Polarization Relaxation Induced by Depolarization Field in Ultrathin   Ferroelectric BaTiO$_3$ Capacitors
  Time-dependent polarization relaxation behaviors induced by a depolarization field $E_{d}$ were investigated on high-quality ultrathin SrRuO$_{3}$/BaTiO$_{3}$/SrRuO$_{3}$ capacitors. The $E_d$ values were determined experimentally from an applied external field to stop the net polarization relaxation. These values agree with those from the electrostatic calculations, demonstrating that a large $E_{d}$ inside the ultrathin ferroelectric layer could cause severe polarization relaxation. For numerous ferroelectric devices of capacitor configuration, this effect will set a stricter size limit than the critical thickness issue. 
D. J. Kim, J. Y. Jo, Y. S. Kim, Y. J. Chang, J. S. Lee, Jong-Gul Yoon,   T. K. Song, T. W. Noh