MEMS Mirror Rotation Sensing via Beam Bending
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Solution Overview
Problem
Measuring angular deflection in MEMS devices using strain-based methods is challenging due to small elongation and shortening of mechanical components, resulting in small associated strains that are difficult to detect accurately.
Innovation Solution
The solution involves translating rotational movement of MEMS assemblies into bending of components, which induces larger strains detectable by piezoresistive, piezoelectric, or metallic strain sensors integrated during the MEMS fabrication process, using a semiconductor beam that elongates with rotation and a sensing circuit to measure the strain-induced resistance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain-based sensors are used to measure angular deflection in MEMS devices, then measurement capability is provided, but the small elongation and shortening of mechanical components result in small strains that are difficult to detect accurately
Solution Approach 1:
The patent introduces a beam as an intermediary mechanical element that translates the small rotational movement of the mirror into larger bending deformation. The beam acts as a mediator between the mirror rotation and the strain sensor, amplifying the mechanical displacement into a more measurable strain signal that can be detected accurately by the piezoresistive sensor.
Solution Approach 2:
The patent replaces direct mechanical strain measurement on the mirror support structure with an indirect measurement system using a separate beam element. This substitution allows the use of piezoresistive sensors that convert mechanical bending into electrical resistance changes, providing a more detectable signal while maintaining the mechanical rotation function.
2Measurement precision
If a beam is introduced to translate rotation into bending, then strain detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges the strain sensing function directly into the beam structure by fabricating piezoresistive sensors within the beam itself during the MEMS fabrication process. This integration combines the mechanical beam element and the sensing function into a single unified structure, reducing the need for separate components and simplifying the overall device architecture.
Solution Approach 2:
The beam serves multiple functions simultaneously: it acts as a mechanical support element, a motion translator converting rotation to bending, and a substrate for the strain sensor. This multi-functionality reduces the number of separate components needed in the device.
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 accurate detection of rotation angles by converting small rotational strains into measurable bending strains, enhancing the precision of angular deflection measurement in MEMS devices.
Implementation Method 1
a piezoresistive sensor that detects strain in the beam
Implementation Method 2
the beam is deformed as a result of the rotation of the mirror
Data Source
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AI summary
Mechanical apparatus includes a base (24), a moving element (26), and a hinge (28), having a first end attached to the moving element. A supporting structure (32) is attached to the base and to the second end of the hinge and has at least a component perpendicular to the hinge so as to translate rotation of the moving element about the hinge into elongation of the component, whereby the moving element rotates about the hinge relative to the base while the supporting structure is deformed as a result of the rotation of the moving element about the hinge. A strain-based rotation sensor (34, 44, 46, 60, 62, 72, 74, 100) is associated with the supporting structure and is configured to provide a signal indicative of the rotation of the moving element responsively to a strain induced due to deformation of the supporting structure as the result of the rotation of the moving element.