The Research On Optimal Design Method Of SOI LIGBT

Insulator Gate Bipolar Transistor (IGBT) is a kind of composite power device, which is made up of combinations of Metal Oxide Semiconductor device structure and Bipolar Junction Transistor device structure. It has the characteristics of both power MOS device and BJT device and it’s a better compromise between on-state current and turn off time. IGBT has taking the place of high-power BJT and power MOSFET in lots of power transformation systems. Lateral Insulator Gate Bipolar Transistor (LIGBT) based on Silicon On Insulator (SOI) material has better insulating property, lower parasitic capacitance, lower leakage current, high integration level and some other advantages, the most important is that the fabrication process is compatible with SOI-CMOS process. It will become the key part of the smart power IC and will be used widely in household electrical appliances, environment friendly motors and industrial production and so on, also it is considered as the most potential power device in the future for SPICs applications.In this paper, the fabrication method of SOI material and its merits and demerits are introduced at first. On the base that the research progress and development trend of SOI LIGBT device is summarized. Secondly the basic structure, operating mode and main electrical characteristics (transfer characteristic, output characteristic, turn-off characteristic and latch-up characteristic) of SOI LIGBT device are described. According to the theory of semiconductor device, the analytical model of threshold voltage is developed to characterize the relationship between threshold voltage and the concentration at the surface of the channel, which paves the way for threshold voltage design. The principles of field plate and RESURF are analyzed, which are used to improve the breakdown voltage of the device and then the parameters of the drift region are estimated to satisfy design targets. The factors influencing latching current are deduced qualitatively and half quantitatively and what measures should be taken are proposed to increase the latching current density, which offers some references for improving device performance. The principle of anti-ESD is analyzed and the device structure with anti-ESD function is designed. Silvaco TCAD-a well-known semiconductor device simulation tool all over the word is introduced and electrical characteristics of the designed device are simulated with the software. In order to improve the breakdown voltage of the device, the relationships among breakdown voltage and the concentration of n-buffer region, the concentration of drift region, the junction depth of n-buffer region, the thickness of buried oxide, the length of field plate have been researched in detail, which leads to a optimal design method correspondingly. To reduce on-state resistance, the factors influencing on-state current are studied. Moreover the factors influencing latch-up current density are studied so as to increase latch-up current density and expand safe operating area of the device. The process flows of the device and process parameters are designed with the assistance of Silvaco TCAD. At last, the layout of the device structure is designed and drawn using Tanner L-Edit. The post simulation results indicate that the performance of the designed device satisfy the requirements of the design specifications.