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.
A Feasibility Study on Ferroelectric Shadow SRAMs Based on Variability-Aware Design Optimization
A feasibility study on Ferroelectric Shadow SRAMs (FE-SRAMs) was performed using circuit simulations. To take into account design constraints set by the cell transistor variability, a simple operation margin search algorithm was proposed and used, which requires only pass/fail information from multiple transient simulations. It was found that stable dynamic recall operations can be achieved by using small enough ferroelectric capacitors, and that non-volatile write energy of well below 10 fJ/bit can be expected, adding minimal area penalty and performance degradation to the base SRAM cell. Scalability to advanced technology nodes is also anticipated. The results show that the FE-SRAM would be an ideal non-volatile memory solution for ultra-low power applications, such as sensor networks powered by energy harvesting.
SOME EXPERIMENTS ON THE MOTION OF 180 DOMAIN WALLS IN BaTiO$sub 3$
Single-crystal BaTiO/sub 3/ samples with aqueous LiCl electrodes in place of the castomary noble metal electrodes are observed to undergo polarization reversal with electric fields of several hundreds of volts per cm in a manner very much analogous to certain ferromagnetic materials. It is shown for the first time that polarization reversal in BaTiO/sub 3/ can take place by the expansion of a few demains through extensive sideways 180 deg domain wall motion. The observed domain configurations show that the smallest switched domains are probably circular in cross section and do not appear to go through the thickness direction of the crystal. The small domains grow through sideways 180 deg domain wall motion into large ones which have approximately square cross sections with the straight sides at 45 deg to the a axes. It is also noted that few, and sometimes no, ferroelectric Barkhausen pulses are observed during polarization reversal, and that Barkhausen pulses can occur when two switched domains come together. (auth)