Design And Research Of High Voltage SOI LDMOS Devices

SOI LDMOS device is a new type power semiconductor device which developed on the basis of LDMOS device. The advantages of SOI are high speed performance, low power dissipation, high integration, perfect anti-irradiation, improved isolation and so on. SOI can also overcome the disadvantages of the bulk silicon. SOI devices are widely used in high voltage integrated circuits and power integrated circuits, which have a promising future in weapons and equipments, power electronic, industrial automation, aerospace industry and other high and new technology industries. At present, many device structures are proposed to improve the SOI LDMOS device by many researchers at home and abroad. The breakdown voltage of the new device is increased and the specific on-resistance of the new device is decreased, so the performance of the new SOI LDMOS device structure is improved.The main contents of this thesis are about the breakdown voltage and the specific on-resistance of SOI LDMOS device. Two device structures are researched:SOI LDMOS device with floating gates (FG SOI LDMOS) and SOI LDMOS device with oxide trenches (T SOI LDMOS). The contents of the research are as follows:(1) In this chapter, SOI LDMOS device with floating gates is researched. The characteristic of this device is in the oxide field, there are some polysilicon gates to modulate the lateral electric field of the device by using the field plate technology, therefore the breakdown voltage of the FG SOI LDMOS device is increased, and the specific on-resistance of the FG SOI LDMOS device is decreased. When the number and the size of the polysilicon gates are optimized, the simulation results by the Silvaco TCAD show that, compared with the normal SOI LDMOS device, the number of polysilicon gates is 5, the lengthen of the polysilicon gates is 0.5μm, the breakdown voltage of FG SOI LDMOS device is increased by 38.9%, the specific on-resistance of FG SOI LDMOS is decreased by 20.5%. Finally, self-heating effect of this device is analysised.(2) In this chapter, SOI LDMOS device with oxide trenches is researched. The characteristic of this device is the oxide trenches are etched under the polysilicon gate edge, in the drift region surface. The material of the trench is silicon dioxide, which has high critical electric field compare with silicon. Therefore, the device with silicon dioxide can bear higher electric field of gate edge. When SOI LDMOS device has oxide trenches, the breakdown voltage of the device is increased, but the specific on-resistance of the device is induced. Therefore, the performance of SOI LDMOS device with oxide trenches is improved. When the lengthen and the depth of the oxide trenches are optimized, the simulation results by the Silvaco TCAD show that, compared with the normal SOI LDMOS device, the lengthen of oxide trenches is 6μm, the depth of oxide trenches is 1.5μm, the breakdown voltage of T SOI LDMOS device is increased by 26.7%, the specific on-resistance of FG SOI LDMOS is decreased by 14.3%. Finally, self-heating effect of this device is analysised, and finds that the self-heating effect of this device is relieved.