It has been revealed that ion bombardment energy and ion flux density play an essentially critical role in SiNx deposition process of PECVD in TFT-LCD production. Ion energy and ion flux density bombarding onto substrate surface are known to be extracted from waveform of RF applied to an electrode. Using this method, we investigated film quality of SiNx formed in the conventional parallel plate PECVD equipment. When N2 + H2 or N2 + Ar is employed as a carrier gas in source gas (SiH4 + NH3), we have defined normalized ion flux density as ion flux density divided by deposited SiNx molecule which must be increased to obtain high quality SiNx film while ion energy is suppressed at low level as not giving damages on the film surface. This technique has made it possible to securely form SiNx film (2500 ) featuring dielectric break-down field intensity of 8.5 MV/cm at 250 on a glass substrate with Cr gate interconnects of 1000 having vertical step struc-ture. One of the important factors to improve film quality of SiNx deposited in PECVD is to increase ion flux density while keeping ion bombardment energy low enough to protect growing surface against any damages. Using this technique inverse-staggered TFT-array featuring field effect mobility of 0.96 cm2/Vs has been demonstrated which gate insulator SiNx, non-doped a-Si: H and a-Si: H(n+) were formed continuously at the identical substrate temperature of 250.

A new evaluation technique of hot carrier degradation is proposed and applied to practical evaluation of p-channel polycrystalline silicon thin film transistors (TFT). The proposed technique introduces emission microscopy which is particularly effective for evaluating TFT devices. We have developed an automatic measurement system in which measurement of the electrical characteristics and monitoring the photo emission are done simultaneously. Using this system, we have identified the dominant mechanism of hot carrier degradation in TFTs, and evaluated the effect of plasma hydrogenation on hot carrier degradation.

A speech analysis/synthesis system that relies on a time-varying Auto Regressive Moving Average (ARMA) process and the Short-Time Fourier Transform (STFT) is proposed. The narrowband components in speech are represented in the frequency domain by a set of harmonic components, while the broadband random components are represented by a time-varying ARMA process. The time-varying ARMA model has a dual function, namely, it creates a spectral envelope that fits accurately the harmonic STFT components, and provides for the spectral representation of the broadband components of speech. The proposed model essentially combines the features of waveform coders by employing the STFT and the features of traditional vocoders by incorporating an appropriately shaped noise sequence.