Integrated PMUT on IC for High-Resolution Fingerprint Sensing

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Solution Overview

Problem

Conventional methods for manufacturing piezoelectric microelectromechanical ultrasound transducers (MUTs) for fingerprint sensing face challenges in achieving high resolution and are prone to skin condition and sensor contamination, leading to inaccurate fingerprint detection.

Innovation Solution

The development of integrated piezoelectric microelectromechanical ultrasound transducers (PMUTs) on integrated circuits (ICs) with a vertically stacked structure, including a piezoelectric material, metal conductive layers, and complementary metal-oxide-semiconductor (CMOS) structures, to enhance resolution and robustness against contamination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional manufacturing methods are used for MUT devices, then fabrication is simpler, but manufacturing precision and resolution are insufficient (cannot achieve 300 dpi or higher)

Engineering Contradiction:

Improvepixel size resolutionVSAvoidfabrication complexity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent transitions from planar manufacturing to three-dimensional vertically stacked structures, integrating piezoelectric MUT devices with CMOS circuits in the vertical dimension. This enables higher resolution pixel sizes (85 μm or smaller) while maintaining fabrication feasibility through standardized vertical integration processes.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The patent merges piezoelectric MUT device fabrication with standard CMOS manufacturing processes into a single integrated flow. This combination achieves high manufacturing precision (300 dpi or higher) by leveraging the precision of semiconductor fabrication while maintaining ease of manufacture through process integration.

Inventive Principle:

Principle #5Merging (Combining)

2Manufacturing precision

If CMUT linear arrays are used for fingerprint detection, then manufacturing precision is achieved, but reliability deteriorates due to skin condition and sensor contamination

Engineering Contradiction:

Improvepixel size resolutionVSAvoiddetection accuracy

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent replaces capacitive sensing (CMUT) with piezoelectric ultrasonic sensing (PMUT). The piezoelectric effect enables mechanical vibration-based fingerprint detection that penetrates skin surfaces, substituting the electrical field-based capacitive method that is susceptible to contamination and skin condition variations.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the detection parameter from electrical capacitance to mechanical acoustic vibration. This parameter change allows the sensor to detect fingerprint ridges through ultrasonic waves that are less affected by skin moisture, oil, and contamination, thereby improving reliability while maintaining manufacturing precision.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If vertically stacked integrated structure is implemented, then device complexity increases, but manufacturing precision and reliability improve

Engineering Contradiction:

Improvepixel size resolutionVSAvoidintegration structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent segments the integrated device into distinct vertical layers: bottom CMOS circuit layer, intermediate piezoelectric MUT layer, and top electrode layer. This segmentation manages device complexity by organizing functions into separate layers while achieving high manufacturing precision through standardized interlayer connections.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent resolves complexity by moving integration into the vertical dimension rather than lateral placement. The vertically stacked structure consolidates multiple functions (signal generation, ultrasonic transmission, reception, and processing) in the z-direction, reducing lateral footprint and simplifying interconnect routing while maintaining high manufacturing precision.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 PMUTs on ICs improve fingerprint sensing resolution and accuracy by providing a high fill factor and mechanical anchoring, reducing parasitics, and effectively addressing issues related to skin condition and sensor contamination.

Implementation Method 1

piezoelectric material disposed within the MEMS device comprising a piezoelectric MUT (PMUT) array of a fingerprint sensor

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

adapted to sense a characteristic of a fingerprint placed adjacent to the MUT structure

Methodology Applied

Scientific EffectPiezoelectric effect: Converse Piezoelectric Effect

Data Source

PatentUS11847851B2Integrated piezoelectric microelectromechanical ultrasound transducer (PMUT) on integrated circuit (IC) for fingerprint sensing

Publication Date: 2023.12.19 INVENSENSE INC

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.