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High Tc structures have raised a great interest for microelectronics applications. We have investigated two layer coplanar structures made of an Ag layer (200nm) sputtered on YBaCuO (300nm). The typical structures are 50Ω coplanar lines and resonator bandpass filters (24 GHz) analyzed from 45MHz to 30GHz. Coplanar lines are studied in the normal and superconducting states whereas filter shows transmitted signals only in the superconducting state. We propose a phenomenologic model taking into account the two layers and their interface. At 60K and 10GHz, the Rs of our YBaCuO layer is roughly 1.5mΩ. A good consistency is observed among the different lines and resonating measurements.

High performance ?-doped double recess 0.1-0.4?m AlGaAs-GaAs S-HEMTs[1] and ?-doped single-recess 0.1-0.7?m AlGaAs/GaInAs/GaAs PM-HEMTs [2-3] are studied from 300K down to 60K. DC and 0.1-40GHz HF measurements followed by electric parameter extractions give extensive evolutions of HEMT electric parameters versus temperature T, gatelength 1 g . The results are interpreted in terms of the transition regime from diffusive to strong overshoot/near ballistic carrier transport under the gate. In the longer devices (1 g =0.4-0.7?m), the latter effects become important at low temperatures and bring frequency intrinsic performance improvement mainly in terms of an increase of maximum intrinsic transconductance g mo . The shorter devices (0.1-0.2?m) appear to be already well in the overshoot regime at 300K due to the high quality epitaxial layers, and their frequency performance improvement upon cooling comes mainly from a reduction of intrinsic capacitance C gsint . The relative increase of intrinsic unity current gain cut-off frequency f tint upon cooling rates at a similar value of 30-40% for all investigated gatelengths(0.1-0.7?m).

We present a coordinated experimental and theoretical investigation of the parameter evolution of ultra-short gate HEMTs down to 0.1?m gate-length, and of the physical and electrical limitations to performance improvements. The study encompasses a broad range of well qualified situations allowing comparisons with previous investigations[1-4]. The main features are,- the exploitation of two reliable technological processes namely planar-doped double- recessed AlGaAs/GaAs HEMT (S-HEMT) and planar-doped pseudomorphic AlGaAs/GaInAs/GaAs HEMT with T-shaped and rectangular gate (PM-HEMT), represented in Fig. 1 and 2), - coherent evolutions of full electrical parameter extractions from dc and 0.1- 40GHz HF coplanar probe on-chip measurements, including capacitances versus gate length down to 0.1?m, - physical modeling based on a quasibidimensional hydrodynamic approach (Q-2D), allowing systematic parametrisation of HEMTs, completed with electromagnetic finite element 2-D modeling of electrostatic parasitic capacitances, - physical modeling based on Monte Carlo simulations (MC) for the investigation of short l g transistors. For the gate width lg?0,1 ?m this analysis shows that the optimization of S- and PM-HEMT depends on three parameters: - a weak influence of V ds on the diffusion under the gate, - a low parasitic electrostatic capacitance, - a high carrier velocity.

The noise performances of a new base-collector self-aligned technology of double-heterojunction single-finger InGaAs-InP bipolar transistor are investigated at 300 K. Noise parameter variations are studied versus frequency in the 2-18 GHz range, versus collector current and emitter area. A low minimum noise figure F/sub min/=0.6 dB is demonstrated at 2 GHz with a 4.8-/spl mu/m/sup 2/ emitter. Variations of F/sub min/ show a minimum versus collector current. The high cutoff frequencies of the devices limit the increase of F/sub min/ versus frequency.

We report the generation of continuous terahertz waves from microwave frequencies up to 2 THz obtained by photomixing two optical waves at 1.55-mum wavelengths in an optimized ion-irradiated In0.53Ga0.47As interdigitated photomixers. Output powers greater than 40 nW at 0.5 THz and 10 nW at 1 THz have been achieved. The optimum excitation conditions regarding optical power and bias voltage are discussed.

Here, we report the gigahertz-rate modulation of a tunable terahertz carrier. Terahertz radiation, tunable from 300 GHz to 1.2 THz, is generated by mixing two telecom lasers with an offset frequency in an ultrafast In0.53Ga0.47As photoconductive device coupled to a broadband antenna. The microwave modulation applied to the telecom lasers is directly transferred to the terahertz carrier. A maximum modulation rate of 20 GHz has been achieved, and the bandwidth is independent of the carrier frequency.

