Dual-Mode Solidly Mounted Resonator-Based Sensor for Temperature and Humidity Detection and Discrimination.

Sensors based on solidly mounted resonators (SMRs) exhibit a good set of properties, such as high sensitivity, fast response, low resolution limit and low production cost, which makes them an appealing technology for sensing applications. However, they can suffer from cross-sensitivity issues, as their response can be altered by undesirable ambient factors, such as temperature and humidity variations. In this work we propose a method to discriminate humidity variations from the general frequency response using an SMR specifically manufactured to operate in a dual-mode (displaying two close resonances).

Homogeneity and Thermal Stability of Sputtered AlScN Thin Films.

This work presents a study on the homogeneity and thermal stability of AlScN films sputtered from Al-Sc segmented targets. The films are sputtered on Si substrates to assess their structural properties and on SiO/Mo-based stacked acoustic mirrors to derive their piezoelectric activity from the frequency response of acoustic resonators. Post-deposition annealing at temperatures up to 700 °C in a vacuum are carried out to test the stability of the AlScN films and their suitability to operate at high temperatures.

Direct growth of few-layer graphene on AlN-based resonators for high-sensitivity gravimetric biosensors.

We present the successful growth of few-layer graphene on top of AlN-based solidly mounted resonators (SMR) using a low-temperature chemical vapour deposition (CVD) process assisted by Ni catalysts, and its effective bio-functionalization with antibodies. The SMRs are manufactured on top of fully insulating AlN/SiO acoustic mirrors able to withstand the temperatures reached during the CVD growth of graphene (up to 650 °C). The active AlN films, purposely grown with the -axis tilted, effectively excite shear modes displaying excellent in-liquid performance, with electromechanical coupling and quality factors of around 3% and 150, respectively, which barely vary after graphene integration.

High-acoustic-impedance tantalum oxide layers for insulating acoustic reflectors.

This work describes the assessment of the acoustic properties of sputtered tantalum oxide films intended for use as high-impedance films of acoustic reflectors for solidly mounted resonators operating in the gigahertz frequency range. The films are grown by sputtering a metallic tantalum target under different oxygen and argon gas mixtures, total pressures, pulsed dc powers, and substrate biases. The structural properties of the films are assessed through infrared absorption spectroscopy and X-ray diffraction measurements.

Influence of crystal quality on the excitation and propagation of surface and bulk acoustic waves in polycrystalline AlN films.

We investigate the excitation and propagation of acoustic waves in polycrystalline aluminum nitride films along the directions parallel and normal to the c-axis. Longitudinal and transverse propagations are assessed through the frequency response of surface acoustic wave and bulk acoustic wave devices fabricated on films of different crystal qualities. The crystalline properties significantly affect the electromechanical coupling factors and acoustic properties of the piezoelectric layers.

DCS Tx filters using AlN resonators with iridium electrodes.

In this paper we present the design, fabrication technology, and characterization of BAW filters for the Digital Cellular System (DCS) Tx-band at 1.75 GHz. The filters are fabricated with AlN-based solidly mounted resonators (SMR) using iridium electrodes, in an attempt to increase the effective electromechanical coupling factor of the BAW devices and achieve the bandwidth requirements of DCS filters.

Sputtered SiO2 as low acoustic impedance material for Bragg mirror fabrication in BAW resonators.

In this paper we describe the procedure to sputter low acoustic impedance SiO(2) films to be used as a low acoustic impedance layer in Bragg mirrors for BAW resonators. The composition and structure of the material are assessed through infrared absorption spectroscopy. The acoustic properties of the films (mass density and sound velocity) are assessed through X-ray reflectometry and picosecond acoustic spectroscopy.

Circuital model for the analysis of the piezoelectric response of A1N films using SAW filters.

In this paper we describe a method to assess the piezoelectric response of a piezoelectric thin film deposited on a conductive substrate. It is based on analyzing the frequency response of a surface acoustic wave (SAW) filter made on the piezoelectric thin film. For this analysis, we use a circuital model that takes into account the theoretical response of the ideal filter along with all the external and internal parasitic effects that deteriorate the response.

Effect of particle bombardment on the orientation and the residual stress of sputtered AlN films for SAW devices.

We present a study of the effect of particle bombardment on the preferred orientation and the residual stress of polycrystalline aluminum nitride (AlN) thin films for surface acoustic wave (SAW) applications. Films were deposited on silicon (100) substrates by radio frequency (RF) sputtering of an aluminum target in an argon and nitrogen gas mixture. The main deposition parameters were changed as follows: the total pressure from 4 mTorr to 11 mTorr, the N2 content in the gas mixture from 20% to 80%, and the substrate self-bias voltage from -10 V to -30 V.