The failure experiments of the P-LDMOS （lateral double diffused metal oxide semiconductor） demonstrate that the high peak electrical fields in the channel region of high-voltage P-LDMOS will reinforce the hot-carrier effect, which can greatly reduce the reliability of the P-LDMOS. The electrical field distribution and two field peaks along the channel surface are proposed by Tsuprem-4 and Medici. The reason of resulting in the two electrical field peaks is also discussed. Two ways of reducing the two field peaks, which are to increase the channel length and to reduce the channel concentration, are also presented. The experimental results show that the methods presented can effectively improve the gate breakdown voltage and greatly improve the reliability of the P-LDMOS.
As the thickness of an SOI layer varies,a minimum breakdown voltage is reached when the thickness is about 2μm. The vertical electric field of the SOI LDMOS with a drift region which is vertically linearly graded is constant. The vertically linearly graded concentration drift can be achieved by impurity implanting followed by thermal diffusion. In this way,the vertical breakdown voltage of SOI LDMOS with 2μm thickness SOI layer can be improved by 43%. The on-state resistance is lowered by 24 % because of the higher impurity concentration of the SOI surface.
