therefore, is a method for reducing leakage current of TFTs of a TFT array substrate that can overcome the above-described problems.
In one preferred embodiment, a method for reducing leakage current of TFTs of a TFT array substrate includes: providing a TFT array substrate, the TFT array substrate including a plurality of gate lines, a plurality of data lines, and a plurality of TFTs, each TFT including a gate electrode, a source electrode and a drain electrode, the gate electrodes being connecting to the gate lines, the source electrodes being connecting to the data lines; providing a same direct current voltage to the source electrodes and the drain electrodes; and providing another direct current voltage to the gate electrodes to turn off the TFTs, and continuing to provide said same direct current voltage to the source electrodes for a predetermined time.
Other novel features and advantages will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
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In step S24, the first power supply source 300 provides a first direct current voltage such as −20 volts to the gate electrodes 251 of the TFTs 250 via the gate lines 220 so as to turn on the plurality of TFTs 250. At the same time, the second power supply source 400 provides a second direct current voltage such as 10 volts to the source electrodes 252 of the TFTs 250 via the data lines 230. Because the TFTs 250 are turned on, the 10 volt direct current voltage is also applied to the drain electrodes 253 of the TFTs 250.
In step S25, the first power supply source 300 provides a third direct current voltage to the gate electrodes 251 of the TFTs 250 via the gate lines 220 so as to turn off the TFTs 250. The third direct current voltage can be 20 volts. When the TFTs 250 are turned off, the second power supply source 400 continues to output the 10 volt direct current voltage to the source electrodes 252 of the TFTs 250 for at least 120 seconds. In one example, such output is for 3600 seconds. This process is defined as a static bias voltage process. In this static bias voltage process time interval, no current flows occur between the source electrodes 252 and the drain electrodes 253 because the source electrodes 252 and the drain electrodes 253 have the same potential.
In step S26, the first power supply source 300 and the second power supply source 400 are disconnected from the TFT array substrate 200.
Because a static bias voltage process is conducted on the TFT array substrate 200, a static electric field is generated in the channel portion of each TFT 250. In particular, a constant (static) junction electric field is generated at the junction between the channel portion and the source electrode 252, and between the channel portion and the drain electrode 253. Some defects are transferred away from these junctions, and other defects are rectified (e.g. broken bonds are repaired). That is, the defects are reduced by the static junction electric field. This results in a low leakage current at these junctions during use of the TFT array substrate 200 thereafter. Therefore, the performance of the TFT array substrate 200 is improved.
Referring to
Further and/or alternative embodiments may include the following. In step S25 of the first embodiment, the third direct current voltage applied to the gate electrodes 251 by the first power supply source 300 can be 0 volts. Furthermore, if the TFTs 250 are N-type LTPS TFTs, all the voltages applied to the TFTs 250 are the reverse polarity of the above-described voltages.
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 95147248 | Dec 2006 | TW | national |
