JP3272331B2 - Pixel capacitance inspection device with leak correction function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a TFT (Thin Fil
The present invention relates to a pixel capacitance inspection apparatus for inspecting the pixel capacitance of an LCD (Liquid Crystal Display).

[0002]

2. Description of the Related Art Flat panel displays (Flat P)
As one of the anel displays, a TFT liquid crystal display (TFT-LCD) is known. With regard to this TFT liquid crystal display, technologies such as large screen, color, high brightness, small size and light weight have advanced, and in recent years it has been adopted in many electronic devices such as workstations and notebook computers. I have.

FIG. 11 schematically shows an example of the structure of a liquid crystal panel of a TFT liquid crystal display. Each pixel is
It is composed of a TFT and a drive electrode. In a TFT liquid crystal display, the contrast of a pixel is controlled by the potential of a driving electrode. That is, the brightness of the pixel is determined by changing the molecular arrangement of the liquid crystal according to the voltage between the common electrode and the driving electrode.

The inspection of each pixel on the glass substrate is performed by measuring the pixel capacitance, that is, the capacitance of a capacitor composed of a common electrode and a drive electrode. By measuring the pixel capacitance, it is possible to detect the presence or absence of disconnection between the TFT and the drive electrode, the presence or absence of a short circuit between the drive electrodes, and the like. In other words, the pixel capacity of each pixel on the glass substrate is set to the default value, but the pixel capacity of the pixel in which the disconnection or the short circuit has occurred largely deviates from the default value.

In addition, when TFTs and drive electrodes are formed on a glass substrate, the pixel capacitance always varies due to variations in film thickness and pattern processing accuracy. Therefore, measuring the pixel capacitance is very important. That is, there is no problem if the pixel capacities of all the pixels fall within the predetermined range. However, if the pixel capacities are out of the predetermined range, they must be removed as defective.

[0006]

The measurement of the pixel capacitance has the following problems. The value of the pixel capacitance is as very small as 0.1 pF to 0.2 pF, and it is difficult to measure accurately. The capacitance and the wiring capacitance of the tester for measuring the pixel capacitance are much larger than the pixel capacitance (100 pF). The capacitance and the wiring capacitance of the tester for measuring the pixel capacitance differ for each inspection system (pixel capacitance inspection device).

A pixel capacitance inspection apparatus for solving these problems has already been disclosed in a Japanese patent application (Japanese Patent Application No. 10-1426).
63). However, in this pixel capacitance inspection apparatus, it is difficult to accurately measure and inspect the pixel capacitance due to a leak occurring in the device to be measured (glass substrate) during the inspection.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks. An object of the present invention is to correct a variation in a measured value due to a leak in an inspection of a pixel capacitance in a TFT liquid crystal display and to accurately inspect the pixel capacitance. Is to do so.

[0009]

According to a first aspect of the present invention, there is provided a pixel capacitance inspection apparatus comprising: a driving electrode of a device to be measured having a pixel including a first switch and a driving electrode connected to one end of the first switch; In a pixel capacitance inspection device for inspecting a generated pixel capacitance Cp, a capacitor having a known reference capacitance ΔCs, a second switch connected between the capacitor and the other end of the first switch, a power supply, and the power supply. A third switch connected between the other ends of the first switches, a measurement circuit for measuring a potential at the other end of the first switches, and controlling the first, second and third switches, and the power supply; And a control circuit.

The control circuit turns on the first and third switches to apply a first potential Vp from the power supply to the drive electrode, and sets the drive electrode to the first potential Vp. Then, the first switch is turned off, the third switch is turned on, second means for applying a second potential Vs from the power supply to the other end of the first switch, and the drive electrode is connected to the first potential. Vp, the other end of the first switch is set to the second potential Vs, then the third switch is turned off, the third switch is turned on, and the third switch is turned on by the third means. Fourth means for measuring the potential of the other end of the first switch immediately before turning on by the measuring circuit, and the other end of the first switch after turning on the first switch by the third means. Measure the potential A fifth means for measuring the circuit,
Inspection of the pixel capacitance based on a potential at the other end of the first switch immediately before turning on the first switch and a potential at the other end of the first switch after turning on the first switch. And a sixth means for performing the following.

