Bipolar Transistor Collector Grading for Linearity and Gain
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Solution Overview
Problem
Bipolar transistors, particularly in power amplifier systems, face challenges in meeting demanding specifications for second channel linearity measures such as ACPR2 and ACLR2 while maintaining RF gain, as conventional designs often result in degraded gain when attempting to improve linearity.
Innovation Solution
A bipolar transistor design featuring a collector with a high doping concentration in a first region and additional gradings in other collector regions, which transition from the high doping concentration to a sub-collector, allowing for increased doping concentration in the first region to improve linearity while compensating for reduced gain through varying doping rates in the gradings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doping concentration in the collector is increased to improve linearity (ACPR2/ACLR2), then linearity performance is improved, but RF gain is degraded
Solution Approach 1:
The patent applies local quality by implementing different doping concentrations in different regions of the collector. The first collector region has a high doping concentration (at least 3×10^16 cm^-3) to improve linearity, while the second collector region has a lower doping concentration that grades away from the first region. This spatial variation in doping quality allows simultaneous optimization of linearity in the first region and gain in the second region.
Solution Approach 2:
The collector is segmented into multiple distinct regions with different doping characteristics. The first collector region abutting the base has high doping for linearity, while the second collector region extends away from the base with grading to maintain gain. This segmentation allows each region to be optimized for its specific function without compromising the other.
2Reliability
If high doping concentration is used in the collector to meet linearity specifications, then manufacturing complexity increases due to precise doping control requirements
Solution Approach 1:
The patent employs parameter changes by varying the doping concentration across different collector regions. The doping concentration is changed from high (at least 3×10^16 cm^-3) in the first collector region to lower concentrations in the second collector region through grading. This parameter variation achieves linearity specifications while the gradual transition simplifies manufacturing control compared to abrupt changes.
Data Source
AI summary
This disclosure relates to bipolar transistors, such as heterojunction bipolar transistors, having at least one grading in the collector. One aspect of this disclosure is a bipolar transistor that includes a collector having a high doping concentration at a junction with the base and at least one grading in which doping concentration increases away from the base. In some embodiments, the high doping concentration can be at least about 3×1016 cm−3. According to certain embodiments, the collector includes two gradings. Such bipolar transistors can be implemented, for example, in power amplifiers.