ITO-Schottky photodiodes for high-performance detection in the UV-IR spectrum

High-performance vertically illuminated Schottky photodiodes with indium-tin-oxide (ITO) Schottky layers were designed, fabricated, and tested. Ternary and quarternary III-V material systems (AlGaN-GaN, AlGaAs-GaAs, InAlGaAs-InP, and InGaAsP-InP) were utilized for detection in the ultraviolet (UV) (/spl lambda/<400 nm), near-IR (/spl lambda//spl sim/850 nm), and IR (/spl lambda//spl sim/1550 nm) spectrum. The material properties of thin ITO films were characterized. Using resonant-cavity-enhanced (RCE) detector structures, improved efficiency performance was achieved. Current-voltage, spectral responsivity, and high-speed measurements were carried out on the fabricated ITO-Schottky devices. The device performances obtained with different material systems are compared.     

Total reflection X-ray fluorescence spectrometry for the introduction of novel materials in clean-room production environments

In this paper, a number of case studies on the analysis of novel metallic contaminants on conventional and alternative substrates using the technique of total reflection X-ray fluorescence spectrometry (TXRF) is presented. Investigated materials include Si and Ge substrates, high-/spl kappa/ dielectric contaminants, and layers, and Si wafers contaminated with elements from metal gates and Cu interconnects. One focus is on the application and optimization of detection limits in direct TXRF. For the TXRF analysis of contaminants on Si wafers, a general conclusion is that a combination of three excitation sources is needed to cover the whole range of interest: a low-energy excitation (about 5 keV, e.g., WM/spl alpha/, Cr K/spl alpha/) for the low Z elements such as Na, Mg, and Al, a moderate-energy excitation (10-20 keV, e.g., WL/spl beta/, MoK/spl alpha/) for the 3d-transition elements, and a high-energy excitation (25-35 keV, e.g., W, continuum) for the analysis of elements such as Zr, Ru, Mo, and Pd. Also, for the analysis of novel substrates using direct TXRF, a careful selection of the excitation source results in better detection limits. In this way, detection limits at 10/sup 10/-10/sup 11/ at/cm/sup 2/ can be achieved, even for novel contaminants and substrates. As the International Technology Roadmap for Semiconductors (ITRS) requires control below 5/spl times/10/sup 9/ at/cm/sup 2/, the application of a preconcentration procedure such as vapor phase decomposition-droplet collection TXRF (VPD-DC-TXRF) is required. Proper use of this procedure allows the improvement of the detection limits by two to three orders of magnitude, depending on wafer size and chemical collection efficiency. The usability of this preconcentration procedure in combination with TXRF will be demonstrated for noble elements and germanium substrates.     

X-Ray Radiation Effect in DRAM Retention Time

For quality verification, an X-ray inspection process is commonly being used for evaluating obscured and defective solder joints in surface-mount technologies, such as ball grid arrays and flip chips. Integrated circuits subjected to any form of radiation, i.e., ionizing or nonionizing, may incur some amount of damage depending on the absorbed dose. Though most X-ray inspections for high-quality imaging require ionizing dose amounts that are considered inconsequential for device failure or non-functionality, the degree of latent damage must be carefully considered. This paper discusses X-ray-induced vulnerabilities of high-density dynamic random access memory exposed to low ionizing radiation levels typical in X-ray inspection systems. We look at critical parameters and their sensitivity in relation to varying dose amounts of X-ray irradiation. In consideration of different methodologies of reducing radiation dose amounts and limiting device exposure, we propose a procedure for attenuating potentially harmful X-ray radiation levels while preserving quality images.     

