Cascaded BJT Structure for High Gain and Breakdown Voltage
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Solution Overview
Problem
Bipolar junction transistors (BJTs) face a tradeoff between breakdown voltage (BVCEO) and current gain, making it difficult to simultaneously achieve high values of both, and traditional Darlington transistors have high electrical resistance.
Innovation Solution
A cascaded BJT structure is formed on a substrate, where two BJTs are connected in a Darlington configuration with an interconnect structure, decoupling the inverse proportional relationship between current gain and BVCEO, and processed using a compatible BCD process to reduce resistance and improve yield and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional BJT structure is used, then current gain (beta gain) can be improved, but breakdown voltage (BVCEO) deteriorates
Solution Approach 1:
The patent divides a single BJT into two separate BJTs (first BJT and second BJT) with different doping concentrations and structures. The first BJT has higher doping concentration for high breakdown voltage, while the second BJT has lower doping concentration for high current gain. By cascading these segmented BJTs, the system achieves both high current gain and high breakdown voltage simultaneously, resolving the technical contradiction.
2Reliability
If high current gain is achieved in traditional BJT, then breakdown voltage decreases
Solution Approach 1:
The patent applies local quality by creating different doping concentrations and structural characteristics in different parts of the cascaded BJT system. The first BJT region is optimized with higher doping for breakdown voltage, while the second BJT region is optimized with lower doping for current gain. This localized optimization allows each region to excel at its specific function while working together as an integrated system.
3Reliability
If cascaded BJT structure is implemented, then current gain increases significantly, but device complexity increases
Solution Approach 1:
The patent merges two separate BJT structures into a single integrated cascaded BJT device with shared substrate and interconnected regions. The first and second BJTs are formed on the same substrate with their collector and emitter regions electrically connected through shared conductive paths. This merging approach achieves high current gain while minimizing the increase in device complexity by consolidating structures rather than using completely separate components.
Data Source
AI summary
A device and methods of forming the same are described. The device includes a substrate and a first bipolar junction transistor (BJT) disposed over the substrate. The first BJT includes a first base region, a first emitter region, and a first collector region. The device further includes a second BJT disposed over the substrate adjacent the first BJT, and the second BJT includes a second base region, a second emitter region, and a second collector region. The device further includes an interconnect structure disposed over the first and second BJTs, and the interconnect structure includes a first conductive line electrically connected to the first emitter region and the second base region and a second conductive line electrically connected to the first collector region and the second collector region.