Fin-Based Bipolar Junction Transistor Emitter Resistance Reduction
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Solution Overview
Problem
Conventional bipolar junction transistors (BJTs) fabricated in CMOS processes have poor performance due to high emitter series resistance and low current conduction capability, as well as high base leakage current, primarily because the emitter is smaller than the base and the base-emitter junction is not well defined.
Innovation Solution
A fin-base bipolar junction transistor is fabricated using a method that includes forming a base well in a wide collector, etching to create a fin base, forming a dielectric layer and gate stack, epitaxially growing a semiconductor layer, and doping to form a narrow base-emitter junction, allowing for improved size ratio and junction definition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional BJT fabrication is integrated into CMOS processes, then manufacturing compatibility is improved, but emitter size is reduced leading to high emitter series resistance
Solution Approach 1:
The patent transforms the conventional planar emitter-base configuration into a three-dimensional fin-based structure. The fin base extends vertically into the collector, creating multiple surfaces for emitter contact. This dimensional change allows the emitter to wrap around and contact multiple surfaces of the fin base, effectively increasing the emitter area and reducing series resistance while maintaining compatibility with standard CMOS fabrication processes.
2Ease of manufacture
If conventional BJT fabrication is integrated into CMOS processes, then manufacturing compatibility is improved, but base-emitter junction definition is poor leading to high base leakage current
Solution Approach 1:
The fin-based structure provides well-defined vertical sidewalls that create sharp, well-defined base-emitter junctions. The etched fin structure exposes multiple surfaces of the base region, allowing for precise junction formation through standard doping processes. This three-dimensional configuration enables better junction definition compared to planar structures, reducing base leakage current while maintaining CMOS process compatibility.
3Manufacturing precision
If emitter is made smaller than base in conventional BJT, then base control is improved, but current conduction capability is reduced
Solution Approach 1:
The fin base structure extends vertically into the collector, creating multiple surfaces for emitter contact. This three-dimensional configuration allows the emitter to maintain good control over the base region while simultaneously increasing the effective emitter area for current conduction. The vertical fin structure provides both the precision needed for base control and the surface area needed for high current capability.
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 fin-based BJT achieves high switching capability and current conduction, reducing emitter series resistance and base leakage current, making it suitable for high-performance applications while being integrated into CMOS processes.
Implementation Method 1
epitaxially growing a semiconductor layer
Data Source
AI summary
According to one exemplary embodiment, a fin-based bipolar junction transistor (BJT) includes a wide collector situated in a semiconductor substrate. A fin base is disposed over the wide collector. Further, a fin emitter and an epi emitter are disposed over the fin base. A narrow base-emitter junction of the fin-based BJT is formed by the fin base and the fin emitter and the epi emitter provides increased current conduction and reduced resistance for the fin-based BJT. The epi emitter can be epitaxially formed on the fin emitter and can comprise polysilicon. Furthermore, the fin base and the fin emitter can each comprise single crystal silicon.