Improvement of electromechanical actuating performances of a silicone dielectric elastomer by dispersion of titanium dioxide powder

This paper presents the first reported data on the embedding of highly dielectric ceramic inclusions in a rubbery host medium as a means to increase the electromechanical material response for dielectric elastomer actuation. The studied polymer/ceramic composite, consisting of a silicone matrix in which titanium dioxide powder was dispersed, exhibited, in comparison with pure silicone, a decreased elastic modulus, as well as an increased dielectric constant. The measured low frequency permittivity resulted in accordance with several classical dielectric mixing rules. The use of this material as elastomeric dielectric for planar actuators enabled a reduction of the driving electric fields, so that a transverse strain of 11% at 10 V//spl mu/m and a transverse stress of 16.5 kPa at 9 V//spl mu/m were obtained. These levels of strain and stress were respectively more than eight and four times higher than the corresponding values generated with the pure polymer matrix for analogous electrical stimuli.     

Thermal-stability improvement of a sulfur-passivated InGaP/InGaAs/GaAs HFET

The temperature-dependent characteristics of an InGaP/InGaAs/GaAs heterostructure field-effect transistor (HFET), using the (NH/sub 4/)/sub 2/S/sub x/ solution to form the InGaP surface passivation, are studied and demonstrated. The sulfur-passivated device shows significantly improved dc and RF performances over a wide temperature range (300-510 K). With a 1/spl times/100-/spl mu/m/sup 2/ gate-dimension HFET by (NH/sub 4/)/sub 2/S/sub x/ treatment, the considerably improved thermal stability over dc performances including lower temperature variation coefficients on the turn-on voltage (-1.23 mV/K), the gate-drain breakdown voltage (-0.05 mV/K), the gate leakage current (1.04 /spl mu/A/mm/spl middot/K), the threshold voltage (-1.139 mV/K), and the drain-saturation-current operating regimes (-3.11/spl times/10/sup -4//K) are obtained as the temperature is increased from 300 to 510 K. In addition, for RF characteristics, the sulfur-passivated device also shows a low degradation rate on drain-saturation-current operating regimes (-3.29/spl times/10/sup -4//K) as the temperature is increased from 300 to 400 K. These advantages provide the promise for high-speed high-frequency high-temperature electronics applications.     

Electrical insulation characteristics of cold dielectric high temperature superconducting cable

For the optimization of electrical insulation design for high temperature superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN/sub 2/ impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN/sub 2/ plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN/sub 2/ impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN/sub 2/ and cable model with short length with polypropylene laminated paper (PPLP/sup /spl reg//), Nomex/sup /spl reg// paper and cellulose paper. PD current pulse was found to have a steep rise time of /spl sim/ ns and amplitude of /spl sim/ tens /spl mu/A at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be /spl sim/ 5 mm under PD-free condition from viewpoint of long-term reliability.     

High-speed InSb photodetectors on GaAs for mid-IR applications

We report p-i-n type InSb-based high-speed photodetectors grown on GaAs substrate. Electrical and optical properties of photodetectors with active areas ranging from 7.06/spl times/10/sup -6/ cm/sup 2/ to 2.25/spl times/10/sup -4/ cm/sup 2/ measured at 77 K and room temperature. Detectors had high zero-bias differential resistances, and the differential resistance area product was 4.5 /spl Omega/ cm/sup 2/. At 77 K, spectral measurements yielded high responsivity between 3 and 5 /spl mu/m with the cutoff wavelength of 5.33 /spl mu/m. The maximum responsivity for 80-/spl mu/m diameter detectors was 1.00/spl times/10/sup 5/ V/W at 4.35 /spl mu/m while the detectivity was 3.41/spl times/10/sup 9/ cm Hz/sup 1/2//W. High-speed measurements were done at room temperature. An optical parametric oscillator was used to generate picosecond full-width at half-maximum pulses at 2.5 /spl mu/m with the pump at 780 nm. 30-/spl mu/m diameter photodetectors yielded 3-dB bandwidth of 8.5 GHz at 2.5 V bias.     

