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Orthorhombic Bi2SiO5 thin films were fabricated on Pt/Ti/SiO2/Si substrates by incorporating a NiO thin layer between Bi2SiO5 and bottom electrode. Compared with those bare Pt/Bi2SiO5/Pt devices, a remarkably improved uniformity of resistive switching parameters such as electroforming voltages, reset voltages, and a resistance ratio of low/high states was demonstrated in the Bi2SiO5 devices with an embedded NiO layer. This improvement was attributed to the formation of the partial conductive filaments resulted from sufficient oxygen vacancies at the interface. Our results provide a method for the optimization of the operation voltage control toward forefront applications in nonvolatile memory.

The interconnected nanoporous lead selenide (PbSe) thin films were synthesized with the aid of polyvinyl alcohol (PVA) as a surface directing agent by simple hydrothermal route. Films were deposited with different time intervals like 1, 2 and 3 h. Effect of time variation was studied by structural, morphological and optical characterizations. XRD analysis revealed that the film exhibit a cubic phase of PbSe. SEM study shows an evolution in nanoflakes like morphological feature. It is observed that, the nanoflakes become denser with an increase in the diameter of the platelets as the deposition time increases. Interconnected nanoporous network, forming well defined 3D nanoenvelopes has been developed to analyze solar cell and resistive switching properties. The photoelectrochemical (PEC) performance of nanoporous PbSe thin films was tested in Polysulfide electrolyte. Among all PbSe films, the sample prepared at 3 h shows higher PEC performance with maximum short circuit current 97 µA/cm2 and open circuit voltage 110 mV. In addition to this, Ag/PbSe/FTO thin film device shows the photo-induced resistive switching behavior. The non-volatile memory results suggested that the memory device is able to switch up to 104 cycles and store the data up to 103 s with good uniformity during the resistive switching process. The analysis of I–V results revealed that the Ohmic and space-charge-limited current are responsible for current conduction in the Ag/PbSe/FTO thin film memory device. The results of present investigation suggest that the nanoporous lead selenide thin films are potential candidate for the photoelectrochemical and resistive switching memory applications.

The Ge2Sb2Te5 is a phase change material (PCM) widely used in non-volatile random-access memory (PC-RAM) devices since 2017. Despite the compound is under intense investigation its electronic structure and nature of a switching mechanism is not fully understood. The present work sheds new light on the nature of memory and switching effects observed in such compounds. Results of our research demonstrate that crystal structure of Ge2Sb2Te5 possess different topological quantum phases: a 2D topological quantum phase is realized at the switching effect and a Weyl semimetal phase or 3D topological crystalline phase is a characteristic of the non-volatile memory effect. Since the structural phase transition can be caused by the external electric field, we discovered that the switching between different topologically non-trivial phases can be driven by variation of electrical potential on the top gate of topological field effect transistor. A similar pattern is observed when the thickness of the layers GeTe/Sb2Te3 changes. The obtained results have been possible to develop a unified physical model that explains the simultaneously observed effects of non-volatile memory and switching.

In the present report, a simple and cost-effective successive ionic layer adsorption and reaction method is employed to develop self-rectifying ZnO thin film memory device. The nature of pinched hysteresis loop and frequency dependent I–V characteristics depicts that the developed device behaves like a memristive device. Moreover, significant pinched hysteresis loop at 1 MHz was observed which could be further exploited for the development of new class of high-frequency circuits by using ZnO memristive device. The observed analog memory with scan rate dependent synaptic weights behavior suggests that the ZnO memristive device is a potential candidate for the development of electronic synaptic devices for neuromorphic computing application. Furthermore, multilevel resistive switching with good memory window was obtained at 0.2 V read voltage. The developed device switched successfully in consecutive 10 k resistive switching cycles and can retain multilevel resistance states over 1000 s without any observable degradation in the resistance states. The insights drawn from electrical characterization indicates that the device charge and charge–magnetic flux relations depend upon the frequency of the applied signal. Furthermore, we have presented the criteria for differentiating the experimental device as a memristor or memristive device based on the nature of time domain charge and double valued charge–magnetic flux relation. The resistive switching effect of the present device is manifested due to the unified effect of the Ohmic and Schottky conduction mechanisms.

