Enhanced-Mode HEMT Structure for High Mobility and Low Gate Leakage

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Solution Overview

Problem

Existing high electron mobility transistors (HEMTs) based on III-V semiconductor compounds face challenges in achieving enhanced-mode operation with reduced circuit complexity and cost, particularly in controlling the electron mobility and gate leakage.

Innovation Solution

The semiconductor structure incorporates a heterojunction between a non-doped narrow-band gap channel layer and a wide-band gap n-type donor-supply layer, with a p-type layer deposited between the source and drain features to deplete the carrier channel, thereby converting the HEMT to an enhanced-mode operation. Additionally, the use of a refractory metal gate electrode and intermetallic compounds like Al, Ti, or Cu in the source/drain features improves electrical connection and reduces gate leakage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a heterojunction is used in HEMT to achieve high electron mobility, then electron mobility is improved, but gate leakage increases

Engineering Contradiction:

Improveelectron mobilityVSAvoidgate leakage

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The gate structure is segmented into multiple layers including a first gate electrode, a second gate electrode, and an intermediate layer between them. This segmentation allows the first gate electrode to control the heterojunction for high electron mobility while the second gate electrode controls gate leakage, resolving the contradiction between improving electron mobility and reducing gate leakage

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An intermediate layer is introduced between the first gate electrode and the second gate electrode. This intermediate layer acts as a mediator that enables the first gate electrode to effectively control the heterojunction interface for high electron mobility while preventing excessive gate leakage that would otherwise occur with direct contact between the gate electrodes and the heterojunction

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If enhancement-mode operation is implemented to reduce circuit complexity, then device simplicity is improved, but control over electron mobility becomes more difficult

Engineering Contradiction:

Improvecircuit complexityVSAvoidcontrol over electron mobility

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The gate structure employs dynamic control through two independently controllable gate electrodes. The first gate electrode dynamically adjusts the electron mobility in the heterojunction by controlling the depletion region, while the second gate electrode dynamically controls the gate leakage. This dynamic control mechanism enables enhancement-mode operation with reduced circuit complexity while maintaining precise control over electron mobility

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the electrical parameters of the gate structure by introducing a dual-gate configuration where the first gate electrode modifies the depletion region width and electron mobility parameters in the heterojunction, while the second gate electrode adjusts the gate leakage parameters. These parameter changes enable enhancement-mode operation that simplifies circuit design while maintaining precise control over electron mobility characteristics

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 achieves high electron mobility and reduced gate leakage, enabling enhanced-mode HEMT operation with improved control over electron mobility and reduced manufacturing costs, as well as increased flexibility in integrating III-V semiconductor processes with silicon-fabrication techniques.

Implementation Method 1

a p-type layer deposited between the source and drain features to deplete the carrier channel

Methodology Applied

Scientific EffectCarrier depletion:

Implementation Method 2

A HEMT is a field effect transistor incorporating a junction between two materials with different band gaps (i.e., a heterojunction) as the channel

Methodology Applied

Scientific EffectHeterojunction:

Implementation Method 3

HEMTs have a number of attractive properties including high electron mobility

Methodology Applied

Scientific EffectElectron mobility:

Implementation Method 4

the use of a refractory metal gate electrode and intermetallic compounds like Al, Ti, or Cu in the source/drain features improves electrical connection and reduces gate leakage

Methodology Applied

Scientific EffectGate leakage reduction:

Data Source

PatentUS12230690B2Method of forming a high electron mobility transistor

Publication Date: 2025.02.18 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

The transistor includes a first III-V compound layer. A second III-V compound layer is disposed on the first III-V compound layer and is different from the first III-V compound layer in composition. A carrier channel is located between the first III-V compound layer and the second III-V compound layer. A source feature and a drain feature are disposed on the second III-V compound layer.