Cascode GaN HEMT Structure for Stable Normally-Off Operation
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Solution Overview
Problem
Nitride semiconductor devices, particularly high-electron-mobility transistors (HEMTs), face challenges in achieving normally-off operation with low temperature dependence of on-resistance, as existing configurations are prone to current collapse and high temperature sensitivity due to lattice oscillations affecting electron movement.
Innovation Solution
A nitride semiconductor device comprising a cascode connection of a depletion mode transistor with an electron transit layer composed of AlxGa1-xN and an electron supply layer of AlyGa1-yN, where 0.1<x<0.2 and 0.25<y<0.4, and an enhancement mode transistor with a GaN electron transit layer and an AlGaN electron supply layer, reducing temperature dependence by minimizing lattice mismatch-induced strain effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a depletion mode gallium nitride HEMT is used, then high electron mobility and power handling capability are achieved, but the device cannot perform normally-off operation and exhibits high temperature dependence of on-resistance
Solution Approach 1:
The device is segmented into two distinct transistor components: a depletion mode gallium nitride HEMT for power handling and an enhancement mode transistor for switching control. This segmentation allows each component to optimize its function independently, achieving normally-off operation while maintaining high power capability.
Solution Approach 2:
The invention uses composite material structures with specific aluminum compositions (0.1<x<0.2 for electron transit layer, 0.25<y<0.4 for electron supply layer) to create the depletion mode HEMT. This composite approach with graded aluminum content optimizes electron mobility while reducing lattice mismatch and temperature dependence.
2Speed
If aluminum composition in electron transit layer is increased, then electron mobility is improved, but lattice mismatch-induced strain increases causing current collapse
Solution Approach 1:
The invention optimizes the aluminum composition parameter within a specific range (0.1<x<0.2) rather than using maximum aluminum content. This parameter optimization balances electron mobility enhancement with lattice mismatch control, preventing strain-induced current collapse while maintaining high electron transport capability.
Solution Approach 2:
Different aluminum compositions are used in different layers: the electron transit layer has lower aluminum content (0.1<x<0.2) to reduce strain, while the electron supply layer has higher aluminum content (0.25<y<0.4) to provide sufficient electrons. This local quality differentiation optimizes both mobility and reliability.
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
The proposed device ensures normally-off operation with significantly reduced temperature dependence of on-resistance, limiting current collapse and enhancing reliability and efficiency in high-temperature applications.
Implementation Method 1
an electron transit layer (56) composed of a nitride semiconductor including aluminum in a crystal composition and an electron supply layer (58) formed on the electron transit layer (56) and composed of a nitride semiconductor including aluminum having a larger composition than that of the electron transit layer (56)
Data Source
AI summary
This nitride semiconductor device is provided with: a depletion type transistor which comprises a first gate terminal, a first source terminal and a first drain terminal; and an enhancement type transistor which comprises a second gate terminal, a second source terminal and a second drain terminal. The second drain terminal is connected to the first source terminal; and the second source terminal is connected to the first gate terminal. The depletion type transistor comprises: an electron transit layer which is configured from a nitride semiconductor that contains aluminum in the crystal composition; and an electron supply layer which is formed on the electron transit layer and is configured from a nitride semiconductor that contains a larger amount of aluminum in the composition than the electron transit layer.