Improved Isolated RESURF Technology for a Multi Power BCD Process

In order to reduce on state resistance of LDMOS transistor, it is necessary to use RESURF structure. However, conventional isolated RESURF structures cannot be used in a multi power BCD process because of the breakdown voltage dependence on epi thickness. Accordingly, we had to use non RESURF LDMOS transistor that has higher on state resistance than RESURF LDMOS transistor in a multi power BCD process. In this paper, we suggested a new isolated RESURF LDMOS structure whose breakdown voltage is independent of epi thickness, and applied this structure to the multi power BCD process that provides 5V CMOS, 20V vertical NPN transistor and 40V / 60V LDMOS transistors. Consequently, we could lower 34 ~ 49% on state resistance of the LDMOS transistors. This newly designed isolated RESURF LDMOS structure will be very useful for many multi power BCD processes