Using high bandwidth resistance measurements, we study the single-shot response of tunnel junctions subjected to spin torque pulses. After the pulse onset, the switching proceeds by a ns-scale incubation delay during which the resistance is quiet, followed by a 400 ps transition terminated by a large ringing that is damped progressively. While the incubation delay fluctuates significantly, the resistance traces are reproducible once this delay is passed. After switching, the time-resolved resistance traces indicate micromagnetic configurations that are rather spatially coherent.

We report the generation of continuous terahertz waves from microwave frequencies of up to 2THz obtained by photomixing two optical waves at 1.55μm wavelengths in ion-irradiated In0.53Ga0.47As interdigitated photomixers. A 200nm thick silicon nitride coating is used for antireflection and passivation layer, improving the reliability and the heat tolerance of the photomixer. In such devices, output powers greater than 40nW at 0.5THz and 10nW at 1THz have been achieved. Considering the observed saturation of the output power with the increase of bias voltage, the optimum excitation conditions regarding optical power and bias voltage are discussed.

We measured the terahertz (THz) emission from heavy-ion irradiated In/sub 0.35/Ga/sub 0.47/As photoconductive (PC) antennas excited at 1550 nm. The In/sub 0.35/Ga/sub 0.47/As layer irradiated at 10/sup 12/ cm/sup -2/ shows a carrier lifetime shorter than 200 fs, a steady-state mobility of 490 cm/sup 2/V/sup -1/s/sup -1/, and a dark resistivity of 3.1 /spl Omega/cm. The spectrum of the electric field radiated from the heavy-ion irradiated In/sub 0.35/Ga/sub 0.47/As antenna extends beyond 2 THz. Comparative measurements performed on In/sub 0.35/Ga/sub 0.47/As PC antennas irradiated at 10/sup 11/ cm/sup -2/ and 10/sup 12/ cm/sup -2/ demonstrate the impact of the defect center scattering on the photo-excited carrier mobility.

Microwave and low frequency noise performance of buried channel SiGe HFETs fabricated on several strain relieved buffer (SRB) are presented. The impact of such SRB on microwave device noise performance is estimated by a proper noise de-embedding technique. The influence of device gate length on high microwave noise parameters is also discussed. High frequency noise properties measured in the 2.5-18 GHz frequency range are simulated means of the small signal equivalent circuit. Good agreement between measurement and modeling is obtained Furthermore, the low frequency noise properties for devices with different gate dimensions are discussed in order to predict further improvements on noise performance when shrinking the gate length below 100 nm.

A 3 dB bandwidth of 35 GHz at 1.31 /spl mu/m and 1.55 /spl mu/m wavelengths is reported for inter-digited germanium on silicon-on-insulator metal-semiconductor-metal photodetector with finger spacing of 500 nm.

We investigate terahertz (THz) emission from heavy-ion-irradiated In0.53Ga0.47As photoconductive antennas excited at 1550 nm. The carrier lifetime in the highly irradiated In0.53Ga0.47As layer is less than 200 fs, the steady-state mobility is 490 cm2 V–1 s–1, and the dark resistivity is 3 Omega cm. The spectrum of the electric field radiating from the Br+-irradiated In0.53Ga0.47As antenna extends beyond 2 THz. The THz electric field magnitude is shown to saturate at high optical pump fluence, and the saturation fluence level increases with the irradiation dose, indicating that defect center scattering has a significant contribution to the transient mobility.

Ion-irradiated InGaAs lattice-matched to InP has been explored in this work and used as the active layer of new photoconductors. Photoconductors with an ion-irradiated InGaAs layer of 0.3 /spl mu/m thickness have been fabricated and the samples were grown by metal organic vapor phase epitaxy lattice-matched to InP substrate. The InGaAs layers were irradiated either by 200 MeV heavy-ion (Au/sup +/) at fluences from 1/spl times/10/sup 10/ to 1/spl times/10/sup 12/ ions/cm/sup 2/ or by 1MeV light ion (H/sup +/) at fluences from 1/spl times/10/sup 13/ to 1/spl times/10/sup 15/ cm/sup 2/. Hall measurements have also been performed on ion irradiated InGaAs layers. We have shown that the ion irradiation of InGaAs layers provides subpicosecond carrier lifetime while preserving good electrical properties of the material. Ion-irradiated InGaAs is very promising for the fabrication of 1.55 /spl mu/m ultrafast sensitive photoconductors.

