bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantifying the Effect of the GST on Inflation in Australia's Capital Cities: An Intervention Analysis
Authors: Valadkhani Abbas , Layton Allan P.
Published: July 2004

This article examines the magnitude and duration of the effect of the Goods and Services Tax (GST) on inflation in Australia's eight capital cities using the Box and Tiao intervention analysis and quarterly data spanning from 1948:4 to 2003:1. We found that the GST had a significant but transitory impact on inflation only in the September quarter of 2000 when this new tax system was implemented. In this quarter inflation showed an additional increase of 2.6 per cent in Sydney (minimum effect) and 2.8 per cent in Australia as a whole, and the figure for Hobart was 3.3 per cent (maximum effect). Based on Wald test results, we also found some evidence that there is no significant (or substantial) difference in the average price changes among capital cities. We could not reject the null hypothesis that the GST increased the consumer price index by 2.8 per cent across the board in various cities. These results are also consistent with previous studies and surveys.
Postsurgical Treatment of Epilepsy
Authors: Berg Anne T.
Published: July 2004

In people with localization-related epilepsy who do not respond well to medication and continue to have seizures despite having been evaluated and treated by an epilepsy specialist, current recommendations are to consider surgery as an alternative to continued trials of different antiepileptic drugs (AEDs).
Glutamate
Authors: Cutrer F. Michael
Published: July 2004

The NMDA Receptor Antagonist MK‐801 Reduces Fos‐like Immunoreactivity Within the Trigeminocervical Complex Following Superior Sagittal Sinus Stimulation in the Cat

Expression of Fos protein is an indicator of neuronal perturbation and is readily observed in the caudal medulla and the spinal cord following trigeminovascular nociceptive activation by electrical stimulation of the superior sagittal sinus (SSS) in the cat. It has been shown in the rat that N‐methyl‐D‐aspartate (NMDA) receptor blockade causes a reduction in Fos protein expression after generalized meningeal irritation. We wished to examine if the same relationship was true in the cat, using the same non‐competitive NMDA receptor antagonist MK‐801, and a trigeminovascular‐specific stimulus. A group of experimental animals underwent stimulation following blinded administration of MK‐801 (4 mg/kg i.v.); control animals underwent stimulation minus MK‐801, and a non‐stimulated control animal underwent surgery alone. The regions examined for Fos‐like immunoreactivity were the trigeminal nucleus caudalis (TNC) and its caudal extension into the C(1) and C(2) levels of the upper cervical spinal cord. The Fos‐positive cell counts for the three regions (TNC, C(1) and C(2)) were grouped together for analysis. In the control stimulated group a median of 78 (56‐99, quartile range, n = 4) cells were Fos‐positive. In the group treated with MK‐801 the median number of Fos‐positive cells was reduced to 40 (30‐48; P < 0.03, n = 7). The large reduction that was observed in SSS stimulation‐evoked Fos protein expression following the administration of MK‐801, taken together with electrophysiological data, indicates a role for glutamate in neurotransmission within the trigeminocervical complex. Understanding glutamatergic mechanisms in the trigeminocervical complex offers mechanistic insight and therapeutic possibilities for primary neurovascular headaches, such as migraine.
A Quantitative Sensitivity Analysis of Cutting Performances in Orthogonal Machining with Restricted Contact and Flat-Faced Tools
Authors: Fang Ning
Published: July 2004

This paper presents a new quantitative sensitivity analysis of cutting performances in orthogonal machining with restricted contact and flat-faced tools, based on a recently developed slip-line model. Cutting performances are comprehensively measured by five machining parameters, i.e., the cutting forces, the chip back-flow angle, the chip up-curl radius, the chip thickness, and the tool-chip contact length. It is demonstrated that the percentage of contribution of tool-chip friction to the variation of cutting performances depends on different types of machining operations. No general conclusion about the effect of tool-chip friction should be made before specifying a particular type of machining operation and cutting conditions.
Characterization of Substrate Materials for System-in-a-Package Applications
Authors: Chen Liu , Andræ Anders S. G. , Zou Gang , Liu Johan
Published: July 2004

System-in-a-Package (SiP) aims to integrate the entire system functions within a system-level package containing multiple ICs and other components interconnected in a high-density substrate. A structure based on the SiP concept is proposed in this paper. Based on this SiP structure, four substrate candidates, namely FR4, liquid crystal polymer (LCP), teflon (PTFE) and low temperature co-fired ceramic (LTCC) were compared by assessing and measuring their mechanical reliability, electrical performance and environmental influence. First, to evaluate long-term reliability, the 3D finite element method (FEM) was used to calculate the stress distribution and warpage of the whole package. Both three-point bending and cooling in the manufacturing process were taken into consideration. The LCP has a coefficient of thermal expansion (CTE) close to that of the silicon chip, and a Young’s module close to that of FR4, which gave the best reliability in both bending and cooling situations. Next, the dielectric constants and the loss tangent for the four substrates were evaluated in the electrical performance investigation. The LCP has a low relative dielectric constant and a low dissipation factor for the frequency range 1 GHz to 35 GHz, making it a good substrate for high frequency applications. An environmental assessment included several environmental impact categories; this assessment indicated that LCP is the most environmentally acceptable substrate.
Finite Element Analysis on Soft-Pad Grinding of Wire-Sawn Silicon Wafers
Authors: Xin X. J. , Pei Z. J. , Liu Wenjie
Published: July 2004

