In this paper, an AIN/free-standing nanocrystalline diamond (NCD) system is proposed in order to process high frequency surface acoustic wave (SAW) resonators for sensing applications. The main problem of synthetic diamond is its high surface roughness that worsens the sputtered AIN quality and hence the device response. In order to study the feasibility of this structure, AIN films from 150 nm up to 1200 nm thick have been deposited on free-standing NCD. We have then analysed the influence of the AIN layer thickness on its crystal quality and device response. Optimized thin films of 300 nm have been used to fabricate of one-port SAW resonators operating in the 10-14 GHz frequency range. A SAW based sensor pressure with a sensibility of 0.33 MHz/bar has been fabricated.
Abstract-This letter describes the procedure to manufacture high-performance surface acoustic wave (SAW) resonators on AlN/diamond heterostructures working at frequencies beyond 10 GHz. In the design of SAW devices on AlN/diamond systems, the thickness of the piezoelectric layer is a key parameter. The influence of the film thickness on the SAW device response has been studied. Optimized thin films combined with advanced e-beam lithographic techniques have allowed the fabrication of one-port SAW resonators with finger width and pitch of 200 nm operating in the 10-14 GHz range with up to 36 dB out-of-band rejection.Index Terms-AlN/diamond, surface acoustic wave (SAW) resonator, super-high-frequency band, thickness influence.
Textured as well as epitaxial thin AlN films are of great interest for a wide range of electro-acoustic and optoelectronic applications. Reduction of the deposition temperature is of vital importance in a number of applications due to thermal budget limitations. In this work we systematically studied the influence of the process parameters on the film properties and identified the factors leading to improved film quality as well as reduced deposition temperature with pulsed direct current sputtering in an Ar/N2 atmosphere. We demonstrated that fully textured (0002) films can be grown under a wide range of conditions. At the same time the full width at half-maximum (FWHM) of the rocking curve of the (0002) XRD peak was found to vary systematically with process conditions—depostion rate, process pressure, gas composition, and substrate temperature. The best films showed a FWHM of 1.2°. We found that by far the most important factor is the arrival energy of the sputtered Al atoms, which is primarily controlled by the process pressure. We report for the first time that fully textured AlN films with a FWHM of under 2° can be grown at room temperature. Other important factors are the ion and electron bombardment of the films and substrate temperature as well as gas composition, although their influence is not as dramatic. Generally, the film quality increases with temperature. Bias and electron bombardment within a certain range also lead to better films.
Diamond has the highest surface acoustic wave (SAW) velocity among all materials and thus provides substantial advantages for the fabrication of high-frequency SAW devices when combined with a piezoelectric thin film. The properties of layered film structures consisting of a piezoelectric material layer, aluminum nitride (AlN), and a polycrystalline diamond layer grown on a silicon substrate have been examined. Highly textured AlN thin films have been sputter-deposited onto polycrystalline diamond substrates at room temperature. X-ray diffraction analysis of the multilayer structure as well as atomic force microscope images of the AlN surface indicate that the deposited AlN films were c-axis oriented with a full width at half maximum of the rocking curve of the AlN-002-peak of 2.1°. The thickness of the AlN layer was of 4.3 μm, whereas the diamond layer was 50 μm thick and resting on a 3-in Si wafer. Standard one-port SAW resonators with aluminum (Al) metallization have been subsequently fabricated and evaluated. Experimental results indicate that the fundamental as well as higher Rayleigh SAW modes are excited. Thus, the phase velocities of the first, second, third, and fourth mode are found to be 6.850, 10.000, 11.800, and 14.450 m/s respectively. A very good out-of-band rejection of −50 dB was obtained.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.