Semiconductor device with functional portions having different operating voltages on one semiconductor substrate

摘要

A single chip microcomputer as a semiconductor device comprises CMOS logic portion and a driver portion operating at a high voltage which can be connected to an external device. In the region of the CMOS logic portion, a P type well layer and an N type well layer are formed on a P type silicon substrate. An N type well layer is formed in the region constituting the driver portion. The junction depth of the N type well layer constituting the driver portion is made deeper than that of the N type well layer constituting the CMOS logic portion. A MOS transistor is formed in the region of each well layer in the CMOS logic portion. A MOS transistor whose drain breakdown voltage is increased is formed in the region of the N type well layer of the driver portion. The junction depth of the N type well layer is made deeper than that of the N type well layer constituting the CMOS logic portion at least below the drain region of this MOS transistor. The MOS transistor constituting the CMOS logic portion operates at a lower voltage while the MOS transistor constituting the driver portion operates at a higher voltage in order to drive external devices such as a fluorescent display tube connected thereto.