bluuebunny/crossref_metadata_2025_split huggingface dataset:
Step Coverage and Composition of Pb(Zr, Ti)O3 Capacitors Prepared on Sub-Micron Three-Dimensional Trench Structure by Metalorganic Chemical Vapor Deposition
Authors: Nagai Atsushi , Asano Gouji , Minamidate Jun , Choi Chel Jong , Cho Choong-Rae , Park Youngsoo , Funakubo Hiroshi 
Published: April 2011

ABSTRACTPb(Zr, Ti)O3 (PZT) films were deposited into sub-micron trench structure consisting of SiO2/TiAlN/Ti/SiO2/Si to investigate their thickness and composition conformality by pulsed-metalorganic chemical vapor deposition (MOCVD) using liquid delivery source-supply system. Bis(dipivaloylmethanato)lead [Pb(DPM)2], tetrakis(1-methoxy-2-methyl-2-propoxy)zirconium [Zr(MMP)4] and tetrakis(1-methoxy-2-methyl-2-propoxy)titanium [Ti(MMP)4] were used as Pb, Zr and Ti source materials, respectively. In Arrhenius plot, the slopes of the straight lines for the constituents Pb, Zr and Ti in PZT film were almost the same at a lower deposition temperature (Td) region as well as a higher Td one. This means the composition change in the film against the Td can be suppressed by using Pb(DPM)2-Zr(MMP)4-Ti(MMP)4-O2 source system. From the results of Arrhenius plot, the Tds were fixed on 450 and 540°C as lower and higher temperatures, respectively. At both Tds, the sidewall-bottom step coverage (SCs-b) was approximately 70 %, while the sidewall step coverage (SCsw) reached excellent values above 90 %. It is suggested that low SCs-b value was caused by crystallization of the PZT films at the bottom of the trench because underlayer of the film at this area was not SiO2 but crystalline TiAlN. On the other hand, no significant composition fluctuation was observed along the depth direction of the sidewall. These results mean that the film deposited at 540°C had almost the same level in terms of thickness and composition conformality as that deposited at 450°C.
Ferroelectric 1-T memory device—will it be viable for nonvolatile memory applications?
Authors: Han Jin-Ping 
Published: April 2011

ABSTRACTThe quest for a nonvolatile memory FET based on the metal-ferroelectric-(insulator)-semiconductor (MF(I)S) gate stack concept has greatly intensified in recent years. In principle, such a memory device (MF(I)S) could be a building block of an ideal memory technology which offers random access, high speed, low power, high density and non-volatility. In practice, however, none of the reported ferroelectric memory transistors has achieved a memory retention time of more than a few days so far. These results are a far cry from the 10-year retention time requirement for non-volatile memory devices. This paper reveals progress and optimization that grain size, interfacial properties, and crystallinity of the annealed ferroelectric SrBi2Ta2O9 (SBT) films have a strong impact on the size of the memory window, as does the choice of the buffer layer material. The properties of SiN buffer layer sandwiched between SBT and Si are discussed. Switches in the polarization of the ferroelectric SBT play a key role for both the ferroelectric-polarization-dominated and the trapping-dominated memory windows. Preliminary results on MFIS capacitors and transistors are reviewed, limited retention time has been observed. A closer look at the physics of device operation reveals two major causes of the short retention time: (1) depolarization fields; (2) finite gate leakage current and the associated charge trapping. Here, the origins of these problems are analyzed and practical difficulties in attempting to realize nonvolatile ferroelectric 1-T memory devices are illustrated. Two possible solutions have been proposed to circumvent problems associated with the finite retention time in ferroelectric FETtype memories: (1) memory refreshes as done in the FEDRAM cell, (2) single-crystallize the ferroelectric film.
Improvement of Ferroelectric and Electrical Properties of Sol-Gel deposited Bi4Ti3Oi2 Thin Films by Multiple Rapid Thermal Annealing Techniques
Authors: Wang Hua. , Ren Minfang 
Published: April 2011

AbstractFerroelectric Bi4Ti3O12 thin films were fabricated by sol-gel method with multiple rapid thermal annealing (MRTA) techniques on Pt/Ti/SiO2/p-Si substrates. The effect of annealing temperature on crystallinity, ferroelectric and electrical properties of Bi4Ti3O12 films derived by MRTA and by normal RTA were investigated. The results reveal that the grain size and the roughness of surface increase with the annealing temperature increase, but the maximal remnant polarization of Bi4Ti3O12
Thin Ferroelectric Film between Double Schottky Barriers
Authors: Delimova Lyuba A. , Grekhov Igor V. , Mashovets Dmitri V. , Shin Sangmin , Koo June-Mo , Kim Suk-Pil , Park Youngsoo 
Published: April 2011

