PMUT Acoustic Reflection Minimization via Substrate Cavity
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Solution Overview
Problem
Conventional piezoelectric ultrasonic transducers face limitations in achieving high-frequency membrane oscillations due to constraints on membrane thickness and radius, which affect displacement and acoustic diffraction, and struggle with spurious reflections and low fill-factor issues.
Innovation Solution
The development of a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) with a substrate and edge support structure, featuring a membrane with a piezoelectric layer and electrodes, and an interior support structure that allows for high-frequency operation, reduced acoustic diffraction, and high fill-factor design to enhance signal transmission and rejection of spurious reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If membrane thickness and radius are constrained to achieve high-frequency oscillations, then frequency is improved, but displacement and acoustic diffraction performance deteriorate
Solution Approach 1:
The patent introduces a vertical cavity dimension beneath the membrane, transforming the problem from a two-dimensional membrane constraint to a three-dimensional acoustic resonance system. The cavity depth is designed to be approximately one-quarter of the ultrasonic wavelength, creating a resonant standing wave pattern that amplifies acoustic output without requiring larger membrane displacement.
Solution Approach 2:
The patent changes the operational parameters by designing the cavity depth to match specific fractions of the ultrasonic wavelength (particularly one-quarter wavelength). This parameter optimization allows the system to operate at resonant frequencies where acoustic energy is maximized, resolving the contradiction between high frequency operation and adequate acoustic output.
2Ease of manufacture
If conventional transducer design is used, then manufacturing is simplified, but spurious reflections and low fill-factor issues occur
Solution Approach 1:
The patent extracts the acoustic resonance function from the membrane itself and places it in a separate cavity structure beneath the membrane. This separation allows the membrane to be optimized for electrical-to-mechanical conversion while the cavity handles acoustic wave management, eliminating spurious reflections that would otherwise occur from the membrane structure itself.
Solution Approach 2:
The cavity acts as an intermediary acoustic chamber between the membrane and the external environment. This intermediate structure manages the acoustic wave propagation, allowing controlled release of ultrasonic energy while preventing unwanted reflections from returning to the membrane, thus reducing spurious signals.
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 PMUT device achieves efficient ultrasonic signal generation and sensing with reduced acoustic diffraction and spurious reflections, enabling better signal quality and higher fill-factor performance for applications like fingerprint sensing and mobile communication systems.
Implementation Method 1
a membrane with a piezoelectric layer and first and second electrodes coupled to opposing sides of the piezoelectric layer
Implementation Method 2
the membrane is configured to vibrate at ultrasonic frequencies
Implementation Method 3
Piezoelectric materials facilitate conversion between mechanical energy and electrical energy. Moreover, a piezoelectric material can generate an electrical signal when subjected to mechanical stress
Data Source
AI summary
An electronic device includes a substrate layer having a front surface and a back surface opposite the front surface, a plurality of ultrasonic transducers formed on the front surface of the substrate layer, wherein the plurality of ultrasonic transducers generate backward waves during operation, the backward waves propagating through the substrate layer, and a plurality of substrate structures formed within the back surface of the substrate layer, the plurality of substrate structures configured to modify the backward waves during the operation.