Silicon is the primary semiconductor material used to fabricate microchips. The quality of microchips depends directly on the quality of starting silicon wafers. A series of processes are required to manufacture high quality silicon wafers. Surface grinding is one of the processes used to flatten the wire-sawn wafers. A major issue in grinding of wire-sawn wafers is the reduction and elimination of wire-sawing induced waviness. Several approaches (namely, combination of grinding and lapping, reduced chuck vacuum, soft-pad, and wax mounting) have been proposed to address this issue. Finite element analysis modeling of these approaches was conducted and the results were published earlier. It was shown that soft-pad grinding was a very promising approach since it was very effective in reducing the waviness and very easily adopted to conventional grinding environment. This paper presents a study of finite element analysis on soft-pad grinding of wire-sawn silicon wafers, covering the mechanisms of waviness reduction and the effects of pad material properties.
A Model for Underfill Viscous Flow Considering the Resistance Induced by Solder Bumps
Authors: Lai Chyi-Lang , Young Wen-Bin
Published: July 2004

During the underfill process, polymers driven by either capillary force or external pressure are filled at a low speed between the chip and substrate. Current methods treated the flow in the chip cavity as a laminar flow between parallel plates, which ignored the resistance induced by the solder bumps or other obstructions. In this study, the filling flow between solder bumps was simulated by a flow through a porous media. By using the superposition of flows through parallel plates and series of rectangular ducts, permeability of the underfill flow was fully characterized by the geometric arrangement of solder bumps and flat chips. The flow resistances caused by adjacent bumps were represented in its permeability. The model proposed in this study could provide a numerical approach to approximate and simulate the undefill process for flip-chip technology. Although the proposed model is applicable for any geometric arrangement of solder bumps, rectangular-array of solder bumps layout was used first for comparison with experimental results of other article. Comparisons of the flow-front shapes and filling time with the experimental data indicated that the flow simulation obtained from the proposed model gave a good prediction for the underfill flow.
Productivity of Paced Parallel-Serial Manufacturing Lines With and Without Crossover
Authors: Freiheit Theodor , Shpitalni Moshe , Hu S. Jack
Published: July 2004

The productivity of a manufacturing system is greatly influenced by the configuration of the manufacturing system. This paper examines the importance of configuration on productivity, and the improvements that can be obtained by bufferless parallel-serial configurations, i.e. multiple machining lines in parallel, both with and without crossover between the operations. Combinatorial algebraic models are developed to quantify the productivity of parallel-serial configurations. It is shown that significant improvements to productivity can be obtained by placing operations in parallel, and that there is a synergistic improvement to productivity from having crossover between the operations.
Improved Inverse Solutions for On-Line Machine Tool Monitoring
Authors: Olson Lorraine , Throne Robert , Rost Eric
Published: July 2004

The identification of tool/chip interface temperatures from remote sensor measurements is a steady inverse heat transfer problem that arises in online machine tool monitoring. In a previous paper we developed a set of inverse approaches, vector projection inverse methods, specifically for this problem. These methods rely on two types of sensor measurements: temperatures and heat fluxes. However, because of the extreme ill-conditioning of the tool configuration we studied previously, only a very limited amount of information could be obtained using any of the inverse approaches examined. In an effort to understand the impact of physical parameters on the conditioning of the problem we examined two modifications to the simulated cutting tool: we increased the thermal conductivity of the tool insert, and we reduced the thickness of the tool insert. Inverse solutions were computed on both configurations with all methods for two temperature profiles and various noise levels. The estimated tool/chip interface temperature for the high conductivity tool showed no improvement compared to the original configuration, since the temperature profiles on the sensor surface were unchanged. However, for the thinner tool, the estimated temperatures were substantially more accurate than with the original configuration. With this thinner tool configuration, an optimal set of four sensors could be used to estimate these temperatures at the tool/chip interface to within a few degrees, even with noisy sensor data.
Liquefier Dynamics in Fused Deposition
Authors: Bellini Anna , Gu¨c¸eri Selc¸uk , Bertoldi Maurizio
Published: July 2004

Layered manufacturing (LM) is an evolution of rapid prototyping (RP) technology whereby a part is built in layers. Fused deposition modeling (FDM) is a particular LM technique in which each section is fabricated through vector style deposition of building blocks, called roads, which are then stacked layer by layer to fabricate the final object. The latest improvements in this technology brought about the possibility of fabricating not only a model but even the finished product. This paper presents the analysis of the liquefier dynamics towards establishing control strategies for flow control during the extrusion phase, which is necessary to achieve the mentioned objective.
Fabrication of carbon nanotube array and its field emission property
Authors: Sato Hideki , Takegawa Hitoshi , Yamaji Hiroki , Miyake Hideto , Hiramatsu Kazumasa , Saito Yahachi
Published: July 2004

A fabrication process for carbon nanotubes (CNTs) field emitter array is reported. This process consists of formation of protrusions on a silicon substrate, selective deposition of catalyst film on tips of the protrusions and direct growth of the CNTs on the tips of the protrusions by plasma-enhanced chemical vapor deposition. In this process, number of the CNTs grown on each tip of the protrusion can be controlled by the size of the protrusion. The CNT field emitter arrays gave better field emission property than a continuous CNT film. A threshold voltage required to obtain 1 μA/cm2 of field emission current from the CNT field emitter array was about 300 V lower than that from the continuous CNT film. This improvement is presumably due to reduction of screening effect, which prevents the field from concentrating on the tip of the CNT emitters.
Molecular beam epitaxial growth of AlGaPSb and AlGaPSb/InP distributed Bragg reflectors on InP
Authors: Klem J. F. , Serkland D. K. , Kim J. , Wang T.-Y.
Published: July 2004

