Horizontal Current Bipolar Transistor Floating Field Regions
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Solution Overview
Problem
High-voltage bipolar transistors face challenges in achieving high breakdown voltages due to stringent collector-emitter breakdown voltage constraints, which are not adequately addressed by existing technologies, particularly in vertical bipolar transistors that require additional processing steps and increased costs when integrated with high-speed transistors.
Innovation Solution
The use of floating field regions in Horizontal Current Bipolar Transistor (HCBT) structures to shape the electric field in the base-collector depletion region, improving breakdown voltages without requiring additional processing steps or increasing costs, by fabricating these regions as stripes forming planar pn junctions, suitable for both double-emitter and single-emitter HCBT configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lower collector doping concentration is used to reduce electric field at base-collector junction, then breakdown voltage is improved, but transistor performance and switching speed deteriorate
Solution Approach 1:
The patent applies local quality by creating a non-uniform doping profile in the collector region through selective ion implantation. The collector has different doping concentrations in different zones: higher doping near the base-collector junction to maintain field control, and lower doping in deeper regions to sustain breakdown voltage. This spatial variation in doping quality resolves the contradiction between speed (requiring high doping) and breakdown voltage (requiring low doping).
Solution Approach 2:
The patent transitions from vertical bipolar transistor architecture to horizontal current bipolar transistor architecture. This dimensional change allows the current flow to be horizontal rather than vertical, enabling independent optimization of the base-collector junction characteristics. The horizontal configuration permits the collector to have optimized doping profiles without compromising the vertical stacking efficiency needed for high-speed operation.
2Reliability
If additional lithography masks and ion implantation steps are added for HV collector regions, then breakdown voltage is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the formation of the high-voltage collector region with the existing high-speed transistor fabrication process. The same lithography masks and ion implantation steps used to create the high-speed collector are also used to form the horizontal current bipolar transistor collector. This consolidation eliminates additional processing steps while achieving the required breakdown voltage characteristics through optimized process parameters and horizontal geometry.
Solution Approach 2:
The patent designs the horizontal current bipolar transistor structure to be fabricated using the same process flow as high-speed transistors. The collector region formation process serves dual purposes: creating the high-speed collector and the HV collector simultaneously. This multi-functionality of the fabrication process reduces manufacturing complexity and cost while achieving high breakdown voltage through the horizontal architecture and optimized doping profiles.
3Reliability
If RESURF effect is used to shape electric field in base-collector depletion region, then breakdown voltage is improved, but device complexity increases
Solution Approach 1:
The patent achieves electric field shaping by changing the doping concentration parameters in the collector region through selective ion implantation. Rather than adding complex structural elements, the patent optimizes the doping parameters (concentration, depth, distribution) to create the desired field distribution. This parameter-based approach simplifies the device structure while achieving breakdown voltage improvement through controlled electric field profiles in the base-collector depletion region.
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
This approach effectively increases the collector-emitter breakdown voltage while maintaining compatibility with CMOS integration and reducing fabrication complexity, allowing for a wide range of selectable breakdown voltages without additional processing costs, thus enhancing the performance and efficiency of high-voltage transistors.
Implementation Method 1
shape the electric field in the base-collector depletion region
Implementation Method 2
the critical electric field for junction avalanche is achieved for higher voltages applied at the collector terminal
Data Source
AI summary
A horizontal current bipolar transistor comprises; an n-hill layer on a substrate, forming a first pn-junction with the substrate; a n+ diffusion layer on the substrate, adjacent to the n-hill layer, forming a n+n junction with the n-hill layer; an intrinsic base layer on the n-hill layer and comprising a portion of a sidewall inclined at an acute angle to the substrate plane, forming a second pn-junction with the n-hill layer; an extrinsic base layer on the n-hill layer, forming a third pn-junction with the n-hill layer, and a p+p junction with the intrinsic base layer; a field limiting region on the n-hill layer, forming a fourth pn-junction with the n-hill layer. The field limiting region is spatially separated from the extrinsic base layer and the n+ diffusion layer. The extrinsic base layer and the field limiting region exhibit substantially equal impurity dopant distribution decay towards the substrate.