JP2001264805A - Method and device for measuring voltage retention rate of tft liquid crystal panel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the voltage retention rate of a TFT liquid crystal display panel, and to enable prehension of the voltage retention rate distribution of a TFT liquid crystal display panel. SOLUTION: A TFT of the TFT liquid crystal panel is driven on the low frequency voltage of about 1 Hz, and the change of transmissivity of passing through a pixel arising from the degradation of a holding voltage held between a pixel electrode corresponding to the pixel of the TFT liquid crystal panel and a common electrode is observed (step S202). The transmissivity just before the polarity of a drain voltage of the TFT is reversed (step S204), is transformed into the holding voltage by using a voltage-transmissivity characteristic curve obtained previously (step S205), and then the voltage retention of the liquid crystal panel is calculated (step S206).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method and an apparatus for measuring a voltage holding ratio of a TFT liquid crystal display panel.

[0002]

2. Description of the Related Art In a TFT liquid crystal display panel, writing to a pixel electrode is controlled by a TFT (thin film transistor).

That is, when a voltage is applied to the gate of a TFT (thin film transistor), a charging voltage is applied from the drain to between the pixel electrode and the common electrode and charging starts, and the charging is performed when the gate of the TFT is in an ON state. Only for several tens of microseconds.

After charging between the pixel electrode and the common electrode in a very short time, the gate of the TFT is turned off,
Each pixel needs to hold the charging voltage until the next charging.
The time interval at which the charging takes place is typically 16.7 milliseconds, corresponding to a 30 Hz operation. The ratio of the holding voltage (charging voltage) held between the pixel electrode and the common electrode to the voltage applied to the gate of the TFT during the period from the charging to the recharging is often called a voltage holding ratio.

The voltage holding ratio is an important parameter which affects the display quality of a TFT liquid crystal panel. However, it is very difficult to obtain electric information for each pixel or even a part of the TFT liquid crystal panel due to its constituent circuit. Therefore, its measurement method has not been established.

For this reason, in the conventional example, the measurement of the voltage holding ratio has been used only for material evaluation using a test cell.

[0007]

However, in order to supply a TFT liquid crystal panel having a high quality display capability, it is necessary to know a voltage holding ratio, which is important information in management in a manufacturing process of the TFT liquid crystal panel. It is desired to know the voltage holding ratio distribution in the plane of the TFT liquid crystal panel.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional example. The voltage holding ratio of a TFT liquid crystal panel as an actual product is measured, and the voltage holding ratio is determined based on the data. An object of the present invention is to provide a method and an apparatus for measuring a voltage holding ratio of a TFT liquid crystal display panel whose distribution can be grasped.

[0009]

In order to achieve the above object, a method for measuring a voltage holding ratio of a TFT liquid crystal panel according to the present invention measures a time change of a transmitted light intensity of the liquid crystal panel when a TFT (thin film transistor) is driven. Using the voltage-transmittance characteristic curve, the measured transmitted light intensity is converted into a voltage, an attenuation value of the voltage with time change of the transmitted light intensity is obtained, and a voltage holding ratio of the TFT liquid crystal panel is obtained. Things.

Further, the voltage is set so that the light transmittance is in the range of 10% to 90% in the voltage-transmittance characteristic curve.
This is applied to the drain of the FT.

The TFT is driven at a low frequency in order to detect a small change in the light transmittance based on the attenuation of the voltage.

[0012] Further, a part of the TFTs incorporated in the TFT liquid crystal panel is driven, and uniform visible light is applied to pixels corresponding to the driven TFTs.

Further, the present invention drives all the TFTs incorporated in the TFT liquid crystal panel, and irradiates uniform visible light to partial pixels corresponding to the driven TFTs.

Further, all the TFTs incorporated in the TFT liquid crystal panel are driven, and uniform visible light is irradiated to all the pixels corresponding to the driven TFTs.

Further, the transmitted light intensity transmitted through the pixels belonging to the partial area of the TFT liquid crystal panel is individually measured for each pixel, and the voltage holding ratio of the pixel group belonging to the partial area is obtained based on the measured data. Things.

Further, the transmitted light intensity transmitted through the pixels belonging to the whole area of the TFT liquid crystal panel is individually measured for each pixel, and the voltage holding ratio of the pixel group belonging to the whole area is obtained based on the measured data. Things.

The transmitted light transmitted through the pixels is observed by an image sensor, and the transmitted light of the liquid crystal panel is measured by separating the pixels into pixels or groups of pixels based on the image data of the image sensor. is there.

Further, an average light intensity of transmitted light transmitted through the pixels belonging to the entire area of the TFT liquid crystal panel is measured.

Further, the voltage holding ratio measuring apparatus for a TFT liquid crystal panel according to the present invention comprises: an arbitrary waveform generator for driving a TFT of the TFT liquid crystal panel; a light source for irradiating the TFT liquid crystal panel with light; A voltage holding ratio measuring device for a TFT liquid crystal panel, comprising: an area image sensor for observing the intensity of transmitted light; and an information processing device having a storage device for controlling operations of the arbitrary waveform generator and the area image sensor. And the TFT
The time change of the transmitted light intensity of the liquid crystal panel at the time of driving the (thin film transistor) is measured based on the observation data by the area image sensor, and a voltage-transmittance characteristic curve is used.
The measured transmitted light intensity is converted into a voltage to obtain an attenuation value of the voltage with time change of the transmitted light intensity,
It has a function of calculating the voltage holding ratio of the liquid crystal panel.

