Extrinsic Base Structure for Lower-Resistance HBTs and BJTs

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Solution Overview

Problem

Semiconductor devices, such as bipolar junction transistors (BJTs) and heterojunction bipolar transistors (HBTs), face limitations in achieving reduced base resistance, which restricts their maximum frequency of oscillation and frequency response, particularly in high-frequency applications like RF, microwave, and millimeter wave technologies.

Innovation Solution

The semiconductor device design incorporates a monocrystalline and polycrystalline region structure for the extrinsic base region, coupled with a monocrystalline base link region, and selective epitaxy for the intrinsic base region, which reduces base resistance by enhancing hole mobility and sheet resistance, thereby improving frequency response.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional base region structure is used, then the device structure is simple, but the base resistance is high which limits maximum frequency of oscillation

Engineering Contradiction:

Improvemaximum frequency of oscillationVSAvoidbase region structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The base region is segmented into three distinct regions: intrinsic base region (undoped or lightly doped), extrinsic base region (heavily doped), and base link region (monocrystalline). This segmentation allows each region to perform its specific function - the intrinsic region provides low resistance, the extrinsic region provides high doping for frequency response, and the base link region provides mechanical support and electrical connection, thereby reducing overall base resistance and increasing maximum frequency of oscillation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the base are given different doping concentrations and crystal structures tailored to local requirements. The intrinsic base region has undoped or lightly doped silicon for low resistance, the extrinsic base region has heavily doped silicon for high frequency response, and the base link region has monocrystalline structure for mechanical strength and electrical connection. This local optimization resolves the contradiction between simplicity and performance.

Inventive Principle:

Principle #3Local quality

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This design effectively decreases base resistance, leading to increased maximum frequency of oscillation and improved frequency response, making the semiconductor devices more suitable for high-frequency applications.

Implementation Method 1

reduces base resistance by enhancing hole mobility and sheet resistance

Methodology Applied

Scientific EffectHole mobility:

Implementation Method 2

selective epitaxy for the intrinsic base region

Methodology Applied

Scientific EffectEpitaxy: Epitaxy

Data Source

PatentEP4386854A1Semiconductor device having an extrinsic base region with a monocrystalline region and method therefor

Publication Date: 2024.06.19 NXP BV

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AI summary

A semiconductor device includes a semiconductor substrate, a collector region having a first width formed within the semiconductor substrate and an intrinsic base region having a second width, disposed over the collector region, wherein the first width is greater than the second width. An extrinsic base region having an upper surface is formed over the collector region and electrically coupled to the intrinsic base region, wherein the extrinsic base region includes a monocrystalline region coupled to the intrinsic base region and a polycrystalline region coupled to the monocrystalline region. An emitter region is formed over the base region.