GaN-Si Cascode Transistor with Diode for Reflux Current
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Solution Overview
Problem
GaN-based semiconductor devices, particularly high electron mobility transistors (HEMTs), are generally normally-on, making it difficult to achieve normally-off operation required for safety in high-power applications, and existing cascode configurations with silicon transistors suffer from inferior body diode recovery characteristics, leading to increased losses due to reflux currents in inverter circuits.
Innovation Solution
A semiconductor device configuration combining a first and second normally-off type silicon transistors and a normally-on GaN-based HEMT, with a diode having superior recovery characteristics, such as a PIN or PN diode, connected in series to enable normally-off operation and improve reflux current handling, reducing power losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cascode connection of a GaN-based normally-on transistor and a Si normally-off transistor is applied, then normally-off operation is achieved, but the body diode recovery characteristic becomes inferior leading to increased losses
Solution Approach 1:
A capacitor is introduced as an intermediary component between the GaN-based transistor and the Si transistor. This capacitor blocks the reflux current from flowing through the Si transistor's body diode during switching operations, thereby preventing the inferior recovery characteristic from causing energy losses while maintaining the normally-off operation capability
Solution Approach 2:
The invention changes the electrical parameters of the circuit by adding a capacitor that modifies the current flow path. This parameter change ensures that the reflux current bypasses the Si transistor's body diode, improving the recovery characteristic and reducing power loss while preserving the normally-off operation
2Power
If a GaN-based HEMT is used, then high breakdown voltage and low power loss are achieved, but the transistor becomes normally-on making normally-off operation difficult
Solution Approach 1:
The transistor system is segmented into two separate transistors: a GaN-based normally-on transistor that provides high breakdown voltage and low power loss, and a Si normally-off transistor that provides the normally-off operation capability. This segmentation allows each transistor to fulfill its specific function while working together in a cascode configuration
Solution Approach 2:
The invention uses a composite structure combining GaN-based semiconductor material and Si semiconductor material in a cascode connection. This composite approach leverages the superior electrical characteristics of GaN for high voltage and low loss, while utilizing Si's ability to provide normally-off operation
Data Source
AI summary
A semiconductor device according to one embodiment includes a first normally-off type transistor including a first source, a first drain, a first gate, and a first body diode, a second normally-off type transistor including a second source connected to the first source, a second drain, a second gate connected to the first gate, and a second body diode, a normally-on type transistor including a third source connected to the first drain, a third drain, and a third gate connected to the second drain, and a diode including an anode connected to the second drain and a cathode connected to the third drain.