The impact of LOC structures on 670-nm (Al)GaInP high-power lasers

We investigate the potential of large optical cavity (LOC)-laser structures for AlGaInP high-power lasers. For that we study large series of broad area lasers with varying waveguide widths to obtain statistically relevant data. We study in detail I/sub th/, /spl alpha//sub i/, /spl eta//sub i/, and P/sub max/, and analyze above-threshold behavior including temperature stability and leakage current. We got as expected for LOC structures minimal /spl alpha//sub i//spl les/1 cm/sup -1/ resulting in /spl eta//sup d/=1.1 W/A for 64/spl times/2000 /spl mu/m/sup 2/ uncoated devices. We obtain total output powers /spl ges/3.2 W (qCW) and /spl ges/1.5 W (CW) at 20/spl deg/C.     

Reliability of pFET EEPROM with 70-/spl Aring/ tunnel oxide manufactured in generic logic CMOS Processes

We investigate the reliability of pFET-based EEPROMs with 70-/spl Aring/ tunneling oxides fabricated in standard foundry 0.35-/spl mu/m, 0.25-/spl mu/m, and 0.18-/spl mu/m logic CMOS processes. The floating-gate memory cell uses Fowler-Nordheim tunneling erase and impact-ionization generated hot-electron injection for programming. We show that charge leakage is dominated by the leakage through interlayer dielectrics. We propose a retention model and show the data retention lifetime exceeds 10 years. These results demonstrate the feasibility of producing nonvolatile memory using standard logic processes that have a 70-/spl Aring/ oxide.     

Design consideration and performance of high-power and high-brightness InGaAs-InGaAsP-AlGaAs quantum-well diode lasers (/spl lambda/=0.98 /spl mu/m)

We conduct a theoretical analysis of the design, fabrication, and performance measurement of high-power and high-brightness strained quantum-well lasers emitting at 0.98 /spl mu/m. The material system of interest consists of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. Some key parameters of the laser structure are theoretically analyzed, and their effects on the laser performance are discussed. The laser material is grown by metal-organic chemical vapor deposition and demonstrates high quality with low-threshold current density, high internal quantum efficiency, and extremely low internal loss. High-performance broad-area multimode and ridge-waveguide single-mode laser devices are fabricated. For 100-/spl mu/m-wide stripe lasers having a cavity length of 800 /spl mu/m, a high slope efficiency of 1.08 W-A, a low vertical beam divergence of 34/spl deg/, a high output power of over 4.45 W, and a very high characteristic temperature coefficient of 250 K were achieved. Lifetime tests performed at 1.2-1.3 W (12-13 mW//spl mu/m) demonstrates reliable performance. For 4-/spl mu/m-wide ridge waveguide single-mode laser devices, a maximum output power of 394 mW and fundamental mode power up to 200 mW with slope efficiency of 0.91 mW//spl mu/m are obtained.     

1.3-/spl mu/m-range GaInNAsSb-GaAs VCSELs

1.3-/spl mu/m-range GaInNAsSb vertical-cavity surface-emitting lasers (VCSELs) with the doped mirror were investigated. GaInNASb active layers that include a small amount of Sb can be easily grown in a two-dimensional manner as compared with GaInNAs due to the suppression of the formation of three-dimensional growth in MBE growth. The authors obtained the lowest J/sub th/ per well (150 A/cm/sup 2//well) for the edge-emission type lasers due to the high quality of GaInNAsSb quantum wells. Using this material for the active media, the authors accomplished the first continuous wave operation of 1.3-/spl mu/m-range GaInNAsSb VCSELs. For the reduction of the threshold voltage and the differential resistance, they used the doped mirror grown by metal-organic chemical vapor deposition (MOCVD). By three-step growth, they obtained 1.3-/spl mu/m GaInNAs-based VCSELs with the low threshold current density (3.6 kA/cm/sup 2/), the low threshold voltage (1.2 V), and the low differential resistance (60 /spl Omega/) simultaneously for the first time. The back-to-back transmission was carried out up to 5 Gb/s. Further, the uniform operation of 10-ch VCSEL array was demonstrated. The maximum output power of 1 mW was obtained at 20/spl deg/C by changing the reflectivity of the front distributed Bragg reflector mirror. GaInNAsSb VCSELs were demonstrated to be very promising material for realizing the 1.3-/spl mu/m signal light sources, and the usage of the doped mirror grown by MOCVD is the best way for 1.3-/spl mu/m VCSELs.     

