bluuebunny/crossref_metadata_2025 huggingface dataset:
A structural analysis of the Pd/GaN ohmic contact annealing behavior
Authors: Kim C. C. , Ruterana P. , Je J. H.
Published: April 2011

For ohmic contact on p GaN, palladium is one of the best candidates showing ohmic characteristics already without annealing. To be realized in devices, it is necessary to know the behavior of the ohmic contacts at accelerated conditions, especially for high temperatures and power. We report on the structural evolution of palladium layers (30 nm) deposited on GaN (0001) by electron beam evaporation without intentional annealing. They were next cut into various pieces which were individually submitted to rapid thermal annealing at 400, 500, 600, 700 and 800°C for 10 sec. We investigate the differences in the microstructure and the location of interfacial phases and their relationships as determined by X-ray diffraction and transmission electron microscopy, we then suggest the formation mechanism based on the relationship. It is shown that the interface is disrupted at annealing above 600°C and by 800°C only very small patches of Pd are still present, however they area completely imbedded in a matrix of intermetallic phases (gallides) formed by the reaction with GaN.
Nitrogen Gas-Cluster Ion Beam – A New Nitrogen Source for GaN Growth
Authors: Shao Y. , Chen T. C. , Fenner D. B. , Moustakas T. D. , Chu George
Published: April 2011

In this paper we report sapphire nitridation and GaN film growth by using ionized nitrogen clusters as a nitrogen source. The clusters, typically 2000–3000 molecules/charge, are generated by a prototype GCIB source. The clusters are accelerated to 10–25 kV and disintegrate upon impact with the substrate surface where they react with Ga atoms to form GaN. The efficiency of this novel nitrogen source was tested by studying the nitridation of (0001) sapphire substrates at relatively low temperatures of 200 - 400°C. The effect of exposure of the substrate to the nitrogen cluster-ion beam was examined by XPS, RHEED and AFM. It was found that the amount of retained surface nitrogen increases nonlinearly with increasing beam energy. There exists a threshold energy, ∼ 20 kV, above which nitrogen retention is significantly enhanced.

GaN films were grown with such nitrogen clusters heteroepitaxially on sapphire/AlN-buffer (MBE grown) and homoepitaxially on thick GaN on sapphire (HVPE grown).TEM cross-section images indicate that the heteroepitaxial GaN films had defect density similar to that of MBE and MOCVD grown films. The homoepitaxially-grown GaN films were found to replicate the GaN templates and show strong cathodoluminescence (CL) emission at 363 nm with FWHM of 9 nm. Furthermore, the spectra show no evidence of yellow band emission.
Growth and Characterization of non-polar (11–20) GaN and AlGaN/GaN MQWs on R-plane (10–12) sapphire
Authors: Iyer Sandeep , Smith David J. , Bhattacharyya A. , Ludwig K. , Moustakas T. D.
Published: April 2011

The majority of GaN films and related devices have been grown along the polar [0001] direction, and epitaxial growth along non-polar directions has received much less attention. In this paper we report the study of material properties of GaN and AlGaN/GaN multiple quantum wells (MQWs) deposited on R-plane (10–12) sapphire substrates using RF plasma-assisted molecular beam epitaxy (MBE). In this growth direction, III-Nitrides grow along the non-polar [11–20] direction, with thec-axis in the plane of growth. Various nucleation steps such as surface nitridation, as well as GaN and AlN buffer layers were investigated. Our results indicate that surface nitridation of R-plane sapphire is an undesirable nucleation step, contrary to what has been observed in the case of (0001) sapphire. The AlN buffer layer leads to well-oriented films along the [11–20] direction with many threading defects and faceted surface morphology whereas the GaN buffer leads to the formation of mis-oriented domains close to the buffer region. However, these domains are overgrown and the films have smoother surface morphology with fewer threading defects. These structural findings are supported by photoluminescence and Hall effect measurements done on the same films. Photoluminescence (PL) measurements of (11–20) AlGaN/GaN MQWs show much higher intensity than for similar structures grown on the C-plane sapphire, consistent with the absence of internal fields in the non-polar direction.
Correlation Between the AlN Buffer Layer Thickness and the GaN Polarity in GaN/AlN/Si(111) Grown by MBE
Authors: Sanchez A. M. , Ruterana P. , Vennegues P. , Semond F. , Pacheco F. J. , Molina S. I. , Garcia R. , Sanchez-Garcia M. A. , Calleja E.
Published: April 2011

In this work it is shown that thin AlN buffer layers cause N-polarity GaN epilayers, with a high inversion domains density. When the AlN thickness increases, the polarity of the epilayer changes to Ga. The use of a low temperature AlN nucleation layer leads to a flat AlN/Si(111) interface. This contributes to decrease the inversion domains density in the overgrown GaN epilayer with a Ga polarity.
Theoretical analysis of <0001> tilt grain boundaries in GaN at the atomic scale
Authors: Chen Jun , Ruterana Pierre , Nouet Gérard
Published: April 2011

Epitaxial layers of GaN contain a very high density of threading dislocations. In the first stage of growth they may form low and high angle grain boundaries. Energetic calculations of <0001> tilt grain boundaries have been performed with the Stillinger-Weber potential modified to take into account the wrong bonds Ga-Ga and N-N. The variation of the energy has been calculated as a function of the rotation angle. Two minima exist with special atomic structures based on a limited number of structural units. They are used to describe the other misorientations in terms of dislocation cores.
Ion Beam Study of Early Stages of Growth of GaN films on Sapphire
Authors: Trifan Eugen M. , Ingram David C.
Published: April 2011