Further, the potential of the other end of the first switch immediately before turning on the first switch measured by the fourth means is _VL, and the potential of the first switch measured by the fifth means is _VL. When the potential of the other end of the first switch after turning on is Va, Va [correction] =
Va + [Delta] _VL , [Delta] _VL = Vs- _VL ([Delta] _VL is the amount of change in the potential due to leakage), and the sixth means includes the Va.
The pixel capacitance is inspected based on [correction].

The control circuit further operates the first to sixth means in a state where the second switch is turned off, and at this time, Va [correction] obtained by the sixth means is changed to a third potential Va1. The seventh means to be [correction] and the first to sixth means are operated while the second switch is turned on. At this time, Va [correction] obtained by the sixth means is changed to a fourth potential Va2. Eighth means to be [correction], and a difference ΔVs1 between the third potential and the two potentials and a difference ΔVs2 between the fourth potential and the two potentials are calculated.
A ninth method for obtaining the pixel capacitance based on s1 and ΔVs2
Means.

A pixel capacitance inspection apparatus according to the present invention inspects a pixel capacitance Cp generated in a drive electrode of a device under test having a pixel including a first switch and a drive electrode connected to one end of the first switch. A capacitor having a known reference capacitance ΔCs;
A second switch connected between the capacitor and the other end of the first switch; a power supply; a third switch connected between the power supply and the other end of the first switch;
A measurement circuit for measuring a potential difference between both ends of the switch, and a control circuit for controlling the first, second, and third switches and the power supply are provided.

Then, the control circuit turns on the first and third switches, applies a first potential Vp from the power supply to the drive electrode, and sets the drive electrode to the first potential Vp. Then, the first switch is turned off, the third switch is turned on, second means for applying a second potential Vs from the power supply to the other end of the first switch, and the drive electrode is connected to the first potential. Vp, the other end of the first switch is set to the second potential Vs, then the third switch is turned off, the third switch is turned on, and the third switch is turned on by the third means. Fourth means for measuring the potential at the other end of the first switch immediately before turning on, and measuring the potential difference between both ends of the third switch after turning on the first switch by the third means. Measured by Fifth means, and a potential difference between the other end of the first switch immediately before turning on the first switch and a potential difference between both ends of the third switch after turning on the first switch. And a sixth means for inspecting the pixel capacitance.

In addition, the above-mentioned measured by the fourth means is
The first switch immediately before turning on the first switch;
Potential at the other end of_LAnd measured by the fifth means.
The third switch after the first switch has been turned on.
When the potential difference between both ends of the switch is ΔVs ′, ΔVs =
ΔVs ′ + ΔV_L, ΔV_L= Vs-V_L(ΔV _L
Is the amount of change in potential due to leakage),
The inspection of the pixel capacitance is performed based on ΔVs.

The control circuit further operates the first to sixth means with the second switch turned off, and at this time, a seventh means for setting ΔVs obtained by the sixth means to ΔVs1. Operating the first to sixth means in a state where the second switch is turned on, based on the eighth means for setting ΔVs obtained by the sixth means at this time to ΔVs2, and based on the ΔVs1 and ΔVs2 Ninth means for obtaining the pixel capacitance.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a pixel capacitance inspection apparatus having a leak correction function according to the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of a pixel capacitance inspection apparatus according to the present invention.
An example is shown. The pixel capacitance inspection apparatus of this example is an improvement of the pixel capacitance inspection apparatus disclosed in Japanese Patent Application (Japanese Patent Application No. 10-142663).

On the device to be measured (glass substrate) side, Cp is a pixel capacitance, and SW1 is a TFT (Thin Film).
Transistor). On the tester side, ΔCs is a reference capacitance, e is a power supply, V is a voltmeter, SW2, SW3
Is a switch. Cs is the wiring capacitance, and includes the wiring capacitance on the device under test side (capacity other than the pixel capacitance) and the wiring capacitance on the tester side.

