Inter-digital Electrodes for Miniaturized Piezoelectric Accelerometers
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Solution Overview
Problem
Miniaturized piezoelectric accelerometers face limitations in electrical voltage output due to small thickness of piezoelectric thin films, and existing designs are prone to mechanical shock and rigidity issues, which affect sensitivity and robustness.
Innovation Solution
A miniaturized piezoelectric accelerometer design featuring a support frame with a cavity and a seismic mass, where inter-digital electrodes are deposited on piezoelectric thin films coated on suspension beams, with terminals connected at the seismic mass to enhance voltage sensitivity and structural robustness, and a method of fabrication using silicon wafers to produce accelerometers with improved consistency and reduced cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If piezoelectric thin films with small thickness are used for miniaturization, then device size is reduced, but electrical voltage output is significantly restricted
Solution Approach 1:
The patent transitions from conventional sandwich electrode configuration (electrodes on top and bottom surfaces) to an in-plane inter-digital electrode configuration where electrodes are arranged laterally on the same surface plane. This dimensional reconfiguration allows the thin piezoelectric film to generate voltage through lateral strain rather than requiring thickness-driven potential difference, thereby maintaining adequate voltage output despite reduced film thickness for miniaturization.
Solution Approach 2:
The patent changes the electrode arrangement geometry from vertical stacking to lateral inter-digital configuration, and aligns electrical polarization with the surface plane rather than perpendicular to it. This parameter change in electrode geometry and polarization orientation enables the thin piezoelectric film to effectively utilize the d33 coefficient for voltage generation, compensating for the reduced thickness effect.
2Volume of moving object
If piezoelectric micro-cantilever structures are used, then miniaturization is achieved, but the structures deform seriously due to large residual stress and are liable to break under mechanical shock
Solution Approach 1:
The patent employs a diaphragm structure made of thin flexible film instead of brittle micro-cantilever structures. The diaphragm can elastically deform under acceleration and mechanical shock without permanent deformation or fracture. The piezoelectric thin film is coated on this flexible diaphragm, allowing the entire structure to accommodate stress through elastic deformation while maintaining structural integrity and reliability.
3Reliability
If piezoelectric diaphragm structures are used, then structural robustness is improved, but the structure becomes very rigid which limits sensitivity at small sizes
Solution Approach 1:
The patent implements local quality by creating inter-digital electrode regions with specific geometric patterns (fingers of varying lengths and spacing) on the diaphragm surface. These localized electrode configurations create regions of concentrated stress and electric field that enhance sensitivity to acceleration while the overall diaphragm maintains its robustness. The inter-digital arrangement maximizes the piezoelectric response in specific local areas without requiring the entire structure to be flexible.
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 design achieves enhanced sensitivity and structural robustness, allowing for highly miniaturized accelerometers with improved flexibility and reliability, while reducing production costs and measurement inaccuracies.
Implementation Method 1
each of the suspension beams having a piezoelectric thin film coated on a top surface thereof
Data Source
AI summary
The miniaturized piezoelectric accelerometer includes a support frame (102) having a cavity (104) and a seismic mass (108) supported by a plurality of suspension beams (110) extending from the support frame (102). Each of the suspension beams (110) has a piezoelectric thin film coated on a top surface thereof, with a pair of inter-digital electrodes (114) deposited on an upper surface of each piezoelectric thin film. The presence of acceleration excites bending and thus strain in the piezoelectric thin film, which in turn causes electrical signals to be generated over terminals of the electrodes (114). To collect constructively the output of the electrodes (114), one terminal of each of the electrodes (114) is routed to and electrically connected at a top surface (308) of the seismic mass (108).