ACTIVATION FIELD OF FERROELECTRIC (PB,LA)(ZR,TI)O-3 THIN-FILM CAPACITORS

We report results on the activation field and frequency dependence of the coercive voltage in epitaxial ferroelectric thin film capacitors. Frequency dependent hysteresis loops and pulse width dependent polariz ation of epitaxial La0.5Sr0.5CoO3/(Pb,La)(Zr,Ti)O-3/La0.5Sr0.5CoO3 cap acitor structures were measured as a function of La content. The coerc ive voltages and their frequency dependence vary systematically with i ncreasing La content. We show that the activation field for polarizati on reversal is directly related to the c/a ratio (tetragonality ratio) of the ferroelectric layer. A larger c/a ratio leads to a larger fiel d to activate the motion of domain walls through the lattice. An impor tant consequence of a larger activation field is a stronger pulse widt h dependence of the pulse switched polarization. (C) 1997 American Ins titute of Physics.