Subsequent projects | Special projects

Start of funding 01.01.2010

Integrated broadband transduction of high Q nanoelectromechanical resonators

Prof. Dr. Eva Weig
Ludwig-Maximilians-University of Munich

Prof. Andrew Cleland
University of California, Santa Barbara
Department of Physics


Nanomechanical systems are promising candidates for electrical filtering and sensing applications. A critical requirement is high-fidelity motion transduction that permits broadband operation while preserving low dissipation (high Q) . This project focuses on developing a hybrid nanomechanical resonator, integrating a doubly clamped flexural resonator with a thin-film piezoelectric, allowing precise and sensitive local actuation and displacement detection. To this end we will combine high Q nanoresonators fabricated from high stress silicon nitride investigated in the Weig group with piezoelectric thin film bulk acoustic resonators (FBAR) developed by the Cleland group which permit displacement sensing approaching the quantum limit. The research effort will combine realistic numerical simulations of hybrid resonator designs with physical realizations of prototype nanoresonators for the ultrasensitive transduction of nanoelectromechanical vibrations in the ultra high frequency range.

Final report:
Nanoelectromechanical systems (NEMS) are promising candidates for electrical filtering, sensing, and transduction applications. The performance of these systems can be significantly enhanced by developing integrated and broadband methods for detecting the mechanical response of NEMS, especially methods that preserve the intrinsic high quality factor of the mechanical modes. We have explored a hybrid approach for reading out the motional displacement of a resonator fabricated from a thin-film piezoelectric, which supports both optical detection and electrical control. To this end, we have characterized the mechanical mode spectrum of a piezoelectric bulk acoustic resonator (FBAR), fabricated from a heterostructure including aluminium metal electrodes and aluminium nitride as the piezoelectric component. The mechanical response has been measured over a very broad range of frequencies, spanning the low frequency flexural modes in the kHz regime to ultra-high frequency bulk acoustic modes in the GHz range. We in part focussed the investigations on the low frequency flexural modes of the FBAR device, on which very little research has been done, in which we excited the flexural motion of the structure through the AlN piezoelectric response, and detected the motion optically using a highly sensitive, very broadband laser interferometry setup. Under vacuum conditions and at room temperature, 20 different mechanical modes with quality factors ranging between 400 and 1000 have been observed in the frequency range from 200 kHz to 45 MHz. The displacement sensitivity in the instrument was sufficient to resolve the Brownian motion of the fundamental flexural mode, allowing both passive and active measurement of this mechanical response. Mounting the sample on a nanopositioning stage allowed us to map out the spatial mode profiles of the observed modes, which we found agreed well with numerical displacement profiles obtained by finite element simulations. Future work will focus on performing the same type of measurements at much higher frequencies, and also performing measurements in which the piezoelectric response is used to detect the mechanical motion directly, over the same range of frequencies.