Further, the observation data by the area image sensor is displayed on an oscilloscope as output waveform data, and the information processing apparatus receives the output waveform data output from the oscilloscope as an input, and uses a voltage-transmittance characteristic curve, Convert the measured transmitted light intensity to voltage,
An attenuation value of the voltage with the time change of the transmitted light intensity is obtained, and a voltage holding ratio of the TFT liquid crystal panel is calculated.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1 and FIG.
When a T (thin film transistor) is driven, a time change of the transmitted light intensity of the liquid crystal panel is measured, and the measured transmitted light intensity is converted into a voltage using a voltage-transmittance curve (FIG. 4) to obtain the transmitted light intensity. Decay value of the voltage with time change of
It is characterized in that a voltage holding ratio of an FT liquid crystal panel is obtained.

According to the present invention, in order to obtain information on the voltage holding ratio of a TFT liquid crystal display panel, the charging voltage after charging is performed between the pixel electrode and the common electrode corresponding to each pixel of the TFT liquid crystal display panel. It focuses on a change in transmitted light intensity of a TFT liquid crystal display panel due to attenuation.

That is, the charge between the pixel electrode corresponding to each pixel of the TFT liquid crystal display panel and the common electrode is usually TF
This is performed by driving T.

Since an applied voltage based on the driving of the TFT is applied between the pixel electrode and the common electrode to control the response of the liquid crystal, a voltage is applied between the pixel electrode and the common electrode of each pixel. Ideally, the charged charge voltage (holding voltage) is held until the next charge (recharge), but between the pixel electrode and the common electrode, and between the drain and the drain of the TFT.
If there is a leak between the sources, the charging voltage (holding voltage) of the liquid crystal layer attenuates with time.

As described above, since the response of the liquid crystal is controlled by the charging voltage, the response of the liquid crystal corresponds to the decay of the charging voltage, and corresponds to the decay of the charging voltage (holding voltage). Thus, the relationship that the intensity of light transmitted through each pixel changes is established.

On the other hand, the transmitted light intensity of the TFT liquid crystal panel is
It changes according to the magnitude of the applied voltage applied between the pixel electrode and the common electrode of each pixel. For example, in the case of a twisted nematic liquid crystal panel, which is a representative of the normally white mode, the light transmittance does not change from 0 volt to the threshold voltage value, and when the threshold voltage is exceeded, the light transmittance decreases rapidly. Voltage-transmittance characteristic (FIG. 4).

Therefore, utilizing the characteristic curve of the voltage-transmittance characteristic, the increase in the light transmittance of the TFT liquid crystal panel is determined by the charging voltage (holding voltage) charged between the pixel electrode corresponding to the pixel and the common electrode. , The change in the voltage held by the pixel, that is, the change in the charging voltage charged between the pixel electrode and the common electrode corresponding to the pixel can be observed.

Therefore, the light transmittance of the TFT liquid crystal panel immediately before the polarity of the applied voltage applied between the pixel electrode corresponding to the pixel and the common electrode is inverted, is converted into a voltage, and the voltage is applied to the applied voltage. By calculating the ratio, the voltage holding ratio of the TFT liquid crystal panel can be obtained.

Further, at the time of measurement, the amount of increase in the transmitted light intensity of the TFT liquid crystal panel depends on the amount of attenuation of the charging voltage charged between the pixel electrode corresponding to the pixel and the common electrode.
The longer the charging time interval, the larger the charging time interval.

Therefore, in order to detect a small difference in the voltage holding ratio of each pixel of the TFT liquid crystal panel, the charging time interval is lengthened to improve the sensitivity, that is, between the pixel electrode and the common electrode. It is desirable to drive the TFT controlling each pixel at a low frequency so that the interval between the applied pulse voltages can be widened.

As described above, in the TFT liquid crystal panel, in the pixel whose voltage holding ratio is deteriorated, the light transmittance changes due to the decay of the charging voltage charged between the pixel electrode and the common electrode. Becomes

Further, as the charging time interval is larger, the amount of attenuation of the charging voltage charged between the pixel electrode and the common electrode increases, so that the change in light transmittance of the TFT liquid crystal panel also increases.

Therefore, by driving the TFT of the TFT liquid crystal panel at a lower frequency than usual and measuring the change in the light transmittance of each pixel, the characteristic curve of the voltage-transmittance characteristic is used to calculate the light transmittance of each pixel. The charging voltage (holding voltage) can be known, and the voltage holding ratio of the TFT liquid crystal panel can be obtained.

Further, by using an area type image sensor such as a CCD camera, change data of light transmittance is obtained for each pixel of the TFT liquid crystal panel, and a voltage holding ratio for each pixel of the TFT liquid crystal panel is determined based on the data. By calculating, the distribution of the voltage holding ratio in the TFT liquid crystal panel can be recognized.

Next, the present invention will be described in detail with reference to specific examples.

(Embodiment 1)

FIGS. 1 and 2 are flowcharts illustrating a method for measuring a voltage holding ratio of a TFT liquid crystal panel according to an embodiment of the present invention, and FIG. 3 is a TF according to an embodiment of the present invention.
FIG. 2 is a configuration diagram illustrating a voltage holding ratio measuring device of a T liquid crystal panel.

FIG. 3 shows a TF according to an embodiment of the present invention.
The voltage holding ratio measuring device of the T liquid crystal panel includes a light source 31, apertures 32 and 33, a photodetector 35, an oscilloscope 38, an information processing device 39 such as a personal computer, a storage device 310, and an arbitrary waveform generator 36. And a DC power supply 37.

In FIG. 3, a light source 31 emits light to the TFT liquid crystal panel 34, and the light source 31
Light emitted from the TFT liquid crystal panel 34 is shaped by an aperture 32, focused on the entire surface or a partial area of the TFT liquid crystal panel 34 and irradiated on the TFT liquid crystal panel 34.
The light is transmitted through pixels of the liquid crystal panel 34.

