AlN films were deposited by reactive radio frequency (RF) sputtering on various bottom electrodes, such as Al, Ti, Mo, Au/Ti, and Pt/Ti. The effects of substrate metals on the orientation of AlN thin films were investigated. The results of X-ray diffraction, atomic force microscopy, and field emission scanning electron microscopy show that the orientation of AlN films depends on the kinds of substrate metals evidently. The differences of AlN films deposited on various metal electrodes are attributed to the differences in lattice mismatch and thermal expansion coefficient between the AlN material and substrate metals. The AlN film deposited on the Pt/Ti electrode reveals highly the c-axis orientation with well-textured columnar structure. The positive role of the Pt/Ti electrode in achieving the high-quality AlN films and high-performance film bulk acoustic resonator (FBAR) may be attributed to the smaller lattice mismatch as well as the similarity of thermal expansion coefficient between the deposited AlN material and the Pt/Ti electrode substrate.
Respiratory rate is a vital physiological signal in laboratory rodents research. This paper presents a noninvasive method based on resonant humidity sensor for monitoring respiratory rate of rats. The sensor is composed of an aluminum nitride (AlN) resonant microcantilever coated with graphene oxide (GO) film. The sensor shows high sensitivity and good repeatability. By combining the sensor with a control circuit, a closed-loop respiration measurement system is realized for fast response. The system can monitor respiratory rate of rats in real time by detecting relative humidity difference between exhaled and inhaled breath. The method has advantages of fast response, small size and low cost. Furthermore, the respiratory rate of rats can be noninvasively monitored by integrating the sensor with a face mask.
The crystal structure and microwave dielectric properties of (1−x)Ca0.61Nd0.26TiO3+xNd(Mg1/2Ti1/2)O3 (0≤x≤1.0) solid solutions incorporated with 1 wt % CuO were investigated. Pure perovskite phases were formed in the whole composition range, and the crystal space group and unit cell volume of the perovskites were analyzed based on x-ray diffraction patterns. The configuration of octahedral tilting and the B-site ordering phase transition between x=0.9 and 1.0 were unambiguously assigned, respectively, to the corresponding superlattice diffractions. Moreover, the two important fingerprints A1g mode and F2g mode in Raman spectra, associated with the evolution of short range ordering and long range ordering of B-site cations, respectively, were further investigated by employing the full width at half-maximum and their Raman shifts to determine the degree of B-site ordering and the crystal bond strength in the perovskites. The microwave dielectric constants, quality factors, and temperature coefficients of resonant frequency of the solid solutions were elaborately investigated and correlated with their crystal structures. The microscopic structure-related thermal parameters in the solid solution were calculated using the Claussius–Mossotti equation to determine the original contributors in the temperature coefficients. Temperature compensated τf value ceramics could be obtained in the range of 0.3<x<0.5. When sintered at 1400 °C for 2.5 h, a dielectric constant εr of 39.9, a quality factor product of 12 600 GHz, and a τf of −25.3 ppm/°C microwave dielectric ceramic were obtained in 0.5Ca0.61Nd0.26TiO3+0.5Nd(Mg1/2Ti1/2)O3+1 wt % CuO composition.
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