bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface-Related Photoluminescence Effects in GaN
Authors: Reshchikov M. A. , Iqbal M. Zafar , Huang D. , He L. , Morkoç H.
Published: April 2011

Photoluminescence (PL) from GaN epilayers is found to be sensitive to the ambient atmosphere and length of UV exposure. We studied the effect of UV illumination in different ambients including air, oxygen, nitrogen and hydrogen gases on room-temperature PL of GaN grown on sapphire by molecular beam epitaxy. In some samples the PL intensity increased markedly in vacuum as compared to excitation in air, whereas in others it decreased appreciably. While air and oxygen showed strong reversible variation of the PL intensity as compared to vacuum, nitrogen and hydrogen atmospheres led to a very small change. In some samples we observed a shift of the yellow luminescence band with change of ambient, in others no shift was detected. PL intensity also changed during UV irradiation when the sample was in air ambient. Possible reasons for our observations are discussed.
High-Temperature Illumination-Induced Metastability in Undoped Semi-Insulating GaN Grown by Metalorganic Vapor Phase Epitaxy
Authors: Fang Z-Q. , Claflin B. B. , Look D. C. , Myers T. H. , Koleske D. D. , Wickenden A. E. , Henry R. L.
Published: April 2011

High-temperature (high-T) illumination-induced metastability in undoped semi-insulating (SI) GaN grown on a-plane sapphire by metalorganic vapor phase epitaxy has been studied using thermally stimulated current (TSC) spectroscopy, photocurrent (PC) and persistent photocurrent (PPC) measurements. The metastability can be induced by illumination at 390>T>300K (using either white or 360-nm light), followed by cooling the sample to 83 K in the dark. Without high-T illumination, the SI-GaN sample stays in its normal state (“off” state), and shows at least six TSC traps, B (0.63 eV), Bx (0.51 eV), C1 (0.44 eV), C (0.32 eV), D (0.23 eV), and E (0.16 eV). However, after high-T illumination the sample goes into a metastable state (“on” state), and shows a strong increase in both the PC at 83 K and the TSC of traps D, C, and E, accompanied by significant change in their relative densities. PPC at 83 K in the “on” state lasts much longer than that in the “off” state. Association of possible point defects and dislocations with the metastability behavior will be discussed.
AlGaN/GaN HFETs for Automotive Applications
Authors: Birkhahn Ronald , Gotthold David , Cauffman Nathan , Peres Boris , Yoshida Seikoh
Published: April 2011

AlGaN/GaN heterojunction field effect transistors (HFET) on sapphire substrates have demonstrated ability as power devices operating with high current densities and high breakdown voltages. Additionally, AlGaN/GaN HFET devices have a very low on-state resistance. This makes these devices ideal for automotive applications such as switching relays, DC-DC converters, and power inverters. By 2006, switching devices using GaN-based FETs are anticipated to be employed in luxury automobiles and transitioned to the mass market by 2009.

In this presentation, data from AlGaN/GaN HFET's grown in an Emcore D180 MOCVD system will be presented. Typical production-scale material results (on 2” sapphire substrates) for these wafers were: μ ∼ 1000 cm2/Vs, Ns = 1.0×1013 cm−2, and Rs ∼ 450 Ω/square with <3% variation across the wafer. These wafers were then processed into devices using Pt/Au gate contacts with 2 μm gate length, 200 μm gate width, and a source to drain spacing of 13 μm. A total of 1000 FETs were combined in parallel for an effective gate width of 20 cm for high current operation (10A). These devices have a lower on-state resistance (<0.01 Ω-cm2) and higher Schottky breakdown voltages (400 V) than the theoretical limit of Si MOSFET devices. These devices demonstrate suitability for insertion in automotive electrical harnesses.
Ti/Al- GaN Reaction Mechanism Forming Low Contact Resistivity
Authors: Fukasawa Yoshimichi , Nakamura Tomonori , Nakamura Tohru
Published: April 2011

The mechanism of Ti/Al reaction to n-GaN was studied to form ohmic contacts with low contact resistivity. N-GaN layers with a carrier concentration of 2.17×1018cm−3were deposited on sapphire substrates. Ti/Al metals were deposited by conventional electron-beam techniques. Contact resistivity decreased as the Ti thickness increased, and increased as the Al thickness increased. The lowest contact resistivity was measured at 1.20 × 10−6Ωcm2for 80 nm Ti /100 nm Al. After annealing at 900 °C, Al/AlTi/TiN layers on GaN were formed and Al Ti alloy thickness decreased as Ti thickness increased, from 1.5 MeV Rutherford Backscattering Spectroscopy(RBS) measurement. It was found that the contact resistivity was reduced as alloy metal thickness into GaN was increased.
Effect of growth temperature on the microstructure of the nucleation layers of GaN grown by MOCVD on (1120) sapphire
Authors: Wojtowicz T. , Ruterana P. , Twigg M. E. , Henry R. L. , Koleske D. D. , Wickenden A. E.
Published: April 2011

Most of the work done on GaN has taken into account layers grown on the (0001) sapphire plane. However one would expect the growth on the (1120) plane to lead to different structural defects. As has been shown, in one direction, the mismatch is rather small. In this work, we have carried out structural analysis of nucleation layers grown at temperatures ranging from 600°C to 1100°C. It is shown that for many of the structural parameters, such as the orientation relationships, the layer morphology and the nucleation mechanism critically depend on the growth temperature. At the lowest temperatures, the growth is completely three dimensional with a mixture of the two traditional orientation relationships, but the coalescence thickness is small. In a next step, the A orientation relationship predominates and the layer roughness tends to slightly decrease. This orientation is never perfect, and there is always 1.5° misorientation to the same direction in sapphire, whereas the B orientation is always perfect. At an intermediate temperature, island growth is predominant, whereas towards the high temperature end the B orientation becomes predominant. For the highest growth temperatures, the nucleated layers are completely flat and with the B orientation, although they contain a quite large number of defects such as inversion domains.
Electrical Properties of GaN/Si Grown by MOCVD
Authors: Yoshida Seikoh , Li Jiang , Wada Takahiro , Takehara Hironari
Published: April 2011