The light transmitted through the pixels of the TFT liquid crystal panel 34 is shaped by the aperture 33 and
5 and the photodetector 35 is based on the optical data input through the aperture 33 and the TFT liquid crystal panel 34
The light intensity of the light transmitted through the pixel is detected.

The oscilloscope 38 includes a light detector 35
The observation data from is displayed as output waveform data.

The information processing device 39 receives the output waveform data output from the oscilloscope 38 and stores the output waveform data in a storage device 310, and reads out the stored output waveform data. hand,
Using the voltage-transmittance characteristic curve shown in FIG. 4, the measured transmitted light intensity is converted into a voltage, the attenuation value of the voltage with time change of the transmitted light intensity is obtained, and the voltage holding ratio of the TFT liquid crystal panel is obtained. Is calculated.

Accordingly, the light emitted from the light source 31 passes through the aperture 32, passes through the TFT liquid crystal panel 34, passes through the aperture 33, and further passes through the photodetector 35.
After the data is temporarily collected by the oscilloscope 38, the data is transferred to the information processing device 39 such as a personal computer.
The information is stored in the storage device 310 attached to the information processing device 39.

TFT incorporated in TFT liquid crystal panel 34
Voltage application to the gate and drain of the (thin film transistor) is performed by the arbitrary waveform generator 36, and the potential of the common electrode paired with the pixel electrode of the pixel is adjusted by the DC power supply 37.

TFT of the TFT incorporated in the liquid crystal panel,
Data of the drain voltage value and the gate voltage value with respect to time are accumulated in the oscilloscope 38 at the same time as the transmitted light intensity, and the data is transferred to the information processing device 39.

The arbitrary waveform generator 36 and the DC power supply 3
7. The operations of the photodetector 35 and the oscilloscope are controlled by the information processing device 39. Information processing device 39
Are stored in the storage device 310.

As the light source 31, a halogen lamp, a metal halide lamp, or a cold cathode tube can be used to irradiate a partial area or a whole area of several tens of square meters or more of the TFT liquid crystal panel. In the case of irradiating each pixel unit, a visible light laser can be used as the light source 31.

When the average light intensity of the visible light irradiated portion is measured, a general light detector capable of measuring the light intensity can be used as the light detector 35. When the transmitted light intensities in a plurality of partial regions are simultaneously measured, it is desirable to use an area image sensor such as a charge coupled device (CCD) solid-state imaging device.

When an area image sensor such as the CCD solid-state imaging device is used, detection light data for each pixel of the area image sensor or detection light data for each pixel in a group is collected by the information processing device 39 and processed. The Rukoto.

If necessary, the TFT liquid crystal panel 34
A lens system for converging light on one or both of the light source side and the photodetector 35 side or a lens system for obtaining parallel rays may be arranged.

In a test liquid crystal cell including one set of electrodes often used for material evaluation, a TFT liquid crystal panel 34
And a polarizing plate is provided between the liquid crystal cell and the light source 31 and between the liquid crystal cell and the photodetector 35, respectively. The driving voltage input to the TFT incorporated in the TFT liquid crystal panel is applied using an impedance converter.

In measuring the voltage holding ratio of the TFT liquid crystal panel according to the present invention, first, the processing of stage A shown in FIG. 1 is executed, and then the processing of stage B shown in FIG. 2 is executed. Done.

Of the above processing, the processing performed in stage A is as follows:
This is a preparatory process for performing the processing of stage B, which is a core part of the measurement method according to the present invention. Therefore, if the data obtained by the processing of stage A has already been obtained, The processing can be omitted.

The transmitted light intensity of the nematic liquid crystal display panel, which has conventionally been the mainstream, has the steepest voltage-transmittance characteristic curve showing the correlation between the applied voltage and the transmittance, that is, the holding voltage in the vicinity of the halftone voltage. It is susceptible to attenuation.

Therefore, when it is desired to detect a slight voltage decay in the charging voltage (holding voltage) held between the pixel electrode corresponding to the pixel of the TFT liquid crystal panel and the common electrode, T
It is preferable in terms of measurement efficiency that the voltage applied to the FT liquid crystal display panel be determined as a steep region of the voltage-transmittance characteristic curve, that is, a halftone voltage.

In the case of the normally white mode, the TFT
FIG. 4 shows a voltage-transmittance characteristic curve showing the correlation between the transmitted light intensity of the liquid crystal display panel and the applied voltage. That is, FIG.
As shown in the graph, the voltage-transmittance characteristic curve Q1 shows that the transmittance shown on the vertical axis is almost constant when the applied voltage of the TFT liquid crystal panel shown on the horizontal axis is about 2V, and when the applied voltage exceeds about 2V, the transmittance becomes higher. The transmittance shows a characteristic that the transmittance sharply decreases and the transmittance gradually decreases when the applied voltage passes about 4 V.

For example, a TFT liquid crystal panel has a voltage-transmittance characteristic curve Q1 shown in FIG.
When a TFT incorporated in a liquid crystal panel is driven by a low-frequency voltage of 1 Hertz, a voltage holding ratio of a holding voltage (charging voltage) held between a pixel electrode corresponding to a pixel of the TFT liquid crystal panel and a common electrode is increased. When a change in transmittance is measured by applying a voltage of 5 volts to a 96% TFT liquid crystal panel, the value of the held voltage is 4.8 volts.
The difference from when 5 volts is applied is only about 0.5%.

However, when the voltage applied to the TFT liquid crystal panel is changed to 3 volts, the holding voltage held between the pixel electrode corresponding to the pixel of the TFT liquid crystal panel and the common electrode is 2.88 volts. The attenuation of the holding voltage when the applied voltage is changed is small, but the difference in transmittance corresponding to the attenuation of the holding voltage is about 8%, which is a sufficiently detectable numerical value.

