Analysis On Static Characteristics And Cut-off Frequency Of Double Doping Polysilicon Gate LDDMOSFET

Over the past decade, RF circuit research had developed greatly which widely applied in wireless communication, medical treatment, remote viewing, global positioning and radio frequency identification. The working frequency of circuit quickly raised, and the requirements of high frequency characteristics for semiconductor devices had become much highed. In recent years, it is unceasing reported that the frequency of the MOSFETs which are made up of semiconductor material such as SiGe, SiC or SOI new structure can reach some hundreds GHz,and show certain advantages in high frequency high temperature and high power field. But, these techniques must be based on advanced and complex manufacturing technology, so their application will be limited commonly.Nowadays, silicon CMOS technology is still the trend of microelectronics. The proposed double doping polysilicon gate(DDPG) LDD MOSFET using pure silicon whose gate have been designed is considered as a new RF structure having excellent performance. The gates consist of S-gate with high workfunction p+polysilicon and D-gate with low workfunction n+polysilicon and are parallel to each other. In the DDPG MOSFET, the threshold voltage near source is greater than it near drain, the step-function profile in the surface potential exhibits improvement in screening of the drain potential variation. The peak in the electric field distribution along the channel ensures more uniformity in the average drift velocity of the electrons and improves current, transconductance and cut-off frequency.The thesis starts with an introduction of the development about semiconductor industry, analysing the challenge of mini-sizing the devices and improving the structure. Then it reveals the structural designing and technical processing of DDPG-LDD MOSFET. After, analyzes in detail the small signal characteristics using equivalent circuit model. and is put to provide the analytic expression of the key parameters on electric field, electric potential, threshold voltage and cut-off frequency. Finally, By simulating, the effects of the parameters are studied, which include the gate length,gate oxide thickness,the junction depth of source and drain regions,gate doping density,substrate doping density and temperature. Meanwhile, compared with the p+doping polysilicon gate MOSFET, the new structure has an improved performance which is discussed further.