SiC BJT Shielding Regions for Punch-Through Prevention
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Solution Overview
Problem
Silicon carbide (SiC) bipolar junction transistors (BJTs) face a trade-off between achieving high emitter current gain and sufficient blocking voltage due to the limitations of base region thickness and doping level, which affects their performance in both on-state and off-state conditions.
Innovation Solution
The introduction of shielding regions with a higher dopant dose and conductivity type opposite to the base region, which electrostatically shield the intrinsic base region from electric fields during off-state blocking conditions, allowing for a thinner and lower-doped base region that enhances current gain while maintaining high blocking voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the base region thickness is reduced to increase current gain, then the emitter current gain is improved, but the base punch-through effect occurs at high collector bias
Solution Approach 1:
The base region is segmented into two distinct portions: a first portion with lower doping concentration and a second portion with higher doping concentration. This segmentation allows the first portion to provide low resistance for high current gain, while the second portion prevents punch-through at high bias, resolving the contradiction between current gain and blocking voltage.
Solution Approach 2:
Different regions of the base are given different doping concentrations tailored to their specific functions. The first portion (near the emitter) has lower doping to minimize recombination and maximize current gain, while the second portion (near the collector) has higher doping to prevent punch-through and maintain blocking voltage, applying local quality to resolve the global contradiction.
2Reliability
If the base region doping level is increased to prevent early punch-through, then the blocking voltage is improved, but the emitter current gain decreases
Solution Approach 1:
The base doping profile is segmented into two zones with different concentrations. The first portion maintains lower doping (1E16 to 1E18 atoms/cm³) to preserve high emitter current gain, while the second portion has higher doping (1E18 to 1E20 atoms/cm³) to prevent punch-through and ensure adequate blocking voltage, thus resolving the contradiction through spatial segmentation of doping levels.
Solution Approach 2:
The base region is assigned different doping qualities at different locations: the first portion near the emitter junction has low doping quality optimized for carrier injection and current gain, while the second portion near the collector junction has high doping quality optimized for electric field control and punch-through prevention, resolving the contradiction through localized property optimization.
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
This design improves blocking capabilities and current gain by reducing the punch-through effect, enabling SiC BJTs to handle higher blocking voltages without compromising on-state performance.
Implementation Method 1
The introduction of shielding regions with a higher dopant dose and conductivity type opposite to the base region, which electrostatically shield the intrinsic base region from electric fields during off-state blocking conditions
Data Source
AI summary
A silicon carbide (SiC) bipolar junction transistor (BJT) and a method of manufacturing such a SiC BJT is provided. The SiC BJT can include a collector region having a first conductivity type, a base region having a second conductivity type opposite the first conductivity type, and an emitter region having the first conductivity type, the collector region, the base region and the emitter region being arranged as a stack. The emitter region defining an elevated structure defined at least in part by an outer sidewall on top of the stack. The base region having a portion capped by the emitter region and defining an intrinsic base region where the intrinsic base region includes a portion extending from the emitter region to the collector region. The SiC BJT can include a first shielding region and a second shield region each having the second conductivity type.