JPS6420651A - Semiconductor output buffer device - Google Patents

Abstract

PURPOSE: To protect a semiconductor output buffer device from static discharge by providing a transistor in which diffusion regions are formed at appropriate intervals as well as an n-channel transistor in an output buffer. CONSTITUTION: In an output buffer formed on the semiconductor surface of a substrate, an n-channel transistor 110 is formed and, at the same time, a transistor 120 is formed in an n-well 122. The gate electrode 124 of the transistor 120 has four fingers each of which overlaps a drain region 126 and a source region 128 in the well 122. An additional n-type diffusion region 140 is formed in the well 122 at a short distance D from the source region 128 on the side face of the source region 128 on the opposite side of the drain region 126. The resistance in the diffusion region 140 becomes smaller as compared with the well 122 and, when extraordinarily large charges are applied upon the output buffer from power sources Vdd and Vss, the breakdown of the p-n junction between the drain region 126 and well 122 can be prevented and the buffer can be protected from static discharge.