Crystal Structure and Electric Properties of (100) Ba(Zr_xTi_1-x)O₃ Thin Films on MgO Substrates by Pulse Laser Deposition Technique

Microwave tunable devices are necessary components for next-generation communication applications. Ferrite, semiconductors, and ferroelectrics are typical tunable materials. Especially ferroelectric thin films have been studied for a long time because of their high dielectric constant and low power consumption. Moreover, microwave dielectric materials show advantages in terms of light weight, compactness, low loss, stability in temperature, and low cost in producing of communication devices. To date, (Ba_1-<i>x</i>Sr<i>_x</i>) TiO₃[BST] has become one of the most popular ferroelectric materials studied and used as tunable microwave devices. However, its dielectric loss is still large, and the temperature dependence of the dielectric constant remains insufficient for applications. It is desirable to have not only high dielectric constant and tunability in a certain electric field range but also low dielectric loss. Ba(Zr<i>_x</i>Ti_1-<i>x</i>)O₃[BZT] solid solutions are also tunable materials with potential use in devices for wireless communications, just above their Curie temperature in a paraelectric state. BZT is a possible alternative to BST in tunable microwave applications Zr⁴⁺ is chemically more stable than Ti⁴⁺ and maintains a low dielectric loss. Furthermore, BZT in the paraelectric phase has higher temperature stability than BST. Therefore, we focused on BZT thin films as a tunable ferroelectric material.<br/>In this work, we fabricated BZT (<i>x</i> = 0 ~ 1.0) thin films with 500nm thick by pulse laser deposition [PLD] technique on MgO(100) and (100)_cSrRuO₃//(100)BaZrO₃//(100)MgO substrates. It enables us to obtain preferential (100)-oriented BZT thin films. The structural properties of the films were characterized by x-ray diffraction [XRD] (MRD, PANalytical). Wavelength-dispersive x-ray fluorescence spectrometry [WDX] (PW2404, PANalytical) was carried out to investigate the composition and thickness of BZT thin films. All the XRD patterns showed only (001)/(100) diffraction peaks and no secondary phase. Reciprocal space mappings (RSMs) of BZT thin films showed that BZT thin films grew epitaxially on (100)MgO and (100)_cSrRuO₃//(100)BaZrO₃//(100)MgO substrates. The electrical properties of the BZT thin films were measured by an impedance analyzer (4194A, Agilent). <i>P-E </i>hysteresis loops of BZT films become increasingly slim in shape with increasing Zr content because of the decrease in grain size. The dielectric constant dependence of electric field indicated that tunability is high in the region of x = 0 ~ 0.5 BZT thin films. The composition dependence of tetragonality, remanent polarization, and dielectric constant suggested that there may be a phase boundary between <i>x</i> = 0.2 and 0.3, and this tendency is similar to BZT ceramics. Therefore, our result suggests that BZT (<i>x</i> = 0 ~ 0.5) can be one of the significant candidates for microwave application which requires high tunability and low loss.