Depletion width in SrTiO3and BaxSr1−xTiO3films

Abstract

This text summarizes only what was new in an invited review, the overal nature of which was to cover device models for ferroelectric thin film memories, including strontium bismuth tantalate (SBT), barium strontium titanate (BST), and lead zirconate titanate (PZT), generally on platinum electrodes. In the written version below I limit the discussion to BST DRAM films. Three problems associated with the earlier trap-free models of Dietz et al. are reconciled: Depletion widths (assumed by them to be as thick as the total film; effective Richardson coefficients A^**, found experimentally to be a million times smaller than predicted by trap-free models; and electronegativity coefficient S = dφ_Bn/dχ, assumed by them to be unity but actually ca. 0.7. Using the result that the value of the dielectric constant within the Schottky barrier in the work of Dietz et al. is ϵ = 5.5 = ϵ_op = n², where n is the index of refraction, I have calculated the value of the depletion width d. and find that it is < 10 nm, in disagreement with their conclusion that films ca. 200 nm thick are fully depleted.