Structure Design Of SOI-LDMOS

The radio frequency circuit is used more and more popular in the fields of mobile communication equipments, wireless local area network, aviation electro-equipments, radar, microwave emitter and so on. The power transistor which bases on the technology of LDMOS leads a key effect in the radio frequency circuit. The technology of LDMOS has a great deal of defects. It has high output capacitance, which can reduce power efficiency and power plus, especially, can make the design of output matching harder. Compared with LDMOS, the SOI-LDMOS has many advantages that completely dielectric isolation, low output capacitance, high power plus and high temperature resistant characteristic. Its technics which is easier than LDMOS is compatible with SOI CMOS.By using the software of ISE, we simulate the electrics performance of the SOI-LDMOS and compare the results with the LDMOS. The results indicate well output characteristics, low output capacitance and etc. However, SOI-LDMOS technology has to face the problem of floating body effects and self-heating effects. We make a try with the patterned SOI-LDMOS, which has a discontinuity BOX. The simulation shows it can eliminate some disadvantages. It also demonstrates the factors which affect the transconductance and offers a reference to increase the transconductance. We also use a great deal of methods to improve the capacitance characteristics.A breakdown model of SOI high voltage device is proposed in this paper. By solving 2-D Poisson equation, the analytical description of the 2-D electric field and potential distributions of the device with uniform, step and linear drift doping profiles for the completely and incompletely drift regions are given. The impact of the geometry parameters and drift doping concentration on breakdown voltage is investigated for the varied drift doping profiles. The method to extract cut-off frequency of high-voltage SOI-LDMOS has been established. Effects of gate oxide thickness, drift-region implant-dose, SOI thickness and field-plate length on cut-off frequency are discussed in detail. A method to improve cut-off frequency of SOI-LDMOS is also proposed.