High frequency tunable LC devices with ferroelectric/ferromagnetic thin film heterostructure

Abstract

Heterostructure tunable LC devices utilizing ferroelectric BST((Ba,Sr)TiO 3 ) and ferromagnetic LSMO((La,Sr)MnO 3 ) thin films were developed. Both LSMO and BST thin films were prepared by chemical solution deposition. New heterostructure tunable devices, which were composed of MIM-type ferroelectric C and spiral-type ferromagnetic L, were fabricated as the following order: ferromagnetic LSMO thin films were deposited on SiO 2 /Si substrate and platinum was deposited as a diffusion barrier and ferroelectric BST thin films were deposited and spiral-type metal (Pt/Ti) coils were patterned using lift-off process. The heterostructure tunable device showed large C-V tunability, 58% and also L-V tunability, 11.5% in voltage ranges of -10 V to + 10 V.1 Introduction Recently, there has been some progress in developing tunable microwave filters and phase shifters utilizing ferroelectric thin films with nonlinear C-V characteristics. RF tunable devices using ferroelectric thin film have faster C-V response, higher power in the GHz frequency range, and could be integrated with smaller and simpler structure as compared with other tunable devices using semiconductors or ferrites [1]. Among various ferroelectric thin films, BST((Ba,Sr)TiO 3 ) thin film is the most attractive candidate for microwave and millimeter-wave frequency devices such as varactors, tunable filters, and tunable phase shifters because of high tunability (field-dependent change of dielectric constant) and low dielectric loss at microwave frequencies [2 -8]. On the other hand, tunable microwave filters and phase shifters utilizing epitaxial ferroelectric/ferromagnetic/superconducting thin films with perovskite structures have been proposed [9]. Because both C and L of a microwave device can be simultaneously changed in this heterostructure, the resonance frequency f r (= 1/2 LC π ) and phase velocity v p (= 1/ LC ) determined by the LC product are very large while maintaining the transmission line characteristic impedance Z 0 (= / L C) that is specially an important property for a phase shifter, resulting in the reduced insertion loss generated between the device and transmission line [9]. Recently, there have been some preliminary reports on tunable microwave filters and phase shifters utilizing layered ferroelectricferromagnetic structure [10,11]. In this work, heterostructure tunable LC devices utilizing ferroelectric BST((Ba,Sr)TiO 3 ) and ferromagnetic LSMO((La,Sr)MnO 3 ) thin films were investigated. The tunable LC devices were composed of MIM-type ferroelectric C and spiral-type ferromagnetic L. LSMO and BST films were prepared on SiO 2 /Si substrates by chemical solution deposition (CSD). C-V and L-V tunabilities of the heterostructure tunable devices were measured. The resonance frequency f r and the

Microstructure of La0.7Sr0.3MnO3/Ba0.7Sr0.3TiO3/La0.7Sr0.3MnO3 epitaxial films grown on (001) SrTiO3 substrate

“…So far, several different conducting oxides, e.g. YBa 2 Cu 3 O 7-d , SrRuO 3 , (La x ,Sr 1Àx )CoO 3 and (La x ,Sr 1Àx )MnO 3 , etc., are proved to be suitable electrodes in epitaxial heterostructures with BST layers and have been used extensively [6][7][8][9]. High-quality films grown on each other are easily obtained for those perovskitetype conducting oxides and ferroelectric layers because of their similar structures and small mismatches in lattice parameters.…”

Influence of Thickness on the Magnetic and Magnetotransport Properties of Epitaxial La0.7Sr0.3MnO3 Films Deposited on STO (0 0 1)

“…Moreover, the room temperature magnetocaloric effect (with different substitutions on the Mn site, such as Ni [13][14][15], Co [16] Cr, St, Ti [17] or with no substitutions at all [18,19]), large planar Hall effect in La 0.7 Sr 0.3 MnO 3 films on MgO (1 0 0) [20], as well as magnetoelastic coupling at the interface between the La 2/3 Sr 1/3 MnO 3 thin films and SrTiO 3 (STO) substrate (due to the STO cubic-tetragonal transition [21]), can be noted. All of these above mentioned magneto-functionalities make La 1−x Sr x MnO 3 systems outstanding candidates for magnetic field sensors [22,23], high-density memory storage devices, tunnel magneto-resistance devices [24,25], pressure sensors [26], micro and nanomechanical resonant sensors [27], solid oxide fuel cells [28], spin injectors in organic spintronics [29] and references therein, non-volatile memory and memristive devices [30], spin light emitting diodes [31], organic light emitting devices (OLEDs) [32,33], spin wave resonance devices [34], uncooled infrared bolometers [35], microwave [36] and radio frequency [37] applications.…”

Tunability of Ferromagnetic (La,Sr) MnO<inf>3</inf> (LSMO) Thin Films for Microwave Applications

“…Furthermore, a differential resistance (dV/dI) at the ambient temperature due to magnetoresistance effect, has been presented in [26]. Ferromagnetic LSMO((La 0.67 , Sr 0.33 )MnO 3 ) thin films have been used in the context of microwave tunability or to assist tunability in other thin films materials such as tunable barium strontium titanate paraelectric films [27]. Recently; Wang et al have investigated the low frequency negative capacitance in La 0.8 Sr 0.2 MnO 3 /Nb-doped SrTiO 3 heterojunction.…”