Effect of oxidizing atmosphere on ferroelectric and piezoelectric response of CaBi2Nb2O9 thin films

Calcium bismuth niobate (CaBi2Nb2O9, CBNO) thin films were evaluated for use as lead-free piezoelectric in micro-electromechanical systems. The films were grown by the polymeric precursor method on Pt/Ti/SiO2/Si (1 0 0) (Pt) substrates and annealed at 700 °C for 2 h in ambient and oxygen atmospheric conditions. The films were characterized by means of XRD, Raman, IR, PFM and electrical measurements. Annealing in ambient condition leads to improved ferroelectric properties, higher fatigue and retention resistances, and improved piezoelectric response. Furthermore, oxygen atmosphere produces bismuth vacancies (V‴Bi) that inhibit the movement of domain walls along the z-axis, and consequently reduces the piezoelectric coefficient. Independently of the applied electric field, the retained switchable polarization approached a nearly steady-state value after a retention time of 10 s.