Since the purpose is to determine the pixel capacitance Cp, the pixel capacitance Cp is unknown. Also, the wiring capacitance Cs
Is also unknown. The reference capacitance ΔCs is known, and is set to a predetermined value within a range of 50 pF to 100 pF, for example. The power supply e generates known potentials Vp and Vs. The voltmeter V is composed of, for example, a differential amplifier. The switch SW3 is composed of, for example, a photo MOS switch. The switch SW2 may be a photo MOS switch or an analog switch.

The control device 11 includes a power supply e, a switch SW
1, SW2 and SW3 are controlled. The pixel capacitance inspection device of this example is characterized by the operation of the control device 11 compared to the invention of the Japanese patent application already filed.

1 will be described below with reference to the waveform diagrams of FIGS. 2 to 5. FIG.

1. First measurement First, switch SW2 is turned off, and switch SW2 is turned off.
1, SW3 is turned on, and the potential Vp is generated by the power supply e. At this time, the potentials at the points A and B become Vp.
Thereafter, the switch SW1 is turned off (period in FIG. 2).

Next, the potential Vs is generated by the power source e,
The potential at the point is set to Vs. Thereafter, the switch SW3 is turned off (period in FIG. 2).

After that, the switch SW1 is turned on. At this time, the potential at point A and the potential at point B are averaged and equalized. Then, the potential at point A (and point B), specifically, the potential difference (voltage) between the potential at point A (and point B) and the potential at point C (ground potential) is measured with a voltmeter V (FIG. 2). Period).

The potential Va1 at the point A (and the point B) is as follows: Va1 = (Cs.Vs + Cp.Vp) / (Cs + Cp) (1)

The difference ΔVs1 between Va1 and Vs is given by: ΔVs1 = Va1-Vs = {(Cs · Vs + Cp · Vp) / (Cs + Cp)} − Vs = (Cp · Vp−Cp · Vs) / (Cs + Cp) = ( Cp / Cs) · (Vp−Vs) (2) However, Cs >> Cp.

Here, the time when the period shifts from the period to the period will be examined.

As shown in FIG. 3, when the period shifts from one period to another, first, the switch SW3 is turned off, the point B is disconnected from the power supply e, and thereafter, the switch SW1 is turned on, and the point A and the point A are turned off. Point B is short-circuited. That is, a certain period T is secured from the time when the switch SW3 is turned off to the time when the switch SW1 is turned on so that the switches SW1 and SW3 are not both turned on.

However, in this period T, the potential at the point B may decrease from Vs by a predetermined amount ΔV _L1 (the charge amount decreases) due to leakage.

In this case, the potential Va1 at the point A (and the point B) when the point A and the point B are short-circuited in the period, that is, the potential measured by the voltmeter V naturally has an error ΔV _L1 due to leakage. Contains.

Therefore, in the present invention, the potential V _{L1 at the} point B immediately before the switch SW1 is turned on is measured by the voltmeter V. That is, by measuring the potential V _{L1 at the} point B immediately before the switch SW1 is turned on, the control circuit 11 causes the error ΔV _L 1 due to leakage to occur.
(= _Vs-V L 1), and can be obtained by calculation.

Therefore, the leak corrected point A (and B)
The potential Va1 [correction] of (point) is Va1 [correction] = Va1 + ΔV _L1 (1) '.

The difference ΔVs1 between Va1 [correction] and Vs
Is, ΔVs1 = Va1 _{[Correction] -Vs = Va1 + ΔV L 1} -Vs = {(Cs · Vs + Cp · Vp) / (Cs + Cp)} + ΔV L 1-Vs = {(Cp · Vp-Cp · Vs) / (Cs + Cp) ｝ + ΔV _L 1 = {(Cp / Cs) · (Vp−Vs)} + ΔV _L 1 (2) ′. However, Cs >> Cp.

2. Second measurement In the first measurement, the switch SW2 is always off, but in the second measurement, the switch SW2 is always on.

First, the switches SW1, SW2, and SW3 are turned on, and the potential Vp is generated by the power supply e. At this time, the potentials at the points A and B become Vp. Thereafter, the switch SW1 is turned off (period in FIG. 4).

Next, a potential Vs is generated by the power source e,
The potential at the point is set to Vs. Thereafter, the switch SW3 is turned off (period in FIG. 4).

