Ultrasound Endoscope cMUT Parasitic Capacitance Reduction
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Solution Overview
Problem
Conventional ultrasound endoscopes with capacitive micro-machined ultrasonic transducers (cMUTs) face reduced sensitivity due to parasitic capacitance, which decreases the capacity change rate during ultrasound reception, limiting the effectiveness of echo signal conversion.
Innovation Solution
The ultrasound unit incorporates a semiconductor-based ultrasound element with a diffusion layer forming a third capacitor with a depletion layer as a gap, serially connected to a second capacitor formed by an insulation member, enhancing the capacity change rate by reducing parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional cMUT ultrasound elements are used, then the basic ultrasound transmission and reception function is achieved, but parasitic capacitance reduces the capacity change rate and limits receiving sensitivity
Solution Approach 1:
The patent segments the capacitance structure into multiple distinct capacitors: a first capacitor formed by the upper and lower electrodes for ultrasound transmission/reception, a second capacitor formed by the insulation member and package member, and a third capacitor formed by the diffusion layer and substrate. This segmentation allows each capacitor to serve a specific function, with the third capacitor's small capacity specifically counteracting parasitic capacitance effects.
Solution Approach 2:
The patent changes the electrical parameters by introducing a third capacitor with a specifically controlled small capacity value. This parameter change modifies the total capacitance characteristics of the ultrasound element, reducing the impact of parasitic capacitance and improving the capacity change rate during ultrasound reception.
2Reliability
If the capacity change rate is increased by reducing parasitic capacitance, then receiving sensitivity is improved, but the device structure becomes more complex with additional capacitors
Solution Approach 1:
The patent merges the formation of multiple capacitors into the standard cMUT manufacturing process. The first, second, and third capacitors are formed using the same fabrication steps involving electrode deposition, insulation layer formation, and diffusion layer creation. This integration approach increases receiving sensitivity while avoiding significant increases in device complexity.
Solution Approach 2:
The patent creates a multi-functional capacitor system where the same structural elements serve multiple purposes: the upper and lower electrodes form the first capacitor for ultrasound function, the insulation member forms the second capacitor for parasitic reduction, and the diffusion layer forms the third capacitor for additional parasitic compensation. This multi-functionality improves reliability without proportionally increasing complexity.
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 increases the capacity change rate during ultrasound reception, thereby improving the receiving sensitivity of the ultrasound unit, allowing for more accurate echo signal conversion and enhanced diagnostic imaging.
Implementation Method 1
upon application of a voltage between the electrodes, the upper electrode is pulled to the lower electrode by an electrostatic force
Implementation Method 2
the upper electrode and the lower electrode being arranged facing each other via a cavity and thereby forming a first capacitor
Implementation Method 3
the membrane is deformed by received ultrasound energy, whereby a distance between the upper electrode and the lower electrode changes
Implementation Method 4
Using a change of a capacity C1 of a capacitor formed by the upper electrode and the lower electrode by ΔC, the received ultrasound energy is converted to an electric signal
Implementation Method 5
a diffusion layer having a polarity that is different from that of a parent material of the silicon substrate and having a resistance that is lower than that of the parent material is formed on the surface of the silicon substrate... a third capacitor (73) in which the depletion layer (19) serves as a gap is formed
Implementation Method 6
a capacity of a third capacitor serially connected to the second capacitor is smaller than a capacity of the second capacitor
Data Source
AI summary
An ultrasound unit includes: ultrasound elements each including a plurality of ultrasound cells formed on a substrate including a semiconductor, the plurality of ultrasound cells each including an upper electrode having a ground potential and a lower electrode to which a drive signal is applied, the upper electrode and the lower electrode being arranged facing each other via a cavity and thereby forming a first capacitor; a package member in which the plurality of ultrasound elements are disposed, the package member having a ground potential; and an insulation member disposed between the package member and each of the ultrasound elements. A second capacitor is formed as a result of the insulation member serving as a gap, and a capacity of a third capacitor serially connected to the second capacitor is smaller than a capacity of the second capacitor.