HEMT Threshold Voltage Control via AlGaN Layer Composition
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Solution Overview
Problem
High electron mobility transistors (HEMTs) face challenges in increasing threshold voltage and reducing on-resistance due to parasitic capacitance and inductance issues, leading to potential device burnout and non-uniform electrical parameters during gate recessing.
Innovation Solution
The implementation of a high electron mobility transistor structure with a buffer layer, a threshold voltage adjustment layer, a channel region, a band adjustment layer, and a first enhancement layer, all made of III-V semiconductors, where the thickness and molar concentration of these layers are fine-tuned to control piezoelectricity and threshold voltage, and the inclusion of a doping region with fluorine to enhance two-dimensional electron gas concentration and reduce on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate recessing is used to form enhancement mode HEMT, then threshold voltage is increased, but process uniformity deteriorates
Solution Approach 1:
The patent changes the material parameters of the barrier layer by adjusting the aluminum molar concentration and thickness of the AlGaN layer. This modifies the piezoelectric effect and band structure to increase threshold voltage without requiring gate recessing, thereby maintaining process uniformity while achieving the desired electrical characteristics.
Solution Approach 2:
The patent employs a composite structure with multiple AlGaN layers having different aluminum molar concentrations (e.g., 0.3-0.5 for the first AlGaN layer, 0.05-0.2 for the second AlGaN layer). This composite material approach allows independent optimization of threshold voltage and electron mobility, resolving the contradiction between increasing threshold voltage and maintaining manufacturing precision.
2Reliability
If threshold voltage is increased to prevent device burnout, then device safety is improved, but on-resistance increases
Solution Approach 1:
The patent applies local quality by creating regions with different aluminum molar concentrations within the barrier layer. The first AlGaN layer with higher aluminum content (0.3-0.5) is positioned to control threshold voltage, while the second AlGaN layer with lower aluminum content (0.05-0.2) is positioned to maintain low on-resistance. This spatial differentiation of material properties resolves the contradiction between device safety and on-resistance.
Solution Approach 2:
The patent transitions from a single-layer barrier structure to a multi-layer barrier structure with vertical dimensionality. By stacking AlGaN layers with different compositions at different depths beneath the gate electrode, the patent independently controls threshold voltage (primarily influenced by the first AlGaN layer) and on-resistance (influenced by the second AlGaN layer and channel), resolving the trade-off between these two parameters.
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 increases the threshold voltage while maintaining uniformity, reduces on-resistance, and prevents device burnout by modulating piezoelectricity and enhancing two-dimensional electron gas concentration, making the HEMT safer and more efficient.
Implementation Method 1
the thickness and molar concentration of these layers are fine-tuned to control piezoelectricity and threshold voltage
Implementation Method 2
the inclusion of a doping region with fluorine to enhance two-dimensional electron gas concentration and reduce on-resistance
Data Source
AI summary
A high electron mobility transistor includes a buffer layer, a threshold voltage adjustment layer, a band adjustment layer, a first enhancement layer, a gate electrode, and source/drain electrodes. The threshold voltage adjustment layer is disposed on the buffer layer. A channel region is disposed in the buffer layer adjacent to an interface between the buffer layer and the threshold voltage adjustment layer. The band adjustment layer is disposed on the threshold voltage adjustment layer. The first enhancement layer is conformally covering the threshold voltage adjustment layer and the band adjustment layer. The gate electrode is disposed on the first enhancement layer. The source/drain electrodes are disposed on the buffer layer through the threshold voltage adjustment layer and the first enhancement layer on opposite sides of the gate electrode respectively. The threshold voltage adjustment layer and the first enhancement layer are III-V semiconductors.