After that, the switch SW1 is turned on. At this time, the potential at point A and the potential at point B are averaged and equalized. Then, the potential at point A (and point B), specifically, the potential difference (voltage) between the potential at point A (and point B) and the potential at point C (ground potential) is measured with a voltmeter V (FIG. 4). Period).

The potential Va2 at point A (and point B) is as follows: Va2 = {(Cs + ΔCs) · Vs + Cp · Vp} / {(Cs + ΔCs) + Cp} (3)

The difference ΔVs2 between Va2 and Vs is given by ΔVs2 = Va2−Vs = [{(Cs + ΔCs) · Vs + Cp · Vp} / {(Cs + ΔCs) + Cp}] − Vs = (Cp · Vp−Cp · Vs) / (Cs + ΔCs + Cp) = {Cp / (Cs + ΔCs)} · (Vp−Vs) (4) However, Cs >> Cp.

Here, the time when the period shifts from the period to the period will be examined.

As shown in FIG. 5, when the period shifts from the period to the period, first, the switch SW3 is turned off, the point B is disconnected from the power supply e, and thereafter, the switch SW1 is turned on, and the point A Point B is short-circuited. That is, a certain period T is secured from the time when the switch SW3 is turned off to the time when the switch SW1 is turned on so that the switches SW1 and SW3 are not both turned on.

However, during this period T, the potential at the point B may decrease from Vs by a predetermined amount ΔV _L2 (the charge amount decreases) due to leakage.

In this case, the potential Va2 at the point A (and the point B) when the point A and the point B are short-circuited in the period, that is, the potential measured by the voltmeter V naturally has an error ΔV _L2 due to leakage. Contains.

Therefore, in the present invention, the potential V _{L2 at the} point B immediately before the switch SW1 is turned on is measured by the voltmeter V. That is, by measuring the potential V _{L2 at the} point B immediately before the switch SW1 is turned on, the control circuit 11 causes the error ΔV _L2 due to the leakage.
The _{(= Vs-V L 2)} , can be obtained by calculation.

Therefore, the leak corrected point A (and B)
The potential Va2 [correction] of (point) is Va2 [correction] = Va2 + ΔV _L2 (3) ′.

The difference ΔVs2 between Va2 [correction] and Vs
ΔVs2 = Va2 [correction] −Vs = Va2 + ΔV _L2 −Vs = [{(Cs + ΔCs) · Vs + Cp · Vp} / Ｖ (Cs + ΔCs) + Cp}] + ΔV _L2 −Vs = ｛(Cp · Vp−Cp · Vs ) / (Cs + ΔCs + Cp)｝ + ΔV _L2 = [{Cp / (Cs + ΔCs)}｝ (Vp−Vs)] + ΔV _L 2 (4) ′. However, Cs >> Cp.

3. Inspection of Pixel Capacitance Cp When the above equation (2) ′ is modified, Cs = {Cp (Vp−Vs) / (ΔVs1−ΔV _L1 )} (5)

[0049] By modifying the (4) 'equation, Cs = {Cp (Vp- Vs) / (ΔVs2-ΔV L 2)} - ΔCs ... a (6).

Therefore, from the above equations (5) and (6),
Clearing the Cs, Cp = {ΔCs · ( ΔVs1-ΔV L 1) · (ΔVs2-ΔV L 2)} / [(Vp-Vs) · {(ΔVs1-ΔV L 1) - (ΔVs2-ΔV L 2) ｝] (7)

[0051] Then, [Delta] V _L 1 and [Delta] V _L 2, the value _V L 1 obtained by the voltmeter V in two measurements of the above,
With V _L 2, calculated in the control circuit _Vs-V L 1,
Determined by _{Vs-V L} 2. ΔVs1 and ΔVs2 are
The value V obtained by the voltmeter V in the above two measurements
The calculation Va1- in the control circuit is performed using a1 and Va2.
Vs, Va2-Vs. ΔCs, V
p and Vs are known. Therefore, from the above equation (7),
The pixel capacitance Cp can be obtained.

If the pixel capacitance Cp of each pixel on the device under test (glass substrate) falls within a predetermined range, it is determined to be non-defective, and if it is outside the predetermined range, it is determined to be defective.