ABSTRACTThin-film uniform metal-ferroelectric-metal (M/F/M) structure between back-to-back Schottky barriers (SBs) is considered. The ferroelectric is assumed to be a p-type semiconductor, and the film thickness is far less than the depletion layer induced by the S.B. Numerical integration of the Poisson equation is used to analyze the influence of double Shottky barriers on the distributions of the electric field, potential, and polarization across the film thickness as functions of external bias and the film electrical history. The range of structure parameters is determined, where the Poisson equation for M/F/M structure can be solved analytically providing an obvious and easy-to-interpret representation of the M/F/M behavior. Electric fields induced by back-to-back SBs under zero external bias compensate each other to a great extent. As a result, the potential across the ferroelectric film remains virtually unchanged providing the flat-band condition in the energy diagram of zero-biased M/F/M structure; in fact, the external bias applied to M/F/M structure exerts influence only on the reverse-biased barrier.
Switching Properties of PST Ferroelectric Films for Memory Applications using Conductive Oxide LSCO Electrodes
Authors: Martínez E. , Blanco O. , Siqueiros J. M. 
Published: April 2011

ABSTRACTWe have investigated the switching properties of ferroelectric lead strontium titanate (Pbx Sr1-x)TiO3 (PST) capacitors using epitaxial and polycrystalline La0.5Sr0.5CoO3 (LSCO) electrodes to evaluate its potential for non-volatile memory applications (FRAM'S). The electrical performance of the PST based capacitors grown on epitaxial and polycrystalline LSCO substrates were evaluated through Polarization-Voltage (P-V) and Fatigue measurements. The [001] preferentially oriented PST ferroelectric capacitor did not show a decrease in polarization up to 108 switching cycles at an applied voltage of 4 volts and a frequency of 100 kHz. Polycrystalline PST films, on the other hand were severely fatigued. It is proposed that the good performance of the PST capacitors can be attributed to the high degree of orientation of the PST films in the [001] direction induced by the epitaxial LSCO film. However, after 1010 switching cycles in the fatigue tests, the decay of the non-volatile polarization of these films was about 18% of its initial value. We use a simple model to describe two major microscopic scenarios for the suppression of polarization at the electrodes interfaces. This model is supported by Auger Electron Spectroscopy to determine the bulk and interfacial characteristics. The depth distribution of the elements of the PST film is nearly uniform throughout the volume of the film; however the relative concentrations of Pb and O were abnormally distributed on the surface. It is concluded that, in spite of the good performance due to the favorable conditions for the growth of the PST films provided by the textured LSCO, higher quality interfaces and better control of composition is necessary to improve on fatigue.
Characterization of Number Fluctuations in Gate-last Metal Nanocrystal Nonvolatile Memory Array beyond 90nm CMOS Technology
Authors: Lee Chungho , Ganguly Udayan , Kan Edwin C. 
Published: April 2011

ABSTRACTExperimental characterization of nanocrystal formation in gate trenches were performed, which includes the analyses of number fluctuation, the size distribution, and the correlation of the size and number density in gate patterns with various feature sizes from 50nm to 150nm. The gate regions with 51nm oxide wall are defined by e-beam lithography and reactive ion etching (RIE). By using direct-deposit self-assembly (i.e., evaporation and post-annealing), Au, Ag, and Pt nanocrystals are formed on the gate tunneling oxide. From the statistical evaluation by scanning electron microscopy (SEM) observation, the number fluctuation of nanocrystals in a gate trench could be always controlled under 12%, while it follows the Poisson distribution in the unconstrained self-assembly. This is mainly due to the confinement effect by the trench sidewalls, corners, and edges. The current study demonstrated that the direct-deposit self-assembly process could be successfully adapted beyond 90nm metal nanocrystal memory technology with satisfactory parametric yield in the nanocrystal number density.
Local Self-Order Observed During Chemical Vapor Deposition of Silicon Quantum Dots for Application in Nanocrystal Memories
Authors: Puglisi Rosaria A. , Nicotra Giuseppe , Lombardo Salvatore , Salvo Barbara De , Gerardi Cosimo 
Published: April 2011

