A dynamic ferroelectric capacitance model for circuit simulators
A dynamic model has been developed that is based on the Preisach approach for ferroelectric capacitors. It accounts for different switching reaction of the dipoles dependent on the applied voltage gradients. A method for extracting the necessary parameters by measuring the coercive voltage versus applied frequency is provided. The model was verified by testing capacitors of different geometries. Excellent agreement was achieved between our measurements and the corresponding circuit simulations. The simulation of a FeRAM-cell with our new dynamic model shows that the bit line signal decreases substantially with fast read/write times.
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 (cid:126) electrostatic channel (cid:33) , as well as dissipative charge displacements (cid:126) electrochemical channel (cid:33) , 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: (cid:126) i (cid:33) a ferroelectric capacitor and (cid:126) ii (cid:33) a ferroelectric memory ﬁeld-effect transistor. The circuits are programmed in SPICE-derived analysis software. We ﬁnd that experimental hysteresis data obtained on Pb (cid:126) Zr,Ti (cid:33) O 3 ceramic capacitors and on thin-ﬁlm transistors with a SnO 2 :Sb semiconductor and a Pb (cid:126) Zr,Ti (cid:33) O 3 ferroelectric insulator can be reproduced and interpreted with the equivalent-circuit models. © 1999 American Institute of Physics. (cid:64) S0021-8979 99 02011-3 (cid:35)
Inhibition of Mild Steel Corrosion Using L-tryptophan and Synergistic Surfactant Additives
The corrosion inhibition characteristics of nitrogen containing amino acid L-tryptophan on mild steel in 0.1 M HCl solution, in the temperature range of 30-50 o C, was studied by weight loss and potentiodynamic polarization measurements. L-tryptophan significantly reduces the corrosion rates of mild steel; the maximum inhibition efficiency being 83% at 50 o C in presence of inhibitor concentration of 500 ppm. The effect of the addition of very small concentrations of anionic surfactant, sodium dodecyl sulfate (SDS), and of cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), on the corrosion inhibition behavior of L-tryptophan was also studied. The inhibition efficiency (IE) of L-tryptophan significantly improved in presence of both surfactants. The effect of SDS and CTAB on the corrosion inhibition behavior of L-tryptophan appears to be synergistic in nature, the values of synergism parameter being greater than unity. The adsorption of inhibitors on mild steel surface obeyed Langmuir’s adsorption isotherm. The calculated thermodynamic parameters for adsorption reveal a strong interaction between the inhibitors and the mild steel surface. The results obtained by electrochemical studies are consistent with the results of the weight loss measurements. L-tryptophan acts more anodic than cathodic inhibitor.