In FIG. 4, V10 represents a voltage applied to the TFT when the transmittance in the initial state where no voltage is applied to the TFT incorporated in the TFT liquid crystal panel changes by 10%, and V90 represents The figure shows the voltage applied to the TFT when the transmittance in the initial state where no voltage is applied to the TFT incorporated in the TFT liquid crystal panel changes by 90%, and is applied to the TFT incorporated in the TFT liquid crystal panel in the present invention. It is desirable that the magnitude of the applied voltage be set in a range between V10 and V90 where the transmittance changes sharply.

Therefore, at the stage A shown in FIG. 1, the voltage-transmittance curve shown in FIG. 4 which is a characteristic of the TFT liquid crystal panel to be measured is measured, and the TFT liquid crystal panel is changed in a range where the transmittance changes sharply. The voltage value of the applied voltage to the TFT which is optimal for measuring the voltage holding ratio of the TFT is determined.

That is, in step S101 shown in FIG. 1, a measurement start voltage corresponding to V10 in FIG. 4 is designated, and in step S102, the alternating voltage at the designated voltage is generated in the TFT of the TFT liquid crystal panel as an arbitrary waveform. And the transmittance of the TFT liquid crystal panel at that time is detected by the photodetector 35.

The data detected by the photodetector 35 is a TFT
Is applied to the oscilloscope 38 together with the applied voltage, and is transferred to the information processing device 39.

Subsequently, in step S103, the TFT
It is checked whether or not the applied voltage to be applied has reached the scheduled measurement end voltage corresponding to V90 in FIG. 4. If the measurement end voltage has not been reached, the process proceeds to step S104.
The applied voltage applied to the FT is increased by one unit, and step S
It returns to the process of 102.

As a result, if the voltage applied to the TFT has reached the measurement end voltage, the process proceeds to step S105,
A voltage-transmittance characteristic curve Q1 is obtained from a relationship between a change in an applied voltage applied to the TFT and a change in light transmittance corresponding to the voltage change, and the voltage-transmittance characteristic curve Q1 is applied to the TFT using the voltage-transmittance characteristic curve Q1. The voltage values of the measurement start voltage and the measurement end voltage for performing the measurement are determined, and the process is terminated.

The method of applying the alternating voltage used here is T
In order to eliminate the influence of the FT characteristics, a DC voltage was applied to the gate of the TFT and the
It is desirable to input a rectangular wave voltage of Hertz or more to the drain of the TFT.

Further, in the processing shown in FIG.
The case where the voltage-transmittance characteristic curve possessed by the TFT liquid crystal panel as a characteristic is measured by applying the voltage to the FT has been described. However, the present invention is not limited to this case. The voltage-transmittance characteristic curve may be measured in a state in which is input to the drain of the TFT. In that case, the processing in FIG. 1 does not require the processing in steps S101, S103, and S104.

Next, in the stage B shown in FIG. 2, the TFT of the TFT liquid crystal panel is driven by a low frequency voltage, and the change in the transmittance of the TFT liquid crystal panel is measured. The voltage holding ratio of the holding voltage held between the electrodes is measured.

That is, in step S201 shown in FIG. 2, a gate signal and a drain signal are output from the arbitrary waveform generator 36 to the gate and the drain of the TFT of the TFT liquid crystal panel, respectively, so that the pixel electrode and the pixel electrode corresponding to the pixel of the TFT liquid crystal panel are Is adjusted by the DC power supply 37.

FIG. 5A shows a gate signal input to the gate of the TFT of the TFT liquid crystal panel.
5B shows a drain signal input to the drain of the TFT of the TFT liquid crystal panel, and FIG. 5C shows the potential of the common electrode. By setting the signal shown in FIG. The display state of the area selected for measuring the voltage holding ratio of the TFT liquid crystal panel is made the same.

For example, if the TFT gate ON time is set to 10
When the gate OFF time is set to about 500 milliseconds and a voltage near the halftone voltage is applied to the drain, the portion where the voltage holding ratio of the TFT liquid crystal panel is deteriorated is applied to the pixel. As shown in FIG. 6B, the holding voltage held between the corresponding pixel electrode and the common electrode changes like a gradually decreasing / gradual increasing waveform according to the polarity of the applied voltage (alternating voltage) to the TFT. The transmittance of the liquid crystal panel changes like a sawtooth waveform as shown in FIG.

In step S202, it is determined whether or not the transmittance of the TFT liquid crystal panel has changed as shown in FIG.

If it is determined that there is a change in transmittance, the process proceeds to the next step S204. On the other hand, if it is determined that there is no change in the transmittance, the process proceeds to step S203, and the frequency of the voltage applied to the TFT is reduced to 1/10, and the measurement is performed again.

Normally, even if the frequency of the voltage applied to the TFT is reduced from 1 Hertz to about 0.1 Hertz, the TF
If no change in the transmittance of the T liquid crystal panel is detected, the measurement may be terminated. However, in the case of performing a more severe evaluation, the frequency of the voltage applied to the TFT is reduced to 0.01 Hz or less. May be performed.

Next, in step S204, FIG.
As shown in (a), the transmittance T immediately before the polarity of the applied voltage applied to the TFT is inverted is obtained. This transmittance T is shown in FIG.
6C, which corresponds to the transmittance when the transmittance changes sharply.

Next, in step S205, the transmittance T obtained in step S204 is converted to a voltage (FIG. 6 (c)) corresponding to the transmittance T using the voltage-transmittance characteristic curve shown in FIG. ) Converts to about 2.4). The converted voltage is obtained as a holding voltage held between the pixel electrode corresponding to the pixel and the common electrode.

