Cross-Shaped Air Gap Structure for Lower RF Switch Off-Capacitance
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Solution Overview
Problem
Conventional semiconductor structures with air gaps in RF switches fail to adequately reduce off-capacitance (Coff) to achieve low loss in radio-frequency signals, as the improvement effect is limited.
Innovation Solution
A semiconductor structure with a cross-like-shaped air gap in the dielectric stack between conductive layers, featuring a widened middle portion, tapered upper and lower portions, and an extension portion of the dielectric layer that conformally covers the sidewalls, along with a silicon oxide layer and low-k dielectric materials, to reduce parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional air gap is formed in the dielectric layer above the gate, then the parasitic capacitance between the gate and adjacent contact plugs and wires is reduced, but the improvement effect is limited and Coff cannot be sufficiently reduced
Solution Approach 1:
The air gap is segmented into a cross-like shape with multiple regions (first air gap region, second air gap region, third air gap region, fourth air gap region) separated by dielectric ridges. This segmentation increases the total air gap area and more effectively reduces parasitic capacitance between the gate and surrounding conductors, directly addressing the limitation of conventional single air gaps
Solution Approach 2:
The air gap structure is extended from a simple planar gap to a three-dimensional cross-like configuration with vertical ridges and multiple horizontal regions. This dimensional expansion allows the air gap to interact with more conductive elements simultaneously, enhancing the reduction of parasitic capacitance in multiple directions
2Object-affected harmful factors
If the dielectric layer is modified to reduce parasitic capacitance, then Coff is reduced, but the structural complexity increases with multiple dielectric layers and air gap formation
Solution Approach 1:
The dielectric layer is segmented into multiple regions with different dielectric materials (first dielectric material in air gap regions, second dielectric material in ridge regions). This segmentation allows each region to be optimized for its specific function while maintaining overall structural integrity
Solution Approach 2:
The cross-like air gap structure is formed by nesting multiple dielectric layers and air gap regions within each other. The dielectric ridges are embedded within the dielectric layer, creating a nested configuration that reduces parasitic capacitance without requiring complete restructuring of the device
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 structure effectively reduces parasitic capacitance, enhancing the on-resistance and off-capacitance characteristics, thereby improving the low-loss performance of RF switches.
Implementation Method 1
reduce the parasitic capacitance between the gate and adjacent contact plugs and wires
Implementation Method 2
a dielectric stack comprising a first dielectric layer disposed on the substrate, a second dielectric layer disposed on the first dielectric layer, and a third dielectric layer disposed on the second dielectric layer
Data Source
Figure 1~2
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Figure 5~6
AI summary
A semiconductor structure with an air gap includes a dielectric stack having a first dielectric layer (111) on a substrate (100, 101), a second dielectric layer (112) on the first dielectric layer (111), and a third dielectric layer (113) on the second dielectric layer (112). A first conductive layer and a second conductive layer are disposed in the dielectric stack. The first conductive layer and the second conductive layer are coplanar. A cross-like-shaped air gap is disposed in the dielectric stack between the first and second conductive layers. An oxide layer (102) is disposed on a sidewall (112s) of the second dielectric layer (112) within the cross-like-shaped air gap.