ABSTRACTA systematic study on the Si dot formation after chemical vapor deposition on silicon oxide substrates is presented. The process has been followed from the early stages of the dot formation up to 25% of coverages. Structural characterization has been performed by means of energy filtered transmission electron microscopy, which allowed us to observe dot sizes down to 0.5 nm in radius. The nanodots are shown to be surrounded by a depleted zone, where no new Si dots are observed to nucleate. This has been attributed to the adatoms capture mechanism by pre-existing dots, during the deposition. The dot radius and the capture size are shown to collapse onto the same curve, thus indicating the scaling behavior of the process. The adatom diffusion process is shown to restrict the number of nucleation sites, the final dot size and the dot position, thus driving the process toward partial self-order.
Polymer electrical bistable device and memory cells
Authors: Ouyang Jianyong , Chu Chih-Wei , Prakash Ankita , Yang Yang 
Published: April 2011

ABSTRACTElectrical bistable states with the conductivity different by more than four orders in magnitude were observed in a polymer film sandwiched between two metal electrodes. This polymer film was composed of gold nanoparticles, 8-hydroxyquinoline and polystyrene, and was formed by a solution process. The film can be programmed between the two electrical states by an electric field. The as-prepared device, which was in a low conductivity state, exhibited an abrupt increase of current when the device was scanned up to 2.8 volt (V). The high conductivity state can be returned to the low conductivity state at a voltage of –1.8 V in the reverse direction. The device has a good stability in both the states. The transitions are nonvolatile, and the transition from the low to the high conductivity state takes place in nanoseconds, so that the device can be used as a low-cost, high-density, high-speed, and nonvolatile memory. The switching mechanism was studied by investigating the current-voltage characteristics, the temperature dependence of the current, the surface potential atomic force microscopy and the energy levels of the materials. The electronic transition is attributed to the electric-field induced charge transfer between the gold nanoparticles and 8-hydroxyquinoline molecules.
Non-Volatile Giant Resistance Switching in Metal-Insulator-Manganite Junctions
Authors: Fors Rickard , Khartsev Sergey I. , Grishin Alexander M. 
Published: April 2011

ABSTRACTHeteroepitaxial CeO2(80nm)/L0.67Ca0.33MnO3(400nm) film structures have been pulsed laser deposited on LaAlO3(001) single crystals to fabricate two terminal resistance switching devices. Ag/CeO2/L0.67Ca0.33MnO3 junctions exhibit reproducible switching between a high resistance state (HRS) with insulating properties and a semiconducting or metallic low resistance state (LRS) with resistance ratios up to 105. Reversible electrical switching is a polar effect achievable both in continuous sweeping mode and in the pulse regime.
Microwave Materials with High Q and Low Dielectric Constant for Wireless Communications.
Authors: Ohsato Hitoshi 
Published: April 2011

ABSTRACTMicrowave dielectrics with high Q and low εr are expected for millimeterwave applications. In this paper the preparation and properties of some candidates for microwave dielectrics such as forsterite, willemite, alumina, corundum-type compounds, green phase of Y2BaCuO5 are presented. High purity forsterite has low εr of 7.0 high Q·f of 270000 GHz and τf of -65ppm/°C. Willemite also has low εr of 6.5, and high Q·f of 160000 GHz. Alumina has ultra high Q·f of 680000GHz with εr of 10.05, and τf of -60 ppm/°C. Mg4(Nb2-x Tax)O9 which belongs to corundum group has εr of 11.5, Q·f of 350000 GHz, and τf of -70ppm/°C. Y2Ba(Cu1/4Zn3/4)O5 which belongs to green phase group has εr of 15.4, Q·f of 220000 GHz. The τf’s of these materials, which are an important property for millimeterwave applications, have been adjusted to zero ppm/°C by the addition of rutile, or adjustment of solid solution composition.
MIM Capacitors Using ALD Al2O3 for RF IC and DRAM Applications
Authors: Ko Sung Yong , Oh Jung Ik , Choi Joung Cheul , Lee Kang Hee , Bae Young Ho , Jung Young Chul , Lee Yong Hyun 
Published: April 2011