GaN growth on Si substrate is very attractive for realizing low cost electronic devices. We grew a thin GaN film on p-type Si(111) substrate using AlGaN high temperature buffer without using a conventional low temperature buffer. A homogeneous buffer layer was obtained at 1093 K and a homogenous 500 nm thick GaN layer was also obtained without any crack. Using a transmission electron microscopy (TEM), we observed that the cross-section of GaN and AlGaN buffer was very smooth and also the surface of GaN was flat although the threading dislocations were observed. Furthermore, we directly fabricated a metal semiconductor field effect transistor (MESFET) using a 500 nm-thick GaN/Si without any high resistive GaN layer. A Schottky electrode was Pt/Au and an ohmic electrode was Al/Ti/Au. A Schottky breakdown voltage was over 100 V. Also, we confirmed a high temperature operation of the MESFET using a thin GaN film on Si substrate at 573 K.
Studies on Epitaxial Relationship and Interface Structure of AlN/Si(111) and GaN/Si(111) Heterostructures
Authors: Rawdanowicz T. A. , Wang H. , Kvit A. , Narayan J.
Published: April 2011

We present the details of epitaxial growth interface structure of single wurtzite AlN thin films on (111) Si substrates by laser-molecular-beam-epitaxy. High quality AlN thin films with atomically sharp interfaces can be obtained by Laser-MBE at a substrate temperature of 650 ±10°C. X-ray diffraction and high resolution transmission electron microscopy was used to study the details of epitaxial growth of AlN on Si(111) substrate. The orientation-relationship of AlN on Si(111) was studied from Si <110> and <112> zone axis and determined to be AlN [2110]|Si[110] and AlN [0110]|Si[211]. The atomic structure of the interface was studied by high-resolution transmission electron microscopy and Fourier filtered image of cross-sectional AlN/Si(111) samples from both Si<110> and <112> zone axis. The results revealed the domain matching epitaxy of 4:5 ratio between the interplanar distances of Si(110) and AlN [2110]. We also present similarities and differences between the growth mechanism of AlN/Si(111) and GaN/Si(111) heterostructures.
Experimental and Theoretical Analysis of Heat and Mass Transport in the System for AlN Bulk Crystal Growth
Authors: Bogdanov M. V. , Karpov S. Yu. , Kulik A. V. , Ramm M. S. , Makarov Yu. N. , Schlesser R. , Dalmau R. F. , Sitar Z.
Published: April 2011

Bulk AlN crystal growth by Physical Vapor Transport (PVT) is studied both experimentally and numerically. This paper presents the analysis of heat and mass transport mechanisms in closed and partially open crucible geometries. The heat transfer in the growth system used at North Carolina State University (NCSU) is simulated. The computed temperature profiles are used in the analysis of mass transport in the growth cell to gain understanding of the effect of species exchange between the crucible and environment on the AlN growth rate. The model predictions are in reasonable agreement with observations.
Production of Sapphire Blanks and Substrates for Blue LEDs and LDs
Authors: Khattak Chandra P. , Schmid Frederick , Guggenheim Paul J. , Smith Maynard B. , Rogers Henry H. , Schmid Kurt
Published: April 2011

The Heat Exchanger Method (HEM) of crystal growing was combined with the Fixed Abrasive Slicing Technology (FAST) to produce low-cost, high-quality sapphire substrates for deposition of the GaN family of compounds. Production quantities of 2-inch diameter blanks have been supplied, and 3-inch diameter material has been qualified. Current technology can be used to prepare sapphire blanks up to 6-inch diameter.
Transport and Chemical Mechanisms in GaN Hydride Vapor Phase Epitaxy
Authors: Karpov Sergey Yu. , Segal Alexander S. , Zimina Darya V. , Smirnov Sergey A. , Sid'ko Alexander P. , Kondratyev Alexey V. , Makarov Yuri N. , Martin Denis , Wagner Volker , Ilegems Marc
Published: April 2011

On the basis of both experimental and theoretical studies, a simple quasi-thermodynamic model of surface kinetics is suggested for Hydride Vapor Phase Epitaxy (HVPE) of GaN, working in a wide range of growth conditions. Coupled with detailed 3D modeling of species transport in a horizontal reactor, the model provides quantitative predictions for the GaN growth rate as a function of process parameters. Significance of transport effects on growth rate uniformity is demonstrated.
Growth of Thick InN by Molecular Beam Epitaxy
Authors: Lu Hai , Schaff William J. , Eastman Lester F. , Wu J. , Walukiewicz Wladek , Look David C. , Molnar Richard J.
Published: April 2011

In this study, InN films with thickness up to 7.5 micron were prepared by molecular beam epitaxy (MBE) on (0001) sapphire and quasi-bulk GaN templates. Previously it has been challenging to grow InN film much beyond 1 micron because the growing surface tended to become rough. Techniques to overcome this limit have been developed. Various buffer techniques were used and compared to optimize the epitaxial growth. It was found that with increasing film thickness, Hall mobility will monotonically increase, while carrier concentration decreases. Hall mobility beyond 2100 cm2/Vs with carrier concentration close to 3×1017 cm−3 was obtained at room temperature. Compared with the lowest carrier concentration ∼2×1018 cm−3 obtained on thin InN films grown at the same condition, the conclusion is that impurities from the growth environment are not responsible for the high background doping of InN. Instead, some structural defects or substrate/buffer impurities may be the major source of the unintentional doping, which can be reduced by growing thicker films.