4. Inspection of disconnection and short circuit In the first measurement or the second measurement described above,
The inspection can be performed by the expression (2) ′ or the expression (4) ′.

Means that [0054] · DerutaVs1 or when ΔVs2 is 0 or near ([Delta] V _L 1 and [Delta] V _L 2 it is assumed that almost 0) pixel capacitance Cp is zero. That is,
This means that the drive electrode and the TFT are disconnected, or that the drive electrode does not exist (a so-called "capacity loss" defect).

When ΔVs1 or ΔVs2 greatly exceeds the predetermined value. The fact that the pixel capacitance Cp greatly exceeds the predetermined value does not mean a variation in the pixel capacitance Cp at the time of manufacturing, but rather the pixel capacitance. This means an intrinsic defect of Cp, for example, a defect such that adjacent drive electrodes are short-circuited to each other.

5. Inspection of Leak in Drive Electrode In the first measurement or the second measurement described above,
The inspection can be performed by the expression (2) ′ or the expression (4) ′.

However, in the above-described first or second measurement, it is necessary to maintain this state for a certain period of time after the point A is set to Vp and the switch SW1 is turned off. Specifically, this fixed time is set to one frame time.

When there is a large amount of leakage at the drive electrode (when there is a leakage failure), the potential Vp at the point A gradually decreases, and in the worst case, becomes 0V. In this case, ΔVs1 or ΔVs2 is equal to “capacity loss” described above.
It becomes 0 or its vicinity.

On the other hand, when there is no leakage at the drive electrode, the potential at the point A remains at Vp even if one frame time elapses.
Or in the vicinity thereof.

FIG. 6 shows a second example of the pixel capacitance inspection apparatus according to the present invention.
An example is shown. The feature of the pixel capacitance inspection device of the present invention is that
The point is that the voltmeter V is connected to both ends of the switch SW3. That is, the voltmeter V can detect a potential difference (voltage) between both ends of the switch SW3.

According to the pixel capacitance inspection apparatus of this embodiment, by connecting the voltmeter V to both ends of the switch SW3, the value ΔVs1 (= Va1) necessary for judging the quality of the pixel capacitance is obtained.
1−Vs) and ΔVs2 (= Va2−Vs) can be obtained immediately by a voltmeter, not by calculation. Therefore,
The inspection time of the pixel capacitance of the TFT liquid crystal display can be reduced.

On the device to be measured (glass substrate) side, Cp is a pixel capacitance, and SW1 is a TFT (Thin Film).
Transistor). On the tester side, ΔCs is a reference capacitance, e is a power supply, V is a voltmeter, SW2, SW3
Is a switch. Cs is the wiring capacitance, and includes the wiring capacitance on the device under test side (capacity other than the pixel capacitance) and the wiring capacitance on the tester side.

Since the purpose is to determine the pixel capacitance Cp, the pixel capacitance Cp is unknown. Also, the wiring capacitance Cs
Is also unknown. The reference capacitance ΔCs is known, and is set to a predetermined value within a range of 50 pF to 100 pF, for example. The power supply e generates known potentials Vp and Vs. The voltmeter V is composed of, for example, a differential amplifier. The switch SW3 is composed of, for example, a photo MOS switch. The switch SW2 may be a photo MOS switch or an analog switch. The control device 11 controls the power supply e and the switches SW1, SW2, SW3.

The operation of the pixel capacitance inspection apparatus of FIG. 6 will be described below with reference to the waveform diagrams of FIGS. 7 to 10.

1. First measurement First, switch SW2 is turned off, and switch SW2 is turned off.
1, SW3 is turned on, and the potential Vp is generated by the power supply e. At this time, the potentials at the points A and B become Vp.
Thereafter, the switch SW1 is turned off (period in FIG. 7).

Next, the potential Vs is generated by the power source e,
The potential at the point is set to Vs. Thereafter, the switch SW3 is turned off (period in FIG. 7).

Then, the switch SW1 is turned on. At this time, the electric charge at the point A and the electric charge at the point B mix, and the electric potential at the point A and the electric potential at the point B are averaged and equalized (period in FIG. 7).

