Post-CMOS-Compatible Aluminum Nitride Resonant MEMS Accelerometers

• Published in: Journal of microelectromechanical systems Vol. 18; no. 3; pp. 671 - 678
• Main Authors: Olsson, Roy H., Wojciechowski, Kenneth E., Baker, Michael S., Tuck, Melanie R., Fleming, James G.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.06.2009; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acceleration; Acceleration measurement; Accelerometers; acoustic devices; acoustic oscillators; acoustic resonators; acoustic transducers; Aluminum nitride; Applied sciences; Bandwidth; beams; Carriers; Exact sciences and technology; Foundries; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Microelectromechanical systems; Micromechanical devices; Micromechanical devices and systems; Noise; Oscillators; Phase noise; Physics; Piezoelectricity; Precision engineering, watch making; Proving; Resonance; Resonators; RLC circuits; Accelerometers; Acceleration sensor; Acoustic transducers; acoustic oscillators; Measurement sensor; Aluminium nitride; acoustic resonators; 1/f noise; Oscillators; acoustic devices; Tuning fork; Acceleration measurement; beams; Thick film devices; Upper bound; Added mass; Quality factor; Complementary MOS technology; Resonance frequency; Piezoelectricity; Foundries; Piezoelectric resonator; Microelectromechanical device
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2009.2020374

This paper describes the development of aluminum nitride (AlN) resonant accelerometers that can be integrated directly over foundry CMOS circuitry. Acceleration is measured by a change in resonant frequency of AlN double-ended tuning-fork (DETF) resonators. The DETF resonators and an attached proof mass are composed of a 1-mum-thick piezoelectric AlN layer. Utilizing piezoelectric coupling for the resonator drive and sense, DETFs at 890 kHz have been realized with quality factors ( Q ) of 5090 and a maximum power handling of 1 muW. The linear drive of the piezoelectric coupling reduces upconversion of 1/ f amplifier noise into 1/ f 3 phase noise close to the oscillator carrier. This results in lower oscillator phase noise, -96 dBc/Hz at 100-Hz offset from the carrier, and improved sensor resolution when the DETF resonators are oscillated by the readout electronics. Attached to a 110-ng proof mass, the accelerometer microsystem has a measured sensitivity of 3.4 Hz/G and a resolution of 0.9 mG/radicHz from 10 to 200 Hz, where the accelerometer bandwidth is limited by the measurement setup. Theoretical calculations predict an upper limit on the accelerometer bandwidth of 1.4 kHz.