Imprint Characteristics Research Articles

Investigation on the electrical characteristics of sol-gel derived Pb1.05(Zr0.53Ti0.47)O3 thin films

Lead zirconate titanate (PZT) thin films with composition Zr/Ti ∼ 0.53/0.47 were deposited by the sol-gel technique. The films were characterized in terms of its polarization relaxation, fatigue and imprint characteristics. We have found that the polarization relaxation is due to the presence of a depolarization field which increases dramatically with the rise in temperature. Improved fatigue performance was observed when the film was fatigued with higher frequency. The direction of imprint depends on the state of polarization. With the increase in net polarization, the trapped charge density at the film-electrode interface increases which leads to imprint characteristics. Also the imprint increases considerably with the rise in temperature. Finally, we have made an attempt to correlate simultaneously fatigue, polarization relaxation, and imprint characteristics with the presence of mobile charge defects (viz. Vo) and defect dipoles (viz. VPb – Vo) in the film.

Imprint Characteristics of SrBi2Ta2O9 Thin Films with Modified Sr Composition

Imprint characteristics of SrBi2Ta2O9 (SBT) thin films with modified Sr composition were investigated under elevated temperatures. A significant shift in readout charge was observed after applying unipolar pulses (dynamic imprint test) at above 100°C, while only a small shift was detected even when the capacitors were held at 150°C for up to 104 s without any electrical signals (static imprint test). The charge shift was due to the internal voltage formed by applying the unipolar pulses. Its increase, that is, degradation of dynamic imprint endurance with increasing temperature is attributed to both an increase of the internal voltage and a decrease of the coercive voltage (Vc). There was no significant difference in the internal voltage between Sr deficient and Sr non-deficient SBT. SBT with a Sr deficient composition had a relatively high dynamic imprint endurance compared to the Sr non-deficient films because of higher remanent polarization and larger Vc.

Evaluation of imprint in fully integrated (La,Sr)CoO3/Pb(Nb,Zr,Ti)O3/(La,Sr)CoO3 ferroelectric capacitors

We have investigated the imprint characteristics of fully integrated ferroelectric lead zirconate titanate based capacitors. These capacitors were fabricated using conducting perovskite La–Sr–Co–O electrodes. We have specifically focused on the effect of several test and capacitor variables, including temperature, unipolar stress amplitude, number of cycles, and device area. Two different figures of merit, one based on coercive voltage changes and the other based on differences in polarization values were used to quantify imprint. The imprint in our capacitors showed a small temperature dependence over the range that we have studied. The unidirectional pulse voltage amplitude had a larger influence on the imprint.

Influence of cationic stoichiometry of La1−xSrxCoO3 electrodes on the ferroelectric properties of lead based thin film memory elements

In earlier publications, we have demonstrated that La0.5Sr0.5CoO3 electrodes dramatically improve the phase stability and electrical properties of lead based ferroelectric capacitors. This study evaluates the influence of deviation from the cationic stoichiometry, La/Sr=1, on the ferroelectric properties. Polycrystalline Pb(Nb0.04Zr0.18Ti0.78)O3 based capacitors were fabricated with La0.5Sr0.5CoO3 as the bottom electrode and either La0.5Sr0.5CoO3 or La0.85Sr0.15CoO3 as the top electrode. The as-grown capacitors with La0.85Sr0.15CoO3 as the top electrode were slightly asymmetric about the voltage axis. However, the asymmetry did not increase when the capacitors were subjected to single side pulses and temperature. Both capacitor structures showed good fatigue (no fatigue up to 1011 cycles), retention, and imprint characteristics. Detailed pulse width and voltage dependent measurements were also carried out to further understand the impact of the change in electrode composition. The polarization values at 1 μs pulse width were as large as 13 μC/cm2, though the dependence was steeper for capacitors with asymmetric electrodes. The resistance to switching during polarization reversal, formally termed activation field, α, was measured from the switching current dependence of the applied field. These values were slightly larger for the capacitors with asymmetric electrodes. The data indicate that the ferroelectric properties of the capacitor are almost not influenced by a change of the top electrode from La0.5Sr0.5CoO3 to La0.85Sr0.15CoO3.

