Characteristics of 0.8- and 0.2-μm gate length InxGa1-xAs/In0.52Al0.48As/InP(0.53⩽x⩽0.70) modulation-doped field-effect transistorsat cryogenic temperatures

The performance characteristics of InP-based pseudomorphic MODFETs with varying the In composition (0.53⩽x⩽0.70), which changes the strain in the channel, were studied. The temperature was varied in the range of 40-300 K, and the devices had gate lengths L _g of 0.8 and 0.2 μm. The analysis predicts an increase in the intrinsic cutoff frequency with increasing In composition and decreasing temperature and gate length. Also, the analysis predicts that the increase in cutoff frequency with decreasing temperature is less significant with increasing In composition and decreasing gate length. Preliminary experimental results show that as In composition increases from 0.53 to 0.70, f_T increases by 30-40%, and as the temperature decreases from 300 to 40 K, f_T improves by 15-30%, both for 0.8- and 0.2-μm devices     

DC and microwave performance of a 0.1 μm gate InAs/In0.52Al0.8As MODFET

The authors have measured and analyzed the performance characteristics of 0.1-μm gate InAs/In_0.52Al_0.48 MODFETs grown by molecular beam epitaxy. The transistors are characterized by measured g_m(max)=840 mS/mm, f_T=128 GHz, and a very high current carrying capability, e.g. I_dss=934 mA/mm at V _gs=0.4 V and V_ds=2.7 V. The value of f _T is estimated from extrapolation of the current gain (H ₂₁) at a -6 dB/octave rolloff. This is the first report on the microwave characteristics of an InAs-channel MODFET and establishes the superiority of this heterostructure system     

Analysis of arbitrarily shaped microstrip patch antennas using the Sommerfeld formulation

Triangular patch modeling is used for analysis of arbitrarily shaped microstrip patch antennas over a single lossy dielectric medium. Since the Sommerfeld formulation is used, both the single dielectric layer (over which the microstrip patch is located) and the ground plane are considered to be infinitely wide. Typical numerical results are presented for rectangular, circular, semicircular, pentagonal, and triangular patch antennas. © 1992 John Wiley & Sons, Inc.     

Lithographic patterning of superconducting YBCO films

Microbridges of YBa₂Cu₃O₇ thin films have been fabricated by conventional photolithography and wet chemical etching using EDTA, and by the lift-off lithography technique. The variation of etch rate with etch time, etchant temperature, and post-deposition sintering temperature has been studied. It has been shown that both techniques are useful for film patterning. However, an additional sintering step is necessary for the chemically etched sample to regain the original film properties. An order of increase in critical current density is observed for the patterned film.     

Familial glaucoma iridogoniodysplasia maps to a 6p25 region implicated in primary congenital glaucoma and iridogoniodysgenesis anomaly

Familial glaucoma iridogoniodysplasia (FGI) is a form of open-angle glaucoma in which developmental anomalies of the iris and irido-corneal angle are associated with a juvenile-onset glaucoma transmitted as an autosomal dominant trait. A single large family with this disorder was examined for genetic linkage to microsatellite markers. A peak LOD score of 11.63 at a recombination fraction of 0 was obtained with marker D6S967 mapping to chromosome 6p25. Haplotype analysis places the disease gene in a 6.4-cM interval between the markers D6S1713 and D6S1600. Two novel clinical appearances extend the phenotypic range and provide evidence of variable expressivity. The chromosome 6p25 region is now implicated in FGI, primary congenital glaucoma, and iridogoniodysgenesis anomaly. This may indicate the presence of a common causative gene or, alternatively, a cluster of genes involved in eye development/function.     

Rheological behaviour of emulsions of avocado and watermelon oils during storage

Rheological properties of emulsions made out of avocado pulp and watermelon seed oils with whey protein concentrate were determined during different storage periods. The oils, as well as the emulsions behaved like non-Newtonian liquids, having shear-thinning characteristics. Both oils showed moderate shear-thinning characteristics as the flow behaviour indices were between 0.86 and 0.88. The shear-rate/shear-stress data could be adequately fitted (r = 0.997–0.999) to a common rheological equation, e.g. the power-law model. Avocado pulp oil was markedly more viscous than was watermelon seed oil which was also evident from the higher apparent viscosity and consistency index values.     

Traumatogenic factors affecting the knees of carpet installers

An ergonomics analysis of carpet installation tasks was performed. The purpose was to identify and quality potential sources of biomechanical trauma that may be responsible for the high rates of knee morbidity found by previous researchers among carpet layers. Nine carpet layers were studied either at an apartment building worksite or at a training school. Results from a job analysis indicated that workers spent approximatately 75% of their time in the kneeling position using a tool called a knee-kicker to stretch and install carpet. Awkward body postures were identified from films of workers installing carpets. At the moment of impact the knee is severely flexed, subtended angles were less than 60 degrees. To obtain measures of impact force on the knee, the kicker-tool was instrumented with a load cell. Workers who executed the hardest kicks with the tool produced impact peak forces that averaged 3019 newtons (N), which is equivalent to about four times body weight. Measures from an accelerometer attached to the worker's knee showed values in ecxess of 120 m/s², which are comparable to those found during vigorous running and jumping exercises. The results imply that repetitive impact of the knee joint from the use of the knee-kicker combined with knee flexion, kneeling and squatting may be responsible for the high level of occupational knee-morbidity found among carpet layers.     

Design, modeling, and characterization of monolithically integratedInP-based (1.55 μm) high-speed (24 Gb/s) p-i-n/HBT front-endphotoreceivers

High-speed, long-wavelength InAlAs/InGaAs OEIC photoreceivers based on a p-i-n/HBT shared layer integration scheme have been designed, fabricated and characterized. The p-i-n photodiodes, formed with the 6000 Å-thick InGaAs precollector layer of the HBT as the absorbing layer, exhibited a responsivity of ~0.4 A/W and a -3 dB optical bandwidth larger than 20 GHz at λ=1.55 μm. The fabricated three-stage transimpedance amplifier with a feedback resistor of 550 Ω demonstrated a transimpedance gain of 46 dBΩ and a -3 dB bandwidth of 20 GHz. The monolithically integrated photoreceiver with a 83 μm p-i-n photodiode consumed a small dc power of 35 mW and demonstrated a measured -3 dB optical bandwidth of 19.5 GHz, which is the highest reported to date for an InAlAs/InGaAs integrated front-end photoreceiver. The OEIC photoreceiver also has a measured input optical dynamic range of 20 dB. The performance of individual devices and integrated circuits was also investigated through detailed CAD-based analysis and characterization. Transient simulations, based on a HSPICE circuit model and previous measurements of eye diagrams for a NRZ 2³¹-1 pseudorandom binary sequence (PRBS), show that the OEIC photoreceiver is capable of operation up to 24 Gb/s