Investigation and minimization of underfill delamination in flip chip packages

A generalized plane strain condition is assumed for an edge interfacial crack between die passivation and underfill on an organic substrate flip chip package. C4 solder bumps are explicitly modeled. Temperature excursions are treated as loading conditions. The design factors studied include underfill elastic modulus, underfill coefficient of thermal expansion (CTE), fillet height, and die overhang. Varying underfill modulus and CTE produces a different stress field at underfill/die passivation interface, different stress intensity factor (SIF), and phase angle (/spl psi/) even under the same loading condition. The baseline case uses underfill with elastic modulus of 6 GPa, CTE of 36 ppm//spl deg/C and fillet height equal to half die thickness. Four more cases involving underfill material properties are investigated by varying elastic modulus between 3 and 9 GPa, and by varying CTE between 26 and 46 ppm//spl deg/C. The effect of fillet height is also studied by assuming no fillet and full fillet, i.e., fillet height equal to die thickness. Finally, two cases concerning the influence of die overhang, defined as the nominal distance between outermost solder joint and die edge, are investigated. Fracture parameters, including energy release rate (G) and phase angle (/spl psi/), are evaluated as a function of dimensions. Underfill material properties (elastic modulus and CTE), fillet configuration, and die overhang can be optimized to reduce the risk of underfill delamination in flip chip or direct chip attach (DCA) applications.     

High field conduction and prebreakdown phenomena in dielectric liquids

The present paper is mainly devoted to phenomena occurring in point-plane electrode geometry, where breakdown is the result of the initiation and propagation of prebreakdown phenomena called "streamers". In this configuration, an investigative study of the streamer initiation processes, requiring very high electric field strengths (/spl sim/ MV/cm), and of propagation (requiring low electric field, /spl sim/ kV/cm) can easily be carried out for negative streamer development as well as for the positive case. From analysis of experimental results in pure liquids the physical processes connected with streamer initiation and propagation, particularly the electronic ones, are presented and discussed. Estimations of the main parameters of slower subsonic streamers and of the faster filamentary ones (such as field strength at the streamer tip, field inside the channel, charge density, etc.) have been obtained from qualitative considerations and compared to experimental data.     

Performance of 20 Gb/s quaternary intensity modulation based on binary or duobinary modulation in two quadratures with unequal amplitudes

2/spl times/10 Gb/s quaternary intensity modulation signals (4-IM) can be generated by combining two modulation signals with unequal amplitudes in quadrature phases or orthogonal polarizations. Two 10-Gb/s nonreturn-to-zero (NRZ) amplitude-shift keying (ASK) signals and a quadrature phase-shift keying (QPSK) modulator allow to generate 4-IM with the same bandwidth as an NRZ-ASK signal (QASK). Measured sensitivity at a bit error rate (BER) of 10/sup -9/ and chromatic dispersion (CD) tolerance are -21.6 dBm and /spl sim/+130 ps/nm, respectively. Two duobinary 10-Gb/s data streams and a QPSK modulator allow to generate a 9-constellation point quaternary intensity signal (QDB), with the same bandwidth as a duobinary signal. A stub filter with frequency response dip at 5 GHz was used to generate the duobinary signals. Detected as a 4-IM, this scheme features a sensitivity and a CD tolerance of -21.2 dBm and /spl sim/+140 ps/nm, respectively. By combining the two duobinary 10-Gb/s data streams with unequal amplitudes in orthogonal polarizations, a 9-constellation point quaternary intensity signal was also obtained (QPolDB). Sensitivity and CD tolerance were -20.5 dBm and /spl sim/+340 ps/nm, respectively. They became -18.4 dBm and /spl sim/+530 ps/nm, respectively, when the frequency response dip of the stub filter was changed to 6 GHz. A polarization and phase-insensitive direct detection receiver with a single photodiode has been used to detect all generated quaternary signals as 4-IM signals.     

Pulsed power production of ozone using nonthermal gas discharges

This paper discusses ozone synthesis by employing a short duration (/spl sim/120 ns) of pulsed power and using positive voltages in dry air and in oxygen, with and without a dielectric barrier. Ozone concentration and ozone production yield (efficiency) are measured at various peak pulsed voltages, pulse repetition rates, varying input energy densities, and different gaseous gap spacings.     

Characterization of Si implants in p-type GaN

Si ion implantation into p-type GaN followed by rapid thermal annealing (RTA) in N/sub 2/ has been performed. X-ray diffraction analyses indicate that ion-implanted damage remains even with 1050/spl deg/C, 60 s RTA. By varying implantation and postimplantation annealing conditions, we could convert carrier concentration from p-type 3 /spl times/ 10/sup 17/ cm/sup -3/ into n-type 2 /spl times/ 10/sup 17/ cm/sup -3/ /spl sim/2 /spl times/ 10/sup 19/ cm/sup -3/. It was found that typical activation energies of Si implants in p-GaN are lower than 10 meV. Such activation energies are smaller than those observed from epitaxially grown Si-doped GaN films. A deep donor level with activation energy of 60 meV was also found from some samples. Photoluminescence studies show that the peak appears at 372 nm might be related to implantation-induced defects. It was also found that a green emission band could be observed from Si-implanted GaN. It was shown that such a green emission is related to the yellow band observed from epitaxially grown Si-doped GaN. The transport properties of these Si-implanted samples were also studied.     