Some results on Mg and Be doping of InN will be reported as well. To date, all Mg and Be doping attempts have resulted in n-type material.
Thermoelectric properties of III-nitrides and III-oxynitrides prepared by reactive rf-sputtering: targetting a thermopower device
Authors: Yamaguchi S. , Iwamura Y. , Yamamoto A.
Published: April 2011

We have studied thermoelectric properties of III-nitrides of Al1-xInxN and III-oxynitrides of Al1-xInxOsNt and InOsNt prepared by radio-frequency sputtering with the aim of fabricating a thermoelectric power device based on III-nitride semiconductors. For Al0.55In0.45N, the maximum value of power factor was 3.63×10−4 W/mK2 at 873K. For Al0.02In0.98O1.14N0.49 and Al0.14In0.86O1.30N0.67, the maximum power factor was 2.82×10−4 W/mK2 and 4.73×10−4 W/mK2 at 873 K, respectively. For InO0.82N0.86, it was 3.75×10−4 W/mK2 at 973 K.
X-Ray Diffraction Analysis of GaN and AlGaN
Authors: Kang H. , Spencer N. , Nicol D. , Feng Z. C. , Ferguson I. , Guo S. P. , Pophristic M. , Peres B.
Published: April 2011

In this paper, threading dislocation densities in GaN and AlGaN epitaxial layers have been evaluated using two different X-ray analysis techniques; a Williamson Hall (WH) plot and reciprocal space mapping (RSM). GaN and AlGaN have crystalline growth composed of columnar structures that can be estimated by coherence length and angular misorientation measured by X-ray. A WH plot can provide information about coherence length and tilt angle from a linear fit to the linewidth of the triple axis rocking curve (000l) symmetric reflections. RSM is typically used to obtain this data, but it is more involved in technique. The two dominant components of threading dislocation densities (screw and edge types) in the GaN and AlGaN epitaxial layers were found to be similar by both techniques. The treading dislocation density correlates to the size of columnar structure as determined by coherence length, tilt angle, and twist angle. The effect of Al composition in AlGaN alloys on these dislocation densities was investigated and found to depend on strongly on the type of nucleation layer, GaN or AlN.
Solar-Blind AlGaN-based Schottky Photodiodes With High Detectivity and Low Noise
Authors: Biyikli Necmi , Aytur Orhan , Kimukin Ibrahim , Tut Turgut , Ozbay Ekmel
Published: April 2011

We report on the design, fabrication and characterization of solar-blind Schottky photodiodes with high detectivity and low noise. The devices were fabricated on n-/n+ AlGaN/GaN hetero-structures using a microwave compatible fabrication process. Using Al0.38Ga0.62N absorption layer, true solar-blind operation with a cutoff wavelength of ∼274 nm was achieved. The solar-blind detectors exhibited < 400 fA dark current in the 0–25 V reverse bias regime, and a maximum responsivity of 89 mA/W around 267 nm. The photovoltaic detectivity of the devices were in excess of 2.6×1012 cmHz1/2/W, and the detector noise was 1/f limited with a noise power density less than 3×10−29 A2/Hz at 10 KHz.
A GaN-free LED Structure for High UV-light Extraction
Authors: Nishida Toshio , Ban Tomoyuki , Kobayashi Naoki
Published: April 2011

We improved the extraction of ultraviolet light from AlGaN-based light emitting diodes (LEDs) at the wavelength of about 350 nm, by introducing a transparent structure that is free from binary GaN. We used an AlN-template layer on a sapphire substrate as starting medium of the metal organic vapor phase epitaxial growth. The buffer layer is an Al0.2Ga00.8N alloy. We also used a short period alloy superlattice as transparent and conductive p-type cladding and p-type contact layers. The resultant epitaxial structure is confirmed to be transparent with the transmittance of about 90% within the wavelength range of 340 – 400 nm. The crystal quality of the Al0.2Ga00.8N buffer layer was estimated by the transmission electron microscope (TEM) observation. The dislocation density of AlGaN buffer layer was highly reduced on the AlN template layer, both of which have a low density of screw and mixed-type dislocations, of the order of 10−8cm−2. We also found that light extraction is improved by a factor of 6 by introducing the transparent LED structure and a p-contact mirror. The resultant LED shows high performance under RT-CW operation, where 1 mW output power at 348 nm with 20 mA injection corresponds to the external quantum efficiency of 1.4 %. The maximum power was 7 mW at 220 mA. The emission spectrum is highly monochromatic with the UV-to-visible intensity ratio of about 1000. We also demonstrate the application of this transparent UV-LED to white light source in a bottom-emission geometry.
Thermal analyses of bulk amorphous oxides and silicates of zirconium and hafnium
Authors: Ushakov S. V. , Brown C. E. , Navrotsky A. , Demkov A. , Wang C. , Nguyen B.-Y.
Published: April 2011

Amorphous pure and Y-doped ZrO2 and HfO2 were prepared by precipitation with ammonia or hydrazine. Amorphous zirconium and hafnium silicates with SiO2 content from 10 to 90 mol % were prepared by sol-gel. Crystallization was studied by differential scanning calorimetry (DSC) at 20 °C/min and crystallite size after crystallization was determined from XRD data. ZrO2 crystallized into the tetragonal phase with ΔH -21 ±2 kJ/mol and HfO2 into the monoclinic phase with ΔH -31 ±2 kJ/mol. Doping with 20 at.% Y decreased crystallite size after crystallization. Crystallization temperatures for pure and Y-doped ZrO2 samples were in the range 420–440 °C. Crystallization temperatures for pure and Y-doped HfO2 samples varied from 470 to 570°C and correlate with surface area. Crystallization onset temperature in silicates increased with silica content from about 650 to 950 °C for ZrO2·SiO2 and from 740 to 1030 °C for HfO2·SiO2. Tetragonal zirconia and hafnia were the only crystalline phases formed below 1100 °C in all zirconium silicates and in hafnium silicates with more than 10 mol% SiO2. Crystallite size after crystallization decreased with increase in silica content. In hafnium silicate, a decrease in HfO2 crystallite size from 5 to 2.5 ±1 nm corresponds to a crystallization enthalpy change from -22 to -15 ±2 kJ/mol. The tetragonal HfO2/amorphous SiO2 interface energy can be calculated from calorimetric data as ∼0.25 J/m2. The critical particle size for the tetragonal to monoclinic transformation of HfO2 in HfO2-SiO2 system is about 6 nm. We predict that tetragonal HfO2 will be stabilized in films thinner than 2 nm.
Atomic Layer Deposition of High-k Gate Dielectrics Using MO Precursor and Cyclic Plasma Exposure
Authors: Endo Kazuhiko , Tatsumi Toru
Published: April 2011

