GaN FET Gate Structure for Threshold Stability and Breakdown
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Solution Overview
Problem
GaN field effect transistors with Schottky contact gate metal layers face instability in threshold voltage due to difficulty in charge discharge and prone breakdown under positive voltage bias, necessitating improved voltage withstand and reliability.
Innovation Solution
The implementation of a field effect transistor with a gate structure comprising a P-type gallium nitride (pGaN) and N-type gallium nitride (nGaN) layer in a stacking manner, replacing the Schottky diode, and ohmic contact between the gate metal layer and nGaN layer to enhance breakdown capability and threshold voltage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a Schottky contact gate metal layer is used, then the device can be manufactured with conventional processes, but the threshold voltage becomes unstable and the device is prone to breakdown under positive voltage bias
Solution Approach 1:
The patent changes the contact type parameter from Schottky contact to ohmic contact between the gate metal layer and the nGaN layer. This parameter change eliminates the formation of back-to-back diodes, enabling proper charge discharge and stabilizing the threshold voltage while maintaining manufacturability through conventional semiconductor processing techniques.
Solution Approach 2:
The patent employs a composite gate structure consisting of multiple layers including the gate metal layer, nGaN layer, and pGaN layer. This composite structure combines the advantages of different materials to achieve both ease of manufacture and improved reliability, with the nGaN/pGaN heterostructure providing enhanced voltage withstand capability.
2Device complexity
If a Schottky diode is used between gate metal layer and gate structure, then the device structure is simple, but the device breaks down easily under positive voltage bias
Solution Approach 1:
The patent replaces the simple Schottky diode with a composite nGaN/pGaN heterostructure that provides superior breakdown capability. The composite structure leverages the different bandgap properties of nGaN and pGaN to achieve high voltage withstand capability while maintaining a relatively simple overall device architecture.
Solution Approach 2:
The patent changes the junction type parameter from Schottky junction to homojunction in the nGaN/pGaN structure. This parameter change fundamentally improves the breakdown characteristics by eliminating the Schottky barrier and utilizing the properties of doped semiconductor junctions, which can withstand higher positive voltages.
3Ease of operation
If a Schottky diode is used between gate metal layer and gate structure, then the device can be operated, but charge cannot be discharged and threshold voltage becomes unstable
Solution Approach 1:
The patent changes the contact parameter from Schottky contact to ohmic contact, which fundamentally alters the electrical characteristics of the gate metal layer interface. Ohmic contact enables bidirectional current flow and proper charge discharge, ensuring stable threshold voltage while maintaining ease of device operation.
Solution Approach 2:
The patent extracts and eliminates the Schottky diode structure that prevents charge discharge. By removing the Schottky barrier and replacing it with ohmic contact, the harmful charge accumulation effect is eliminated, allowing the device to operate reliably with stable threshold voltage.
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 significantly increases gate voltage withstand capability, improves reliability by reducing charge storage effects, and ensures stable operation by applying most voltages to the active area, thereby enhancing the overall performance of the field effect transistor.
Implementation Method 1
an nGaN/pGaN reverse bias diode is used to replace a gate metal/pGaN Schottky diode in a current technology to withstand a voltage
Implementation Method 2
the gate metal layer is in ohmic contact with the nGaN layer. Forming ohmic contact between metal and a semiconductor means that a pure resistor is at a contact point, and smaller resistance is better
Data Source
AI summary
A field effect transistor includes a channel layer, a source, a drain, a gate structure, and a gate metal layer; and the gate structure includes a P-type gallium nitride layer and an N-type gallium nitride layer that are disposed in a stacking manner, so that a gate metal/pGaN Schottky diode is replaced with an nGaN/pGaN reverse bias diode, to improve a gate voltage-withstand capability of the field effect transistor, thereby improving a breakdown capability of the field effect transistor. A doping density of the P-type gallium nitride layer is between 1×1018 cm−3 and 1×1019 cm−3, so that a charge storage effect during operation of a device can be reduced, carriers at the pGaN layer can be exhausted as much as possible, and redundant-charge storage is avoided, thereby improving operating threshold voltage stability of the device.