Thermochemistry and electrical contact properties at the interface between semiconducting BaTiO 3 and (AuTi) electrodes

  • PDF / 166,040 Bytes
  • 4 Pages / 612 x 792 pts (letter) Page_size
  • 81 Downloads / 242 Views

DOWNLOAD

REPORT


MATERIALS RESEARCH

Welcome

Comments

Help

Thermochemistry and electrical contact properties at the interface between semiconducting BaTiO3 and (Au–Ti) electrodes David P. Cann and Clive A. Randall The Center for Dielectric Studies, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 18 July 1996; accepted 11 March 1997)

The interfacial characteristics of positive temperature coefficient of resistance (PTCR) BaTiO3 -electrode interfaces were studied. Sessile drop wetting experiments in combination with measurements of the contact resistance of the interface were used to establish a fundamental perspective of the electrode-ceramic interface. It was shown that the thermodynamic work of adhesion sWad d, which is the sum of the strengths of chemical interactions present at the interface, can be manipulated by the addition of chemically active elements to the electrode metal which enhance adhesion. This same procedure is shown to modify the important electrical interfacial properties such as the contact resistance.

Electrode contacts to semiconducting oxides in thermistor applications are required to have a high conductivity and to form an ohmic contact to the semiconductor.1 With continued trends in miniaturization, there exists a need to further understand the area of electroding of electroceramic materials. Early studies of the Schottky barriers in semiconducting perovskite systems include BaTiO3 , 2–10 SrTiO3 ,11 K(Ta, Nb)O3 ,8,12–14 and TiO2 .5,15 There exists a great deal of scatter in the magnitudes of the barrier heights presumably due to variations in the processing and surface characteristics of the semiconductor substrates. In Heywang’s2 work on the electrical properties of PTCR BaTiO3 thermistors, the contact resistance of a number of different metals was measured. The general trend was observed that metals which have a large affinity for oxygen tended to yield ohmic contacts (e.g., Zn, Fe, Sn, Ni, and Cd). More noble metals, such as Au, Pd, and Cu, produced non-ohmic contacts. The compositional dependence of the Schottky barrier height on semiconductors has been studied extensively in the literature.16–20 In general, the electrical properties of the interface are related to the chemical stability of the phases present at the interface. From the work of Brillson,18 it was found that strong chemical interactions at the interface produce low barrier heights, while chemically inert interfaces tended to have large barrier heights. Typically, predictions about an electrode’s ohmic or non-ohmic character are based upon its driving force for a chemical reaction with the semiconducting substrate. Parameters such as the free energy of formation of an interfacial phase and the free energy of formation (dissociation) of the semiconductor are often used as a measure of the chemical stability J. Mater. Res., Vol. 12, No. 7, Jul 1997

http://journals.cambridge.org

Downloaded: 05 Apr 2015

of the electrode-semiconductor interface, and hence the contact properties. In this work, the thermod

Data Loading...