Piezoresistive and electrical properties of Cr containing diamond-like carbon films

In the present study Cr containing diamond-like carbon (DLC) films were deposited by radio frequency diode sputtering on polycrystalline alumina and monocrystalline silicon substrates. Piezoresistive properties and the thermal coefficient of resistance (TCR) were investigated. Structure and chemical composition of the synthesized films were studied by Raman scattering spectrometry and X-ray photoelectron spectroscopy (XPS). It was found, that the sp3/sp2 ratio in the synthesized Cr, containing DLC films, increased with C2H2/Ar gas flux ratio, while Cr atomic concentration in the deposited DLC films decreased with the increase of C2H2/Ar gas flux ratio. For the Raman scattering spectra of the samples deposited by using 1 and 1.5% C2H2/Ar gas flux ratio, photoluminescence background was observed. It was revealed, that gauge factor of Cr containing DLC films increased with increase of the C2H2/Ar gas flux ratio. The gauge factor of Cr containing DLC films deposited by using > 1.5% C2H2/Ar gas flux was directly proportional to the sp3/sp2 ratio and increased with decrease of the sp2 cluster size. TCR of those films decreased with the decrease of sp3/sp2 ratio and increase of the sp2 cluster size. TCR increased at higher C2H2/Ar flux ratios, while negative TCR was observed for Cr containing DLC film deposited by using C2H2/Ar gas flux ratio 1.5%. The gauge factor and TCR of Cr containing DLC films linearly decreased with increase of the Cr/C atomic concentration ratio. The gauge factor of Cr containing DLC films increased with resistance by law k ~ log(R). The observed results are in good accordance with the percolation model of conductor–insulator compounds.