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Register a new userUltrawide Band Gap beta-Ga2O3 Nanomechanical Resonators with Spatially Visualized Multimode Motion
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Beta gallium oxide (beta-Ga2O3) is an emerging ultrawide band gap (4.5 - 4.9 eV) semiconductor with attractive properties for future power electronics, optoelectronics, and sensors for detecting gases and ultraviolet radiation. beta-Ga2O3 thin films made by various methods are being actively studied toward such devices. Here, we report on the experimental demonstration of single-crystal beta-Ga2O3 nanomechanical resonators using beta-Ga2O3 nanoflakes grown via low-pressure chemical vapor deposition (LPCVD). By investigating beta-Ga2O3 circular drumhead structures, we demonstrate multimode nanoresonators up to the 6th mode in high and very high frequency (HF / VHF) bands, and also realize spatial mapping and visualization of the multimode motion. These measurements reveal a Youngs modulus of E_Y = 261 GPa and anisotropic biaxial built-in tension of 37.5 MPa and 107.5 MPa. We find that thermal annealing can considerably improve the resonance characteristics, including ~40% upshift in frequency and ~90% enhancement in quality (Q) factor. This study lays a foundation for future exploration and development of mechanically coupled and tunable beta-Ga2O3 electronic, optoelectronic, and physical sensing devices.
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Complex oxide thin films and heterostructures exhibit a profusion of exotic phenomena, often resulting from the intricate interplay between film and substrate. Recently it has become possible to isolate epitaxially grown single-crystalline layers of these materials, enabling the study of their properties in the absence of interface effects. In this work, we create ultrathin membranes of strongly correlated materials and demonstrate top-down fabrication of nanomechanical resonators made out of ce{SrTiO3} and ce{SrRuO3}. Using laser interferometry, we successfully actuate and measure the motion of the nanodrum resonators. By measuring their temperature-dependent mechanical response, we observe signatures of structural phase transitions in ce{SrTiO3}, which affect the strain and mechanical dissipation in the resonators. This approach can be extended to investigate phase transitions in a wide range of materials. Our study demonstrates the feasibility of integrating ultrathin complex oxide membranes for realizing nanoelectromechanical systems on arbitrary substrates.
Observation of resonance modes is the most straightforward way of studying mechanical oscillations because these modes have maximum response to stimuli. However, a deeper understanding of mechanical motion could be obtained by also looking at modal responses at frequencies in between resonances. A common way to do this is to force a mechanical object into oscillations and study its off-resonance behaviour. In this paper, we present visualisation of the modal response shapes for a mechanical drum driven off resonance. By using the frequency modal analysis, we describe these shapes as a superposition of resonance modes. We find that the spatial distribution of the oscillating component of the driving force affects the modal weight or participation. Moreover, we are able to infer the asymmetry of the drum by studying the dependence of the resonance modes shapes on the frequency of the driving force. Our results highlight that dynamic responses of any mechanical system are mixtures of their resonance modes with various modal weights, further giving credence to the universality of this phenomenon.
Beta-Ga2O3 has emerged as a promising candidate for electronic device applications because of its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt. However, its thermal conductivity is at least one order of magnitude lower than that of other wide bandgap semiconductors such as SiC and GaN. Thermal dissipation in electronics made from beta-Ga2O3 will be the bottleneck for real-world applications, especially for high power and high frequency devices. Similar to GaN/AlGaN interfaces, beta-(AlxGa1-x)2O3/Ga2O3 heterogeneous structures have been used to form a high mobility two-dimensional electron gas (2DEG) where joule heating is localized. The thermal properties of beta-(AlxGa1-x)2O3/Ga2O3 are the key for heat dissipation in these devices while they have not been studied before. This work reports the first measurement on thermal conductivity of beta-(Al0.1Ga0.9)2O3/Ga2O3 superlattices from 80 K to 480 K. Its thermal conductivity is significantly reduced (5.7 times reduction) at room temperature comparing with that of bulk Ga2O3. Additionally, the thermal conductivity of bulk Ga2O3 with (010) orientation is measured and found to be consistent with literature values regardless of Sn doping. We discuss the phonon scattering mechanism in these structures by calculating their inverse thermal diffusivity. By comparing the estimated thermal boundary conductance (TBC) of beta-(Al0.1Ga0.9)2O3/Ga2O3 interfaces and Ga2O3 maximum TBC, we reveal that some phonons in the superlattices transmit through several interfaces before scattering with other phonons or structural imperfections. This study is not only important for Ga2O3 electronics applications especially for high power and high frequency applications, but also for the fundamental thermal science of phonon transport across interfaces and in superlattices.
We report on the non-destructive measurement of Youngs modulus of thin-film single crystal beta gallium oxide (beta-Ga2O3) out of its nanoscale mechanical structures by measuring their fundamental mode resonance frequencies. From the measurements, we extract Youngs modulus in (100) plane, EY,(100) = 261.4+/-20.6 GPa, for beta-Ga2O3 nanoflakes synthesized by low-pressure chemical vapor deposition (LPCVD), and Youngs modulus in [010] direction, EY,[010] = 245.8+/-9.2 GPa, for beta-Ga2O3 nanobelts mechanically cleaved from bulk beta-Ga2O3 crystal grown by edge-defined film-fed growth (EFG) method. The Youngs moduli extracted directly on nanomechanical resonant device platforms are comparable to theoretical values from first-principle calculations and experimentally extracted values from bulk crystal. This study yields important quantitative nanomechanical properties of beta-Ga2O3 crystals, and helps pave the way for further engineering of beta-Ga2O3 micro/nanoelectromechanical systems (M/NEMS) and transducers.
We report on the first beta gallium oxide (beta-Ga2O3) crystal feedback oscillator built by employing a vibrating beta-Ga2O3 nanoresonator as the frequency reference for real-time middle ultraviolet (MUV) light detection. We fabricate suspended beta-Ga2O3 nanodevices through synthesis of beta-Ga2O3 nanoflakes using low-pressure chemical vapor deposition (LPCVD), and dry transfer of nanoflakes on microtrenches. Open-loop tests reveal a resonance of the beta-Ga2O3 device at ~30 MHz. A closed-loop oscillator is then realized by using a combined optical-electrical feedback circuitry, to perform real-time resonant sensing of MUV irradiation. The oscillator exposed to cyclic MUV irradiation exhibits resonant frequency downshifts, with a measured responsivity of $mathscr{R}$ = -3.1 Hz/pW and a minimum detectable power of delta Pmin = 0.53 nW for MUV detection.
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