Influence of deposition time on the microstructure and dielectric properties of AlN/Si thin films for enhanced hydrogen sensing application

Abstract

Thin films of aluminum nitride (AlN) were prepared on Si (100) substrate by dc reactive magnetron sputtering. The influence of sputter deposition time on the properties of the AlN films was studied. The films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR) and Scanning Electron Microscope. Dielectric properties of the film were investigated using impedance analyzer. XRD measurements showed the presence of hexagonal wurtzite structure. The crystal orientation of the AlN films changed from (100) to (002) with increase in deposition time. The peak found in FTIR spectra was attributed to A1 (To) phonon modes. The morphology of the film improved with the increase in deposition time. MIS capacitors were fabricated on n type silicon substrates, and the dependence of dielectric parameters with deposition time was investigated. Dielectric constants of 6.0–6.8 were obtained at 1MHz. Response of AlN/Si films of different thicknesses, with Al and Pd catalytic over layers, was investigated for 50ppm hydrogen. Pd/AlN/Si device fabricated with 114nm layer of AlN revealed an enhanced response in the C–V characteristics, while Al/AlN/Si device did not show any effect, indicating that the hydrogen sensitivity is highly dependent on the gate outer surface and deposition time.