The molecular beam epitaxial growth of GaPSb and Ga-rich AlGaPSb nearly lattice matched to InP has been investigated. The effect of growth temperature, P flux, Ga flux, and Sb flux on the alloy P/Sb ratio was examined. The 300 K band gap of lattice-matched GaPSb was estimated to be 0.84 eV based on photoluminescence measurements, and the shift of band gap energy with Al content in AlGaPSb alloys with Al fractions of 0.03–0.04 was investigated. A conduction band offset of approximately 0.15 eV in a type-II configuration was estimated between lattice-matched Al0.04Ga0.96P0.35Sb0.65 and InP based on photoluminescence characterization of multiple quantum well structures. AlGaPSb/InP distributed Bragg reflectors (DBRs) with a stopband centered on 1550 nm were grown with excellent lattice matching and good surface morphology. A refractive index difference of 0.41 between these materials was estimated based on a fit to the DBR reflectance spectrum.
Integration of field emitters into scanning probe microscopy sensors using focused ion and electron beams
Authors: Lehrer C. , Frey L. , Petersen S. , Ryssel H. , Schäfer M. , Sulzbach Th.
Published: July 2004

Material processing by focused ion-beam milling and electron-beam-induced deposition was applied for the integration of field emitters into scanning probe microscopy (SPM) sensors. Geometry of the silicon probes was adapted to the integration of an emitter gate structure with a diameter in the range of micrometers. Processing of the silicon probes was modified to replace the apex by mesas with diameters between 1 μm and 15 μm. Parasitic effects originating from material processing with focused particle beams were investigated by transmission electron microscopy. A process combining focused ion-beam milling and wet chemical etching was used to remove ion-beam-induced damage and contamination due to ion implantation. Leakage current caused by absorption of precursor material during deposition of emitters was removed by thermal annealing. Field emitter structures were fabricated by focused particle beam processing revealing emission currents of 0.6 μA/tip for a gate voltage of 90 V.
Characterization of enhanced field emission from HfC-coated Si emitter arrays through parameter extraction
Authors: Nicolaescu D. , Sato T. , Nagao M. , Filip V. , Kanemaru S. , Itoh J.
Published: July 2004

A nonlinear least-squares fitting procedure for array model parameter extraction using field emission (FE) data has been developed and extensively applied for Si and Si/HfC-coated arrays with 1024, 4000, and 16 000 tips measured in ultrahigh vacuum conditions. The array FE model is built up using equations that describe the electron emission current from individual emitters of given radius R and work function φ together with nonuniform distribution functions giving the dispersion of these parameters within the array. A combined numerical/analytical approach is used to accurately express the electric field for the actual gated emitter configuration. The FE current is computed through integration of the current density over the emitter tip surface and as a sum of all tip currents in the array. The program, developed as a MATHCAD application using the intrinsic “minerr” routine, extracts array parameters of physical interest and does not make use of “area” and “field enhancement” factors. HfC-coated FE arrays perform better than (noncoated) Si arrays when comparing the total emission current, the spatial uniformity and number of active tips, and the stability in long-term operation.
Extraction of emission area from Fowler–Nordheim plots
Authors: Forbes Richard G. , Deane Jonathan H. B. , Hamid Nabil , Sim Hwa San
Published: July 2004

The process of deriving emission-area estimates from Fowler–Nordheim (FN) plots is investigated, using emission-area extraction functions and an iterative procedure suggested earlier [R. G. Forbes, J. Vac. Sci. Technol. B 17, 526 (1999)]. Simulated FN-plot data have been prepared using free-electron theory and three different tunneling-barrier models (elementary triangular barrier, image-rounded “Schottky–Nordheim” barrier, and a quadratically enhanced barrier). These have been analyzed using two area-extraction spreadsheets with different models (elementary triangular barrier and Schottky–Nordheim barrier) embedded in them. It is confirmed that significant errors in the area estimate may occur if the emission model used to analyze the FN-plot data does not correspond well with the model/physics responsible for generating the data. It is also concluded that parameters used in the area-extraction process should correspond to emission variables in the midrange of the FN-plot data.
Structure–property relationships in porous GaN generated by Pt-assisted electroless etching studied by Raman spectroscopy
Authors: Williamson Todd L. , Dı́az Diego J. , Bohn Paul W. , Molnar Richard J.
Published: July 2004

Porous GaN (PGaN) produced by Pt-assisted electroless etching has been studied by Raman spectroscopy. Three different unintentionally doped GaN films grown by hydride vapor phase epitaxy on sapphire were used for this study. Pt-assisted electroless etching takes place without external contact to a current source, simplifying the generation of porous semiconductors. Raman spectra were excited with both subband gap (441.6 nm) and above-band gap (325 nm) radiation, and collected in an unpolarized backscattering configuration. In both cases, a strong increase in scattering is observed for the Raman modes, depending on the depth of the porous layer. With visible excitation, symmetry-forbidden A1(TO) and E1(TO) are observed in PGaN, and spectral line shape analysis reveals the presence of the forbidden E1(LO) mode as well. Raman spectra were also analyzed using an effective medium theory, revealing extraordinary LO phonon scattering with visible, and Fröhlich scattering with UV, excitation. In addition a quasi-LO phonon is observed in the visible spectrum. All of the characteristic features of PGaN Raman scattering: symmetry-forbidden modes, quasi-LO scattering, and strong Fröhlich mode scattering, can be attributed to the dendritic porous morphology of PGaN.
Effect of buffer layer on InSb quantum wells grown on GaAs (001) substrates
Authors: Mishima T. D. , Santos M. B.
Published: July 2004

