GaN HEMT Channel Stack Field Management
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Solution Overview
Problem
Conventional GaN transistors face issues with high threading dislocation density, electric field concentration at the gate edge, reduced maximum current, increased on-resistance, and leakage due to threading dislocations, which affect reliability and performance, especially at high temperatures.
Innovation Solution
A normally off nitride-based transistor with a junction structure of a first conductive nitride semiconductor layer and an intrinsic nitride semiconductor layer is developed, featuring a nucleation layer for TD concentration and a high resistance nitride-based semiconductor buffer layer to prevent electric field concentration and maintain a constant turn-off blocking electric field, thereby reducing leakage and on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If AlGaN/GaN HEMT is formed on inexpensive substrate such as sapphire or silicon, then cost is reduced, but threading dislocation density increases leading to reliability degradation
Solution Approach 1:
The device is segmented into distinct functional regions: a first region with high threading dislocation density formed on the inexpensive substrate, and a second region with low threading dislocation density formed through selective epitaxial growth. This segmentation allows the device to utilize the cost advantage of inexpensive substrates while isolating the critical channel region from dislocation damage, thereby maintaining both low cost and high reliability
Solution Approach 2:
Different regions of the substrate are given different qualities: the first region is designed to accommodate high dislocation density for cost-effectiveness, while the second region is engineered with low dislocation density through selective growth conditions for high-performance operation. This local differentiation allows each region to serve its specific function optimally
2Reliability
If recess gate or p-GaN gate is used to achieve normally off characteristic, then switching performance is improved, but threshold voltage control becomes difficult and productivity decreases
Solution Approach 1:
The invention changes the fundamental parameter approach from geometric control (recess depth, p-GaN thickness) to material composition control (Al content gradient in AlGaN barrier layer). By adjusting the aluminum composition ratio in the barrier layer, the threshold voltage and normally off characteristics are achieved through a well-controlled epitaxial growth process, avoiding the difficult etching and doping processes required by conventional methods
3Device complexity
If conventional horizontal AlGaN/GaN HEMT structure is used, then manufacturing is simplified, but electric field concentration at gate edge reduces breakdown voltage
Solution Approach 1:
The gate structure employs asymmetric field plates extending from opposite sides of the gate electrode, creating an asymmetric electric field distribution that actively counteracts the natural electric field concentration at the gate edge. This asymmetric design redistributes the electric field more uniformly across the gate region, preventing breakdown while maintaining a relatively simple overall device structure
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 solution effectively prevents electric field concentration, maintains high breakdown voltage, and reduces leakage and on-resistance rise in high temperature operations, enhancing the reliability and performance of the nitride-based transistor.
Implementation Method 1
a junction structure of a first conductive nitride semiconductor layer and an intrinsic nitride semiconductor layer such that a fixed turn-off blocking electric field is generated in the channel
Implementation Method 2
featuring a nucleation layer for TD concentration
Implementation Method 3
a high resistance nitride-based semiconductor buffer layer to prevent electric field concentration and maintain a constant turn-off blocking electric field
Data Source
AI summary
A normally off nitride-based transistor may include a source electrode and a drain electrode, a channel layer serving as a charge transfer path between the source electrode and the drain electrode, and a gate electrode that controls charge transfer of the channel layer. The channel layer may have a junction structure of a first conductive nitride semiconductor layer and an intrinsic nitride semiconductor layer such that a fixed turn-off blocking electric field is generated in the channel layer between the source electrode and the drain electrode in a turn-off state. The intrinsic nitride semiconductor layer may include an intrinsic GaN semiconductor layer, and the first conductive nitride semiconductor layer may include a p type GaN semiconductor layer stacked over the intrinsic GaN semiconductor layer.