LC Material Characteristics Measurement System Model 6254 Application Note #001
Introduction
It is known that one of the causes of the LCD display failure is adverse effects of impurity ion 1) 2). However, there are various kinds of display failures, such as image persistence, flicker, and chrominance non-uniformity (mura). Therefore, it cannot always be said that all display failures are caused by the impurity ion. Use of LC Material Characteristics Measurement System Model 6254 developed by TOYO Corporation makes it possible to measure the ion density used to quantify the impurity ion in the test panel, the voltage holding ratio used to check whether or not the materials can be used for the TFT drive, and the residual DC voltage used to measure the DC voltage inside the test panel. Therefore, this LC Material Characteristics Measurement System Model 6254 is useful to analyze the display failures described above. In the experiment described below, the LC test panels having different alignment layers are measured using this Model 6254, and then the correlation among the voltage holding ratio, ion density, and residual DC is investigated.
Measurement
Samples used for measurement
LC test panels having different alignment layer types, 7 pcs.
Measurement conditions
Measurement of voltage holding ratio
Applied pulse: 60μsec.
Frame period: 16.67msec.
Applied voltage: ±5V
Measurement of ion density
Frequency: 0.01Hz
Voltage: ±10V
Measurement of residual DC voltage
Stress: 10V DC voltage applied for 1 hr.
Discharge: 1 sec.
Measurement: 10 min.
Measurement temperature
60°C
Consideration
Figures 1, 2, and 3 show the measured results of the voltage holding ratio, ion density, and residual DC voltage, respectively.
 Figure 1 Measurement of voltage holding ratio  Figure 2 Measurement of ion density  Figure 3 Measurement of residual DC voltage |
When checking the measured results of the voltage holding ratio shown in Figure 1, it is understood that the voltage holding ratio of the sample of channel 7 (brown) is high (holding ratio by area ratio: 99.14%). When checking the ion density of this sample (Figure 2), the ion volume of this sample shows the least data (pink) among seven samples. The peak area at the center of the data corresponds to the ion volume. According to these, it is understood that there is a correlation between the voltage holding ratio and ion density. Subsequently, when checking the measured results of the residual DC voltage shown in Figure 3, the sample of channel 7 shows the largest residual DC voltage (brown). According to this, it is not always said that there is a correlation between the holding ratio or ion density, and the residual DC voltage. In this experiment, it is understood that the alignment layer of the sample connected to channel 7 is made of materials, which produce less impurity ion when compared to the alignment layer of other samples. However, since the residual DC voltage of this test panel is very large, it is thought that flickers may occur 3). The cause of the residual DC voltage generation is changed by not only large or small volume of impurity ion but also by a combination of the liquid crystal and alignment layer 4). Thus, it is absolutely necessary to know the material characteristic values (dielectric constant and specific resistance) of each material. References1）
Inoue, Nakanowatari;
Lecture preliminary
report for 21st Japanese Liquid Crystal Society Forum, 3B19 (1995) |
