Theoretical Research On 2-D Field Plates In The SOI Lateral Power Devices

As a practical junction termination techonology, field plate(FP) has been widely used in power MOSFET, HVIC and SPIC with the merits of small occupied area, simple manufacturing process and so on. While field plate is applied to SOI lateral power devices, not only are the advantages of SOI technology such as improved isolation, reduced leakage current, low power dissipation, high speed performance, and perfect irradiation hardness used, but also the distribution of surface electric field is effectively modified, consequently the device's breakdown characteristics will be greatly improved. Further researches show that there are different abilities of improving the surface electric field distribution for different type of field plates. Therefore, it is very significant to develop analytical models for the surface potential and electric field distributions of SOI lateral power devices with different type of field plates. These models enable clarifying the effects of the field plates on the surface electric field distribution and investigating the breakdown mechanism of SOI lateral power devices with field plates. In this thesis, based on solving 2-D Possion equations, a relatively complete theory of 2-D field plates in the SOI lateral power devices is developed to model the surface potential and electric field distributions for the SOI lateral power devices with common metal field plates, step field plates and floating field plates.1) Common metal field plates: Firstly, the analytical models are developed to describe the surface potential and electric field distributions of SOI lateral power devices with gate field plate as well as drain field plate respectively. A unified analytical expression is derived for the different depletion cases under various bias voltages. Then, using device simulator Silvaco, the influences of the gate field plate and drain field plate on the electricstatic potential and electric field distributions along the drift region surface under various depletion cases are investigated in detail. Finally, a universal analytical model is developed when the gate field plate and drain field plate are used at same time. The simulation results show a well agreement with the analytical results, which verify the accuracy of models.2) Step field plates: The analytical models for the surface potential and electric field distributions of SOI lateral power devices with n-step gate field plates and n-step drain field plates are developed respectively. Using device simulator Silvaco, the influences of the step number of the gate and drain field plates on the surface electric field distributions are researched. Finally, a universal analytical model for the surface potential and electric field distributions of the devices is developed when the gate and drain field plates with arbitrary step are valid at same time. The accuracy of these models is verified by the accordance between the numerical and analytical results. These models provide a theoretical guidance for analyzing the breakdown mechanism of SOI lateral power devices with all kinds of step field plates.3) Floating field plates: The analytical models for the surface potential and electric field distributions of SOI lateral power devices with single-floating field plates(SFFP) as well as muti-floating field plates(MFFP) are developed respectively. To overcome the problem of the determination of bias voltages on the floating field plates, we propose an approximately analytical formula by comparing the simulated potential profiles in the field oxide with and without floating field plate. Based on the formula, a novel analytical model for the device with arbitrary floating field plates is developed. The modeling results agree well with the simulations using Silvaco, which verifies the accuracy of the analytical models.