CMOS-Integrated PMUT Array Layout for High-Resolution Fingerprint Sensing
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Solution Overview
Problem
Conventional MEMS devices for fingerprint sensing, such as CMUT linear arrays, face challenges in achieving high resolution due to manufacturing limitations and are prone to errors from skin conditions and sensor contamination.
Innovation Solution
The integration of piezoelectric MEMS transducers (PMUTs) on integrated circuit (IC) for fingerprint sensing, which includes a PMUT structure with a piezoelectric material, a first metal conductive layer, and a plurality of metal electrodes forming electrical connections between the conductive layers and a CMOS structure, vertically stacked to enhance resolution and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional manufacturing processes (traditional polishing and sawing from bulk piezoelectric materials) are used, then ease of manufacture is maintained, but manufacturing precision deteriorates (cannot achieve required 300 dpi or higher resolution)
Solution Approach 1:
The patent divides the bulk piezoelectric material into multiple thin layers through lamination of separate piezoelectric layers onto a substrate. This segmentation enables achieving high resolution (300 dpi or higher) by creating thinner, more precisely controllable individual layers, while still using conventional manufacturing processes for each layer.
Solution Approach 2:
The patent transitions from conventional planar manufacturing to a vertically stacked laminated structure. By adding the vertical dimension with multiple piezoelectric layers laminated onto the substrate, the patent achieves higher resolution in the horizontal plane while maintaining compatibility with existing manufacturing processes.
2Manufacturing precision
If CMUT linear arrays are used for fingerprint detection, then manufacturing precision is improved (can achieve required resolution), but reliability deteriorates (prone to skin condition and sensor contamination errors)
Solution Approach 1:
The patent uses composite piezoelectric materials (PZT and PVDF) with different properties - PZT provides high piezoelectric coefficient for strong signal, while PVDF offers flexibility and resistance to contamination. This composite approach maintains high resolution while improving reliability against skin conditions and sensor contamination.
Solution Approach 2:
The patent changes the material parameter from capacitive (CMUT) to piezoelectric (PMUT), fundamentally altering the detection mechanism. This parameter change makes the sensor less susceptible to skin conditions and contamination, improving reliability while maintaining the required manufacturing precision.
3Measurement precision
If piezoelectric materials are integrated on IC for fingerprint sensing, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the piezoelectric transducer structure with the CMOS substrate by laminating piezoelectric layers directly onto the IC. This merging integrates the sensing function with the processing substrate, improving measurement precision while managing device complexity through a unified stacked architecture.
Solution Approach 2:
The patent creates a multi-functional integrated device where the stacked structure serves multiple purposes: the piezoelectric layers provide sensing capability, the CMOS substrate provides processing capability, and the combined structure enables both high measurement precision and compact integration.
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 proposed solution improves the resolution and accuracy of fingerprint sensing by overcoming manufacturing limitations and reducing the impact of skin and sensor contamination, while also integrating effectively with CMOS structures for enhanced performance.
Implementation Method 1
piezoelectric material disposed within the MEMS device comprising a piezoelectric MUT (PMUT) array of a fingerprint sensor
Implementation Method 2
piezoelectric material disposed within the MEMS device comprising a piezoelectric MUT (PMUT) array of a fingerprint sensor adapted to sense a characteristic of a fingerprint
Data Source
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AI summary
Microelectromechanical (MEMS) devices and associated methods are disclosed. Piezoelectric MEMS transducers (PMUTs) suitable for integration with complementary metal oxide semiconductor (CMOS) integrated circuit (IC), as well as PMUT arrays having high fill factor for fingerprint sensing, are described.