Design and characterization of an air-coupled capacitive ultrasonic sensor fabricated in a CMOS process

This work presents a CMOS micromachined capacitive sensor for the detection of acoustic pressure transmitted through the air. The microstructure has a suspended plate of 65 µm in diameter that produces a sensing capacitance of 35 fF and a resonant frequency of 1.2 MHz. The post-CMOS fabrication can effectively reduce the parasitic capacitance to enhance the signal-to-noise ratio. The measured input-referred circuit noise is 0.35 µV Hz1/2 at 40 kHz. The measured sensor output is 3.5 µV under a dc bias of 10 V, equivalent to a capacitance change of 1.7 × 10−2 aF. The corresponding electrode displacement and acoustic pressure are 4.1 × 10−2 A and 1.3 Pa, respectively.

[1]  D.A. Hutchins,et al.  Micromachined ultrasonic capacitance transducers for immersion applications , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[2]  O. Oralkan,et al.  Forward-viewing CMUT arrays for medical imaging , 2004, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[3]  D. Greve,et al.  Electrical characterization of coupled and uncoupled MEMS ultrasonic transducers , 2003, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[4]  D A Hutchins,et al.  The characterization of capacitive micromachined ultrasonic transducers in air. , 2002, Ultrasonics.

[5]  B. Khuri-Yakub,et al.  Characterization of one-dimensional capacitive micromachined ultrasonic immersion transducer arrays , 2001, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[6]  K. Niederer,et al.  Micromachined ultrasound transducers with improved coupling factors from a CMOS compatible process , 2000, Ultrasonics.

[7]  S. Mir,et al.  A CMOS Compatible Ultrasonic Transducer Fabricated With Deep Reactive Ion Etching , 2006, Journal of Microelectromechanical Systems.

[8]  Christofer Hierold,et al.  Surface micromachined ultrasound transducers in CMOS technology , 1996, 1996 IEEE Ultrasonics Symposium. Proceedings.

[9]  S.T. Hansen,et al.  Air-coupled nondestructive evaluation using micromachined ultrasonic transducers , 1999, 1999 IEEE Ultrasonics Symposium. Proceedings. International Symposium (Cat. No.99CH37027).

[10]  Oliver Brand,et al.  Ultrasound-transducer using membrane resonators realized with bipolar IC technology , 1994, Proceedings IEEE Micro Electro Mechanical Systems An Investigation of Micro Structures, Sensors, Actuators, Machines and Robotic Systems.

[11]  O. Oralkan,et al.  3-D ultrasound imaging using a forward-looking CMUT ring array for intravascular/intracardiac applications , 2006, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[12]  Butrus T. Khuri-Yakub,et al.  Fabrication and characterization of surface micromachined capacitive ultrasonic immersion transducers , 1999 .

[13]  G.K. Fedder,et al.  A low-noise low-offset capacitive sensing amplifier for a 50-/spl mu/g//spl radic/Hz monolithic CMOS MEMS accelerometer , 2004, IEEE Journal of Solid-State Circuits.

[14]  S. Sherman,et al.  Single-chip surface micromachined integrated gyroscope with 50°/h Allan deviation , 2002, IEEE J. Solid State Circuits.

[15]  B. Khuri-Yakub,et al.  Surface micromachined capacitive ultrasonic transducers , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[16]  B. Khuri-Yakub,et al.  Defect imaging by micromachined ultrasonic air transducers , 1998, 1998 IEEE Ultrasonics Symposium. Proceedings (Cat. No. 98CH36102).

[17]  G. Fedder,et al.  A Low-Noise Low-Offset Capacitive Sensing Amplifier for a 50-g = Hz Monolithic CMOS MEMS Accelerometer , 2004 .

[18]  Qiuting Huang,et al.  A CMOS ultrasound range finder microsystem , 2000, 2000 IEEE International Solid-State Circuits Conference. Digest of Technical Papers (Cat. No.00CH37056).