GaN FET Multi-Section Channel for Normally-Off High-Voltage Switching
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Solution Overview
Problem
Current high-power gallium nitride (GaN)-based heterostructure field effect transistors (HFETs) are normally-on devices, leading to performance limitations due to high leakage current, lower breakdown voltage, and reduced reliability, especially when attempting to achieve a normally-off condition, which is crucial for power electronics applications.
Innovation Solution
A field effect transistor design featuring a channel with multiple threshold voltages, including a normally-off section connected to a source electrode and a normally-on section between the source and drain electrodes, with a charge-controlling electrode extending over the gate and gap-filling material to control the on/off state, allowing for high voltage operation and improved reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a GaN-based HFET is designed as a normally-on device to achieve high power and breakdown voltage, then high power and breakdown voltage are improved, but reliability deteriorates due to gate voltage source failure resulting in extremely high currents
Solution Approach 1:
The channel is divided into multiple adjacent sections with different threshold voltages. The first section (adjacent to source) has a higher threshold voltage and is normally-off, while the second section (between source and drain) has a lower threshold voltage and is normally-on. This segmentation allows the device to achieve normally-off operation for safety while maintaining high power capability through the normally-on section.
2Ease of operation
If a recessed gate structure is used to achieve normally-off condition, then normally-off operation is improved, but leakage current increases and breakdown voltage decreases
Solution Approach 1:
Different sections of the channel are given different electrical characteristics. The first section has a higher threshold voltage for normally-off operation, while the second section has a lower threshold voltage to maintain low leakage current and high breakdown voltage. This local differentiation of channel properties resolves the contradiction between achieving normally-off operation and maintaining reliable electrical characteristics.
3Ease of operation
If a cascode circuit with Si-based devices is used to achieve normally-off condition, then normally-off operation is improved, but parasitic parameters increase and series resistance increases
Solution Approach 1:
The invention merges the normally-off and normally-on characteristics into a single integrated device structure rather than using separate cascode devices. The multi-section channel integrates the functions of both normally-off and normally-on operation in one device, eliminating the need for additional Si-based devices and reducing parasitic parameters and series resistance.
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 design enables a low on-resistance, high-voltage power switch with enhanced breakdown voltage and reliability by controlling the on/off state of the channel sections, addressing the limitations of existing GaN-based HFETs.
Implementation Method 1
a charge-controlling electrode connected to the source electrode, wherein the charge-controlling electrode extends from the source electrode over the gate without contact and over a portion of the gap-filling material with contact; wherein a potential difference between the charge-controlling electrode and the channel controls the on/off state of the normally-on section of the channel
Data Source
AI summary
A device having a channel with multiple voltage thresholds is provided. The channel can include a first section located adjacent to a source electrode, which is a normally-off channel and a second section located between the first section and a drain electrode, which is a normally-on channel. The device can include a charge-controlling electrode connected to the source electrode, which extends from the source electrode over at least a portion of the second section of the channel. During operation of the device, a potential difference between the charge-controlling electrode and the channel can control the on/off state of the normally-on section of the channel.