Fin-Based RF Diode Junction Area Optimization
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Solution Overview
Problem
Conventional fin-based RF diodes face challenges with increased parasitic resistance and capacitance due to reduced junction area and scaling down of IC devices, leading to higher leakage current and capacitance, which affects their performance in high-frequency applications.
Innovation Solution
The method involves forming fins with optimized widths for larger diode junction regions, implementing shallow trench isolation, and varying dopant concentrations to reduce parasitic resistance and capacitance, while increasing the junction area and forward current capacity by forming a junction region around the depletion area and using silicide materials for improved switching characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fin width is reduced to scale down IC devices, then device integration is improved, but parasitic capacitance increases and junction area decreases
Solution Approach 1:
The patent transitions from a planar diode structure to a three-dimensional fin-based structure with vertical sidewalls. This dimensional change allows the junction area to extend vertically along the fin sidewalls, compensating for the reduced horizontal fin width and maintaining adequate junction area while achieving device scaling.
Solution Approach 2:
The diode structure is segmented into distinct regions: a lightly-doped drift region forming the fin, a heavily-doped contact region at the bottom, and a junction region along the sidewalls. This segmentation allows optimization of each region's doping profile to balance junction area, parasitic capacitance, and current handling capabilities.
2Volume of moving object
If junction area is reduced due to scaling, then device size is reduced, but leakage current increases
Solution Approach 1:
The patent applies different doping concentrations to different regions of the fin structure. The contact region at the bottom is heavily doped to reduce series resistance, while the drift region maintains lower doping to extend depletion width and reduce leakage. The junction region along the sidewalls has optimized doping to balance breakdown voltage and leakage current.
Solution Approach 2:
The diode employs a composite doping structure combining lightly-doped silicon in the drift region with heavily-doped regions at the contact and junction areas. This composite approach allows the structure to simultaneously achieve low leakage through extended depletion width and low series resistance through heavy doping at critical interfaces.
3Reliability
If dopant concentration is increased to reduce series resistance, then current flow is improved, but junction capacitance increases
Solution Approach 1:
The patent implements spatially varying doping concentrations: heavy doping in the contact region to minimize series resistance, moderate doping in the junction region for adequate breakdown voltage, and light doping in the drift region for extended depletion width. This local optimization resolves the trade-off between series resistance and junction capacitance.
4Volume of moving object
If fin width is reduced for scaling, then device density is improved, but forward current capacity decreases
Solution Approach 1:
The patent compensates for reduced horizontal fin width by extending the junction area vertically along the fin sidewalls. The junction region forms a three-dimensional structure around the depleted region, maintaining adequate junction area for current handling while preserving the scaled-down horizontal dimensions for high device density.
Solution Approach 2:
The composite doping structure with heavily-doped contact regions and optimally-doped junction regions enables the scaled fin to maintain adequate forward current capacity. The heavy doping at the contact region reduces series resistance, while the optimized junction region doping ensures sufficient breakdown voltage and current handling capability.
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 results in higher current capacity, reduced capacitance, and faster switching between on and off states, enhancing the performance of fin-based RF diodes by optimizing fin dimensions and doping levels, thereby addressing the limitations of conventional fin-type diodes.
Implementation Method 1
implanting the lower portion of each fin with a first-type dopant; implanting the upper portion of each fin, above the STI region, with the first-type dopant
Implementation Method 2
forming a junction region around a depletion region and along exposed sidewalls and a top surface of the upper portion of each fin
Implementation Method 3
forming a contact on exposed sidewalls and a top surface of each junction region
Data Source
AI summary
Methods for forming a fin-based RF diode with improved performance characteristics and the resulting devices are disclosed. Embodiments include forming fins over a substrate, separated from each other, each fin having a lower portion and an upper portion; forming STI regions over the substrate, between the lower portions of adjacent fins; implanting the lower portion of each fin with a first-type dopant; implanting the upper portion of each fin, above the STI region, with the first-type dopant; forming a junction region around a depletion region and along exposed sidewalls and a top surface of the upper portion of each fin; and forming a contact on exposed sidewalls and a top surface of each junction region.