HEMT Gate Electrode Stack With Diffusion Barrier for Low Leakage
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Solution Overview
Problem
High electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures face significant gate leakage current issues due to reduced Schottky barrier potential, which affects their radiofrequency (RF) performance, and existing solutions like using Nickel as a contact metal are not optimal as they either contaminate CMOS production lines or fail to effectively reduce leakage current.
Innovation Solution
A method for manufacturing HEMT devices involves forming a gate electrode with a stack of metal layers, including a first metal layer for Schottky contact, a protection layer to prevent diffusion, and a second metal layer with Aluminium to improve conductivity, while the third metal layer includes Aluminium to reduce leakage current, with a Tungsten Nitride layer acting as a barrier against Aluminium diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If Nickel is used as contact metal to form Schottky contact with high work function, then gate leakage current is reduced, but electrical resistance increases and contamination of CMOS production lines occurs
Solution Approach 1:
The gate electrode is divided into multiple functional layers: a first metal layer (Nickel) for forming Schottky contact with high work function to reduce leakage current, and a second metal layer (Aluminium) for providing low electrical resistance. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
A diffusion barrier layer is introduced as an intermediary between the Aluminium layer and the AlGaN barrier layer. This intermediary prevents Aluminium atoms from diffusing into the heterostructure while allowing the Schottky contact formed by the Nickel layer to maintain its high work function properties for leakage current reduction.
2Loss of energy
If Aluminium is used as gate electrode material to reduce electrical resistance, then conductivity improves, but Aluminium diffuses in heterostructure forming conductive paths that increase leakage current
Solution Approach 1:
A diffusion barrier layer is positioned between the Aluminium gate electrode and the AlGaN heterostructure to act as an intermediary that blocks Aluminium atom diffusion while maintaining the electrical conductivity function of the Aluminium layer.
Solution Approach 2:
The gate electrode structure is segmented into distinct functional layers: the Aluminium layer provides low resistance conductivity, while the diffusion barrier layer prevents Aluminium migration into the heterostructure, thereby eliminating conductive leakage paths.
3Object-affected harmful factors
If multi-layer gate electrode structure is formed with diffusion barrier, then Aluminium diffusion is prevented, but manufacturing process complexity increases
Solution Approach 1:
The diffusion barrier function is extracted as a separate, dedicated layer between the Aluminium gate electrode and the AlGaN heterostructure. This allows the barrier layer to be optimized specifically for diffusion prevention while the Aluminium layer maintains its conductivity function, simplifying the overall design despite the additional layer.
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 approach effectively reduces gate leakage current in HEMT devices, enhancing their RF performance and compatibility with CMOS production lines without the contamination issues associated with previous methods.
Implementation Method 1
a first gate metal layer configured to form a Schottky contact with the heterostructure
Implementation Method 2
depositing in the through opening and onto the sacrificial structure, by an evaporation process, a first gate metal layer
Implementation Method 3
depositing a second gate metal layer, by a sputtering process, on and in direct contact with the first metal layer and with the dielectric layer
Implementation Method 4
The second gate metal layer forms a barrier against diffusion of Aluminium atoms from the third metal layer towards the heterostructure
Data Source
AI summary
A method for manufacturing a HEMT device includes forming, on a heterostructure, a dielectric layer, forming a through opening through the dielectric layer, and forming a gate electrode in the through opening. Forming the gate electrode includes forming a sacrificial structure, depositing by evaporation a first gate metal layer layer, carrying out a lift-off of the sacrificial structure, depositing a second gate metal layer by sputtering, and depositing a third gate metal layer. The second gate metal layer layer forms a barrier against the diffusion of metal atoms towards the heterostructure.