Bipolar Transistor Base Width Variation for Lower Contact Resistance
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Solution Overview
Problem
Conventional bipolar transistors, such as vertical transistors and silicon germanium transistors, face challenges in meeting certain operational constraints and are costly, 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, and a spacer between the emitter/collector layer and the base layer, allowing for improved design and fabrication methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional vertical bipolar transistors or silicon germanium bipolar transistors are used, then operational constraints are met, but manufacturing cost increases
Solution Approach 1:
The base layer is designed with varying horizontal width, creating different regions (lower base region with smaller width and upper base region with larger width) that serve different functional purposes. This local variation in geometry allows optimization of electrical performance in specific areas while maintaining cost-effective manufacturing processes
Solution Approach 2:
The invention transitions from conventional uniform base structures to a base layer with dimensional variation in the horizontal plane. The upper base region extends beyond the lower base region, creating a stepped configuration that adds geometric complexity without requiring advanced manufacturing techniques
2Reliability
If base contacts are formed in conventional bipolar transistors, then electrical connection is established, but resistance is high and formation is difficult
Solution Approach 1:
The upper base region is designed with larger horizontal width specifically to accommodate base contacts, creating a localized area optimized for electrical connection. This wider region reduces contact resistance and simplifies the formation process by providing a larger target area for contact deposition
Solution Approach 2:
The varying width of the base layer is established during the base formation process itself, before contact deposition. This preliminary geometric configuration prepares the structure for easier contact formation by already providing the optimized width profile needed for low-resistance connections
3Ease of manufacture
If base layer has uniform width, then fabrication is simple, but electrical performance is limited
Solution Approach 1:
The base layer incorporates regions of different horizontal widths to optimize electrical performance. The lower base region with smaller width provides good current confinement, while the upper base region with larger width improves contact formation and reduces resistance, achieving enhanced electrical performance without complex fabrication
Solution Approach 2:
The base layer is effectively segmented into different functional regions based on horizontal width variation. The lower and upper base regions serve distinct electrical functions, allowing independent optimization of each region's geometry to achieve overall performance improvement
Data Source
AI summary
Embodiments of the disclosure provide a bipolar transistor structure having a base with a varying horizontal width and methods to form the same. The bipolar transistor structure includes a first emitter/collector (E/C) layer on an insulator layer. A base layer is over the insulator layer. A spacer between the first E/C layer and the base layer. The base layer includes a lower base region, and the spacer is adjacent to the lower base region and the first E/C layer. An upper base region is on the lower base region and the spacer. A horizontal width of the upper base region is larger than a horizontal width of the lower base region.