HEMT Gate Region Structure for Schottky Junction Integrity
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Solution Overview
Problem
High electron mobility transistors (HEMTs) experience undesired drain leakage current due to the use of metal elements with low work functions in the gate region, which can lead to contamination and junction damage, especially when high work function metals are not used due to cost or contamination concerns.
Innovation Solution
The HEMT design incorporates a gate region with a nickel bottom portion and an aluminum top portion, along with a tungsten nitride or tantalum nitride intermediate layer and an aluminum top region, which reduces gate resistance without causing contamination and prevents aluminum diffusion, thereby maintaining the integrity of the Schottky junction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal elements with low work functions are used in the gate region, then gate resistance is reduced, but drain leakage current increases and contamination occurs
Solution Approach 1:
A barrier layer made of titanium nitride or tantalum nitride is introduced between the aluminum gate electrode and the AlGaN layer. This intermediary layer prevents aluminum diffusion into the semiconductor while allowing the aluminum to maintain its low work function characteristics for reduced gate resistance. The barrier layer thus mediates between the conflicting requirements of low gate resistance and prevention of contamination.
Solution Approach 2:
The gate region employs a composite structure combining multiple materials: nickel (for magnetic properties and adhesion), titanium nitride or tantalum nitride (as barrier layer), and aluminum (for low work function). This composite material approach allows each layer to contribute its specific properties, achieving both low gate resistance and prevention of drain leakage current while avoiding contamination.
2Reliability
If metal elements with low work functions are used in the gate region, then gate resistance is reduced, but the Schottky junction integrity is compromised
Solution Approach 1:
The barrier layer of titanium nitride or tantalum nitride serves as a mediator that protects the Schottky junction from aluminum diffusion while permitting the aluminum gate electrode to maintain electrical contact with the AlGaN layer. This intermediary structure preserves the integrity of the Schottky junction despite the presence of low work function aluminum metal.
Solution Approach 2:
The gate region is segmented into distinct functional layers: a nickel bottom portion for magnetic properties and adhesion, a titanium nitride or tantalum nitride barrier layer for preventing diffusion, and an aluminum top portion for low work function characteristics. This segmentation allows each layer to perform its specific function without compromising the overall junction integrity.
3Stability of the object's composition
If high work function metals are used in the gate region, then junction damage is prevented, but drain leakage current increases
Solution Approach 1:
The gate electrode is divided into multiple segments with different materials and functions: the nickel bottom portion provides magnetic properties and adhesion, the titanium nitride or tantalum nitride barrier layer prevents aluminum diffusion, and the aluminum top portion provides low work function for reduced drain leakage current. This segmentation resolves the contradiction by assigning different properties to different segments.
Solution Approach 2:
The gate structure uses a composite of nickel, titanium nitride/tantalum nitride, and aluminum, where each material contributes specific properties. The composite structure achieves both junction protection (through the barrier layer) and reduced drain leakage current (through the aluminum's low work function), overcoming the limitations of using single high work function metals.
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 effectively minimizes drain leakage current and maintains the integrity of the Schottky junction, even when using low work function metals, without causing contamination, thus enhancing the performance and reliability of the HEMT.
Implementation Method 1
Contact between the bottom portion 12 of the gate region 10 and the top layer 6 forms a metal-semiconductor junction of a Schottky type, i.e., a rectifying junction.
Implementation Method 2
The HEMT design incorporates a gate region with a nickel bottom portion and an aluminum top portion, along with a tungsten nitride or tantalum nitride intermediate layer and an aluminum top region, which reduces gate resistance without causing contamination and prevents aluminum diffusion
Data Source
AI summary
An HEMT includes a semiconductor body, which includes a semiconductor heterostructure, and a conductive gate region. The gate region includes: a contact region, which is made of a first metal material and contacts the semiconductor body to form a Schottky junction; a barrier region, which is made of a second metal material and is set on the contact region; and a top region, which extends on the barrier region and is made of a third metal material, which has a resistivity lower than the resistivity of the first metal material. The HEMT moreover comprises a dielectric region, which includes at least one front dielectric subregion, which extends over the contact region, delimiting a front opening that gives out onto the contact region; and wherein the barrier region extends into the front opening and over at least part of the front dielectric subregion.