Embedding epitaxial VO_(2)film with quality metal-insulator transition to SAW devices

Epitaxial VO_(2)films grown by pulsed laser deposition(PLD)method with superior phase transition related switching characteristics are successfully embedded to SAW devices using concept of the“impedance loaded SAW sensor”.A resistance of VO2 sensor abruptly drops from 0.7 MΩto 90Ωwhen it is heated above~65℃and shows a narrow hysteresis loops when switching.Two designs of SAW devices are examined in which RF signal is reflected back from interdigital transducer(IDT)or a surface acoustic waves(SAW)is transferred through a coupler and the RF response is altered 2 and 3 times correspondingly upon the phase transition in VO2.In the proposed devices with external load,a SAW does not propagate via VO2 film and therefore is not attenuated which is beneficiary for wireless applications.Additionally,a SAW phase shift as great as 50°is induced to the SAW transferred through the coupler due to the phase transition in VO2.The proposed approach may boost the development of remotely controlled autonomous sensors,including those based on VO2 metamaterials and hybrid plasmonic structures for near IR/middle IR and sub-THz/THz applications.

Synthesis of ZnO nanorods for piezoelectric resonators and sensors

Efficiency of the piezoelectric chemisensors may be considerably enhanced by use of zinc oxide nanorods as sensing elements.ZnO nanorod arrays being good piezoelectric materials possess large surface area,which provides extra benefits for chemisorption and photodetection.Highly oriented nanorod arrays are typically prepared onto highly crystalline substrates,whereas the nanorods growth onto metal contacts meets significant technological difficulties.In this paper,we report on carbothermal,electrochemical,and hydrothermal techniques of ZnO nanorod arrays synthesis on metal contacts.The optical and structural properties of the obtained nanorods were studied using scanning electron microscopy,X-ray diffraction(XRD),Raman spectroscopy,and lumi-nescence spectroscopy.A reliable technique was developed for obtaining ohmic contact with the grown nanorods.I-U curves of prepared contact were studied.Carbothermal synthesis made it possible to obtain the most crystallinely perfect,homogeneous,and dense arrays of nanorods and control the concentration of point defects by changing the synthesis parameters over a wide range.The electrochemical synthesis demonstrated excellent results for synthesis of ZnO nanorods on the surface of resonator electrodes.

Optimizing VO_(2)film properties for use in SAW devices

The aim of this study is to optimize the conditions for producing thin VO_(2)films for their use in SAW devices.We used the pulsed laser deposition(PLD)method to produce VO_(2)films.We used a metallic vanadium target.The dependence of the oxygen pressure during PLD on the resistive metal-insulator transition(MIT)on substrates of c-sapphire and LiNbO_(3)YX/128°was studied.The resulting films had sharp metal-insulator temperature transitions on c-Al_(2)O_(3).The most high-quality films showed resistance change by four orders of magnitude.At the lower point of the hysteresis,the resistance of these samples was in the range of 50-100Ω.The synthesized VO_(2)films had a sharp temperature transition and a relatively small width of thermal hysteresis.The SAW damping during its passage through a VO_(2)/ZnO/LiNbO_(3)YX/128°film at the metal-insulator phase transition temperature was studied.Attenuation SAW decreases with increasing temperature from 52 dB/cm to 0 dB/cm.