Effects of rare earth Eu doping on ferroelectric properties of PbZr 0.52Ti 0.48O 3 thin films by sol–gel methods

Abstract

Samples of (100)-oriented PZT thin films with 0–2 at% rare earth Eu dopant (PEZT) were fabricated on (111)Pt/Ti/SiO 2/Si substrate by a sol–gel method. Ferroelectric properties such as P– V loop, C– V and I– V characteristics were investigated with RT-66A tester and HP4194 impendence analyzer, respectively. Improved polarization ( P r=37.5 μC/cm 2), the low leakage current ( J=1×10 −9 A/cm 2 at the electric field of 400 mV/m) were obtained in the PZT thin films with 1 at% Eu dopant (denoted as PEZT1), comparing to the pure PZT thin films ( P r=30.4 μC/cm 2, J=5×10 −9 A/cm 2 at the electric field of 400 mV/m). The Rayleigh constant was introduced to clarify the nature of Eu doping effects on the ferroelectric properties of PZT thin films. Up to 1 at% Eu dopant, the Rayleigh constant reaches its highest value, which indicates the minimal intrinsic defects in the PEZT1 lattice. According to the plot of ionic radii vs. % B site occupancy of the added dopants, calculated by Roy et al. [Interg. Ferroelectrics 43 (2002) 373], Eu additive mainly occupied the A site and served as donor dopant. Therefore, it was speculated that the improvement of ferroelectric properties shown in the PEZT1 thin films is due to the minimal intrinsic defects present in the crystal lattice. The deteriorate effects exhibited in the PZT thin films with more than 2% Eu dopant (denoted as PEZT2) was caused by the increased intrinsic defects or the increased concentration of the B site substitution or acceptor dopants. As a demonstration, sharp and symmetric switching peaks were observed in PEZT1 film capacitors, while broadened and asymmetric switching peaks were shown in PEZT2 ones in the C– V curves, compared with pure PZT film capacitors.