Bidirectional Semiconductor Switch With Passive Substrate Discharge
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Solution Overview
Problem
Conventional bidirectional switches with a common drain configuration face performance degradation due to the inability to maintain the substrate voltage close to 0V during the on-state, leading to large negative potentials and inefficient switching behavior.
Innovation Solution
A passive discharge circuit is integrated with the bidirectional switch, providing a discharge path for the substrate and voltage blocking capabilities without requiring additional gate drivers or control components, utilizing a combination of normally-on and normally-off devices to manage substrate potential during both on and off-states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If back-to-back diodes are integrated to provide discharge path, then discharge function is provided, but substrate voltage cannot be held close to 0V during on-state and large negative potential occurs
Solution Approach 1:
The patent changes the electrical parameters of the discharge path by using a transistor with controllable resistance instead of fixed diodes. The transistor's resistance is dynamically adjusted through gate control to provide low-impedance discharge path during off-state while preventing substrate voltage deviation during on-state, thus resolving the contradiction between providing discharge function and maintaining substrate voltage control.
Solution Approach 2:
The discharge path circuit is designed to automatically activate and deactivate based on the bidirectional switch state without external control. The transistor in the discharge path turns on automatically when the bidirectional switch is off, providing self-service discharge function, and turns off when the bidirectional switch is on, preventing substrate voltage control issues.
2Adaptability or versatility
If substrate is kept floating with one source biased at high voltage, then bidirectional operation is enabled, but substrate voltage drifts away from ground potential during on-state
Solution Approach 1:
The patent introduces a transistor-based discharge path as an intermediary element between the substrate and ground. This intermediary actively manages substrate voltage by providing a controlled discharge path to ground when needed, enabling the substrate to remain stable at ground potential even while supporting high-voltage bidirectional operation through the main switch.
3Reliability
If passive discharge circuit is added to maintain substrate voltage, then substrate voltage control is improved, but device complexity increases
Solution Approach 1:
The patent merges the discharge path transistor with the bidirectional switch structure, sharing common substrates and integrating the discharge transistor alongside the main switch transistors. This integration approach reduces overall device complexity compared to adding a completely separate discharge circuit, while still achieving effective substrate voltage control through the combined structure.
Data Source
AI summary
A semiconductor device includes: a semiconductor body having an active region and a substrate region beneath the active region; a bidirectional switch having first and second gate structures configured to control a conductive state of a channel in the active region, and first and second input-output terminals electrically connected to the channel; and a passive discharge circuit in parallel with the bidirectional switch and configured to utilize a fraction of a voltage across the first and second input-output terminals to switch on a transistor device that electrically connects the substrate region to the input-output terminal at the lower potential during an off-state of the bidirectional switch and during ZVS (zero-voltage switching) transition periods.