CMUT Membranes with Multilayered Electrodes for Ultrasonic Transducers
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Solution Overview
Problem
Existing ultrasonic transducers face challenges in optimizing independent emission and reception functions, with piezoelectric transducers being temperature-sensitive and unsuitable for mass production, and capacitive transducers lacking in solid interface performance.
Innovation Solution
The development of capacitive micromachined ultrasonic transducers (CMUTs) with multilayered electrodes embedded within the membrane thickness, allowing for separate transmission and reception functions, optimized by using highly doped silicon substrates and microfabrication techniques to enhance energy conversion and prevent membrane collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If piezoelectric materials are used for ultrasonic transducers, then high energy conversion factors are achieved, but temperature sensitivity and aging issues occur
Solution Approach 1:
The patent changes the fundamental operating principle from piezoelectric to electrostatic, altering the physical parameter basis of the transducer. This parameter change eliminates temperature sensitivity while maintaining high energy conversion factors through electrostatic force generation in the capacitive membrane structure
Solution Approach 2:
The patent replaces the piezoelectric mechanical system with an electrostatic field-based system. By substituting the piezoelectric effect with electrostatic force generation between biased electrodes, the system achieves similar mechanical displacement for ultrasonic wave generation without the temperature sensitivity inherent in piezoelectric materials
2Ease of manufacture
If capacitive membranes are used for ultrasonic transducers, then suitability for mass production is improved, but performance with solid interfaces deteriorates
Solution Approach 1:
The patent employs composite material structures including silicon nitride membranes combined with metal electrodes (aluminum, gold, or tungsten) and silicon dioxide layers. This composite construction maintains the ease of microfabrication while enhancing solid interface performance through optimized material properties and interfacial characteristics
Solution Approach 2:
The patent transitions from two-dimensional planar capacitive structures to three-dimensional multilayered configurations with electrodes positioned above and below the membrane. This dimensional enhancement improves solid interface coupling by providing multiple contact surfaces and enhancing mechanical impedance matching
3Device complexity
If single-layer membranes are used, then device complexity is reduced, but independent control of emission and reception functions is lost
Solution Approach 1:
The patent segments the electrode system into multiple independent layers (first electrode above the membrane, second electrode below the membrane). This segmentation allows independent control of emission and reception functions by applying different voltages to different electrode layers, enabling bidirectional operation with optimized performance for each function
Solution Approach 2:
The patent adds the vertical dimension by positioning electrodes above and below the membrane, creating a multilayered structure. This three-dimensional electrode arrangement enables independent control of transmission and reception by applying voltages to different layers, providing functional versatility while maintaining fabrication simplicity
4Measurement precision
If membrane thickness is reduced to improve sensitivity, then reception sensitivity is improved, but membrane collapse risk increases
Solution Approach 1:
The patent uses composite material structures with silicon nitride membranes combined with supportive layers of silicon dioxide and metal electrodes. This composite construction provides the thin membrane needed for high sensitivity while the supporting layers prevent collapse by providing mechanical strength and structural stability
Solution Approach 2:
The patent introduces intermediary support layers (silicon dioxide and metal electrodes) between the thin membrane and the substrate. These intermediary layers act as mechanical supports that prevent membrane collapse while allowing the thin membrane to maintain its high sensitivity for ultrasonic wave detection
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 CMUTs achieve independent control of emission and reception functions, improving energy conversion efficiency and sensitivity, while minimizing membrane collapse and temperature sensitivity, enabling effective ultrasonic energy transmission and reception across various frequencies.
Implementation Method 1
use an electrostatic force for moving capacitive membranes. The basic principle is quite simple and has been successfully implemented in condenser microphones having passive components. For capacitive transducers, the operation is governed by a voltage oscillation over its electrostatic field. This oscillation causes the membrane to vibrate, therefore producing the emission of ultrasonic waves.
Implementation Method 2
the reception of a pressure force at the surface of biased membranes will cause deformation of the surface thereby resulting in oscillation of the output voltage
Data Source
AI summary
A micro-machined ultrasonic transducer substrate for immersion operation is formed by a particular arrangement of a plurality of micro-machined membranes that are supported on a silicon substrate. The membranes, together with the substrate, form surface microcavities that are vacuum sealed to provide electrostatic cells. The cells can operate at high frequency and can cover a broader bandwidth in comparison with conventional piezoelectric bulk transducers.