The effects of buffer layers on structural defects in InSb/AlxIn1−xSb quantum wells (QWs) have been investigated using transmission electron microscopy. Buffer layers with different nucleation layer materials (InSb or AlSb) and intermediate layer structures (Al0.09In0.91Sb/InSb strained-layer superlattice or InSb interlayer) were deposited on GaAs (001) substrates prior to the growth of InSb QW structures. Among the samples studied, the one with a 1 μm AlSb nucleation layer and a 200 nm InSb interlayer yielded the lowest densities of microtwins and dislocations in the InSb QW.
Composite thin films of (ZrO2)x-(Al2O3)1−x for high transmittance attenuated phase shifting mask in ArF optical lithography
Authors: Lai Fu-Der
Published: July 2004

Stoichiometric (ZrO2)x-(Al2O3)1−x composite thin films are obtained by using rf unbalanced magnetron sputtering in an atmosphere of argon and oxygen. All the deposited composite thin films are amorphous. The ZrO2-Al2O3 composite thin films will be nearly completely oxidized when the O2/Ar flow rate ratio exceeds 0.5. The optical constants of the thin films are calculated and measured. The measured values agree well with the ones calculated by applying the Hunderi effective medium model. The optical constants can be tuned by controlling the volume fraction of the ZrO2 and Al2O3 films. The optical requirements for a high-transmission attenuated phase-shifting mask (HT-APSM) blank can be satisfied by a suitable choice of volume fraction. An optimized ArF lithography transmittance value of 18%–20%, which conforms to the typical value for an HT-APSM blank, can be realized for a ZrO2 volume fraction in the range of 54.8% to 48.8%. To be used as a HT-APSM blank, one π-phase-shifted ZrO2-Al2O3 composite thin film with optimized transmittance is fabricated and is shown to satisfy the optical requirements of an HT-APSM blank.
Luminescent properties of SrGa2S4:Sm thin-film phosphors under low-voltage excitation
Authors: Iwamaru Masashi , Nakajima Hiroyoshi , Kominami Hiroko , Nakanishi Yoichiro , Hatanaka Yoshinori
Published: July 2004

Sm-activated SrGa2S4 thin-film phosphors (TFPs) were prepared in order to develop red-emitting TFPs, because so far we have reported on low-voltage cathodoluminescence (CL) properties of Ce- or Eu-activated SrGa2S4 TFPs showing blue or green emission, respectively. The films were prepared by multisource deposition (MSD), and annealed in H2S atmosphere after the deposition. It was shown by x-ray diffraction (XRD) measurement that from the as-deposited films containing GaS phase, SrGa2S4 phase was formed by the annealing. The formation mechanism of SrGa2S4 thin film is thought to be due to the reaction Sr+2GaS+2H2S→SrGa2S4+2H2↑ during the annealing. The films annealed at temperatures higher than 800 °C showed a red emission with a broad band peaked at about 700 nm, which might be based on the transition of 4f55d→4f6 of Sm2+, although the CL intensity was weak.
GaInNAs(Sb) vertical-cavity surface-emitting lasers at 1.460 μm
Authors: Wistey M. A. , Bank S. R. , Yuen H. B. , Goddard L. L. , Harris J. S.
Published: July 2004

We demonstrate a top emitting, electrically pumped, GaInNAsSb vertical-cavity surface-emitting laser (VCSEL) grown monolithically on GaAs, lasing pulsed at a wavelength of 1.460 μm, at a chuck temperature of −10 °C, with a threshold current of 550 mA (16 kA/cm2) and a duty cycle of 0.1% for large mesas. Dilute nitrides, such as GaInNAs, have proven effective for lasers operating at 1.31 μm, but reaching longer wavelengths has proven difficult due to defects from low-temperature growth, surface roughening, and nitrogen-related defects. Reduction of oxygen contamination and careful attention to plasma conditions allow a similar extension to laser wavelength, by minimizing crystal defects introduced during growth. This is the first VCSEL on GaAs beyond 1.31 μm to date.
Recent advances in processing of ZnO
Authors: Pearton S. J. , Norton D. P. , Ip K. , Heo Y. W. , Steiner T.
Published: July 2004

A review is given of recent results in developing improved fabrication processes for ZnO devices with the possible application to UV light emitters, spin functional devices, gas sensors, transparent electronics, and surface acoustic wave devices. There is also interest in integrating ZnO with other wide band-gap semiconductors, such as the AlInGaN system. In this article, we summarize recent progress in controlling n- and p-type doping, materials processing methods, such as ion implantation for doping or isolation, Ohmic and Schottky contact formation, plasma etching, the role of hydrogen in the background n-type conductivity of many ZnO films, and finally, the recent achievement of room-temperature ferromagnetism in transition-metal (Mn or Co)-doped ZnO. This may lead to another class of spintronic devices, in which the spin of the carriers is exploited rather than the charge as in more conventional structures.
Multicolumn cell: Evaluation of the proof of concept system
Authors: Haraguchi T. , Sakazaki T. , Satoh T. , Nakano M. , Hamaguchi S. , Kiuchi T. , Yabara H. , Yasuda H.
Published: July 2004

The beam performance of the electron optics proof of concept (POC) multicolumn-cell (MCC) system has been evaluated. The two beams at the near center of a 4×4 layout with 25 mm pitch show good uniformity and low interference. The MCC system is imaged with a variable-shaped beam and character projection electron optical system having a vector scan beam deflection and a “write-on-the-fly” stage motion control. Cost performance analysis gives the most effective number of column cells in the MCC system.
Formation and blistering of GaAsN nanostructure layers
Authors: Weng X. , Ye W. , Goldman R. S. , Mabon J. C.
Published: July 2004

