U.S. patent application number 15/058174 was filed with the patent office on 2017-08-03 for tft switch and method for manufacturing the same.
This patent application is currently assigned to Shenzhen China Star Optoelectronics Technology Co., Ltd.. The applicant listed for this patent is Shenzhen China Star Optoelectronics Technology Co., Ltd.. Invention is credited to Cheng-hung CHEN, Peng DU.
Application Number | 20170221784 15/058174 |
Document ID | / |
Family ID | 49799260 |
Filed Date | 2017-08-03 |
United States Patent
Application |
20170221784 |
Kind Code |
A1 |
DU; Peng ; et al. |
August 3, 2017 |
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.
Inventors: |
DU; Peng; (Shenzhen, CN)
; CHEN; Cheng-hung; (Shenzhen, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shenzhen China Star Optoelectronics Technology Co., Ltd. |
Shenzhen |
|
CN |
|
|
Assignee: |
Shenzhen China Star Optoelectronics
Technology Co., Ltd.
Shenzhen
CN
|
Family ID: |
49799260 |
Appl. No.: |
15/058174 |
Filed: |
March 2, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14119189 |
Nov 20, 2013 |
9680025 |
|
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15058174 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 27/1244 20130101;
H01L 22/34 20130101; H01L 29/66742 20130101; H01L 29/78696
20130101; H01L 22/14 20130101; H01L 27/127 20130101; H01L 29/78648
20130101; H01L 29/78609 20130101 |
International
Class: |
H01L 21/66 20060101
H01L021/66; H01L 29/786 20060101 H01L029/786; H01L 27/12 20060101
H01L027/12 |
Claims
1. A thin film transistor (TFT) switch, comprising a gate, a gate
insulation layer formed on the gate, a drain and a source formed on
the gate insulation layer and spaced from each other by a gap
therebetween, a semiconductor layer formed on the gate insulation
layer, the drain and the source, an n+ layer formed between the
semiconductor layer and each of the source and the drain, and a
fourth electrode formed on and in direct contact with the
semiconductor layer and located above the gap between the drain and
the source, wherein the drain is adapted to connect with a first
signal and the gate is adapted to connect with a control signal to
selectively control the TFT switch on or off so that the source
outputs the first signal when the switch turns on; wherein the
fourth electrode and the gate are respectively located at opposite
sides of the semiconductor layer; wherein when the switch turns on,
the gate and the fourth electrode are connected to high voltage
levels; and wherein the first signal is a test signal and the
source is adapted to connect to a data line under test; wherein the
high voltage level to which the fourth electrode is connected is
identical to the high voltage level to which the gate is
connected.
2. (canceled)
3. The TFT switch as claimed in claim 1, wherein the high voltage
level to which the fourth electrode is connected is different from
the high voltage level to which the gate is connected.
4. The TFT switch as claimed in claim 1 further comprising a
passivation layer formed on the semiconductor layer and surrounding
the fourth electrode in such a way that a gap is present between
the passivation layer and the fourth electrode.
5. The TFT switch as claimed in claim 1, wherein when the TFT
switch turns off, the gate is connected to a low voltage level and
the fourth electrode is grounded to drain off electrons that are
accumulated in the semiconductor layer at a location distant from
the gate.
6. 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 drain and a source on the gate
insulation layer; forming a semiconductor layer on the drain and
the source in such a way as to contact the gate insulating layer,
wherein an n+ layer is formed between the semiconductor layer and
each of the drain and the source 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 semiconductor layer such that the fourth electrode is in direct
contact with the semiconductor layer and forming a passivation
layer on the semiconductor layer such that the passivation layer
surrounds the fourth electrode, 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; 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.
7. (canceled)
8. The method as claimed in claim 6, 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.
9. The method as claimed in claim 6, wherein when the TFT switch
turns off, the gate is connected to a low voltage level and the
fourth electrode is grounded to drain off electrons that are
accumulated in the semiconductor layer at a location distant from
the gate.
10. A thin film transistor (TFT) switch, comprising a gate, a gate
insulation layer formed on the gate, a drain and a source formed on
the gate insulation layer and spaced from each other by a gap
therebetween, a semiconductor layer formed on the gate insulation
layer, the drain and the source, an n+ layer formed between the
semiconductor layer and each of the source and the drain, and a
fourth electrode formed on and in direct contact with the
semiconductor layer and located above the gap between the drain and
the source, wherein the drain is adapted to connect with a first
signal and the gate is adapted to connect with a control signal to
selectively control the TFT switch on or off so that the source
outputs the first signal when the switch turns on; wherein the
fourth electrode and the gate are respectively located at opposite
sides of the semiconductor layer; wherein when the switch turns on,
the gate and the fourth electrode are connected to high voltage
levels; and wherein the first signal is a test signal and the
source is adapted to connect to a data line under test; wherein
when the TFT switch turns off, the gate is connected to a low
voltage level and the fourth electrode is grounded to drain off
electrons that are accumulated in the semiconductor layer at a
location distant from the gate.
11. The TFT switch as claimed in claim 10, wherein the high voltage
level to which the fourth electrode is connected is different from
the high voltage level to which the gate is connected.
12. The TFT switch as claimed in claim 10 further comprising a
passivation layer formed on the semiconductor layer and surrounding
the fourth electrode in such a way that a gap is present between
the passivation layer and the fourth electrode.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of co-pending patent
application Ser. No. 14/119,189, "TFT Switch and Method for
Manufacturing the Same", filed on Nov. 20, 2013.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a liquid crystal display
(LCD) technology field, and more particularly, to a thin film
transistor (TFT) switch and a method for manufacturing the
same.
