Effect of nitrogen partial pressure on the piezoresistivity of magnetron sputtered ITO thin films at high temperatures

Various ITO thin films were deposited by RF magnetron sputtering with different nitrogen partial pressure (NPP) of 10 %∼40 % to quantitatively modify their high temperatures piezoresistivity. The valence band structures and element states of the ITO thin films were examined by X-ray photoelectron spectroscopy. Results show that the Fermi energy level (EF) shifts closer to the maximum energy of valence band with the growth of the NPP, which will cause a reduction of the number of electrons ionized to the conduction band. The 20 %N2 ITO thin film shows the smallest content change rates of nitrogen (3.8 %) and oxygen (1.6 %) after the piezoresistivity test at 600 °C, 800 °C and 1000 °C. The lowest resistance drift rate was also observed in the 20 %N2 ITO thin film in the above test due to its chemical stability of the incorporated nitrogen. Moreover, the gauge factor (GF) declines from 2.28 to 1.48 with the increase of the NPP at 600 °C due to the decline of the amounts of electrons ionized to the conduction band since the shift of the EF. The 20 %N2 ITO thin film strain gauge has the highest GF at 800 °C and 1000 °C owing to its smallest content change rates.