Fabrication and characterization of a high frequency and high coupling coefficient CMUT array

• Published in: Microsystem technologies : sensors, actuators, systems integration actuators, systems integration, 2017-10, Vol.23 (10), p.4965-4977
• Main Authors: Manwar, R., Simpson, T., Bakhtazad, A., Chowdhury, S.
• Format: Article
• Language: English
• Subjects: Electronics and Microelectronics; Engineering; Instrumentation; Mechanical Engineering; Nanotechnology; Technical Paper
• ISSN: 0946-7076; 1432-1858
• DOI: 10.1007/s00542-016-3225-4

Fabrication and initial measurement results of a bisbenzocyclobutene (BCB) based capacitive micromachined ultrasonic transducer (CMUT) linear phased array has been presented. The 32 channel 40 MHz CMUT array has been fabricated using a BCB based adhesive wafer bonding technique where BCB has been used as the diaphragm structural material, the bottom insulation layer, and also as the interelectrode insulator. The array has an aperture size of 0.62 mm. Each element consists of 264 square shaped cells. Each CMUT cell was designed to have a diaphragm sidelength of 10 μm with a cavity thickness of 0.75 μm. A low resistivity (0.01 Ω-cm) silicon wafer has been used as the bottom electrode. Series resonance of the array elements has been measured as 48 MHz which is within 20% agreement with the 3D FEA values simulated using IntelliSuite™, a MEMS design tool. Electromechanical coupling coefficient has been extracted to be 0.66 from the electrical input impedance measurement using an Agilent vector network analyzer with 20 V bias voltage. The measured static capacitance of individual cell is in excellent agreement with the 3-D FEA model with a deviation of 1.27%. The fabricated array can be used for anterior segment ophthalmic imaging, cardiovascular imaging, dermatology, small animal imaging, and biometric authentication. The technique can be used to fabricate high performance CMUT arrays for other applications.