We report the formation and blistering of GaAsN nanostructure layers induced by nitrogen ion implantation into GaAs followed by high-temperature rapid thermal annealing. The GaAsN nanostructure layers consist of zincblende GaN-rich GaAsN nanostructures in an amorphous matrix, apparently formed near the depth of maximum ion damage. Cross-sectional transmission electron microscopy reveals a series of nanometer-sized cavities near the depth of maximum nitrogen concentration, suggesting the formation of nitrogen gas bubbles during annealing. The nitrogen bubbles coalesce and push away the GaAsN nanostructure layer, forming micrometer-sized blisters. The simultaneous formation and blistering of GaAsN nanostructure layers may provide an opportunity for the integration of the nanostructure layers with a variety of substrates.
Influence of N2O plasma treatment on microstructure and thermal stability of WNx barriers for Cu interconnection
Authors: Tsai Kou-Chiang , Wu Wen-Fa , Chen Jen-Chung , Pan Te-Jen , Chao Chuen-Guang
Published: July 2004

Thermal stabilities of Cu-contacted n+–p junctions with tungsten nitride (WNx) diffusion barriers deposited at various nitrogen flow ratios are investigated. N2O plasma treatment is applied to improve thermal stability and barrier performance of WNx film. Sheet resistance of Cu/N2O plasma-treated WNx/Si is fairly stable even after annealing at 750 °C for 30 min. Moreover, N2O plasma treatment enables the Cu/WNx/n+–p junction diodes to sustain thermal annealing at 600 °C without electrical degradation. Auger electron spectroscopy depth profiles show that Cu diffusion through the N2O plasma-treated WNx barrier is extremely limited, even after annealing at 675 °C. Analyses of transmission electron microscopy and x-ray photoemission spectroscopy show that nitridation and oxidation on the WNx barrier occur and an amorphous layer is formed after N2O plasma treatment.
Reduction of ohmic contact on p-GaN with surface treatment using Cl2 inductively coupled plasma
Authors: Su S. H. , Tseng C. T. , Hau C. C. , Yokoyama M. , Chen S. M.
Published: July 2004

A reduction of Ni/Au ohmic contact on p-type GaN is obtained with surface treatment on GaN films using Cl2 inductively coupled plasma (ICP). X-ray photoelectron spectroscopy (XPS) shows the modifying of the surface atomic ratio after the Cl2 ICP treatment. The atomic ratio of nitrogen to gallium becomes larger after the Cl2 ICP treats samples for 5 s. It suggests that GaClx and/or GaOx is formed and then removed in the boiling HCl solution. The Ga vacancies at the p-type GaN surface are therefore produced and act as acceptors for holes. It leads to the reduction of the contact resistance through the decrease of the resistivity for the conduction of holes.
Enhancement-mode In0.52Al0.48As/In0.6Ga0.4As tunneling real space transfer high electron mobility transistor
Authors: Chen Yen-Wei , Chen Yeong-Jia , Hsu Wei-Chou , Hsu Rong-Tay , Wu Yue-Huei , Lin Yu-Shyan
Published: July 2004

An enhancement-mode In0.52Al0.48As/In0.6Ga0.4As tunneling real-space transfer high electron mobility transistor (HEMT) was fabricated. The studied device operates as a conventional enhancement-mode HEMT under a low gate electrode bias. As the gate electrode bias increases, the electric field applied between the gate electrode and the InGaAs channel increases and the electrons in the channel become “hot.” If the transverse field is sufficiently large, then the electrons in the InGaAs channel layer may have enough energy to overcome the barrier and tunnel into the gate electrode, thus IDS decreases as IG increases. Therefore, pronounced N-shaped negative differential resistance phenomenon and negative transconductance are observed in the studied device.
Fabrication of low-gate-current triode field emitters with planar carbon nanoparticle cathodes
Authors: Seo Woo Jong , Choi Seungho , Lee Soonil , Koh Ken Ha
Published: July 2004

We modified the structure of triode field emitters with planar carbon nanoparticle cathodes to reduce the gate currents. As it turned out, a simple insertion of an extra metal layer between the gate insulator and the cathode layer was sufficient for the substantial reduction of gate currents; the gate currents of the triode emitter with the modified structure never exceeded 4% of the anode currents up to anode currents of ∼250 nA, corresponding to a gate voltage of 67 V and an anode voltage 900 V. The fabrication of the modified triode structure required only four extra processing steps, compared to that of conventional triode structure, while using only conventional photolithography with a single mask. We were able to account for the gate-current reduction in terms of the modification in the electric field distribution.
Photoresponse of a p-type Si field emitter
Authors: Mimura H. , Ukeba T. , Shimawaki H. , Yokoo K.
Published: July 2004

Enhancement of electron emission by illumination of a gated single-tip p-type field emitter was studied using a GaAlAs pulse laser. The increase of the emission current under the illumination is proportional to the emission current without laser at low gate voltages and tends to saturate with increase of the gate voltage. A modulation electron beam is generated directly from the emitter by the pulse laser. The rise time of the photoresponse in the emitter is al least less than 4 μs. On the other hand, the fall time of the photoresponse is about 40 μs, which is determined by the diffusion process of the electrons photogenerated outside the depletion layer in the emitter.
Fabrication of carbon-nanotube field-emitter array using polymer insulator
Authors: Nishimura Kunihiko , Shen Zhiying , Fujikawa Masahiro , Hosono Akihiko , Hashimoto Noritsuna , Kawamoto Satoru , Watanabe Shoyu , Nakata Shuhei
Published: July 2004