An innovative approach for in-situ characterization has been used in this work to investigate the composition, growth mode, morphology and crystalline ordering of the early stages of growth of GaN films grown on sapphire by MOCVD for substrate temperatures in the range of 450°C to 1050°C. We have performed in-situ characterization by Rutherford Backscattering Spectroscopy (RBS), Ion Channeling, X-ray Photoelectron Spectroscopy (XPS), and Low Energy Electron Diffraction. Ex-situ the films have been characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and thickness profilometry. The films have been grown in an in-house designed and build MOCVD reactor that is attached by UHV lines to the analysis facilities. RBS analysis indicated that the films have the correct stoichiometry, have variable thickness and for low substrate temperature completely cover the substrate while for temperatures 850°C and higher islands are formed that may cover as few as 5 percent of the substrate. From Ion Channeling and LEED we have determined the crystallographic phase to be wurtzite. The crystalline quality increases with higher deposition temperature and with thickness. The films are epitaxialy grown with the <0001> crystallographic axis and planes of the GaN films aligned with the sapphire within 0.2 degrees.
Comparisons of Gallium Nitride and Indium Nitride Properties after CF4 / Argon Reactive Ion Etching
Authors: Wintrebert-Fouquet Marie , Scott K. , Butcher A. , Lam Simon K H
Published: April 2011

We present a comparative study of the effects of low power reactive ion etching (RIE) on GaN and InN. This new, highly chemical, dry etching, using CF4 and Ar, has been developed for thin nitride films grown at low temperature in our laboratories. GaN films were grown by remote plasma enhanced-laser induced chemical vapor deposition and InN films were grown by radio-frequency RF reactive sputtering. Commercial GaN samples were also examined. Optical and electrical characteristics of the films are reported before and after removing 100 to 200 nm of the film surface by RIE. We have previously shown that the GaN films, although polycrystalline after growth, may be re-crystallized below the growth temperature. Removal of the surface oxide has been found to be imperative since a polycrystalline residue remains on the surface after re-crystallization.
The Properties of a P-Implanted GaN Light-Emitting Diode
Authors: Kikawa J. , Yoshida S. , Itoh Y.
Published: April 2011

Electroluminescence measurements of P-implanted GaN light-emitting diodes were performed. The measured peak densities of P in the GaN were 5×10 cm−3 and 4×10 cm−3 based on secondary ion mass spectroscopy. The EL spectra had a broad blue-band emission at the peak energy from around 2.8 eV to 3.3 eV and yellow-band emission at an energy centered at 2.2 eV. The blue-band emission could decompose into two components at energy positions of 2.9 eV and 3.2 eV. The former component is considered to be emission due to the recombination of the bounding exciton by P atoms, known as an isoelectronic trap in GaN.
Surface acoustic wave resonator from thick MOVPE-grown layers of GaN(0001) on sapphire
Authors: Pettersen Sverre V. , Tybell Thomas , Rønnekleiv Arne , Rooth Stig , Schwegler Veit , Grepstad Jostein K.
Published: April 2011

We report on fabrication and measurement of a surface acoustic wave resonator prepared on ∼10m thick GaN(0001) films. The films were grown by metal-organic vapor phase epitaxy on a c-plane sapphire substrate. The surface morphology of the films were examined with scanning electron and atomic force microscopy. A metallic bilayer of Al/Ti was subsequently evaporated on the nitride film surface. Definition of the resonator interdigital transducers, designed for a wavelength of λ=7.76m, was accomplished with standard UV lithography and lift-off. S-parameter measurements showed a resonator center frequencyf0=495MHz at room temperature, corresponding to a surface acoustic wave velocity of 3844m/s. The insertion loss at center frequency was measured at 8.2dB, and the loaded Q-factor was estimated at 2200. Finally, measurements of the resonator center frequency for temperatures in the range 25–155°C showed a temperature coefficient of -18ppm/°C. The intrinsic GaN SAW velocity and electromechanical coupling coefficient were estimated at νSAW=383 1m/s andK2=1.8±0.4·10−3.
High Power 325 Light Emitting Diode Arrays by Flip-Chip Packaging
Authors: Chitnis Ashay , Shatalov Maxim , Adivarahan Vinod , Zhang Jian Ping , Wu Shuai , Sun Jie , Asif Khan M.
Published: April 2011

We report flip-chip 325 nm emission light emitting diodes over sapphire with dc powers as high as 0.84 mW at 180mA and pulse powers as high as 6.68 mW at 1A. These values to date are the highest reported powers for such short wavelength emitters. Our data shows the device output power under dc operation to be limited by the package heat dissipation. A study is presented to determine the role of thermal management in controlling the power output for the reported 325 nm ultraviolet light emitting diodes.
Epitaxial Growth for Solar-Blind AlGaN Photodetector Imaging Arrays by Metalorganic Chemical Vapor Deposition
Authors: Chowdhury Uttiya , Collins Charles J. , Wong Michael M. , Zhu Ting Gang , Denyszyn Jonathan C. , Choi Jin Ho , Yang Bo , Campbell Joe C. , Dupuis Russell D.
Published: April 2011

Solar-blind imaging arrays based on AlGaN p-i-n structures are of high interest for defense applications. We have studied the material issues involved in development of such imaging arrays and have developed discrete photodetector devices with a high external quantum efficiency (EQE) and imaging arrays of high operability.

