Trench Gate MOSFET Structure for Bidirectional Blocking and Conduction
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Solution Overview
Problem
Conventional power MOS devices have unidirectional blocking and conduction characteristics due to their asymmetric drain-source structure, limiting their application in bidirectional switching applications such as low-power DC-DC converters and lithium-ion battery charging/discharging.
Innovation Solution
A bidirectional conduction trench gate power MOS device is developed, featuring a trench gate structure with interchangeable source and drain electrodes, allowing for bidirectional blocking and conduction within a single power MOS transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two discrete power MOS devices are connected in anti-series to achieve bidirectional conduction, then bidirectional conduction capability is established, but the on-resistance of the circuit greatly increases and cost increases
Solution Approach 1:
The patent merges two separate power MOS devices into a single integrated device structure. The trench gate structure combines two unidirectional conduction paths in one device, allowing bidirectional current flow while maintaining low on-resistance. The shared substrate, epitaxial layer, and trench gate structure eliminate the need for two discrete devices, directly reducing the total on-resistance compared to anti-series connections.
Solution Approach 2:
The single power MOS device structure performs multiple functions: it provides both unidirectional and bidirectional conduction capabilities, voltage blocking in both directions, and current switching. The interchangeable source and drain electrodes enable the device to function as two unidirectional devices connected in anti-series, while maintaining the benefits of a single integrated structure.
2Adaptability or versatility
If two discrete power MOS devices are connected in anti-series to achieve bidirectional conduction, then bidirectional conduction capability is established, but system integration is reduced and cost increases
Solution Approach 1:
The patent merges two separate power MOS devices into a single integrated device structure. The trench gate structure combines two unidirectional conduction paths in one device, allowing bidirectional current flow while maintaining low on-resistance. The shared substrate, epitaxial layer, and trench gate structure eliminate the need for two discrete devices, directly reducing the total on-resistance compared to anti-series connections.
3Ease of manufacture
If conventional vertical trench gate power MOS device structure is used, then manufacturing cost is reduced, but the device does not achieve bidirectional conduction capability
Solution Approach 1:
The patent introduces asymmetry in the doping distribution within the trench gate structure. The first conductivity type lightly doped region has a bottom that is lower than the bottom of the trench, creating an asymmetric doping profile that enables bidirectional conduction. This asymmetric design maintains compatibility with conventional manufacturing processes while achieving the new functionality.
Solution Approach 2:
The patent extends the lightly doped region vertically below the trench bottom, adding a depth dimension to the doping structure. This three-dimensional doping configuration enables the device to support bidirectional conduction while maintaining a planar surface structure that is compatible with conventional manufacturing processes.
4Ease of manufacture
If lateral planar gate power MOS device structure is used, then manufacturing is simplified, but the device has large on-resistance due to large size
Solution Approach 1:
The patent transitions from a purely lateral planar structure to a three-dimensional trench gate structure with vertical components. The trench extends into the epitaxial layer, and the lightly doped region extends below the trench bottom, utilizing the vertical dimension to reduce the required lateral area while maintaining low on-resistance through optimized current paths.
Data Source
AI summary
A bidirectional conduction trench gate power MOS device and a manufacturing method thereof are provided. A gate electrode, a source electrode and a drain electrode are formed on a surface of a silicon wafer to realize a bidirectional conduction and bidirectional blocking power MOS device used in an application environment such as lithium battery BMS protection. A device structure of the bidirectional conduction trench gate power MOS device has advantages compared with double-transistor series connection used in a conventional BMS and other structures for realizing a bidirectional conduction: firstly, the bidirectional conduction trench gate power MOS device needs to occupy half or less area compared with a conventional mode, improving a degree of integration; secondly, the device structure has a simple manufacturing process and a low manufacturing cost reducing manufacturing problems; thirdly, the drain electrode and the source electrode of the device structure are exchanged to realize a symmetrical structure.