Jason M. Gray

High-Q GaN nanowire resonators and oscillators

We report high mechanical quality factors Q for GaN nanowire cantilevers grown by molecular beam epitaxy. Nanowires with 30–500nm diameters and 5–20μm lengths having resonance frequencies from 400kHzto2.8MHz were measured. Q near room temperature and 10−4Pa ranged from 2700 to above 60 000 with most above 10 000. Positive feedback to a piezoelectric stack caused spontaneous nanowire oscillations with Q exceeding 106. Spontaneous oscillations also occurred with direct e-beam excitation of unintentionally doped nanowires. Doped nanowires showed no oscillations, consistent with oscillation arising via direct actuation of piezoelectric GaN.

On-chip optical interconnects made with gallium nitride nanowires.

In this Letter we report on the fabrication, device characteristics, and optical coupling of a two-nanowire device comprising GaN nanowires with light-emitting and photoconductive capabilities. Axial p-n junction GaN nanowires were grown by molecular beam epitaxy, transferred to a non-native substrate, and selectively contacted to form discrete optical source or detector nanowire components. The optical coupling demonstrated for this device may provide new opportunities for integration of optical interconnects between on-chip electrical subsystems.

Large Arrays and Properties of 3-Terminal Graphene Nanoelectromechanical Switches

Large arrays of 3-terminal nanoelectromechanical graphene switches are fabricated. The switch is designed with a novel geometry that leads to low actuation voltages and improved mechanical integrity, while reducing adhesion forces, which improves the reliability of the switch. A finite element model including non-linear electromechanics is used to simulate the switching behavior and to deduce a scaling relation between the switching voltage and device dimensions.

Ultra‐thin 3D Nano‐Devices from Atomic Layer Deposition on Polyimide

N. T. Eigenfeld, Dr. J. M. Gray, Dr. J. J. Brown, Prof. V. M. Bright Department of Mechanical Engineering University of Colorado at Boulder 1111 Engineering Drive, 427 UCB, Boulder , CO 80309–0427 , USA E-mail: victor.bright@colorado.edu Prof. S. M. George Department of Chemistry and Biochemistry and Department of Mechanical Engineering University of Colorado at Boulder, 215 UCB, Boulder , CO 80309–0215 , USA Dr. G. D. Skidmore Network and Imaging Systems DRS ITS Texas Site 13532 North Central Expwy SC Bldg, Dallas , TX 75243 , USA

Low-frequency noise in gallium nitride nanowire mechanical resonators

We report on the low-frequency 1/f (flicker) parameter noise displayed by the resonance frequency of doubly clamped c-axis gallium nitride nanowire (NW) mechanical resonators. The resonators are electrostatically driven and their mechanical response is electronically detected via NW piezoresistance. With an applied dc voltage bias, a NW driven near its mechanical resonance generates a dc and Lorentzian rf current that both display 1/f noise. The rf current noise is proportional to the square of the derivative of the Lorentzian lineshape with a magnitude highly dependent on NW dc bias voltage conditions, consistent with a model wherein noise in the NWs electrical impedance leads to temperature noise from local Joule heating, which in turn generates resonance frequency noise via thermal expansion and the temperature-dependent Youngs modulus. An example device with a 27.8 MHz resonance frequency experiences an approximate resonance frequency shift of −1.4 Hz/nW. The resonance frequency noise increases as t...

Gallium nitride nanowire electromechanical resonators with piezoresistive readout

The authors report on the fabrication, piezoresistive readout, and frequency response of doubly clamped c-axis gallium nitride nanowire (NW) resonators that show mechanical quality factors exceeding 10 000. The devices are fabricated using a combination of lithographic patterning and dielectrophoresis to suspend NWs across 10 μm gaps. An electrostatic gate induces NW vibration, which is electronically detected via NW piezoresistance. The naturally occurring range of NW diameters results in lowest beam resonances in the range of 9–36 MHz, consistent with a Young’s modulus of roughly 300 GPa. Mechanical quality factors, Q, as high as 26 000 under vacuum at 8 K are observed. Selective variation of NW temperature by local joule heating while maintaining cold mechanical clamps demonstrates the dominant role of the polycrystalline metallic end clamps in the room-temperature mechanical dissipation.

Specific heat capacity of ultra-thin atomic layer deposition nanobridges for microbolometers

This paper presents the first reported specific heat capacity measurements of ultra-thin atomic layer deposited W/Al2O3 thin films. The thermal time constants of suspended ALD nanobridges were measured and a new model was derived to fit the data and extract the specific heat capacity. The accuracy of the new model was compared against a traditional model using finite element and analytical modeling. Application of these ultra-thin materials for microbolometer performance enhancement is discussed.

High-Q Gallium Nitride Nanowire Resonators With Piezoresistive Readout

We report on the fabrication and piezoresistive readout of doubly-clamped c-axis GaN nanowire (NW) mechanical resonators. As-grown GaN-NW resonators have demonstrated exceptional mechanical quality factors (Q, defined as resonance frequeny over full width at half maximum power) in the range of 104 –105 [1]. This work confirms the NWs can retain this high Q even after removal from the growth substrate and placement on lithographically-defined test structures, with a highest Q to date of 26,000 at 10−5 Pa and 8 K. Wires range from 100–500 nm in diameter and 15–18 micrometers in length. We fabricate the devices using a combination of lithographic patterning and dielectrophoresis to suspend NWs over 8 or 10 micrometer gaps. We deposit an electrostatic gate ∼1 micrometer away from the NW to induce vibration, with readout utilizing the piezoresistivity of GaN. Observed resonances range from 9–36 MHz, consistent with a Young’s modulus of roughly 300 GPA. At room temperature and under vacuum, Q for these fabricated devices is typically around 103 , significantly lower than the 104 –105 range of the as-grown wires. However, the larger Q can be recovered by cooling the substrate. We find that by ∼10 K, Q increases by an order of magnitude to above 104 . We will discuss the temperature dependence, as well as fabrication and processing effects, on the NW resonance and Q.Copyright