For the discrete devices, a record EQE of 58.1% peaking at 274 nm under zero volt bias was obtained without using an anti-reflecting (AR) coating. The EQE was seen to have a slight voltage dependence: going up to 64.5% at –5V reverse bias. The responsivity had a drop-off by one order of magnitude for a wavelength change of 4 nm on both the shorter and longer wavelength side. The material quality and uniformity was found to be very good leading to the development of 256 × 256 arrays. A high yield along with uniform, high EQE was obtained for the detector devices in the array leading to a high operability of 99.8%.
Self-Heating Effects in Multi-Finger AlGaN/GaN HFETs
Authors: Kuball M. , Rajasingam S. , Sarua A. , Uren M. J. , Martin T. , Balmer R. S. , Hilton K. P.
Published: April 2011

We report on the in-situ measurement of temperature, i.e., self-heating effects, in multi-finger AlGaN/GaN HFETs grown on SiC substrates. Optical micro-spectroscopy was used to measure temperature with 1m spatial resolution. Thermal resistance (temperature rise per W/mm) was measured as a function of device pitch and gate finger width. There is significant thermal cross talk in multi-finger AlGaN/GaN HFETs and this needs to be seriously considered for device performance and ultimately device reliability. A comparison with theoretical modeling is presented. Uncertainties in modeling parameters currently make modeling less reliable than experimental temperature assessment of devices.
Nickel, Platinum and Zirconium Germanosilicide Contacts to Heavily Phosphorous Doped Silicon-Germanium Alloys for Advanced CMOS Source/Drain Junctions
Authors: Mo Hongxiang , Liu Jing , Öztürk Mehmet C.
Published: April 2011

As the MOSFET dimensions continue to shrink, source/drain contact resistance is emerging as the dominant component of the MOSFET parasitic series resistance. To meet the series resistance requirements of future MOSFETs, contact resistivity values near 10-8 ohm-cm2 are required. Selective Si1-xGex source/drain technology has been proposed as an alternative to ionimplantation to form the ultra-shallow junctions of future CMOS technology nodes. One of the key advantages of this technology is the smaller band gap of Si1-xGex, which provides a smaller contact barrier height, an essential requirement for reducing the contact resistivity. We have previously reported low-resistivity of Ni germanosilicide NiSi1-xGex and Pt germanosilicide PtSi1-xGex contacts to boron doped Si1-xGex alloys. In this work, Zr germanosilicide, Zr(Si1-xGex)2 was considered as an alternative material with a higher thermal stability than Ni and Pt germanosilicides. The contact resistivity values for different contact materials were measured using four-terminal Kelvin structures. The results from this work show that both Zr and Pt germanosilicides yield high contact resistivity values around 10-7 ohm-cm2. On the other hand Ni germanosilicide contacts can reach 10-8 ohm-cm2 with further improvements using a thin layer of Pt under Ni.
Ni Silicide Formation on Polycrystalline SiGe and SiGeC Layers
Authors: Haralson Erik , Jarmar Tobias , Seger Johan , Radamson Henry H. , Zhang Shi-Li , Östling Mikael
Published: April 2011

The reactions of Ni with polycrystalline Si, Si0.82Ge0.18 and Si0.818Ge0.18C0.002 films in two different configurations during rapid thermal processing were studied. For the usually studied planar configuration with 20 nm thick Ni on 130–290 nm thick Si1-x-yGexCy, NiSi1-xGex(C) forms at 450°C on either Si0.82Ge0.18 or Si0.818Ge0.18C0.002, comparable to NiSi formed on Si. However, the agglomeration of NiSi1-xGex(C) on Si0.818Ge0.18C0.002 occurs at 625°C, about 50°C higher than that of NiSi1-xGex on Si0.82Ge0.18. For thin-film lateral diffusion couples, a 200-nm thick Ni film was in contact with 80–130 nm thick Si1-x-yGexCy through 1–10 μm sized contact openings in a 170 nm thick SiO2 isolation. While the Ni3Si phase was formed for both the Si0.82Ge0.18 and Si0.818Ge0.18C0.002 samples, the presence of 0.2 at.% C caused a slightly slower lateral growth.
Physical and Electrical Properties of Al2O3, HfO2, and their Alloy Films Prepared by Atomic Layer Deposition for 65nm CMOS Gate Dielectric
Authors: Kawahara Takaaki , Torii Kazuyoshi , Fukuda Seiichi , Maeda Takeshi , Horiuchi Atsushi , Ito Hiroyuki , Muto Akiyoshi , Kato Yoshitake , Kitajima Hiroshi
Published: April 2011

We have investigated physical and electrical properties of Al2O3, HfO2, and their alloy films deposited on 300mm Si wafers by Atomic Layer Deposition (ALD). It is found that Al2O3 films are not crystallized even after the heat treatment of 1050°C, while HfO2 films are already crystallized even after a-Si deposition (530°C). The crystallization temperature can be higher by adding Al2O3 to HfO2. It is confirmed by in-plane XRD and plane views of TEM that HfAlOx films with lower Hf content (Hf/(Hf+Al) <30%) are amorphous without phase separation after annealing at 1050°C and 5sec. The dependences of equivalent oxide thicknesses (EOT) on the physical thicknesses of Al2O3, HfAlOx (Hf/(Hf+Al)∼22%), and HfO2 films in poly-silicon gate capacitors indicate that those dielectric constants k are ∼9, 14, and 23, respectively. The gate dielectric with EOT of 1.5nm and the leakage current density Jg of 3mA/cm2 can be fabricated with 2nm-thick HfAlOx (22%) film.
Copper Diffusion Characteristics in Single Crystal and Polycrystalline TaN
Authors: Wang H. , Tiwari Ashutosh , Zhang X. , Kvit A. , Narayan J.
Published: April 2011