We have successfully achieved an ALD like deposition of ZrO2 or HfO2 by using a MO precursor. The MO precursor used in this study was zirconium tetra-tert-butoxide (ZTB) Zr(t-OC(CH3)3)4 and hafnium tetra-tert-butoxide (HTB) Hf(t-OC(CH3)3)4. Because MO precursors are very sensitive to H2O, we used oxygen plasma as an oxidizer instead of H2O in order to reduce background H2O pressure and suppress the background reaction. As a result, we successfully achieved an ALD-like deposition proved by a self-limiting adsorption of MO precursor. The carbon content in the films was suppressed due to highly reactive oxygen plasma. The leakage current of the film with plasma oxidation is much lower than that of film with H2O oxidation. Thus, MO-ALD using a plasma oxidation is a promising candidate for the high-k gate deposition process.
Measuring The Work Functions Of PVD TaN, TaSiN And TiSiN Films With A Schottky Diode CV Technique For Metal Gate CMOS Applications
Authors: Pan James , Woo Christy , Ngo Minh-Van , Tracy Bryan , Adem Ercan , Robie Stephen , Xiang Qi , Lin Ming-Ren
Published: April 2011

The metal gate process becomes a promising candidate for sub-65nm CMOS, due to the elimination of polysilicon depletion effects, and the possibility of adjusting the CMOS threshold voltage without more threshold implants. Our goal is to process mteal films with tunable work functions, in order to meet the demand of sub-65nm metal gate CMOS.

PVD TaN films are deposited with various processing conditions. Auger analysis shows that by changing the nitrogen flow rate and the plasma power, the nitrogen content in the TaN films can be adjusted. In order to accurately determine the work function of these TaN materials, we have developed a Schottky Diode CV technique (or Metal-Silicon CV, or MS-CV). This approach not only improves the accuracy of the metal work function measurement, compared with the traditional MOS-CV technique (which is affected by the thickness and quality of the oxide), but also simplifies the fabrication.

With the MS-CV's, we have successfully measured the work functions of Ni and Co, and compared the data with published references. The work function of PVD TaN actually decreases with higher nitrogen content, according to the Auger data and the MS-CV measurement, ranging from 3.42 – 4.20 Volts. The MS-CV technique is shown to be independent to the size of the capacitors, and is little affected by the measurement frequency. By changing the frequency from 100KHz to 1MHz, the error in the work function is less than 50mV.
Trap Spectroscopy in Si3N4 Ultrathin Films Using Exoelectron Emission Method
Authors: Naich M. , Rosenman G. , Molotskii M. , Roizin Ya.
Published: April 2011

We developed an original thermally stimulated exoelectron emission spectroscopy method (TSEE) of measurements of the activation energy Φ of electron (hole) traps in ultrathin Si3N4 films. The temperature spectra of TSEE of 50A silicon nitride films demonstrate several peaks: three low temperature peaks (T1 =373K, T2=423K, T3=498K) and a high temperature maximum at T4 ∼750K. The obtained values of the energy activation are Φ1=0.82 eV, Φ2=0.93 eV, Φ3=1.09 eV, and Φ4=1.73 eV. TSEE results are shown to be consistent with Φ estimates obtained from microFLASH® two bit per cell memory transistor measurements. Electrons stored at traps with Φ4=1.73 eV explain excellent microFlash retention properties. We believe that deep traps in Silicon Nitride are Hydrogen containing centers, while Hydrogen hopping is the route cause of observed material degradation in course of TSEE measurements.
Ultrathin Zirconium Dioxide Chemically Deposited at a Low Thermal Budget
Authors: Harasek Stefan , Wanzenboeck Heinz D. , Langfischer Helmut , Bertagnolli Emmerich
Published: April 2011

We report on metal-organic chemical vapor deposition (MOCVD) of ultrathin zirconium dioxide on (100) silicon. Special emphasis is put on the evolution of surface topography and the impact of processing parameters on the chemical composition of the films. Electrical characterization by means of MOS structures has been performed to assess the interface quality and the dielectric properties of the layers. Interface trap density is observed to be around 5.1011 cm-2.eV-1 at midgap for (100)-oriented substrates. Leakage currents in the ultrathin regime are significantly reduced compared to equivalent SiO2-layers. Trap density and leakage current are strongly sensitive to annealing in different atmospheres. However, electrical characteristics are shown to be positively affected rather by annealing in slightly reducing than in oxidizing atmospheres. All temperatures throughout the gate insulator formation process do not need to exceed 650°C, and thus allow to keep the thermal budget low.
Oxygen vacancy defects in tantalum pentoxide: a density functional study
Authors: Ramprasad R. , Sadd Michael , Roberts Doug , Remmel Tom , Raymond Mark , Luckowski Eric , Kalpat Sriram , Barron Carole , Miller Mel
Published: April 2011

