Comparison of memory effect between YMnO₃ and SrBi₂Ta₂O₉ ferroelectric thin films deposited on Si substrates

For the ferroelectric gate-type capacitors, we have fabricated Pt/YMnO₃(YMO)/Si and Pt/SrBi₂Ta₂O₉(SBT)/Si structures. We have used the highly c-axis oriented hexagonal YMO thin films (εr ≈ 19) and the polycrystalline SBT thin films (ε_r ≈ 150) with a dominant (115) orientation, respectively. The memory effect resulting from the ferroelectric switching properties is investigated as a function of the dielectric constant of ferroelectric thin films with 150 nm in thickness. About 3 times wider memory window is obtained by using a relatively low dielectric constant of YMO than that using a relatively high dielectric constant of SBT. Typical memory windows of the Pt/YMO/Si and the Pt/SBT/Si capacitors are 1.24 and 0.34 V, respectively, at a gate voltage of 5 V.