Vertical Stopper for Selective Damping in Capped MEMS Devices
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Solution Overview
Problem
Microelectromechanical systems (MEMS) devices face challenges in controlling the quality factor (Q) of movable proof masses due to unregulated damping, which affects their performance in applications like resonators, accelerometers, and gyroscopes, as existing capping structures do not allow for selective damping of motion in specific components.
Innovation Solution
Incorporating a stopper within the capping structure that is shaped and positioned to overlie a significant portion of the movable proof mass, thereby controlling the damping by limiting gas flow and adjusting the quality factor, allowing for selective damping of specific components like resonators or accelerometers without affecting others.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capping structure is used to seal MEMS devices, then the device is protected and sealed, but the damping of movable proof masses cannot be controlled, affecting quality factor
Solution Approach 1:
The patent applies local quality by introducing a stopper with specific geometric features (protrusions, recesses, or patterns) that create localized damping regions. The stopper is positioned to overlie specific portions of the movable proof mass, providing damping only in those local areas rather than uniformly across the entire device. This allows selective control of damping at specific locations while maintaining other performance characteristics.
Solution Approach 2:
The patent employs parameter changes by varying the stopper's geometric parameters (such as protrusion height, recess depth, pattern density, or material properties) to adjust the damping characteristics. By modifying these parameters, the quality factor of the movable proof mass can be controlled and optimized for specific applications, transforming the unregulated damping into a tunable parameter.
2Ease of operation
If damping is increased to control motion, then motion control improves, but quality factor of resonators and accelerometers decreases
Solution Approach 1:
The stopper provides localized damping by overlying only specific portions of the movable proof mass. This selective positioning allows motion control in targeted areas while preserving the quality factor in other regions, resolving the contradiction between motion control and quality factor maintenance.
Solution Approach 2:
The stopper can be designed with segmented or patterned structures that divide the damping function into discrete regions. This segmentation allows different areas of the movable proof mass to experience different damping levels, enabling simultaneous motion control and quality factor preservation in different segments of the device.
3Reliability
If selective damping is applied to resonators, then resonator Q is controlled, but Coriolis proof masses are also affected
Solution Approach 1:
The stopper is positioned and shaped to overlie the resonator components while avoiding the Coriolis proof mass. This precise local positioning creates selective damping that affects only the resonator, allowing independent control of resonator Q without impacting the Coriolis proof mass performance.
Solution Approach 2:
The device structure is segmented into distinct functional zones with the stopper confined to the resonator region. This spatial segmentation isolates the damping effect to the resonator, enabling independent optimization of resonator Q while maintaining Coriolis proof mass performance for gyroscope operation.
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 configuration enables precise control of the quality factor of MEMS devices, allowing for higher accelerometer Q at lower pressures while maintaining resonator Q, and reduces electrical coupling and noise in gyroscopes by selectively damping resonators without affecting Coriolis proof masses.
Implementation Method 1
the stopper damps motion of the one or more movable masses by limiting gas flow
Data Source
AI summary
Capped microelectromechanical systems (MEMS) devices are described. In at least some situations, the MEMS device includes one or more masses which move. The cap may include a stopper which damps motion of the one or more movable masses. In at least some situations, the stopper damps motion of one of the masses but not another mass.