Proceedings Article | 7 September 2001
KEYWORDS: Copper, Aluminum, Resistance, Oxides, Metals, FT-IR spectroscopy, Sputter deposition, Absorption, Transparency, Thin films
A novel class of complex metal oxides that have potential as transparent conducting oxides (TCOs) for the electromagnetic-interference (EMI) shielding on IR-seeker windows and missile domes has been identified. These complex metal oxides exhibit the rhombohedral (R3m) crystalline structure of naturally occurring delafossite, CuFeO2. The general chemical formula is ABO2 where A is a monovalent metal (Me+1 such as Cu, Ag, Au, Pt or Pd, and B is a trivalent metal (Me3+) such as Al,Ti,Cr,Co,Fe,Ni,Cs,Rh,Ga,Sn,In,Y,La,Pr,Nd,Sm or Eu. By adjusting the oxygen content, the conductivity can be varied over a wide range so that the delafossites behave as insulators, semiconductors or metals. This paper presents results for films of p-type CuxAlyOz and n-type CuxCryOz deposited by reactive magnetron co-sputtering from high-purity-metal targets. Films have been deposited using conventional RF- and DC-power supplies, and a new asymmetric-bipolar-pulsed- DC-power supply. Similar to the high-temperature-copper- oxide superconductors, the presence of Cu-O bonds is critical for the unique properties. Fourier transform infrared (FTIR) and electron spectroscopy for chemical analysis (ESCA) are used to understand the relationship between the optoelectornic properties and the molecular structure of the films. For example, FTIR absorption bands at 1470 and 1395cm-1 are present only in CuxAlyOz films that exhibit enhanced electrical conductivity. When these bands are absent, the CuxAlyOz films have high values of resistivity. In addition to the 1470 and 1395cm-1 bands observed in CuxAlyOz films, another pair of bands at 1040 and 970cm-1 is present in CuxCryOz films.
