Depletion width in SrTiO3 and BaxSr1-xTiO3 films

This text summarizes only what was new in an invited review, the overal nat ure of which was to cover device models for ferroelectric thin film memorie s, 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. Thre e problems associated with the earlier trap-free models of Dietz ct 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 mi llion times smaller than predicted by trap-free models; and electronegativi ty coefficient S = d Phi (Bn)/d chi, assumed by them to be unity but actual ly ca. 0.7. Using the result that the value of the dielectric constant with in the Schottky barrier in the work of Dietz et al. is epsilon = 5.5 = epsi lon (op) = n(2), where n is the index of refraction, I have calculated the value of the depletion width d, and find that it is < 10 nn, in disagreemen t with their conclusion that films ca. 200 nm thick are fully depleted.