Next, in step S206, the ratio of the holding voltage obtained in step S206 to the voltage applied to the TFT is calculated, whereby the TFT
Find the voltage holding ratio of the liquid crystal panel.

The above measurement may be performed either in a unit of a partial area set on a part of the TFT liquid crystal panel or in a unit of the entire area set on the entire surface of the TFT liquid crystal panel.

In the above description, a liquid crystal cell corresponding to a pixel of a TFT liquid crystal panel is referred to as a TFT (thin film transistor).
However, when a TFT liquid crystal panel is driven by a TFT, a pseudo TFT driving method shown in FIG. 7 may be used, and this driving method is also included in the TFT driving method. .

The pseudo TFT driving method shown in FIG. 7 will be described. In the case where a single pixel liquid crystal cell is operated as a pseudo TFT,
As shown in FIG. 7A, a circuit configuration including a waveform generator 71, an impedance converter 72, and a liquid crystal cell 73 corresponding to a unit pixel of a TFT liquid crystal panel is constructed. Then, a voltage pulse having a waveform shown in FIG. 7B is generated from the waveform generator 71, and based on the voltage pulse, the impedance converter 72 performs an operation of alternately repeating a high impedance state and a low impedance state, thereby forming a thin film transistor (TF).
The above measurement is performed by applying voltage pulses having different polarities at a constant period to the liquid crystal cell 73 as shown in FIG.

As described above, according to the embodiment of the present invention,
The voltage holding ratio of a TFT liquid crystal panel as an actual product is measured, and the in-plane distribution of the voltage holding ratio can be grasped based on the data.

Next, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1 In Example 1 of the present invention, a simple cell in which a nematic liquid crystal was twist-aligned was used.
The voltage holding ratio of the TFT liquid crystal panel measured using the present invention is compared with the voltage holding ratio of the TFT liquid crystal panel measured using the electric method according to the conventional example, and the validity of the measuring method according to the present invention is explained. I do.

The liquid crystal cell used in Embodiment 1 of the present invention is shown in FIG.
As shown in (a) and (b), an indium tin oxide (ITO) film is formed on a 3 cm × 4 cm glass substrate 81 made of Corning 7059.
A pixel electrode 82 of centimeter X1 centimeter is formed at the center, and an extraction electrode 83 is formed from the pixel electrode 82 to the periphery of the substrate.

After forming the electrode, polyamic acid was spin-coated and calcined at 90 ° C. for 30 minutes.
The main baking is performed at 00 ° C. for one hour to form a polyimide alignment film 84.

In order to assemble one liquid crystal cell,
Two substrates 81 with the alignment film are required. Poly (4,4′-oxydiphenylene pyromellitic acid) was used as the polyamic acid. The thickness of the polyimide alignment film 84 measured by a reflection ellipsometer was 78 nm to 82 nm.

The rubbing was performed once using a rayon roll under the conditions of a rotation speed of 800 rotations / min, an indentation of 0.6 mm, and a stage speed of 20 mm / s.

After the rubbing, the two glass substrates 81 are overlapped so that the respective rubbing directions are 90 °.
It was fixed with an epoxy adhesive 85 mixed with spacer particles having a diameter of 5 micrometers. No cleaning after rubbing was performed. This cell contains a fluorine-based nematic liquid crystal 8
Inject 6 into the isotropic phase and seal with UV curable resin.
A 0 ° twist cell was used. Although not shown,
A light-shielding film is formed on the glass substrate except for the pixel electrodes.

The thus formed liquid crystal cell shown in FIG. 8 is measured by using the measuring device shown in FIG. 3, and as shown in FIG. 9, the space between the liquid crystal cell 90 and the aperture 32 and the liquid crystal cell 90 The polarizers 91 and 92 are provided between the apertures 33, respectively. FIG. 10 shows the relationship between the rubbing directions of the polarizers 91 and 92 and the alignment film 84 at this time. In the figure, the polarization directions of polarizers 91 and 92 are indicated by arrows 101 and 10 respectively.
The rubbing direction of the polyimide alignment film 84 is indicated by arrows 103 and 104.

As shown in FIG. 10, the polarization directions of the polarizers 91 and 92 are orthogonal to each other, and the polarization directions are parallel to the rubbing direction.

That is, the rubbing direction 10 of the incident side substrate
3 is parallel to the polarization direction 101 of the polarizer 91,
The rubbing direction 104 of the emission side substrate is parallel to the polarization direction 102 of the polarizer 92, and the rubbing direction of both substrates and the polarization direction of the polarizer are perpendicular.

A plurality of liquid crystal cells are prepared as described above, the ion density is determined from the response current when a triangular wave voltage is applied, and those for which the ion current cannot be confirmed are used as reference for measuring the voltage-transmittance characteristic curve. A liquid crystal cell in which an ionic current is recognized is used as a liquid crystal cell to be measured.

First, the voltage-transmittance characteristic curve of the reference liquid crystal cell is measured by the processing of the stage A shown in FIG.

That is, using the measuring device shown in FIG.
0 Hz square wave voltage from 0 volts to ± 5 volts.
The reference liquid crystal cell is driven by increasing the voltage in units of 05 volts and applying the voltage to the TFT using the arbitrary waveform generator 36, and the transmitted light intensity transmitted through the reference liquid crystal cell for each voltage value is measured. In this case, the light from the light source 31 is applied to a part of the surface of the reference liquid crystal cell using an aperture 32 having a diameter of 5 mm, so that the intensity of the transmitted light passing through the reference liquid crystal cell is detected by the photodetector 35. It was measured. The transmitted light intensity data detected by the photodetector 35 and the data of the applied voltage were recorded in the storage device 310 in association with each other.

