Strain engineered barium strontium titanate for tunable thin film resonators

Abstract

Piezoelectric properties of epitaxial (001) barium strontium titanate (BST) films are computed as functions of composition, misfit strain, and temperature using a non-linear thermodynamic model. Results show that through adjusting in-plane strains, a highly adaptive rhombohedral ferroelectric phase can be stabilized at room temperature with outstanding piezoelectric response exceeding those of lead based piezoceramics. Furthermore, by adjusting the composition and the in-plane misfit, an electrically tunable piezoelectric response can be obtained in the paraelectric state. These findings indicate that strain engineered BST films can be utilized in the development of electrically tunable and switchable surface and bulk acoustic wave resonators.

Misfit strain phase diagrams of epitaxial PMN–PT films

“…The misfit strain required to stabilize the m-phase at RT for PMN-PT is in the range of À0.43% < u m < 0.65% depending on the composition. The range of u m over which the m-phase can be stabilized in (001) BST and PZT systems is substantially smaller (À0.13% < u m < 0.14% and À0.015% < u m < 0.007%, respectively 14,27 ) compared to PMN-PT. This is reflective of the weaker crystallographic anisotropy of polarization in relaxor-based solid solutions as compared with conventional ferroelectrics.…”

“…The initial work of Pertsev et al and follow-on studies have generated the misfit strain (u m )-temperature (T) phase diagrams for epitaxial thin films of PbTiO 3 , PZT, BaTiO 3 , SrTiO 3 , and Ba 1Àx Sr x TiO 3 (BST), and the dielectric, pyroelectric/electrocaloric, and piezoelectric properties as a function of the misfit strain and temperature have been computed. [11][12][13][14][15][16][17] Although monocrystalline PMN-PT compositions located near the morphotropic phase boundary (MPB) exhibit outstanding piezoelectric properties (d 33 > 1500 pC/m and electromechanical coupling factors k 33 > 0.92), 18 the lack of a Landau-Devonshire free energy function hindered the development of u m -T diagrams for PMN-PT materials. Such diagrams would particularly be important in the development of new generation of electrically switchable and tunable surface and bulk acoustic wave (SAW and BAW, respectively) resonators for a variety of applications, including remote controls, microprocessor clocks, mobile phones, and industrial controllers.…”

Enhanced tunability of sandwich-like structural barium strontium titanate thin films on stainless steel substrates

“…Details for this model and the parameters of BST thin films can be found in some available references [12][13][14][15][16][17]. In our calculation, lattice misfit stress [12,13], thermal misfit stress [14], and the effect of film thickness [12,13] are considered at the same time.…”

Structures and dielectric properties of multilayer BST/ST/BST and ST/BST/ST sandwich structures

“…As nonlinear ferroelectric materials, Ba 1-x Sr x TiO 3 (BST) films have been the most promising candidates for applications in radio frequency/microwave tunable devices including phase shifters, tunable filters, sensors, resonators, and varactors [1][2][3][4] since the dielectric constant (ε r ) of the materials can be adjusted with an applied electric field. However, it is difficult for pure BST films to simultaneously achieve the required dielectric properties, especially low dielectric loss and high tunability.…”