Effect of Bottom Electrode System on Ferroelectric Properties of Sputter Deposited PZT Capacitors

AbstractRF magnetron sputter deposited PZT films were prepared on various bottom electrode systems such as Pt/Ti/SiO2/Si, IrO2/SiO2/Si, Pt/IrO2/SiO2/Si and Ir/IrO2/SiO2/Si substrates using the ceramic PZT target with Pb1.1(Zr0.52Ti0.48)O3 composition. In order to obtain single perovskite phase, PZT films were sputter-deposited at room temperature under Ar only plasma condition followed by high temperature annealing under oxygen ambient. Regardless of the bottom electrode system, reasonable ferroelectric properties such as 2Pp, Vc could be obtained by 650°C post annealing. Their values were over 20μ C/cm2 and below ± 1.OV when drive voltage was ± 3V, respectively. Hybrid electrode system, namely, thick Pt or Ir and thin IrO2 shows good leakage current characteristics, of ∼ 10−8A/cm2. Fatigue properties of PZT capacitor depend on the test condition. However, retention after 3×104sec showed a degradation of 15% when writing voltage was −5V irrespective of bottom electrode system. Imprint characteristics also showed good results within ± 1 as a figure of merit (FOM).

Thermally Induced Imprint of PZT and SBT Thin Films

AbstractThe imprint characteristics of chemical solution deposited Pb(Zr,Ti)O3 (PZT) and SrBi2Ta2O9(SBT) thin films have been investigated. The imprint properties were evaluated by polarization-electric field hysteresis measurements. Imprint was measured at the elevated temperatures to accelerate imprint rate. Several parametric variables such as voltage and DC bias were also used to investigate possible imprint mechanisms. To quantify imprint, two different standards for evaluation of ferroelectric capacitors were compared: voltage shift and asymmetric polarization shift. Two types of PZT thin films with the same Zr/Ti composition were prepared to investigate the influence of loop shape on the rate of imprint. In addition, the imprint behavior of SBT was also investigated. It is shown that the imprint rate is strongly dependent upon the method of evaluation as well as the loop shape.

La 0.5 Sr 0.5 CoO 3 /Pb(Nb 0.04 Zr 0.28 Ti 0.68 )O 3 /La 0.5 Sr 0.5 CoO 3 thin film heterostructures on Si using TiN/Pt conducting barrier

A high density ferroelectric memory process flow requires the integration of conducting barrier layers to connect the drain of the pass-gate transistor to the bottom electrode of the ferroelectric stack. We are studying the effect of crystallinity of the TiN/Pt barrier layer with Si wafers on the ferroelectric properties of La0.5Sr0.5CoO3/Pb(Nb0.04Zr0.28Ti0.68)O3/La0.5Sr0.5CoO3 (LSCO/PNZT/LSCO) capacitors. Structural studies indicate complete phase purity (i.e., fully perovskite) in both epitaxial and polycrystalline materials. The polycrystalline capacitors show lower remnant polarization and coercive voltages. However, the retention, fatigue, and imprint characteristics are similar, indicating minimal influence of crystalline quality on the ferroelectric properties.

Capacitor test simulation of retention and imprint characteristics for ferroelectric memory operation

Ferroelectric memory devices are subject to failure due to both a simple loss of retention or due to imprint. The difference between retention and imprint as described here depends on the test history of the device. A pulsed capacitor test has been devised to simulate the signal available to a typical memory cell after time and temperature stress. The test sequence consists of individual pulses used to compare the switched component to the non-switched component with the difference being the signal available for memory operation. It has been found that this signal when plotted versus log time for a fixed bake temperature stress produces a straight line.

Pulsed laser deposition of Bi4Ti3O12 thin films and their anomalous imprint characteristics

Using La0.5Sr0.5CoO3(LSCO) or Pt film as a bottom electrode layer, epitaxial Bi4Ti3O12(BTO) thin films were deposited on MgO(001) substrates by pulsed laser deposition. X-ray diffraction patterns showed that the c-axes of BTO films are oriented normal to the substrate surface. Interestingly, an epitaxial Pt/BTO/Pt film showed a strongly preferred polarization state directed towards the top electrode in spite of the symmetric electrode configuration. The inprint state did not change significantly in the pulse test with DC bias. These anomalous behaviors suggest that the imprint characteristic is highly correlated with interfacial states between the electrodes and the BTO films. To understand space charge effects in the metal-ferroelectric contacts, imprint characteristics of the thin film capacitors with various top electrodes were investigated. Auger Electron Spectroscopy(AES) depth profile was measured, to check the possibility of a interdiffusion of the bottom electrode with the BTO layer. Interdiffusion (or reaction) between the BTO and Pt (bottom electrode) seems to be responsible for the strongly preferred polarization.

