Varactor With Meander Diffusion Region for High Frequency Q-Factor
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Solution Overview
Problem
Varactors used in high-frequency applications, such as millimeter wave circuits, experience a significant decrease in quality factor (Q-factor) at frequencies above 5 GHz, leading to performance degradation.
Innovation Solution
A varactor structure is developed with a substrate featuring alternately arranged gate structures, meander diffusion regions, and strategically placed contact plugs to reduce parasitic capacitance and resistance, improving the varactor's quality factor at high frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional MOS structure varactor is used, then the device can operate at high frequencies, but the quality factor decreases greatly at frequencies greater than 5 GHz
Solution Approach 1:
The gate structure is divided into multiple segments including a base portion and multiple line portions that are alternately arranged. This segmentation reduces parasitic capacitance and resistance, allowing the varactor to maintain high quality factor at frequencies above 5 GHz while operating at high frequencies
Solution Approach 2:
The invention transitions from a conventional planar gate structure to a three-dimensional meander diffusion region structure that surrounds the line portions. This dimensional change increases the effective area for charge storage while minimizing parasitic effects, resolving the contradiction between high-frequency operation and quality factor maintenance
2Object-generated harmful factors
If the gate structure uses multiple line portions in alternately arranged pattern, then parasitic capacitance is reduced, but the device complexity increases
Solution Approach 1:
Multiple line portions are merged into a continuous meander diffusion region that surrounds the alternately arranged line portions. This merging approach maintains the low parasitic capacitance benefits of segmented gates while simplifying the fabrication process and reducing overall device complexity
Data Source
AI summary
A varactor structure includes a substrate. A first and second gate structure are disposed on the substrate. The first and second gate structures each include a base portion and a plurality of line portions connected thereto. The line portions of each of the first and second gate structures is alternately arranged. A meander diffusion region is formed in the substrate and surrounds the line portions. A first set of contact plugs is planned with at least two columns or rows and disposed on the base portions of the first and second gate structures. A second set of contact plugs is planned with at least two columns or rows and disposed on the meander diffusion region. A first conductive layer is disposed on a top end of the first set of contact plugs. A second conductive layer is disposed on a top end of the second set of contact plugs.