bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of Quaternary AlInGaN/GaN Heterostructures by Plasma Assisted MBE
Authors: Monroy E. , Gogneau N. , Jalabert D. , Enjalbert F. , Bellet-Amalnc E. , Hon Y. , Dang Le Si , Daudin B.
Published: April 2011

Epitaxial growth of quaternary AlGalnN compounds by plasma-assisted molecular beam epitaxy has been demonstrated. Two-dimensional growth is achieved under In excess, with a monolayer of In segregating at the growth front. The maximum In incorporation is significantly affected by the substrate temperature and the Al mole fraction of the alloy. This behavior has been attributed to the enhancement of In segregation due to the high binding energy of A1N compared to InN and GaN.
Deep Donor-Acceptor Pair Luminescence in Codoped GaN
Authors: Han Bing , Gregie Joel M. , Ulmer Melville P. , Wessels Bruce W.
Published: April 2011

Deep level defects formed in p-type GaN:Mg codoped with shallow donors have been investigated by photoluminescence (PL) spectroscopy. A donor-acceptor pair (DAP) luminescence band peaked at 2.45 eV dominates the room temperature PL spectrum in heavily codoped epilayers. A superlinear dependence of PL intensity on excitation density is observed for this band, with an exponent of 1.4∼1.7. The intensity of this band increases with increasing temperature with a maximum at 264K. To explain the luminescent behavior a DAP model was developed whereby the recombination involves a deep donor and shallow Mg acceptor. The deep donor is tentatively attributed to a DX center.
Deposition of GaN Films on Glass Substrate and Its Application to UV Electroluminescent Devices
Authors: Honda Tohru , Iga Kenichi , Kawanishi Hideo , Sakaguchi Takahiro , Koyama Fumio
Published: April 2011

GaN films were deposited on glass substrates using a compound-source molecular beam epitaxy technique. Electroluminescent devices with a double-insulator structure were also fabricated using the deposited films. When the devices were operated using a sine-wave voltage, one of the emission peaks was located in the UV spectral region. Introducing a small ammonia flow increased the deposition rate.
Crack Nucleation in AlGaN/GaN Heterostructures
Authors: Parbrook Peter J. , Whitehead Malcolm A. , Lynch Richard J. , Murray Robert T.
Published: April 2011

The tensile strain in AlGaN layers on GaN is well established to lead to cracking if a critical thickness is reached, unless measures such as interlayers are applied to prevent their formation. However in devices, such as HFETs such an approach is impractical. Growth of AlGaN-GaN structures was carried out by MOVPE using a standard two stage process for the growth of the GaN on sapphire. The crack structures were examined by optical and atomic force microscopy. Studies on thin AlGaN layers on GaN close to the crack critical thickness show the stress centres from which the cracks propagate are threading dislocations with cracks often initially forming to link together these stress centres if they are in close proximity. These cracks then extend and “lock” into the generally observed 〈2110〉 direction in more highly strained layers. A macroscopically uniform crack array is observed in these thin AlGaN samples.
Micro-Raman Spectroscopy: Self-Heating Effects In Deep UV Light Emitting Diodes
Authors: Sarua A. , Kuball M. , Uren M. J. , Chitnis A. , Zhang J. P. , Adivarahan V. , Shatalov M. , Asif Khan M.
Published: April 2011

Ultraviolet light emitting diodes (LED) based on GaN and its ternary alloy AlGaN are key devices for applications such as solid state white lighting and chemical sensing. Ultraviolet LEDs are prone to self-heating effects, i.e., temperature rises during operation, contributing significantly to the commonly observed saturation of light output power at relatively low input currents. Rather little, however, is known about the actual device temperature of an operating ultraviolet LED. Using micro-Raman spectroscopy temperature measurements were performed as a function of input current on 325nm-Al0.18Ga0.82N/Al0.12Ga0.88N multiple quantum wells LEDs grown on sapphire substrates, flip-chip mounted on SiC for heat-sinking. Temperature maps were recorded over the active device area. Temperature rises of about 65 °C were measured at input currents as low as 50mA (at 8V) for 200 μm x 200 μm size LEDs despite flipchip mounting the devices. Temperature rises at the device edges were found to be higher than in the device center, due to combined heat sinking and current crowding effects. Finite difference heat dissipation simulations were performed and compared to the experimental results.
Formation of quantum dots by self-rearrangement of metastable 2D GaN
Authors: Gogneau N. , Jalabert D. , Monroy E. , Adelmann C. , Daudin. B.
Published: April 2011

We propose a new procedure to grow GaN quantum dots (QDs) on AlN by using the Ga surfactant effect in plasma-assisted molecular beam epitaxy. Self-formed GaN islands were spontaneously generated under vacuum from a GaN 2D layer grown under Ga-rich conditions. Island characteristics (size and density) are studied as a function of the GaN coverage. We demonstrate that the QD density can be controlled in the 1010 cm−2 to 2 × 1011 cm−2 range. It is shown that beyond a given GaN thickness there is a coexistence between elastic and plastic relaxation.
Gate Current Modeling for Insulating Gate III-N Heterostructure Field-Effect Transistors
Authors: Clarke Frederick W. , Ho Fat Duen , Asif Khan M. , Simin Grigory , Yang J. , Gaska Remis , Shur Michael S. , Deng Jianyu , Karmalkar S.
Published: April 2011

