CMUT Membrane Structure for Higher Sound Pressure at Lower Drive Voltage
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Solution Overview
Problem
Conventional capacitive micromachined ultrasonic transducer (CMUT) elements face challenges in maximizing sound pressure while minimizing drive voltage, as the membrane's vibration amplitude is unevenly distributed, leading to inefficient use of the vibrating area and potential issues like dielectric breakdown and charging of insulating films.
Innovation Solution
The CMUT element is designed with a layered structure that includes a substrate, electrodes, insulating films, and cavity layers, where a second cavity layer or a material with low elastic modulus is used between connection portions to enhance membrane vibration, allowing for a more piston-like motion and increased effective vibration area without increasing drive voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the membrane area is increased to maximize sound pressure, then the transmission sound pressure is improved, but the drive voltage must be increased which causes dielectric breakdown and charging of insulating films
Solution Approach 1:
The patent applies local quality by creating a non-uniform membrane structure with different regions having different vibration characteristics. The center region allows larger vibration amplitude while the peripheral region has reduced amplitude, optimizing the distribution of vibration energy to maximize sound pressure without requiring proportional increase in drive voltage.
Solution Approach 2:
The patent changes the vibration amplitude parameter distribution across the membrane surface. By controlling the vibration amplitude to be maximum at the center and gradually decrease toward the periphery, the system achieves more efficient ultrasonic wave transmission with reduced drive voltage requirements compared to uniform vibration distributions.
2Stability of the object's composition
If the membrane is fixed at the periphery to support vibration, then the structural stability is improved, but the vibration area is reduced as the fixed portion does not contribute to sound wave transfer
Solution Approach 1:
The patent implements local quality by differentiating the functional characteristics of different membrane regions. The peripheral region serves primarily for structural support with minimal vibration contribution, while the central region provides the main vibration and sound wave generation function. This spatial differentiation of functions optimizes both structural stability and effective vibration area.
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 suppresses bending of the membrane, reduces the need for higher drive voltages, and increases the transmission sound pressure by expanding the vibration area, thereby improving the efficiency of ultrasonic wave transmission.
Implementation Method 1
When a DC voltage and an AC voltage are superimposed between the upper electrode 104 and the lower electrode 101, an electrostatic force works between the upper electrode 104 and the lower electrode 101, the membrane 105 vibrates by a frequency of the applied AC voltage, and the ultrasonic waves are generated.
Implementation Method 2
the membrane 105 vibrates by a pressure of the ultrasonic wave reached the surface of the membrane 105. Then, since a distance between the upper electrode 104 and the lower electrode 101 changes, an electrostatic capacitance changes, and the ultrasonic wave can be detected.
Implementation Method 3
the vibration amplitude is generated by a bending caused by an elastic deformation of the membrane.
Data Source
AI summary
An ultrasonic transducer element includes a substrate, a lower electrode on a first surface of the substrate, a first insulating film on the lower electrode, a first cavity layer on the first insulating film, a second insulating film on the first cavity layer, an upper electrode on the second insulating film that overlaps the first cavity layer, a third insulating film on the upper electrode, a second cavity layer on the third insulating film, a fourth insulating film on the second cavity layer, a fixing portion formed by the second to fourth insulating films, a movable portion in a membrane insides the second cavity layer, a first connection portion and a second connection portion that are stacked with a gap and the connection portions are configured by the second to fourth insulating films connecting the movable portion and the fixing portion.