DeMiguel-Ramos M, Mirea T, Olivares J, Clement M, Sangrador J, Iborra E. Assessment of the shear acoustic velocities in the different materials composing a high frequency solidly mounted resonator.
ULTRASONICS 2015;
62:195-199. [PMID:
26081919 DOI:
10.1016/j.ultras.2015.05.017]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Revised: 05/19/2015] [Accepted: 05/20/2015] [Indexed: 06/04/2023]
Abstract
Thin film acoustic resonators operating in the shear mode are being increasingly used for in-liquid sensing applications. A good design of such sensors requires accurate knowledge of the acoustic properties of the materials composing the whole device, which specifically includes their shear velocities. Here we present a method to assess the shear acoustic velocity of high and low acoustic impedance films commonly used in AlN-based solidly mounted resonators (SMRs), using test devices specifically designed to induce a half-wavelength resonance in the layer under study. Provided that the thickness and mass densities of all the layers are known, fitting the electrical response by Mason's model over a wide frequency range gives accurate values of both longitudinal and shear mode velocities. The assessment of porous and dense SiO2, Mo, W and Ta2O5 sputtered films yields shear velocities of 3150m/s, 3950m/s, 3450m/s, 3350m/s and 2900m/s, respectively. In addition, the resonances stimulated in the Ir and Au top electrodes enable deriving their shear modes velocities, with values of 3950m/s and 2350m/s, respectively.
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