CMUT Fabrication Based On A Thick Buried Oxide Layer.

Area of Science:

• Microelectromechanical Systems (MEMS)
• Ultrasonic Transducer Technology
• Materials Science

Background:

• Capacitive Micromachined Ultrasonic Transducers (CMUTs) are crucial for various sensing and imaging applications.
• Existing fabrication methods often involve complex processes and limited design flexibility.
• There is a need for a robust and adaptable CMUT fabrication platform.

Purpose of the Study:

• To introduce a versatile and flexible fabrication process for direct wafer-bonded CMUTs.
• To enable the creation of single element transducers, 1D and 2D arrays, and reconfigurable arrays.
• To enhance device reliability and expand the design space for CMUTs.

Main Methods:

• Utilized direct wafer bonding for CMUT fabrication.
• Employed a low number of litho masks (five for a 2D array) and standard MEMS tools.
• Integrated hot electrodes via a buried oxide layer in SOI substrates, connecting to silicon electrodes within CMUT cells.
• Used vertical insulation trenches for electrode isolation and defined array elements by etching trenches into the handle wafer.

Main Results:

• Achieved a flexible fabrication platform for diverse CMUT configurations.
• Demonstrated improved device reliability and a wide design space for operational frequency and geometric parameters.
• Ensured a continuous front face connected to ground for enhanced signal-to-noise ratio (SNR) and safety.
• Successfully isolated high electric fields to the evacuated gap region, preventing insulation layer breakdown.

Conclusions:

• The proposed fabrication process offers a versatile and efficient platform for CMUT development.
• This method facilitates the creation of advanced CMUT arrays with enhanced performance and safety features.
• The process is compatible with standard MEMS tools, reducing fabrication complexity and cost.