TFT switch and method for manufacturing the same

Abstract

A thin-film transistor (TFT) switch includes a gate, a drain, a source, a semiconductor layer, and a fourth electrode. The drain is connected to a first signal. The gate is connected to a control signal to control the switch on or off. The source outputs the first signal when the switch turns on. The fourth electrode and the gate are respectively located at two sides of the semiconductor layer. The fourth electrode is conductive and is selectively coupled to different voltage levels, thereby reducing leakage current in a channel to improve switch characteristic when the switch turns off.

Claims

1. A method for manufacturing a thin-film transistor (TFT) switch, comprising the following steps: forming, in sequence, a gate and a gate insulation layer on a base, wherein the gate is adapted to connect with a control signal for selectively switching the TFT switch on or off; forming a semiconductor layer on the gate insulating layer; forming a drain and a source on the semiconductor layer and covering the semiconductor layer, the drain, and the source with a passivation layer, wherein the drain and the source each comprise, as a part thereof, an n+ layer, which is located between the drain or the source and the semiconductor layer; and wherein the drain is adapted to connect with a first signal so that when the TFT turns on, the source outputs the first signal; and forming a fourth electrode on the passivation layer such that the fourth electrode and the gate are respectively on opposite sides of the semiconductor layer, wherein the fourth electrode is adapted to selectively connect with different voltage levels; wherein when the TFT switch turns on, the gate and the fourth electrode are set at high voltage levels; and wherein the first signal is a test signal and the source is connected to a data line under test.

2. The method as claimed in claim 1, wherein the high voltage level of the fourth electrode is identical to the high voltage level of the gate when the TFT switch turns on.

3. The method as claimed in claim 1, wherein the high voltage level of the fourth electrode is different from the high voltage level of the gate when the TFT switch turns on.

4. The method as claimed in claim 1, wherein when the switch turns off, the gate is connected to a low voltage level and the fourth electrode is first connected to a high voltage level to drain off electrons that are accumulated in the semiconductor layer at a location distant from the gate and then connected to a low voltage level.

5. The method as claimed in claim 4, wherein the low voltage level to which the fourth electrode is connected is identical to the low voltage level to which the gate is connected.

6. The method as claimed in claim 4, wherein the low voltage level to which the fourth electrode is connected is different from the low voltage level to which the gate is connected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a circuit diagram of a conventional switch TFT.

(2) FIG. 2 shows a TFT switch according to a first embodiment of the present invention.

(3) FIG. 3 is a cross-sectional view of the TFT switch according to the first embodiment of the present invention.

(4) FIG. 4 is a cross-sectional view of a TFT switch according to a second embodiment of the present invention.

(5) FIG. 5 is a flowchart of a manufacturing method for the TFT switch shown in FIG. 3.

(6) FIG. 6 is a flowchart of a manufacturing method for the TFT switch shown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) Please refer to FIG. 2. FIG. 2 shows a TFT switch according to a first embodiment of the present invention. As shown in FIG. 2, a TFT switch 20 comprises a gate G, a drain D, a source S, a semiconductor layer 23 among the gate G, the drain D and the source S, and a fourth electrode B. The drain D is connected to a first signal, and the gate G is connected to a control signal to control the switch 20 turning on or turning off. The first signal is outputted from the source S when the switch 20 turns on. The fourth electrode B and the gate G are respectively locate at two sides of the semiconductor layer 23. The fourth electrode B is selectively connected to different voltage levels. The gate G, the drain D, the source S and the fourth electrode B are made of a conductive material.

(8) In the present invention, the TFT switch 20 can be applied to different circuits like a TFT switch coupled to a pixel electrode, a test circuit, or a layout circuit of an active-matrix LCD. Preferably, the TFT switch 20 is for use in the test circuit. At this time, the first signal connected to the drain D is a test signal, and the drain S is connected to the circuit under test, which is data line DL or scanning line GL. The following takes a TFT switch applied to the test circuit as an example.

(9) In the embodiment, the gate G and the fourth electrode B are connected to a high voltage level when the switch 20 turns on. At this time, the voltage level of the fourth electrode B is either the same as or different from that of the gate G. It is noted that the difference between the two voltage levels is in a limited range. When the switch 20 is to turn off, the gate G is connected to low voltage level, and the fourth electrode B is selectively connected to different voltage levels for conducting the leakage current far away from the gate G side in the semiconductor layer 23. And, then, the fourth electrode B is also connected to low voltage level. The voltage level of the fourth electrode B is either the same as or different from that of the gate G. It is noted that the difference between the two voltage levels is in a limited range.

(10) FIG. 3 is a cross-sectional view of the TFT switch according to the first embodiment of the present invention. As illustrated in FIG. 3, the switch 20 is structured to arrange the gate G on a base 21, a gate insulating layer 22 on the gate G, and the semiconductor layer 23 on the gate insulating layer 22. Both of the drain D and the source S are set up on the semiconductor layer 23 and separated by a passivation layer 24. The passivation layer 24 also covers the whole surface. The fourth electrode B is disposed over a gap between the drain D and the source S and extends onto the drain D and the source S. Two higher electron concentration n+ layers 25 are respectively set up between the drain D and the semiconductor layer 23 and between the source S and the semiconductor layer 23. The two n+ layers 25 are each a part of the drain D or the source S and greatly reduce channel resistance when the switch 20 turns on.