By controlling the voltage-polarity, a bipolar resistive switching (RS) behavior was observed in CVD grown tungsten disulfide (WS2) thin film memory device fabricated on Pt/Ti/SiO2/Si substrate with top Al contacts. The RS performance of the device did not degrade even after repetitive voltage cycles, which indicate uniformity and reproducibility. A decent on/off ratio, high retention time, and a large endurance were respectively recorded to establish the non-volatile memory characteristics in a device with thin layer of WS2. The XRD, Raman, FESEM and EDAX measurement were included as the structural and compositional details of CVD grown WS2 thin film. The current conduction mechanisms were discussed on the basis of experimental data using various existing fitting models. This work also explained the mechanism of resistance switching in CVD grown Tungsten Disulfide. The findings offered a feasible approach towards fabrication and application of the Al/WS2/Pt/Ti/SiO2/Si device.

The memristive devices are getting a lot of interest in recent years due to its applications in the field of resistive memory and brain-inspired computing. In the present work, we have developed a ZnO memristive device using the reflux method. We have demonstrated non-volatile memory properties and mimicked the basic synaptic properties of using Al/ZnO/FTO thin film device. The structural, morphological and compositional studies of ZnO thin film were carried out by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The co-existence of analog and digital resistive switching in a ZnO memristive device was achieved by properly tuning the external electrical stimulus. The developed ZnO memristive device mimics the basic synaptic properties such as potentiation-depression, symmetric Hebbian and antisymmetric Hebbian learning rules at a lower voltage bias (±1 V to ± 3 V). Whereas, non-volatile memory properties (endurance and retention) were achieved at a higher voltage bias (±4 V to ± 6 V). The Al/ZnO/FTO thin film memory device shows good resistive switching memory properties such as 104 endurance cycles and 104 s retention period with good uniformity during the cycle to cycle operation. The detailed analysis of I–V results suggested that the Schottky conduction model is responsible for the analog mode of operation, whereas, space charge limited current governs the device dynamics during the digital mode of operation. A possible resistive switching model is also presented.

A molecular design for the electret material of n-operating organic field-effect transistor-based (OFET) memories is introduced. A large memory window and high operating speed were achieved while the polar groups are connected to the polymer chain of polyimide, which plays the role of electret of a transistor memory device. The phase variation of electrical force microscopy images showed that polarization field induces charge trapping states on the surface of electret layer and accumulates charged carriers within the conducting channel of OFET to achieve high-performance memory and transistor simultaneously. An extra-large memory window was also obtained by introducing photo-induced charge transfer effect.

In polymer-based ferroelectric diodes, films are composed of a semiconducting polymer and a ferroelectric polymer blend sandwiched between two metal electrodes. In these thin films, the ferroelectric phase serves as the memory retention medium while the semiconducting phase serves as the pathway to read-out the memory in a nondestructive manner. As such, having distinct phases for the semiconducting and ferroelectric phases have proven critical to device performance. In order to evaluate this crucial structure-property relationship, we have fabricated ordered ferroelectric devices (OFeDs) through common lithographic techniques to establish systematically the impact of nanoscale structure on the macroscopic performance. In particular, we demonstrate that there is an optimal domain size (∼400 nm) for the interpenetrating networks, and we show that the ordered device, with semiconducting domains that span the entire length of the active layer film, provides a significant increase in the ON/OFF ratio relative to the blended film fabricated using standard solution blending and spin-coating techniques. This improved performance occurs due to a combination of the ordered nanostructure and the nature of the ferroelectric-semiconductor interface. As this is the first demonstration of macroscopic OFeDs, this work helps to elucidate the underlying physics of the device operation and establishes a new archetype in the design of polymer-based, nonvolatile memory devices.

