CMUT Electrode Extraction for Charge Injection Prevention
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Solution Overview
Problem
Ultrasonic transducers face challenges in maintaining reliability and sensitivity due to charge injection issues and increased driving voltage when using capacitive micromachined ultrasonic transducers (CMUTs) with projections jutting out to hollow portions, as existing solutions either reduce electric field strength or increase driving voltage, degrading receiving sensitivity.
Innovation Solution
The ultrasonic transducer design includes a lower electrode, a hollow portion enclosed with an insulating film, an upper electrode, and plural projections of the insulating film, with rigid members disposed over the hollow portion to increase the membrane's rigidness and maintain a voltage margin, preventing charge injection and enhancing transmission sound pressure and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If projections of insulating film are formed in hollow portion and electrodes are layered over them, then charge injection into insulating film is prevented, but driving voltage increases and receiving sensitivity degrades
Solution Approach 1:
The patent extracts the upper electrode from the projections area, creating a through-hole in the upper electrode that exposes the projection. This removes the harmful layering configuration while maintaining the protective function of the projection against charge injection
Solution Approach 2:
The patent introduces an insulating film filling the through-hole of the upper electrode, which acts as an intermediary between the upper electrode and the projection. This maintains electrical insulation while allowing the projection to function without direct electrode layering
2Reliability
If portions of electrode are pierced to avoid charge injection, then charge injection is suppressed, but area of layered portions diminishes and receiving sensitivity degrades
Solution Approach 1:
The patent applies local quality by creating a through-hole only in the specific region where the projection is located, while maintaining the continuous layered structure of electrodes in other regions. This localized modification prevents charge injection at the projection site without reducing the overall electrode area
Solution Approach 2:
The insulating film filling the through-hole serves as an intermediary that maintains electrical insulation properties while allowing the projection to be exposed, thus preventing charge injection without compromising the electrode's functional area
3Measurement precision
If rigid members are introduced to adjust membrane rigidness, then center frequency and bandwidth are controlled, but driving voltage rises
Solution Approach 1:
The patent applies local quality by forming projections only in specific locations within the hollow portion, rather than uniformly increasing rigidness across the entire membrane. This localized approach controls frequency characteristics without requiring high driving voltage
Solution Approach 2:
Instead of adding rigid members to increase membrane rigidness, the patent inverts the approach by creating projections of insulating film that locally modify the electric field distribution, achieving frequency control through field manipulation rather than mechanical rigidness increase
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 achieves high transmission sound pressure and receiving sensitivity while improving the reliability of the ultrasonic transducer by minimizing charge injection and maintaining a voltage margin, thus preventing membrane contact with the hollow portion bottom.
Implementation Method 1
a voltage margin between the instant projection undersurfaces come into contact with a hollow portion bottom and the instant a membrane undersurface comes into contact with the hollow portion bottom is preserved, charge injection into a membrane insulating film is suppressed
Implementation Method 2
Ultrasonic transducers that transmit or receive an ultrasonic wave are employed in diagnosis of a tumor or the like in a human body
Implementation Method 3
Ultrasonic transducers that utilize vibrations of a piezoelectric entity have been used in the past
Data Source
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Figure 5~6
AI summary
High transfer sound pressure and high reception sensitivity are realized, and reliability is improved in terms of long term operation, in a capacitive detector-type ultrasonic transducer (CMUT). The ultrasonic transducer, which has a lower electrode (201), a hollow portion (202) that is formed on the lower electrode and surrounded by insulating films (209,208), an upper electrode (205) that is formed on the hollow portion, and a plurality of insulating film projections (204) that are formed in the hollow portion (202), comprises a plurality of rigid members (203) that are formed on the hollow portion, either the lower electrode (201) and/or the upper electrode (205) is disposed in a position that does not overlap with the insulating film projections (204) when viewed from the upper surface by carving out the portion that overlaps with the insulating film projections (204), and the respective rigid members (203) are disposed such that a region is present that overlaps with the insulating film projections (204) when viewed from the upper surface.