Composition dependence of the ferroelectric properties of lanthanum-modified bismuth titanate thin films grown by using pulsed-laser deposition

Lanthanum-modified bismuth titanate, Bi_{4-cursive Greek chi}La_{cursive Greek chi}Ti₃O₁₂ (BLT), thin films with a La concentration of 0.25≤ cursive Greek chi ≤1.00 were grown on Pt/Ti/SO₂/Si substrates by using pulsed-laser deposition. The BLT films showed well-saturated polarization-electric field curves whose remnant polarizations were 16.1 μC/cm², 27.8 μC/cm², 19.6 μC/cm², and 2.7 μC/cm², respectively, for cursive Greek chi=0.25, 0.50, 0.75, and 1.00. The fatigue characteristics became better with increasing cursive Greek chi up to 0.75. The Au/BLT/Pt capacitor with a La concentration of 0.50 showed an interesting dependence of the remanent polarization on the number of repetitive read/write cycles. On the other hand, the capacitor with a La concentration of 0.75 showed fatigue-free characteristics.