TaN has become a very promising diffusion barrier material for Cu interconnections, due to the high thermal stability requirement and thickness limitation for next generation ULSI devices. TaN has a variety of phases and Cu diffusion characteristics vary with different phases and microstructures. We have investigated the diffusivity of copper in single-crystal (NaCl-structured) and polycrystalline TaN thin films grown by pulsed laser deposition. The polycrystalline TaN films were grown directly on Si(100), while the single crystal films were grown with TiN buffer layers. Both of poly and single-crystal films with Cu overlayers were annealed at 500 °C, 600 °C, 650 °C, and 700 °C in vacuum to study the copper diffusion characteristics. The diffusion of copper into TaN was studied using STEM-Z contrast, where the contrast is proportional to Z (atomic number), and TEM. The diffusion distances are found to be about 5nm at 650°C for 30 min annealing. The diffusivity of Cu into single crystal TaN follows the relation D = (160±9.5)exp[-(3.27 ±0.1)eV/kBT]cm2s-1 in the temperature range of 600°C to 700°C. We observe that Cu diffusion in polycrystalline TaN thin films is nonuniform with enhanced diffusivities along the grain boundary.
Low Thermal Budget NiSi Films on SiGe Alloys
Authors: Ray S. K. , Adam T. N. , Kar G. S. , Swann C. P. , Kolodzey J.
Published: April 2011

Nickel silicides were formed on Si (100) substrates and CVD grown Si0.9Ge0.1/Si layers by low thermal budget annealing of evaporated Ni films to evaluate their utility for ultra shallow junctions. The phase formation and microstructure of silicides formed using conventional furnace and rapid thermal annealing were studied by x-ray diffraction, Rutherford backscattering (RBS), x-ray photoelectron spectroscopy (XPS) and atomic force microscopy. RBS simulations and XPS study revealed the formation of a ternary nickel germanosilicide phase for the SiGe alloy. The incorporation of Ge resulted in a higher temperature window for the stability of low-resistive monosilicide phase. Electrical properties of the grown silicides were characterized by four-probe resistivity and contact resistance measurements.
Atomic Structure, Band Offsets and Hydrogen in High K oxide:Silicon interfaces
Authors: Robertson J , Peacock P W
Published: April 2011

The bonding, electronic structure and valence band offsets are calculated for various atomic models of interfaces between Si and high dielectric constant insulators ZrO2 and SrTiO3. A non-polar face of the oxide does not necessarily give a semiconducting interface, because of the need to fill Si dangling bond states on the Si side. This can be achieved by stoichiometry changes. Band offsets of semiconducting interfaces are generally the same as those found from bulk charge neutrality levels, indicating no dipole layers. Dipole layers are present at some configurations, where the offset is then changed by up to 1 eV. The states of hydrogen in the oxides are also considered.
The Influence of Defects on Compatibility and Yield of the HfO2-PolySilicon Gate Stack for CMOS Integration
Authors: Kaushik V. S. , DeGendt S. , Carter R. , Claes M. , Rohr E. , Pantisano L. , Kluth J. , Kerber A. , Cosnier V. , Cartier E. , Tsai W. , Young E. , Green M. , Chen J. , Jang S-A. , Lin S. , Delabie A. , Elshocht S.V. , Manabe Y. , Richard O. , Zhao C. , Bender H. , Caymax M. , Heyns M.
Published: April 2011

Hafnium-based dielectrics are under wide consideration for high-K gate dielectric applications. Since the gate electrode typically used in CMOS integration consists of polysilicon with n- or p-type dopants, compatibility of the HfO2layer with the polySi deposition and dopant activation steps is critical. Capacitors were fabricated with HfO2films deposited by ALD and MOCVD, and using polysilicon gate electrodes deposited by CVD processes. These devices showed leakage failures with yields that were observed to depend on the area, dielectric thickness and annealing conditions during the process. Investigation of the root cause of these leakage failures suggested that the leakage failures may be caused by a defect-related mechanism. The implication of this is that the leakage occurs at localized ‘defect’ sites rather than broadly through the HfO2layer. Emission microscopy analysis and physical characterization of the HfO2film were used to corroborate the proposed model. Defect density was observed to be strongly dependent on the processing of the dielectric film. In order to make Hf-based dielectric stacks compatible with polysilicon for conventional CMOS transistor integration with acceptable yield, further postdeposition treatment may be necessary to eliminate or cure the defects.
Conduction Mechanisms in SrTiO3 Thin Films on Silicon
Authors: Mereu Bogdan , Sarau George , Alexe Marin
Published: April 2011

New materials with high dielectric constant are currently being explored to replace silicon dioxide as gate dielectric for device scaling below 0.1 μm. With respect to conventional SiO2, these high permittivity dielectrics provide the required equivalent oxide thickness (EOT) without of further reduction of the insulator physical thickness, which is a key issue to limit gate leakage current and to maintain comparable MOSFET operation and reliability. The present paper presents preliminary results on conduction mechanisms in thin epitaxial SrTiO3 films grown by MBE on Si (100). I-V measurements were performed on Al/STO/Si structures at temperatures ranging from 40 K to 290 K. At temperatures lower than 100 K the conduction mechanism of electrons from gate electrode across the oxide barrier neither Schottky emission nor tunneling. For temperatures higher than 100 K Schottky emission occurs and barrier heights were extracted, showing an approximate linearly increase with temperature. In case of Si/STO interface, a Fowler-Nordheim tunneling mechanism was detected at 40 K and at intermediate fields. The extracted barrier heights are: 0.07 eV at Si/STO interface and from 0.26 eV (130 K) to 0.53 eV (290 K) at Al/STO interface.
Enhancement of Remanent Polarization of BIT-based Thin Films by Ti-site Substitution using Ions with Higher Charge Valences
Authors: Uchida Hiroshi , Okada Isao , Matsuda Hirofumi , Iijima Takashi , Watanabe Takayuki , Funakubo Hiroshi
Published: April 2011

Bismuth titanate (Bi4Ti3O12; BIT) -based ferroelectric thin films fabricated from a view point of “the site-engineering technique” have been expected to improve the fatal disadvantage of a ferroelectric BIT film, i.e., its low spontaneous polarization; here, Bi- and Ti-site ions in the BIT crystal are cosubstituted by lanthanoid ions and cations with a higher charge valence, respectively, In the present study, we have mainly focused on Ti-site substitution of bismuth titanate (Bi4Ti3O12; BIT)-based thin films using some ions with higher charge valences (V5+, Nb5+, Ta 5+ and W6+; in this study) to enhance the ferroelectric properties of those materials. The BIT-based films with various chemical compositions were fabricated on a (111)Pt/Ti/SiO2/(100)Si substrate by a chemical solution deposition method.