Thereafter, the information processing device 39 is made to perform arithmetic processing based on the program stored in the storage device 310, and based on the transmitted light intensity data detected by the photodetector 35 and the data of the applied voltage, The transmitted light intensity at the time of applying 0 volt was set to 100%, and the transmitted light intensity at the time of applying ± 5 volts was set to 0%, and the transmitted light intensity was converted into transmittance. FIG. 11 shows a voltage-transmittance characteristic curve obtained as a result.

The applied voltage value for measuring the voltage holding ratio of the liquid crystal cell was determined to be ± 3 volts from the voltage-transmittance characteristic curve shown in FIG.

[0097] Five test liquid crystal cells to be tested were prepared in this example, and their voltage holding ratios were measured by the present invention and the conventional electrical method. The measurement voltage has already been determined to be 3 volts.

A ± 3 volt, 1 Hz rectangular wave voltage is input from one output channel of the arbitrary waveform generator to the impedance converter, and a pulse width of 100 microseconds, a pulse interval of 499.9 milliseconds, 5 The pseudo TFT driving was performed by inputting a pulse voltage of volt to the impedance converter as a control signal. The change in transmittance and the change in holding voltage in this state were measured simultaneously, and the voltage holding ratio obtained from the transmittance and the voltage holding ratio obtained from the holding voltage were compared.

FIG. 1 shows an example of the measured transmittance and holding voltage.
It is shown in FIG. In the case of FIG. 12, the holding voltage obtained from the voltage-transmittance characteristic curve of FIG. 11 was 2.202 volts, and the voltage holding ratio was 73.4%. The holding voltage measured directly was 2.183 V, and the voltage holding ratio was 72.8%.

(Evaluation) Table 1 shows the results of comparing the holding voltage and the voltage holding ratio obtained in the present invention with the values measured by the conventional method. Although there are some differences, the results of the two agree well, indicating that the present invention is effective for measuring the voltage holding ratio.

[0101]

[Table 1]

(Example 2) In this example, the voltage holding ratio of a TFT liquid crystal panel which is driven and controlled by a TFT (thin film transistor) to perform monochrome display was measured.

As shown in FIG. 13, a portion of the TFT liquid crystal panel which is connected to the gate G and the drain D of the TFT is partially connected, and a region where the drain line and the gate line intersect is about 1 cm × 1 cm. Two measurement points 1 and 2 having a meter area were set. The area where the transmitted light intensity was actually measured among these 1 cm squares was set to an area within a circle having a diameter of 5 mm using a mask.

First, a voltage-transmittance characteristic curve was measured. A DC voltage of 20 volts was applied to the gate line to keep the TFT in the ON state, and a triangular wave voltage was applied to the drain line to measure the intensity of transmitted light passing through the liquid crystal cell. The measurement area is measurement point 1 in FIG. The triangular wave voltage was ± 5 volts and the frequency was 0.1 hertz. The transmitted light intensity is defined as 100% when the applied voltage is -0.2 volt to 0.2 volt, and the transmitted light intensity for 4.8 volt to 5 volt and the transmitted light for -4.8 volt to -5 volt. The intensity was converted to transmittance with 0%. The result is shown in FIG.

Next, the COM potential is 4 volts, the gate pulse voltage is 20 volts, the width is 100 microseconds, and the interval is 4 volts.
At 99.9 milliseconds, the drain voltage was set to ± 2 V, and the transmittance change at the measurement points 1 and 2 was measured.

FIG. 15A shows the measurement result at the measurement point 1, and FIG. 15B shows the measurement result at the measurement point 2. The transmittance immediately before the inversion of the polarity of the drain voltage is 61.9% at the measurement point 1, the holding voltage obtained from the voltage-transmittance characteristic curve in FIG. 14 is 1.904 volts, and the voltage holding ratio is 95. 2%. The transmittance at measurement point 2 is 6
1.3%, the holding voltage was 1.910 volts, and the voltage holding ratio was 95.5%.

(Embodiment 3) In this embodiment, a black-and-white TF driven and controlled by a thin film transistor (TFT) is used.
The voltage holding ratio of a display abnormal part and a normal part in the T liquid crystal display panel was measured. As shown in FIG. 16, the measurement place 3 of the display abnormal part and the measurement place 4 of the normal part are driven,
The terminal of the gate G and the terminal of the drain D were partially connected. The driving region is approximately one part where the drain line and the gate line cross.
It is an area of centimeter x 1 centimeter.

The area where the transmitted light intensity was actually measured in these 1 cm squares was within a circle having a diameter of 5 mm using the mask shown in FIG.

A 30 Hz rectangular wave was used for the measurement of the voltage-transmittance curve. A DC voltage of 20 volts is applied to the gate line so that the TFT is always turned on, and a 30-Hz rectangular wave voltage of 0.05 to 5 volts is applied to the drain from 0 volts to 5 volts.
The transmitted light intensity was measured by applying a voltage in volt steps. The measurement point of the voltage-transmittance curve is the measurement point 4 in FIG. 16 which is a normal display part. The transmitted light intensity was converted to transmittance by setting 100% when the applied voltage was from 0 volt to 0.2 volt, and setting the transmitted light intensity for 4.8 to 5 volt to be 0%.

Next, the COM potential is 4 volts, the gate pulse voltage is 20 volts, the width is 100 microseconds, and the interval is 4 volts.
99.9 milliseconds, the drain voltage was set to ± 2.2 V, and the change in transmittance at the measurement points 3 and 4 was measured. The holding voltage obtained from the transmittance immediately before the polarity of the drain voltage was inverted was 1.714 volts at the measuring point 3 and the holding voltage was
Was 2.116 volts. The respective voltage holding ratios were 77.9% at the measurement point 3 and 96.2 at the measurement point 4.
%Met.

