Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1998-09-29
2001-07-24
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S701000
Reexamination Certificate
active
06265889
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a semiconductor testing circuit and a method of testing a semiconductor circuit.
The present invention has many applications which include, but not be limited to, a liquid crystal display device in which a plurality of video signals are selected to drive pixels.
A known active matrix-type liquid crystal display device (LCD) has a structure shown in
FIG. 13
, for example. The LCD includes a circuit array substrate, a counter substrate provided opposite to the array substrate with a counter electrode
16
, and a liquid crystal layer
15
held between the array substrate and the counter electrode
16
. The array substrate is provided with (m×n) pixel electrodes
14
disposed in a matrix form, m scanning lines Y
1
through Ym provided along the columns of the pixel electrodes
14
, n signal lines X
1
through Xn, thin film transistors (TFTs)
13
provided in the vicinities of crossing points of the scanning lines Y
1
through Ym and the signal lines X
1
through Xn a scanning line driver circuit
18
to drive the scanning lines Y
1
through Ym, and a signal line driver circuit
19
to drive the signal lines X
1
through Xn. Each TFT is used for a switching element which supplies a video signal voltage, when it is turned on, in response to a scanning voltage applied to its corresponding scanning line. The pixel electrode
14
and the counter electrode
16
are made of a transparent and electrically conductive material. The counter electrode
16
is driven by a counter electrode driving circuit
20
.
The scanning line driver circuit
18
sequentially supplies the scanning voltage to the scanning lines Y
1
through Ym during a horizontal scanning period. The signal line driver circuit
19
supplies the video signal voltage to the signal lines X
1
through Xn during the horizontal scanning period. The liquid crystal layer
15
is driven by the difference between the video signal voltage supplied to the pixel electrode
14
and predetermined voltages supplied to the counter electrode
16
from the counter electrode driving circuit
20
. The liquid crystal layer
15
passes light beams from the pixel electrode
14
to the counter electrode
16
in accordance with its voltage-optical transmission characteristic.
The signal line driver circuit
19
plays an important role in supplying pixel (video) signals to the pixel electrodes
14
If the signal line driver circuit
19
has malfunctions in its output circuit, it stops furnishing pixel signals to rows of the pixel electrodes
14
corresponding thereto and line defects appear on the screen of the liquid crystal display device. Even if only one line defect exists on the screen, it is fatal to the liquid crystal display device. In order to secure its efficiency and reliability, it should not be shipped unless the output of such a signal line driver circuit has been tested. Further, analysis and assessment of actual defects in liquid crystal display devices are useful for increase of the production yield of products to be manufactured from now on. Thus, it is essential to test an output of a key circuit like the signal line driver circuit.
Further, both signal lines and a signal line driver circuit are made on a glass substrate in a driver circuit integrated-type LCD. In this case, since the degree of integration is quite high and a physical space is hardly left to contact the probes to the output terminals, the testing, itself, becomes quite difficult.
As explained above, it is difficult to test the output of the signal driver circuit in the conventional LCDs though such a test is important to secure the reliability and improve the production yield.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor test circuit and a method of testing a semiconductor circuit in which many probes are not needed for testing an output of semiconductor circuits.
A semiconductor test circuit of this invention includes a substrate, first and second busses disposed on the substrate which are supplied with first and second voltages, respectively, signal lines disposed on the substrate, first and second semiconductor switching circuits to connect the first and second busses to the signal lines, respectively, driver circuits to drive the first and second semiconductor switching circuits and detection circuits to detect electric properties between the busses and the first and second semiconductor switching circuits when the driver circuits drives simultaneously the first and second semiconductor switching circuits, thereby to check whether the first and second semiconductor switching circuits and/or the busses function correctly.
The semiconductor test circuit further includes scanning lines disposed at substantially right angle with the signal lines, transistors provided in the vicinities of crossing points between the signal lines and the scanning lines, and pixel electrodes connected to the transistors.
In the semiconductor test circuit, the first and second voltages supplied to the first and second busses are different in polarity with respect to a reference voltage.
In the semiconductor test circuit, the first and second semiconductor switching circuits include P-channel and N-channel semiconductor elements, respectively, which have poly-crystalline active layers.
In the semiconductor test circuit, the driver circuits include shift registers.
Further, a testing method of the present invention is applied to a semiconductor circuit which includes a substrate, first and second busses disposed on the substrate, power sources to supply first and second voltages to the first and second busses, signal lines disposed on the substrate, first and second semiconductor switching circuits to connect the first and second busses to the signal lines, respectively, driver circuits to drive the first and second semiconductor switching circuits, and detection circuits to detect electric current passing through the first and second busses. The testing method carries out by supplying the first and second busses with the first and second voltages, respectively, driving the first and second semiconductor switching circuits simultaneously to connect the first and second busses to the signal lines, and enabling the detection circuit to detect the electric current when the first and second semiconductor switching circuits are simultaneously driven so that the detection circuit checks whether the first and second switching circuits and/or the first and second busses function correctly.
In the semiconductor circuit to be examined in accordance with the testing method, a pair of the first and second semiconductor switching circuits is provided to each of the signal lines.
The enabling operation further enables the driver circuit to covert the electric current into an electric resistance.
The detecting operation checks the electric resistance as to whether the first and second switching circuits and/or the first and second busses function correctly.
The semiconductor circuit to be examined in accordance with the testing method further includes a third bus disposed closely at the first and second busses, and the supplying operation further provides the third bus with a third voltage which is different in value from the first and second voltages.
The detecting operation detects the electric current to check whether the third bus is short-circuited with the first or second bus.
The semiconductor circuit to be examined in accordance with the testing method further includes scanning lines disposed at substantially right angle with the signal lines, transistors provided in the vicinities of crossing points between the signal lines and the scanning lines, and pixel electrodes connected to the transistors.
In the semiconductor circuit, the substrate is made of glass and the transistors include active layers made of poly-crystalline silicon.
According to the present invention set forth above, a malfunction of the driver circuit can be detected by observing electric current flow
Konda Nobuo
Tomita Satoru
Kabushiki Kaisha Toshiba
Nguyen Vinh P.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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