To produce organic non-volatile organic memory transistors, graphene oxide (GO) nanoparticles were embedded in the floating gate of an all organic memory structure using polymethylmethacrylate as the dielectric and pentacene as the organic semiconductor. The current–voltage characteristics and the memory behaviour of the GO-based organic thin film memory transistors are reported. GO-based memory transistors were shown to produce reliable and large memory windows by virtue of high capacity and reduced charge leakage. The hysteresis in the output and transfer characteristics and shifts in the threshold voltage of the transfer characteristics were attributed to the charging and discharging of the floating gate. Fast switching and large memory windows (∼26 V) exhibiting high charge density (6.25 × 1012 cm−2) were achieved.

We report clocked sequential complementary circuits that operate at 5 V in which the active semiconductors are deposited by inkjet printing. The p-channel thin-film transistors (TFTs) employ a network of predominantly semiconducting (>98%) single-walled carbon nanotubes and the n-channel TFTs employ amorphous zinc tin oxide formed from a printed precursor solution. The gate insulator material in both cases is zirconium oxide, deposited from solution. Edge triggered D flip-flops operate at clock speeds of 2.5 kHz. Our results suggest that this materials combination is promising for use in printed electronics.

In this study, unipolar resistive switching (URS) characteristics in ZnO thin film memory devices were systematically investigated with variable defect content. ZnO films displayed typically URS behavior while oxygen-deficient ZnO 1− x films did not show resistive switching effects. The devices with two intentional Ohmic interfaces still show URS. These results show that appearance of URS behavior can be dominated by initial oxygen vacancy content in ZnO thin films. Modest increase in oxygen vacancy content in ZnO films will lead to forming-free and narrower distributions of switching parameters (set and reset voltage, high and low resistance states). It indicates that controlling the initial oxygen vacancy content was an effective method to enhance the URS performance.

We report nonvolatile resistive switching in anodic niobium pentoxide thin-film memory cells. Highly dielectric Nb2O5 films were prepared at room temperature by the anodic oxidation of submicrometer-thick Nb films sputtered onto an Si wafer. After the electroforming process, Au/Nb2O5/Nb/Si sandwich memory cells demonstrate reproducible direct current and pulse mode switching between two resistance states with a resistance on-off ratio around 103. Low and high resististive states show ohmic conductivity and field-assisted Poole-Frenkel-type conductivity, respectively. Nonvolatile resistance storage was traced within 40 days to quantify retention characteristics of the Nb2O5 memristor. The low-temperature anodic oxidation of Nb was found to be feasible to fabricate high-density cross-point memory with 3-D stack structures.

Nonpolar bistable resistive switching behaviors of sol-gel derived bismuth titanate oxide (BTO) thin film are investigated in this study. The BTO thin film memory device without thermal treatment shows higher resistance ratio (∼ 10 4 ) than the other annealed devices. The resistive switching behavior of the Pt/BTO/LNO/Pt device is reproducible and can be traced over 100 times. Both low resistance state (ON-state) and high resistance state (OFF-state) are stable over 10 4 s under 0.3 V voltage stress at room temperature (RT) and 85°C. The retention behaviors of both memory states in the Pt/BTO/LNO/Pt device are very stable over 2 × 10 6 s at RT and 85°C, showing that the BTO thin film memory device is a good candidate for nonvolatile memory application

A simple model for a thin film memory based on a first neighbor interacting model is studied in detail. We have found that the minimum possible value for the thickness (D) as a function of the lateral size of the memory (L), the screening of the charges at the substrate (S) and the strength of the ferroelectric interaction (J), in order to obtain spontaneous polarization is D = SL/2J. We propose a new mechanism to obtain miniaturization of thin film memories to a single layer based on the use of relaxor ferroelectrics instead of regular ferroelectrics. Under the hypothesis of an internal organization of the random fields inside the nanofilm we show analytically how it should be possible to miniaturize the memory to a width as small as D = 1 for any value of L, J and S.