Here, the potential Va1 at point A (and point B)
Can be represented by the above formula (1). The potential at point D is maintained at Vs by the power supply V. That is, the potential difference between both ends of the switch SW3 is ΔVs1 ′ (= Va1
−Vs).

When leak correction is not performed, ΔVs
1 ′ can be used as it is as ΔVs1 in the above equation (2). On the other hand, when performing leak correction, a value obtained by adding an error ΔV _L1 due to leak to ΔVs1 ′ is used as ΔVs1 in the above equation (2). That is, ΔVs1 = ΔVs1 ′ + ΔV _L1 (8)

Note that ΔVs1 ′ can be immediately obtained by the voltmeter V as a potential difference (voltage) generated at both ends of the switch SW3. ΔV _L 1 is equal to the above-described first value.
As in the example, it can be determined by calculating the Vs-V L _1.

Further, V _L 1 can be easily obtained by newly connecting a voltmeter between points B and C, for example, as in the first example described above. Also, V L ₁ is, for example, when measuring the V L _1, by the point D to the ground potential, without connecting a new voltmeter between points B and C, voltmeter V Can be measured more easily.

2. Second measurement In the first measurement, the switch SW2 is always off, but in the second measurement, the switch SW2 is always on.

First, the switches SW1, SW2, and SW3 are turned on, and the potential Vp is generated by the power supply e. At this time, the potentials at the points A and B become Vp. Thereafter, the switch SW1 is turned off (period in FIG. 9).

Next, the potential Vs is generated by the power source e,
The potential at the point is set to Vs. Thereafter, the switch SW3 is turned off (period in FIG. 9).

After that, the switch SW1 is turned on. At this time, the electric charge at the point A and the electric charge at the point B mix, and the electric potential at the point A and the electric potential at the point B are averaged and equalized (period in FIG. 9).

Here, the potential Va2 at point A (and point B)
Can be represented by the above equation (3). The potential at point D is maintained at Vs by the power supply V. That is, the potential difference between both ends of the switch SW3 is ΔVs2 ′ (= Va2
−Vs).

When leak correction is not performed, ΔVs
2 ′ can be used as it is as ΔVs2 in the above equation (4). On the other hand, when the leak correction is performed, a value obtained by adding the error ΔV _L2 due to the leak to ΔVs2 ′ is used as ΔVs2 in the above equation (4). That is, ΔVs2 = ΔVs2 ′ + ΔV _L2 (9).

Note that ΔVs2 ′ can be immediately obtained by the voltmeter V as a potential difference (voltage) generated between both ends of the switch SW3. Further, ΔV _L2 is equal to the above-described first value.
As in the example, it can be determined by calculating the Vs-V L _2.

V _L 2 can be easily obtained by newly connecting a voltmeter between points B and C, for example, as in the first example. Also, V L ₂ is, for example, when measuring the V L _2, by the ground potential point D, without connecting a new voltmeter between points B and C, voltmeter V Can be measured more easily.

3. Inspection of Pixel Capacitance Cp It can be obtained by the above equation (7). The above equation (7) is as follows. Cp = {ΔCs · (ΔVs1- ΔV L 1) · (ΔVs2-ΔV L 2)} / [(Vp-Vs) · {(ΔVs1-ΔV L 1) - (ΔVs2-ΔV L 2)}] ... (7 Here, ΔV _L1 and ΔV _L2 are, for example, the values V _L1 and V obtained by the voltmeter V in the above two measurements.
It is determined by calculation using _L2 . ΔVs1 and ΔVs2
Can be obtained immediately by the voltmeter V in the two measurements described above. Further, ΔCs, Vp, and Vs are known. Therefore, the pixel capacitance Cp can be obtained from the above equation (7).

The pixel capacitance Cp of each pixel of the device under test
However, if it falls within the predetermined range, it is determined to be non-defective, and if it is out of the predetermined range, it is determined to be defective.

4. Inspection of disconnection and short circuit In the first measurement or the second measurement described above, an inspection can be immediately performed using the values ΔVs1 and ΔVs2 obtained by the voltmeter V.

