Collector-Up Bipolar Transistor Base Resistance Optimization
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Solution Overview
Problem
Bipolar transistors face a trade-off between high power performance, high frequency performance, and cost, with conventional designs struggling to optimize maximum oscillation frequency (fMAX) due to the limitations of base resistance and collector-base capacitance, where reducing one parameter often worsens the other.
Innovation Solution
The use of a bottom-up bipolar transistor with a laterally extending collector that extends past the base edge, allowing for improved breakdown performance and flexibility in device layout, combined with a dielectric layer for mechanical stability and a collector gate for field shaping, which enhances breakdown voltage and cut-off frequency without increasing base resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the base resistance is reduced by increasing the doping level in the base, then the maximum oscillation frequency fMAX is improved, but the collector current decreases and consequently fT is lowered
Solution Approach 1:
The patent applies local quality by creating different doping levels in different regions of the base. The extrinsic base region has higher doping to reduce resistance and improve fMAX, while the intrinsic base region maintains lower doping to preserve collector current and fT. This spatial differentiation of doping quality resolves the contradiction between reducing base resistance and maintaining collector current.
2Speed
If the collector-base capacitance CBC is reduced by changing device architecture, then the maximum oscillation frequency fMAX is improved, but the device complexity increases
Solution Approach 1:
The patent inverts the conventional transistor architecture by placing the collector above the base instead of below it. This inverted configuration naturally reduces the collector-base capacitance CBC because the collector contact area with the base is minimized, directly improving fMAX without requiring complex architectural modifications.
3Power
If long finger-like transistor shapes are used to increase transistor area and current, then the output power is improved, but the intrinsic base resistance increases and fMAX deteriorates
Solution Approach 1:
The patent segments the base region into extrinsic and intrinsic portions, allowing the transistor to use long finger-like shapes for increased area and power while the extrinsic base region compensates for the increased intrinsic base resistance. This segmentation enables both high power and high frequency performance to coexist.
Data Source
Figure 1A~2
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AI summary
A semiconductor device and a method of making the same. The device includes a semiconductor substrate. The device also includes a bipolar transistor on the semiconductor substrate. The bipolar transistor includes an emitter. The bipolar transistor also includes a base located above the emitter. The bipolar transistor further includes a laterally extending collector located above the base. The collector includes a portion that extends past an edge of the base.