GaN-Si Cascode Transistor Gate Control for Overvoltage Prevention
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Solution Overview
Problem
Existing semiconductor devices using GaN-based HEMT transistors face challenges in achieving a normally off operation, leading to increased power losses due to reflux currents and reliability issues, particularly in high-voltage applications, as they rely on cascode-connected normally on GaN and normally off Si transistors with inferior recovery characteristics.
Innovation Solution
A semiconductor device configuration that includes a normally off Si transistor and a normally on GaN HEMT transistor, with a capacitor and diodes to control the gate voltage, ensuring the normally on transistor is turned off before the normally off transistor, thereby preventing overvoltage and improving recovery characteristics by using a Schottky barrier diode with superior recovery characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cascode connection of normally on GaN transistor and normally off Si transistor is used to achieve normally off operation, then safety and normally off operation are improved, but power loss increases due to inferior recovery characteristics of Si body diode
Solution Approach 1:
The patent changes the material parameter of the diode from silicon to GaN, exploiting the superior recovery characteristics of GaN material to reduce power loss while maintaining normally off operation capability
Solution Approach 2:
The patent creates a composite structure combining GaN HEMT with superior recovery characteristic diodes, integrating materials with complementary properties to achieve both normally off operation and low power loss
2Device complexity
If body diode of Si transistor is used to handle reflux current, then circuit simplicity is maintained, but recovery characteristics deteriorate leading to increased power loss
Solution Approach 1:
The patent changes the recovery characteristic parameter by selecting diodes with superior recovery properties (Schottky barrier diodes or first recovery diodes) to replace the standard Si body diode, reducing reverse recovery time and power loss
3Reliability
If normally on GaN transistor is used in cascode configuration, then normally off operation is achieved, but overvoltage risks and current collapse occur during state transitions
Solution Approach 1:
The patent applies preliminary action by turning off the normally on GaN transistor before the normally off transistor during state transitions, preventing overvoltage generation and current collapse before they can occur
Solution Approach 2:
The patent implements feedback control through gate voltage management, using the capacitor to maintain gate voltages that prevent harmful effects during switching transitions
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 enhances reliability by preventing overvoltage and improving recovery characteristics, reducing power losses and maintaining stable operation in high-voltage applications, especially in motor control systems.
Implementation Method 1
a capacitor having one end connected to between the first gate and the common gate terminal and the other end connected to the second gate
Implementation Method 2
a Schottky barrier diode or first recovery diode to manage reflux currents and prevent overvoltages
Data Source
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AI summary
A semiconductor device according to an embodiment includes a normally off transistor (10) having a first source (11), a first drain (12), a first gate (13) connected to a common gate terminal (300), and a body diode (14), a normally on transistor (20) having a second source (21) connected to the first drain, a second drain (22), and a second gate (23), a capacitor (40) provided between the common gate terminal and the second gate, a first diode (30) having a first anode (31) connected to the second gate and a first cathode (32) connected to the first source, and a second diode (50) having a second anode (51) connected to the first source and a second cathode (52) connected to the second drain.