The composite films of potassium nitrate (KNO3):poly(vinyl alcohol) (PVA) have been prepared at different temperatures by spray-deposition technique. Ferroelectric hysteresis loops were traced at room temperature for the composite films using modified Sawyer and Tower circuit. The X-ray diffraction studies confirm the existence of ferroelectric phase III of KNO3 in the composite films at the room temperature, where this phase in pure KNO3 films is known to exist in the temperature range 110°–124°C. The composite films deposited at 200°C shows the optimum remanent polarization, Pr∼17 μC/cm2. The Pr was studied in the frequency range 10 Hz–1 kHz. The stability of the Pr in the composite films exhibits improved fatigue compared with that of quenched KNO3 films. The capacitance–voltage (C–V) characteristics exhibits butterfly features which supports the presence of ferroelectric phase in the composite films. The atomic force microscopy images show that the composite films have uniform dispersion of KNO3 particles in the PVA matrix.

Ferroelectric Phase Stability Studies in Spray Deposited KNO3:PVA Composite Films

Thin film ferroelectric memory devices have displayed ideal memory characteristics such as nonvolatility, radiation hardness and fast switching times. The simulation of the digital circuits using thin film ferroelectric memory devices necessitates an equivalent circuit model for these thin film device structures. The basic switching characteristics of a device is nonlinear in nature and requires a generating source in the equivalent circuit model. This current source is related to the polarization current as a function of time.The capacitance-voltage and hysteresis data on capacitor type device structures suggest the existance of an interfacial layer at the metal-ferroelectric interface. The interfacial layers are characterized by appropriate RC networks. The bulk ferroelectric material is modeled as a linear capacitance (dielectric) in parallel with a bulk resistance in parallel with the current generating source. This equivalent circuit model is simulated on the IBM 4381 mainframe computer using SPICE. ...

A circuit model for a thin film ferroelectric memory device

The composite films of ferroelectric potassium nitrate (KNO3):poly(vinyl alcohol) (PVA) with different weight percentages of KNO3 have been prepared at 200degC using the spray-deposition technique. The remanent polarization (Pr) and peak current density for all composite films was estimated by tracing the polarization-electric field (P-E) hysteresis loop and current density-electric field (J-E) loop, respectively, using a modified Sawyer-Tower circuit. Pure KNO3 is known not to exhibit any ferroelectricity under ambient conditions, but the X-ray diffraction (XRD) studies of PVA:KNO3 composite films reveal the presence of a ferroelectric phase III of KNO3 in the composite films at room temperature. The composite film containing KNO3:PVA in equal proportions shows maximum Pr and peak intensity ratio of approximately 20.10 muC/ cm2 and 2.67, respectively, at room temperature. The J-E and capacitance voltage (C-V) characteristics exhibit butterfly features that supports the presence of a ferroelectric phase in the composite films. The field emission scanning electron microscopy (FE-SEM) image of the composite film containing equal proportions of KNO3 and PVA shows the homogenous distribution of spherical grains of KNO3 of size ~225 nm.

Preparation and Characterization of the Ferroelectric Potassium Nitrate: Poly(vinyl alcohol) Composite Films

Ferroelectric Films for Integrated Electronics

The current-voltage (I–V) characteristics of the ferroelectric potassium nitrate (KNO3): poly vinyl fluoride (PVF) has been investigated. The current–voltage characteristics gave the peak-to-valley ratio (PVR) of 4.5:1 for the forward bias voltage of +2V at room temperature. The non-linear and butterfly features of the capacitance-voltage (C–V) curves strongly corroborate the presence of ferroelectricity in the composite films. The Negative Differential Resistance (NDR) phenomenon has been observed with applied dc bias voltages and indicates the Resonant Tunneling type characteristics.

Bias Dependent Current-Voltage (I–V) Characteristics of Ferroelectric Potassium Nitrate: Poly (Vinyl Fluoride) Composite Films

Several fabrication and processing parameters such as deposition rate, thickness of the sample, annealing time and temperature, and electrode materials were varied in Au–KNO3 –Au thin‐film ferroelectric memory devices to optimize the electrical properties of these devices. The deposition rate was varied from 2.5 to 10 nm/min in steps of 2.5 nm/min. The samples deposited at a rate of 5 nm/min yielded better electrical results compared to samples deposited at other rates. The electrical testing involved pulse testing and capacitance–voltage measurements. The switching time of these devices decreased with a decrease in the thickness of KNO3 as expected. However, the switching thresholds were sharper in the 200‐nm‐thick KNO3, as compared to 160‐ and 120‐nm‐thick KNO3 samples. The samples were annealed in forming gas at 6, 10, 17, 21, 24, and 44 h and no significant changes were observed in the switching time and polarization. Instead of gold electrodes, indium–tin electrodes gave better performance but they were not easily repeatable.

Dependence of the electrical properties of KNO3 memory devices on fabrication and processing parameters

The terminal fatigue characteristics of vacuum deposited phase-III potassium nitrate (KNO/sub 3/-III) ferroelectric memory devices are reported. It is concluded that the decrease in the polarization values after several million read/write cycles is probably due to the interfacial degradation at the gold/KNO/sub 3/ interface observed by Auger electron-spectroscopy techniques. >

S. E. Adams

Papers

Dependence of the electrical properties of KNO3 memory devices on fabrication and processing parameters

Fatigue mechanisms in thin film potassium nitrate memory devices