First principles total energy calculations were performed in order to characterize O vacancy defects in Ta2O5. A simplified version of the crystalline orthorhombic phase of Ta2O5 was used in this study. Results indicate that O vacancies in Ta2O5 can be broadly classified based on their location in the lattice. One type of vacancies (occupying the “in-plane” sites) displays deep or mid gap occupied states, and shallow unoccupied states, while a second type (occupying “cap” sites) results in shallow occupied states. For a wide range of local Fermi level or chemical potential, the neutral and +2 charged states of the in-plane type vacancy and the +2 charge state of the cap type vacancy are found to be most stable. Migration energies of the two types of vacancies in the neutral and +2 charge states are markedly different, with the “cap” type of vacancies displaying very high barriers to migration (∼ 5 eV) compared to the “in-plane” type (∼ 0.5–1.0 eV).
Novel Chain Stack Capacitor for 32Mb FeRAM and Beyond
Authors: Bruchhaus R. , Ozaki T. , Ellerkmann U. , Lian J. , Kumura Y. , Kanaya H. , Yabuki M. , Tsuchya T. , Hilliger A. , Egger U. , Tomioka K. , Moon B. K. , Itokawa H. , Zhuang H. , Natori K. , Beitel G. , Sugimoto S. , Yamakawa K. , Kunishima I. , Nagel N.
Published: April 2011

For high density FeRAM devices small cell sizes are essential. The combination of the capacitor on plug (COP) structure with the Chain FeRAM™ cell design is used to develop a 32Mb FeRAM. Based on a 0.2 μm standard CMOS process a silicide capped polysilicon plug is used to contact the bottom electrode of the ferroelectric capacitor to the transistor. The barrier contact to the plug is formed by IrO2/Ir and a sputter deposited PZT (40/60) is used as ferroelectric material. The function of SrRuO3 (SRO) layers at the electrode/PZT interfaces is described in more detail. Double sided SRO results in slightly lower coercive voltage and imprint behavior compared to capacitors without SRO. Double sided SRO is essential to achieve excellent fatigue behavior measured up to 1×1011 switching cycles.
Fabrication and Properties of Thin Pb(Zr,Ti)O3 Film Pockels Cell
Authors: Vieitez M. O. , Khartsev S. I. , Grishin A. M.
Published: April 2011

Longitudinal Pockels cell as a vertical ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT) thin film capacitor was fabricated by pulsed laser deposition technique onto the both side polished YAlO3 + 1% Nd2O3 single crystal substrate. At first, conducting La0.5Sr0.5CoO3 (LSCO) 100 nm thick layer was deposited as an atomic template for 1 m thick PZT film. Epitaxial quality (exceptional c-axis orientation and coherent in-plane texture) of PZT/LSCO/Nd:YAlO3 (001) heterostructure has been confirmed by x-ray diffraction. On the top, semitransparent 100 nm thick Au electrode was deposited by thermal evaporation. Intensity of the chopped 670 nm polarized laser radiation transmitted through the Au/PZT/LSCO/Nd:YAlO3 cell was measured using lock-in amplifier. Special precautions were employed to get reproducible transmittance vs. temperature scans up to 400 °C. Phenomenon of critical opalescence (scattering of the light with critical fluctuations of polarization) was observed in the vicinity of Curie temperature at 208 °C. Modulation of the transmitted light as high as 3% was achieved applying 20 V (200 kV/cm) across the capacitive cell, whereas the voltage tunability measured at 1 kHz from C-V characteristics was about 70%.
Wafer Bonding and Layer Transfer For Thin Film Ferroelectrics
Authors: Ruglovsky Jennifer L. , Park Young-Bae , Ryan Cecily A. , Atwater Harry A.
Published: April 2011

We report on the layer transfer of thin ferroelectric materials onto silicon substrates. H+ and He+ ion implantation created a buried sacrificial layer in the c-cut BaTiO3 and LiNbO3 single crystals. Bubble formation and thermodynamics of cavity at the bonding interface have been investigated, and single crystal thin film layers were transferred onto crystalline silicon substrates. We have found that defects generated by ion implantation in ferroelectric materials can be significantly recovered with the subsequent annealing for layer splitting.
Combinatorial Laser Processing Of Dielectric/Ferroelectric Thin and Thick Films
Authors: Das R. N. , Lew C. , Zergioti I. , Thompson M. O. , Giannelis E. P.
Published: April 2011

A library of different crystalline sol-gel thin films with a composition of BaxTiyOz (where x = 1,2; y = 1,2,9 and z = 3, 7, 20) has been generated using variable multi-step laser and thermal annealing. Point by point X-ray diffraction characterization revealed the presence of high dielectric (BaTiO3) and low dielectric (Ba2Ti2O7 and Ba2Ti9O20) phases. Appropriate laser and thermal annealing controlled crystallinity, phase content, morphology and dielectric property of libraries. We have extended the process to BaTiO3 based thick-films and investigated the surface morphology of laser-annealed films.
Ferroelectric and Dielectric Properties of Chemical-Solution-Derived Bismuth Lanthanum Titanate Thin Films with Various Bismuth Oxide Template layers
Authors: Bao Dinghua , Wakiya Naoki , Shinozaki Kazuo , Mizutani Nobuyasu
Published: April 2011

(Bi,La)4Ti3O12 (BLT) thin films with various Bi2O3 template layers were prepared on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. Both of the BLT films with a thin Bi2O3 template layer and those without a Bi2O3 layer had a highly c-axis oriented growth, while both of the BLT films with a thin Bi2O3 bottom layer and those with a Bi2O3 intermediate layer were highly c-axis oriented. It was found that the use of Bi2O3 template layers improved significantly the ferroelectric properties of BLT thin films. In addition, the thin films with a thin Bi2O3 template layer showed good dielectric properties. All the capacitors with Bi2O3 template layers showed high polarization fatigue resistance and good retention properties.
A Novel Ruthenium Precursor for MOCVD without Seed Ruthenium Layer
Authors: Shibutami Tetsuo , Kawano Kazuhisa , Oshima Noriaki , Yokoyama Shintaro , Funakubo Hiroshi
Published: April 2011

Ruthenium thin films were deposited on SiO2/Si substrates at 275 – 400 °C by metalorganic chemical vapor deposition (MOCVD) using liquid precursor (2.4-dimethylpentadienyl)(ethylcyclopentadienyl)ruthenium [Ru(DMPD)(EtCp) DMPD: 2.4-dimethylpentadienyl EtCp: etylcyclopentadienyl]. Deposition characteristics of the films were compared with those using bis(ethylcyclopentadienyl)ruthenium.

