TiN Gate Metallization for GaN HEMT Reliability
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Solution Overview
Problem
Conventional Ni/Au-based Schottky gate metallizations in Group III-nitride high electron mobility transistors (HEMTs) suffer from gate degradation due to nickel migration into nearby metal and semiconductor layers under electrical and thermal stress, limiting their reliability.
Innovation Solution
The use of low atom migration metal nitride alloy materials, such as titanium nitride (TiN), which are deposited using techniques like atomic layer deposition, to form Schottky diodes and gates, reducing diffusion and enhancing thermal stability and breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Ni/Au-based Schottky gate metallization is used, then device fabrication is achieved, but gate degradation occurs due to nickel migration into nearby metal and semiconductor layers under electrical and thermal stress
Solution Approach 1:
A titanium nitride (TiN) barrier layer is introduced between the nickel metal layer and the gallium nitride semiconductor layer. This intermediary TiN layer prevents nickel atoms from migrating into the GaN material during thermal stress, while still allowing the nickel to form a functional Schottky contact. The TiN acts as a diffusion barrier that blocks the harmful nickel migration pathway.
Solution Approach 2:
The gate metallization structure is changed from a simple Ni/Au bilayer to a composite multilayer structure comprising Ni/Au/TiN/GaN. This composite structure combines the advantages of each material: Ni provides Schottky contact formation, Au provides thermal stability and connectivity, TiN provides diffusion barrier functionality, and GaN is the semiconductor substrate. The composite structure resolves the contradiction by assigning different functional roles to different material layers.
2Reliability
If nickel metal is in direct contact with III-nitride alloy material, then Schottky junction is formed, but atom diffusion occurs with thermal stress causing degraded junction reliability
Solution Approach 1:
The titanium nitride layer serves as an intermediary barrier between the nickel metal and III-nitride semiconductor. This intermediate layer maintains the Schottky junction functionality while preventing direct atomic contact and diffusion between Ni and GaN, thereby preserving compositional stability under thermal stress.
Solution Approach 2:
The work function of the metal contact is modified by introducing TiN, which has a different work function compared to pure Ni. This parameter change in the metal stack composition allows optimization of the Schottky barrier height while simultaneously providing diffusion protection, resolving the contradiction between forming a good Schottky junction and preventing atomic diffusion.
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
TiN-gated HEMTs exhibit improved reliability with higher breakdown voltage and thermal stability, reducing leakage current and maintaining performance under extended electrical and thermal stress, compared to Ni/Au-gated devices.
Implementation Method 1
wherein the atoms comprising the metal nitride alloy material layer have low migration (low diffusion) into the III-Nitride material
Implementation Method 2
deposited using techniques like atomic layer deposition
Data Source
AI summary
Systems and methods are provided that enable the production of semiconductor devices having a metal nitride layer in direct contact with a semiconductor layer to form a Schottky diode, such as a TiN gate on an AlGaN/GaN high electron mobility transistor (HEMT). Metal nitrides offer exceptional thermal stability and a lower diffusion coefficient. Technology enabled by embodiments of the present disclosure improves the reliability of GaN-based microwave power transistors.