Ti-site substitution of BIT films by the higher-valent ions, Bi3.99(Ti2.97V0.03)O12, Bi3.99(Ti2.97Nb0.03)O12, Bi3.99(Ti2.97Ta0.03)O12 and Bi3.98(Ti2.97W0.03)O12, reduced the leakage current density of BIT films from ∼ 10-6 down to ∼ 10-7 A/cm2 at an applied field of 50 kV/cm, while the substitution by the same-valent cation, e.g., Bi4.00(Ti2.97Zr0.03)O12, did not affect the behavior of leakage current. Whereas polarization (P) - electrical field (E) hysteresis loops of non-substituted and Zr-substituted BIT films were distorted due to the leakage current, non-distorted P-E loops were obtained at V5+-, Nb5+-, Ta5+- and W6+-substituted BIT films.

Also, Ti-site substitution was effective for improving the ferroelectric properties in lanthanoid-substituted BIT films. In the case of La3+-substituted BIT film (BLT), remanent polarization (Pr) of V5+- and W6+-substituted BLT films, (Bi3.24La0.75)(Ti2.97V0.03)O12 and (Bi3.23La0.75)(Ti2.97W0.03)O12 (13 and 12 μC/cm2, respectively), were larger than those of Zr4+- and non-substituted BLT films, (Bi3.25La0.75)(Ti2.97Zr0.03)O12 and (Bi3.25La0.75)(Ti3.00)O12 (8 and 9 μC/cm2, respectively), while those films had similar coercive field (Ec) of approximately 120 kV/cm. Also in the case of Nd3+-substituted BIT film (BNT), Pr and Ec values of V5+-substituted BNT film, (Bi3.24Nd0.75)(Ti2.98V0.02)O12, were 37 μC/cm2 and 119 kV/cm, respectively, which were comparable with those of conventional Pb-based ferroelectrics such as lead zirconate titanate, Pb(Zr,Ti)O3. We concluded that enhancement of the Pr value was achieved by the charge compensation of oxygen vacancies in BIT-based ferroelectrics using higher-valent cations than Ti4+ ion whereas no obvious differences were found in the crystal orientation and or microstructure of these films.
Preparation of Bi2SiO5-SrBi2Ta2O9 Ferroelectric Thin Films by RF Magnetron Sputtering
Authors: Kikuchi Shin , Ishiwara Hiroshi
Published: April 2011

Si-added SrBi2Ta2O9 (SBT) ferroelectric films were prepared by RF magnetron sputtering on a Pt/Ti/SiO2/Si (100) structure. The films were deposited at temperatures below 100°C for preventing Bi evaporation and crystallized at 800°C in air. A typical composition was Sr0.79Bi2.37Ta2.00Si0.2Ox. The remnant polarization value(2Pr) of the Si-added SBT film was 16C/cm2 and leakage current density was 5×10-8A/cm2. The current density was significantly decreased by adding Si atoms.
Microstructure and dielectric properties of epitaxial BaTiO3 films and BaTiO3/SrTiO3 multilayers
Authors: Visinoiu A. , Scholz R. , Alexe M. , Hesse D.
Published: April 2011

Epitaxial BaTiO3 films and BaTiO3/SrTiO3 multilayers were grown by pulsed laser deposition (PLD) on (001)-oriented Nb-doped SrTiO3 (SrTiO3:Nb) substrates. Measurements of the dielectric properties were performed comparing BaTiO3 films and BaTiO3/SrTiO3 multilayers of different number of individual layers, but equal overall thickness. The dielectric loss saturates for a thickness above 300 nm, and linearly decreases with decreasing film thickness below a thickness of 75 nm, and it is independent on the number of multilayers, pointing to some interface effect. The thickness dependence of the dielectric constant of BaTiO3 films and BaTiO3/SrTiO3 multilayers exhibits a change in the linear slope at a thickness of 75 nm. This behavior is explained by the change observed in the morphology at a thickness of 75 nm. In order to explain the thickness dependence of the dielectric constant, two approaches are considered in this paper, viz. a “series capacitor” model and a “dead layer” model.
Barium Strontium Titanate Thin Film Capacitors for Low Inductance Decoupling Applications
Authors: Baniecki J. D. , Shioga T. , Kurihara K.
Published: April 2011