The decomposition temperature of Ru(DMPD)(EtCp) was 80 °C lower than Ru(EtCp)2. Both films consisted of Ru single phase for all deposition temperature range and showed an resistivity bellow 20 μΩcm for the films deposited above 300 °C. The initial nucleation of Ru films from Ru(DMPD)(EtCp) precursor was smaller in size and denser than that from Ru(EtCp)2. The deposition process from Ru(DMPD)(EtCp) has much shorter incubation time than that from Ru(EtCp)2.
Characterization of Epitaxial Pb(Zrx,Ti1-x)O3 Thin Films with Composition Near the Morphotropic Phase Boundary
Authors: Saito Keisuke , Kurosawa Toshiyuki , Akai Takao , Yokoyama Shintaro , Morioka Hitoshi , Oikawa Takahiro , Funakubo Hiroshi
Published: April 2011

200-nm-thick Pb(Zrx,Ti1-x)O3 (PZT) thin films with zirconium composition in the range from 0% to 65% were epitaxially grown on (001)c SrRuO3 (SRO)//SrTiO3 (STO) single crystal substrates by pulsed metalorganic chemical vapor deposition (pulsed MOCVD). Constituent crystallographic phases were characterized by high-resolution X-ray diffraction reciprocal space mapping. It was found that PZT thin films having zirconium composition from 45% to 60% show mixed tetragonal and pseudocubic phases and their lattice parameters remained constant in this composition range.
New Line of Solid Solution System of Oxide Ferroelectrics
Authors: Kijima Takeshi , Ishiwara Hiroshi
Published: April 2011

Ferroelectric random access memory is one of the most promising candidates of non-volatile memories and has already been commercialized. However there still exist some problems to be solved on the ferroelectric materials. We succeeded in solving these problems by forming solid solutions between Bi2SiO5 and conventional ferroelectric materials such as Bi4Ti3O12, SrBi2Ta2O9 and Pb(Zr,Ti)O3. It was found that Bi2SiO5 enhanced crystallization of the ferroelectric materials and finally formed solid solutions with them. As a result, the crystallization temperature of the films decreased by 150 to 200 °C, and the ferroelectric and leakage current characteristics did not degrade even in an ultra-thin film of 13 nm in thickness. On the other hand, it was also found that the ferroelectric and insulating characteristics of the BSO-added films were dramatically improved by annealing in high-pressure oxygen up to 9.9 atms.[1] Three-orders-of-magnitude improvement of the leakage current density was observed in BSO-added BLT films after annealing at 9.9 atms, while pronounced increase of the saturation polarization was observed in BSO-added SBT and PZT films. From cross-sectional TEM (Transmission electron microscopy) observation, origin of the improved characteristics was speculated to be the structural change of the films.[2]
Hrteminvestigation of 90° Domain Configureuration and P-E Hysteresis Loop of Epitaxial PZT Multilayered Thin Films
Authors: Kiguchi Takanori , Wakiya Naoki , Shinozaki Kazuo , Mizutani Nobuyasu
Published: April 2011

Multi-layered epitaxial Pb(Zrx,Ti1-x)O3 (PZT) films of x=0.2–0.5 were deposited on La0.5Sr0.5CoO3-x (LSCO)/ (001)STO and LSCO/CeO2/YSZ/(001)Si substrates with buffer layers. It was investigated how the 90° domain structure and the P-E hysteresis character depend on the difference of the thermal expansion coefficient by changing the Zr/Ti composition and the substrates, using HRTEM and XRD methods. XTEM analysis showed that usual lamella configuration of 90° domains of 8–30nm in width penetrated the columnar grain and the PZT layer in the PZT stacked film of Zr/Ti=20/80, 30/70, 40/60. On the other hand, the close-packed 90° domains of 4–5nm in width existed in a epitaxial columnar grain in the PZT50/50 stacked film. The P-E hysteresis loops of PZT20/80 stacked films deposited on STO and Si substrates show the remanent polarization of 2Pr=136μC/cm2, 2Pr=80μC/cm2, respectively. On the other hands, those of PZT50/50 stacked films deposited on STO and Si substrates show the polarization of 2Pr=125μC/cm2, 2Pr=36μC/cm2, respectively. Thus, the P-E hysteresis loop of PZT50/50 has remarkable difference of 2Pr between the substrates.
Sm Doping Effects on Electrical Properties of Sol-Gel Derived SrBi2Ta2O9 Films
Authors: Tokumitsu Eisuke , Kishi Masahito
Published: April 2011

We have characterized (Sr,Sm)Bi2Ta2O9 (SSBT) films fabricated by the sol-gel technique on Pt/Ti/SiO2/Si substrates. For ferroelectric-gate FET applications, a ferroelectric film which has a small remanent polarization and a relatively large coercive field is required. It is demonstrated that Sm doping in ferroelectric SBT films is effective to reduce the remanent polarization and enhance the coercive field. Sr0.5Sm0.2Bi2.2Ta2O9 films (150nm) crystallized at 850°C exhibits good electrical properties with a remanent polarization of 1.7 μC/cm2 and a coercive fields of 85 kV/cm. These values are suitable for ferroelectric-gate FET applications.
MFIS and MFS structures using SrBi2Ta2O9 thin films for the FRAM applications
Authors: Victor P. , Bhattacharyya S. , Saha S. , Krupanidhi S. B.
Published: April 2011