(Embodiment 4) In this embodiment, a black and white TF controlled by a TFT (thin film transistor) is controlled.
The T liquid crystal display panel was driven in the same state on the entire surface, and the distribution of the voltage holding ratio in the panel surface was measured.

As shown in FIG. 17, the XY stage 17
4, the measurement position was changed by moving the liquid crystal panel 170, and the in-plane distribution of the voltage holding ratio was measured. As the liquid crystal display panel 170 to be measured, a liquid crystal display panel in which polarizing plates 172 and 173 are attached to a liquid crystal cell 171 is used.

When a polarizing plate is not attached, a polarizer is provided between the liquid crystal cell and the aperture. Light source 17
A halogen lamp is used for 7, and the intensity of transmitted light within a circle having a diameter of 5 mm is measured by the photodetector 178 by the aperture 175 on the entrance side and the aperture 176 on the exit side.

The gate terminal and the drain terminal of the liquid crystal display panel 170 were all connected, and the entire surface of the liquid crystal panel was driven under the same conditions. The gate voltage signal and the drain voltage signal input to the liquid crystal are output from an arbitrary waveform generator. The current is amplified by a power amplifier and then input to each terminal of the liquid crystal panel. A 30 Hz rectangular wave was used for measuring the voltage-transmittance characteristic curve.

A DC voltage of 20 volts is applied to the gate G so that the TFT is always turned on, and a 30 Hz rectangular wave voltage of 0.05 to 5 volts is applied to the drain D from 0 volts to 5 volts.
The transmitted light intensity was measured by applying a voltage in volt steps.

The measurement point of the voltage-transmittance characteristic curve is shown in FIG.
2 were measured and averaged at two points indicated by F and G near the center of the liquid crystal panel. The transmitted light intensity is defined as 100% when the applied voltage is from 0 volt to 0.2 volt, and 4.8.
And the transmittance was converted to transmittance with the transmitted light intensity for 5 volts being 0%.

The COM potential is 4 volts, the gate pulse voltage is 20 volts, the width is 100 microseconds, and the interval is 499.
FIG. 18 shows A for 9 milliseconds and a drain voltage of ± 2.1 V.
The transmittance was measured at twelve portions indicated by L, and the voltage holding ratio of each portion was determined. Table 2 shows the results.

[0118]

[Table 2]

(Embodiment 5) In this embodiment, a black-and-white display TF driven and controlled by a thin film transistor (TFT) is used.
The T liquid crystal display panel is driven in the same state on the entire surface, and the CCD
Using a detector, the distribution of the voltage holding ratio in the panel plane was measured simultaneously. The liquid crystal panel measured in Example 3 was used.

As shown in FIG. 19, the configuration of the measuring apparatus is different from the apparatus shown in FIG. 3 only in the optical system, and the configuration of the apparatus other than the optical system is provided between the arbitrary waveform generator and the liquid crystal panel. It was the same as FIG. 3 except that a power amplifier was used.

The liquid crystal display panel 190 to be measured has polarizing plates 192 and 193 on the liquid crystal cell 191 as in the above embodiment.
Is used. A halogen lamp was used as the light source 197, and the light was converted into a parallel light by the lens 194 on the incident side, and was irradiated on a part or the entire surface of the liquid crystal display panel 190. The light was condensed again by the exit lens 195 and detected by the CCD detector 196.

The gate terminal and the drain terminal of the liquid crystal display panel 190 were all connected to each other, and the entire surface of the liquid crystal panel was driven under the same conditions. The gate voltage signal and the drain voltage signal input to the liquid crystal are output from an arbitrary waveform generator. The current is amplified by a power amplifier and then input to each terminal of the liquid crystal panel. The voltage-transmittance curve used in Example 3 was used.

The COM potential is 4 volts, the gate pulse voltage is 20 volts, the width is 100 microseconds, and the interval is 499.
The liquid crystal panel was driven at a drain voltage of ± 2.2 V for 9 milliseconds, and a change in transmittance was measured. CCD detector 1
The transmittance information detected by 96 is subjected to data processing by averaging for each area when the vertical and horizontal directions of the liquid crystal display panel are divided into ten, and calculating a voltage holding ratio of a total of 100 areas as shown in FIG. did.

FIG. 20 shows the distribution of the voltage holding ratio in the liquid crystal panel in 5% steps. In a region where a display abnormality has been confirmed, a distribution in which the voltage holding ratio is low appears, and a good match with the display state of the liquid crystal panel is recognized.

[0125]

As described above, according to the present invention, the voltage holding ratio is measured by detecting the change in the transmittance accompanying the holding voltage attenuation of the liquid crystal panel, so that the voltage holding ratio in the panel can be known. .

Further, since the distribution of the voltage holding ratio in the panel surface and the voltage holding ratio in the local area can be known, it is possible to provide an effective means for analyzing the operation / failure of the liquid crystal panel.

Further, since the time from the occurrence of the problem to the acquisition of the voltage holding ratio information in the liquid crystal is short, the industrial utility value is extremely large.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for measuring a voltage holding ratio of a TFT liquid crystal panel according to an embodiment and an example of the present invention.

FIG. 2 is a flowchart illustrating a method for measuring a voltage holding ratio of a TFT liquid crystal panel according to embodiments and examples of the present invention.

FIG. 3 is a configuration diagram showing a voltage holding ratio measuring device of a TFT liquid crystal panel according to embodiments and examples of the present invention.

FIG. 4 is a characteristic diagram for explaining the embodiment of the present invention.

FIG. 5 is a voltage waveform diagram for explaining the embodiment of the present invention.

