Ferroelectric Charge Research Articles

Ferroelectric Space Charge Non-Destructive Read-Out memory

Abstract The Ferroelectric Space Charge (FESC) Memory is a technique to achieve Non-Destructive Read-Out (NDRO) of a ferroelectric memory that employs standard metal-ferroelectric-metal memory capacitors. The NDRO technique allows the polarization state of the capacitor to be read without altering the polarization. This provides the advantage that the memory capacitor is not subjected to the destructive read/rewrite cycle commonly employed in ferroelectric memories, so the lifetime of the device is limited only by the number of times the memory is written. In addition, the NDRO avoids the period of data volatility in the time interval between the read pulse and the subsequent rewrite of the data. The FESC NDRO approach utilizes changes in the dielectric response of the ferroelectric due to interactions between the internal space charges, the spontaneous polarization, and internal and external electrical potentials. The NDRO is implemented entirely in circuitry and does not require specialized ferroelectri...

Modeling of metal-ferroelectric-semiconductor field effect transistor subthreshold current

Abstract A subthreshold current model for metal-ferroelectric-semiconductor field effect transistor (MFSFET) is derived from a new analytical ferroelectric hysteresis model,1.2 the semiconductor surface model,3 the classical diffusion current model,4 as well as the Maxwell equations. The model predicates the shift of MFSFET subthreshold current between forward sweep and backward sweep of gate bias. The simulation results show the effects of coercive voltage, the remanent polarization, the saturation polarization, and the free interface charge between ferroelectric and semiconductor. The external field effect on the saturation polarization (better known as ferroelectric space charge effect) is also modeled. The conventional method to evaluate the interface trapped charge for metal-oxide-semiconductor system is also proposed for MFS system based on the ideal subthreshold current model and its experimental data.

Multilayer ferroelectric-semiconductor structures for controlled sensors with memory

Abstract The results of the experiments on the ferroelectric field effect in thin film semiconductors deposited on different ferroelectrics due to the application of the repolarizing electric field, light and temperature are described. Electric field and light controlled resistors and capacitors with memory with satisfactory parameters in a wide temperature range have been obtained by the deposition of thin semiconductor films of Te, PbSe, SnO2-X, VO2-X, CdS, a-Si:H on ferroelectric single crystals, ceramics and films. The interpretation of the observed effects is based on a model of the existence of nonuniform potential relief at the ferroelectric-semiconductor interface and of potential barriers at the grain boundaries of a semiconductor and their dependence on the value and sign of the ferroelectric polarizing charge. It is concluded that the ferroelectric-semiconductor structure can be used as the basis for creation of controlled resistors and photoresistors, capacitors and photocapacitors with memory...

POLARONS IN HIGH INSULATORS

Using a special lock-in amplifier, the surface and volume conductivities of three kinds of high insulators are measured from -20℃ to 180℃. Hopping and band conductions of conductive polarons are observed in LiNbO3, the transition temperature between the two- conductive states is about 38℃. A conductive polaron can be captured by a trap and becomes a bound polaron. The bound polaron is not an electric carrier, but under the action of external field, its position may be changed to give an ultralow frequency polarization effect. There are many ferroelectric screenning charges on the surface of LiNbO3 and LiTaO3, however, their conductive currents are not so large as those of glass. But the screenning charges supply very large displacement currents. The fact shows that these screenning charges are in bound polaron state. The phenomenon of that the displacement current shows anomalous at about 45, 75, and 130℃ is observed in LiNbO3.

Piezoelectric Properties of Polycrystalline Lead Titanate Zirconate Compositions

Detailed data are given for the piezoelectric, elastic, and dielectric properties of lead titanate zirconate ceramic compositions near the rhombohedral-tetragonal phase boundary. These compositions have markedly higher electromechanical coupling factors, remanent ferroelectric charge, and coercive field, than ceramic barium titanate. Another interesting feature is a pronounced change in the free permittivity Є33T by the poling process; this change is in opposite directions for rhombohedral and tetragonal compositions. The dielectric and elastic anisotropy ratios of poled lead titanate zirconate are much greater than those of barium titanate, indicating a greater degree of alignment of domains during poling.