The Research Of The High Voltage Power Mosfet Breakdown

Blocking capacity is the key parameter of Power MOSFET. Usually in the device selection, the breakdown voltage is considered as a primary indicator. For breakdown voltage less than100V VDMOS devices, it is not difficult to design to meet the target breakdown voltage, which mainly focus on the trade-off between on resistance and breakdown voltage. But for high voltage VDMOS devices, to improve the breakdown voltage is the most difficult work of the chip design. Under high reverse bias, if no protective measures in the outer ring of the cell area will lead to chip breakdown ahead. The role of the termination is the use of the special design of a lateral structure for gentle transition of the high electric potential difference between the drain and the source. Generally, as long as the termination breakdown voltage reaches the target specifications, then the overall blocking capacity of the chip can be guaranteed.This thesis is the research of the high voltage VDMOS termination. Typical specifications as a high voltage device,600V VDMOS termination had been optimized design in this work.First of all, the mechanism of avalanche breakdown occuring conditions was been studied, substituted into the electric field equation of each model of the plane junction and the cylindrical junction, then the breakdown voltage analytical solution had been got. Infinite plane junction model is suitable for the selection of epitaxial wafers doping concentration and thickness, and what we get is the optimal solution between on-resistance and breakdown voltage trade-off.Cylindrical junction model is applied to calculate the breakdown voltage of the edge of the main junction, the junction curvature radius and the breakdown voltage were calculated to be direct proportion. This theory is the foundation of a variety of basic principles of termination technology, especially the field limiting ring technique and other junction termination technique, that is, by increasing the curvature radius of the depletion layer to get a high breakdown voltage.Then design and optimize the structure of Multi-FLR-FP termination. Single field limiting ring and a single field plate model had been simulated to explore the shape and location led to changes in the characteristics of the termination electrical properties, including the surface electric field distribution, the impact ionization rate distribution, the depletion boundary shape, and breakdown voltage of the trend. This will guide the adjustment and optimization of the composite structure of the termination. After works of simulation with TCAD software ISE, optimized Multi-FLR-FP structure termination had been designed, which breakdown voltage is690.2V, and the width is150μm.In this paper, a shallow trench negative slope termination structure had also been designed, which was based on the principle of surface deformation. Get a width of126.7μm, and the breakdown voltage of724.8V termination structure.