Composite Semiconductor Device with Series Unipolar Rectifiers
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Solution Overview
Problem
Conventional composite semiconductor devices using a Zener diode to prevent breakdown of normally-off field effect transistors suffer from low operation speed, leading to drain-source voltage exceeding the transistor's withstand voltage, potentially causing device failure.
Innovation Solution
A composite semiconductor device is designed with N unipolar rectifier elements, such as Schottky diodes, connected in series between the drain and source of the normally-off field effect transistor, ensuring the voltage across the drain and source is restricted to a level not higher than the transistor's withstand voltage, utilizing materials with higher energy band gaps like AlxGa1-xN, SiC, or GaN, to enhance operation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Zener diode is used to restrict drain-source voltage of the second field effect transistor, then the transistor is protected from breakdown, but the operation speed is too slow and the voltage may exceed withstand voltage causing breakdown
Solution Approach 1:
The patent changes the key parameter of the rectifier element from slow-response Zener diode characteristics to fast-response unipolar diode characteristics. By selecting unipolar rectifier elements with significantly faster operation speed than Zener diodes, the system achieves both voltage restriction functionality and high-speed operation, resolving the contradiction between reliability protection and speed performance.
2Reliability
If N unipolar rectifier elements are connected in series, then the operation speed increases and breakdown is prevented, but the device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the voltage restriction function into N separate unipolar rectifier elements connected in series. Each element handles a portion of the total voltage, and their combined effect provides the necessary voltage restriction. This segmentation approach enables the use of simpler, faster unipolar elements instead of a single complex Zener diode, achieving reliability improvement while managing device complexity through functional distribution.
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 use of high-speed unipolar rectifier elements effectively prevents the normally-off field effect transistor from breaking down by maintaining the drain-source voltage within safe limits, improving operational reliability compared to Zener diode-based systems.
Implementation Method 1
N (N being a natural number) unipolar rectifier elements connected in series between the drain and the source of the second field effect transistor in a forward direction and rendered conductive when a voltage across the drain and the source of the second field effect transistor exceeds a predetermined voltage
Data Source
AI summary
This composite semiconductor device has a normally-on first field effect transistor and a normally-off second field effect transistor connected in series between first and second terminals, gates of the first and second field effect transistors being connected to second and third terminals, respectively, and N diodes being connected in series in a forward direction between a drain and a source of the second field effect transistor. Therefore, a drain-source voltage (Vds) of the second field effect transistor can be restricted to a voltage not higher than a withstand voltage of the second field effect transistor.