Gate current plays an important role in determining the characteristics and limiting performance of GaN-based field effect transistors. In GaN-based HFETs, the gate current limits the gate voltage swing and, hence, the maximum device current. Since the electron transport across the wide band gap barrier layer involves trapping, under certain bias conditions, the gate current leads to the threshold voltage shifts and causes reliability problems. Under reverse bias, the gate leakage in GaN-based HFET dominates the minimum (pinch-off) drain current. Insulating gate HFETs (i.e. Metal Oxide Heterostructure Field Effect Transistors – MOSHFETs) have the gate leakage currents 4 – 6 orders of magnitude lower than HFETs, even at elevated temperatures up to 300 °C. In this paper, we report on the gate current characteristics in these devices at room and elevated temperatures. We propose a semi-empirical model for the current-voltage characteristics in these devices, which is in good agreement with experimental data. Our data also show that both tunneling and temperature activation are important factors in MOSHFETs. These results are important for possible applications of GaN MOSHFETs in high power amplifiers and power switches as well as in non-volatile memory devices and integrated circuits that will operate in a much wider temperature range than conventional silicon and GaAs devices.
High-Quality AlGaN/GaN HFET Structures Grown by MOCVD Using Intermediate High Temperature AlGaN/GaN Superlattices
Authors: Demchuk Alexander , Olson Don , Shin Minseub , Olson Dan , Nussbaum Peter , Strom Andy , Bates Simon , Hofmann Frank , Munns Gordon
Published: April 2011

We report on device quality Al0.28Ga0.72N/GaN heterostructures growth by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) using intermediate AlxGa1-xN/GaN superlattices (SL) with x<0.15. High-quality Al0.28Ga0.72N/GaN heterostructures have been confirmed with HRXRD analysis by measurement of mosaic twist and tilt in growth films, SEM with selective etching and Van der Pauw Hall measurements. The edge and threading dislocations were efficiently filtered by the AlGaN/GaN SL resulting in further reduction dislocation densities at the channel. Additionally, the superlattice served to improve the planarity of the channel heterointerface as evidenced by x-ray and AFM analysis. The increase of 2-DEG mobility from ∼1187 cm2/V s to ∼1443 cm2/V s was obtained at the carrier density of 1.0 to 1.2×1013 cm−2 on heterostructures with intermediate AlGaN/GaN SL grown on sapphire.
Thermal Stability of High k Layers
Authors: Zhao C. , Cosnier V. , Chen P. J. , Richard O. , Roebben G. , Maes J. , Van Elshocht S. , Bender H. , Young E , Van Der Biest O. , Caymax M. , Vandervorst W. , De Gendt S. , Heyns M.
Published: April 2011

Thermal stability of amorphous phases in various high-k layers (Al2O3, ZrO2, HfO2, ZrAlOx, HfAlOx and HfSiOx) and the phase transformation of crystalline ZrO2 and HfO2 were studied experimentally, as functions of surface preparation, deposition conditions, material composition and post deposition thermal treatment. It is found that pure ZrO2 and HfO2 show relatively low crystallization onset temperatures. The crystalline ZrO2 or HfO2 phases are tetragonal or monoclinic, depending on the layer thickness. The phase transformation of metastable t-phase into stable m-phase has been observed in ZrO2 and HfO2. Crystallization behavior of Al2O3 depends on the surface preparation of the substrate. ALCVD grown Al2O3 layers on an oxide-based surface remain amorphous after 1100°C spike annealing, while those on HF-last surface crystallize at temperatures around 800°C. Alloying Al2O3 into ZrO2 and HfO2 can improve their resistance to crystallization under thermal exposure. The kinetics of the crystallization in the alloys can be described by linear TTT curves. Hf-aluminates show better thermal stability than Zr-aluminates. A defect model relative to the phase transformation is discussed, based on the above observations.
Screening the High-k Layer Quality by Means of Open Circuit Potential Analysis and Wet Chemical Etching
Authors: Claes Martine , De Gendt Stefan , Witters Thomas , Kaushik Vidya , Chen Jerry , Conard Thierry , Delabie Annelies , Van Elshocht Sven , Heyns Marc
Published: April 2011

A fast way to monitor the quality of high-k dielectric layers is wet etching, either monitored by Open Circuit Potential analysis or by Scanning Electron Microscopy. Defect densities in the order of 1.109 defects/cm2 are observed for as-deposited HfO2 layers. It is assumed that the mechanism for wet chemical defect observation is either due to crystallization and/or due to an oxygen deficient HfO2 layer resulting in Si/SiO up-diffusion upon thermal treatment. However, after appropriate post deposition annealing wet etch defect free layers can be prepared.
X-ray absorption studies of high performance Low-k dielectric materials
Authors: Yoda T. , Miyajima H. , Shimada M. , Nakata R. , Hashimoto H.
Published: April 2011

The XAFS measurement of the MSQ type low-k dielectrics (LKD™) was conducted to clarify the structure change with and without the EB cure. Furthermore, three different types of other MSQ films, the ladder structure, the random structure and the CVD film, have been investigated as references. We have determined Si-O-Si bond angle and Si-O(Si-C) bond length by fitting the Fourier transformed EXAFS spectra.

The ladder structure and the random structure have Si-O-Si bond angle of 133 and 146, respectively.

Si-O-Si bond angle of LKD™ film is among that of the ladder and the random structure, and the XANES spectrum of LKD™ film displays two broad features, corresponding to the mixture of both structures. In contrast, Si-O-Si angles of the EB cured LKD™ film and the CVD film resemble each other, and the XANES features of both films are almost identical with that of the random structure.