This article reports the fabrication process of a carbon-nanotube (CNT) field-emitter array with the silicon-ladder polymer insulator polyphenylsilsesquioxane (PPSQ), whose feature is heat resistance, high breakdown voltage, and low outgassing. CNT islands are formed with a screen-printing method, polymer-insulator coating is carried out (8 μm in thickness), and the gate electrodes are deposited, followed by patterning of the electrodes. PPSQ insulator is applied reactive ion etching (RIE) to reveal CNT emitters. Because of using mixed gases of CF4 and O2, the etching rate for CNT is half that for PPSQ, there is a margin to stop etching with enough CNT left. After reactive ion etching, emission-current density from the revealed CNT is degraded, so laser activation treatment is applied and the emission current density is boosted by a hundredfold. In the case of the triode mode, the laser condition was chosen to prevent gate damage and to improve emission characteristics. Current density of 3 mA/cm2 is obtained at the driving voltage of 35 V.
Terahertz magneto-photoconductive characterization of hydrogenic barrier donors in GaAs/AlGaAs epitaxial thin films
Authors: Naweed Ahmer , Goodhue William D. , Gorveatt William J. , Giles Robert , Waldman Jerry , Menon Vinod
Published: July 2004

Barrier shallow donor states have been investigated in Si-doped GaAs/AlGaAs quantum well structures by means of magneto-photoconductive spectroscopy. In order to promote formation of barrier-only donors, only barrier regions have been doped in the present work. High resolution and signal-to-noise ratio barrier donor spectra have been obtained, which clearly demonstrate the advantage of the photoconduction measurement technique. Observation of barrier donor transitions in a single quantum well structure is also reported. Good agreement is found between experimentally and theoretically determined magnetic field dependence of donor transition energies.
Growth of Be-doped GaInP/GaAs heterostructure bipolar transistor by all solid-source multiwafer production molecular beam epitaxy
Authors: Wilk A. , Zaknoune M. , Godey S. , Dhellemmes S. , Gérard P. , Chaix C. , Mollot F.
Published: July 2004

The rapid setup of the molecular beam epitaxy (MBE) growth process for GaInP/GaAs heterostructure bipolar transistor (HBT) in an all solid-source multiwafer production MBE system is reported. The first 100×100 μm2 large area test structures enable determination of the static gain, which is above 200. rf measurements on 8×10 μm2 devices exhibit a cut-off frequency fT of 34 GHz. Although most publications concerning production of such devices are related to metalorganic chemical vapor deposition grown material, we intend to demonstrate that MBE is a very efficient method for high volume production of GaInP/GaAs HBT. In particular we emphasize the fact that MBE growth for production of benchmark HBT devices is a high yield process that is attainable in a very short time. In order to optimize device characteristics further work focuses on metallurgical and electrical emitter/base interface studies by means of photoluminescence and I/V measurements on processed PN junctions.
Sulfur and low-temperature SiNx passivation of self-aligned graded-base InGaAs/InP heterostructure bipolar transistors
Authors: Jin Zhi , Prost W. , Neumann S. , Tegude F. J.
Published: July 2004

The passivation of self-aligned InGaAs/InP heterostructure bipolar transistors (HBTs) with graded base by the combination of S and low-temperature deposited SiNx was investigated. Base current was found to decrease after the passivation. Collector current significantly increases at low base-emitter voltages. The increase is attributed to the leakage current of the base-collector diode. The current gain was found to increase. When annealing was performed at 300 °C for 5 min, the base current decreases further and the collector current decreases. The leakage of collector current was found to be suppressed. The current gain was further improved and the leakage current can affect the Gummel plots. The leakage source was identified to be the interface between the semiconductor and the SiNx layer. The leakage current can be decreased by the annealing process.
Molecular beam epitaxy growth of ZnO using initial Zn layer and MgO buffer layer on Si(111) substrates
Authors: Fujita Miki , Kawamoto Noriaki , Sasajima Masanori , Horikoshi Yoshiji
Published: July 2004

We have compared the quality of ZnO films grown on Si(111) substrates by two different methods: (1) initial Zn layer deposition followed by its oxidation and (2) thin MgO buffer layer deposition prior to the growth. All the layers are deposited by molecular beam epitaxy using a radio frequency radical cell. X-ray diffraction measurements reveal that (0001)-oriented ZnO films are grown on Si(111) substrates in both cases. However, the ZnO films grown by using initial Zn layer exhibit straight lines along the principal axes of Si(111) surface. In addition, their x-ray diffraction 2θ/ω spectra often show double peaks. These results are probably caused by the cracks due to the difference in thermal expansion coefficients between ZnO and Si. This phenomenon is alleviated considerably by introducing a thin MgO buffer layer. The samples with thin MgO buffer layer show no double peaks in their x-ray diffraction spectra, and the full width at half maximum value for both 2θ/ω, and ω scan are as narrow as 0.038° and 0.26°, respectively. The photoluminescence emission intensity is also improved by using thin MgO buffer layer.
Carbon nanotube growth from Cu–Co alloys for field emission applications
Authors: Hofmeister W. , Kang W. P. , Wong Y. M. , Davidson J. L.
Published: July 2004