[0004] 2. The Related Arts
[0005] In detection of an LCD panel, there are two common designs
for detecting circuits. One is that a detecting circuit is directly
coupled to scanning lines or data lines in a display area of the
panel, and it needs to cut a connection between a test circuit and
a circuit in the display area by using laser after the detection.
The other is that the test circuit is coupled to a signal line in
the display area via a TFT switch. A signal is fed to the display
area through the TFT switch when a high voltage level is applied to
a gate of the TFT switch to turn it on. On the contrary, since the
TFT switch turns off for disconnection between the test line and
the scanning or data line in response to a low voltage level
applied on the gate of the TFT switch when the panel operates
normally, a process of laser cutting is therefore omitted.
[0006] Conventionally, there are three electrodes of the TFT switch
for detecting circuits, i.e. a gate, a drain and a source. The gate
of the TFT is in negative bias in a long term when the panel works
normally, and therefore electrical characteristic of the
semiconductor layer of the TFT varies to increase leakage current.
FIG. 1 shows a circuit diagram of a conventional switch TFT. As
shown in FIG. 1, a shorting bar is connected to drains 11 and 14 of
the two TFTs. Sources 12 and 15 of the two TFTs are respectively
connected to different scanning lines (GL) or data tines (DL). When
two gates 13 and 16 of the TFTs are applied with a low voltage, the
two TFTs switch off. If a leakage current passing through the two
TFTs and the shorting bar occurs, a short circuit between the
different scanning lines or data lines, i.e. a short circuit
between different signals, happens and deteriorates display
quality.
SUMMARY OF THE INVENTION
[0007] The present invention provides a TFT switch and the method
of manufacturing the same for reducing leakage current in a channel
of the TFT switch to improve switch characteristic when the switch
turns off.
[0008] According to the present invention, a thin film transistor
(TFT) switch comprises 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 connected to different
voltage levels.
[0009] In one aspect of the present invention, the gate and the
fourth electrode are connected to a high voltage level when the
switch turns on.
[0010] In another aspect of the present invention, the voltage
level of the fourth electrode is identical to that of the gate.
[0011] In another aspect of the present invention, the voltage
level of the fourth electrode is different from that of the
gate.
[0012] In another aspect of the present invention, the TFT switch
further comprises a passivation layer and a gate insulating layer
between the gate and the semiconductor layer. The drain and the
source are located between the semiconductor layer and the
passivation layer. The fourth electrode is located on the
passivation layer. When the switch turns off, the gate is connected
to a low voltage level. The fourth electrode is connected to a high
voltage level to conduct accumulated electrons away from the gate
side in the semiconductor layer and afterwards connected to the low
voltage level.
[0013] In another aspect of the present invention, a voltage level
of the fourth electrode is identical to that of the gate when the
fourth electrode is connected to the low voltage level.
[0014] In still another aspect of the present invention, a voltage
level of the fourth electrode is different to that of the gate when
the fourth electrode is connected to the low voltage level.
[0015] In still another aspect of the present invention, the TFT
switch further comprises a passivation layer and a gate insulating
layer on the gate. The drain and the source are located between the
gate insulating layer and the semiconductor layer. The fourth
electrode is located on the semiconductor layer. The passivation
layer surrounds the fourth electrode. When the switch turns off,
the gate is connected to a low voltage level, and the fourth
electrode is grounded to conduct accumulated electrons away from
the gate side in the semiconductor layer.
[0016] In yet another aspect of the present invention, the first
signal is a test signal, and the source is connected to a scanning
or data line under test.
[0017] According to the present invention, a method for
manufacturing a TFT switch comprises forming a gate connected to a
control signal to control the TFT switch turning on or turning off,
and a gate insulating layer on a substrate in order; forming a
semiconductor layer on the gate insulating layer; forming a drain
connected to a first signal and a source on the semiconductor
layer, respectively, and covering the semiconductor layer with a
passivation layer; and forming a fourth electrode on the
passivation layer, wherein the fourth electrode is selectively
connected to different voltage levels.
[0018] According to the present invention, a method for
manufacturing a TFT switch comprises: forming a gate connected to a
control signal to control the switch on or off, and a gate
insulating layer on a substrate in order; forming a drain connected
to a first signal, and a source on the gate insulating layer
respectively; forming a semiconductor layer on the drain and the
source to contact the gate insulating layer; and forming a fourth
electrode on the semiconductor layer and covering and surrounding
the fourth electrode with a passivation layer, wherein the fourth
electrode is selectively connected to different voltage levels.
[0019] The benefit of the present invention is that in addition to
a gate, a drain and a source inherent to a conventional TFT switch,
a fourth electrode is added in the TFT switch. The drain is coupled
to a first signal, and the gate is coupled to a control signal to
control the switch turning on or off. The first signal is outputted
from the source when the switch turns on. The fourth electrode and
the gate are respectively locate at two sides of a 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a circuit diagram of a conventional switch
TFT.
[0021] FIG. 2 shows a TFT switch according to a first embodiment of
the present invention.
[0022] FIG. 3 is a cross-sectional view of the TFT switch according
to the first embodiment of the present invention.
[0023] FIG. 4 is a cross-sectional view of a TFT switch according
to a second embodiment of the present invention.
[0024] FIG. 5 is a flowchart of a manufacturing method for the TFT
switch shown in FIG. 3.
[0025] FIG. 6 is a flowchart of a manufacturing method for the TFT
switch shown in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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:
[0034] 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.
[0035] Step S102: forming a semiconductor layer on the gate
insulating layer.
[0036] 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.
[0037] Step S104: forming a fourth electrode on the passivation
layer, wherein the fourth electrode is selectively connected to
different voltage levels.
[0038] 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.
[0039] 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:
[0040] 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.
[0041] 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.
[0042] Step S203: forming a semiconductor layer on the drain and
the source and contacting the gate insulating layer.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
* * * * *