We have confirmed that the EB cure process for LKD™ film makes drastic structure change from the mixture of ladder and random structure to the random network structure.
A Selective Etching Process for Chemically Inert High-k Metal Oxides
Authors: Saenger Katherine L. , Okorn-Schmidt Harald F. , D'Emic Christopher P.
Published: April 2011

Once annealed, high-k metal oxides such as HfO2 and Al2O3 can be extremely difficult to etch by wet chemical methods. Here we describe how ion bombardment at relatively low energy (a few hundred eV) can be used to make exposed regions of annealed HfO2 films etchable in aqueous HF-based solutions. HfO2 layers, 2–5 nm in thickness, were deposited by atomic layer chemical vapor deposition (ALCVD) on Si substrates, annealed at 700 °C, and subjected to selected-area ion bombardment supplied by an oxygen plasma in a reactive ion etching tool. Etch times (as indicated by time to “dewet“) were examined as a function of HfO2 thickness, the power and time of oxygen plasma treatments, post-oxygen-plasma anneals, and wet etch chemistry. Strategies for etching thicker films and additional data provided by electrochemical open circuit potential (OCP) measurements will also be discussed.
Phase Formation in Ti (Ta)-Ni and Co-Ti Films Deposited on (001)Si in N2 Atmospheres.
Authors: Vasiliev A. L. , Aindow M. , Vasiliev A. G. , Horin I. A. , Orlikovsky A. A.
Published: April 2011

A series of electron microscopy investigations on the microstructure produced by surface-diffusion reactions between Si substrates heated to 700–800°C and Ti-Co, Ti-Ni or Ta-Ni alloys deposited in a nitrogen ambient with and without barrier layers are described. The TEM data show clear phase separation into TaSi2 and NiSi2 for the Ta-Ni film deposited in a high N2 pressure ambient. Deposition at lower N2 pressure led to the formation of a mixed Ni-Ta-Si layer. The phase separation effect was also absent for Ni-Ti films even at high N2 pressure. The presence of barrier layers strongly affected the surface diffusion reactions in the Co-Ti-Si system. Formation of Ti-(O) or CoSix amorphous layers at the Si surface prevented the interdiffusion of Si and Co, such that even pure Co or Co2Si layers could be formed.
Kinetics of agglomeration of NiSi and NiSi2 phase formation.
Authors: Detavernier C. , Özcan A. , Lavoie C. , Sweet Jean-Jordan , Harper J. M. E.
Published: April 2011

We have studied the kinetics of NiSi agglomeration and NiSi2 phase formation during heating of NiSi on Si, using simultaneous in situ measurements of resistance, light scattering and x-ray diffraction. NiSi is a desirable contact to Si because of its low resistivity, limited Si consumption and low formation temperature. However, the formation of the higher resistivity phase NiSi2 must be avoided for device applications. Ni thin films 5 to 30 nm thick were deposited on substrates of poly-Si and silicon-on-insulator (SOI) and were studied using heating rates from 0.3 to 27 °C/s. At low heating rates and for the thinnest films studied, NiSi agglomeration precedes NiSi2 nucleation by as much as 350°C. The agglomeration temperature decreases with decreasing film thickness and linewidth. Once the film is agglomerated, the formation of NiSi2 is delayed to higher temperature by its low nucleation site density and decreased contact area. We conclude that agglomeration is the primary failure mechanism limiting the morphological stability of NiSi as a contact material to Si devices.
Formation of Ni mono-germanosilicide on heavily B-doped epitaxial SiGe for ultra-shallow source/drain contacts
Authors: Isheden Christian , Seger Johan , Radamson Henry H. , Zhang Shi-Li , Östling Mikael
Published: April 2011

The formation of Ni germanosilicides during solid-state interaction between Ni and heavily B-doped strained epitaxial Si1-xGex films with x=0.18, 0.32 and 0.37 is studied. No NiSi2 is found in these samples even after annealing at 850 °C, which can be compared to the formation of NiSi2 at 750 °C on Si(100). Resistance and diffraction studies for the Si0.82Ge0.18 sample indicate that NiSi0.82Ge0.18 forms and the NiSi0.82Ge0.18/Si0.82Ge0.18 structure is stable from 400 to 700 °C. For the NiSi1-uGeu formed in all Si1-xGex samples, where u can be different from x, a strong film texturing is observed. When the Ge fraction is increased from 18 at.% to 32–37 at.%, the morphological stability of the film is degraded and a substantial increase in sheet resistance occurs already at 600 °C. The contact resistivity for the NiSi0.8Ge0.2/Si0.8Ge0.2 interface formed at 550 °C is determined as 1.2×10-7 Ωcm2, which satisfies the RS contact resistivity requirement for the 70 nm technology node.
ALD HfO2 surface preparation study
Authors: Delabie Annelies , Caymax M. , Maes J. W. , Bajolet P. , Brijs B. , Cartier E. , Conard T. , De Gendt S. , Richard O. , Vandervorst W. , Zhao C. , Green M. , Tsai W. , Heyns M. M.
Published: April 2011

A fast screening technique is used to study the ALD HfO2 growth behavior on different types of starting surfaces (H-passivated, chemical oxide, thermal oxide). The amount of Hf deposited at the early stages of the ALD process is measured by means of RBS. The HfO2 film quality on different starting surfaces is examined with ToFSIMS. The results suggest an island growth mechanism on a H-terminated starting surface: nucleation, development of separated nuclei and flattening. It is shown that ALD growth starts faster if –OH groups are present on the surface. A remote H2 plasma surface pre-treatment at room temperature is also studied. The influence of the plasma exposure time and number of water pulses prior to HfO2 deposition was examined. The H2 plasma surface pre-treatment can be considered as a promising candidate for sub 1 nm EOT performance.
A New Approach for Metal Oxide Film Growth: Vapor-Liquid Hybrid Deposition (VALID)
Authors: Yasuda Tetsuji , Kuse Ronald
Published: April 2011

