Symmetrical Vertical TVS Device Doping Profile
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Solution Overview
Problem
Conventional punchthrough diode based transient voltage suppressors (TVS) devices suffer from asymmetrical breakdown voltages and process sensitivity due to variations in epitaxial layer thickness and doping concentrations, leading to inconsistent protection against transient voltage fluctuations.
Innovation Solution
A vertical TVS device with a thick epitaxial layer and high energy base implantation to create a symmetrical doping profile, ensuring symmetrical breakdown voltages and reducing sensitivity to fabrication process variations, achieved through high energy ion implantation and buried layer technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional epitaxial growth or ion implantation is used to form stacked layers, then TVS device breakdown voltage can be achieved, but the breakdown voltage becomes asymmetrical and highly sensitive to process variations
Solution Approach 1:
The patent intentionally introduces asymmetry in the form of a buried layer at the bottom of the epitaxial layer, which compensates for the natural asymmetry caused by out-doping from the substrate. This buried layer creates a symmetrical doping profile relative to the base region, ensuring symmetrical breakdown voltages in both forward and reverse directions while reducing sensitivity to epitaxial layer thickness variations.
2Volume of moving object
If a thin epitaxial layer is used, then device size is reduced, but out-doping from the substrate adversely affects doping concentration and causes asymmetrical breakdown voltages
Solution Approach 1:
The buried layer is formed at the bottom of the epitaxial layer before final device fabrication steps. This preliminary action prevents out-doping from the substrate from affecting the base region by creating a doping barrier, thus maintaining precise doping concentration control even in thin epitaxial layers while enabling smaller device sizes.
3Ease of manufacture
If conventional doping profiles with concentration gradients are used, then base region formation is achieved, but asymmetrical breakdown voltages and process sensitivity result
Solution Approach 1:
The patent applies different doping characteristics to different regions: the buried layer at the bottom provides a specific doping concentration that compensates for substrate out-doping, while the base region maintains its required concentration gradient for proper transistor operation. This local differentiation ensures symmetrical breakdown voltages while maintaining ease of base region formation through conventional doping techniques.
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 solution results in a robust TVS device with symmetrical breakdown voltages, insensitive to epitaxial layer thickness and doping variations, providing reliable protection against both positive and negative voltage transients.
Implementation Method 1
a base region of a second conductivity type implanted in the epitaxial layer
Data Source
AI summary
A vertical transient voltage suppressing (TVS) device includes a semiconductor substrate of a first conductivity type where the substrate is heavily doped, an epitaxial layer of the first conductivity type formed on the substrate where the epitaxial layer has a first thickness, and a base region of a second conductivity type formed in the epitaxial layer where the base region is positioned in a middle region of the epitaxial layer. The base region and the epitaxial layer provide a substantially symmetrical vertical doping profile on both sides of the base region. In one embodiment, the base region is formed by high energy implantation. In another embodiment, the base region is formed as a buried layer. The doping concentrations of the epitaxial layer and the base region are selected to configure the TVS device as a punchthrough diode based TVS or an avalanche mode TVS.