A miniaturized test method for the mechanical characterization of structural materials for fusion reactors

This work deals with a non-destructive method for mechanical tests which is based on the indentation of materials at a constant rate by means of a cylinder with a small radius and penetrating flat surface. The load versus penetration depth curves obtained using this method have shown correspondences with those of tensile tests and have given indications about the mechanical properties on a reduced scale. In this work penetration tests have been carried out on various kinds of Cr martensitic steels (MANET-2, BATMAN and modified F82H) which are of interest for first wall and structural applications in future fusion reactors. The load versus penetration depth curves have been examined with reference to data obtained in tensile tests and to microhardness measurements. Penetration tests have been performed at various temperature (from −180 to 100°C). Conclusions, which can be drawn for the ductile to brittle transition, are discussed for MANET-2 steel. Preliminary results obtained on BATMAN and modified F82H steels are reported. The characteristics of the indenter imprints have been studied by scanning electron microscopy.

Electrical properties of PZT thin films for memory application

Abstract The development of ferroelectric memory device requires improvements in electrical characteristics such as fatigue, retention, imprint and other properties. Fatigue properties of PZT thin films were improved by using Pt/IrO2 or Ir/IrO2 used as electrodes, we reported. This report presents a study of the retention and the imprint characteristics of PZT thin films on various electrodes. Pt/IrO2 and Ir/IrO2 layer structures were used as electrodes of the PZT capacitors. In the case of using an Ir/IrO2 electrode, the improvements in electrical properties from the measurements of the retention and the imprint characteristics.

Electrical Properties of Pb(Zr,Ti)O 3 Thin Film Capacitors on Pt and Ir Electrodes

Pb(ZrxTi1-x)O3 (PZT) thin films were prepared on Ir/IrO2 and Pt/IrO2 electrodes. We have already reported that fatigue properties of PZT thin films were improved by using these electrodes due to barrier effects of IrO2. In this present paper we describe a study of the imprint characteristics of PZT thin films on these electrodes. There is little difference in fatigue properties between the PZT films on Pt/IrO2 and Ir/IrO2. However, we find some difference in imprint characteristics between the PZT films on these electrodes. In the case of Ir/IrO2 electrode, improvements in the electrical properties are observed in the measurements of the imprint characteristics. Moreover, improvements in imprint characteristics were also obtained with good (111)-axis orientation of PZT films when PtxIr1-x/IrO2 electrodes were used.

Pulsed laser ablation synthesis and characterization of layered Pt/SrBi2Ta2O9/Pt ferroelectric capacitors with practically no polarization fatigue

Pulsed laser ablation deposition was used to synthesize polycrystalline SrBi2Ta2O9 layered ferroelectric thin films on platinized silicon substrates. Top electrodes were produced by dc magnetron sputter deposition to fabricate capacitors for electrical tests. The polarization electric field hysteresis loops showed saturation in the 2–4 V range with a coercive field of 25 kV/cm. The capacitors showed practically no polarization fatigue up to 1011 switching cycles. The resistivity of the SrBi2Ta2O9 for a coercive field of 100 kV/cm was approximately 2×1011 Ω cm. Retention and imprint characteristics of these capacitors showed no degradation as a function of cumulative waiting times.

Is imprinting such a special case?

As the result of relatively brief exposure to a particular type of object early in life, many birds and mammals will form strong and exclusive attachments to that object. This is known as ‘filial imprinting’. Early experience can also have long-lasting effects on sexual preferences, but the conditions are different from those in which the first attachments are formed. Some of the characteristics of imprinting are undoubtedly because of the naive animal searching for and responding selectively to particular stimuli. But that is not all. At least two types of plastic change seem to be involved: establishing an internal representation of the familiar object and pre-emptive capturing by that representation of the systems controlling filial behaviour and, much later in development, sexual behaviour. The second plastic change is likely to generate the phenomenon of a sensitive period and gives the formation of social attachments some of its other peculiar properties. The first change is likely to be the process used in most forms of recognition. Distinguishing between the sub-processes that underlie an overall change in behaviour serves to make some overdue links between different areas of knowledge about learning which have hitherto been poorly connected.

