Bipolar Transistors With Super Junction Collector Columns
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Solution Overview
Problem
Conventional bipolar transistors face a tradeoff between collector resistance (Rcs) and breakdown voltage, with reduced collector doping or length leading to increased Rcs and decreased breakdown voltage, necessitating a method to minimize size while improving Rcs without sacrificing breakdown voltage.
Innovation Solution
The implementation of a super junction structure in bipolar transistors, where alternating P and N doped columns are used to increase doping on the lightly doped side and reduce its length, allowing for total depletion before breakdown, thereby extending the column's electric field and improving breakdown voltage while reducing Rcs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If collector doping is reduced to minimize Rcs, then collector resistance decreases, but breakdown voltage is reduced
Solution Approach 1:
The collector is segmented into alternating P-type and N-type doped columns, creating a super junction structure. This segmentation allows the lightly doped regions to be fully depleted at breakdown, extending the depletion layer and increasing breakdown voltage, while the heavily doped regions provide low resistance paths, thus resolving the contradiction between breakdown voltage and collector resistance
Solution Approach 2:
Different regions of the collector are given different doping qualities - alternating between lightly doped (for high breakdown voltage) and heavily doped (for low resistance) columns. This local quality variation allows simultaneous optimization of both breakdown voltage and collector resistance, as each region performs its specialized function
2Reliability
If collector length is reduced to minimize Rcs, then collector resistance decreases, but breakdown voltage is reduced
Solution Approach 1:
The collector length is effectively extended through the super junction structure's alternating doped columns, which create a longer depletion path. This allows the physical collector length to be reduced while maintaining or increasing breakdown voltage, as the segmented structure provides both electrical length and resistance reduction
3Area of stationary object
If transistor size is reduced, then device area decreases, but Rcs increases
Solution Approach 1:
The super junction structure implements local quality variations with alternating heavily doped (low resistance) and lightly doped (high breakdown) columns throughout the collector area. This allows the overall transistor area to be reduced while maintaining low Rcs, as the heavily doped regions provide efficient current paths in the reduced area
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 super junction structure achieves reduced collector resistance and improved breakdown voltage, enabling the formation of bipolar transistors with enhanced performance and reduced size, with NPN and PNP devices demonstrating up to three times lower Rcs and twice the breakdown voltage of conventional devices.
Implementation Method 1
allowing for total depletion before breakdown, thereby extending the column's electric field and improving breakdown voltage
Implementation Method 2
The super junction structure achieves reduced collector resistance and improved breakdown voltage
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
In accordance with the invention, there are various methods of making an integrated circuit comprising a bipolar transistor. According to an embodiment of the invention, the bipolar transistor can comprise a substrate, a collector comprising a plurality of alternating doped regions, wherein the plurality of alternating doped regions alternate in a lateral direction from a net first conductivity to a net second conductivity, and a collector contact in electrical contact with the collector. The bipolar transistor can also comprise a heavily doped buried layer below the collector, a base in electrical contact with a base contact, wherein the base is doped to a net second conductivity type and wherein the base spans a portion of the plurality of alternating doped regions, and an emitter disposed within the base, the emitter doped to a net first conductivity, wherein a portion of the alternating doped region under the emitter is doped to a concentration of less than about 3 x 10-12 cm-2.