Equivalent-circuit modeling of ferroelectric switching devices

A compact equivalent-circuit model for ferroelectric switching devices is derived from a general model for local charge displacements. The general model consists of a matrix of repeat units describing local dissipationless charge displacements (electrostatic channel), as well as dissipative charge displacements (electrochemical channel), the channels being coupled due to the electrical charge of the moving species. The derived model for ferroelectric charge displacements is used to simulate both hysteresis and transient characteristics, and applied to two devices: (i) a ferroelectric capacitor and (ii) a ferroelectric memory field-effect transistor. The circuits are programmed in SPICE-derived analysis software. We find that experimental hysteresis data obtained on Pb(Zr,Ti)O3 ceramic capacitors and on thin-film transistors with a SnO2:Sb semiconductor and a Pb(Zr,Ti)O3 ferroelectric insulator can be reproduced and interpreted with the equivalent-circuit models. © 1999 American Institute of Physics

Motion and accumulation of charge-carriers in organic semiconductors

Applied Science

Mobile Charge Carriers in Pulse-Irradiated Poly- and Oligothiophenes

Lower limits of the intrinsic charge carrier mobility in the solid phase of a series of oligothiophene compounds were determined with the pulse-radiolysis time-resolved microwave conductivity technique, PR-TRMC. The mobility values fall roughly into two regimes and show no correlation with the number of conjugated thiophene units. Relatively low mobilities (in the range of 3-6·10-4 cm2/Vs) were found for a series of cyclohexyl-endcapped thiophenes, while significantly higher values of 0.01-0.02 cm2/Vs were obtained for several n-hexyl and n-dodecyl substituted compounds and for sexithiophene. Interestingly, these latter values are similar to those of n-alkyl substituted polythiophenes measured earlier.