Acoustic response of cartilage during laser-mediated stress relaxation

In this study, laser reshaping of porcine septal cartilage was performed using an Nd:YAG laser (/spl lambda/=1.32 /spl mu/m), while changes in acoustic waves were observed, in an attempt to develop technique to monitor the reshaping process. Concurrent measurements of strain (during tensile compression and tension, as well as flexure), temperature, and a 5-MHz ultrasonic signal were recorded during laser irradiation (/spl lambda/=1.32 /spl mu/m, 4 W, 13 s). The sample was set up in a water bath to enhance acoustic coupling. From the ultrasonic signal, both time of flight (TOF) and signal amplitude as reflected from the back wall of the cartilage were extracted and correlated with temperature and strain measurements. The onset of stress relaxation of the cartilage generally occurred between 50/spl deg/C and 60/spl deg/C. While TOF measurements indicated a generally constant increase in the speed of sound of the cartilage during the irradiation period, the amplitude of the reflected acoustic signal correlated directly with the stress relaxation of the cartilage. At the point of stress relaxation, the amplitude of the acoustic signal consistently attenuated to roughly 50% of its original magnitude.     

Determination of the step response function of a dielectric in the presence of noise

In the time domain characterization of dielectrics a fundamental measure is the dielectric response function /spl Phi/(t). This function permits the relaxation time and the complex permittivity of the dielectric under test to be determined, allowing the complete characterization of the dielectric properties. To calculate the /spl Phi/(t) function a time domain deconvolution algorithm (TDD), developed in a previous work, is employed. In this paper a new technique to enhance the calculation of the /spl Phi/(t) function in the time domain, is presented, avoiding the instability problems inherent to the TDD algorithm. The method consists in the use of appropriate digital lowpass filter in several stages of the time domain deconvolution algorithm to calculate the /spl Phi/(t) function. This procedure provides an enhanced precision for /spl Phi/(t) even for very short times (/spl ap/ 10 ps for the time domain reflectometry system used).     

Low-temperature deposition of hafnium silicate gate dielectrics

The physical and electrical properties of hafnium silicate (HfSi/sub x/O/sub y/) films produced by low-temperature processing conditions (/spl les/150/spl deg/C) suitable for flexible display applications were studied using sputter deposition and ultra-violet generated ozone treatments. Films with no detectable low-/spl kappa/ interfacial layer were produced. Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy were used to determine the composition, chemical bonding environment, thickness, and film interface. The electrical behavior of the as-deposited and annealed hafnium silicate films were determined by current-voltage (I--V) and capacitance-voltage (C--V) measurements.     

Pulsed HV vacuum breakdown of polished, powder coated, and e-beam treated large area stainless steel electrodes with 0.5 to 7 mm gaps

An investigation of the HV vacuum breakdown between polished, powder coated, and e-beam treated 304L and 316L stainless steel electrodes is described. Tests were performed with 160 ns, 1-cos(/spl omega/t), and 260 ns flat-top voltage pulses of up to 500 kV. The high voltage hold-off for the 160 ns pulse was /spl sim/130 kV/mm for 2 mm gaps for 80-mm diameter polished stainless steel electrodes, and 15% lower for 120-mm polished and e-beam treated electrodes. The longer 260 ns pulse gave 15% lower hold-off for 80-mm electrodes. These electrodes showed voltage hold-off that scaled as the square root of the gap between 0.5 and 7 mm. This total voltage effect has been interpreted in the past as due to accelerated particles. We analyze our data in terms of this mechanism and show that only nanoparticles of molecular size could be responsible. We also discuss how ions or background gas could affect the breakdown thresholds but existing models do not predict square root dependence. We test how extremely fine powers affect hold-off and show that contaminated surfaces have relatively constant reduced breakdown E-fields that intersect the clean-electrode voltage-dependent breakdown at critical gaps defined by the type and quantity of contamination. The hold-off was /spl sim/55 and 65 kV/mm with copper powder on the cathode and anode for 2 to 6.5 mm gaps, respectively, and /spl sim/95 and 75 kV/mm for talc powder on the cathode and anode for gaps <3.5 and 6.5 mm. Optical diagnostics show no difference in the light emission from clean and contaminated electrode breakdown arcs.     