[0083] · DerutaVs1 or when ΔVs2 is 0 or near (ΔV _L 1, assumed to be [Delta] V _L 2 is approximately 0) pixel capacitance Cp is meant to be 0. That is,
This means that the drive electrode and the TFT are disconnected, or that the drive electrode does not exist (a so-called "capacity loss" defect).

When ΔVs1 or ΔVs2 greatly exceeds the predetermined value. The fact that the pixel capacitance Cp greatly exceeds the predetermined value does not mean a variation in the pixel capacitance Cp at the time of manufacturing, but rather the pixel capacitance. This means an intrinsic defect of Cp, for example, a defect such that adjacent drive electrodes are short-circuited to each other.

5. Inspection of Leak in Drive Electrode In the above-described first measurement or second measurement, it is possible to immediately inspect using the values ΔVs1 and ΔVs2 obtained by the voltmeter V.

However, in the above-described first measurement or second measurement, it is necessary to keep point A at Vp, turn off switch SW1, and maintain this state for a certain period of time. Specifically, this fixed time is set to one frame time.

When there is a large amount of leakage at the drive electrode (when there is a leakage failure), the potential Vp at the point A gradually decreases, and in the worst case, becomes 0V. In this case, the values ΔVs1 and ΔVs2 obtained by the voltmeter V are 0 or near the same as in the above “capacity loss”.

On the other hand, if there is no leakage at the drive electrode, the potential at point A remains at Vp even after one frame time has elapsed.
Or in the vicinity thereof. Therefore, the values ΔVs1 and ΔVs2 obtained by the voltmeter V do not become 0 or near.

[0089]

As described above, according to the pixel capacitance inspection apparatus of the present invention, immediately after the switch SW3 is turned off and immediately before the switch SW1 is turned on, the potential V _{L1,1 at the} point B is obtained. measuring the V _L 2, on the basis of the _{V L} 1, _V L 2, the correction value in the leak correction ΔV _L 1 _{(Vs-V L}
1), to obtain [Delta] V _L 2 a _{(= Vs-V L 2)} . This correction value is added to Va1 and Va2 as shown in the above equations (1) ′ and (3) ′ (first example), and is also shown in the above equations (8) and (9). Thus, ΔVs
By adding to 1 ′ and ΔVs2 ′ (second example), the inspection of the pixel capacitance can be performed accurately.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of a pixel capacitance inspection device of the present invention.

FIG. 2 is a diagram showing the operation of the apparatus of FIG.

FIG. 3 is a diagram showing the operation of the apparatus of FIG. 1;

FIG. 4 is a diagram showing the operation of the device of FIG. 1;

FIG. 5 is a diagram showing the operation of the device of FIG. 1;

FIG. 6 is a diagram showing a second example of the pixel capacitance inspection device of the present invention.

FIG. 7 is a diagram showing the operation of the device of FIG. 6;

FIG. 8 is a diagram showing the operation of the device of FIG. 6;

FIG. 9 is a diagram showing the operation of the device of FIG. 6;

FIG. 10 is a diagram showing the operation of the device of FIG. 6;

FIG. 11 illustrates an example of a liquid crystal panel of a TFT liquid crystal display.

[Explanation of symbols]

11: control circuit, e: power supply, SW1: switch (TF
T), SW2, SW3: switch on the tester side, Cp: pixel capacitance, Cs: wiring capacitance, ΔCs: reference capacitance, V: voltmeter.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 31/00 G01R 27/26 G02F 1/13 G02F 1/1365

Claims (6)

