We investigated the abnormal degradation of high-voltage p-type MOSFET (HV pMOSFET) under negative AC gate bias stress. In HV pMOSFET with n+ polycrystalline silicon (poly-Si) gate, the abnormal degradation occurs after the gradual degradation during negative AC stress. The abnormal degradation is suppressed by changing the gate material from n+ poly-Si to p+ poly-Si, and it is caused by hot holes produced by the impact ionization near the surface when electrons move from the gate toward the gate oxide. We suggest a possible mechanism to explain the improvement of degradation by using p+ poly-Si as a gate material.

The distortion of electric field and abnormal light transmission characteristics due to foreign particles were studied in IPS and TN mode TFT LCD. The dielectric and ionic particles with varying sizes were considered for the simulation according to their electric characteristics. The simulation shows that the foreign particle introduced into a pixel changes the electric fields within a pixel and affects the light transmission characteristics of the pixel. In both TN and IPS mode TFT LCD, the presence of the ionic particle affects the light transmittance a great deal.