Role of film stoichiometry and interface quality in the performance of (Ba,Sr)TiO3 tunable capacitors with high figures of merit

Abstract

Parallel plate capacitors with quality factors exceeding 1000 were fabricated using Ba0.3Sr0.7TiO3 (BST) thin films grown by hybrid molecular beam epitaxy on epitaxial Pt bottom electrodes. The influence of film stoichiometry was investigated by varying the (Ba + Sr)/Ti ratio around the stoichiometric composition. The quality factor is highest for stoichiometric films, but (Ba + Sr)-rich films can be biased to higher fields. Furthermore, two different processes were used to deposit the top electrodes of the parallel plate capacitors. While the quality of the top contact/BST interface did not strongly affect the device quality factor, an enhancement in the dielectric tunability was seen for capacitors with top electrodes deposited at high temperatures, which effectively removes interfacial contamination layers.

Frontiers in the Growth of Complex Oxide Thin Films: Past, Present, and Future of Hybrid MBE

“…[159] RHEED was found to exhibit a c(4×4) reconstruction, similar to reports of SrTiO 3 , [131] however, on relaxed Ba 0.30 Sr 0.70 TiO 3 films the surfaces were found to contain additional crystalline phases when grown under both, stoichiometric and non-stoichiometric conditions. [215] The films were fully relaxed, and it was found that the lattice parameter linearly changed with composition x, as shown in Figure 27 samples. [216] In contrast, the quality factor for hMBE grown Ba 1-x Sr x TiO 3 larger than 1000 was found.…”

“…[212] Ba 1-x Sr x TiO 3 films were grown on SrTiO 3 after sputter deposition of 100-nm-thick epitaxial Pt layers used as bottom electrode. [212,215] Stoichiometric conditions were identified from the minimum out-of-plane lattice parameter for the compositions x = 0.19, 0.30, 0.35, 0.46. While this criteria is consistent with the stoichiometric condition of SrTiO 3 films [98] , it differs from that of BaTiO 3 .…”

Robust Tunability and Newly Emerged Q Resonance of Ba0.8Sr0.2TiO3-Based Microwave Capacitors under Gamma Irradiations

“…The trade-off between Q and n has long been stymieing the application of BST x -based tunable capacitance devices. Much effort has been devoted to innovating the Sr m+1 Ti m O 3m+1 Ruddlesden−Popper phase crystal structure 10,11 and utilizing the hybrid molecular beam epitaxy growth of defect-free high-quality BST x thin films 12,13 to extend their frequency limitations and figure of merits 14,15 by suppressing dielectric losses from local defects, 16 degenerate phonon distributions, 17,18 and polar regions in nanoscale. 19,20 Recently, a fundamentally distinct approach has been put forward to enhance the dielectric responses by the introduction of ferroelectric nanodomain structures in a Ba 0.8 Sr 0.2 TiO 3 (BST 0.8 ) thin film slightly below the Curie transition temperature, realizing an order of magnitude increase of n and high Q values simultaneously facilitated by the ferroelectric domain-wall fluctuation at room temperature.…”

Effect of internal interface layer on dielectric properties of doped Ba0.6Sr0.4TiO3 thin films and its simulation in filters

“…However, the performance of ferroelectric phase shifters and tunable filters is usually measured by the tunability (T r ) and quality factor (Q F ). Their definitions are as follows [12][13][14] T…”