Polycrystalline Ba0.6Sr0.4TiO3 thin films on r-plane sapphire: Effect of film thickness on strain and dielectric properties

Abstract

Polycrystalline Ba 0.6 Sr 0.4 TiO 3 ͑BST͒ films grown on r-plane sapphire exhibit strong variation of in-plane strain over the thickness range of 25-400 nm. At a critical thickness of ϳ200 nm, the films are strain relieved; in thinner films, the strain is tensile, while compressive strain was observed in the 400 nm film. Microwave properties of the films were measured from 1 to 20 GHz by the interdigital capacitor method. A capacitance tunability of 64% was observed in the 200 nm film, while thinner films showed improved Q factor. These results demonstrate the possibility of incorporating frequency agile BST-based devices into the silicon on sapphire process.

Effect of crystal orientation on the segregation of aliovalent dopants at the surface of La0.6Sr0.4CoO3

“…19,20 Surface degradation of perovskites oen takes place in the form of enrichment of dopant cations at the surface and the formation of dopant-rich insulating phases such as SrO. 19,21,22 For example, although La 0.6 Sr 0.4 CoO 3 (LSC64) is one of the promising cathode materials, having a very low area specic resistance of 0.01 ohm cm 2 at 600 C, it is not stable and undergoes dopant segregation and phase separation at its surface at elevated temperatures. 23 Segregation of the dopant Sr and precipitation of SrO-like insulating phases at the cathode surface may result in the complete coverage of the surface.…”

LOW THIRD-ORDER INTERMODULATION DISTORTION IN Ba_0.6Sr_0.4TiO₃ THIN FILM INTERDIGITAL CAPACITORS

“…Note that the highest tunability of 64% was recorded with the 200 nm BST films but compensated by the lowest Q-factor in the range of ∼ 7.8 to 32.2 [4]. The reduction in the tunability of the measured 50 nm BST film was caused by the tensile strain.…”

“…The BST thin films were initially deposited on the 500 µm thick sapphire substrates by pulsed laser deposition (PLD). The details of the BST thin film deposition and material characterisation can be found in [4,14]. The fabrication of IDCs was realized in a multistep process.…”

“…This technology uses a very thin layer of silicon deposited on an r-plane sapphire substrate, which provides a suitable orientation for the growth of silicon [3]. By depositing the BST film early in the SoS process, the high deposition temperature can be tolerated without affecting the silicon epilayer [4]. Some frequency agile microwave devices that have the potential to be incorporated in this technology had been developed with epitaxial BST thin films on rplane sapphire substrates at 10 GHz and above such as interdigital capacitors (IDCs) [4], bandpass filters [5] and phase shifters [6].…”

Effect of oxygen pressure on preferential orientation, microstructure and functional properties of Bi1.5MgNb1.5O7 thin films prepared by pulsed laser deposition

“…In such applications, it is desirable to possess a low dielectric loss and a large dielectric constant change ratio (tunability = (ε max − ε min )/ε max ) by applying a relatively low electric field [4,5]. Ba 1−x Sr x TiO 3 (BST) has attractive much attention as a promising candidate because of its unique combination of high dielectric constant and large tunability [6][7][8][9]. However, BST thin films have the essential problem of high dielectric loss [10,11].…”