Sputter deposited barium strontium titanate (BST) based thin film capacitors have been developed for use in GHz LSI decoupling applications. The fabricated 1.60×1.85 mm2 BST chip decoupling capacitors with Pt electrodes and 150 μm bump pitch, have a capacitance density of 1.2 μF/cm2, low equivalent series inductance of 15 pH, and a low equivalent series resistance of 0.02 Ω. The impedance of the chip capacitors at 1 GHz is over 1000 times lower than conventional multilayered ceramic capacitors. Fundamental electrical and reliability properties of Pt/BST/Pt thin film capacitor structures were also investigated. Capacitors with 200 nm thick BST thin films deposited at 500 °C by RF magnetron sputtering achieved a C/A of 1.8 μF/cm2, leakage current density < 10-9 A/cm2 at 2 volts, and a breakdown field > 2.5 MV/cm at 20 °C. A fit of the failure data to a Weibull distribution indicated at least two different physical mechanisms causing capacitor failure. The primary failure mechanism for 1.5 volt operation was due to resistance degradation without catastrophic capacitor failure. At higher applied voltages, catastrophic capacitor failure occurred with the breakdown event characterized by a thermal runway process. The physical mechanisms contributing to capacitor failure are interpreted to be due to ionic migration and charge injection, and the contribution of these mechanisms to the degradation process could be partially resolved by bi-polar voltage pulse stressing. The projected mean time to failure for 1.5 volt operation is extrapolated to be in excess of 104 years at 75 °C and 126 years at 125 °C. The results indicate that sputter deposited BST thin film capacitors are promising for future GHz LSI decoupling applications.
Nucleation and growth of thin (Ba,Sr)TiO3 films in a MOCVD reactor
Authors: Regnery S. , Ding Y. , Ehrhart P. , Fitsilis F. , Jia C. L. , Szot K. , Waser R. , Schienle F. , Schumacher M. , McEntee T.
Published: April 2011

(BaxSr1-x)TiO3 thin films were deposited on Pt electrodes in a planetary multi-wafer MOCVD reactor combined with a liquid delivery system. The nucleation behavior and the size of the stable nuclei were investigated by different SPM techniques and by XPS. Characteristic differences were observed between deposition temperatures of 565°C and 655°C, i.e. a homogeneous nucleation of small BST grains on the larger Pt grains (100 − 200 nm in-plane size) at low temperatures and a dominating nucleation at the grain boundaries at high temperatures. Further film growth was investigated for nominal film thickness between 5 and 100 nm and details of the grain structure are revealed by HRTEM, e.g., randomly oriented grains (typical in-plane size 10–20nm) with a high density of twins at 565°C and (100)-oriented defect free grains of slightly increased size at 655°C. As the electrical properties like permittivity and also leakage current depend on film thickness the final discussions of the electrical properties are based on thickness series and evaluated within the phenomenological dead layer model.
Thermodynamic Analysis of the Hysteresis Offsets from Polarization Graded Ferroelectric Materials
Authors: Ban Z.-G. , Alpay S. P. , Mantese J. V.
Published: April 2011

Polarization graded ferroelectrics exhibit unconventional electrical properties that are not usually observed from homogenous ferroelectrics. Systematic spatial variations in the polarization in a ferroelectric material can be achieved by composition, temperature, and stress gradients; resulting in the displacement of the polarization vs. electric field hysteresis curve along the polarization axis. In this paper, this unusual phenomenon of hysteresis offset has been examined in BaTiO3 and BaxSr1-xTiO3 material systems using a Landau-Ginzburg phenomenological model for the first time. It is shown that the spatial non-uniformities can give rise to non-uniformities in polarization with corresponding spatial variations. This non-uniform polarization results in asymmetrical hysteresis with “up” or “down” charge offsets which are strongly dependent upon the magnitude and direction of the temperature, composition and stress gradients for three graded ferroelectrics.
Investigation of Ferroelectric Properties of Vinylidene Fluoride Oligomer Evaporated Films
Authors: Noda K. , Ishida K. , Mochizuki K. , Kubono A. , Horiuchi T. , Yamada H. , Matsushige K.
Published: April 2011

Structures and electrical properties of newly synthesized vinylidene fluoride (VDF) oligomer [CF3(CH2CF2)17I] films evaporated onto various substrates around liquid nitrogen temperature were investigated. As a result, the VDF oligomer films were mainly formed with ferroelectric phase (form I) crystals and the molecular chains were oriented parallel to the substrate surfaces regardless of both the kind of the substrates and the thickness of the VDF oligomer films. In addition to these properties, the VDF oligomer films showed polarization reversal due to 180° rotation of the polar VDF oligomer molecules according to the applied voltages. This ferroelectric behavior was verified by local poling and piezoresponse measurements with an atomic force microscope, and by measurements of D-E hysteresis curves.
Structural and Vibrational Properties of Ferroelectric Pb1-xSrxTiO3 Thin Films and Powders
Authors: Jain M. , Savvinov A. , Dobal P. S. , Majumder S. B. , Katiyar R. S. , Bhalla A. S.
Published: April 2011

In this work we present the structural, and vibrational properties of ferroelectric Pb1-xSrxTiO3 (PST). Thin films of PST were prepared by using sol-gel technique for various compositions with x values ranging from 0.0–1.0. Respective compositions were also prepared in ceramic and powder forms using sol-gel and solid-state reaction methods. X-ray diffraction was used for the structural characterization of these materials. Raman spectroscopy was utilized to study the phases and lattice vibrational modes, especially the soft mode in PST compositions. The temperature dependence of the soft mode frequency for different PST compositions revealed that the phase transition temperatures increased with increasing Pb contents in PST system. Ferroelectric properties of the films were correlated with the substitution-induced changes in the material.
Submicron Ferroelectric Elements Fabricated by Direct Electron Beam Lithography
Authors: Kim Dong-Joo , Im Jin Seo , Thompson Carol , Streiffer S. K. , Wiederrecht G. , Auciello O.
Published: April 2011

To realize Gigabit density ferroelectric memory devices, downscaling issues involving processing, materials, and fundamental ferroelectric behavior must be resolved. To address patterning and characterizing ferroelectric films at the nanoscale, we have prepared different lateral sizes of ferroelectric PZT capacitors down to 120 nm, using direct-write electron beam lithography. Characterization of the piezoelectric activity of the patterned elements was performed by means of piezoelectric-sensitive scanning probe microscope in the contact mode. Switching of single 120 nm cells was achieved.
Dielectric Properties of (Ba,Sr)TiO3 Thin Film Capacitors Fabricated on Alumina Substrates
Authors: Koutsaroff I. P. , Kassam A. , Zelner M. , Woo P. , McNeil L. , Bernacki T. , Cervin-Lawry A. , Patel A.
Published: April 2011

