RF MEMS Isolation via Poly-Resistors and Ground-Shields
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Solution Overview
Problem
Integrating passive RF devices on silicon substrates with CMOS circuits poses challenges due to signal coupling, leading to electric and magnetic losses that reduce the effective Q of capacitors and introduce noise, impacting overall system performance.
Innovation Solution
The integration of MEMS RF variable capacitors with CMOS circuits on the same chip is achieved by isolating the RF switch from the substrate using a ground-shield and high-resistance poly-resistors to decouple the MEMS device from the control circuit, maintaining high Q factors and minimizing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If passive RF devices are integrated on silicon substrate with CMOS circuits, then high volume production and low cost are achieved, but signal coupling causes electric and magnetic losses that reduce effective Q and introduce noise
Solution Approach 1:
The patent segments the RF signal path from the CMOS substrate by introducing isolation structures (ground shields, isolation resistors, and air bridges) that divide the monolithic integration into isolated functional zones. This allows the RF capacitor to benefit from CMOS fabrication while preventing substrate losses, resolving the contradiction between mass production capability and RF performance.
Solution Approach 2:
The patent uses intermediary structures such as ground shields, isolation resistors, and air bridges as mediators between the RF capacitor and CMOS substrate. These intermediaries block the coupling path that causes electric and magnetic losses, enabling both high-volume CMOS production and low-loss RF operation to coexist on the same chip.
2Reliability
If MEMS devices are isolated from substrate using ground-shield and high-resistance poly-resistors, then substrate losses are reduced and Q factor is maintained, but device complexity increases
Solution Approach 1:
The patent changes the electrical parameters of the substrate interface by introducing high-resistance poly-resistors (with resistance values in the mega-ohm range) and ground shields. These parameter changes create high-impedance paths that block RF signal coupling to the lossy substrate, maintaining high Q factors despite the added structural complexity.
3Ease of manufacture
If MEMS switch is integrated on CMOS chip, then monolithic integration is achieved, but noise and spurious disturbs from CMOS circuits affect RF performance
Solution Approach 1:
The patent extracts the harmful noise and spurious disturbances from the RF signal path by using isolation structures (ground shields, isolation resistors, and air bridges) that physically and electrically separate the RF capacitor from the noisy CMOS circuits. This extraction allows monolithic integration while removing the harmful effects of CMOS noise.
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 allows for monolithic integration of high-performance RF capacitors on silicon chips, reducing substrate losses and maintaining required RF performance, enabling efficient high-frequency communications.
Implementation Method 1
a pull-up electrode or a pull-down electrode to move the MEMS device between a first position spaced a first distance from an RF electrode and a second position spaced a second distance different than the first distance from the RF electrode
Data Source
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AI summary
The present invention generally relates to an architecture for isolating an RF MEMS device from a substrate and driving circuit, series and shunt DVC die architectures, and smaller MEMS arrays for high frequency communications. The semiconductor device has one or more cells with a plurality of MEMS devices therein. The MEMS device operates by applying an electrical bias to either a pull-up electrode or a pull-down electrode to move a switching element of the MEMS device between a first position spaced a first distance from an RF electrode and a second position spaced a second distance different than the first distance from the RF electrode. The pull-up and/or pull-off electrode may be coupled to a resistor to isolate the MEMS device from the substrate.