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We present here the implementation of an optoelectronic oscillator (OEO) that leverages the optical comb produced by a silicon add-drop ring resonator to directly convert signals from optical to microwave domain. The OEO comprises a CW laser, an intensity modulator, a silicon add-drop ring, a photodetector, and radiofrequency amplifier. By using millimeter-long silicon-on insulator micro-ring resonator, we generated an oscillation signal with a frequency determined by the free spectral range (FSR) of the ring. In this scheme, the sharp transmission peaks in the drop port of an add-drop silicon resonator are used as the optical comb. The optimised ring has a length of 5.8 mm with a measured FSR of 112 pm, an extinction ratio of 20 dB and an optical quality factor of 2.2 × 10 5 . The complete OEO loop yields a 14.12 GHz signal with a phase noise level of -100 dBc/Hz at an offset of 100 kHz from the carrier. This result shows that OEOs directly based on millimeters long silicon rings are a promising path for generating low-noise microwave signals.

Conductor-backed coplanar waveguide on 30-μm-thick BCB polymer is fabricated. In order to eliminate unwanted propagation modes for these lines designed for frequencies up to 1 THz, electroplated vias interconnect each coplanar ground to the backed conductor. Transmission line properties are extracted here up to 67 GHz, showing a characteristic impedance of about 50 Ω, but with high conduction losses for this frequency range due to the thin metal layer used. Thru-reflect-line correction and a de-embedding with electrical circuit of accesses are applied to extract line properties. The comparison with a coplanar waveguide model leads to a relative permittivity of 2.676 for the BCB in this low-frequency range.

Integrated silicon nanophotonics has progressed a lot over past decades with great promises for many surging applications in optoelectronics, information and communication technologies, sensing or health monitoring. Enabling low-cost, dense integration, and compatibility with modern semiconductor nanofabrication processes, silicon nanophotonics deliver compact and high-performance devices on single chips. A variety of nanophotonic functionalities, both passive and active, are nowadays available on semiconductor substrates, leveraging the maturity of open-access silicon foundries and epitaxial germanium integration. It encompasses essential functions such as light generation and amplification, fast electro-optical modulation, and reliable conversion of optical into electrical signals. Germaniumbased optical photodetectors are main building blocks within the library of integrated silicon nanophotonics, with performances that are nowadays on par with their III-V-based counterparts. Germanium photodetectors integrated at the end of waveguides are attractive for next-generation on-chip interconnections, because of their compactness, bandwidth and speed, energy consumption and cost. In this work, we present our latest advances on silicon-germanium p-i-n waveguide-integrated photodetectors based on lateral silicon-germanium-silicon heterojunctions. Our hetero-structured photodetectors were fabricated on top of 200-mm silicon-on-insulator substrates using industrial-scale fabrication processes compatible with complementary metal-oxide-semiconductor technology. Silicon-germanium p-i-n photodetectors operated under low bias voltages exhibited low dark-currents (~100 nA), cut-off frequencies beyond 50 GHz, and photo-responsivities of about 1.2 A/W. Photodetector sensitivities of -14 dBm and -11 dBm were achieved for communication data rates of 10 Gbps and 25 Gbps, respectively. P-i-n photodetectors with lateral heterojunction operated in an avalanche regime offered an additional degree of freedom to improve device performances. High-speed and low-noise characteristics were obtained in our p-i-n photodetectors upon avalanche operation, with a gain-bandwidth product of 210 GHz and a low carrier impact ionization ratio of about 0.25. The measured sensitivity of avalancheoperated devices was -11 dBm for 40 Gbps signal detection. As demonstrated in the reported achievements, heterostructured p-i-n photodetectors are thus suitable communication devices in future intra-data center links or high-speed optical interconnects.

Applications relying on mid-infrared radiation (λ ~ 3-30 μm) have progressed at a very rapid pace in recent years, stimulated by scientific and technological breakthroughs like mid-infrared cameras and quantum cascade lasers. On the other side, standalone and broadband devices allowing control of the beam amplitude and/or phase at ultra-fast rates (GHz or more) are still missing. Here we show a free-space amplitude modulator for mid-infrared radiation (λ ~ 10 μm) that can operate at room temperature up to at least 1.5 GHz (−3dB cutoff at ~750 MHz). The device relies on a semiconductor heterostructure enclosed in a judiciously designed metal–metal optical resonator. At zero bias, it operates in the strong light-matter coupling regime up to 300 K. By applying an appropriate bias, the device transitions towards the weak-coupling regime. The large change in reflectance is exploited to modulate the intensity of a mid-infrared continuous-wave laser up to 1.5 GHz., Broadband integrated electrical modulators are key components for photonic systems. Here, the authors present a room temperature mid-IR free-space amplitude modulator based on a semiconductor heterostructure that exploits the change in reflectance occurring at the change between weak and strong coupling.

