A microlens array type of liquid crystal cell is prepared by arranging a great number of homeotropic-aligned liquid crystal microlenses randomly in a cell. Light scattering properties are measured for various wavelength of incident light, and a possibility of application to a new type of liquid crystal optical device without polarizers is investigated.
Dynamic measurements on leakage current of an amorphous silicon thin film transistor (TFT) under gate side illumination have been achieved. The samples used in the experiment were inverted staggered type amorphous silicon TFTs. The measured dynamic leakage current was different from that obtained by static measurement. The off current flowed with the delay time for up to 10 msec after the channel turned off-state and reached saturation. Rise time, which was the increasing point of off leakage current, depended on gate pulse width of on state, illumination intensity, and gate voltage level of off state. the rise time was larger than frame time of TFT-LCD. Therefore, the actual off leakage current of TFT under LCD operation is lower than that for static characteristics.
A computer simulation program has been developed in order to analyze the electro-optical properties of TFT-LCD more precisely by modifying SPICE. It contains a device model of amorphous silicon TFT with distribution of band-gap states, in which dynamic behavior is described as well as static one, and then transient anaslysis of TFT-LCD panel circuit has been done. The level shift caused by parasitic component between gate and source electrodes can be calculated numerically, and it predicts well the data voltage dependence of the level shift. The calculation of transmittance of LCD was based on the Berreman 4 × 4 matrix.
We examined the switching characteristics of amorphous silicon thin-film transistors by a large area ion doping technique without mass-separation. The off-current of the ion-doped TFTs was reduced by increasing the acceleration voltages of the ion doping. Under illumination, the photo-current of the ion-doped TFTs was 1〜2-figures lower than that of the conventional P-CVD deposition-doped TFTs. We believe that the ion-doped TFTs can be well applied to the switching elements of liquid crystal displays.
We have studied the fabrication of hydrogenated amorphous silicon(a-Si : H) thin film transistors by ramots-plasma chemical vapour deposition(RP-CVD). The effects of rf power, buffer layer between the gate insulator and a-Si : H, ohmic contact, and the surface oxidation on the performances on the a-Si : H TFT's have been investigated. As a result of the optimization of preparation conditions, we have made a TFT with a mobility of 1.2 cm^2/Vs, threshold voltage of 2.0V, and on/off current ratio of >10^6.