Integration of Ba1−xSrxTiO3-based active thin films with silicon-compatible materials and process science protocols to enable affordable on-the-move communications technologies

Abstract

Integration of Ba1−xSrxTiO3- (BST) based thin films with affordable Si substrates has a potentially significant commercial impact as the demand for high-frequency tunable devices intensifies. Utilizing a coplanar device design we have monolithically integrated, optimized, and fabricated a high-performance composite bilayer heterostructure, Si∕Ta2O5∕BST, whereby the base layer film Ta2O5 serves as a passive buffer layer to allow integration of BST active thin films with affordable Si substrates. Optimization of this design configuration was achieved by evaluating two heterostructure processing protocols: (1) a single-anneal and (2) a dual-anneal process protocol. The reliability susceptibility, i.e., the nonabrupt defect-laden bilayer film interface, of the single-anneal protocol deemed it inappropriate for the fabrication of this monolithic heterostructure design. In contrast, the defect-free, structurally abrupt bilayer and buffer layer film-substrate interfaces suggest the dual anneal process to be an excellent method for realizing monolithic integration of BST with affordable Si substrates. This work suggests that the coefficient of thermal expansion mismatch between the Ta2O5 buffer and the BST thin films in the coplanar device design serves to enhance the dielectric tunability of the device. Realization of this materials integration technology serves to promote broadscale implementation of affordable tunable microwave devices across a variety of advanced communications platforms.

Effect of (Ba+Sr/Ti) ratio on the dielectric properties for highly (111) oriented (Ba,Sr)TiO3 thin films

“…For instance, BST films have been widely studied as high-density dynamic random access memory (DRAM) devices [3], microwave tunable devices [4], field effect transistors (FETs) [5], and electrooptic devices [6]. Although single-crystal substrates such as LaAlO 3 , MgO and SrTiO 3 have been adopted due to the good lattice match and low substrate dielectric loss, Si wafers have intrigued great interest in order to make multifaceted devices in the integrated microelectronics field [7][8][9]. Gao et al fabricated (0 0 1) BST film on platinized Si by metalorganic chemical vapor deposition and investigated a mechanistic study of MOCVD growth [10].…”

Ba(Zr Ti1−)O3 thin films for tunable microwave applications

“…A high operating frequency in these microwave applications requires dielectric materials with a low dielectric constant and a low dielectric loss [5][6][7]. To date, (Ba 1 À x Sr x )TiO 3 (BST) has become one of the most popular ferroelectric materials currently being studied and implemented for tunable microwave devices [8][9][10][11][12].…”

Structural and dielectric properties of epitaxial Ba0.6Sr0.4TiO3 thin films grown on Si substrates with thin SrO buffer layers

“…For applications of frequency-agile devices, it is highly desirable to have as large a dielectric permittivity change ratio [dielectric tunability = (ɛ max −ɛ min )/ɛ max , where ɛ max and ɛ min are the maximum and minimum value of permittivity, respectively] and as low a dielectric loss as possible. To date, there have been extensive studies to increase the dielectric tunability and to reduce the dielectric loss of BST thin films grown on single crystal substrates such as LaAlO 3 [2] and MgO [3], among others, however, the use of these substrates is associated with major drawbacks from an industrial point of view due to their high cost and small-sized geometry [4,5]. Furthermore, the mounting techniques of components during the fabrication of hybrid microwave-integrated circuits are not simple.…”