In this paper, we have successfully fabricated poly-Si-oxide-nitride-oxide-silicon (SONOS)-type poly-Si-thin-film transistor (TFT) memories employing hafnium silicate as the trapping layer with low-thermal budget processing (les600degC). It was demonstrated that the fabricated memories exhibited good performance in terms of relatively large memory window, high program/erase speed (1 ms/10 ms), long retention time (>106 s for 20% charge loss), and 2-bit operation. Interestingly, we found that these memories depicted very unique disturbance behaviors, which are obviously distinct from those observed in the conventional SONOS-type Flash memories. We thought these specific characteristics are closely related to the presence of the inherent defects along the grain boundaries. Therefore, the elimination of the traps along the grain boundaries in the channel is an important factor for achieving high performance of the SONOS-type poly-Si-TFT Flash memory

Two kinds of Ti-rich TiNi shape memory thin films were deposited onto monocrystal silicon substrates at room temperature and high temperature by using the magnetron-sputtering technique. Their crystallizing procedures are different from each other. The first type of film was originally amorphous and post-crystallized at a higher annealing temperature (600 °C) after sputtering, but the second film type was crystallized in situ during sputtering at about 500 °C. It was found that there are clear differences of microstructure and characteristics between both kinds of film, such as grain size, growth texture, stress range, phase transformation behaviors etc. In order to improve and enhance film properties, the objective of the present work is to reveal the reason for these differences occurring and understand the relationship between the crystallizing procedures, microstructures and characteristics of the films.

Recently, organic nonvolatile memory devices have attracted considerable attention due to their low cost and high performance. This article reviews recent developments in organic nonvolatile memory and describes in detail an organic electrical bistable device (OBD) that has potential for applications. The OBD consists of a tri-layer of organics/metal nanoclusters/organics sandwiched between top and bottom electrodes. A sufficiently high applied bias causes the metal nanoparticle layer to become polarized, resulting in charge storage near the two metal/organic interfaces. This stored charge lowers the resistance of the device and leads to an electrical switching behavior. The ON and OFF states of an OBD differ in their conductivity by several orders of magnitude and show remarkable bistability—once either state is reached, the device tends to remain in that state for a prolonged period of time. More important, the conductivity states of an OBD can be precisely controlled by the application of a positive voltage pulse (to write) or a negative voltage pulse (to erase). Device performance tests show that the OBD is a promising candidate for high-density, low-cost electrically addressable data storage applications.

NiTi shape memory thin films are potentially desirable for MEMS actuators. Traditionally, there are two approaches to obtain NiTi shape memory thin films. One is to anneal amorphous NiTi films in a vacuum chamber and the other is to deposit NiTi on a high temperature substrate (about 500 °C). Both approaches have difficulty in terms of compatibility with traditional IC techniques, and are not applicable for annealing a prescribed local area of a NiTi film at the micron scale. In this paper, a new approach, CO2 laser annealing, which can overcome both problems mentioned above, is presented. Results of optical microscopy, x-ray diffraction (XRD) and atomic force microscopy (AFM) reveal the crystalline structures and phase transformation in annealed NiTi films. Furthermore, a CO2 laser annealed line, about 100 µm in width, demonstrates the capability of a CO2 laser for local annealing of NiTi thin film.

Rapid advances in portable communication and computing systems are creating an increasing demand for nonvolatile random access memory that is both high-density and highspeed. Existing solid-state technologies are unable to provide all of the needed attributes in a single memory solution. Therefore, a number of different memories are currently being used to achieve the multiple functionality requirements, often compromising performance and adding cost to the system. A new technology, magnetoresistive random access memory (MRAM) based on magnetoresistive tunneling, has the potential to replace these memories in various systems with a single, universal solution. The key attributes of MRAM are nonvolatility, high-speed operation. and unlimited read and write endurance. This technology is enabled by the ability to deposit high-quality, nanometer scale tunneling barriers that display enhanced magnetoresistive response. In this article we describe several fundamental technical and scientific aspects of MRAM with emphasis on recent accomplishments that enabled our successful demonstration of a 256-Kb memory chip.

We review three subtopics: Fatigue, nano-phase ferroelectric capacitors, and oxygen vacancy clustering. In each case we try to emphasize problems which are still unsolved

The structure of a molecular memory cell with its work based on the phenomenon of structural instability of one-dimensional conductive molecular systems is offered. Electrophysical parameters of the molecular analogue memory cell were investigated. It was established that a memory cell has an S-shaped voltage–current characteristic with memory. Any impedance of the memory cell can be obtained in the interval between ∼10 MΩ and ∼100 Ω depending on the switching condition. A conclusion is drawn that the design of memory chips based on the molecular analogue memory cell is promising.