ABSTRACTMetal-insulator-metal (MIM) capacitors were fabricated in a coplanar waveguide type using the Al2O3 thin film. The Al2O3 film was grown by atomic layer deposition(ALD) using Methyl-Pyrolidine-Tri-Methyl-Aluminum (MPTMA) and H2O on Ti. The capacitance per unit area of the fabricated MIM capacitor was 0.229 μF/cm2. And it had lower voltage coefficient of capacitance (VCC) and lower leakage current than that of Al2O3 MIM capacitor prepared by Al oxidation and Si3N4 MIM capacitor prepared by PECVD respectively. The fabricated Al2O3 MIM capacitors prepared by ALD exhibited low VCC, low leakage current, small frequency-dependent capacitance reduction, low temperature coefficient of capacitance (TCC) and good reliability. The characteristics of the device were suitable for RF ICs and DRAM.
A Study on Thin Film Microstructure and Its Effects on Acoustic Film Velocity Through Picosecond Ultrasonics Technique
Authors: Li Ta-Ching , Pu Nen-Wen , Lwo Ben-Je , Kao Chin-Hsing , Hu Long-Jang 
Published: April 2011

ABSTRACTIn acoustic devices such as film bulk acoustic resonators (FBAR), it is most essential to accurately determine the thin-film sound velocities in situ. In this work, we analyzed the microstructure properties of the zirconia thin films deposited by RF magnetron reactive sputtering with various oxygen partial pressures, and measured the longitudinal film velocity with picosecond ultrasonic technique. The picosecond ultrasonic waves were produced by irradiating the testing samples with an ultrafast laser pulse generated by a self-made mode-locked Ti: Sapphire laser, and detected by a delayed probe laser pulse. The acoustic velocities of the thin films were next determined from the echo times of the ultrasonic waves. To derive more accurate and reliable velocity, three different reflective layers were employed so that the echo shapes and intensities of ultrasonic wave can be compared. It was found in this work that the thin film velocities we measured were less than the bulk value, which can be calculated from Young's modulus and the density. Meanwhile, with the measurement results, it is also found that the measured acoustic velocity and the microstructure of films have strong dependence on the growth conditions. Consequently, accurate thin film velocity will be obtained for an SMR designer through better controlling on deposition conditions during manufacturing process.
Width and Gap Dependent Performance of Ferroelectric Coplanar Waveguide Phase Shifter Based on Ba1-xSrxTiO3 Thin Films
Authors: Moon Seung Eon , Kim Eun-Kyoung , Kwak Min Hwan , Kim Young-Tae , Ryu Han-Cheol , Lee Su-Jae , Kang Kwang-Y ong , Kim Won-Jeong 
Published: April 2011

ABSTRACT(001) oriented (Ba, Sr)TiO3 (BST) thin films were deposited on MgO (001) single crystal substrates by the pulsed laser deposition method. Structural properties of BST films were investigated using X-ray diffractometer. Coplanar waveguide (CPW) device based on BST/MgO layer structure was fabricated by dc sputtering deposition, photolithography and etching process. To study the geometrical factor dependent microwave performance of the CPW phase shifter based on (001) oriented BST film, the CPW devices having various gap and width were fabricated. The microwave dielectric properties of BST CPW phase shifter devices were examined by calculating the scattering parameter obtained using a HP 8510C vector network analyzer with the frequency range 0.5 ∼ 20 GHz at room temperature under the dc bias field of 0 ∼ 40V. The measured return loss and insertion loss at 10 GHz with no dc bias were about -12 ∼ -4 dB and -14 ∼ -3 dB, respectively, which mainly depended on the impedances of the CPW transmission lines. The measured differential phase shift values were about 20 ° ∼ 140 ° at 10 GHz with 40 V dc bias variations, which depended on the gap size.
Optimization of Passive Isolator Based On Barium Ferrite Sputtered Films
Authors: Le Berre M. , Capraro S. , Chatelon J. P. , Rouiller T. , Bayard B. , Barbier D. , Rousseau J. J. 
Published: April 2011

ABSTRACTFerrites have magnetic properties suitable for electronic applications, especially in the microwave range (circulators and isolators). Hexagonal ferrite, such as barium ferrite (BaFe12O19 or BaM), which have a large resistivity and high permeability at high frequencies are of great interest for microwave device applications.This contribution deals with BaM films, 1 to 36 microns thick, which were deposited under optimized conditions by RF magnetron sputtering. The films were then crystallized using a 800°C thermal annealing. Isolators were then realized using patterning of coplanar wave guides with standard lift-off technique. The slots and the central width were 300 μm wide, gold was used for the conductor lines. We evaluated the influence of various parameters on the device performances: the magnetic film thickness, the positioning of the magnetic film (CPW deposited onto the magnetic film or directly on the substrate) and the CPW metallic thickness. As standard design, the CPW were deposited on the top of the magnetic film. For the first design, transmission coefficients showed a non reciprocal effect, which reaches 7 dB per cm of line length at 50 GHz for a 26.5 μm thick BaM film. Both the insertion losses and the non-reciprocal effect measured increased with the magnetic film thickness with a saturation effect. In the second design where the CPW is deposited directly on the substrate, the BaM film was selectively wet etched prior to the metal deposition everywhere except between the conductors. In that case we measured that the non reciprocal effect reached high values for lower BaM thicknesses than in comparison to design # 1 and that the insertion losses also decreased. Moreover for the design # 2, also in relation with the localization of the BaM between the conductors, the non reciprocal effect improved with increasing conductor thickness as the interaction between the field lines created by the conductors and the magnetic film is then favored.
Recent Advances in Microwave Applications of Thin Ferroelectric Films at the NASA Glenn Research Center
Authors: Romanofsky Robert R. , Miranda Felix A. , Van Keuls Fred W. , Valerio Matthew D. 
Published: April 2011