FIG. 6 is a waveform chart for explaining the embodiment of the present invention.

FIG. 7A is a circuit diagram for explaining an embodiment of the present invention, and FIGS. 7B and 7C are voltage waveform diagrams.

FIG. 8A is a pattern diagram for explaining Example 1 of the present invention, and FIG. 8B is a sectional view of the same.

FIG. 9 is an optical system configuration diagram of an apparatus for explaining Embodiment 1 of the present invention.

FIG. 10 is a layout diagram of a polarizing plate for explaining Embodiment 1 of the present invention.

FIG. 11 is a characteristic diagram for explaining Example 1 of the present invention.

FIG. 12 is a waveform chart for explaining the first embodiment of the present invention.

FIG. 13 is a configuration diagram of a liquid crystal panel for explaining a second embodiment of the present invention.

FIG. 14 is a characteristic diagram for explaining Example 2 of the present invention.

FIG. 15 is a waveform chart for explaining Example 2 of the present invention.

FIG. 16 is a configuration diagram of a liquid crystal panel for explaining a third embodiment of the present invention.

FIG. 17 is a configuration diagram of a measuring apparatus for explaining Embodiment 4 of the present invention.

FIG. 18 is a diagram showing measurement points for explaining Embodiment 4 of the present invention.

FIG. 19 is an optical system configuration diagram of an apparatus for explaining Embodiment 5 of the present invention.

FIG. 20 is a voltage holding ratio distribution diagram for explaining Example 5 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 31 Light source 32, 33 Polarizer 34 Liquid crystal cell 35 Photodetector 36 Arbitrary waveform generator 37 DC power supply 38 Oscilloscope 39 Information processing device 310 Storage device

Claims (12)

[Claims] 1. A method for measuring a change in transmitted light intensity over time during driving of a TFT (thin film transistor), converting the measured transmitted light intensity into a voltage using a voltage-transmittance characteristic curve, A voltage holding ratio measuring method for a TFT liquid crystal panel, wherein a voltage holding ratio of a TFT liquid crystal panel is obtained by obtaining a decay value of the voltage with time change of light intensity. 2. A voltage is applied to the TF so that light transmittance is in a range of 10% to 90% in a voltage-transmittance characteristic curve.
2. The voltage holding ratio measuring method according to claim 1, wherein the voltage is applied to a drain of T. 3. The voltage holding ratio measurement of a TFT liquid crystal panel according to claim 1, wherein the TFT is driven at a low frequency in order to detect a minute change in the light transmittance based on the attenuation of the voltage. Method. 4. The TFT according to claim 1, wherein a part of the TFTs incorporated in the TFT liquid crystal panel is driven, and uniform visible light is applied to pixels corresponding to the driven TFTs. Method for measuring voltage holding ratio of TFT liquid crystal panel. 5. The method according to claim 1, wherein all of the TFTs incorporated in the TFT liquid crystal panel are driven, and uniform visible light is applied to partial pixels corresponding to the driven TFTs. The method for measuring a voltage holding ratio of a TFT liquid crystal panel described in the above. 6. The liquid crystal display according to claim 1, wherein all the TFTs incorporated in the TFT liquid crystal panel are driven, and uniform visible light is applied to all the pixels corresponding to the driven TFTs. Method for measuring voltage holding ratio of TFT liquid crystal panel. 7. A transmission light intensity transmitted through the pixels belonging to a partial area of the TFT liquid crystal panel is individually measured for each pixel, and a voltage holding ratio of a pixel group belonging to the partial area is measured based on the measured data. 7. The method for measuring a voltage holding ratio of a liquid crystal panel according to claim 1, wherein the voltage holding ratio is obtained. 8. The intensity of transmitted light transmitted through the pixels belonging to the whole area of the TFT liquid crystal panel is individually measured for each pixel, and the voltage holding ratio of the pixel group belonging to the whole area is measured based on the measurement data. 7. The method for measuring a voltage holding ratio of a liquid crystal panel according to claim 1, wherein the voltage holding ratio is obtained. 9. Observing the transmitted light transmitted through the pixel by an image sensor, and measuring the transmitted light of the liquid crystal panel by separating the pixel into pixels or groups of pixels based on image data of the image sensor. The method for measuring a voltage holding ratio of a liquid crystal panel according to claim 7 or 8, wherein: 10. The voltage holding of the liquid crystal panel according to claim 1, wherein an average light intensity of transmitted light transmitted through the pixels belonging to the entire area of the TFT liquid crystal panel is measured. Rate measurement method. 11. An arbitrary waveform generator for driving a TFT of a TFT liquid crystal panel, a light source for irradiating light to the TFT liquid crystal panel, an area image sensor for observing an intensity of light transmitted through the TFT liquid crystal panel, Governs the operation of the arbitrary waveform generator and the area image sensor,
What is claimed is: 1. A voltage holding ratio measuring device for a TFT liquid crystal panel, comprising: an information processing device having a storage device; Using a voltage-transmittance characteristic curve, the measured transmitted light intensity is converted into a voltage,
A voltage holding ratio measuring device for a TFT liquid crystal panel, having a function of calculating a voltage holding ratio of the TFT liquid crystal panel by obtaining an attenuation value of the voltage with a time change of the transmitted light intensity. 12. An oscilloscope displays data observed by the area image sensor as output waveform data, and the information processing apparatus receives the output waveform data output from the oscilloscope as an input, and uses a voltage-transmittance characteristic curve. Converting the measured transmitted light intensity into a voltage, and obtaining an attenuation value of the voltage with time change of the transmitted light intensity,
11. The apparatus for measuring a voltage holding ratio of a liquid crystal panel according to claim 10, wherein the device calculates a voltage holding ratio of a TFT liquid crystal panel.