Soft-mode hardening in SrTiO3 thin films

A. A. Sirenko, C. Bernhard, A. Golnik, Anna M. Clark, Jlanhua Hao, Weldong Si, X. X. Xi

Research output: Contribution to journalArticlepeer-review

231 Scopus citations

Abstract

Understanding the behaviour of the dielectric constant in ferroelectric thin films remains a challenging problem. These ferroelectric materials have high static dielectric constants, and so are important for their applications in high-storage-density capacitor structures such as dynamic random access memory (DRAM). But the dielectric constant tends to be significantly reduced in thin films, thereby limiting the potential benefit of ferroelectrics for memory devices. Extensive studies have shown that this phenomenon could be caused by a 'dead layer' of very low dielectric constant between the ferroeletric film and the electrode. And, although very few direct measurements are in fact available, it has been recognized that the lattice dynamical properties in the thin films should also play a key role in the reduction of the dielectric constant. Here we report far-infrared ellipsometry and low-frequency dielectric measurements in SrTiO3 thin films, which demonstrate that the Lyddane-Sachs-Teller relation between the optical- phonon eigenfrequencies and the dielectric constant is fully maintained, as is the case in the bulk material. This indicates that the dramatic reduction of the dielectric constant is a consequence of a profound change of the lattice dynamical properties, in particular of the reduced softening of its lowest optical-phonon mode. Our results therefore provide a better understanding of the fundamental limitations of the dielectric constant values in ferroelectric thin films.

Original languageEnglish (US)
Pages (from-to)373-376
Number of pages4
JournalNature
Volume404
Issue number6776
DOIs
StatePublished - Mar 23 2000
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General

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