We propose a new process for forming ultra-thin metal oxide films called vapor-liquid hybrid deposition (VALID). This process consists of two steps: i) adsorption of a metal-organic or metal-halide precursor from the gas phase, and ii) liquid-phase hydrolysis of the adsorbed precursors. Al2O3 films were grown using Al(CH3)3 and water. Growth rate was 0.18 nm per cycle at room temperature. The interface layer thickness was less than 1 nm after post-deposition annealing in vacuum at 750°C. C-V and I-V characteristics of Au/Al2O3/Si capacitors fabricated using VALID were well-behaved suggesting that this concept is a viable approach to form device-quality dielectrics.
Interface Quality and Electrical Performance of Low-Temperature Metal Organic Chemical Vapor Deposition Aluminum Oxide Thin Films for Advanced CMOS Gate Dielectric Applications
Authors: Skordas Spyridon , Papadatos Filippos , Consiglio Steven , Eisenbraun Eric , Kaloyeros Alain
Published: April 2011

In this work, the electrical performance and interfacial characteristics of MOCVD-grown Al2O3 films are evaluated. Electrical characteristics (dielectric constant, leakage current) of as-deposited and annealed capacitor metal-oxide-semiconductor (MOS) stacks were determined using capacitance-voltage (C-V) and current-voltage (I-V) measurements. It was observed that the electrical properties were dependent upon specific annealing conditions, with an anneal in O2 followed by forming gas being superior with respect to leakage current, resulting in leakage characteristics superior to those of SiO2. All annealing conditions evaluated led to an increase in dielectric constant from 6.5 to 9.0–9.8. Also, Al2O3 growth and interfacial oxide growth characteristics on oxynitride/Si and Si substrates were evaluated and compared using spectroscopic ellipsometry. A parasitic oxide layer was observed to form on silicon during the initial stages of MOCVD Al2O3 growth, while a thin oxynitride layer deposited on Si prevented the growth of interfacial oxide.
Effect of Post-Metallization Hydrogen Annealing on C-V Characteristic of Zirconia Grown Using Atomic Layer Deposition
Authors: Chakraborty Arpan , Mane Anil U. , Shivashankar S. A. , Venkataraman V.
Published: April 2011

Substantial amount of fixed charge present in most of the alternative gate dielectrics gives rise to large shifts in the flat-band voltage (VFB) and charge trapping and de-trapping causes hysterectic changes on voltage cycling. Both phenomena affect stable and reliable transistor operation. In this paper we have studied for the first time the effect of post-metallization hydrogen annealing on the C-V curve of MOS capacitors employing zirconia, one of the most promising gate dielectric. Samples were annealed in hydrogen ambient for up to 30 minutes at different temperatures ranging from room temperature to 400°C. C-V measurements were done after annealing at each temperature and the hysteresis width was calculated from the C-V curves. A minimum hysteresis width of ∼35 mV was observed on annealing the sample at 200°C confirming the excellent suitability of this dielectric.
MOCVD of HfO2 from Alkoxide and Alkylamide Precursors
Authors: Roberts John L. , Williams Paul A. , Jones Anthony C. , Marshall Paul , Chalker Paul R. , Bickley Jamie F. , Davies Hywel O. , Smith Lesley M.
Published: April 2011

The alkoxide and alkylamide complexes [Hf(mmp)4] and [Hf(NMe2)4] 2 are both promising precursors for the MOCVD of HfO2. A comparison has shown that [Hf(NMe2)4] 2 deposits oxide at lower temperatures and over a wider temperature range then [Hf(mmp)4].
Advanced PECVD-Based Anti-Reflective Coating for 90nm Generation Interconnects
Authors: Ahn Sang H. , Fung Miguel , Jung Keebum , Zhu Lei , Bencher Chris , Kim B H , M'Saad Hichem
Published: April 2011

A plasma-enhanced chemical vapor deposition-based nitrogen-free dielectric anti-reflective coating was successfully developed for use in 90nm interconnects in conjunction with low κ materials. By choosing N-free precursors, it was possible to eliminate any adverse interactions between the NH2 amine group and the DUV 193nm photoresist that is directly in contact with the anti-reflective coating (ARC), thus eliminating major source of photoresist poisoning-induced footing. N-free dielectric ARC demonstrated a wide tunable range of its optical properties at 193nm in a single wafer PECVD reactor: 1.6<n<1.9 and 0< k<1.1. This range enables cost-effective and in-situ deposition of a dual-layer dielectric ARC on the low λ dielectric layers during the dual damascene process. The dual-layer coating, which consists of a phase-shift layer on an absorbing layer, can keep the substrate reflectivity below 1% across the wafer, minimizing CD swing. N-Free dielectric ARC can be easily integrated with low κ dielectrics. Its adhesion with low κ materials is excellent and it can be etched and chemically and mechanically polished together with low κ dielectrics.
Characteristics of Ultra Shallow B Implantation with Decaborane
Authors: Li Cheng , Albano Maria A. , Gladczuk Leszek , Sosnowski Marek
Published: April 2011

The characteristics of ultra shallow B implantation with mass-analyzed decaborane cluster ions (B10Hx+) are presented. Depth profiles of B and co-implanted H were measured by SIMS, before and after annealing. Annealing results in the increase in the depth of B distribution, due to diffusion, but most of H diffuses out of Si. While the sputtering yield of Si per incoming B in a cluster was found to be comparable to the estimated sputtering yield of Si with B+ ions of the equivalent energy (∼ 1.2 keV), the surface effects of the two types of ions may be quite different. Atomic force microscopy revealed that the smoothing effect of the small decaborane cluster ions, observed previously by us on a surface of amorphous Si, is also present on crystalline Si and even on a much rougher surface of polycrystalline Ta film. The smoothing affects different parts of the power density spectra as functions of spatial frequency in the amorphous and crystalline materials. The smoothing on c-Si surfaces is in sharp contrast to roughening of these surfaces by irradiation with monomer Ar ions, which was done for reference. This indicates that different ion-surface interaction mechanisms are needed to describe impacts of cluster and of monomer ions. All other effects of Si implantation with B10Hx+ measured to date were found to be the same as those with B+ ions of equivalent energy and dose, which confirms that decaborane implantation is an alternative to the very low energy B implantation for ultra shallow p-type junctions in Si devices.
Growth Temperature Effects on Deep-Levels in Si Grown by Low Temperature Molecular Beam Epitaxy
Authors: Chung Sung-Yong , Berger Paul R. , Fang Z-Q. , Thompson Phillip E.
Published: April 2011

