Bipolar Transistor Charge Control Structure

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Solution Overview

Problem

Transistors exhibit gain variation due to changes in collector voltage, leading to harmonic distortion, as the effective base width changes with collector-emitter voltage, causing different signal portions to be subjected to different gains.

Innovation Solution

A charge control structure is introduced adjacent the base-collector interface, comprising an electrode extending vertically between the collector and emitter regions, separated by an insulating dielectric layer, to reduce base width variation and stabilize collector current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional bipolar transistor structure is used, then the transistor provides amplification function, but the gain varies with collector-emitter voltage due to base width modulation (Early effect)

Engineering Contradiction:

Improvegain stabilityVSAvoidharmonic distortion

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

An insulating region is introduced as an intermediary between the collector and base regions. This insulating region modifies the electric field distribution and reduces the modulation of the base width by collector voltage, thereby stabilizing the gain and reducing harmonic distortion caused by the Early effect

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the collector-emitter voltage changes, then the transistor operates over a wider voltage range, but the effective base width changes causing gain variation

Engineering Contradiction:

Improvevoltage rangeVSAvoidbase width control

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The insulating region acts as a mediator that decouples the collector voltage changes from the base width. By introducing this intermediate layer, the transistor can operate over a wider voltage range while maintaining more precise control over the effective base width, reducing the sensitivity to voltage variations

Inventive Principle:

Principle #24Intermediary (Mediator)

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 configuration enhances transistor linearity, reduces gain variation with collector voltage, and increases Early voltage, resulting in reduced harmonic distortion and improved gain uniformity across a range of collector voltages.

Implementation Method 1

the charge control structure is separated from the collector of the transistor by an insulating region such that there is no significant current flow between the charge control structure and the collector or base regions of the transistor. The insulating region preferably comprises a layer of a dielectric material.

Methodology Applied

Scientific EffectElectrical insulation: Dielectric

Implementation Method 2

The Early effect (named after its discoverer James Early) describes how an effective width of a base region of a bipolar transistor changes with collector-emitter voltage. The width of the base affects the gain of the transistor.

Methodology Applied

Scientific EffectEarly effect:

Data Source

PatentUS10468484B2Bipolar transistor

Publication Date: 2019.11.05 ANALOG DEVICES INT UNLTD CO

AI summary

A modified bipolar transistor is provided which can provide improved gain, Early voltage, breakdown voltage and linearity over a finite range of collector voltages. It is known that the gain of a transistor can change with collector voltage. This document teaches a way of reducing this variation by providing structures for the depletion regions with the device to preferentially deplete with. As a result the transistor's response can be made more linear.