SOI Vertical Bipolar Transistor Structure for Low Collector Resistance
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Solution Overview
Problem
Vertical bipolar transistors face performance limitations due to increased collector resistance and complex manufacturing processes, which hinder high-speed operation and increase costs, while lateral bipolar transistors are simpler but less effective for high-speed applications.
Innovation Solution
The development of a semiconductor on insulator (SOI) technology-based vertical bipolar transistor structure with a base region, emitter region, and collector region, where the collector region is embedded within a buried insulator layer, allowing for reduced capacitance and noise isolation, and utilizing an ultra-narrow SiGe core with a graded Ge profile for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a vertical bipolar transistor structure is used, then the transistor can achieve high-voltage RF device performance, but the collector resistance increases due to the deep collector region formation, limiting high-speed operation
Solution Approach 1:
The patent transitions from a conventional vertical bipolar transistor structure to a planar transistor structure fabricated on SOI substrate. This dimensional change allows the collector region to be formed in the plane of the substrate rather than requiring deep vertical formation, thereby reducing collector resistance while maintaining high-voltage capability through the SOI buried oxide layer's natural isolation and voltage blocking properties.
Solution Approach 2:
The patent utilizes the unique parameters of SOI technology, specifically the buried oxide layer thickness and semiconductor layer properties, to achieve both high-voltage operation and low collector resistance. By adjusting the SOI substrate parameters (oxide thickness, semiconductor layer doping), the transistor achieves optimized performance for both power and speed requirements.
2Reliability
If a vertical bipolar transistor is manufactured with deep trench isolation, high-concentration buried layer, and collector epitaxial layer, then the transistor structure is complete, but the number of process steps increases and costs increase
Solution Approach 1:
The SOI substrate serves multiple functions simultaneously: it provides the base region, the buried oxide layer provides isolation and voltage blocking, and the structure enables planar fabrication. This multi-functionality eliminates the need for separate deep trench isolation and buried layer formation steps required in conventional vertical bipolar transistors, significantly reducing process complexity while maintaining structural integrity.
3Ease of manufacture
If a lateral bipolar transistor is used, then the structure is simpler and manufacturing is easier, but the collector electrode cannot be directly brought into contact with the collector region, reducing high-speed operation effectiveness
Solution Approach 1:
The patent segments the transistor into distinct planar regions (emitter, base, collector) formed on the SOI surface, with each region independently optimized. The collector region is directly accessible in the planar structure, allowing direct electrode contact while maintaining the simplicity of lateral device fabrication. This segmentation enables both manufacturing ease and high-speed performance.
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to bipolar transistors and methods of manufacture. The structure includes: a base region composed of a semiconductor on insulator material; an emitter region above the base region; and a collector region under the base region and within a cavity of a buried insulator layer.