MEMS Device Dynamic Stiffness Tuning via Feedback Control
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Solution Overview
Problem
Microelectromechanical systems (MEMS) devices face significant performance variations due to fabrication mismatches, process uncertainties, and environmental disturbances, leading to deviations from intended performance specifications, which existing tuning methods and design adjustments have not adequately addressed.
Innovation Solution
A MEMS device with a mechanical subsystem, actuator, sensing capacitor, measurement circuit, and control circuit that applies time-varying control signals to adjust the effective stiffness, damping, and mass, allowing for dynamic tuning and optimization of design parameters to reduce performance variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If feedback control is applied to tune microstructures, then performance parameters such as quality factor, linearity, and bandwidth are improved, but device complexity increases due to additional control circuits and sensors
Solution Approach 1:
The patent implements feedback control by sensing the actual position of the movable electrode using capacitance measurement and applying corrective voltage through the actuator. The control circuit continuously monitors displacement and adjusts the actuation voltage to compensate for fabrication variations, maintaining consistent performance across different devices
Solution Approach 2:
The patent introduces an intermediary control system that mediates between the actuator and the mechanical structure. The control circuit acts as an intermediary layer that translates desired position commands into actual positions by compensating for manufacturing errors, isolating the mechanical design from performance variations
2Manufacturing precision
If design parameters are adjusted to account for fabrication variations, then manufacturing precision is improved, but the design process becomes more complex and computationally intensive
Solution Approach 1:
The patent applies preliminary action by pre-compensating for expected fabrication errors in the design phase. Design parameters are intentionally adjusted to account for anticipated manufacturing variations, so that the final device performance matches specifications despite dimensional deviations during fabrication
Solution Approach 2:
The patent utilizes parameter changes by systematically varying design parameters such as electrode dimensions, gap distances, and material properties to find optimal values that are robust against fabrication variations. Multiple parameter sets are evaluated to identify combinations that maintain performance consistency across manufacturing tolerances
3Measurement precision
If Monte Carlo algorithms are used to analyze design uncertainties, then measurement precision of performance variation is improved, but computational cost increases significantly
Solution Approach 1:
The patent applies partial action by performing uncertainty analysis on only the most critical design parameters rather than all parameters. By identifying and focusing computational resources on parameters with the greatest impact on performance, the analysis achieves sufficient precision without the full computational burden of analyzing every parameter
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 solution effectively reduces sensitivity to process variations and geometry/material properties, achieving desired performance specifications with reduced computational costs and increased precision, enabling precise control of MEMS devices.
Implementation Method 1
a sensing capacitor including a first plate attached to and movable with the driven mass and a second plate substantially fixed in position, wherein a capacitance of the sensing capacitor varies as the driven mass moves
Implementation Method 2
an actuator responsive to a time-varying control signal to apply force to the driven mass
Data Source
AI summary
A microelectromechanical-systems (MEMS) device includes a driven mass and has a natural stiffness or damping. An actuator applies force to the mass, movement of which is measured by a sensing capacitor. A control circuit operates the actuator per displacement or velocity of the driven mass, so that a characteristic stiffness or damping of the mechanical subsystem is different from the respective natural value. A method of transforming a MEMS device design includes determining an aim performance value of the design and a baseline performance uncertainty of the design, selecting candidate sets of parameter values, determining a candidate, first, and second performance value for each, scoring the candidates, and repeating until one of the candidates satisfies a termination criterion, so the transformed design using that candidate set has the aim performance value and the respective first and second performance values closer to each other than the baseline performance uncertainty.