Flip-Chip pMUT-CMOS Assembly for Low-Interference 3D Imaging

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Solution Overview

Problem

Conventional ultrasound probes using piezoelectric materials like PZT and PMN-PT are expensive and require high drive voltages, and silicon-based cMUTs face performance issues due to charge build-up and non-linear transfer functions, making them unsuitable for low-cost 3D imaging. Integrating pMUTs with CMOS dies using flip-chip technology is challenging due to electromagnetic interference and impractical wire bonding.

Innovation Solution

A transducer assembly is developed with a MEMS die containing piezoelectric elements electrically coupled to a CMOS die via bumps, integrated using flip-chip technology, which reduces manufacturing costs and minimizes electromagnetic interference by ensuring close proximity and direct electrical connectivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional bulk piezoelectric elements are used for transducers, then high imaging performance is achieved, but manufacturing cost increases and high drive voltage is required

Engineering Contradiction:

Improveimaging performanceVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces conventional bulk piezoelectric elements with piezoelectric micromachined ultrasound transducers (pMUTs) fabricated using MEMS technology. This substitution enables batch fabrication on silicon wafers, dramatically reducing manufacturing costs while maintaining imaging performance. The pMUTs use thin piezoelectric films deposited onto silicon substrates, eliminating the need for expensive precision cutting of bulk PZT materials.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the drive voltage parameter from high voltage (200V required by conventional piezoelectric elements) to low voltage operation. The pMUTs achieve adequate performance with much lower drive voltages due to their micromachined structure and thin piezoelectric film configuration, reducing power consumption and simplifying driver circuit requirements.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If cMUTs are used for batch fabrication on silicon wafers, then manufacturing cost is reduced, but performance deteriorates due to charge build-up and non-linear transfer function

Engineering Contradiction:

Improvebatch fabrication capabilityVSAvoidtransducer performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the material parameter from capacitive (cMUT) to piezoelectric (pMUT). This fundamental material parameter change eliminates the charge build-up issue inherent in capacitive structures and provides a linear transfer function, enabling both batch fabrication on silicon wafers and reliable high-performance operation.

Inventive Principle:

Principle #35Parameter changes

3Ease of operation

If wire bonding is used to connect pMUT die and CMOS die, then electrical connectivity is achieved, but electromagnetic interference increases and complexity increases

Engineering Contradiction:

Improveelectrical connectivityVSAvoidelectromagnetic interference

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The patent merges the pMUT die and CMOS die into a single integrated package with direct electrical connectivity. By eliminating wire bonds and using direct bonding or flip-chip techniques, the invention reduces electromagnetic interference and simplifies the overall structure while maintaining electrical connectivity between the transducer elements and control circuits.

Inventive Principle:

Principle #5Merging (Combining)

4Power

If high drive voltage is used for conventional piezoelectric transducers, then adequate signal generation is achieved, but power consumption increases

Engineering Contradiction:

Improvesignal generation capabilityVSAvoidpower consumption

Core Design Contradiction:

PowerVSUse of energy by moving object

Solution Approach 1:

The patent changes the drive voltage parameter from high (200V) to low voltage operation. The pMUT structure with thin piezoelectric films on silicon substrates achieves adequate acoustic signal generation with much lower drive voltages, significantly reducing power consumption while maintaining imaging capability.

Inventive Principle:

Principle #35Parameter changes

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 enables low-cost, high-performance 3D imaging with reduced electromagnetic interference, allowing for efficient signal processing and image generation using lower drive voltages.

Implementation Method 1

pMUT's piezoelectric layer is used to deflect a diaphragm using much lower voltage than cMUT

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The plurality of piezoelectric elements generates a pressure wave, develop an electrical charge in response to a pressure wave received from outside

Methodology Applied

Scientific EffectPiezoelectric effect: Converse Piezoelectric Effect

Data Source

PatentUS20250268575A1Integrated ultrasonic transducers

Publication Date: 2025.08.28 EXO IMAGING INC

AI summary

Described are transducer assemblies and imaging devices comprising: a microelectromechanical systems (MEMS) die including a plurality of piezoelectric elements; a complementary metal-oxide-semiconductor (CMOS) die electrically coupled to the MEMS die by a first plurality of bumps and including at least one circuit for controlling the plurality of piezoelectric elements; and a package secured to the CMOS die by an adhesive layer and electrically connected to the CMOS die.