Determination of diffusion in polycrystalline platinum thin films

Grain boundary diffusion of titanium through platinum thin films has been c arried out in the temperature range from 200 to 600 degrees C. Five differe nt platinum/titanium bilayer thicknesses, from 35 to 800 Angstrom Pt, were annealed in 5% O-2/95% N-2. The accumulation of titanium at the platinum su rface layer was measured by x-ray photoelectron spectroscopy (XPS) to deter mine the grain boundary diffusion coefficient (D-b). Diffusivity values wer e calculated based on two different analysis methods assuming type C kineti cs. For Pt layers thicker than 200 Angstrom, the activation energy (Q(b)) f or titanium diffusion was found to be 118 +/- 15 kJ/mol (1.22 +/- 0.16 eV). For Pt layers thinner than 200 Angstrom, there was a thickness dependence on the diffusion kinetics, resulting in activation energies as low as 20 +/ - 4 kJ/mol (0.21 +/- 0.04 eV). XPS results gave no evidence for any Pt-Ti a lloy formation in these layers. The suppression of alloy formation may be a ttributed to the presence of oxygen at the Pt/Ti interface during layer dep osition. The quantitative analysis of titanium interdiffusion in platinum p rovides valuable information regarding Pt/Ti surface concentrations in thin -film chemical sensors, and for understanding changes in operational charac teristics of platinum electrodes. (C) 1999 American Institute of Physics. [ S0021-8979(99)04321-2].