Tunable thin film bulk acoustic wave resonator based on Ba_xSr_1-xTiO₃ thin film

Abstract

A tunable membrane-type thin film bulk acoustic wave resonator (TFBAR) based on a Ba(0.3)Sr(0.7)TiO(3)(BST) thin film has been fabricated. The resonance and antiresonance frequencies of the device can be altered by applying a dc bias: both shift down with increasing dc electric field. The resonance and antiresonance frequencies showed a tuning of -2.4% and -0.6%, respectively, at a maximum dc electric field of 615 kV/cm. The electromechanical coupling factor of the device increased up to 4.4%. We demonstrate that the tuning of the TFBAR is nonhysteretic. The Q-factor of the device showed some variation with dc bias and is about 200. The tuning of the TFBAR is caused by the dc bias dependence of the sound velocity and the intrinsic electromechanical coupling factor of the BST layer. We apply our recently developed theory on the electrical tuning of dc bias induced acoustic resonances in paraelectric thin films to successfully model the tuning behavior of the TFBAR. The modeling enabled us to de-embed the intrinsic electromechanical properties of the BST thin film. We show that the mechanical load of our device does not significantly degrade the tuning performance of the BST layer. The performance of the TFBAR is compared with the available data on varactor tuned TFBARs.

Correlations between microstructure and Q-factor of tunable thin film bulk acoustic wave resonators

“…Microstructure Figure 5 shows the XRD patterns of the Bragg reflector stack (1), the Bragg reflector with Pt bottom plate (2), and the complete BAW-SMR test structure, including the BSTO film grown at 585 C (3). The Bragg reflector stack and Bragg reflector with Pt bottom plate are annealed at conditions of growth of the BSTO film.…”

“…The product Q x f, where f is frequency, of the best reported tunable Ba x Sr 1-x TiO 3 (BSTO) BAW resonators, both membrane type and solidly mounted resonators (SMR), are in the range 400-600 GHz. [1][2][3][4] Simulations show that product Q x f of a BAW resonator used in a ladder filter should be more than 2000 GHz. 5 For comparison, the nontunable BAW resonators utilizing AlN films reveal average Qf % 3000 GHz.…”

MOD deposited thin film BST based bulk acoustic wave resonators

“…Recently, tunable thin film BST and ST bulk resonators are attracting the attention of many investigators [5][6][7][8][9][10]. These resonators have applications as filters in cell phones over surface acoustic wave devices because of their small size, high quality factor, sharp filter skirts and ease of integration.…”

“…There are generally two approaches for implementing thin film bulk resonators. In one approach, free standing piezoelectric films between metal electrodes are fabricated by bulk micromachining techniques [6,10]. In another approach, the substrate is acoustically isolated using Bragg reflectors [5].…”

Effect of interface roughness on acoustic loss in tunable thin film bulk acoustic wave resonators

“…[1][2][3][4] However, the practical applications of the BSTO FBARs are hindered by their relatively low acoustic Q-factor resulting in low figure of merit, i.e., Qf product typically below 600 GHz. 4 Application of the FBARs in a ladder filter, for example, requires Qf product at least 2000 GHz.…”