We have developed a method of catalyst preparation for carbon nanotube (CNT) growth that uses solid-state diffusion to precipitate Co particles in a Cu matrix and control the size and size distribution of catalyst particles. Copper is an excellent electrical and thermal conductor, and has a small or negligible solubility for Co. Cu–Co alloys of approximately 5 atm% Co were formed in bulk by splat quenching the liquid alloy and on Si substrates by e-beam evaporation of the alloy, sputtering of the alloy, and sputter deposition of thin films of pure Cu and Co. The Co easily precipitates from dilute solutions of Cu–Co with heat treatment. These alloys and films were used to generate uniform distributions of Co precipitates, and CNTs were successfully grown by plasma enhanced chemical vapor deposition (PE-CVD) and thermal CVD on the materials. These alloys can be patterned by photolithography and sputtering in order to grow CNTs in defined locations. Therefore, the technique is amenable to very large scale silicon integration for field emission applications. The results of this work and data from field emission studies are presented herein.
Field emission characteristics of defect-controlled polyimide tunneling cathode
Authors: Baba Akiyoshi , Yoshida Tomoya , Asano Tanemasa
Published: July 2004

We proposed a novel defect-controlled tunneling cathode using ion-beam modified polyimide film as a tunneling insulator. Our aim is to achieve high efficiency electron emission by means of hot electrons generated by passage through defects in the ion-beam modified polyimide film. The emission characteristics and energy distribution of emitted electrons were measured with a triode configuration. The material was spin-coated and then irradiated with Ar ions to modify its electrical characteristics. The cathode was fabricated with a conventional thin film process. Current-voltage characteristics of the cathode and the energy distribution of emitted electrons were investigated. Electron emission took place upon the application of electrical stress that decreased the gate current by three orders of magnitude, a phenomenon that is called forming. After forming, a threshold voltage of about 30 V and emission efficiency of 7% at 70 V with a relatively uniform spatial distribution was achieved. The peak of energy distribution of emitted electrons was raised when the applied gate voltage was increased. The electron energy distribution analysis clearly shows that hot electrons generated in the cathode are emitted in vacuum.
Advanced techniques for the fabrication of square spiral photonic crystals by glancing angle deposition
Authors: Kennedy S. R. , Brett M. J.
Published: July 2004

Using the glancing angle deposition thin film fabrication technique, it is possible to create tailored, three-dimensional periodic square spiral photonic crystals that exhibit a band of forbidden electromagnetic frequencies related to the dimensions of the nanostructures. Typically, when fabricating square spirals by traditional means, several problems arise due to nonuniform shadowing that results in column broadening and the loss of required periodicity for thicker crystals. Through the use of complex substrate motion that imposes greater restrictions on growth and shadowing, many of these problems have been overcome, in particular through the implementation of two new algorithms: the slow corner and the variable angle post methods. These motion algorithms have been implemented in conjunction with square spiral photonic crystal fabrication to provide more uniform spiral structures along with more stringent periodicity across the crystal that will allow for photonic band gap structures with more ideal characteristics.
Preparation of highly textured Mo and AlN films using a Ti seed layer for integrated high-Q film bulk acoustic resonators
Authors: Lee Hee-Chul , Park Jae-Young , Lee Kyung-Hak , Bu Jong-Uk
Published: July 2004

Effects of seed layers on the properties of Mo and AlN/Mo (AlN on Mo) films were extensively investigated for developing high-Q film bulk acoustic resonator (FBAR) devices. The Mo films deposited onto a Ti seed layer were more textured and smoother than those deposited with no seed layer, whereas the use of Cr and Ta seed layers degraded the quality of Mo films. The influence of Mo sputtering conditions on the quality of Mo films was also checked, but the effect was negligible in the case of using a Ti seed layer. The AlN films deposited on top of Mo films with a Ti seed layer showed better c-axis orientation and smoother surface morphology than the AlN films without any seed layers. The AlN/Mo films with a Ti seed layer had full width at half-maximum (FWHM) values ranging from 1.6° to 1.8° and surface roughness ranging from 6.0 to 7.4 Å, while the AlN/Mo films without any seed layers had a FWHM value of 3.6° and surface roughness of 12.6 Å. It is considered that properties of AlN films are very dependent on the quality of the bottom electrodes. Film bulk acoustic resonators in the form of a membrane type were fabricated by using a bulk micromachining method and their resonance characteristics were measured and compared. The resonator comprised of Mo/AlN/Mo/Ti/membrane films had an effective mechanical coupling coefficient of 7.3% and a quality factor of 1514, while the resonator without a Ti seed layer had an effective mechanical coupling coefficient of 6.9% and a quality factor of 630, respectively.
Improved quality and reliability of ultrathin (1.4–2.3 nm) gate oxides by radical-assisted oxidation utilizing a remote ultraviolet ozone source
Authors: Song Young-Joo , Mheen Bongki , Kim Sang-Hoon , Bae Hyun-Chul , Kang Jin-Young , Lee Young-Shik , Lee Nae-Eung , Shim Kyu-Hwan
Published: July 2004

A low-temperature and high-purity radical-assisted oxidation (RAO) process for the growth of ultrathin (1.4–2.3 nm) gate oxides was successfully developed utilizing a remote ultraviolet ozone source. The metal–oxide–semiconductor transistors with RAO gate oxides showed improved device characteristics and oxide reliability, in comparison with the devices with non-RAO or standard furnace oxides. The RAO process in this study was proven to be an effective technique to make the oxide network robust and dense, without an increase of growth temperature.
Method to improve chemical-mechanical-planarization polishing rate of low-k methyl-silsesquiazane for ultralarge scale integrated interconnect application
Authors: Chang T. C. , Tsai T. M. , Liu P. T. , Yan S. T. , Chang Y. C. , Aoki H. , Sze S. M. , Tseng T. Y.
Published: July 2004

