Enhanced tunable performance of high Q-factor Ba_xSr_1−xTiO₃ film bulk acoustic wave resonators

Abstract

Emerging intrinsically tunable film bulk acoustic wave(BAW) resonators allow the development of new generation reconfigurable and agile microwave circuits. In this paper, we demonstrate the enhancement of tunable performance of the high Q-factor BaxSr1−xTiO3 BAW – solidly mounted resonators (BAW–SMR) by varying Ba concentration. The Ba0.5Sr0.5TiO3 BAW–SMR reveal tunability of series resonance frequency up to 2.4%, electromechanical coupling coefficient up to 7.5% and rather high Q-factor, up to 250 at 5.3 GHz. Correlations between the measured electroacoustic parameters are analyzed using the theory of dc field-induced piezoelectric effect in paraelectric phase ferroelectrics. Higher coupling coefficient and tunability of resonance frequency of the Ba0.5Sr0.5TiO3 BAW–SMR are associated with higher tunability of permittivity. Strong anisotropy in field-induced piezoelectric effect is predicted with highest coupling coefficient in (001) direction of the BaxSr1−xTiO3 films. It is also shown that the tunability of series resonance frequency of Ba0.5Sr0.5TiO3 BAW–SMR is limited by relatively high and negative nonlinear electrostriction coefficient which is found to be m ≈ −4·1010 m/F. The BAW–SMR Q-factor is limited significantly by extrinsic acoustic loss associated with wave scattering at reflection from relatively rough top interface. The results of analysis show possible ways of further improvement of the performance of tunable BAW–SMR.

Intrinsically switchable thin film bulk acoustic wave resonators

“…This is because the definition (2) makes the Q s equal to the purely mechanical Q-factor. 16 The Q p1 values are reduced by additional contribution of the dielectric loss. 16 It can be seen from Fig.…”

Intrinsically tunable bulk acoustic wave resonators based on sol-gel grown PMN-PT films

“…This is relatively less accurate method than the atomic force microscopy, which we used before. 6,7,18,26,28 However, this accuracy is sufficient for our analysis below demonstrating relationship between the Q-factors associated with the scattering loss and overall losses within the PMN-PT film. The error in the Q-factor evaluation is less than 69%.…”

“…0.5 reveal positive tunability of the parallel resonance frequency, i.e., stiffening. 28,29 This can be explained by lower l value due to higher permittivity of the material with higher Ba concentration and, hence, domination of the term c in the sum of c þ l/2. For the PMN-PT, no published data on the non-linear electrostrictive coefficients are available to the authors' knowledge, which does not allow for correct analysis of the relationship between c and l. We suppose that the observed positive tunability of the parallel resonance frequency (Figs.…”

Effect of growth conditions on microstructure of BiFeO3-0.33BaTiO3 films and performance of bulk acoustic wave resonators

“…14 and coupling coefficients of the BAW resonators because of the inherent anisotropy of the components of the tensors of linear and nonlinear electrostriction. 13,15 In this paper, we demonstrate variations of the BF-BT film microstructure with position on the condensation surface in the PLD system relative to the laser beam-plume interaction area. Analysis of the correlations between the BF-BT film microstructure and the acoustic performance of the BAW resonators allows for an optimization of the PLD system configuration and achieving the high resonator performance.…”

“…11 The film surface roughness is responsible for the main extrinsic acoustic loss mechanism in the ferroelectric BAW resonators associated with wave scattering at reflection from a rough interface. 7,12,13 Thus, an asymmetric distribution of the Q-factors of the BAW resonators with respect to the plume axis is expected. Additionally, the surface distribution of the energy of the adparticles can alter the surface distribution of the grain orientation, i.e., texturing, if the growth rate in a certain crystallographic direction is governed by the lowest free surface energy.…”