MEMS Mirror Strain Sensing With Differential Piezoelectric Readout
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Solution Overview
Problem
Existing MEMS devices face challenges with piezoresistive and piezoelectric sensors for detecting the deformation of deformable structures, including low measurement sensitivity, high electrical consumption, complex manufacturing processes, and material instability, which affect the accuracy and reliability of mirror element control.
Innovation Solution
The MEMS device incorporates piezoelectric actuators and sensors with distinct piezoelectric materials for actuation and detection, using aluminum nitride (AlN) for actuators and PZT for sensors, separated by insulating layers to optimize actuation and detection, and employs differential reading to enhance measurement sensitivity and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If piezoresistive sensors are used to detect the position of the mirror element, then the position can be detected, but the measurement sensitivity is low, electrical consumption is high, and manufacturing complexity increases
Solution Approach 1:
The patent replaces piezoresistive sensors with capacitive sensors that detect mirror element position through capacitance changes rather than mechanical resistance changes. This substitution eliminates the need for complex piezoresistive sensor fabrication and reduces manufacturing steps while maintaining position detection capability
Solution Approach 2:
The patent introduces an intermediary readout circuit that measures capacitance changes of the deformable structure to infer mirror element position. This intermediary approach provides high measurement sensitivity without requiring direct mechanical coupling between sensor and mirror, simplifying the overall device structure
2Measurement precision
If piezoresistive sensors are used to detect the position of the mirror element, then the position can be detected, but the electrical consumption is high
Solution Approach 1:
The patent replaces power-hungry piezoresistive sensors with capacitive sensors that require minimal electrical energy to operate. Capacitive measurement involves simple voltage sensing without the need for constant current driving, dramatically reducing electrical consumption while maintaining position detection accuracy
3Measurement precision
If piezoelectric sensors with single-ended reading are used, then the position can be detected, but the measurement sensitivity is low and noise is high
Solution Approach 1:
The patent employs asymmetric capacitor configuration where the deformable structure serves as one electrode and a fixed electrode on the substrate serves as the other. This asymmetric arrangement optimizes the capacitive coupling for detection while minimizing noise pickup, improving signal-to-noise ratio compared to symmetric single-ended readings
Solution Approach 2:
The patent implements closed-loop feedback control where the capacitive position detection signal is fed back to adjust the mirror element position. This feedback mechanism continuously compensates for noise and drift, maintaining high measurement precision over time
4Ease of manufacture
If piezoelectric sensors and actuators use the same material layer, then manufacturing is simplified, but the piezoelectric material becomes unstable over time
Solution Approach 1:
The patent segments the piezoelectric function into separate components: PZT piezoelectric material is used exclusively for actuation layers while AlN piezoelectric material is used for sensor layers. This segmentation allows each material to be optimized for its specific function and prevents the instability issues that arise from using a single material for both actuation and sensing
Solution Approach 2:
The patent employs a composite piezoelectric structure with multiple material layers (PZT and AlN) that combine the advantages of different piezoelectric materials. PZT provides strong actuation capability while AlN provides stable sensing performance, creating a composite system that overcomes the limitations of single-material approaches
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 improves measurement sensitivity, reduces manufacturing complexity, and enhances the accuracy and reliability of mirror element control, overcoming the limitations of previous technologies.
Implementation Method 1
a deformable structure which includes a piezoelectric actuator, for controlling the deformation of the deformable structure
Implementation Method 2
The piezoelectric sensor comprises a respective sensitive element of piezoelectric insulating material which biases, thus generating a potential difference thereacross, when subject to a mechanical deformation
Data Source
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AI summary
MEMS device (20) comprising: a semiconductor body (21) including a fixed structure (24) defining a cavity (23), and a deformable main body (31) suspended on the cavity (23); a piezoelectric actuator (38) on the deformable main body (31); and a piezoelectric sensor element (41) on the deformable main body (31), which forms with the deformable main body (31) a strain sensor (50). The piezoelectric sensor element (41) comprises: a detection piezoelectric region (51B) of aluminum nitride on the deformable main body (31); and an intermediate detection electrode (60B) on the detection piezoelectric region (51B). The deformable main body (31), the detection piezoelectric region (51B) and the intermediate detection electrode (60B) form a first detection capacitor (70') of the strain sensor (50). The deformable main body (31), the piezoelectric actuator (38) and the piezoelectric sensor element (41) form a deformable structure (30) suspended on the cavity (23) and deformable by the piezoelectric actuator (38), wherein the strain sensor (50) allows the deformation of the deformable structure (30) to be detected.