MEMS Digital Variable Capacitor Isolated Well Noise Reduction
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Solution Overview
Problem
Existing MEMS digital variable capacitor (DVC) devices experience variation in RF isolation and dynamic behavior due to substrate resistance and noise coupling, leading to inconsistent performance across MEMS cells.
Innovation Solution
Surrounding poly-resistors with isolated p-wells or n-wells coupled to an RF ground shield reduces substrate resistance influence and noise, ensuring consistent dynamic behavior and improved RF isolation by directly coupling noise to CMOS ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If poly-resistors are connected between waveform controller and MEMS electrodes, then RF isolation and damping are provided, but substrate resistance influences dynamic behavior and noise couples into RF signal
Solution Approach 1:
An isolated well structure is introduced as an intermediary element between the poly-resistor and the substrate. This isolated well acts as a mediator that blocks the coupling path for noise and substrate resistance effects while maintaining the necessary electrical connections for RF isolation and damping functionality.
Solution Approach 2:
The harmful influence of substrate resistance and noise is extracted or removed from the signal path by using an isolated well that prevents substrate coupling. The isolated well effectively separates the poly-resistor from the noisy substrate environment while preserving the beneficial RF isolation properties.
2Productivity
If multiple MEMS DVC cells are arranged around RF-pin, then RF performance is optimized, but variations in substrate resistance cause inconsistent performance across cells
Solution Approach 1:
The isolated well serves as a standardized intermediary structure for each MEMS DVC cell, providing uniform noise isolation and substrate decoupling. This ensures that all cells regardless of their position around the RF-pin experience consistent electrical characteristics and performance.
Solution Approach 2:
Each MEMS DVC cell is equipped with its own isolated well structure, providing localized noise isolation and substrate decoupling. This local implementation ensures that performance consistency is achieved at each cell level, compensating for variations in substrate resistance across different positions.
3Object-affected harmful factors
If substrate ground-contacts are avoided near MEMS devices, then noise coupling is reduced, but RF isolation and damping become insufficient
Solution Approach 1:
The isolated well acts as an intermediary that enables both noise reduction and maintained RF isolation/damping. It provides a controlled coupling path that blocks high-frequency noise while preserving the necessary electrical characteristics for RF performance.
Solution Approach 2:
The solution moves the grounding and isolation function to a different dimensional level by using the isolated well structure that extends vertically from the substrate. This allows noise isolation in the vertical dimension while maintaining horizontal RF isolation and damping characteristics.
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 solution enhances RF isolation, reduces spurious noise, and ensures identical dynamic performance across MEMS cells, facilitating easier optimization of switch times and improved RF signal quality.
Implementation Method 1
an isolated p-well or an isolated n-well surrounding the poly-resistor. The isolated well is coupled to an RF ground shield that is disposed between the poly-resistor and the MEMS element
Implementation Method 2
The isolated well is coupled to an RF ground shield that is disposed between the poly-resistor and the MEMS element
Implementation Method 3
These resistors provide for damping of the MEMS devices within the MEMS DVC cells which allows for fast operation
Data Source
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AI summary
The present invention generally relates to a MEMS DVC. The MEMS DVC has an RF electrode and is formed above a CMOS substrate. To reduce noise in the RF signal, a poly-resistor that is connected between a waveform controller and the electrodes of the MEMS element, may be surrounded by an isolated p-well or an isolated n-well. The isolated well is coupled to an RF ground shield that is disposed between the poly-resistor and the MEMS element. Due to the presence of the isolated well that surrounds the poly-resistor, the substrate resistance does not influence the dynamic behavior of each MEMS element in the MEMS DVC and noise in the RF signal is reduced.