(57) [Claims] 1. A pixel capacitance inspection apparatus for inspecting a pixel capacitance Cp generated in a drive electrode of a device under test having a pixel composed of a first switch and a drive electrode connected to one end of the first switch, Known reference capacity ΔC
s, a second switch connected between the capacitor and the other end of the first switch, a power supply, and a third switch connected between the power supply and the other end of the first switch. A measuring circuit for measuring a potential at the other end of the first switch, and a control circuit for controlling the first, second, and third switches and the power supply, wherein the control circuit includes the first and second switches. A first means for turning on a third switch to apply a first potential Vp to the drive electrode from the power source; and setting the drive electrode to the first potential Vp, and then turning off the first switch and setting the third switch to Is turned on, a second means for applying a second potential Vs from the power supply to the other end of the first switch, the drive electrode to the first potential Vp, and the other end of the first switch to a second potential Vs
And turning on the third switch, turning off the first switch, turning on the first switch, and turning on the other end of the first switch immediately before turning on the first switch by the third means. Fourth means for measuring the potential by the measuring circuit, fifth means for measuring the potential at the other end of the first switch by the measuring circuit after the first switch is turned on by the third means, Inspection of the pixel capacitance is performed based on the potential at the other end of the first switch immediately before turning on the first switch and the potential at the other end of the first switch after turning on the first switch. And a sixth means for performing the test. 2. The method according to claim 1, wherein said first means is measured by said fourth means.
The potential at the other end of the first switch immediately before the switch is turned on is set to _VL, and the potential at the other end of the first switch after the first switch is turned on is measured by the fifth means. Where Va [correction] = Va
+ ΔV _L , ΔV _L = Vs−V _L (ΔV _L is the amount of change in potential due to leakage), and the sixth means performs an inspection of the pixel capacitance based on the Va [correction]. The pixel capacitance inspection device according to claim 1. 3. The pixel capacitance inspection device according to claim 2, wherein the control circuit further comprises the first to sixth switches in a state where the second switch is turned off.
Means is operated, and Va [correction] obtained by the sixth means at this time is set to a third potential Va1 [correction].
Means; and the first through sixth switches with the second switch turned on.
Means is operated, and at this time, Va [correction] obtained by the sixth means is set to a fourth potential Va2 [correction].
Means, a difference ΔVs1 between the third potential and the second potential, and the fourth
The difference ΔVs2 between the potential and the second potential is calculated,
A ninth method for obtaining the pixel capacitance based on s1 and ΔVs2
Means for testing pixel capacitance. 4. A pixel capacitance inspection apparatus for inspecting a pixel capacitance Cp generated in a drive electrode of a device under test having a pixel including a first switch and a drive electrode connected to one end of the first switch, Known reference capacity ΔC
s, a second switch connected between the capacitor and the other end of the first switch, a power supply, and a third switch connected between the power supply and the other end of the first switch. A measuring circuit for measuring a potential difference between both ends of the third switch, and a control circuit for controlling the first, second and third switches and the power supply, wherein the control circuit comprises the first and third switches. Turning on a switch, first means for applying a first potential Vp from the power supply to the drive electrode, and setting the drive electrode to the first potential Vp, then turning off the first switch, turning off the third switch. A second means for turning on the power supply and applying a second potential Vs from the power supply to the other end of the first switch; a drive potential of the first potential Vp; and a second end of the first switch being a second potential Vs.
And turning on the third switch, turning off the first switch, turning on the first switch, and turning on the other end of the first switch immediately before turning on the first switch by the third means. A fourth means for measuring a potential, and the third means after the first switch is turned on by the third means.
Fifth means for measuring the potential difference between both ends of the switch by the measurement circuit, and the potential at the other end of the first switch immediately before the first switch is turned on and the potential after the first switch is turned on. And a sixth unit for inspecting the pixel capacitance based on a potential difference between both ends of the third switch. 5. The method according to claim 5, wherein the first means is measured by the fourth means.
The potential at the other end of the first switch immediately before the switch is turned on is set to _VL, and the potential difference between both ends of the third switch after the first switch is turned on measured by the fifth means is calculated. When ΔVs ′, ΔVs = ΔV
s' + [Delta] _VL , [Delta] _VL = Vs- _VL ([Delta] _VL is the amount of change in potential due to leakage),
The pixel capacitance inspection device according to claim 4, wherein the inspection of the pixel capacitance is performed based on s. 6. The pixel capacitance inspection device according to claim 5, wherein the control circuit further comprises the first to sixth switches in a state where the second switch is turned off.
Operating the means, and at this time, the seventh means for setting ΔVs obtained by the sixth means to ΔVs1, and the first to sixth means with the second switch turned on.
Operating means, and at this time, an eighth means for setting ΔVs obtained by the sixth means to ΔVs2, and a ninth means for obtaining the pixel capacitance based on the ΔVs1 and ΔVs2. Pixel capacitance inspection device.