Surface acoustic wave devices on bulk ZnO crystals at low temperature

Abstract

Surface acoustic wave (SAW) devices based on thin films of ZnO are a well established technology. However, SAW devices on bulk ZnO crystals are not practical at room temperature due to the significant damping caused by finite electrical conductivity of the crystal. Here, by operating at low temperatures, we demonstrate effective SAW devices on the (0001) surface of bulk ZnO crystals, including a delay line operating at SAW wavelengths of λ = 4 and 6 µm and a one-port resonator at a wavelength of λ = 1.6 µm. We find that the SAW velocity is temperature dependent, reaching v ≃ 2.68 km/s at 10 mK. Our resonator reaches a maximum quality factor of Q i ≃ 1.5 × 10 5 , demonstrating that bulk ZnO is highly viable for low temperature SAW applications. The performance of the devices is strongly correlated with the bulk conductivity, which quenches SAW transmission above about 200 K.

Quantum Acoustics with Surface Acoustic Waves

“…In 20 , results are reported on a delay line and a one-port resonator fabricated on a 0.5 mm thick high quality ZnO substrate, measured in a dilution refrigerator down to 10 mK. We summarize the important results in Fig.…”

“…One example of this is ZnO, which although commonly used as a thin film transducer on nonpiezoelectric substrates such as sapphire, diamond or SiO 2 /Si 15,33 , is not viable as a bulk crystal substrate at room temperature due to a substantial electrical conductivity, which damps the SAWs. This problem disappears at low temperature 20 , making a very low loss SAW substrate, as discussed in Sec. IV.…”

“…When cooled to low temperatures, SAW devices show good performance in this frequency range, where suspended mechanical resonators tend to suffer from high losses. Indeed, recent experiments report Q-values above 10 5 at millikelvin temperatures for SAWs confined in acoustic cavities 20 . Another recent experiment has shown that it is possible to couple SAW waves to artificial atoms in a way very similar to waveguide QED 21 .…”

Universal Quantum Transducers Based on Surface Acoustic Waves

“…(3) Our scheme is built upon an established technology [14,15]: Lithographic fabrication techniques provide almost arbitrary geometries with high precision as evidenced by a large range of SAW devices such as delay lines, bandpass filters, resonators, etc. In particular, the essential building blocks needed to interface qubits with SAW phonons have already been fabricated, according to design principles familiar from electromagnetic devices: (i) SAW resonators, the mechanical equivalents of Fabry-Perot cavities, with low-temperature measurements reaching quality factors of Q ∼ 10 5 even at gigahertz frequencies [22][23][24], and (ii) acoustic waveguides as analog to optical fibers [14]. (4) For a given frequency in the gigahertz range, due to the slow speed of sound of ∼10 3 m=s for typical materials, device dimensions are in the micrometer range, which is convenient for fabrication and integration with semiconductor components, and about 10 5 times smaller than corresponding electromagnetic resonators.…”

Multilayer-graphene-based amplifier of surface acoustic waves

“…[9][10][11] A series of related studies was performed recently to understand (i) the conductivity of graphene and its carrier dynamics, [12][13][14][15][16][17] (ii) plasmonic effects, [18][19][20][21] (iii) the own phonon generation by the carrier current, [22][23][24][25] (iv) the interaction between graphene electrons and SAWs, [26][27][28][29] and (v) sandwich-like "graphene-piezoelectric" structures, which allow one to create a new class of opto-acousto-electronic devices. [30][31][32][33][34] Nevertheless, the problem of modeling SAW amplification in graphene-based SAW amplifiers has not been studied systematically to date.…”