Thin titanium oxide films deposited by e-beam evaporation with additional rapid thermal oxidation and annealing for ISFET applications

Titanium oxide (TiO2) has been extensively applied in the medical area due to its proved biocompatibility with human cells [1]. This work presents the characterization of titanium oxide thin films as a potential dielectric to be applied in ion sensitive field-effect transistors. The films were obtained by rapid thermal oxidation and annealing (at 300, 600, 960 and 1200 °C) of thin titanium films of different thicknesses (5 nm, 10 nm and 20 nm) deposited by e-beam evaporation on silicon wafers. These films were analyzed as-deposited and after annealing in forming gas for 25 min by Ellipsometry, Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy (RAMAN), Atomic Force Microscopy (AFM), Rutherford Backscattering Spectroscopy (RBS) and Ti–K edge X-ray Absorption Near Edge Structure (XANES). Thin film thickness, roughness, surface grain sizes, refractive indexes and oxygen concentration depend on the oxidation and annealing temperature. Structural characterization showed mainly presence of the crystalline rutile phase, however, other oxides such Ti2O3, an interfacial SiO2 layer between the dielectric and the substrate and the anatase crystalline phase of TiO2 films were also identified. Electrical characteristics were obtained by means of I–V and C–V measured curves of Al/Si/TiOx/Al capacitors. These curves showed that the films had high dielectric constants between 12 and 33, interface charge density of about 1010/cm2 and leakage current density between 1 and 10−4 A/cm2. Field-effect transistors were fabricated in order to analyze ID x VDS and log ID × Bias curves. Early voltage value of −1629 V, ROUT value of 215 MΩ and slope of 100 mV/dec were determined for the 20 nm TiOx film thermally treated at 960 °C.