Perovskites

Sputtertarget auf einer Vakuumkammer

Thin Films and Interfaces of Dielectric and Ferroelectric Perovskites

Perovskites are important materials for electronic and electromechanical devices. They are used e.g. in metal-insulator-metal thin film capacitor stacks in storage devices or as actuators for mechanical positioning and fuel injection. Prototype perovskite materials are SrTiO3 and BaTiO3. Perovskites can be dielectric (like SrTiO3) or ferroelectric. The most widely used ferroelectric materials are BaTiO3 and Pb(Zr,Ti)O3 (PZT).

Metallic electrodes are typically required for device operation. It is well known that the choice of the metal electrode can considerably impact the performance, which at least is partially related to the possibility for charge injection at the interface. This can particularly occur if the barrier height at the interface is small. The metallic contact can have a strong impact on the leakage current behaviour. In addition, dielectric properties, cycling stability, and dielectric losses are influenced by the contact properties.

In the frame of the collaborative research center SFB 595, we are studying the influence of electrodes on the electrical fatigue of ceramic PZT actuators. We are developing dedicated electrodes for controlled suppression or enhancement of charge injection. The electronic and chemical structure of the electrodes is characterized by XPS/UPS.

Research

XPS survey spectra of an in-situ prepared (Ba,Sr)TiO3 thin film
XPS survey spectra of an in-situ prepared (Ba,Sr)TiO3 thin film

We are studying the chemical and electronic structure of the interfaces of perovskites using photoelectron spectroscopy in order to understand basic mechanisms of contact formation and their impact on device performance. In one project thin films of (Ba,Sr)TiO3 are prepared by magnetron sputtering and processed by our colleagues in the electrical engineering department to tunable capacitors for microwave applications. In addition we are studying the barrier formation with different metals. Our experimental setup (DAISY-Mat) allows for in-situ analysis of interface formation using photoelectron spectroscopy.

General Information on Materials

  • R. Waser, Nanoelectronics and Information Technology, (Wiley-VCH, Weinheim, 2003)
  • A. J. Moulson, J M Herbert, Electroceramics, (John Wiley & Sons, 2003)

Studied Systems

  • Sputter deposition of (Ba,Sr)TiO3 and BaTiO3 thin films
  • Interface formation of (Ba,Sr)TiO3 and BaTiO3 with different metals
  • Dependence of SrTiO3/Pt and (Ba,Sr)TiO3/Pt barrier height on processing
  • Interface formation between SrTiO3 and RuO2
  • Interface formation between SiO2 and (Ba,Sr)TiO3
  • Interface between PZT and Ag
Barrier heights at Pt/SrTiO3/Pt stacks as determined from XPS. The barrier height at the top electrode is increased after annealing in oxygen.
Barrier heights at Pt/SrTiO3/Pt stacks as determined from XPS. The barrier height at the top electrode is increased after annealing in oxygen.

Cooperations

  • Microwave Components: Prof. Rolf Jakoby, Electrical Engineering, TU Darmstadt
  • Electrical Properties of PZT: Prof. Heinz von Seggern, Materials Science, TU Darmstadt
  • Dielectric Properties and Interfaces: Dr. Mario Maglione, ICMCB, Bordeaux, France. This cooperation is embedded in the European Network of Excellence FAME

Publications

A list of publications concerning this field is soon to follow.