Experiments and simulations of short-pulse laser-pumped extreme ultraviolet lasers

Recent experimental work on the development of extreme ultraviolet lasers undertaken using as the pumping source the VULCAN laser at the Rutherford Appleton Laboratory is compared to detailed simulations. It is shown that short duration (/spl sim/picosecond) pumping can produce X-ray laser pulses of a few picosecond duration and that measurement of the emission from the plasma can give an estimate of the duration of the gain coefficient. The Ehybrid fluid and atomic physics code developed at the University of York is used to simulate X-ray laser gain and plasma emission. Two postprocessors to the Ehybrid code are utilized: 1) to raytrace the X-ray laser beam amplification and refraction and 2) to calculate the radiation emission in the kiloelectronvolt photon energy range. The raytracing and spectral simulations are compared, respectively, to measured X-ray laser output and the output of two diagnostics recording transverse X-ray emission. The pumping laser energy absorbed in the plasma is examined by comparing the simulations to experimental results. It is shown that at high pumping irradiance (>10/sup 15/ Wcm/sup -2/), fast electrons are produced by parametric processes in the preformed long scalelength plasmas. These fast electrons do not pump the population inversion and so pumping efficiency is reduced at high irradiance.     

Device performance and wavelength tuning behavior of ultra-short quantum-cascade microlasers with deeply etched Bragg-mirrors

The fabrication and characteristics of edge-emitting quantum-cascade (QC) lasers and microlasers with monolithically integrated deeply etched semiconductor-air Bragg-mirrors based on GaAs is reported. We observe a reduction of the threshold current density by 25% and an increase of the operation temperature by 23 K to a maximum of 315 K for 800 /spl mu/m long devices by employing Bragg-mirrors. Devices with ultra-short cavities of about 100 /spl mu/m (/spl sim/40 times the wavelength) operate up to 260 K. At 80 K, these devices show threshold currents as low as 0.63 A and output levels up to 56 mW. In these devices, longitudinal single mode operation with output levels exceeding 7.7, 5.6, and 2.8 mW was measured at 180, 200, and 240 K, respectively. This can be attributed to the limited gain bandwidth of QC lasers and the large mode spacing in these devices. By temperature control the emission wavelength can be tuned without mode jumps over 80 nm. The feasibility to pre-select the emission wavelength by a direct control of the Fabry-Perot mode was demonstrated by microlasers with 1 /spl mu/m cavity length difference.     

Impact of high-/spl kappa/ dielectric HfO/sub 2/ on the mobility and device performance of sub-100-nm nMOSFETs

Scaling of Si MOSFETs beyond the 90-nm technology node requires performance boosters in order to satisfy the International Technology Roadmap for Semiconductors requirements for drive current in high-performance transistors. Amongst the preferred near term solutions are transport enhanced FETs utilizing strained Si (SSi) channels. Additionally, high-/spl kappa/ dielectrics are expected to replace SiO/sub 2/ around or after the 45-nm node to reduce the gate leakage current problem, facilitating further scaling. However, aside from the many technological issues such as trapped charge and partial crystallization of the dielectric, both of which are major issues limiting the reliability and device performance of devices employing high-/spl kappa/ gate stacks, a fundamental drawback of MOSFETs with high-/spl kappa/ dielectrics is the mobility degradation due to strong soft optical phonon scattering. In this work we study the impact of soft optical phonon scattering on the mobility and device performance of conventional and strained Si n-MOSFETs with high-/spl kappa/ dielectrics using a self-consistent Poisson Ensemble Monte Carlo device simulator, with effective gate lengths of 67 and 25-nm. Additionally we have also briefly investigated the effect (the percentage change) that a trapped charge within the gate oxide will have on the drive current for both a SiO/sub 2/ oxide and an equivalent oxide thickness of high-/spl kappa/ dielectric.     

