Bipolar Transistor Base Layer Angled Sections
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Solution Overview
Problem
Existing bipolar junction transistor structures and fabrication methods require improvements to enhance performance metrics such as maximum frequency, transit frequency, and gain, particularly in reducing collector-base capacitance and base resistance.
Innovation Solution
A device structure for a bipolar junction transistor is developed, featuring a substrate with a trench isolation region, a collector, a base layer with angled sections, and an extrinsic base layer positioned over the trench isolation region, along with a self-aligned emitter formation process, which includes forming a trench isolation region, a collector, and a base layer with angled sections to reduce collector-base capacitance and improve base resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bipolar junction transistor structure is used, then the device can be fabricated with standard processes, but the collector-base capacitance and base resistance remain high, limiting maximum frequency and gain
Solution Approach 1:
The base layer is segmented into multiple sections with different orientations. The first base layer section is oriented at a first angle relative to the collector, while the second base layer section is oriented at a second angle relative to the collector. This segmentation allows optimization of electrical properties in different regions, reducing overall base resistance and collector-base capacitance while maintaining fabricability with standard processes
Solution Approach 2:
Different sections of the base layer are given different local properties through varying their orientations. The first base layer section has a first orientation optimized for certain electrical characteristics, while the second base layer section has a second orientation optimized for other characteristics. This local quality variation enables simultaneous reduction of base resistance and collector-base capacitance in different regions of the device
2Reliability
If the base layer is oriented at an angle relative to the collector, then collector-base capacitance is reduced, but fabrication alignment precision must be improved
Solution Approach 1:
The base layer is formed with predetermined angular orientations (first angle and second angle relative to the collector) during the fabrication process. By establishing these orientations in advance during layer formation rather than attempting post-fabrication adjustment, the design achieves reduced collector-base capacitance while using standard fabrication capabilities
Solution Approach 2:
Instead of optimizing only in the vertical dimension, the invention introduces angular orientation as an additional degree of freedom. The base layer sections are oriented at different angles in the lateral plane relative to the collector, creating a two-dimensional optimization space that reduces collector-base capacitance without requiring extreme precision in vertical stacking
Data Source
AI summary
Device structures and fabrication methods for a bipolar junction transistor. The device structure includes a substrate and a trench isolation region in the substrate. The trench isolation region surrounds an active region of the substrate. The device structure further includes a collector in the active region of the substrate, a base layer having a first section positioned on the active region and a second section oriented at an angle relative to the first section, an emitter positioned on the first section of the base layer, and an extrinsic base layer positioned over the trench isolation region and adjacent to the emitter. The second section of the base layer is laterally positioned between the extrinsic base layer and the emitter.