Low-Resistivity Trench Capacitor Structure for Better Frequency Response
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Solution Overview
Problem
Trench capacitor devices experience high series resistance due to the high resistivity of their electrodes, leading to poor frequency response in high-frequency decoupling applications.
Innovation Solution
The design incorporates a trench capacitor structure with a doped region in a substrate, featuring a thick bottom insulating layer, an inner electrode, and outer electrodes with a metallic layer, where the outer electrodes are shallower and protrude above the substrate surface, connected through a connection portion, and surrounded by a capacitor dielectric layer, reducing overall resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doped poly-Si is used for electrodes in trench capacitors, then the capacitor structure is simple and manufacturable, but the series resistance is high leading to poor frequency response
Solution Approach 1:
The patent employs composite electrode structures combining doped poly-Si with metallic layers (Al or Cu) to achieve low resistivity while maintaining the trench capacitor's structural simplicity. The metallic layers are deposited on the doped poly-Si electrodes, creating a composite that leverages the low resistivity of metals and the manufacturing compatibility of poly-Si, thereby resolving the contradiction between simple structure and high frequency response
Solution Approach 2:
The invention applies local quality by selectively depositing metallic layers only in specific regions where resistivity reduction is most critical. The doped poly-Si electrodes retain their properties in areas where mechanical support and capacitance are needed, while metallic coatings are applied to surfaces and interfaces where current flow is highest, optimizing frequency response without unnecessarily complicating the overall structure
2Reliability
If the outer electrode depth is reduced to protrude above substrate surface, then the series resistance is decreased improving frequency response, but the capacitor occupies more vertical space
Solution Approach 1:
The patent resolves this contradiction by transitioning from a fully planar electrode configuration to a three-dimensional structure where the outer electrode protrudes above the substrate surface. This vertical extension in the third dimension provides additional surface area for current flow and reduces series resistance, while the overall footprint remains constrained. The dimensional change allows simultaneous optimization of electrical performance and spatial efficiency
Data Source
AI summary
A trench capacitor includes a trench disposed in a substrate; an inner electrode disposed in a central portion of the trench and having a top surface and a bottom surface; an outer electrode disposed symmetrically with respect to the inner electrode, the outer electrode having a depth shallower than a depth of the inner electrode with respect to a top surface of the substrate; a thick bottom insulating layer disposed below the inner electrode and the outer electrode; and a capacitor dielectric layer surrounding the outer electrode. The outer electrode protrudes above the top surface of the substrate and has a top surface that is higher than the top surface of the inner electrode.