RF sputtering deposited a-IGZO films for LCD alignment layer application

In this paper, amorphous indium gallium zinc oxide (a-IGZO) inorganic films were deposited at a fixed oblique angle using radio-frequency sputtering on indium tin oxide (ITO) glass as alternative alignment layer for liquid crystal displays. A series of experiments have been carried out to reveal the physical characteristics of the a-IGZO films, such as optical transmittance, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The special treatment a-IGZO films were used to fabricate liquid crystal (LC) cells and investigate the performances of these cells. Pretilt angles were measured with anti-parallel LC cells and voltage-transmittance (V-T) curve, contrast ratio, and response time were evaluated with optically compensated bend (OCB) LC cells. The electro-optical characteristics of the aligned homogenous LCs, and OCB mode cells based on the a-IGZO alignment layer were compared to those based on rubbing processed polyimide (PI). The results showed that the average transmittance in the visible wavelength range was higher than 90% for the a-IGZO alignment layer. The LC pretilt angle has been determined at about 6°. The evaluted cell critical voltage at maximum transmittance was 1.8 V, lower than the control cell using PI alignment layer. The OCB cell rise time and fall time were 1.55 ms and 3.49 ms, respectivly. A very quick response time of 5.04 ms has thus been achived. In addition, the study of V-T characteristics suggested higher contrast ratio for LCD display applications.