Gallium Nitride Nanowire Electromechanical Resonators
PIs: Charles Rogers, Victor M. Bright
Students: Josh Montague
Project field/specialty: NEMS, nanowires, resonators
Project Description:
One of the early high-impact results at iMINT was the discovery of extraordinarily low energy dissipation in gallium nitride nanowire (GaN NW) mechanical resonators [1]. Typical quality (Q) factors (defined as the ratio of resonant frequency to resonance full width at half maximum amplitude) are on the order of 104-105, an order of magnitude larger than comparably sized, stress-free structures of other material. Figure 1 shows an electron micrograph of a vibrating nanowire.
To further our understanding of the nanowire resonance behavior, we investigated their response to atomically-thin added layers of varying material [2]. From this work, we discovered that the resonance frequencies of GaN NWs can be tuned relatively easily, but at the expense of increased dissipation.
The most current research has involved investigating a contact-free measurement technique using a microwave homodyne reflectometer to detect NW motion [3]. This technique should allow us to explore how varying external parameters affects GaN NW resonance behavior.
[1] S.M. Tanner, J.M. Gray, C.T. Rogers, K.A. Bertness, and N.A. Sanford, Appl. Phys. Lett. 91, 203117, (2007).
[2] J. Montague, M. Dalberth, J. Gray, D. Seghete, K. Bertness, S. George, V. Bright, C. Rogers, and N. Sanford, Sens. Actuators, A 165(1), 59 (2011).
[3] S. Hoch, J. Montague, V. Bright, C. Rogers, K. Bertness, J. Teufel, K. Lehnert, Appl. Phys. Let. 99, 053101 (2011).
Figure 1: Example of the two non-degenerate fundamental resonant modes of the single GaN NW shown in (a). In (b) and (c), respectively, the NW is driven at its fundamental frequencies near 851 kHz and 691 kHz. Periodic motion results in apparent “fanning” of NW when viewed in an SEM. Accompanying arrows illustrate the direction of NW motion. Scale bars are 100 nm.
Figure 2: Increase in six different GaN NW resonant frequencies after ALD alumina coatings of 4.6 nm 4.5 nm, and 3.9 nm. “HF etch” and “RIE” correspond, respectively, to a hydrofluoric acid etch and O2 plasma RIE that remove the ALD film and return the NWs to their original resonance positions.
Funding Source: iMINT
