Bipolar transistor with a ring emitter

US5786622A · kind A · utility

Assignee

• Tritech Microelectronics International Ltd. · SG

Inventor

• Hannu O. Ronkainen · Hyrynsalmi, FI

Key dates

• Filing date: May 16, 1997
• Grant date: Jul 28, 1998
• Expiry date: May 16, 2017

Classification

• Technology area (CPC H): Electricity
• CPC primary: H10D84/401

Abstract

A novel ring shaped emitter structure with an extrinsic base and base contact in the central portion of the ring is described. This structural configuration is useful for improving the performance of bipolar transistors used in BiCMOS integrated circuits with only minimal changes to conventional CMOS processing technology. A single additional mask is required to form the intrinsic base region of the transistor. The emitter is diffused from a polysilicon layer which also serves as the emitter contact. The polysilicon layer overlies a perimeter portion of an active region defined by an opening in a field oxide and rises up over the field oxide itself. The active emitter region then forms a ring along the perimeter of the active region. The extrinsic base is formed through an opening within the polysilicon layer representing a central portion of the active region. This configuration improves transistor performance by reducing the characteristic spacings and thereby reducing component resistances and capacitances and increasing the cut-off frequency. The improved emitter-base design thereby results in higher bipolar transistor performance in BiCMOS integrated circuits at minimal cost.