Characterization of Polyurethane Foam Dielectric Strength

Internal flashovers in hollow insulation systems can produce serious damage. Frequently, SF₆ or N₂ is used to eliminate this problem, but possible gas leakage may endanger the insulation. This paper proposes the use of polyurethane foams to fill the hollow spaces in insulation systems. Thus far, few publications deal with the dielectric properties of foams. This paper demonstrates the dielectric strength of three different foams which are investigated using ac and lightning impulse voltages under different humidity and temperature conditions. The results show that polyurethane foams have 2-3 times better dielectric strength than air. The breakdown strength decreases with the thickness of the foam; temperature and humidity have negligible effects on the breakdown voltage. The major parameter is the size of the voids in the foam. Reducing the size of the voids increases the breakdown strength. This can be achieved by improving the manufacturing technology.     

High-power/high-brightness diode-pumped 1.9-/spl mu/m thulium and resonantly pumped 2.1-/spl mu/m holmium lasers

We report high power (>36 W) with beam propagation factor M/sup 2//spl sim/2 in a diode end-pumped Tm:LiYF/sub 4/ (Tm:YLF) laser generating output near the 1.91-/spl mu/m region. Using the 1.91-/spl mu/m emission and high brightness achieved with the Tm:YLF laser we resonantly end-pump the Holmium /sup 5/I/sub 7/ manifold in Ho:YAG and demonstrate /spl sim/19 W of continuous-wave (CW) output. The diode-to-Holmium optical to-optical conversion efficiency achieved is /spl sim/18%. Using a CW pumped and repetitively Q-switched configuration, the Tm:YLF pumped Ho:YAG laser achieves >16 W of output power with an M/sup 2//spl sim/1.48 at 15 kHz. A Q-switched frequency range of 9 to >50 kHz is also achieved.     

Single-mode distributed feedback and microlasers based on quantum-dot gain material

Quantum-dot gain material fabricated by self-organized epitaxial growth on GaAs substrates is used for the realization of 980-nm and 1.3-/spl mu/m single-mode distributed feedback (DFB) lasers and edge-emitting microlasers. Quantum-dot specific properties such as low-threshold current, broad gain spectrum, and low-temperature sensitivity could be demonstrated on ridge waveguide and DFB lasers in comparison to quantum-well-based devices. 980-nm DFB lasers exhibit stable single-mode behavior from 20/spl deg/C up to 214/spl deg/C with threshold currents < 15 mA (1-mm cavity length). Utilizing the low-bandgap absorption of quantum-dot material miniaturized monolithically integrable edge-emitting lasers could be realized by deeply etched Bragg mirrors with cavity lengths down to 12 /spl mu/m. A minimum threshold current of 1.2 mA and a continuous-wave (CW) output power of >1 mW was obtained for 30-/spl mu/m cavity length. Low-threshold currents of 4.4 mA could be obtained for 1.3-/spl mu/m emitting 400-/spl mu/m-long high-reflection coated ridge waveguide lasers. DFB lasers made from this material by laterally complex coupled feedback gratings show stable CW single-mode emission up to 80/spl deg/C with sidemode suppression ratios exceeding 40 dB.     

