p-GaN HEMT MIS Shield Structure for Threshold Voltage Stability
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Solution Overview
Problem
p-GaN gate HEMTs face instability in threshold voltage when switching between OFF-state and ON-state due to drain voltage, leading to unreliable operation.
Innovation Solution
A transistor design with a MIS shield structure, including a p-doped III-V compound conductive member and a dielectric stack with specific trench configurations, where the gate metal contacts the conductive member through one trench and the first dielectric layer through another, providing a field plate and shielding the p-GaN junction from reverse bias.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a p-GaN gate HEMT is used to achieve normally-off operation, then enhancement mode operation and ease of mass production are improved, but threshold voltage stability deteriorates when drain voltage switches between OFF-state and ON-state
Solution Approach 1:
A MIS shield structure is introduced as an intermediary element between the gate and the channel. This shield comprises a conductive member (such as p-doped III-V compound) covered by a dielectric layer, which mediates the electric field distribution and protects the p-GaN gate from direct exposure to reverse bias, thereby stabilizing threshold voltage while maintaining enhancement mode operation
Solution Approach 2:
The solution adds a vertical dimension to the device structure by stacking the dielectric layer over the conductive member, creating a three-dimensional MIS shield configuration. This vertical stacking allows the shield to effectively manage electric fields in the vertical direction without interfering with the lateral current flow, resolving the threshold voltage instability issue
2Ease of manufacture
If the gate metal directly contacts the p-GaN junction, then simple fabrication is achieved, but drain-induced shifts and leakage current increase
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the gate metal and the conductive member, creating a MIS (Metal-Insulator-Semiconductor) structure. This dielectric barrier prevents direct contact that would cause harmful drain-induced shifts, while still allowing electric field modulation for proper device operation
Solution Approach 2:
The harmful direct contact between gate metal and p-GaN junction is extracted/removed from the structure. Instead, the gate metal contacts only the dielectric layer, which then interfaces with the conductive member, separating the gate control function from the high-field region to eliminate drain-induced threshold voltage shifts
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 MIS shield structure stabilizes the threshold voltage, enhances p-GaN gate reliability by concentrating the electric field at the MIS shield, reducing drain-induced shifts and leakage current, and maintaining efficient operation.
Implementation Method 1
stabilizes the threshold voltage, enhances p-GaN gate reliability by concentrating the electric field at the MIS shield
Implementation Method 2
The dielectric stack may be on the barrier layer and on the conductive member. The gate metal may contact the conductive member through the first trench and may contact the first dielectric layer through the second trench
Data Source
AI summary
A transistor may include a buffer layer, source and drain contacts on the buffer layer, a barrier layer on the buffer layer, a conductive member on the barrier layer, a dielectric stack, and a gate metal. The barrier layer may be between the source and drain contacts. The conductive member may include a p-doped III-V compound. The dielectric stack may be on the barrier layer and on the conductive member. The dielectric stack may include a first dielectric layer and a second dielectric layer on the first dielectric layer. First and second trenches may extend through the dielectric stack to the conductive member and to the first dielectric layer, respectively. The gate metal may be on the dielectric stack, and may contact the conductive member through the first trench and may contact the first dielectric layer through the second trench.