HEMT Barrier Layer Structure for Normally Off Gate Operation
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Solution Overview
Problem
Existing methods for fabricating high electron mobility transistors (HEMTs) face challenges in achieving optimal device performance, particularly in switching from 'normally on' to 'normally off' operation, due to limitations in etching processes and barrier layer thickness control.
Innovation Solution
The method involves forming a buffer layer on a substrate, followed by the formation of a first and second barrier layer with specific Al concentrations and thicknesses. A patterned mask is used to define the gate electrode location, and the gate electrode, source, and drain electrodes are formed after removing the mask, thereby preventing damage to the underlying regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional etching processes are used to form gate electrode location, then the fabrication process is simple, but the underlying regions are damaged and device performance is compromised
Solution Approach 1:
A mask layer is formed over the barrier layer before etching the gate electrode location. This preliminary protective action prevents the etching process from damaging the underlying barrier layer and active regions, thereby improving device performance without significantly complicating the fabrication process
Solution Approach 2:
The mask layer serves as an intermediary protective element between the etching process and the underlying sensitive regions. It allows the etching to proceed while protecting critical structures, resolving the contradiction between fabrication simplicity and device reliability
2Manufacturing precision
If the barrier layer thickness is not precisely controlled, then the fabrication process is easier, but the 2DEG concentration cannot be optimized for normally off operation
Solution Approach 1:
The patent employs atomic layer deposition (ALD) to precisely control the barrier layer thickness at the nanometer scale. By changing the deposition parameters and monitoring the thickness during the process, the 2DEG concentration can be optimized to achieve normally off operation, transforming an easily fabricated but imprecise process into a precisely controlled one
3Adaptability or versatility
If a single barrier layer is used, then the structure is simple, but the device cannot switch between normally on and normally off operation modes
Solution Approach 1:
The barrier layer is segmented into multiple distinct layers with different aluminum concentrations and thicknesses. This segmentation allows independent optimization of each layer's function, enabling the device to switch between normally on and normally off operation modes while maintaining a relatively simple overall structure
Solution Approach 2:
Different regions of the barrier structure have different properties - the first barrier layer has one aluminum concentration and thickness optimized for certain functions, while the second barrier layer has different properties optimized for other functions. This local differentiation enables operation mode switching without excessive structural complexity
Data Source
AI summary
A method for fabricating high electron mobility transistor (HEMT) includes the steps of: forming a buffer layer on a substrate; forming a barrier layer on the buffer layer; forming a gate dielectric layer on the barrier layer; forming a work function metal layer on the gate dielectric layer; patterning the work function metal layer and the gate dielectric layer; forming a gate electrode on the work function metal layer; and forming a source electrode and a drain electrode adjacent to two sides of the gate electrode.