Recently there is an increasing demand and extensive research on high density memories, in particular to the ferroelectric random access memory composed of 1T/1C (1 transistor/1 capacitor) or 2T/2C. FRAM's exhibit fast random acess in read/write mode, non - volatility and low power for good performance. An integration of the ferroelectric on Si is the key importance and in this regard, there had been various models proposed like MFS, MFIS, MFMIS structure etc., Choosing the proper insulator is very essential for the better performance of the device and to exhibit excellent electrical characteristics. ZrTiO4 is a potential candidate because of its excellent thermal stability and lattice match on the Si substrate. SrBi2Ta2O9 and ZrTiO4 thin films were prepared on p - type Si substrate by pulsed excimer laser ablation technique. Optimization of both ZT and SBT thin films in MFS and MFIS structure had been done based on the annealing, oxygen partial pressures and substrate temperatures to have proper texture of the thin films. The dc leakage current, P - E hysteresis, capacitance - voltage and conductance - voltage measurement were carried out. The effect of the frequency dependence on MFIS structure was observed in the C – V curve. It displays a transition of C - V curve from high frequency to low frequency curve on subjection to varied frequencies. Density of interface states has been calculated using Terman and high - low frequency C - V curve. The effect of memory window in the C - V hysteresis were analysed in terms of film thickness and annealing temperatures. DC conduction mechanism were analysed in terms of poole - frenkel, Schottky and space charge limited conduction separately on MFS, MIS structure.
•• Recent Progress in Ferroelectic-gate FETs
Authors: Ishiwara Hiroshi , Park Byung-Eun
Published: April 2011

Recent progress in the research of ferroelectric-gate FETs is reviewed mainly from a view-point of the data retention characteristics. First, importance of insulator-inserted gate structures such as an MFIS (M; metal, F; ferroelectric, I; insulator, S; semiconductor) or MFMIS structure is described and the necessary conditions for the insulating buffer layer and the ferroelectric film are discussed. Then, experimental results for the SiO2 and high-k dielectric buffer layers combined with such ferroelectric films as SBT (SrBi2Ta2O9) and BLT ((Bi,La)4Ti3O12) are presented, in which particular attention is paid to the discussion on the induced charge matching between the buffer layer and the ferroelectric film. As an example, it is shown in a Pt/BLT/LaAlO3/Si diode that the high and low capacitance values written by positive and negative pulses can be retained at least for 3 days. Finally, recent experimental results on the data retention characteristics of the ferroelectric-gate FETs are presented.
Bilinear Behavior in the Indentation Size Effect: A Consequence of Strain Gradient Plasticity
Authors: Elmustafa A. A. , Lou J. , Adewoye O. , Soboyejo W. O. , Stone D. S.
Published: April 2011

This paper examines the effects of stacking fault energy on the micro- and nano-indentation behavior of face-centered-cubic thin films. These include: LIGA nickel MEMS structures, alpha brass, copper and high purity aluminum. The measured hardness are then fitted to a strain gradient plasticity model based on the Taylor dislocation hardening model. Hardness is shown to exhibit a size dependence with different characteristic slopes in the micron and nano-scale regimes. Deep indents are shown to exhibit classical linear behavior. However, shallow indents exhibit an abrupt decrease in slope (almost by a factor of 10), giving rise to a bi-linear behavior. Furthermore, as the gradients become less sharp, the trends in the nano-hardness data become similar to those of the microhardness data predicted by the strain gradient plasticity model. Finally, the effects of stacking fault energy are then discussed within the context of cross-slip and hardening associated with Shockly partials.
Thermal Stability of Nanocrystalline Diamond Films Grown by Microwave Plasma Chemical Vapor Deposition
Authors: Bulut Mevlut , Catledge Shane A. , Vohra Yogesh K. , Camata Renato P.
Published: April 2011

In this work, the open-air thermal stability of nanocrystalline diamond films grown on mirror-polished titanium alloy substrates by the Microwave Plasma Chemical Vapor Deposition (MPCVD) technique was studied. The results of this investigation show that nanocrystalline diamond films are highly stable in air up to 600°C with no significant change in mechanical properties. Samples annealed between 600°C and 650°C, however, exhibit values of hardness lower by as much as 40% compared to as-grown samples. Above 650°C serious delamination effects were observed in the coatings.
Structural Investigation of Alumina Thin Films Deposited by Chemical Vapor Deposition
Authors: Bahlawane Naoufal , Blittersdorf Sabine , Kohse-Höinghaus Katharina , Atakan Burak , Müller Jürgen
Published: April 2011

The present study concerns the deposition of α–Al2O3 for diffusion barrier applications on superalloy substrates. The growth of α–Al2O3 has been achieved by chemical vapor deposition (CVD) using an AlCl3/CO2/H2 gas mixture at 1080 °C. Among several growth-controlling parameters with potential importance for the whisker growth process, the reactor pressure during deposition seems to be highly influential on the resulting film structure. Deposited films at low pressure presented solely a fine whisker structure. This non-closed structure is not suitable as diffusion barrier; however, the observed high porosity makes the deposit a potential candidate as a catalysis support. An increase of the deposition pressure led to a competitive growth of whiskers and grains. A suitable microstructure was attained at relatively high pressure (100 mbar) where the surface was fully covered by 2 μm large alumina crystals that formed a closed structure. Further increase of the pressure led to an irregular and rough surface microstructure.
Structure and Electrical Properties of Pulsed Laser Deposited Amorphous Carbon Nitride Thin Films
Authors: Aoi Yoshifumi , Ono Kojiro , Sakurada Kunio , Kamijo Eiji
Published: April 2011