Thin films which have electrical bistable effects are mostly metal-organic complexes and/or organic-organic (all-organic) complexes. Very recently some simple (mono-molecular) organic materials have been discovered which have bistable states at room temperature, too. The threshold voltage across these organic films with a thickness of 60 nm is 4–6 V and the transition time is 5–10 ns. Therefore, they are suitable to make ultrafast, non-volatile, organic memories (WORM or EPROM). Another possible application for an STM type ultrahigh-capacity memory is also illustrated.

This letter introduces a polycrystalline silicon (poly-Si) thin-film nonvolatile memory (NVM) with a nanocrystal (NC) indium-gallium-zinc-oxide (IGZO) charge-trapping layer. Experimental results indicate that this NVM exhibits high and symmetric program/erase speeds through the Fowler-Nordheim tunneling mechanism. The memory window loss of the NVM with NC IGZO charge-trapping layer is 25% after 104 s at 85°C due to deep quantum well, as well as high-density and deep trap sites in NC IGZO charge-trapping layer. Accordingly, a poly-Si thin-film transistor with NC IGZO charge-trapping layer is promising for NVM applications.

Nanocrystalline-silicon (nc-Si) nonvolatile memory (NVM) devices with oxynitride-nitride-oxide stack structures were fabricated with directly deposited nanocrystalline-silicon thin films using a low-temperature process. The fabricated bottom-gate nc-Si NVM devices have a wide memory window with a low operating voltage during programming and erasing due to an effective control of the gate dielectrics. In addition, after ten years, the memory device retains a memory window of over 67% between the programming and erasing states. These results demonstrate that these low-priced nc-Si NVM devices have a suitable programming and erasing efficiency for data storage under low-voltage conditions, in combination with excellent charge retention characteristics.

A high-performance gate-all-around (GAA) poly-Si nanowire (NW) SONOS-type memory thin-film transistor (TFT) is presented. The presence of the corners of the GAA structure resulted in the program speed and memory window of this device being superior to those of a planar poly-Si TFT device. When erasing, planar devices exhibit a threshold-voltage shift resulting from gate injection; the GAA device was immune to this behavior. The presence of a nonuniform electric field in the channel region during programming and erasing was confirmed through simulation. The device also exhibited superior endurance and data-retention behavior.

Experimental results on the ac characteristics of electro-formed Cr/p/sup +/ hydrogenated amorphous silicon (a-Si:H)/V thin film memory devices are presented. The impedance spectrum of the memory switching device has been measured over a wide frequency range from 1 Hz-32 MHz while keeping the ac voltage amplitude below 0.02 V. Simulation of the measured impedance spectrum using an equivalent circuit indicates that the capacitance associated with a conducting filament tends to increase as the memory resistance decreases. This is explained on the basis of an activated tunnelling mechanism. Charge transport is dominated by electron tunnelling via metallic particles in the filament, and hence small changes in interparticle spacing influences the tunnelling process considerately, leading to changes in both memory resistance and effective dielectric constant.

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...

Transparent ferroelectric field-effect transistors of oxidic thin films have been fabricated, showing a memory effect with an on/off ratio of the channel conductance of more than three orders of magnitude. The devices consist of a 10 nm n -type SnO 2 :Sb semiconductor channel with a 10 nm BaZrO 3 capping layer, In 2 O 3 :Sn contact pads, a 250 nm PbZr 0.2 Ti 0.8 O 3 layer as a ferroelectric insulator, and conducting SrRuO 3 as gate electrode. After deposition, the layers were structured by means of reactive ion etching. All materials were structured with a lithographically defined mask in a CHF 3 Ar plasma. Etching with CHF 3 Ar does not produce any volatile etch products but contrary to pure Ar sputter etching, no redeposited materials were found on the structures.

This review deals with the tasks involved in integrating ferroelectric thin films for memory applications. Main emphasis is put on process integration. Some of the results presented (especially dry etching ones) come from the European ESPRIT project called FELMAS. The compatibility of CMOS devices and ferroelectric capacitors is discussed and main issues toward the development of VLSI memories, are outlined.

