Patterned Protective Film for CMUT Vibration Sensitivity
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Solution Overview
Problem
The protective film on capacitive micromachined ultrasonic transducers adds excessive mass, leading to decreased sensitivity and increased risk of destruction during mounting due to lack of cushioning, particularly for low-frequency transducers.
Innovation Solution
A protective film is divided into patterns with gaps to provide cushioning and prevent direct contact with foreign matter, optimizing thickness and spacing to reduce the risk of destruction and maintain sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective film is formed over the entire surface of the capacitive micromachined ultrasonic transducer, then the insulation properties are ensured and foreign matter adhesion is prevented, but excessive mass is added to the vibration film causing sensitivity decrease
Solution Approach 1:
The protective film is divided into multiple patterns (such as grid patterns, circular patterns, or rectangular patterns) with gaps between them. This segmentation allows the protective film to provide insulation and foreign matter protection while reducing the total mass covering the vibration film, thereby maintaining sensitivity.
Solution Approach 2:
The protective film is applied selectively in specific regions rather than uniformly across the entire surface. The patterned structure provides different properties in different areas: regions with protective film provide insulation and protection, while gap regions minimize mass addition and allow vibration film performance.
2Weight of moving object
If the protective film is limited to only the vicinity of electrodes and wirings, then sensitivity is maintained, but foreign matter can directly contact and destroy the vibration film during mounting
Solution Approach 1:
The protective film is segmented into patterns that extend beyond just the electrode and wiring regions. This segmentation provides coverage over the vibration film area to prevent foreign matter adhesion while the gaps between patterns minimize the total mass added, thus protecting against destruction during mounting while maintaining sensitivity.
Solution Approach 2:
The patterned protective film provides a cushioning effect before foreign matter can directly contact the vibration film during the mounting process. The film acts as a protective barrier that absorbs or distributes impact forces, preventing direct destruction of the vibration film while the patterned structure minimizes mass addition.
3Reliability
If a continuous protective film is used, then complete coverage and protection are provided, but the cushioning effect is insufficient for thin vibration films in low-frequency transducers
Solution Approach 1:
The protective film is divided into patterns with gaps, which creates a distributed cushioning structure. Each patterned region provides localized protection and cushioning, while the gaps allow the vibration film to maintain its mechanical properties. This segmented approach provides better cushioning distribution compared to a continuous film, especially for thin vibration films in low-frequency transducers.
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 design suppresses manufacturing yield decreases without compromising sensitivity, especially for low-frequency transducers, by providing effective cushioning against foreign matter and reducing the risk of vibration film destruction.
Implementation Method 1
the protective film is divided into a plurality of patterns arranged with a gap having a predetermined spacing formed therebetween... provide cushioning and prevent direct contact with foreign matter
Implementation Method 2
By applying a voltage between the lower electrode and the upper electrode and generating a potential difference, an electrostatic force is generated in the vibration film above the cavity
Implementation Method 3
When transmitting an ultrasonic wave, the electrostatic force applied to the vibration film is temporally varied by applying an AC voltage superimposed on a DC bias voltage, thereby vibrating the vibration film
Implementation Method 4
when receiving an ultrasonic wave, displacement of the vibration film is detected as a capacitance change between the upper and lower electrodes
Data Source
AI summary
A capacitive micromachined ultrasonic transducer 111A includes: a silicon substrate 101; an insulating film 102 formed over the silicon substrate 101; a lower electrode 103; insulating films 104 and 106; a cavity 105 constituted by a void formed in a portion of the insulating film 106; an upper electrode 107; insulating films 108 and 114; and a protective film 109. In addition, the insulating film 106, upper electrode 107, insulating film 108 and insulating film 114 above the cavity 105 configure a vibration film 110, and the protective film 109 above the vibration film 110 is divided into a plurality of isolated patterns regularly arranged with a gap 115 having a constant spacing formed therebetween.