Broadband dielectric spectroscopy of Ruddlesden–Popper Srn+1TinO3n+1 (n=1,2,3) thin films

Abstract

We explore the frequency-dependent relative permittivity of Ruddlesden-Popper series Sr n+1 Ti n O 3n+1 (n = 1, 2, 3) thin films as a function of temperature and dc electric field. Interdigitated capacitors and coplanar waveguides were used to extract the frequency response from 500 Hz to 40 GHz. At room temperature, the in-plane relative permittivities (ǫ 11 ) obtained for Sr n+1 Ti n O 3n+1 (n = 1, 2, 3) were 42±3, 54±3, and 77±2, respectively, and were independent of frequency. At low temperatures, ǫ 11 increases and electric field tunability develops in Sr 4 Ti 3 O 10 . 1The Ruddlesden-Popper (RP) homologous series Sr n+1 Ti n O 3n+1 is a unique set of materials whose dielectric properties have yet to be fully explored and have the potential for far reaching applications much like SrTiO 3 , the n = ∞ member of this series [1]. Series members n = 1, 2, 3 are predicted to have fairly high relative permittivities [2]. Although historically RP materials have been the focus of a variety of theoretical [2,3,4] and experimental [5,6,7,8] research, until the recent growth of single-phase RP thin-films [9,10,11,12,13,14,15,16,17], detailed dielectric measurements of single-phase materials have been challenging [18]. The synthesis of stable, singlephase RP thin films opens new possiblities for applications in multilayer heterostructures and suggests experiments to explore the role of their unique crystal structures in ferroelectricity [19].The Sr n+1 Ti n O 3n+1 RP series is of particular interest, because SrTiO 3 is already commonly used in a number of applications: a substrate for perovskite films, integrated nonlinear compensation devices [20], and to enhance ferroelectricity [21]. When strained, SrTiO 3 can exhibit ferroelectricity even at room temperature and at modest bias fields [22]. This increase in tunability unfortunately signifies a remarkable increase in both the relative permittivity and loss, rendering them less useful for high-frequency applications. The Sr n+1 Ti n O 3n+1 RP series may provide a new class of tunable materials which have decreased loss, yet still retain many of the characteristics that make SrTiO 3 so useful.Typical radio frequency dielectric measurements focus on a single frequency [13] or a small range of frequencies, even though frequency dependence carries important information about disorder and relaxation mechanisms. Resonant techniques, such as evanescent microwave microscopy, yield very accurate measurements of local material properties, but are limited in their ability to extract broadband frequency information [23,24]. Consequently, lumped element capacitors are often used, an example of which are interdigitated capacitors (IDCs). Distributed effects, which are often overlooked, can compromise results from such devices at high frequencies, where the guided wavelength is comparable to the length of the device [25].Here, we report quantitative measurements of in-plane relative permittivity (ǫ 11 ) for Sr n+1 Ti n O 3n+1 thin films (n = 1, 2, 3) by means of an ultra-wide...

Influence of the central mode and soft phonon on the microwave dielectric loss near the strain-induced ferroelectric phase transitions inSrn+1TiGoian1, Kamba2, Orloff3 et al. 2014Phys. Rev. B13280View full textAdd to dashboardCite

“…At room temperature, the relative ε increases from 37 (for n = 1) to 100 (for n = 4) [10]. On cooling, ε and its temperature dependence increases with the parameter n, but no FE phase transition has been observed even down to liquid helium temperatures [11,12]. Interestingly, the permittivity exhibits no frequency dispersion in the MW region [11,12]; therefore, Sr n+1 Ti n O 3n+1 ceramics and unstrained films exhibit low dielectric loss, making them attractive for low-temperature MW devices [13].…”

“…As shown in several reports [10,11], the Sr n+1 Ti n O 3n+1 series is of particular interest. Notably, the parameter n enables the value of ε in Sr n+1 Ti n O 3n+1 to * Corresponding author: kamba@fzu.cz be tuned in ceramics [10] and thin films [12]. At room temperature, the relative ε increases from 37 (for n = 1) to 100 (for n = 4) [10].…”

“…On cooling, ε and its temperature dependence increases with the parameter n, but no FE phase transition has been observed even down to liquid helium temperatures [11,12]. Interestingly, the permittivity exhibits no frequency dispersion in the MW region [11,12]; therefore, Sr n+1 Ti n O 3n+1 ceramics and unstrained films exhibit low dielectric loss, making them attractive for low-temperature MW devices [13]. The n = ∞ end member of the RP series, bulk SrTiO 3 , has ε = 290 at 300 K. SrTiO 3 is perhaps the bestknown quantum paraelectric material, where ε increases on cooling, saturating at ß25 000 below 10 K [14].…”

Quantitative Nanometer‐Scale Mapping of Dielectric Tunability

“…[5][6][7] Apparently, such approach is capable of delivering information only about fi lm properties averaged over a relatively large area. While this can be appropriate for single-crystalline epitaxial thin fi lms, the information about properties of single morphological elements of polycrystalline fi lms-such as fabricated by magnetron sputtering-cannot be obtained.…”

The Controlled Synthesis of Metastable Oxides Utilizing Epitaxy and Epitaxial Stabilization

“…The preparation of these materials as epitaxial films has allowed their properties to be explored. The full dielectric constant tensor of the Sr n11 Ti n O 3n11 epitaxial films has been measured 377 as a function of frequency and temperature and compared with theory. 378 Preparation of the n 5 1-5 Sr n11 Ru n O 3n11 Ruddlesden-Popper phases has allowed the effects of dimensionality on the magnetic properties of these phases to be established.…”