The effect of temperature and humidity on interdiffusion of gold and titanium in thin films

Gold-titanium thin films are frequently used in a number of devices where gold is the conductor and titanium the bonding agent between gold and glass or ceramic substrates. Exposed to the corrosive environments, gold-titanium metallizations deteriorate and lead to failure of the devices. In this work, a preliminary study, the effect of humidity and temperature on interdiffusion of gold and titanium films was investigated. It was found that during the initial exposure period of gold-titanium thin film samples, the electrical resistance decreased. This decrease of electrical resistance occurs at temperatures as low as 70° C and can probably be ascribed to annealing processes in the samples. Exposure of the samples to higher temperatures results in the diffusion of titanium along the grain boundaries of the gold to the surface of the sample and in an increase of electrical resistance. It was observed that at 325° C titanium diffuses from grain boundaries into the gold grains and forms a gold-titanium alloy. An addition of the water vapour to the agron atmosphere does not noticeably affect the diffusion process. Optical microscope observations, of the titanium diffusion to the sample surface were confirmed by scanning electron microscopy and by X-ray fluoroscence counts in a scanning electron microscope.