Nanocrystalline Diamond Nano-Mechanical Resonators

Nano-electro-mechanical systems (NEMS) incorporating miniature scale mechanical elements into electronic circuits are of interest in applications ranging from atomic resolution mass spectrometers¹ to single electron spin detectors². For resonating structures, the frequency of operation is proportional to the acoustic velocity of the material from which they are fabricated, making diamond with its unrivalled value of 18000 m/s ideally suited for use in high frequency NEMS with minimal dissipation from scaling induced losses. While offering the benefits of diamond but in thin-film form, the use of nanocrystalline diamond (NCD) for smaller scale NEMS however is often prohibited by its considerable columnar growth induced roughness, complicating fabrication and resulting in significant surface associated dissipation³. In addition, the concentration of strain at the attachment points of typically used geometries is expected to radiate energy away from the device and lead to substantial loss that scales with frequency⁴. Through combining the use of chemical mechanical polished (CMP) stock with advanced geometries it is therefore expected that dissipation can be minimised in thin-film diamond based NEMS⁵.<br/><br/>To this end, metallised doubly clamped and ‘free-free’ geometry resonators incorporating flexural supports were fabricated from intrinsic NCD films with and without CMP. The devices were then placed in a Quantum Design Physical Property Measurement System at cryogenic temperatures, and actuated magnetomotively through sweeping the frequency of an applied AC signal while in the presence of a static magnetic field^6,7. Upon comparing the resulting resonances, a ~5-fold reduction in dissipation was observed upon switching from rough to polished films and the addition of 2^nd mode flexural supports, highlighting the benefits of CMP and the use of anchor-loss minimising geometries.<br/><br/><b>References</b><br/>1. K. Jensen, <i>et al. Nat Nano. </i><b>3 </b>(2008), 533-537.<br/>2. D. Rugar, <i>et al. Nature </i><b>430 </b>(2004), 329-332.<br/>3. X. M. H. Huang, <i>et al. New J. Phys. </i><b>7</b> (2005), 247.<br/>4. M. Imboden, <i>et al.</i> <i>Appl. Phys. Lett. </i><b>90 </b>(2007), 173502.<br/>5. E. L. H. Thomas, <i>et al. Carbon </i><b>68 </b>(2014), 473-479.<br/>6. K. L. Ekinci, <i>et al. Appl. Phys. Lett. </i><b>81</b> (2002), 2253-2255.<br/>7. T. Bautze, <i>et al. Carbon </i><b>72</b> (2014), 100-105.