Monolithic Bidirectional Trench FET for Low On-Resistance
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Solution Overview
Problem
Conventional power MOSFET switches require two transistors in series to achieve bidirectional functionality, which doubles on-resistance and chip area, making them inefficient and costly.
Innovation Solution
A monolithic bidirectional trench field effect transistor (FET) with multiple gate and shield electrodes connected through a control structure, utilizing a single metal layer and offset shield electrode contacts to reduce on-resistance and enhance breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two power MOSFETs are connected in series to achieve bidirectional functionality, then bidirectional current blocking capability is improved, but on-resistance doubles
Solution Approach 1:
The device is segmented into two symmetrical halves, each functioning as a complete bidirectional switch with its own gate electrode. This segmentation allows each half to independently block current in both directions, eliminating the need for series connection and reducing total on-resistance while maintaining bidirectional blocking capability
Solution Approach 2:
The patent employs asymmetric doping profiles within each device half, with different dopant concentrations in the source and drain regions. This asymmetry optimizes the electrical characteristics for bidirectional operation, enabling low on-resistance in both directions while maintaining effective voltage blocking capability
2Reliability
If two power MOSFETs are connected in series to achieve bidirectional functionality, then bidirectional current blocking capability is improved, but chip area doubles
Solution Approach 1:
The patent merges two bidirectional switch functions into a single integrated device structure. By sharing common elements such as the substrate and optimizing the layout of the two device halves, the total chip area is reduced compared to using two separate power MOSFETs connected in series, while maintaining full bidirectional blocking capability
Solution Approach 2:
Each device half is designed as a universal bidirectional switch that can operate independently in both current directions. This multi-functionality allows a single device to replace what would traditionally require two separate transistors, reducing the overall chip area while maintaining the required bidirectional functionality
3Reliability
If two power MOSFETs are connected in series to achieve bidirectional functionality, then bidirectional current blocking capability is improved, but specific on-resistance quadruples
Solution Approach 1:
The patent employs parameter changes including optimized dopant concentrations, adjusted junction depths, and modified geometric dimensions of the device structures. These parameter optimizations reduce the on-resistance of each device half, and when combined, the total specific on-resistance is significantly lower than the quadrupled value that would result from series connection of two conventional power MOSFETs
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 solution enables efficient bidirectional current conduction and blocking with reduced on-resistance and chip area, improving the performance and cost-effectiveness of semiconductor devices.
Implementation Method 1
bidirectional trench field effect transistor (FET)
Implementation Method 2
The shield electrodes 28, 32 are configured to control the width of a depletion layer between the body regions 40
Data Source
AI summary
In one embodiment, a structure for a semiconductor device has trench shield electrodes formed above and below a gate electrode. The structure can be configured to function as a bidirectional power field effect transistor.