Normally-off GaN Transistor with Optimized Gate Insulator
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Solution Overview
Problem
Conventional normally-off transistors using GaN materials face challenges in achieving a high enough threshold voltage and stable breakdown voltage, with existing methods struggling to accurately control the thickness of channel layers and dopant concentrations, leading to inadequate off characteristics and limited mobility and breakdown voltage.
Innovation Solution
A normally-off field effect transistor with a III-nitride semiconductor layer, featuring a gate insulating film of specific thickness and composition, and a RESURF region with controlled sheet carrier concentration, allowing for precise adjustment of threshold voltage and enhanced breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an insulating film is placed between gate electrode and GaN layer to achieve normally-off characteristics, then the transistor can be turned off at 0V gate voltage, but parasitic resistance increases and adequate off characteristics cannot be assured
Solution Approach 1:
The patent changes the physical and chemical parameters of the gate insulating film, including its thickness (5nm-50nm), material composition (Al2O3, HfO2, SiO2, or their combinations), and dielectric constant, to optimize the balance between achieving adequate off characteristics and minimizing parasitic resistance. By precisely controlling these parameters, the invention resolves the contradiction between ensuring transistor turn-off capability and maintaining low resistance.
2Reliability
If channel layer thickness is reduced or dopant concentration is adjusted to increase threshold voltage, then normally-off characteristics improve, but manufacturing precision becomes difficult to control
Solution Approach 1:
The patent shifts the control parameter from channel layer thickness to gate insulating film thickness and dopant concentration in the AlGaN layer. This allows for more precise control of threshold voltage through atomic layer deposition (ALD) techniques that can accurately control film thickness at the nanometer and sub-nanometer scale, thereby improving manufacturing precision while maintaining reliable normally-off characteristics.
Solution Approach 2:
The patent introduces a preliminary p-type AlGaN layer with controlled dopant concentration before forming the n-type channel layer. This preliminary doping action establishes a foundation for achieving the desired threshold voltage without requiring extreme precision in the subsequent channel layer thickness control, as the p-type layer's dopant concentration can be more easily controlled during growth.
3Ease of manufacture
If conventional GaN transistor structures are used, then manufacturing is simpler, but breakdown voltage and mobility are limited
Solution Approach 1:
The patent employs composite material structures including AlGaN/GaN heterostructures with multiple layers having different aluminum compositions, and composite gate insulating films combining different dielectric materials (Al2O3, HfO2, SiO2). These composite structures enable higher breakdown voltage and improved mobility while maintaining compatibility with existing manufacturing processes, thus resolving the contradiction between manufacturing simplicity and performance enhancement.
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
The solution enables a higher gate threshold voltage, improved breakdown voltage, and increased current, contributing to more efficient and reliable power source performance.
Implementation Method 1
a gate insulating film formed on the III-nitride semiconductor layer and controlled having such a thickness that a predetermined threshold voltage is obtained based on a concentration of the acceptor and a concentration of the donor
Implementation Method 2
a RESURF region with controlled sheet carrier concentration, allowing for precise adjustment of threshold voltage and enhanced breakdown voltage
Data Source
AI summary
Provided is a normally-off field effect transistor using a III-nitride semiconductor. The transistor is provided with a III-nitride semiconductor layer grown on a substrate by including an acceptor and a donor; a gate insulating film which is formed on the III-nitride semiconductor layer to have a thickness to be at a prescribed threshold voltage based on the concentration of the acceptor and that of the donor; a gate electrode formed on the gate insulating film; a first source/drain electrode formed on the III-nitride semiconductor layer to one side of and separate from the gate electrode, directly or via a high dopant concentration region; and a second source/drain electrode formed away from the gate electrode and the first source/drain electrode, on or under the III-nitride semiconductor layer, directly or via a high dopant concentration region.