Trench VJFET Gate Structure With Silicon Layer for Breakdown Control
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Solution Overview
Problem
Existing junction field effect transistors face challenges in balancing area-specific on-state resistance and reliability, particularly in terms of electric breakdown capability, as device geometries shrink to improve functionalities per unit area.
Innovation Solution
A vertical junction field effect transistor (VJFET) with a trench structure featuring a silicon layer at the bottom side of the trench, where the gate region thickness at the bottom side is greater than at the sidewalls, allowing for independent optimization of electric contact properties and voltage blocking capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device geometries are shrunk to improve functionalities per unit area, then productivity and device density are improved, but reliability and electric breakdown capability deteriorate
Solution Approach 1:
The device structure is segmented into distinct regions with different gate thicknesses: a first gate region at the bottom of the trench with greater thickness for voltage blocking, and a second gate region at the sidewalls with smaller thickness for conduction control. This segmentation allows each region to be optimized for its specific function, resolving the contradiction between high-density geometry and reliability.
Solution Approach 2:
Different parts of the gate structure have different thicknesses tailored to their specific functional requirements. The bottom gate region has increased thickness locally to provide superior voltage blocking and electric breakdown capability, while the sidewall gate region maintains reduced thickness for effective conduction control. This local differentiation enables simultaneous optimization of both reliability and productivity.
2Reliability
If gate region thickness is increased to improve voltage blocking capability, then reliability is improved, but device area and integration density worsen
Solution Approach 1:
The gate structure is divided into multiple segments with different thicknesses positioned at different locations. Only the bottom gate region requires increased thickness for voltage blocking, while the sidewall regions use reduced thickness. This segmentation concentrates the area penalty only where necessary for reliability, minimizing the overall area impact.
Solution Approach 2:
Increased gate thickness is applied locally only at the bottom gate region where voltage blocking is critical, rather than uniformly across the entire gate structure. This localized quality enhancement achieves the required reliability without proportionally increasing the total device area, as the sidewall regions maintain compact dimensions.
3Ease of operation
If gate region thickness is reduced to improve conduction control, then ease of operation is improved, but voltage blocking capability and reliability worsen
Solution Approach 1:
The gate structure is segmented into a bottom gate region with greater thickness for voltage blocking and sidewall gate regions with smaller thickness for conduction control. This segmentation allows each region to be independently optimized: the sidewall regions provide effective conduction control with reduced thickness, while the bottom region ensures adequate voltage blocking capability.
Solution Approach 2:
Reduced gate thickness is applied locally only at the sidewall gate regions where conduction control is the primary function, while the bottom gate region maintains greater thickness for voltage blocking. This local differentiation enables the sidewall regions to achieve superior conduction control without compromising the overall voltage blocking capability provided by the thicker bottom region.
Data Source
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AI summary
A vertical junction field effect transistor, VJFET (100), is proposed. The VJFET includes a trench structure (102) laterally arranged between mesa regions (1041, 1042) along a first lateral direction (x1). The trench structure (102) extends into a semiconductor body (106) from a first surface (108) of the semiconductor body (106). Each of the mesa regions (1041, 1042) includes a mesa channel region (110) of a first conductivity type. The VJFET (100) further includes a gate region (112) of a second conductivity type. The gate region (112) adjoins at least part of opposite sidewalls (1021, 1022) of the trench structure (102) and to a bottom side (1023) of the trench structure (102). The trench structure (102) includes a silicon layer (114) adjoining the gate region (112) at the bottom side (1023) of the trench structure (102). A first thickness (t1) of the gate region at the bottom side (1023) of the trench structure (102) is larger than a second thickness (t2) of the gate region (112) at each of the opposite sidewalls (1021, 1022) of the trench structure.