Vertical Parasitic PNP Transistor in SiGe BiCMOS
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Solution Overview
Problem
Conventional silicon-germanium BiCMOS processes face challenges in achieving high cut-off frequencies and current amplification due to the large base width of lateral PNP transistors, which limits their application in radio frequency devices and increases manufacturing costs.
Innovation Solution
A parasitic PNP bipolar transistor with a vertical structure is developed, featuring a base region with an L-shaped configuration, an N-type pseudo buried layer, a P-type pseudo buried layer, and a P-type silicon-germanium epitaxial emitter region, allowing for reduced device area and adjustable breakdown voltage through layout modifications, while maintaining compatibility with the silicon-germanium BiCMOS process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a lateral PNP transistor structure is used in SiGe BiCMOS process, then the collector region can be easily picked up, but the base width becomes large and current gain becomes small
Solution Approach 1:
The patent transitions from a conventional lateral PNP transistor structure to a vertical PNP transistor structure. This dimensional change allows the current flow to be perpendicular to the substrate surface rather than lateral, thereby reducing the base width from micrometer scale to sub-micrometer scale while maintaining ease of collector region pickup through the vertical architecture.
2Speed
If advanced process is used to achieve high cut-off frequency, then frequency performance improves, but research and development cost increases significantly
Solution Approach 1:
The patent achieves high cut-off frequency (above 40 GHz) by optimizing device structure parameters rather than relying on advanced process nodes. Specifically, the vertical structure with reduced base width, optimized doping profiles, and adjusted geometric dimensions enable high frequency performance using existing mature SiGe BiCMOS processes, thereby avoiding high R&D costs associated with advanced process development.
3Reliability
If the base region width is reduced to improve current gain, then current amplification improves, but the device area and manufacturing complexity increase
Solution Approach 1:
By adopting a vertical structure, the patent reduces base width in the vertical dimension while maintaining manageable device footprint. The vertical architecture with stacked emitter-base-collector regions allows for precise control of base width through epitaxial growth and ion implantation techniques, achieving high current gain without proportionally increasing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The vertical structure significantly reduces the base width, enhancing current amplification and making it easier to adjust breakdown voltage, thus improving the device's performance and keeping the manufacturing process cost-effective and compatible with existing silicon-germanium BiCMOS processes.
Implementation Method 1
the first region is formed by a first N-type ion implantation region in the active area; the second region is formed by a second N-type ion implantation region formed in an upper part of the first region
Implementation Method 2
an emitter region, which is formed by a P-type silicon-germanium epitaxial layer formed on top of the active area
Data Source
AI summary
A parasitic PNP bipolar transistor, wherein a base region includes a first and a second region; the first region is formed in an active area, has a depth larger than shallow trench field oxides, and has its bottom laterally extended into the bottom of the shallow trench field oxides on both sides of an active area; the second region is formed in an upper part of the first region and has a higher doping concentration; an N-type and a P-type pseudo buried layer is respectively formed at the bottom of the shallow trench field oxides; a deep hole contact is formed on top of the N-type pseudo buried layer to pick up the base; the P-type pseudo buried layer forms a collector region separated from the active area by a lateral distance; an emitter region is formed by a P-type SiGe epitaxial layer formed on top of the active area.