The high frequency and noise performances of n- and p-SiGe based MODFETs are reviewed. Their excellent HF and low noise behavior makes them well suited for RF mobile communications. We discuss their physical modeling, design optimization and self-heating effects.

We study the precessional switching of the magnetization in microscopic spin valve cells induced by ultra short in-plane hard axis magnetic field pulses. Stable and highly efficient switching is monitored following pulses as short as 140 ps with energies down to 15 pJ. Multiple application of identical pulses reversibly toggles the cell's magnetization be-tween the two easy directions. Variations of pulse duration and amplitude reveal alter-nating regimes of switching and non-switching corresponding to transitions from in-phase to out-of-phase excitations of the magnetic precession by the field pulse. In the low field limit damping becomes predominant and a relaxational reversal is found allowing switching by hard axis fields below the in-plane anisotropy field threshold., 17 pages, 4 figures

High frequency small-signal measurements provide information for time-domain device characterisation. Parasitic phenomena associated with probe and interconnect-metal lines surrounding the device, have an impact on measurements during wafer test. The aim of this work was to subtract the small-signal high-frequency access path effects, using an equivalent model in the 45 MHz-10 GHz range. We propose to apply to bipolar silicon technology a de-embedding GaAs-MESFET method for which the effect of access path are considerably lowered and therefore can be neglected. This correction can then be taken into account for each frequency value during a time domain modelisation.

A family of fully monolithic power amplifiers processed on a PM-HFET (Pseudomorphic Heterojunction FET) technology is presented. They operate in the 18 GHz to 70 GHz frequency range. The output powers vary between 18 dBm and 28 dBm according to the operating frequency. This paper describes their design, topology and exhibited performances.

The symptomatic treatment of hydrocephalus remains cerebrospinal fluid (CSF) drainage to an external reservoir (external CSF drainage) or to an internal cavity mainly the peritoneum or the right atrium via a unidirectional valve (internal CSF drainage) and finally by endoscopic ventriculocisternostomy. Local anaesthesia is adequate for external CSF drainage in adults and children above 10 years while general anaesthesia is required in all other cases. The main problems encountered in these patients are difficult intubation and full stomach associated with increased intracranial pressure. The anaesthetic approach should favour homeostasis. With the exception of ketamine and enflurane, the majority of anaesthetic drugs can be used. Anti-epileptic drug are mandatory. Antibioprophylaxis mainly against staphylococcus is systematic in internal CSF drainage. Rapid emergence from anaesthesia and extubation should be encouraged. Complications (infectious, mechanical and bleeding kinds) are frequent and are often the cause of reinterventions or revisions of the device, exposing the patients to iterative anaesthesia. Furthermore, patients with shunts are at risk of malfunction of the device when exposed to situations like pregnancy, magnetic resonance imaging, or laparoscopy. Under these circumstances, it is recommended to associate the neurosurgical team in the management of these patients and to verify that the shunt is working well before and after the procedure or event.

We report on ultrafast GaN/AlGaN waveguide quantum cascade detectors with a peak detection wavelength of 1.5 μm. Mesa devices with a size of 7 × 7 and 10 × 10 μm2 have been fabricated with radio-frequency impedance-matched access lines. A strong enhancement of the responsivity is reported by illuminating the waveguide facet, with respect to illumination of the top surface. The room temperature responsivity is estimated to be higher than 9.5 ± 2 and 7.8 ± 2 mA/W, while the −3dB frequency response is extracted to be 42 and 37.4 GHz for 7 × 7 and 10 × 10 μm2 devices, respectively.

Among the techniques of cerebral protection, the use of controlled arterial hypertension is based on the following arguments: 1) Cerebral ischaemia is the final common pathway of any insult to the brain, particularly through secondary lesions. Causes of secondary cerebral lesions include pressure under the brain retractors, temporary clipping, arterial hypotension, hypoxaemia, anaemia and hypercapnia. 2) In the brain, the critical lower value for cerebral blood flow is around 25 mL.100g-1.min-1, under which two types of ischaemic areas can be defined: the penlucida type where cerebral function is abolished, without permanent cerebral lesion and the penumbra type where cerebral tissue recovers only if flow is rapidly restored. In the latter case the duration of ischaemia is very important. 3) Cerebral blood flow is maintained stable within a large range of variations of mean arterial pressure through the autoregulation mechanisms, which is based on vasomotricity of the cerebral circulation, which implies major variations in cerebral blood volume. However, autoregulation needs several dozens of seconds to be achieved. Therefore, sudden variations in mean arterial pressure are associated with short lasting but major variations in cerebral blood volume. 4) In case of increased intracranial pressure, a decrease in cerebral perfusion pressure causes cerebral vasodilation through the autoregulation mechanism, with an increase in cerebral blood volume which will, in turn, increase intracranial pressure and thus decrease cerebral perfusion pressure, and so on. This is the vasodilatory cascade. The therapeutical increase in mean arterial pressure will correct this phenomenon and decrease intracranial pressure. This is called the vasoconstrictive cascade.(ABSTRACT TRUNCATED AT 250 WORDS)