Deep-level transient spectroscopy (DLTS) measurements were performed on Si:Sb and Si:B n+-p step junction diodes grown by LT-MBE at various growth temperatures. The trap density dependence on growth temperature decreases with increasing temperature. However, segregation and diffusion increase with increasing temperature. Electron traps, E1 (0.42–0.45eV) and E2 (0.257eV), and hole traps, H1 (0.38–0.41eV), were found in B-doped layer grown at 370°C, 420°C, 500°C, and 600°C. These traps have been characterized by their capture cross-section, activation energy level, and trap density. The origins of the dominating electron traps are hypothesized as the association with pure divacancy defects. E1 level can be assigned for singly negatively charged divacancy V(0/-) + α and E2 level for doubly negatively charged divacancy V(-2/-).
High κ Gate Dielectrics For Si And Compound Semiconductors By Molecular Beam Epitaxy
Authors: Raynien Kwo J. , Hong Minghwei
Published: April 2011

The ability of controlling the growth and interfaces of ultrathin dielectric films on Si and compound semiconductors by ultrahigh vacuum physical vapor deposition has led to comprehensive studies of gate stacks employing the high κ gate oxide Ga2O3(Gd2O3), and the rare earth oxides Gd2O3and Y2O3. The epitaxy and the interfaces of Gd2O3on GaAs, GaN, and Si were characterized with atomic precision, and show strong tendency to conform to the underlying substrate, thus providing insight into the fundamental mechanism for low interfacial state density and effective passivation of GaAs and GaN surfaces. These Gd2O3and Y2O3gate stacks of abrupt interfaces and controlled microstructures were employed as a model system to elucidate critical issues of materials integration in CMOS scaling.
Improvement of capacitance-voltage (C-V) characteristics of YSZ/Si(001) and ZrO2/Si thin film by Nb-doping
Authors: Wakiya Naoki , Moriya Tomohiko , Shinozaki Kazuo , Mizutani Nobuyasu
Published: April 2011

Yttria stabilized zirconia (YSZ) and zirconia (ZrO2) thin films without and with Nb-doping were prepared on Si substrate by rf-magnetron sputtering. Undoped YSZ and ZrO2 thin films had (001) orientation, and the orientation was unchanged by the Nb-doping. For both undoped YSZ and ZrO2 thin films, around 2.0 V ion-drift type hysteresis was clearly observed in capacitance-voltage (C-V) characteristics. Nb-doping into YSZ brought about the increase of lattice parameter up to 20 mol% of Nb, which suggests that Nb was incorporated into YSZ lattice up to 20 mol%. By the Nb-doping, the hysteresis in C-V characteristics for YSZ thin film was considerable decreased to around 0.1 V. Drastic suppression of the hysteresis in C-V characteristics was observed for Nb-doped ZrO2 thin film. In this case, the hysteresis was completely disappeared. These facts suggest that oxygen vacancies in YSZ and ZrO2 thin films would be suppressed or disappeared by Nb-doping. This means that Nb is a excellent dopant for both YSZ and ZrO2 to suppress the ion-drift type hysteresis.
Study of interface formation of (Ba,Sr)TiO3 thin films grown by rf sputter deposition on bare Si and thermal SiO2/Si substrates.
Authors: Suvorova N. A. , Mueller A. H. , Suvorova A. A. , Saunders M. , Irene E. A.
Published: April 2011

(Ba,Sr)TiO3 (BST) thin films were deposited by ion beam sputtering on both bare and oxidized Si. Spectroscopic ellipsometry (SE) model results have shown an increase in the SiO2 layer thickness for bare substrates and those with a 1 nm initial oxide layer, and a decrease for thicker (3.5 nm) initial SiO2 films. This result was confirmed by high resolution electron microscopy (HREM) analysis of the films, and it is believed to be due to simultaneous subcutaneous oxidation of Si and reaction of the BST layer with SiO2. From high-frequency capacitance-voltage (C-V) analysis, a decrease in the interface trap density Dit of an order of magnitude was observed for oxidized Si substrates.
A study of Al2O3:C films on Si(100) grown by low pressure MOCVD
Authors: Singh M. P. , Thakur C. S. , Bhat N. , Shivashankar S. A.
Published: April 2011

We report the characterization of carbonaceous aluminium oxide, Al2O3:C, films grown on Si(100) by metalorganic chemical vapor deposition. The focus is on the study of the effects of carbon on the dielectric properties of aluminium oxide in a qualitative manner. The carbon present in the aluminium oxide film derives from aluminium acetylacetonate used as the source of aluminium. As-grown films comprise nanometer-sized grains of alumina (∼ 20–50 nm) in an amorphous carbonaceous matrix, as examined by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The films are shiny; they are smooth as observed by scanning electron microscopy (SEM). An attempt has been made to explore the defects (viz., oxide charge density) in the aluminium oxide films using room temperature high frequency capacitance – voltage (C-V) and current–voltage (I-V) measurements. The hysteresis and stretch-out in the high frequency C-V plots is indicative of charge trapping. The role of heteroatoms, as characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy, in the transport of charge in Al2O3:C films is discussed.
Measurement of Three Dimensional Polarization Direction in Ferroelectric Thin Films Using Scanning Nonlinear Dielectric Microscopy with Rotating Electric Field
Authors: Odagawa Hiroyuki , Cho Yasuo
Published: April 2011

