Bipolar Transistor Base Width Variation for Frequency and Contact Control
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Solution Overview
Problem
Conventional bipolar transistors, such as vertical bipolar transistors and silicon germanium (SiGe) bipolar transistors, are costly and may not meet certain operational constraints, limiting their effectiveness in integrated circuits.
Innovation Solution
A bipolar transistor structure with a base layer having a varying horizontal width is developed, featuring a lower base region and an upper base region with a wider horizontal width than the lower base region, where the upper base region may overhang the spacer, allowing for improved electrical performance and easier contact formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional vertical bipolar transistors or SiGe bipolar transistors are used, then device performance can be maintained, but manufacturing cost increases and operational constraints are not met
Solution Approach 1:
The base layer is designed with non-uniform thickness, creating a graded structure where the thickness varies laterally. This local variation in geometric quality allows different regions of the base to provide different functional characteristics, enabling improved device performance while using standard manufacturing processes for the overall structure
Solution Approach 2:
The invention changes the geometric parameter of the base layer thickness from a constant value to a variable value that changes laterally across the device. This parameter modification is achieved through standard semiconductor fabrication techniques such as selective epitaxial growth or deposition, avoiding the need for expensive alternative transistor architectures
2Ease of manufacture
If conventional uniform base structure is used, then manufacturing is simpler, but electrical performance control over threshold frequency and maximum frequencies is weaker
Solution Approach 1:
The base layer incorporates a graded thickness profile where specific lateral regions have different thicknesses. This local geometric variation enables precise control over the electrical characteristics including threshold frequency and maximum frequency, while the overall structure remains compatible with standard manufacturing processes
Solution Approach 2:
The invention transitions from a two-dimensional uniform base structure to a three-dimensional structure with vertical thickness variation. By introducing variation in the vertical dimension across the lateral extent of the base, the design achieves enhanced electrical performance control without complicating the manufacturing approach
3Reliability
If conventional base structure is used, then contact formation is more difficult and resistance between emitter and collector terminals is higher
Solution Approach 1:
The base layer is designed with a graded thickness profile that creates locally optimized regions for different functions. The varying thickness provides natural pathways that facilitate easier contact formation and reduce resistance between emitter and collector terminals, while maintaining compatibility with standard fabrication processes
Data Source
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AI summary
A bipolar transistor structure comprising, a first emitter/collector layer on an insulator layer; a base layer over the insulator layer; and a spacer on the first emitter/collector layer, wherein the base layer includes a lower base region, wherein the spacer is adjacent to the lower base region and the first emitter/collector layer, and an upper base region on the lower base region and the spacer, wherein a horizontal width of the upper base region is larger than a horizontal width of the lower base region.