SiC VJFET Inactive Source Regions for Thermal Management
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Solution Overview
Problem
Silicon carbide vertical junction field effect transistors (VJFETs) face challenges in heat dissipation during high current flow due to the close proximity of source fingers, which can lead to increased temperature, while widening the trench to improve heat dissipation alters electrical characteristics.
Innovation Solution
The implementation of electrically inactive source regions, achieved by selectively etching trenches and depositing dielectric layers to prevent electrical contact with the source metal, allows for improved heat dissipation while maintaining desired electrical characteristics by keeping the trench width small and the P+ gate implant profile intact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If source fingers are placed at small pitch to improve specific on-resistance and normalized saturated drain current, then electrical performance is improved, but heat dissipation deteriorates due to close proximity of source fingers
Solution Approach 1:
The device is segmented into electrically active source fingers and electrically inactive source fingers. The inactive fingers are separated from active fingers by trenches filled with dielectric material, allowing heat dissipation without compromising the electrical performance of active fingers. This segmentation enables independent optimization of thermal and electrical characteristics.
Solution Approach 2:
Different regions of the device are assigned different electrical properties: active source fingers maintain low resistance for current conduction, while inactive source fingers are isolated by dielectric trenches to serve primarily as heat dissipation structures. This local differentiation allows simultaneous optimization of both electrical performance and thermal management.
2Temperature
If trench width is increased to improve heat dissipation, then temperature rise is reduced, but electrical characteristics such as threshold voltage change from desired design targets
Solution Approach 1:
The device structure is segmented into active and inactive regions separated by dielectric trenches. The trenches are positioned only between active and inactive fingers, not between active fingers themselves. This allows the trench width to be optimized for heat dissipation without affecting the electrical characteristics of active source fingers, as the trenches are electrically isolated from the active regions.
Solution Approach 2:
Dielectric material is introduced as an intermediary substance in the trenches between active and inactive source fingers. This dielectric layer provides thermal isolation and heat dissipation pathways while electrically isolating the inactive fingers from active fingers, thereby preventing any influence on the electrical characteristics of active regions.
3Temperature
If source fingers are placed further apart to improve heat dissipation, then temperature rise is reduced, but the packing density of source fingers decreases
Solution Approach 1:
The source finger array is segmented into alternating active and inactive fingers. Inactive fingers are separated from active fingers by dielectric trenches, while active fingers remain closely spaced to maintain high packing density. This segmentation allows inactive fingers to serve as thermal management structures without reducing the density of current-conducting active fingers.
Solution Approach 2:
The source finger structure is given multi-functionality: active source fingers perform electrical conduction, while inactive source fingers serve primarily as heat dissipation structures. Both types of fingers are part of the same source region array, allowing the device to simultaneously achieve high packing density through active fingers and effective heat dissipation through inactive fingers.
Data Source
AI summary
Vertical junction field effect transistors (VJFETs) having improved heat dissipation at high current flow while maintaining the desirable specific on-resistance and normalized saturated drain current properties characteristic of devices having small pitch lengths are described. The VJFETs comprise one or more electrically active source regions in electrical contact with the source metal of the device and one or more electrically inactive source regions not in electrical contact with the source metal of the device. The electrically inactive source regions dissipate heat generated by the electrically active source regions during current flow.