Several metal oxide perovskites and Bi layered perovskites are of substantial interest for integrated circuit memories. Strontium titanate, barium strontium titanate, and lead zirconate titanate based paraelectrics are of particular interest for dynamic memory applications since they have high charge storage densities, low leakage currents, and resistance against time dependent dielectric breakdown sufficient to achieve gigabit densities and beyond. The high remanent polarization of ferroelectric lead zirconate titanate and strontium bismuth tantalate hold out the promise of low-voltage, high-speed, non-volatile memories. Advances are being made in the reliability of ferroelectric memories.

Modified scheme of the non-volatile memory cell for ferroelectric SRAM is proposed allowing an enhanced reliability and essential lowering of demands to the electrical properties of the ferroelectric capacitors (FECAPs). It is shown that the successful integration of sol-gel FECAPs into a Si-based CMOS technology is possible using the common lift-off and wet-etching photolithography. The FECAPs fatigue problem and its possible physical mechanisms are discussed.

Deposition and patterning processes to produce 9×9μm ferroelectric capacitor (FECAP) structures, and the back-end processes necessary to integrate them with silicon-on-sapphire (SOS) circuits have been developed with the aim of demonstrating a 4kbit non-volatile RAM (NVRAM) on SOS. PZT thin film deposition by a sol-gel route has been characterised and dielectric, ferroelectric and fatigue measurements taken.

One of the basic properties of thin ferroelectric films is the ability to switch polarization under the influence of an external electric field. The application of such thin films as memory devices is based on this phenomenon. The switching process of the thin films has some distinctive features. These include, for example, the dependence of the switching time on the electrode surface and an anomalous variation of the switching time curve with the amplitude of bipolar rectangular electric voltage impulses. To describe the physical nature of these peculiarities a simple model is developed. The qualitative compatibility between experiment and the model is shown on the basis of the Pb(Zr,Ti,B′,B″) O3 (PZT)-type thin films with the chemical constitution Pb(Zr0.53 Ti0.45 W0.01 Cd0.01) O3.

Transition of thin film memory element based on tellurium in a metastable state with quasimetallic conductivity is followed by structural transformations, which leads to a charge ordering of electron density as a result of reallocation of atoms with different valences. The memory effects in these structures are conditioned by cooperative effects of interacting dipole complexes.

Isomerizations of [2.2](4,4′)-azobenzenophane (1) in polycarbonate films were investigated spectrophotometrically, and the light-intensity dependent efficiency of the photoisomerization of macrocyclic azobenzene dimers, including 1, was analyzed theoretically. It is demonstrated that the efficiency of photoisomerization of 1 is dependent on the light intensity, even in a polymer film. A correlation between the lifetimes of the trans-cis isomers of macrocyclic azobenzene dimers and light intensities, where the efficiency of photoisomerization becomes dependent on light intensity, is also described. A photochromic memory composed of 1 and polycarbonate shows a non-destructive read-out property.

A new category of erasable information storage media, M 1−β (TCNQ) films, is described. The photochromatic effect of this organometallic charge-transfer complex can give high-contrast patterns produced directly on a fine-grain film by pulsed photon beams generated from a gas or semiconductor laser. The patterns are erasable. For a radiation with 632.8 nm, the number of write-erase cycles N > 1000 has been obtained with a coefficient of contrast K > 50%. Moreover, the non-linear I–V characteristics of the fine-grain M 1−β (TCNQ) film can be used as a bistable electric switching. An organometallic memory (OMM) with a storage density of 1 Mb cm −2 can be proposed and is compatible with silicon IC chips. To avoid the decoder, an electron-beam operated ‘erasable access storage tube (EAST)’ with a multi-layered M 1−β (TCNQ) target was designed. Its storage density can approach that of a laser disc and the access time is as short as a semiconductor memory. Since no single crystal or p-n junction is needed, the technology is relatively simple and a lower price per bit of memory can be expected.

