Multi-Material PMUT Structure for Transmit and Receive Sensitivity

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Solution Overview

Problem

Traditional piezoelectric micromachined ultrasound transducers (PMUTs) are limited in sensitivity due to the inability to optimize piezoelectric material constants for both transmitter and receiver modes, leading to reduced performance in ultrasonic systems used in medical imaging, ranging, non-destructive testing, and gesture recognition.

Innovation Solution

The use of multiple piezoelectric materials with distinct properties for each mode of operation, such as aluminum nitride (AlN) for receiver sensitivity and lead zirconate titanate (PZT) for transmitter output, allows for optimized performance as both a transmitter and receiver.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single piezoelectric material is used in PMUTs, then the device structure is simple and manufacturing is easier, but the sensitivity is reduced because material constants cannot be optimized for both transmitter and receiver modes

Engineering Contradiction:

Improvetransducer sensitivityVSAvoiddevice structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The piezoelectric layer is segmented into multiple distinct piezoelectric materials (e.g., PZT and AlN) with different material constants. Each material is assigned to specific regions or layers to optimize performance for different operating modes - transmit or receive - thereby resolving the contradiction between sensitivity and structural simplicity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite piezoelectric structures combining multiple piezoelectric materials with complementary properties. This composite approach enables simultaneous optimization of transmit sensitivity (using materials with high piezoelectric coefficients) and receive sensitivity (using materials with appropriate dielectric constants and mechanical properties) while maintaining a unified device structure

Inventive Principle:

Principle #40Composite materials

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 approach significantly enhances the transmit and receive sensitivity of PMUTs, improving overall system performance by leveraging the unique properties of different materials for each operational mode.

Implementation Method 1

A voltage is applied across the electrodes, which induces a transverse stress in the piezoelectric layer via the inverse piezoelectric effect, resulting in an out-of-plane deflection which transmits an ultrasonic pressure wave

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

when the PMUT is used as a receiver, the applied pressure results in out-of-plane bending and the generation of measureable charge via the direct piezoelectric effect

Methodology Applied

Scientific EffectDirect piezoelectric effect: Piezoelectric Effect

Data Source

PatentUS11711067B2Micromachined ultrasound transducer using multiple piezoelectric materials

Publication Date: 2023.07.25 INVENSENSE INC

AI summary

A transducer includes first and second piezoelectric layers made of corresponding different first and second piezoelectric materials and three or more electrodes, implemented in two or more conductive electrode layers. The first piezoelectric layer is sandwiched between a first pair of electrodes and the second piezoelectric layer is sandwiched between a second pair of electrodes. The first and second pairs of electrodes contain no more than one electrode that is common to both pairs.