Promising fluorescent probes from phycobiliproteins

Phycobiliproteins are brilliant-colored and water-soluble pigment-protein complexes existing widely in cyanobacteria, red algae, and cryptophytes. They function as predominant light-harvesting complexes to absorb the sunlight from 480 to 660 nm, and efficiently transfer the energy to chlorophyll a. The phycobiliproteins are classified into three types based on their absorption spectra: phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (AP). They are all composed of hetero-subunits /spl alpha/ and /spl beta/ and commonly exist in trimer (/spl alpha//spl beta/)3 or hexamer (/spl alpha//spl beta/)6 made up of equimolar monomer (/spl alpha//spl beta/). One monomer contains two to five chromophore phycobilins. In cyanobacteria and red algae, phycobiliproteins assemble a macromolecular particle, phycobilisome. Efficient excitation energy coupling among the chromophores in the phycobiliprotein trimer/hexamer and among the phycobiliproteins in the phycobilisome gives them some special spectroscopic properties superior to organic fluorescent dyes. These properties make the phycobiliproteins become promising fluorescent probes used in various fields of biological investigation.     

Power frequency dependence of space charge behavior and partial discharge characteristics in SF/sub 6/ gas

The partial discharge (PD) and breakdown (BD) characteristics in SF/sub 6/ gas under commercial and higher frequency (/spl sim/600 Hz) ac voltage applications were investigated using high-speed electrical and optical measuring techniques with phase gate control method. Experimental results revealed that 400 Hz BD voltage at a certain gas pressure range was higher than that for 60 Hz and PD characteristics especially at the positive PD inception phase were much influenced by the applied power frequency. From these results, we clarified the dependence of space charge behavior on the applied power frequency and discussed the physical mechanism of PD and BD in SF/sub 6/ gas with consideration of the space charge behavior generated by PD in the previous half cycle of ac voltage.     

Production and probing of atomic wavepackets with ultrafast laser pulses: applications to atomic and molecular dynamics

We demonstrate that atomic wavepackets can serve as sensitive detectors for investigating atomic and molecular dynamics. In concert with parametric four-wave mixing, the interference between coherent superpositions of atomic excited states produced by ultrafast (/spl sim/150 fs) pump and probe pulses provides a new and powerful tool with which fundamental processes, such as molecular dissociation and Rydberg-Rydberg atomic collisions, can be observed with the extraordinary sensitivity afforded by a coherent nonlinear optical process. Experiments are described in which the dissociation of an electronically excited molecule (Rb/sub 2/) and the distribution of atomic fragments into excited states spanning >10 000 cm/sup -1/ are observed. Also, resonant collisions between Rb atoms in the 7s and 5d states are detected by monitoring the shift in the frequency of an atomic wavepacket induced by the dipole-dipole interaction.     

Electrical conductivity and space charge in LDPE containing TiO/sub 2/ nanoparticles

Electrical conductivity (DC) and space charge accumulation were studied in samples of low density polyethylene to which nano-sized and micro-sized TiO/sub 2/ (anatase) particles and a dispersant had been added. Sample thicknesses were in the range 150-200 /spl mu/m. At applied field strengths of 10 and 20 kV/mm, the conductivity at 30 /spl deg/C, measured in vacuum in samples containing 10 % w/w nano-sized TiO/sub 2/, decreased by 1-2 orders of magnitude relative to samples with dispersant but without TiO/sub 2/, and by three orders of magnitude at 70 /spl deg/C. In air at 30 /spl deg/C the corresponding decrease was an order of magnitude at 10 kV/mm, and a factor of four at 20 kV/mm. In samples containing 10 % w/w micro-sized TiO/sub 2/ the conductivity increased in air and in vacuum, but only by factors in the range 2-10 depending on temperature and field. Space charge profiles were obtained using the laser-intensity-modulation-method (LIIMM), irradiating both surfaces of the sample. The micro-sized TiO/sub 2/ particles are associated with increased charge injection from the electrodes and increased charge trapping in the sample bulk, increasing the conductivity overall. The nano-sized particles generate very little charge in the sample bulk, but render the electrodes partially-blocking and so lower the conductivity.