Behavioral Stock-Isolating Mechanisms in Great Lakes Fishes with Special Reference to Homing and Site Imprinting

A moderately high degree of reproductive isolation is necessary for the formation and maintenance of discrete stocks of fish. This reproductive isolation can be developed through spawning site imprinting and homing—behavioral mechanisms that are apparently very common in fish. During some part of their early life history, the fish become imprinted to, or conditioned to, environmental characteristics of the spawning site and/or to the pheromonal characteristics of their stock. At sexual maturity, they show an orientation-homing behavior back to the natal area where spawning then occurs reinitiating the cycle. Over time, stock-specific adaptations are made to the local environment which can involve changes in the morphological, physiological, or behavioral characteristics of the fish. Research on salmonids has provided the best evidence for site imprinting and natal homing in fish. Tagging and transplantation experiments with these species have been especially important sources of information. In coho salmon (Oncorhynchus kisutch), olfactory homing and olfactory site imprinting have been demonstrated by artificial imprinting techniques; it was found that the critical period for imprinting occurred during smoltification at an age of 15 or 16 mo. Most species do not undergo smolting, and imprinting occurs at a very early stage in the life history. It is hypothesized that the information which is imprinted about the natal site may be obtained from one or more of the following: odors in the water flowing over the site; odors originating from the site itself; and stock-specific pheromones emitted directly from the fish or from their waste products. Differences in characteristics of homing and imprinting in relation to the formation and maintenance of stocks are discussed for several Great Lake species including coho salmon, pink salmon (O. gorbuscha), lake trout (Salvelinus namaycush), white bass (Morone chrysops), and walleye (Stizostedion vitreum vitreum). Inferences are made about how these characteristics relate to the rehabilitation of fish stocks in the Great Lakes and their tributaries.Key words: stock-isolating mechanisms, Great Lakes fish, homing, site imprinting

The taxonomic status of the genus Rubidgea

The genus Rubidgea Tate of the fossil family Glossopteridaceae was reduced to a synonym of Glossopteris by Seward (1907). Seward’s conclusion is now confirmed by a study of a wide range of imprints from a quarry near Hammanskraal, South Africa. The upper and lower surface imprints of a single leaf found on a split fragment of carbonaceous shale provides the main evidence presented. The finely striated upper surface imprint of the leaf could be identified with Rubidgea, whereas the lower surface imprint represents the typical strong venation of a Glossopteris. The type species of Rubidgea is transferred to Glossopteris as G. mackayi (Tate) Kovacs comb. nov. The characteristics of upper and lower surface imprints of a number of Glossopteris species are discussed.

Characteristics of neonatal androgen-induced imprinting of rat hepatic microsomal monooxygenases

Both the apparent K m of hepatic microsomal ethylmorphine N-demethylase and the responsiveness of this enzyme to testosterone treatment in adult rats are imprinted neonatally by androgen. The maintenance of these imprinted male-specific characteristics of this enzyme activity depends on the presence of an intact pituitary. Hypophysectomy alters the apparent K m of this enzyme activity from male into female type, whereas castration, thyroparathyroidectomy or adrenalectomy does not. Androgen or estrogen administration has opposite effects on the apparent K m , but similar effects on plasma FSH and LH concentrations. These results tend to mitigate against mediator roles for ACTH, TSH, LH and FSH. The sensitive periods for androgen-induced imprinting of the apparent K m of ethylmorphine N-demethylase differs from that of the responsiveness of this enzyme. With the former, imprinting occurs at days 2 and 4 of age, whereas the latter extended beyond days 2 and 4 to days 12 and 14 of age. Unlike imprinting in the CNS, neonatally administered estradiol-17β is ineffective in inducing the male characteristics of this enzyme activity. Although hypophysectomy alters the imprinted male characteristics of the ethylmorphine N-demethylase (apparent K m and responsiveness) to the female type, it shifts the neonatal androgen-imprinted differences in the turnover of cytochrome P-450 from female toward that of the male type. These results suggest that different hypophyseal factors may be responsible for the regulation of these neonatal androgen-imprinted male characteristics in hepatic microsomal monooxygenases.