CMUT Insulator Thickness for Sensitivity and Withstand Voltage
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Solution Overview
Problem
Conventional capacitive micromachined ultrasonic transducers (CMUTs) face challenges in maintaining receiver sensitivity and withstand voltage due to the inability to independently control the distance between electrodes in parts with and without a cavity portion, leading to increased parasitic capacitance and reduced sensitivity.
Innovation Solution
The design incorporates a structure where the sum total of insulator thickness between electrodes in parts without a cavity portion is greater than in parts with a cavity portion, allowing independent control of electrode spacing, and a manufacturing method involving sacrificial layers and insulator deposition to form the cavity portion, which enhances the thickness of insulators in non-cavity regions without affecting the cavity region spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the distance between electrodes is reduced to maintain receiver sensitivity, then the capacitance change during ultrasonic wave reception is maintained, but the parasitic capacitance increases and withstand voltage decreases
Solution Approach 1:
The patent applies different insulator thicknesses in different regions: the first insulator layer has uniform thickness across the entire electrode surface, while the second insulator layer provides additional thickness only in the non-cavity region. This local differentiation allows the cavity region to maintain small electrode spacing for sensitivity while the non-cavity region has increased spacing to reduce parasitic capacitance.
2Reliability
If the insulator thickness is increased to reduce parasitic capacitance, then the withstand voltage improves, but the distance between electrodes in cavity region increases and receiver sensitivity decreases
Solution Approach 1:
The patent uses a two-layer insulator structure where the first layer provides baseline insulation everywhere, and the second layer adds extra insulation thickness specifically in the non-cavity region. This ensures that the cavity region maintains its original small electrode spacing for high sensitivity, while the non-cavity region achieves increased spacing for reduced parasitic capacitance and improved withstand voltage.
3Reliability
If the electrode spacing is uniformly increased to reduce parasitic capacitance, then the withstand voltage improves, but the capacitance change during reception decreases and sensitivity is reduced
Solution Approach 1:
The patent implements spatially varying insulator thickness through a two-layer structure: the first insulator layer has uniform thickness across all regions, while the second insulator layer is positioned only in the non-cavity region to provide additional thickness. This allows the cavity region to maintain small electrode spacing for maximum capacitance change and sensitivity, while the non-cavity region achieves increased spacing to reduce parasitic capacitance and improve withstand voltage.
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 decrease in receiver sensitivity and improves the withstand voltage of the ultrasonic transducer by maintaining the capacitance change during ultrasonic wave reception and reducing parasitic capacitance.
Implementation Method 1
the sum total of thickness of insulators between the first electrode and the second electrode in a part not having the cavity portion is larger than sum total of thickness of insulators between the first electrode and the second electrode in a part having the cavity portion
Implementation Method 2
The ultrasonic transducer utilizing the vibration of a piezoelectric body has been used so far
Implementation Method 3
When DC voltage and AC voltage are superimposed to the upper electrode 105 and the lower electrode 101, electrostatic force acts between the upper electrode 105 and the lower electrode 101, and the upper electrode 105 and the insulator 104 on the cavity portion 103 constituting the membrane 106 vibrate at the frequency of the applied AC voltage
Implementation Method 4
Since the distance between the upper electrode 105 and the lower electrode 101 changes due to this vibration, the ultrasonic waves can be detected as the change in the electric capacitance between the electrodes
Data Source
AI summary
A technology capable of improving receiver sensitivity and improving insulation withstand voltage in an ultrasonic transducer is provided. An ultrasonic transducer comprises: a lower electrode; an insulator covering the lower electrode; a cavity portion disposed on the insulator so as to overlap with the lower electrode; and an upper electrode disposed so as to overlap with the cavity portion. In this ultrasonic transducer, an insulator is inserted between the upper and lower electrodes in a part not having the cavity portion. By this means, sum total of thickness of insulators between the upper and lower electrodes in a part not having the cavity portion is larger than sum total of thickness of insulators between the upper and lower electrodes in a part having the cavity portion.