Heterojunction Bipolar Transistor Graded Collector Linearity

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Solution Overview

Problem

Heterojunction bipolar transistors (HBTs) used in power amplifiers face a decrease in linearity of input-output characteristics and distortion at high output due to the blocking effect caused by energy barriers at interfaces between semiconductor layers, which inhibits the improvement of efficiency and radio-frequency characteristics.

Innovation Solution

The configuration of the HBT includes a graded semiconductor layer in the collector layer with increasing electron affinity towards the base layer, eliminating the energy barrier at the base-collector interface and omitting the delta-doped layer, allowing for improved linearity and radio-frequency characteristics by suppressing the blocking effect and maintaining flat cutoff frequency characteristics across a wide range of collector currents.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a delta-doped layer is disposed at the interface between the inversely graded semiconductor layer and the graded semiconductor layer to lower the energy barrier, then the efficiency is improved, but the linearity of input-output characteristics decreases and distortion increases at high output

Engineering Contradiction:

ImproveefficiencyVSAvoidlinearity of input-output characteristics

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent removes the delta-doped layer from the collector structure. By extracting this high-concentration doped layer, the harmful capacitance effect that degrades linearity and increases distortion is eliminated, while the graded semiconductor layer alone maintains sufficient electron transport for efficiency

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent modifies the doping concentration parameter in the collector layer by eliminating the delta-doped layer's high-concentration region. This parameter change reduces the base-collector capacitance and its voltage dependence, thereby improving linearity and reducing distortion while maintaining acceptable efficiency through the graded band structure

Inventive Principle:

Principle #35Parameter changes

2Strength

If an inversely graded semiconductor layer is disposed between the graded semiconductor layer and the base layer, then the energy barrier is formed, but the blocking effect inhibits electron transport and reduces efficiency

Engineering Contradiction:

Improveenergy barrierVSAvoidefficiency

Core Design Contradiction:

StrengthVSUse of energy by moving object

Solution Approach 1:

The patent inverts the conventional approach by using only a graded semiconductor layer with electron affinity increasing toward the base layer, rather than using an inversely graded layer. This inversion eliminates the energy barrier and blocking effect while maintaining the heterojunction structure for efficiency

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the electron affinity parameter gradient in the collector layer, making it increase from the sub-collector layer toward the base layer. This parameter change creates a favorable potential slope for electron transport, eliminating the blocking effect while maintaining the heterojunction benefits

Inventive Principle:

Principle #35Parameter changes

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 the linearity of input-output characteristics, improves the adjacent channel leakage ratio (ACLR), and maintains high efficiency and radio-frequency performance even at high output levels, preventing the reduction in ACLR and ensuring flat ft-Ic characteristics.

Implementation Method 1

the collector layer includes a graded semiconductor layer in which an electron affinity increases from a side closer to the sub-collector layer toward a side closer to the base layer

Methodology Applied

Scientific EffectEnergy band gradient:

Data Source

PatentUS11705509B2Heterojunction bipolar transistor

Publication Date: 2023.07.18 MURATA MFG CO LTD

AI summary

A heterojunction bipolar transistor includes a collector layer, a base layer, and an emitter layer that are stacked on a substrate. The collector layer includes a graded semiconductor layer in which an electron affinity increases from a side closer to the base layer toward a side farther from the base layer. An electron affinity of the base layer at an interface closer to the collector layer is equal to an electron affinity of the graded semiconductor layer at an interface closer to the base layer.