GaN Semiconductor Mesa Cap Layer Gate Leakage Reduction
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Solution Overview
Problem
Transistors using GaN-based nitride semiconductors face high gate leakage currents due to ohmic coupling between p-type nitride semiconductors and gate electrodes, which hinders their performance and scalability.
Innovation Solution
A semiconductor device structure featuring a mesa-type cap layer and a Schottky-joined gate electrode, with a specific layer configuration of nitride semiconductor layers to suppress two-dimensional electron gas formation under the gate, reducing gate leakage currents and enabling normally-off characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type nitride semiconductor layer is used under the gate electrode to achieve normally-off characteristics, then the transistor can be turned off at zero gate voltage, but the gate leakage current becomes very high due to ohmic coupling
Solution Approach 1:
The patent changes the electrical parameters of the cap layer by controlling its thickness (5 nm to 50 nm) and composition (AlGaN with varying Al content), transforming it from a p-type layer that causes ohmic coupling to an undoped or lightly-doped layer that forms a Schottky junction, thereby reducing gate leakage current while maintaining normally-off characteristics
Solution Approach 2:
The cap layer serves as an intermediary between the gate electrode and the underlying nitride semiconductor layers. By introducing this intermediate layer with specific properties (undoped or lightly-doped AlGaN), the patent mediates the electrical interaction to achieve Schottky junction formation, eliminating direct ohmic coupling while preserving the normally-off functionality
2Device complexity
If the gate electrode is directly coupled to the nitride semiconductor layer to simplify the structure, then the device complexity is reduced, but the gate leakage current increases significantly
Solution Approach 1:
The patent segments the gate structure by introducing a distinct cap layer between the gate electrode and the underlying nitride semiconductor. This segmentation creates a Schottky junction interface that physically separates the gate electrode from direct contact with the channel-forming layers, thereby reducing gate leakage current while maintaining structural clarity and manufacturability
3Loss of energy
If a thicker cap layer is used to reduce gate leakage current, then the gate leakage current is suppressed, but the two-dimensional electron gas formation under the gate is affected and normally-off characteristics may be lost
Solution Approach 1:
The patent optimizes the cap layer thickness parameter within a specific range (5 nm to 50 nm) to achieve the right balance. Within this range, the cap layer is thick enough to suppress gate leakage current through Schottky junction formation but thin enough to allow the underlying AlGaN barrier layer to maintain the two-dimensional electron gas and normally-off characteristics
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 reduces gate leakage currents, allowing for improved transistor performance, reduced power loss, and enhanced scalability, while maintaining normally-off characteristics.
Implementation Method 1
The gate electrode and the cap layer are Schottky-joined
Data Source
AI summary
Characteristics of a semiconductor device are improved.A semiconductor device of the present invention includes a buffer layer composed of a first nitride semiconductor layer, a channel layer composed of a second nitride semiconductor layer, and a barrier layer composed of a third nitride semiconductor layer, which are sequentially laminated, and a cap layer composed of a fourth nitride semiconductor layer of mesa type, which is formed over the barrier layer. The semiconductor device also includes a source electrode formed on one side of the cap layer, a drain electrode formed on the other side of the cap layer, and a first gate electrode formed over the cap layer. The first gate electrode and the cap layer are Schottky-joined. A Schottky gate electrode (the first gate electrode) is provided over the cap layer in this way, so that when a gate voltage is applied, an electric field is applied to the entire cap layer and a depletion layer spreads. Therefore, it is possible to suppress a gate leakage current.