ABSTRACTWe report on recent developments in microwave applications and understanding of thin Ba50Sr50TiO3films. Most of our recent efforts have focused on developing low loss, wide band phase shifters from X-band (8.4 GHz) to Ka-Band (26.5 GHz) for scanning reflectarray antennas. Attempts to reduce tanδ by Mn-doping Ba50Sr50TiO3films are briefly discussed. We have demonstrated a hybrid device at X-band that produces in excess of 300 degrees of phase shift with about 3.5 dB insertion loss and greater that 10% bandwidth. Preliminary results are presented here. The effects of mild (600 rad Si) proton radiation on device performance will also be discussed. Preliminary results on optical phase shifters will be included.
Novel nonreciprocal materials based on magnetic photonic crystals
Authors: Figotin A. , Vitebskiy I. 
Published: April 2011

ABSTRACTMagnetic photonic crystals are spatially periodic dielectric composites with at least one of the constitutive components being a magnetically polarized material. Magnetic polarization, either spontaneous or induced, is always associated with nonreciprocal circular birefringence (Faraday rotation), which can bring qualitatively new features to the electrodynamics of photonic crystals. If the geometry of the periodic array meets certain symmetry criterion, the electromagnetic properties of the composite appear similar to those of a hypothetical bianisotropic medium with gigantic linear magnetoelectric effect. In particular, such a photonic crystal can display sptrong spectral asymmetry, which implies that electromagnetic waves propagate from left to right significantly faster or slower than from right to left. The strong spectral asymmetry can result in the phenomenon of electromagnetic unidirectionality. A lossless unidirectional medium, being perfectly transmissive for electromagnetic wave of certain frequency, “freezes” the radiation of the same frequency propagating in the opposite direction. The frozen mode is a coherent Bloch wave with nearly zero group velocity and drastically enhanced amplitude. The phenomenon of electromagnetic unidirectionality is essentially nonreciprocal and unique to gyrotropic photonic crystals. Physical conditions for the phenomenon include (i) significant Faraday rotation in the magnetic component of the composite structure at the frequency range of interest and (ii) the proper spatial arangement of the constituents. Unidirectional photonic crystals can be very attractive for a variety of applications.
Magneto-optical response of a one-dimensional all-garnet photonic crystal in transmission and reflection
Authors: Kahl S. , Grishin A. M. 
Published: April 2011

ABSTRACTWe present spectra of transmittance, reflectance, and Faraday rotation of transmitted and reflected light for a periodic garnet multilayer structure with a central defect layer. The multilayer consists of alternating layers of bismuth and yttrium iron garnet, is 1.5 μm thick, and was prepared by pulsed laser deposition. For the reflection measurements, a silver mirror was evaporated on top of the multilayer. Faraday rotation is strongly enhanced at resonances in transmission and reflection. The peak value obtained at 748 nm in transmission is 5.3 deg and at 733 nm in reflection is 18 deg. A single layer BIG film of equivalent thickness shows 2.2 deg Faraday rotation at 748 nm. We find rather good agreement between measured and calculated spectra. Using calculations of the distributions of light intensities at different wavelengths inside the multilayer, we are able to give consistent qualitative explanations for the enhancement of Faraday rotation. We also find numerically that - at moderate strengths of the optical resonances - a linear relation exists between Faraday rotation and the intensity integrated over all magneto-optically active layers, if absorption is neglected.We suggest to modify the usual sensor film for magneto-optical imaging by introducing a Bragg mirror consisting of heteroepitaxial garnet layers between the substrate and sensor film. For one example situation, we show by calculation that the quality factors of image contrast and optical efficiency can be higher for heteroepitaxial garnet multilayers than for single-layer iron garnet films currently in use as sensor films.