Amorphous CNx thin films were deposited by pulsed laser deposition (PLD) combined with a nitrogen rf radical beam source which supplies active nitrogen species to the growing film surface. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS), Raman scattering, and Fourier transform infrared (FTIR) spectroscopy. Nitrogen content of the deposited films increased with increasing rf input power and N2 pressure in the PLD chamber. The maximum N/C ratio 0.23 was obtained at 400 W of rf input power and 1.3 Pa. XPS N 1s spectra shows the existence of several bonding structures in the deposited films. Electrical properties of the deposited films were investigated. The electrical conductivity decreased with increasing N/C atomic ratio. Temperature dependence of electrical conductivity measurements indicated that electronic conduction occurred by variable-range hopping between p electron localized states.
Reactive Sputtering of Nanostructured WCx
Authors: Rumaiz Abdul K , Ismat Shah S. , Ni C. , Derek Demaree J. , Hirvonen J. K.
Published: April 2011

Nanostructured WCx thin films were reactively sputtered in argon-methane plasma. A DC planar magnetron with a pure tungsten target was used. Films were deposited on glass, quartz, silicon and sapphire substrates at temperatures up to 700 °C. The carbon content in the film was varied by changing the partial pressure of methane. The carbon content in the films was analyzed by using X-ray Photon Spectroscopy (XPS) and Rutherford Backscattering Spectroscopy (RBS).

The effect of temperature on the grain size was studied using Transmission Electron Microscopy (TEM). The target poisoning behavior was studied by measuring the target current. The critical methane concentration at which the metal – poison mode transition occurs was measured to be around 42% of CH4 in Ar. This transition is characterized by a sharp fall in the target current. The hysteresis in the target current can also be attributed to target poisoning. In this paper we describe the effects of film growth parameters on the film composition. We also discuss an alternate sputtering technique, hollow cathode sputtering, and the advantages of this technique over the conventional planar magnetron technique.
Properties Oftetrahedralamorphous Carbon Films Deposited By the Filtered Cathodicarc Method
Authors: Nagata Naruhisa , Kusakawa Kazuhiro , Kumagai Akiyasu , Matsuyama Hideaki
Published: April 2011

First, we studied the relation between the sp3 bond ratio and the hardness of 100-nm-thick tetrahedral amorphous carbon (ta-C) films deposited by a Filtered Cathodic Arc (FCA) system at different substrate bias voltages. For comparison, sputtered amorphous carbon (a-C) films and Highly Oriented Pyrolytic Graphite (HOPG) were also analyzed. According to the results, ta-C film deposited at a -70 volt substrate bias voltage had high hardness and high sp3 bond ratio of up to 88 GPa and 85%, respectively, whereas those of sputtered a-C were 29 GPa and 28%. Furthermore, we found that the hardness of carbon films, including sputtered a-C and HOPG, increased with increasing sp3 bond ratio. Based on this relation, the chemical bond structures of carbon films are considered to be closely related to their mechanical properties. Secondly, we investigated the relation between sp3 bond ratio and ta-C film thickness, over the range from 1 to 10 nm. The measurements showed that a 2-nm-thick initial layer grown on the surface of CoCrPt magnetic film had low sp3 bond ratios. It is suggested that this reduction in sp3 bond ratio in the initially grown layer seriously degrades the film's performance as a hard disk media overcoat. Further efforts to improve ta-C film processing will be required to improve its mechanical properties.
Towards an improvement of performance of TiAlN hard coatings using metal interlayers
Authors: Castanho J. M. , Vieira M. T.
Published: April 2011

TiAlN sputtered coatings have been used with success in high-speed cutting tools in the last few years. However, the adhesive failures of the coatings refrain its application in more severe wear conditions like as high-speed machining. The assumptions for the present research were based on the hypothesis that thin metal interlayers will behave as shear stress sinkers, which could decrease the delamination of the thin films. In the present work, coatings of TiAlN with thin ductile metallic interlayers (Al, Ti, Cu and Ag) were deposited by reactive d.c. magnetron sputtering. Multilayer coatings with aluminum, titanium and silver interlayers achieve higher adhesion values (70N) than TiAlN monolithic coating (40N). Three and five metal ductile layers contribute to an increase of hardness and Young's modulus without change the residual stresses of the monolithic coating. Contrarily, the introduction of copper layers reduces all the studied mechanical properties of the TiAlN monolithic coatings, which are related to the different deformation mechanisms of the ductile interlayers.
Structural and Tribological Properties of Molybdenum Disulfide/Metal Multilayered Films Deposited by Pulsed Laser Deposition
Authors: Phani A. R. , Krzanowski J. E. , Nainaparampil J. J.
Published: April 2011

The structural, mechanical and tribological properties of MoS2/metal and MoS2/carbide multilayer thin films have been examined in this study. The films were deposited by pulsed laser deposition of sequential layers of MoS2 and either Ti, Cr or TiC. The compositions of the films were analyzed by wavelength dispersive spectroscopy (WDS) and confirmed the presence of the deposited elements. X-ray diffraction and cross-section SEM methods were employed to characterize the films. The XRD results did not reveal the presence of separate Ti, Cr or TiC phases, and the SEM did not show any multilayer structures. From these results, it was concluded that the added metal or carbide elements are present as either a dispersed nano-structured phase or in solid solution with the MoS2. Nonetheless, friction and wear testing showed dramatic improvements over MoS2 films when tested in a humid (45% r/h) environment.
Atomic-Scale Dynamic Deformation Behavior of BN Thin Films
Authors: Iwamoto Chihiro , Yang Hangsheng , Yoshida Toyonobu
Published: April 2011

Deformation behavior of the BN film was dynamically observed by high-resolution transmission electron microscopy. BN thin films were deposited on a narrow edge of Si flakes, using inductively coupled plasma-enhanced chemical vapor deposition. High-resolution observation of the sample revealed that the BN film was possibly deposited on the edge of the Si thinned to less than 10 nm in thickness, whose morphology varied depending on the thickness of the Si edge. Intriguing mechanical properties of the BN films, especially relating their dynamic behavior, were clearly verified by the high-resolution observation with piezo-ceramic tube for three-axis positioning of an indenter.