The effects of CrRu underlayers on the grain size, lattice matching, magnetic, recording and thermal stability characteristics for CoCrPtTa thin film media are presented, CrRu/sub 10/ and CrRu/sub 20/ underlayers produced about 800-960 Oe higher coercivity compared to media with a Cr underlayer. At 300 kfci recording density the CoCrPtTa/CrRu media has about 10-15% lower media noise and about 1-1.5 dB higher SNR compared to the similar media with Cr underlayer. X-ray diffraction data suggest somewhat better lattice matching between the CoCrPtTa/CrRu media due to the addition of Ru to the Cr underlayer compared to CoCrPtTa/Cr media. The CoCrPtTa/CrRu media has an average grain size of 12 nm in comparison to the average grain size of 15 nm for the CoCrPtTa/Cr media. The thin film media with CrRu/sub 10/ underlayer has smaller grain size but similar thermal stability performance compared to Cr underlayer.

We report a systematic experimental study of magnetic interactions and thermal stability in very thin films of CoSm fabricated by DC magnetron sputtering on glass substrates, CoSm/Cr films with CoSm thickness 6 to 14 nm yield high remanent coercivities H/sub cr//spl les/3.8 kOe and low remanent moment thickness product, Mr/spl delta/

Co/sub 77/Cr/sub 20/Ta/sub 3/ films were deposited on a Pt seed layer, and their crystallographic and magnetic characteristics were investigated. The Co-Cr-Ta/Pt bilayered films deposited at the substrate temperature of 250/spl deg/C revealed excellent c-axis orientation and exhibited high perpendicular coercivity. For the Co-Cr-Ta/Pt/Ti trilayered films, Ti underlayer promoted fine granulation in the Pt layer and improved magnetic characteristics of the ultra-thin Co-Cr-Ta recording layer. Media noise level of the Co-Cr-Ta/Pt disk was small at high recording density range. The Co-Cr-Ta/Pt bilayered films are useful for fabrication of perpendicular magnetic recording media.

The Ta content in the CoCrTa/sub x/ intermediate layer effectively influences the crystallographic texture, the grain size and the magnetic properties of NiAl/CrV/CoCrTa/CoCrTaPt thin film media. The thin film media have a preferred in-plane Co (10.0) texture and about 10 nm of mean grain size with more uniform distribution, when the Ta content is in the range of 0-5 at.%. Once Ta content exceeds 7 at.%, the texture of the Co-alloy changed from in-plane to out-of-plane, the grain size increased with wide distribution and the coercivity decreased dramatically. It was found that the grain size becomes small; coercivity, exchange decoupling and thermal stability increase; and the switching volume is reasonably small as the Ta content is increased from 0 to 5 at.%.

The example of ferroelectric films of barium strontium niobate (BSN) deposited on a silicon substrate with a thin ( ca . 10 nm) silicon nitride sublayer was used to show that the specific features of the process of injected charge accumulation in metal-insulator-ferroelectric-semiconductor structures manifest themselves in the effect of amplification of the charge carrier injection from the semiconductor due to the formation of the polarization charge in the ferroelectric, as compared with the corresponding metal-insulator-semiconductor structures. It was established that the introduction of an additional layer of BSN into standard metal-nitride- oxide-semiconductor (MNOS) memory elements leads to a decrease in the writing voltage by a factor of 1.5–2.5, with a simultaneous increase in the number of write- erase cycles by 2–3 orders of magnitude, while the charge storage time remains the same as for the MNOS structures.

Understanding charging mechanisms and charge retention dynamics of nanocrystal memory devices is important in optimization of device design. Capacitance spectroscopy on PECVD grown germanium nanocrystals embedded in a silicon oxide matrix was performed. Dynamic measurements of discharge dynamics are carried out. Charge decay is modelled by assuming storage of carriers in the ground states of nanocrystals and that the decay is dominated by direct tunnelling. Discharge rates are calculated using the theoretical model for different nanocrystal sizes and densities and are compared with experimental data. Experimental results agree well with the proposed model and suggest that charge is indeed stored in the quantized energy levels of the nanocrystals., 10 pages, 5 figures