Double layer (DL) Ba0.7Sr0.3TiO3 (BST) capacitors with Pt electrodes have been fabricated with similar growth conditions on different substrates. The substrates used in the present study were r-plane sapphire, polycrystalline alumina Al2O3 (99.6% and 96%), and glazed polycrystalline alumina. BST films were grown by metal-organic decomposition (MOD) method. By varying the annealing conditions which affects the formation of the crystalline structure, significant changes in the dielectric properties of the BST films have been observed. BST films were characterized by Field Emission Scanning Electron Microscopy (FE-SEM) and Powder X-ray Diffractometer (PXRD). These observations showed that BST films grown at lower temperatures on alumina substrates exhibited the smallest grain size. BST films of the same thickness prepared under the same thermal processing conditions showed higher capacitance when grown on all types of alumina-based substrates compared to those deposited on control SiO2/Si. The higher capacitance on alumina was always associated with larger dissipation factor, and lower or similar leakage current density. The final tuning, of the dielectric properties of BST DL capacitors on non-silicon substrates, was correlated to the initial film formation temperature and post-annealing conditions of the BST films. The leakage current density, of DL BST capacitors fabricated on glazed alumina, becomes smallest when the BST processing temperature was lowered by 100 °C compared to the control SiO2/Si. The typical achieved leakage current density for 1500×1500 μm2 DL capacitors on glazed alumina was 3.8×10-9 A/cm2 at 250 kV/cm (36.5 fF/μm2), about 3 times lower than on SiO2/Si substrates (1.1×10-8 A/cm2 at 250 kV/cm, 31 fF/μm2).
Leakage Current Experiments in STO and BST Thin Films
Authors: Schroeder Herbert , Schmitz Sam
Published: April 2011

We have performed experiments on steady state leakage currents through insulating thin films of high permittivity dielectrics such as strontium-titanate (STO) and barium-strontium-titanate (BST) in order to contribute to the understanding of the mechanism limiting the current. Furthermore, as BST is a candidate as a dielectric in the capacitor of future Gb-generation DRAM cells, the absolute value of the current in dependence of external parameters is interesting for the application.

Besides external parameters such as applied voltage and temperature we have investigated the dependence on dielectric film thickness between 20 nm and 150 nm with symmetrical Pt electrodes. For some selected films the influence of asymmetric electrodes has also been investigated: While the bottom electrode was always Pt, the top electrodes were Pt, Au and Al. An epitaxial STO film with oxide electrode bottom electrode has also been tested.

The main results are as follows:

The field dependence of the leakage current quite often shows a linear behavior in a “Schot-tky”-plot, i.e. log (current density) vs. sqrt (applied field). At constant applied field the thinner films show much lower leakage currents than the thicker ones. The leakage currents increase using Pt, Au and Al as cathode, respectively. The leakage in the epitaxial STO film is much smaller with an oxide electrode (SrRuO3) as cathode than with a platinum one.

All these results will be discussed within a modified model, in which the current is bulk-limited, and compared to numerical simulation results of this model.
Influence of Ta2O5, TiO2, and ZrO2 Interfacial Layers on Structural and Electrical Properties of Laser Ablated Ba0.5Sr0.5TiO3 Thin Films
Authors: Das Suprem R. , Das Rasmi R. , Bhattacharya P. , Katiyar Ram S.
Published: April 2011

Pulsed laser deposition technique was used to fabricate Ba0.5Sr0.5TiO 3 (BST) thin-films on Pt/TiO 2/SiO2/Si substrates. The influence of thin interfacial layers of Ta2O5, TiO2, and ZrO2, on the structural and electrical properties of BST thin films was investigated. Insertion of interfacial layers does not affect the perovskite phase formation of BST thin films. Buffer layers helped to make uniform distribution of grains and resulted in a relative increase in the average grain size. The dielectric tunability of BST thin films was reduced with the presence of buffer layers. A BST thin film having a dielectric permitivity of 470 reduced to 337, 235 and 233 in the presence of Ta2O5, TiO2, and ZrO2 layers, respectively. The reduction of the relative dielectric permittivity of BST films with the insertion of interfacial layers was explained in terms of a series capacitance effect, due to the low dielectric constant of interfacial layers. The TiO2 layer did not show any appreciable change in the leakage current density. Deposition of thin Ta2O5 and ZrO2 interfacial layer on top of Pt reduced the leakage current density by an order of magnitude.
Thin Film Capacitors Cut from Single Crystals Using Focused Ion Beam Milling
Authors: Saad M. M. , Donnelly N. J. , Bowman R. M. , Gregg J. M.
Published: April 2011

The Focused Ion Beam Microscope (FIB) has been used to fabricate capacitors from single crystals of BaTiO3 and SrTiO3 with electrode areas ∼200μm2, and thickness of single crystal dielectric between 2μm and 500nm. Cross-sectional transmission electron microscopy revealed that during capacitor fabrication, the FIB rendered around 20nm of dielectric at the electrode-dielectric interface amorphous, associated with local gallium impregnation. Such a region would act electrically in series with the single crystal and would presumably have a considerable negative influence on dielectric properties. However, annealing prior to electrode deposition was found to fully recover the single crystal, and homogenise the gallium profile. Some subsequent dielectric testing of SrTiO3 was performed yielding a room temperature dielectric constant of ∼150 and loss tangent of 0.015 at 100kHz. A technique has therefore been demonstrated which allows fabrication of capacitors in which size-effects in ‘thin-films’ can be studied, without the influence of grain boundaries, and other issues associated with conventional thin film growth.
Characterization of Shape Memory and Superelastic Effects by Instrumented Indentation Experiments
Authors: Ni Wangyang , Cheng Yang-Tse , Grummon David S.
Published: April 2011

