CMUT Ring Electrode Parasitic Capacitance Reduction
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Solution Overview
Problem
Ultrasound devices face reduced sensitivity due to parasitic capacitance caused by membrane contact with sensing electrodes, leading to ineffective ultrasonic signal production and noise interference.
Innovation Solution
Designing ultrasound devices with a ring-shaped sensing electrode lacking a central portion to minimize parasitic capacitance, combined with trench isolation for bond pads and a redistribution layer for noise reduction, enhancing signal-to-noise ratio and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complete sensing electrode is used, then electrical coverage is maximized, but parasitic capacitance increases reducing sensitivity
Solution Approach 1:
The patent removes the central portion of the sensing electrode to eliminate the source of parasitic capacitance that causes membrane contact. This extraction of the problematic central region reduces unwanted electrical coupling while preserving the functional outer regions of the electrode for ultrasonic signal detection.
Solution Approach 2:
The sensing electrode is segmented into an outer functional region and a removed central region. This segmentation allows the electrode to maintain electrical coverage at its periphery for effective signal detection while eliminating the central area that generates parasitic capacitance and causes membrane contact issues.
2Reliability
If bond pads are directly connected to the membrane, then electrical connection is achieved, but electrical isolation is compromised
Solution Approach 1:
A trench structure is introduced as an intermediary element between the bond pad and the membrane. This trench provides electrical isolation by creating a physical barrier that prevents unwanted electrical coupling, while still allowing the bond pad to maintain its functional connection to the membrane through controlled pathways.
3Measurement precision
If standard electrode design is used, then manufacturing is simplified, but signal-to-noise ratio deteriorates
Solution Approach 1:
The electrode geometry is modified by changing its parameter configuration - specifically creating a ring shape with a removed central portion. This parameter change optimizes the signal-to-noise ratio by reducing parasitic capacitance effects while maintaining manufacturability through standard fabrication processes adapted for annular structures.
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
The solution increases the sensitivity and signal-to-noise ratio of ultrasonic signals, improving image formation capabilities without affecting ultrasonic signal production.
Implementation Method 1
an ultrasonic transducer disposed on a complementary metal-oxide-semiconductor (CMOS) substrate
Implementation Method 2
having an electrode wherein a central portion of the electrode is absent
Implementation Method 3
sound waves are reflected off the tissue with different tissues reflecting varying degrees of sound. These reflected sound waves may then be recorded and displayed as an ultrasound image
Data Source
AI summary
An ultrasound device is described. The ultrasound device may include a cavity, a membrane, and a sensing electrode. When an electrical signal is applied to the sensing electrode and a static bias is applied to the membrane, the membrane vibrates within the cavity and produces ultrasonic signals. The cavity, the membrane, and the sensing electrode may be considered a capacitive micromachined ultrasonic transducer (CMUT). The sensing electrode may be shaped as a ring, whereby the central portion of the sensing electrode is removed. Removal of the central portion of the sensing electrode may reduce the parasitic capacitance without substantially affecting the production of ultrasonic signals by the CMUT. This, in turn, can result in an increase in the signal-to-noise ratio (SNR) of the ultrasonic signals. The ultrasound device may further include a bond pad configured for wire bonding, and a trench electrically isolating the bond pad from the membrane.