Size effects with critical thickness or minimum volume for ferroelectricity are of importance in the application of polycrystalline PZT thin films as future memory devices and as storage media. Isolated dots of perovskite phases in the matrix of pyrochlore were synthesized by isothermal annealing through transformation from amorphous to perovskite. Control of the transformation kinetics allows us to produce the isolated ferroelectric dots with a diameter of 50 nm. Domain structure of the isolated dots is also studied by piezoresponse force microscopy. As prepared, all isolated dots contain perpendicularly polarized monodomains. Domain structures and switching behaviors of the isolated dots are similar to those of the single crystalline PZT films. Polycrystalline PZT films with a thickness of 50 nm were also investigated. They show excellent piezoresponse properties and switching behaviors. Ultra-thin polycrystalline PZT films can play a major role in the application of future ferroelectric memories and field-effect transistors as well as for storage media using the local probe technique.

A linear noncontact position sensor using Co/Cu giant magneto-resistance (GMR) multilayers as the sensing material and incorporating a magnetic memory layer has been designed and modeled. A magnetic head assembly acts as the position locator and the presence of a memory layer makes the throw length unlimited. A numerical model using charge sheets and finite elements has been used to optimize the physical dimensions of the magnetic layers for different magnetic materials and determine their spacing from the Co/Cu GMR sensing material. The output from the sensor has been simulated as the head moves back and forth along the track. These results show that hysteresis in the memory layer can be overcome by optimizing the head design. Using easily available materials, the modeling has shown that a device using second anti-ferromagnetic (AF) peak Co/Cu is realizable. The model has also be used to identify desirable material parameters for potential future engineered materials with the aim of utilizing high GMR first AF peak Co/Cu material in the sensor.

TiNi films were deposited on silicon by co-sputtering TiNi target and a separate Ti target at a temperature of 450°C. Results from differential scanning calorimeter, in-situ X-ray diffraction and curvature measurement revealed clearly martensitic transformation upon heating and cooling. Two types of TiNi/Si optical micromirror structures with a Si mirror cap (20 micron thick) and TiNi/Si actuation beams were designed and fabricated. For the first design, three elbow shaped Si beams with TiNi electrodes were used as the arms to actuate the mirror. In the second design, a V-shaped cantilever based on TiNi/Si bimorph beams was used as the actuation mechanism for micromirror. TiNi electrodes were patterned and wet-etched in a solutions of HF:HNO 3 :H 2 O (1:1:20) with an etch rate of 0.6 μm/min. The TiNi/Si microbeams were flat at room temperature, and bent up with applying voltage in TiNi electrodes (due to phase transformation and shape memory effect), thus causing the changes in angles of micromirror.

It has been proved that NiTi shape memory alloy thin film is the best one for micro actuators as compared with the others, e.g., electrostatic, electromagnetic and piezoelectric thin films. If the deposition of NiTi thin films on silicon wafers is carried out at room temperature, the resultant thin films are normally amorphous without shape memory. Subsequent annealing in a high vacuum chamber is required for re-crystallization. In this paper, we present an alternative annealing approach, namely by CO 2 laser. After laser annealing, optical microscope, X-ray diffraction (XRD) and atomic force microscope (AFM) were applied to characterize the NiTi thin films. Strong austenite/martensite lattice structures were observed by XRD. The relationship between the surface roughness of the annealed NiTi thin film and temperature was obtained using AFM. The results indicate that the CO 2 laser annealed NiTi thin films are with shape memory.

A novel micropump actuated by thin film shape memory alloy has been designed, fabricated and tested. It is one of the membrane reciprocating micropumps which is driven by shape recoverable force of NiTi thin film and biasing force of Si membrane. The micropump is composed of a deformable chamber and two Si flap check valves. The structure of pump is simple. The pump was manufactured by Si surface and bulk micromachining technologies, Au-Si eutectic and epoxy bonding. The outer dimension of the micropump is 6*6*1.5 mm/mm/mm. The NiTi/Si composite actuator has an area of 3*3mm/mm with a thickness of 20micrometers Testing result show that the pump has extremely good performance, such as high pumping yield, low power consumption high working frequency. All these advantages are attributed to the patterning of NiTi thin film used as self-heating element and optimizing design of NiTi/Si actuated structure.