The shape memory and superelastic effects of martensitic and austenitic NiTi alloys were studied by instrumented indentation experiments. The shape memory effect was quantitatively characterized by the thermo-activated depth recovery ratio of the residual indentation depth. The superelasticity of austenitic NiTi was quantitatively characterized by the depth and work recovery ratios obtained from the load-displacement curves. The shape memory and superelastic effects under different indenters (Berkovich, Vickers, and spherical) and loads were rationalized using the concept of the representative strain and maximum strain. This study demonstrates that instrumented indentation techniques are useful in the quantitative characterization of the shape memory and superelastic effects in micro- and nano-meter length scale.
Film Stress Characterization Using Substrate Shape Data and Numerical Techniques
Authors: Feng Zhaohua , Lovell Edward G. , Engelstad Roxann L. , Mikkelson Andrew R. , Reu Phillip L. , Sohn Jaewoong
Published: April 2011

Intrinsic stress in a film-substrate system can have deleterious effects. To facilitate an understanding of stress generation and control film quality, measuring film stress is essential. In recent years research laboratories and industry have increasingly adopted indirect methods, which are usually based on the measurement of substrate deformation. The film stress is calculated by equations relating the stress to the deformation, such as the well-known Stoney's equation. However, when the two principal stresses at each point in the film plane are not equal and their distribution is nonuniform, the local application of Stoney's equation does not provide correct stress results. A numerical technique is presented, which overcomes these limitations and makes accurate stress determination possible.
Interaction of C60 with Isoelectronic Surfaces: Graphite and Hexagonal Boron Nitride
Authors: Reinke P. , Feldermann H. , Oelhafen P.
Published: April 2011

In the present study we focus on the interaction of C60 with sp2 boron nitride (BN), a surface that is isoelectronic to graphite. The nanocrystalline BN substrate was deposited by mass selected ion beam and consists of an sp2 surface layer, which covers a cubic-BN film. The interaction and electronic properties of the C60-BN system are observed by photoelectron spectroscopy in the x-ray (XPS) and ultraviolet regime (UPS). The experiment is initiated by sequential deposition of C60 and the overlayer growth proceeds via island formation. In a second step the sample is annealed at a rate of 5–10 K/minute while simultaneously recording the UPS spectra. The majority of C60 desorbs from the sp2 BN surface at 493 K. The remaining C60 (initially about 0.6 ML) is gradually removed with increasing temperature (up to 813 K) but never completely desorbed and presumably attached at surface imperfections or grain boundaries of the nanocrystalline material. No carbide formation, preferential interaction of C60 with either element or a charge transfer are observed. The presence of C60 induces an upward band bending and related peak shifts in the sp2 BN surface layer and to a lesser extent in the underlying c-BN bulk. An upward band bending is likewise observed in the C60 overlayer, and the Fermi level has therefore to be pinned by defects in the interface region. The layered structure of the BN film allows to probe the extension of the space charge layer in the BN film.
Microstructure and Stress Analyses of Copper Films Deposited on Biased Substrates by Microwave Plasma-Assisted Sputtering
Authors: Thièry François , Pauleau Yves , Arnal Yves , Pelletier Jacques , Ortega Luc
Published: April 2011

Pure copper films have been deposited on <100> Si substrates either at the floating potential or biased to various dc voltages ranging from 0 to - 125 V. Argon ions from the discharge produced in a distributed electron cyclotron resonance microwave plasma reactor were used for sputtering of a copper target biased to various dc voltages. For sputter deposition, the Si substrates placed on a water-cooled substrate holder were maintained at ambient temperature. The argon pressure was 0.13 Pa and the dc target voltage was fixed at - 600 V. The deposition rate of films was investigated as a function of the substrate bias voltage. The crystallographic structure of films and size of copper crystallites were determined by x-ray diffraction analyses. The surface morphology of films was examined by atomic force microscopy. The electrical resistivity of films was deduced from the thickness and sheet resistance of films determined by profilometry and four point probe measurements, respectively. The magnitude of residual stresses in copper films was calculated from the radius of curvature of Cu/Si samples deduced from profilometry measurements. The evolution of the microstructure, surface morphology and electrical resistivity of films as well as the magnitude of residual stresses developed in these films were studied as functions of the substrate bias voltage. These major characteristics of films were found to be dependent on the energy of argon ions impinging on the surface of films grown on biased substrates. The effect of the ion energy on the physical features of films is analyzed and discussed in this paper.
Surface Modification of Sputtered SiO2 Thin Films by Metal Doping
Authors: Takeda Satoshi , Fukawa Makoto
Published: April 2011

The effects of metal doping on the surface properties of sputtered silicon dioxide (SiO2) thin films were investigated. The aluminum (Al), titanium (Ti) or zirconium (Zr) doped SiO2 thin films were deposited onto glass by RF magnetron sputtering. The optical transmission spectra of the films were almost same as that of undoping film when the doping concentration was lower than ∼3 at %. The contact angle of water droplets was measured for the films as a function of elapsed time. The hydrophobicity, resulting from the adsorption of organic substances in the atmosphere, was significantly altered by the metal doping. The surface reactivity of the film with a fluoroalkyl isocyanate silane was also changed. These alternations were due to the difference in surface OH group density of the film, which was induced by the metal doping. These results suggest that the surface properties can be modified by controlling the surface OH group density of the films.