(11) In the embodiment, the gate G is located at one side of the semiconductor layer 23 while the drain D and the source S are located at an opposite side of the semiconductor layer 23. The gate G is connected to a low voltage level and the fourth electrode B is connected to a high voltage level to conduct accumulated electrons away from the gate G side in the semiconductor layer 23 for reducing leakage current when the switch 20 turns off. The low voltage level of the fourth electrode B is either the same as or different from that of the gate G. It is noted that the difference between the two voltage levels is in a limited range. The situation that a transition from high to low voltage level applied to the fourth electrode B is similar to a transition from high to low voltage level applied to the gate G when the switch 20 turns off. Therefore, the electrons gathered at a location away from the gate G side in the semiconductor layer 23 are conducted off, similar to the electrons at a location close to the gate G side in the semiconductor layer 23.

(12) FIG. 4 is a cross-sectional view of a TFT switch according to a second embodiment of the present invention. As illustrated in FIG. 4, the switch 30 comprises a gate G on a base 11, a gate insulating layer 32 on the gate G. A drain D and a source S are set up on the gate insulating layer 32 and are separated by a semiconductor layer 33. The semiconductor layer 33 also covers the whole drain D and source S. A fourth electrode B is disposed over a gap between the drain D and the source S and extends onto the drain D and the source S but doe not cover the whole drain D and source S. The rest of the surface is covered by a passivation layer 34 surrounding the fourth electrode B and there is a certain gap between the passivation layer 34 and the fourth electrode B. Two higher electron concentration n+ layers 35 are respectively set up between the drain D and the semiconductor layer 33 and between the source S and the semiconductor layer 33. The two layers 35 are each a part of the drain D or the source S and greatly reduce channel resistance when the switch 30 turns on. The gate G, the drain D, the source S and the fourth electrode B are conductive.

(13) In the embodiment, the gate G, the drain D and the source S are located at the same side of the semiconductor layer 33, and the fourth electrode B and the gate G are respectively located at two sides of the semiconductor layer 33. When the switch 30 turns off, the gate G is connected to a low voltage level and the fourth electrode B is grounded to conduct accumulated electrons away from the gate G side in the semiconductor layer 33 for reducing leakage current. When the fourth electrode B is connected to a low voltage level, electrons are directly conducted away from the side of the semiconductor layer 33 that is distant from the gate G, which is close to the fourth electrode B, via the fourth electrode B because the fourth electrode B directly contacts the semiconductor layer 33. The voltage level of the fourth electrode B is either the same as or different from that of the gate G. It is noted that the difference between the two voltage levels is in a limited range.

(14) Please refer to FIG. 5. FIG. 5 is a flowchart of a manufacturing method for the TFT switch shown in FIG. 3. As shown in FIG. 5, the manufacturing method for the TFT switch comprises the following steps:

(15) Step S101: forming a gate, for connecting to a control signal to control a switch on or off, and a gate insulating layer on a substrate in order.

(16) Step S102: forming a semiconductor layer on the gate insulating layer.

(17) Step S103: forming a drain, for connecting to a first signal, and a source on the semiconductor layer respectively and covered with a passivation layer. When the TFT switch is used in a test circuit, the first signal is a test signal and the drain connects to the test circuit. The test circuit is either a data line or a scanning line.

(18) Step S104: forming a fourth electrode on the passivation layer, wherein the fourth electrode is selectively connected to different voltage levels.

(19) In the embodiment, the gate is located at one side of the semiconductor layer while the drain and the source are located at an opposite side of the semiconductor layer. The fourth electrode and the gate are connected to high voltages when the switch turns on, and the voltage of the fourth electrode is either identical to or different from that of the gate. The gate is connected to a low voltage, and the fourth electrode is connected to a high voltage to conduct accumulated electrons away from the gate side in the semiconductor layer for reducing leakage current when the switch turns off. Afterwards, the fourth electrode is connected to a low voltage, and the voltage of the fourth electrode is either identical to or different from that of the gate. It is noted that the difference between the two voltage levels is in a limited range.

(20) Please refer to FIG. 6. FIG. 6 is a flowchart of a manufacturing method for the TFT switch shown in FIG. 4. As shown in FIG. 6, the manufacturing method for the TFT switch comprises the following steps:

(21) Step S201: forming a gate, for connecting to a control signal to control a switch on or off, and a gate insulating layer on a substrate in order.

(22) Step S202: forming a drain, for connecting to a first signal, and a source on the gate insulating layer respectively. When the TFT switch is used in a test circuit, the first signal is a test signal, and the source is used for connecting to the circuit under test. The test circuit is either a data line or a scanning line.

(23) Step S203: forming a semiconductor layer on the drain and the source and contacting the gate insulating layer.

(24) Step S204: forming a fourth electrode on the semiconductor layer and covering the surrounding of the fourth electrode with the passivation layer, and the fourth electrode is selectively connected to different voltage levels.

(25) In the embodiment, the gate, the drain, and the source are located at the same side of the semiconductor layer. The fourth electrode and the gate are connected to high voltages when the switch turns on, and the voltage of the fourth electrode is either identical to or different from that of the gate. The gate is connected to a low voltage, and the fourth electrode is grounded to conduct electrons away from the gate side in the semiconductor layer for reducing leakage current when the switch turns off. The voltage of the fourth electrode is either identical to or different from that of the gate after the switch turns off. It is noted that the difference between the two voltage levels is in a limited range.

(26) In summary, the present invention provides a TFT switch, which comprises a gate, a drain, a source, and a fourth electrode. The drain is connected to a first signal, and the gate is connected to a control signal to control the switch on or off. The source transmits the first signal when the switch turns on. The fourth electrode and the gate are located at two sides of the source and the drain. The fourth electrode is conductive and is selectively connected to different voltage levels, thereby reducing leakage current in a channel to improve switch characteristic when the switch turns off.

(27) Those skilled, in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.