We present a study of the large-signal switching characteristics on a picosecond time scale of an AlGaAs/InGaAs modulation-doped field-effect transistor (MODFET) using electrooptic sampling. The MODFET has been of great interest for high-speed digital and analog applications since its demonstration. Recent progress in the fabrication of such devices has resulted in devices with extrinsic cutoff frequencies exceeding 250GHz, corresponding to response times on the order of a picosecond. The rapid increase in the speed of MODFET devices has outstripped the ability to measure their performance with all-electronic equipment. Devices are most often characterized at lower frequencies and then the results are extrapolated to much higher frequency. These difficulties can be avoided using very high bandwidth optoelectronic techniques based on ultrafast lasers, where it is routine to generate and detect electrical signals with subpicosecond rise and fall times. These optoelectronic techniques have been applied to small-signal characterization of passive coplanar striplines to 1THz and MOD-FET devices to 100GHz. In addition to the very high bandwidth of optoelectronic methods, the ability to generate large electrical signal amplitudes allows the study of switching of active devices. Large-signal characterization of active devices is important because of the wide range of high-speed large-signal device applications, including analog sampling circuits, oscillators, and all digital circuits. It is also important in understanding device operation since large-signal operation on very short time scales involves rapid changes of carrier distributions throughout the device. As the time scale of the signals at the device input and output approaches that required for re-equilibration of carrier distributions, it will become necessary to include these non quasi-static effects in nonlinear device models. Large-signal measurements on a very short time scale will allow the development and verification of nonlinear circuit models, and their comparison with existing models based on bias-dependent small-signal measurements.

We have measured the distribution of switching times in spin-transfer switching induced by fast current pulses in two pillar-shaped systems: (i) spin valves and (ii) MgO-based magnetic tunnel junctions. (i) Spin valves can sustain high currents, such that the application of pulsed currents of amplitude a few times that of the static switching threshold is possible. This makes subnanosecond switching within reach. In that limit, the pulse durations leading to switching follow a multiply stepped distribution at 300K and a regular distribution at 40K. At 300K, this reflects the precessional nature of the switching, which proceeds through a small number of precession cycles. The switching time distribution can be modeled from the thermal variance of the initial magnetization orientations. At 40K, nonuniform magnetization switching occurs. (ii) In MgO-based tunnel junctions, we could follow individual time-resolved switching events with a 13GHz bandwidth. The switching proceeds through a nanosecond-scale rando...

We report the fabrication and the characterization of interdigited metal-germanium on silicon metal photodetectors (metal-semiconductor-metal or MSM) for operation at both optical telecommunication wavelengths: 1.31 and 1.55μm. Femtosecond impulse and frequency experiments have been carried out to characterize those MSM Ge photodetectors. For both wavelengths, the measured 3dB bandwidth under 2V bias are close to 10, 18, 20, and 35GHz for electrode spacings equal to 2000, 1000, 700, and 500nm, respectively.

De-embedded high frequency (HF) noise parameters of Ge p-channel modulation doped field effect transistors (MODFETs) on a Si0.4Ge0.6 virtual substrate have been determined for the first time. The 0.1 × 100 µm devices have a minimum noise figure NFmin = 0.3 dB (0.5 dB) ± 0.2 dB, a noise resistance Rn = 95 Ω (90 Ω) ± 5 Ω, an optimum reflection coefficient Γopt = 0.7∠6° and an associated gain Gass = 14 dB (13 dB) at 1.2 GHz (2.5 GHz), at a bias corresponding to the optimum unity current-gain frequency fT = 55 GHz and the maximum oscillation frequency fMAX = 135 GHz. Noise results are given in the 1.2–12 GHz frequency range and 20–160 mA/mm current range.

The measurement of high dielectric constants materials in a coaxial line, using an automatic network analyser (ANA), must take the actual diameter of the sample into consideration. The error on the measured e r value may be approximated by the fractional diameter deviation times e r 2 . A correction method is proposed