The performance of poly-Si TFTs and CMOS circuits with various active films prepared by different deposition processes and annealing methods, such as SPC(Solid Phase Crystallization) and ELA(Excimer Laser Annealing), have been investigated. We have examined the effects of DC characteristics of poly-Si TFT, such as mobility, threshold voltage and ON- OFF- current level, on the dynamic performance of the CMOS circuits.
We have fabricated poly-Si TFT devices and CMOS circuits with various process conditions, such as active layer preparation source gases, annealing method, film thickness and source/drain impurity doping. The TFTs with ELA active films exhibit much higher field effect mobility and ON/OFF current ratio than those with SPC active film due to low intragranular trap state density. The TFTs with active film deposited using Si2H6 have higher mobility and sub-threshold slope than those with active film deposited using SiH4 because of the large poly-Si grain size and less grain boundary defects. We have observed that the device ON-current, mobility and VTH are the dominant characteristics to control the operation speed of CMOS circuits. We have also found that the effects of active film thickness and source/drain doping process on the performance of CMOS ring oscillator may not be neglected and that it should be optimized for AMLCD applications.