On the ferroelectric and piezoelectric properties of CSD derived hafnium-cerium-oxide thin films

Thin film capacitors utilizing ferroelectric Hf_xCe_1-xO₂ are fabricated on Pt substrates using the chemical solution deposition technique. The influence of the film thickness, Cerium content and annealing conditions on the ferroelectric properties are investigated. The phase composition is analyzed using grazing incidence x-ray diffraction. Hysteresis and piezoelectric displacement loops are recorded at various temperatures ranging from -150 °C to 150 °C. Fatigue, relaxation and capacitance measurements are carried out in a temperature range of 10 K to 450 K. The results show that the addition of Cerium between 10 mol% and 20 mol% to the Hafnium oxide material system can successfully stabilize the ferroelectric phase. The films yield a remanent polarization (2Pr) of up to 33.6 µC/cm². From piezoelectric displacement measurements, a d₃₃ coefficient of 10 pm/V can be extracted. In addition, relaxation based loss of polarization is improved compared to doped Hafnium-Zirconium based thin films.

Figure 1: Hystereses and displacement measurement of 130 nm thick Hafnium-Cerium-Oxide thin film (15 mol% Ce)

Figure 2: Dependence of the remanent polarization on the Cerium concentration