Electrical properties and thermistor behavior of TiAlN thin films deposited by combinatorial sputtering

Abstract

A combinatorial deposition was performed by direct current magnetron sputtering (DCMS) to develop Ti1-xAlxN thin films with different Ti/Al ratios and investigate the electrical response to temperature. The crystal structure as a function of the x was studied by X-ray diffraction, and sheet resistance response was measured up to 200 °C. From x = 0.16 to x = 0.56, the film shows an fcc phase with Al in solid solution in the TiN matrix, whilst, from x ≥ 0.69, a mixture of hcp (AlN) and fcc phases is observed. A negative temperature coefficient (NTC) thermistor behavior was found from x = 0.21 onwards, and a maximum sensitivity β of 1600 K was observed for x = 0.56 and 0.69. One fcc sample (x = 0.46) was selected to analyze the chemical states by X-ray photoelectron spectroscopy and the impedance behavior with the temperature by electrical impedance spectroscopy. The crystal structure, bond states and impedance analysis were compared with an AlN thin film. It is concluded that the conduction mechanism for x = 0.46 is based upon electron hopping, and the effect of the grain boundary is more relevant than the grain at low temperatures. We demonstrate that it is possible to use TiAlN as an NTC-thermistor with different crystal structures and chemical compositions.