Lateral SiGe Bipolar Transistor Structure for High-Speed RF
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Solution Overview
Problem
Vertical bipolar transistors face limitations in high-speed operation due to increased collector resistance and complex manufacturing processes, while lateral bipolar transistors are simpler but require additional layers for high-speed performance.
Innovation Solution
A lateral bipolar transistor with a SiGe base having a gradient concentration of Ge is developed, utilizing fully depleted semiconductor on insulator (SOI) technology, featuring an ultra-narrow base and raised emitter and collector regions, fabricated using integrated circuit techniques to reduce capacitance and noise isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vertical bipolar transistor structure is used, then transistor gain is improved, but collector resistance increases and manufacturing complexity increases
Solution Approach 1:
The patent inverts the conventional vertical bipolar transistor architecture by adopting a lateral configuration where the current flow path is reversed relative to the substrate surface. This inversion allows the collector to be positioned closer to the surface, reducing collector resistance while simplifying the manufacturing process by eliminating the need for deep trench isolation and complex epitaxial growth sequences.
Solution Approach 2:
The patent transitions from a vertical current flow path (perpendicular to substrate surface) to a lateral current flow path (parallel to substrate surface). This dimensional change enables the collector region to be accessed more directly, reducing the effective collection distance and associated resistance while allowing for simpler planar fabrication processes.
2Ease of manufacture
If lateral bipolar transistor structure is used, then manufacturing simplicity is improved, but additional layers are required for high-speed performance
Solution Approach 1:
The patent introduces a SiGe alloy layer with graded germanium concentration specifically in the base region, creating local compositional variation that enhances carrier transport properties. This localized material modification improves high-speed performance without requiring additional structural layers throughout the entire device, maintaining manufacturing simplicity while achieving the desired performance enhancement.
Solution Approach 2:
The patent modifies the base region by incorporating SiGe alloy with varying Ge concentration (graded profile) to alter the material parameters such as band structure and carrier mobility. This parameter change enables faster carrier transit through the base region, achieving high-speed performance without adding extra functional layers to the lateral transistor structure.
3Strength
If collector region is positioned deep from wafer surface, then transistor breakdown voltage is improved, but collector resistance increases
Solution Approach 1:
The patent inverts the conventional approach by positioning the collector region closer to the substrate surface in a lateral configuration. The breakdown voltage is maintained through the lateral geometry and doping profile design rather than relying on deep collector positioning, thereby achieving low collector resistance without sacrificing voltage handling capability.
Solution Approach 2:
The patent transitions from vertical collector positioning (deep from surface) to lateral collector positioning (close to surface but extended in-plane). This dimensional change allows the collector to be physically closer to the surface, reducing resistance, while the lateral extent and doping design maintain the necessary breakdown voltage characteristics.
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to a lateral bipolar transistor and methods of manufacture. The structure includes: an extrinsic base having at least one sidewall with a gradient concentration of semiconductor material; an emitter on a first side of the extrinsic base; and a collector on a second side of the extrinsic base.