A scanning nonlinear dielectric microscope (SNDM) probe, called theε311 -type probe, and a system to measure the ferroelectric polarization component parallel to the surface using rotating electric field have been developed. This is achieved by measuring the ferroelectric material's nonlinear dielectric constant ε311 instead of ε333, which is measured in conventional SNDM. Experimental result shows that we can successfully determine polarization component parallel to the surface. The SNDM system can measure polarization at any angle from the surface normal which is often of interest.
Local Electromechanical Properties and Grain Size Effects in Ferroelectric Relaxors Studied by Scanning Piezoelectric Microscopy
Authors: Kholkin A. L. , Shvartsman V. V. , Woitas M. , Safari A.
Published: April 2011

The local electromechanical properties of relaxor 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 (PMN-PT) films are investigated by Scanning Force Microscopy (SFM) in a piezoelectric contact mode. The domain contrast is observed only in some grains (∼20 % of the entire surface), which showed clear ferroelectric behavior. Thus on the microscopic level the material behaves as a composite with ferroelectric regions embedded in the non-polar matrix. This was attributed to the relaxor-to-ferroelectric phase transition induced by the internal bias field. The local hysteresis loops are found to depend on the size of the grains. A distinct correlation between the values of the effective piezoelectric coefficients, deffi and the size of the respective grains is observed. Small grains exhibit slim piezoelectric hysteresis loops with low remanent deff while relatively strong piezoelectric activity is characteristic of larger grains. In addition, large grains exhibit longer relaxation time after poling with an effective time constant increasing with the grain size. The nature of size effect is discussed taking in terms of dynamics of nanopolar clusters and SFM instrumentation.
Platinum-Accelerated Phase Transition in Bismuth-Based Layer-Structured Ferroelectric Thin Films
Authors: Kato Kazumi , Suzuki Kazuyuki , Fu Desheng , Nishizawa Kaori , Miki Takeshi
Published: April 2011

The phase transition of non ferroelectric pyrochlore to ferroelectric perovskite in CaBi4Ti4O15 thin films depended on matching of the atomic arrangements in platinum bottom electrodes to the Ca-Bi-Ti-O thin films. CaBi4Ti4O15 thin films crystallized on (200)-oriented platinum at 650°C showed c-axis orientation. In contrast, thin films randomly crystallized on highly crystalline (111)-oriented platinum at the same temperature contained pyrochlore phase and showed P-V hysteresis loops. The ferroelectric properties improved with the degrees of (h00) orientation.
Ferroelectric Properties in Ca Substituted SrBi2Nb2O9 Thin Films
Authors: Das Rasmi R. , Pérez W. , Bhattacharya P. , Katiyar Ram S.
Published: April 2011

We have studied the influence of partial substitution of Ca (0%, 5%, 10% and 15%) on the structural and electrical properties of SrBi2Nb2O9 (SBN) thin films. Pulsed laser deposition technique was used to grow thin films on platinized silicon substrates. X-ray diffraction data confirmed the polycrystalline nature of the films with preferential orientation along the polarization axis. Incorporation of Ca at Sr-site of SBN reduced the lattice parameter and was attributed to the smaller ionic radii of Ca. The soft mode frequency at 29.5 cm-1 of SBN shifted towards higher wavenumber implied increasing the transition temperature upon Ca substitution. The grain sizes of SBN thin films vary from oval to rod like structures and improving the homogeneous distribution of grains with the increase in Ca contents. The ferroelectric properties of the films enhanced with maximum remanent polarization of 35.3 mC/cm2. The increase in the coercive field with incorporation of Ca at Sr-site was attributed to the higher electronegativity of Ca. The SBN thin films with the incoporation of Ca exhibited poor leakage current behavior. The reduction of dielectric permittivity with Ca concentration was attributed to the lower dielectric permittivity of CaBi2Nb2O9.
PbZr0.53Ti0.47O3 (PZT) Thin Films on La0.5Sr0.5CoO3 (LSCO) Bottom Electrodes Prepared by Chemical Solution Deposition and Annealed at Different Temperatures
Authors: Malic Barbara , Javoric Sasa , Kosec Marija , Jiménez Ricardo , Alemany Carlos
Published: April 2011

PbZr0.53Ti0.47O3 (PZT) films on La0.5Sr0.5CoO3 (LSCO) /Pt electrodes crystallize in the perovskite phase at 550°C. Cross section SEM shows a columnar grain structure of PZT films on fine-grained LSCO. The ferroelectric response of the heterostructures depends on the annealing temperature of the LSCO layer. The remanent polarization and coercive field of the PZT annealed at 550 °C deposited on LSCO annealed at 800 °C are 25 μC/cm2 and 99 kV/cm respectively, comparable to the values obtained for PZT films on platinized silicon substrate.
Self-poling Effects in Sol-gel Derived Pb(Zr1-xTix)O3 Thin Films
Authors: Cheng Jinrong , Li Nan , Eric Cross L. , Meng Zhongyan
Published: April 2011

Based on the direct piezoelectric effect, the measurement of piezoelectric module d33 was conducted to examine the self-poling effect in sol-gel derived Pb(Zr1-xTix)O3 (PZT) thin films. It is observed that as-prepared PZT thin films have piezoelectric responses being dependent upon the film thickness and composition. The higher d33 of 26 pC/N is achieved for ∼0.4 μm thick PZT thin films with Zr/Ti ratio of 53/47. The d33 value decreases with increasing the film thickness for as-prepared PZT thin films, however, increases for the same film after external poling. The origin of the self-poling effect was briefly discussed based on the formation of an internal bias field in PZT thin films.
Contribution of Pb to Ferroelectricity in Perovskite-type Oxides
Authors: Miyazawa Hiromu , Ishii Fumiyuki , Ishida Masaya , Natori Eiji , Shimoda Tatsuya , Oguchi Tamio
Published: April 2011

