RF-magnetron sputtering deposition of ultra-thin Hf_0.5Zr_0.5O₂ films for non-volatile memory applications

This study reports on-axis sputter deposition of Hf_0.5Zr_0.5O₂ thin films on platinized silicon substrates (Pt/Al₂O₂/SiO₂/Si) as well as boron doped silicon substrates (P-Si), using a table top RF-magnetron sputtering unit. Through optimization steps of deposition parameters, as revealed by X-ray photoelectron spectroscopy, stoichiometric Hf_0.5Zr_0.5O₂ films were obtained at low sputtering pressure of 5 mTorr and a power density ∼4W/cm². Fine grained surface morphology for Hf_0.5Zr_0.5O₂ films and rms roughness comparable to the underlying Pt surface were observed by atomic force microscopy. The effect of synthesis temperature and film thickness on the ferroelectric properties was investigated by piezoresponse force microscopy. Ferroelectricity in a two unit cell-thick layer of Hf_0.5Zr_0.5O₂ (t≈1nm) was observed. This result is of great interest for the fabrication of ferroelectric tunnel junction memories. Furthermore, current-voltage measurements confirm that resistive switching occurs in 7-nm thick Hf_0.5Zr_0.5O₂ samples, suggesting another potential application as a resistive random access memory.