CMUT Insulating Film Projections Suppress Charge Accumulation
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Solution Overview
Problem
Conventional capacitive micromachined ultrasonic transducers (CMUTs) face challenges in maintaining stability and sensitivity due to electrical charge accumulation in the insulating film, which affects the membrane's vibration and reception sensitivity, especially when operating close to the collapse voltage.
Innovation Solution
The ultrasonic transducer employs a specific disposition pattern of projections on the insulating film within the hollow part, optimizing the number and position of these projections to prevent electrical charge accumulation while maintaining a sufficient overlapping area between electrodes, thereby controlling the driving voltage and enhancing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of projections is increased to prevent electrical charge accumulation, then receiving sensitivity is improved, but the overlapping area between electrodes decreases and driving voltage increases
Solution Approach 1:
The patent applies local quality by creating projections only at specific locations where electrical charge accumulation occurs, rather than uniformly across the entire insulating film. This localized approach prevents charge accumulation at critical points while preserving electrode overlapping area in other regions, thus maintaining driving voltage at acceptable levels while improving receiving sensitivity.
2Reliability
If the number of projections is increased to prevent electrical charge accumulation, then receiving sensitivity is improved, but device complexity increases
Solution Approach 1:
The patent segments the insulating film into multiple projection structures at different locations, where each projection handles charge accumulation at its specific position. This segmentation allows the system to manage electrical charge distribution effectively while keeping each individual projection simple in structure, thus improving receiving sensitivity without excessively increasing device complexity.
3Reliability
If projections are added to the insulating film, then electrical charge accumulation is prevented, but manufacturing precision requirements increase
Solution Approach 1:
By concentrating projections at specific local positions where charge accumulation occurs, the patent reduces the overall manufacturing precision requirements compared to requiring uniform projection distribution across the entire insulating film. The localized approach allows for more tolerant positioning at non-critical areas while maintaining charge stability at projection locations.
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 approach effectively suppresses the increase in driving voltage and maintains high receiving sensitivity by determining the optimal projection positions and number, ensuring stable membrane operation and improved ultrasonic wave transmission and reception.
Implementation Method 1
If a DC voltage and an AC voltage are superimposed between the upper electrode 104 and the lower electrode 101, an electrostatic force is generated between the upper electrode 104 and the lower electrode 101, and a membrane 105 constituted by the insulating film 103 and the upper electrodes 104 above the hollow part 102 vibrates at the frequency of the applied AC voltage to transmit ultrasonic waves.
Implementation Method 2
In contrast, in the case of reception, the membrane 105 is vibrated by pressure of ultrasonic waves that arrive at the surface of the membrane 105. Then, the distance between the upper electrode 104 and the lower electrode 101 changes, and therefore ultrasonic waves can be detected as change of the electrostatic capacitance.
Implementation Method 3
CMUT is usually driven at such a DC voltage that the electrostatic force between the electrodes and the spring restoring forth are balanced.
Data Source
AI summary
For disposing projections of insulating film protruding into a hollow part in CMUT in order to suppress injection of electrical charge into the insulating film due to contact of a lower surface of a membrane with a lower surface of the hollow part, there are provided a structure of disposed projections preferred for suppressing increase in driving voltage for CMUT and decrease in receiving sensitivity, and an ultrasonic diagnostic apparatus using the same. The ultrasonic transducer of the present invention comprises a first electrode, a lower insulating film formed on the first electrode, an upper insulating film provided so as to form a hollow part above the lower insulating film, and a second electrode formed on the upper insulating film, and is characterized in that the lower insulating film or the upper insulating film has projections on the side of the hollow part, and the first electrode or the second electrode has openings formed at positions corresponding to the positions at which the projections are formed.