We have studied the nature of the covalent bond between Pb 6s, 6p and O 2p orbitals in perovskites based on first-principles calculations. We conclude that the Pb 6p - O 2p covalent bond, not a bond involving Pb 6s, is crucial for the large ferroelectric effect in PbTiO3. The Pb 6s states behave like a shallow core level. To examine the effect of a Pb atom at the A site in the perovskite-type structure, we compared several calculated properties of PbTiO3 and BaTiO3 - the electric polarization, piezoelectric stress tensor and Young's modulus. The piezoelectric stress tensor e33 was calculated through Berry phase theory. BaTiO3 was found to have a larger e33 value than PbTiO3. In the case of BaTiO3, the response of Ti-O(2) to c-axis distortion is larger than in PbTiO3. We found that PbTiO3 is softer than BaTiO3 because of the cooperation of both Ti-O(2) and Pb-O(1) covalent bonds. We also found that the ferroelectric state is much softer than the paraelectric state. We propose that in the structural phase transition the system with the lower symmetry avoids ion repulsion through the additional degree of freedom available from atom displacement.
Retention characteristics of Pb(Zr, Ti)O3 films deposited by various methods for high-density non-volatile memory
Authors: Shin Sangmin , Hofmann Mirko , Lee Yong Kyun , Cho Choong Rae , Lee June Key , Park Youngsoo , Lee Kyu Mann , Song Yoon Jong
Published: April 2011

Retention loss is a significant issue for an application of ferroelectric thin films to high-density non-volatile memory devices. We investigated the polarization retention characteristics of ferroelectric Pb(Zr,Ti)O3 (PZT) thin films which were fabricated on Pt/IrO2/Ir substrates by different deposition methods. In thermally-accelerated retention failure tests, Pb(Zr,Ti)O3 (PZT) films which were prepared by a chmeical solution deposition (CSD) method showed rapid decay of retained polarization charges as the films became thinner down to 1000 Å, while the films which were grown by metal organic chemical vapor deposition (MOCVD) showed relatively large nonvolatile charges at the same thickness. We concluded that in the CSD-grown films, the relatively large interfacial passive layer compared with the MOCVD-grown films had an unfavorable effect on retention behavior. We observed the existence of such interfacial layers by extrapolation of the total capacitance with thickness of the films and the capacitance of this layer was larger in MOCVD-grown films. It means that the possibility of the accumulation of space charges at the interface was reduced, so that less imprint and less retention loss could be observed in the MOCVD-grown films.
SrTiO3 Thin Film Varactors on Si for Microwave Applications
Authors: Vorobiev Andrei , Rundqvist Par , Khamchane Khaled , Gevorgian Spartak
Published: April 2011

Dielectric properties of SrTiO3 (STO) thin films in Au/Pt/STO/Pt/TiO2/SiO2/Si structure are studied at microwave frequencies. STO films with thickness of 300 nm were grown by laser ablation at different temperatures on templates of Pt/TiO2/SiO2 on Si with resistivity of 5 kQ-cm. XRD measurements reveal highly textured (111)STO films with small amount of (100) and (110) domains. The full with at half maximum of the rocking curve of (11 1)STO domains is about 2 degrees. Circular Au/Pt top electrodes with diameters in the range of 10–60 μm were formed by e-beam evaporation and lift-off process. The on chip microwave impedance of devices was measured in the frequency range of 45 MHz-45 GHz as a function of DC electric field in the range of 0–800 kV/cm. The loss tangent is less than 0.06 in the whole frequency range. Application of DC bias results in resonant absorption of microwave power at frequencies of 1.3, 3.0, 4.7, 6.4, and 9.7 GHz. The relative change of the dielectric permittivity under 800 kV/cm DC field is more than 20% in the whole frequency range. The results indicate that the varactors based on these STO films are suitable for tunable microwave applications.
Possible Artefacts in Measurement of Hardness and Elastic Modulus on Superhard Coatings and the Verification of the Correctness of the Data
Authors: Veprek S. , Mukherjee S. , Karvankova P. , Männling H.-D. , He J. L. , Xu J. , Prochazka J. , Argon A. S. , Li A. S. , Fang Q. F. , Li S. Z. , Manghnani M. H. , Tkachev S. , Zinin P.
Published: April 2011

Measurements of the hardness and Young's modulus of superhard coatings (HV≥40 GPa) by means of automated load-depth-sensing indentation technique can be subject to a number of errors that are discussed and exemplified here. Only load-independent values of hardness for loads larger than 30–50 mN can be considered reliable when the technique of Doerner and Nix (linear extrapolation of the unloading curve) is used to determine the corrected indentation depth. The results are compared with values of Vickers hardness calculated from the contact area of the remaining plastic deformation which was measured by means of calibrated scanning electron microscope. The values of Young's modulus obtained from the indentation are close to the zero-pressure shear modulus of the coatings as measured by means of Vibrating Reed and surface Brillouin scattering techniques.
Adhesion Thin Ductile Films Using Stressed Overlayers and Nanoindentation
Authors: Cordill M. J. , Moody N. R. , Bahr D. F.
Published: April 2011

Differently stressed films of tungsten on silicon dioxide have been studied to determine the interfacial fracture toughness and the Mode I fracture energy release rate of tungsten on glass. Tungsten films with a low compressive stress (less than 1GPa) had nanoindentation tests performed on them to induce buckling. Using mechanics based models and the dimensions of the buckles the fracture energy release rate and the phase angle of loading (Ψ) were calculated to be between 3.8 and 13 J/m2. By varying the residual stress in the film it was possible to examine regions of pure shear (Mode II) interfacial fracture as well as mixed mode interfacial fracture toughness of this system. A similar tungsten film was then used as stressed overlayer on sputtered Pt films on silicon dioxide to determine the fracture energy release rate. Nanoindentation was required to induce buckling, as the overlayer alone did not cause spontaneous buckling. The stressed overlayer method and nanoindentation were used to determine the interfacial toughness of the Pt/silica system to be 1.4 J/m2.
Novel Nanostructured Metal and Ceramic Composites
Authors: Narayan J.
Published: April 2011