In this work, characteristics of low-k methyl-silsesquiazane (MSZ) for the chemical-mechanical-planarization (CMP) process using oxygen plasma pretreatment were investigated in detail. The low-dielectric-constant (low-k) MSZ was prepared by a spin-on deposition process. The resultant wafers were followed by an oxygen (O2) plasma treatment. After oxygen plasma treatment, the CMP process was implemented. Electrical and material analyses were utilized to explore the characteristics of post-CMP MSZ. Experimental results showed that the polish rate of MSZ film with O2 plasma pretreatment was increased as much as two times in magnitude, as compared to that of the MSZ without O2 plasma pretreatment. In addition, the post-CMP MSZ exhibited superior electrical properties. These results clearly indicated that the modification surfaces that resulted from O2-plasma treatment facilitated CMP MSZ. After CMP polishing, the MSZ film still maintained low-k quality.
Investigation of radiative and nonradiative trap centers in ZnSe:Al layers grown by molecular beam epitaxy
Authors: Oh D. C. , Makino H. , Hanada T. , Cho M. W. , Yao T. , Song J. S. , Chang J. H. , Lu F.
Published: July 2004

Radiative and nonradiative trap centers for two typical sets of ZnSe:Al layers in a carrier compensation region, grown by molecular beam epitaxy, were investigated in terms of photoluminescence (PL) and photocapacitance (PHCAP) measurements. One set includes lightly doped ZnSe:Al layers whose net-doping density is 2×1018 cm−3, the other set includes heavily doped ZnSe:Al layers whose net-doping density is 1×1017 cm−3 due to carrier compensation. In 10 K PL spectra, the lightly doped ZnSe:Al layer shows dominant donor-bound exciton emission, while the heavily doped ZnSe:Al layer shows strong deep-level emission via radiative trap centers at 1.97 eV (RD1) and 2.23 eV (RD2). Moreover, the heavily doped ZnSe:Al layer shows another nonradiative electron trap center at 2.35 eV (ND3) in 100 K PHCAP spectra. Consequently, it is suggested the two radiative trap centers (RD1 and RD2) and one nonradiative trap center (ND3) contribute to carrier compensation in ZnSe:Al layers.
Thymic Origin of Intestinal αß T Cells Revealed by Fate Mapping of RORγt
+
Cells
Authors: Eberl Gérard , Littman Dan R.
Published: July 2004

Intestinal intraepithelial T lymphocytes (IELs) are likely to play a key role in host mucosal immunity and, unlike other T cells, have been proposed to differentiate from local precursors rather than from thymocytes. We show here that IELs expressingthe αβ T cell receptor are derived from precursors that express RORγt, an orphan nuclear hormone receptor detected only in immature CD4
+
CD8
+
thymocytes, fetal lymphoid tissue–inducer (LTi) cells, and LTi-like cells in cryptopatches within the adult intestinal lamina propria. Using cell fate mapping, we found that all intestinal αβ T cells are progeny of CD4
+
CD8
+
thymocytes, indicatingthat the adult intestine is not a significant site for αβ T cell development. Our results suggest that intestinal RORγt
+
cells are local organizers of mucosal lymphoid tissue.
Thinning and Flow of Tibetan Crust Constrained by Seismic Anisotropy
Authors: Shapiro Nikolai M. , Ritzwoller Michael H. , Molnar Peter , Levin Vadim
Published: July 2004

Intermediate-period Rayleigh and Love waves propagating across Tibet indicate marked radial anisotropy within the middle-to-lower crust, consistent with a thinning of the middle crust by about 30%. The anisotropy is largest in the western part of the plateau, where moment tensors of earthquakes indicate active crustal thinning. The preferred orientation of mica crystals resulting from the crustal thinning can account for the observed anisotropy. The middle-to-lower crust of Tibet appears to have thinned more than the upper crust, consistent with deformation of a mechanically weak layer that flows as if confined to a channel.
Derivatives of Erythropoietin That Are Tissue Protective But Not Erythropoietic
Authors: Leist Marcel , Ghezzi Pietro , Grasso Giovanni , Bianchi Roberto , Villa Pia , Fratelli Maddalena , Savino Costanza , Bianchi Marina , Nielsen Jacob , Gerwien Jens , Kallunki Pekka , Larsen Anna Kirstine , Helboe Lone , Christensen Søren , Pedersen Lars O. , Nielsen Mette , Torup Lars , Sager Thomas , Sfacteria Alessandra , Erbayraktar Serhat , Erbayraktar Zubeyde , Gokmen Necati , Yilmaz Osman , Cerami-Hand Carla , Xie Qiao-wen , Coleman Thomas , Cerami Anthony , Brines Michael
Published: July 2004

Erythropoietin (EPO) is both hematopoietic and tissue protective, putatively through interaction with different receptors. We generated receptor subtype–selective ligands allowing the separation of EPO's bioactivities at the cellular level and in animals. Carbamylated EPO (CEPO) or certain EPO mutants did not bind to the classical EPO receptor (EPOR) and did not show any hematopoietic activity in human cell signaling assays or upon chronic dosing in different animal species. Nevertheless, CEPO and various nonhematopoietic mutants were cytoprotective in vitro and conferred neuroprotection against stroke, spinal cord compression, diabetic neuropathy, and experimental autoimmune encephalomyelitis at a potency and efficacy comparable to EPO.