Impact of top (Pt, Au, and Al) electrodes on HfAl O_x -based MIM capacitors

The electrical and dielectric properties of HfAl O_x films deposited by radio frequency magnetron cosputtering of Hf O₂ and Al₂ O₃ targets with Au as the bottom electrode and Pt, Au, and Al as the top electrodes forming metal-insulator-metal (MIM) structures have been studied. HfAl O_x layers are characterized by X-ray photoelectron spectroscopy to examine the chemical composition. Atomic force microscopy morphology study shows that root mean square value of surface roughness of the film decreases after annealing. From grazing incidence X-ray diffraction study, it is observed that the deposited films remain amorphous up to 600°C annealing temperature. For electrical characterization, current-voltage and capacitance-voltage characteristics were studied in the frequency range of 1 kHz-1 MHz. MIM capacitors with Pt (φ_pt ∼5.6 eV) top electrode were found to have the lowest leakage current of ∼6× 10^-6 A cm^-2 (at -1 V) and low energy dissipation with improved voltage coefficients of capacitance values (81 ppm/ V²). Low field (<1 MV/cm) conduction mechanism was found to be dominated by Schottky emission, while at high field (>1 MV/cm) it is dominated by Poole-Frenkel mechanism. Change in the quadratic voltage coefficient of capacitance under different stress voltages was found to be the lowest with Pt top electrode.