We have designed a unique synthesis procedure to create nonomaterials of uniform grain size and control the chemistry of interfaces between the grains. The metastability of nanocrystalline materials is a major challenge which can be addressed by controlling the chemistry of interfaces. The hardness of these films having a uniform size was measured as a function of grain size using a nanoindentation technique. It was found that hardness increased with decreasing grain size in accordance with Hall-Petch model. However, below a critical grain size we observed a decrease or softening with a further decrease in grain size. These observations in metals and ceramics are modeled in view of intragrain deformation (Hall-Petch regime) and intergrain deformation (grain boundary shear/sliding )in the softening regime. Since we can change the alloying of interfacial region, we can address the metastability as a function of temperature, which is crucial from applications viewpoint of these materials.
Novel Composite Coatings With 3D Coating Architectures for Tribological Applications Fabricated Using Semiconductor Patterning Processes
Authors: Krzanowski James E. , Endrino Jose L. , Hirschman Karl
Published: April 2011

Composite coatings consisting of hard compounds and soft solid lubricant phases have been actively investigated as tribological coatings for reducing friction while improving wear resistance. In most cases structural modifications in these coatings have been achieved by either natural phase separation or sequential layer deposition. In this study, we explore the concept of creating a three-dimensional structure in a tribological composite coating by using well-established semiconductor patterning methods. Using photolithography, we have patterned the substrate surface with a regular array of micron-size islands. The substrate was then coated with various metal and carbide coatings, including Cr and TiC, using sputter deposition. The substrates were sonicated in a solvent to remove the photoresist islands leaving an array of holes. MoS2 was then deposited onto the substrates. A pin-on-disk friction and wear test was conducted on a TiC/MoS2 sample to examine the effects of these islands on wear morphology. The results showed that the MoS2-filled holes can act as lubricant reservoirs, and the areas of the sample coated with TiC/MoS2 provided better wear protection than areas coated with only MoS2.
Nanocomposite Tribological Coatings for Rolling Element Bearings
Authors: Evans Ryan D. , Cooke Elizabeth P. , Ribaudo Carl R. , Doll Gary L.
Published: April 2011

The performance of rolling element bearings is enhanced by the application of nanocomposite coatings that are composed of metal carbides incorporated into an amorphous hydrogenated carbon matrix (MC/a-C:H). When applied to the rolling elements in tapered roller bearings, MC/a-C:H coatings were found to help increase fatigue life, rib-roller end scuffing resistance, and false brinelling resistance in poorly lubricated environments. This series of performance tests were conducted with both coated and uncoated rollers. The results are attributed to the minimization of adhesive interactions and desirable counterface micro-polishing due to the presence of the thin hard coatings on rollers in the bearings.
Evaluation of Tribological and Mechanical Properties of Nitride Thin Films Prepared by Cathodic ARC Deposition
Authors: Shukla Pallavi , Sikder A. K. , Kumar Ashok , Durvin Robert , McDonough Mark , Smith M. D.
Published: April 2011

Mechanical and tribological properties of thin films draw special attention and differ from those of bulk materials due to the effects of interfaces, microstructure and thick underlying substrates. In this study hard wear resistant nitride coatings (TiN, ZrN, TiAlN, TiCN and CrN) were coated on high speed steel substrates using cathodic arc deposition method. Mechanical properties of the films were evaluated using nanoindentation technique. Continuous stiffness method was employed to evaluate the depth sensing hardness and modulus values. Studies of tribological properties were performed using ball-on-disk friction and wear test. We have also investigated the wear track using optical microscopy. Variation of coefficient of friction with time has been analyzed and coating endpoint was estimated. Nanoindentation evaluation of mechanical properties along with the measurement of tribological properties is very useful in order to use them as wear resistant hard coatings.
MOCVD of Aluminum Oxide Barrier Coating
Authors: Nable Jun C. , Gulbinska Malgorzata A. , Suib Steven L. , Galasso Francis S.
Published: April 2011

High temperature materials such as nickel superalloys require the development of corrosion resistant coatings. These coatings must be thermally stable and chemically inert in order to protect the substrate material. Aluminum oxide is one such candidate. Aluminum acetylacetonate was used as the precursor for metal-organic chemical vapor deposition at atmospheric pressure. Uniform, amorphous, and multi-colored protective coatings were deposited onto nickel substrates at 400 to 500°C and dark gray, and powdery coatings were obtained at higher temperatures of 550 to 600°C. The coating was free from cracks when higher carrier gas flow rate were used.
Ion Beam Etching of CVD Diamond Enhanced by Prior Au and O Implantation.
Authors: Leech Patrick W. , Reeves Geoffrey K. , Holland Anthony S. , Ridgway Mark C.
Published: April 2011

Diamond films were implanted with Au or O ions at multiple energies in order to produce a uniform region of C vacancies. Analysis of the implanted films by Raman spectroscopy has shown that the proportion of non-diamond or amorphous carbon increased with dose (5 × 1013 − 5 × 1015 ions/cm2). For implantation with Au ions, a complete amorphisation near to the surface was evident at a dose of 5 × 1015 ions/cm2. We have examined the ion beam etch (IBE) rate of the films as a function of the implant species and dose. The etching experiments were performed using either Ar or Ar/O2 gases at a bias energy of 500 -1,000 eV. In Ar gas, the process of sputter etching has produced a similar increase in etch rate with dose for both the Au and O implants. In Ar/ O2 gases, the process of ion-enhanced chemical etching produced greater etch rates than obtained in Ar gas with higher rates for the Au than the O implants.