GaN HEMT Cap Layer Segmentation for Threshold Stability
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Solution Overview
Problem
High electron mobility transistors (HEMTs) using gallium nitride (GaN) experience a positive shift in threshold voltage over time, leading to decreased drain current due to cap layer thickness affecting long-term stability.
Innovation Solution
A high electron mobility transistor design with a cap layer thickness of 5 nm or less, featuring a rest region in the insulating layer opening, where the gate is formed on the cap layer, reducing the cap layer thickness to 0.5 to 2.0 nm, and using chloride plasma processing to create this configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the cap layer thickness is increased to control or adjust the threshold voltage, then the threshold voltage control is improved, but the long-term stability of the HEMT performance deteriorates
Solution Approach 1:
The cap layer is segmented into two distinct regions: a first region with a first thickness and a second region with a second thickness different from the first thickness. This segmentation allows different portions of the cap layer to serve different functions - one region for threshold voltage control and another for maintaining long-term stability, thereby resolving the contradiction between voltage control and stability.
Solution Approach 2:
Different regions of the cap layer are assigned different thicknesses to optimize local properties. The first region has a thickness optimized for threshold voltage control, while the second region has a thickness optimized for long-term stability. This local differentiation enables simultaneous achievement of both control precision and reliability.
2Reliability
If the cap layer thickness is reduced to improve long-term stability, then the stability is improved, but the threshold voltage control capability deteriorates
Solution Approach 1:
The cap layer is divided into two regions with different thicknesses, allowing one region to be thin enough for stability while another region maintains sufficient thickness for effective threshold voltage control. This segmentation resolves the trade-off between stability and control capability.
Solution Approach 2:
Different thicknesses are applied to different regions of the cap layer, with each region's thickness locally optimized for its specific function. This local quality approach ensures that no single thickness value compromises either stability or control capability.
3Reliability
If the cap layer thickness is uniformly reduced to suppress positive threshold voltage shift, then the threshold voltage stability is improved, but the overall cap layer functionality deteriorates
Solution Approach 1:
The cap layer is segmented into regions with different thicknesses, allowing the device to maintain full functionality while suppressing positive threshold voltage shift. The segmented structure ensures that critical functional regions retain adequate thickness while other regions are thinner for stability.
Solution Approach 2:
Different regions of the cap layer have different thicknesses locally optimized for their specific functional requirements. This ensures that threshold voltage stability is improved without compromising the overall functionality of the cap 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 configuration effectively suppresses the positive shift of the threshold voltage and reduces long-term degradation of the drain current, maintaining drain current stability without significant cap layer thickness reduction.
Implementation Method 1
using chloride plasma processing to create this configuration
Data Source
AI summary
A high electron mobility transistor (HEMT) made of nitride semiconductor materials, and a method to form the HEMT are disclosed. The HEMT includes a channel layer made of GaN, a barrier layer made of one of AlGaN, InAlN, and InAlGaN on the GaN channel layer, a cap layer made of n-type GaN on the barrier layer, and an insulating layer on the cap layer. The insulating layer has an opening into which the gate is formed. The cap layer has a region in the opening that has a thickness smaller than a thickness of portions of the cap layer that are outside of such region. The outside portions have a thickness that is preferably 5 nm at most.