Gate Contacts With Airgap Isolation For Low-Noise Amplifiers
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Solution Overview
Problem
In semiconductor device fabrication, particularly for low-noise amplifiers, the reduction of gate resistance to improve noise figure in the 2 GHz to 28 GHz band is hindered by increased parasitic capacitance due to contacts placed directly over the gate, which degrades gain and noise figure.
Innovation Solution
The implementation of a structure with trench isolation regions and airgaps in the dielectric layer over field-effect transistors, positioning gate contacts in a manner that creates airgaps between them to reduce parasitic capacitance, utilizing a dielectric layer and metal wires to form these airgaps during the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate contacts are placed directly over the gate within the active region, then gate resistance is reduced, but parasitic capacitance increases
Solution Approach 1:
The gate contact structure is segmented into multiple portions positioned over different regions of the gate, with airgap isolation regions separating them. This segmentation allows the contact to achieve low resistance through multiple contact points while the airgap regions eliminate parasitic capacitance between adjacent contact portions, resolving the contradiction between reducing gate resistance and minimizing parasitic capacitance.
Solution Approach 2:
Airgap isolation regions are introduced as intermediary elements between adjacent gate contact portions. These airgap regions act as mediators that prevent direct capacitive coupling between contact portions while allowing the contact structure to maintain electrical connection to the gate through multiple paths, thus reducing parasitic capacitance without sacrificing gate resistance performance.
2Reliability
If parasitic capacitance is increased to reduce gate resistance, then gate resistance improves, but gain and noise figure are degraded
Solution Approach 1:
The gate contact is divided into multiple segmented portions separated by airgap isolation regions. This segmentation enables the contact to maintain low gate resistance through multiple contact points while the airgap regions eliminate parasitic capacitance, thereby preserving gain and noise figure performance without the tradeoff present in conventional continuous contact structures.
Solution Approach 2:
The invention converts the potentially harmful effect of close contact between gate contact portions (which would increase parasitic capacitance) into a benefit by deliberately introducing airgap isolation regions. These airgaps transform what would be capacitive coupling into isolated regions, eliminating parasitic capacitance while maintaining the low-resistance electrical connection to the gate, thus improving both noise figure and gain.
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 airgaps effectively reduce parasitic capacitance, thereby alleviating the negative impact on gain and noise figure, improving the performance of low-noise amplifiers by minimizing the degradation caused by increased capacitance.
Implementation Method 1
increases parasitic capacitance as a tradeoff. An increase in the parasitic capacitance tends to degrade gain and the noise figure
Implementation Method 2
a dielectric layer over the field-effect transistor
Data Source
AI summary
Structures for a semiconductor device including airgap isolation and methods of forming a semiconductor device structure that includes airgap isolation. The structure includes a trench isolation region, an active region of semiconductor material surrounded by the trench isolation region, and a field-effect transistor including a gate within the active region. The structure further includes a dielectric layer over the field-effect transistor, a first gate contact coupled to the gate, and a second gate contact coupled to the gate. The first and second gate contacts are positioned in the dielectric layer over the active region, and the second gate contact is spaced along a longitudinal axis of the gate from the first gate contact. The structure further includes an airgap including a portion positioned in the dielectric layer over the gate between the first and second gate contacts.