Differential gain and linewidth-enhancement factor in dilute-nitride GaAs-based 1.3-/spl mu/m diode lasers

The effect of the quantum-well nitride content on the differential gain and linewidth enhancement factor of dilute-nitride GaAs-based near 1.3-/spl mu/m lasers was studied. Gain-guided and ridge waveguide lasers with 0%, 0.5%, and 0.8% nitrogen content InGaAsN quantum wells were characterized. Experiment shows that the linewidth enhancement factor is independent on the nitride content, and is in the range 1.7-2.5 for /spl lambda/=1.22--1.34 /spl mu/m dilute-nitride GaAs-based lasers. Differential gain and index with respect to either current or carrier concentration are reduced in dilute-nitride devices.     

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.     

Effects of electrical leakage currents on MEMS reliability and performance

Electrostatically driven MEMS devices commonly operate with electric fields as high at 10/sup 8/ V/m applied across the dielectric between electrodes. Even with the best mechanical design, the electrical design of these devices has a large impact both on performance (e.g., speed and stability) and on reliability (e.g., corrosion and dielectric or gas breakdown). In this paper, we discuss the reliability and performance implications of leakage currents in the bulk and on the surface of the dielectric insulating the drive (or sense) electrodes from one another. Anodic oxidation of poly-silicon electrodes can occur very rapidly in samples that are not hermetically packaged. The accelerating factors are presented along with an efficient early-warning scheme. The relationship between leakage currents and the accumulation of quasistatic charge in dielectrics are discussed, along with several techniques to mitigate charging and the associated drift in electrostatically actuated or sensed MEMS devices. Two key parameters are shown to be the electrode geometry and the conductivity of the dielectric. Electrical breakdown in submicron gaps is presented as a function of packaging gas and electrode spacing. We discuss the tradeoffs involved in choosing gap geometries and dielectric properties that balance performance and reliability.     

Reliability of InGaAs waveguide photodiodes for 40-Gb/s optical receivers

The reliability of 1.55-/spl mu/m wavelength InGaAs waveguide photodiodes (WGPDs) fabricated by metal-organic chemical vapor deposition is investigated for 40-Gb/s optical receiver applications. Reliability for both high-temperature storage and accelerated life tests obtained by monitoring both the dark current and the breakdown voltage is examined. The median device lifetime and the activation energy of the degradation mechanism are extracted for WGPD test structures. The device lifetimes are examined via statistical analysis which is highly reliable in predicting the device lifetime under practical conditions. The degradation mechanism for the WGPD test structures can be explained by the formation of leakage current path by ionic impurities in the passivation layer on the exposed p-n junction. Nevertheless, it can be concluded that the WGPD test structures exhibit sufficient reliability for practical 40-Gb/s optical receiver applications.     

Reliability of high-speed SiGe heterojunction bipolar transistors under very high forward current density

As device scaling for higher performance bipolar transistors continues, the operation current density increases as well. To investigate the reliability impact of the increased operation current density on Si-based bipolar transistors, an accelerated-current wafer-level stress was conducted on 120-GHz SiGe heterojunction bipolar transistors (HBTs), with stress current density up to as high as J/sub C/=34 mA//spl mu/m/sup 2/. With a novel projection technique based on accelerated-current stress, a current gain shift of less than /spl sim/15% after 10/sup 6/ h of operation is predicted at T=140/spl deg/C. Degradation mechanisms for the observed dc parameter shifts are discussed for various V/sub BE/ regions, and the separation of the current stress effect from the self-heating effect is made based on thermal resistance of the devices. Module-level stress results are shown to be consistent with wafer-level stress results. The results obtained in this work indicate that the high-speed SiGe HBTs employed for the stress are highly reliable for long-term operation at high operation current density.     

