PNP BJT Fin Structure for Lower Vbe Mismatch
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Solution Overview
Problem
Bipolar junction transistors (BJTs) in analog integrated circuits are sensitive to Vbe (base-emitter voltage) value and Vbe mismatch, which affects their performance and accuracy in applications like band-gap voltage reference circuits.
Innovation Solution
A semiconductor structure with a specific configuration of deep N-type and P-type well regions, and active regions forming a PNP BJT, where the base region has higher resistance due to the absence of active regions between the emitter and collector regions, enhancing beta gain and reducing Vbe mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If base region active regions are present between emitter and collector regions, then manufacturing process is simpler, but base resistance decreases and beta gain reduces
Solution Approach 1:
The invention extracts and removes the base region active regions from between the emitter and collector regions. This extraction eliminates the harmful effect of low base resistance that would reduce beta gain, while the emitter and collector regions remain directly adjacent to maintain high beta gain performance.
Solution Approach 2:
The invention introduces an intermediate isolation structure (such as shallow trench isolation or oxide layer) between the emitter and collector regions to replace the function of base region active regions. This intermediary maintains electrical isolation and structural integrity while allowing the base resistance to remain high for improved beta gain.
2Device complexity
If base region active regions are present between emitter and collector regions, then device structure is more complete, but base current noise increases and Vbe mismatch varies
Solution Approach 1:
The invention extracts the base region active regions that cause base current noise and Vbe mismatch variation. By removing these regions, the harmful electrical noise and voltage mismatch are eliminated, improving measurement precision and circuit accuracy.
Solution Approach 2:
The invention converts the structural gap where base region active regions would be into a beneficial feature. The absence of these regions creates high base resistance that reduces base current noise and stabilizes Vbe mismatch, turning what could be seen as an incomplete structure into a performance-enhancing design.
3Reliability
If emitter and collector regions are directly adjacent, then beta gain increases, but manufacturing precision requirements increase
Solution Approach 1:
The invention introduces an intermediate isolation structure between the emitter and collector regions that serves as a manufacturing reference and buffer. This intermediary layer (such as shallow trench isolation or oxide) provides a defined boundary that simplifies alignment during fabrication while allowing the emitter and collector to be directly adjacent for high beta gain.
Solution Approach 2:
The invention changes the physical and electrical parameters of the interface between emitter and collector regions by introducing isolation materials. This parameter change allows direct adjacency for high beta gain while the isolation structure provides manufacturing tolerance and precision control during fabrication.
Data Source
AI summary
Semiconductor structures of bipolar junction transistor (BJT) are provided. A first active region of a collection region is formed over a first P-type well region. Second and third active regions of a base region are formed over an N-type well region. A fourth active region of an emitter region is formed over a second P-type well region. The first active region includes a plurality of first fins and a plurality of first source/drain features epitaxially grown on the first fins. Each of the second and third active regions includes a plurality of second fins and a plurality of second source/drain features epitaxially grown on the second fins. The fourth active region includes a plurality of third fins and a plurality of third source/drain features epitaxially grown on the third fins. The second and third active regions are disposed on opposite sides of the fourth active region.