ESD-induced oxide breakdown on self-protecting GG-nMOSFET in 0.1-/spl mu/m CMOS technology

Historically, the failure mode of the nMOS/lateral n-p-n (L/sub npn/) bipolar junction transistor (BJT) due to electrostatic discharge (ESD) is source-to-drain filamentation, as the temperature exceeds the melting temperature of silicon. However, as the gate-oxide thickness shrinks, the ESD failure changes over to oxide breakdown. In this paper, transmission line pulse (TLP) testing is combined with measurements of various leakage currents and numerical simulations of the electric field to examine the failure mode of an advanced 0.1-/spl mu/m CMOS technology, which is shown to be through gate-oxide breakdown. It is also shown by I/sub D/-V/sub G/ and I/sub G/-V/sub G/ measurements that the application of nondestructive ESD pulses causes gradual degradation of the oxide well before failure is reached, under the (leakage current) failure criteria used. Finally, the latent effects of stress-induced oxide degradation on the failure current I/sub f/ of the nMOS/L/sub npn/ are studied, and it is shown that as the device ages from an oxide perspective, its ESD protection capabilities decrease.     

GaAsSb: a novel material for near infrared photodetectors on GaAs substrates

We have studied the molecular beam epitaxy (MBE) growth of GaAsSb on GaAs substrates. The optical properties and composition of GaAsSb layer strongly depend on the growth temperature, the Ga growth rate, and the As and Sb fluxes and their ratios. We also report on two GaAsSb-GaAs photodiode structures operating at 1.3 /spl mu/m. The peak quantum efficiency was 54% for the GaAsSb resonant-cavity-enhanced (RCE) p-i-n photodiode and 36% for the RCE GaAsSb avalanche photodiode (APD) with separate absorption, charge, and multiplication regions (SACM). At 90% of the breakdown, the dark current of the SACM APD was 5 nA. The GaAsSb SACM APD also exhibited very low multiplication noise and k/sub eff/ was approximately 0.1, which is the lowest ever reported for APDs operating at 1.3 /spl mu/m.     

Vacuum electrical breakdown characteristics and surface condition of Ti electrodes with oxidation conditions

Outgassing from an electrode surface is regarded as a major factor leading to electrical breakdowns in vacuum. Recently oxidation treatment at 200/spl deg/C was reported as an effective means of reducing Ti outgassing. In this paper, we report our measurement and comparison of the electrical breakdown characteristics of Ti electrodes with different oxidation conditions (without oxidation, oxidation at 200/spl deg/C, oxidation at 450/spl deg/C). In addition, we analyzed electrode surfaces before and after breakdown experiments in situ with X-ray photoelectron spectroscopy (XPS). Before oxidation, we machined the electrode's surfaces to the roughness of 0.8 /spl mu/m Rmax with diamond turning. Breakdown experiments demonstrated that the breakdown field is highest at the first application of voltage to electrodes with oxidized at 200/spl deg/C. Before breakdown experiment, surface analysis revealed that all the sample electrodes had a large amount of carbon originating from the hydrocarbons of contaminants, and after the experiments, they revealed that the carbons had disappeared. To obtain breakdown characteristics of electrodes with smoother surfaces, we conducted experiments on electrodes with a surface roughness of 0.05 /spl mu/m Ra. For these electrodes, the breakdown field was higher at first breakdown; the repetitions required to achieve saturated breakdown fields were significantly fewer, and the amount of carbon on electrode surfaces before breakdown was less.     

Determination of piezoelectric and pyroelectric coefficients and thermal diffusivity of 1-3 PZT/epoxy composites

PZT/epoxy composites with 1-3 connectivity were prepared using the dice-and-fill technique. The samples were poled with an electric field of 10 MV/m for 30 minutes at room temperature. The piezoelectric and pyroelectric coefficients for the composites were measured. From the laser interferometric measurements, it was found that the piezoelectric d/sub 33/ coefficients for the composites were independent of the volume fraction and averaged (190 /spl mnplus/ 10) pm/V, which was about half of the measured value of lead zirconate titanate (PZT) ceramic. Measurements of the pyroelectric coefficient showed that the coefficients increased with the ceramic content and reached values as large as 54 /spl mu/C/m/sup 2/ /spl deg/C. The thermal diffusivity of the composites was also determined using a technique based on the measurement of the phase retardation of a thermal wave passing through the material. The average value for the composites was (2.15/spl mnplus/ 0.05) /spl times/ 10/sup -7/ m/sup 2//s.