We have developed a free-space amplitude modulator for mid-IR radiation $(\lambda=10\mu \mathrm{m})$ that can operate up to at least 1.5 GHz (-3dB cut-off at _ 750 MHz) and at room-temperature. The device relies on a semiconductor heterostructure enclosed in a judiciously designed metal-metal optical resonator. At zero bias, it operates in the strong light-matter coupling regime up to 300K. By applying an appropriate bias, the device transitions to the weak coupling regime. The large change in reflectivity due to the disappearance of the polaritonic states is exploited to modulate the intensity of a mid-IR continuous-wave laser up to speeds of more than 1.5 GHz.

We report on the first demonstration of high-speed optical modulation exploiting Pockels effect in strained silicon waveguides. Bandwidths larger than 20 GHz and low insertion loss have been achieved at a wavelength of 1550 nm.

A process for microelectronic technology is developed for integration of passive devices with existing active device technology for submillimeter wave and THz frequency range applications. Performances of a conductor-backed coplanar waveguide on BCB polymer and interconnecting via between ground planes are presented up to 67 GHz with a 50 Ω characteristic impedance and a BCB relative permittivity of 2.676.

International audience; Hetero-structured silicon-germanium-silicon photodetectors operating under low-reverse-voltages with high responsivity, fast response, and low dark-current levels are reported. A bit-error-rate of 10-9 is experimentally achieved for conventional data rates of 10, 20, and 25 Gbps, providing optical power sensitivities of-13.9,-12.7, and-11.3 dBm.

In this work, a 25 Gb ps silicon push-pull Mach-Zehnder modulator operating in the O-Band (1260 nm – 1360 nm) of optical communications and fabricated on a 300 mm platform is presented. The measured modulation efficiency (VπLπ) was comprised between 0.95 V cm and 1.15 V cm, which is comparable to the state-of-the-art modulators in the C-Band, that enabled its use with a driving voltage of 3.3 Vpp, compatible with BiCMOS technology. An extinction ratio of 5 dB and an on-chip insertion losses of 3.6 dB were then demonstrated at 25 Gb ps.

Optical modulation in the O-Band using a Mach-Zehnder modulator in push-pull configuration is presented and experimentally demonstrated. Open eye diagrams at 25 GBps have been obtained with more than 8 dB extinction ratio with an active length of only 1 mm.

Silicon photonics has generated a strong interest in recent years, mainly for optical communications and optical interconnects in CMOS circuits. The main motivations for silicon photonics are the reduction of photonic system costs and the increase of the number of functionalities on the same integrated chip by combining photonics and electronics, along with a strong reduction of power consumption. However, one of the constraints of silicon as an active photonic material is its vanishing second order optical susceptibility, the so called χ(2) , due to the centrosymmety of the silicon crystal. To overcome this limitation, strain has been used as a way to deform the crystal and destroy the centrosymmetry which inhibits χ(2). The paper presents the recent advances in the development of second-order nonlinearities including discussions from fundamental origin of Pockels effect in silicon until its implementation in a real device. Carrier effects induced by an electric field leading to an electro-optics behavior will also be discussed.

The evolution of silicon optical modulators is recalled, from the first effect demonstrations to the characterization of high-performance devices integrated in optical waveguides. Among possibilities to achieve optical modulation in silicon-based materials, the carrier depletion effect has demonstrated good capacities. Carrier depletion in Si and SiGe/Si structures has been theoretically and experimentally investigated. Large phase modulation efficiency, low optical loss, and large cutoff frequency are obtained by considering simultaneously optical and electrical structure performances. Integrated Mach-Zehnder interferometers and resonators are compared to convert phase modulation into intensity modulation. Finally, recent results on high-speed and low-loss silicon optical modulator using an asymmetric Mach-Zehnder interferometer are presented. It is based on a p-doped slit embedded in the intrinsic region of a lateral pin diode integrated in a silicon-on-insulator waveguide. This design allows a good overlap between the optical mode and carrier density variations. An insertion loss of 5 dB has been measured with a -3 dB bandwidth of 15 GHz.

Silicon-based photonics has generated a strong interest in the last years, mainly for optical telecommunications and optical interconnects in microelectronic circuits and industrial breakthroughs have been even performed by companies like IBM, Luxtera, INTEL, and ST Microelectronics. The main future rationales are the reduction of photonic system costs, the increase of the number of functionalities on the same integrated chip by combining photonics and electronics, and the decrease of power consumption. During the DACINCT workshop, we will present recent results on ultrafast optical modulators based on carrier depletion effect and germanium photodetectors integrated in silicon on insulator (SOI) waveguides. Both optoelectronic devices have been fabricated on a CMOS 300mm platform. The achieved performances constitute a new milestone towards new generations of several Tb/s chips merging electronics and photonics.

A system dynamics model was created to simulate fuel cycle interactions between two separate nuclear entities, and this model was employed to investigate fuel leasing arrangements. The model was also adapted to evaluate proliferation and economic implications of an international leasing regime. For a nuclear growth scenario, an open fuel cycle results in extensive spent-fuel accumulation. For a closed fuel cycle, the leasing fuel cycle shows potential to reduce proliferation concern, especially if coupled with improved security and safeguard technology.

We present the state of the art of microwave performances of silicon heterostructures FETs (hetero-FETs). Recent advances are illustrated on using DaimlerChrysler (DC) technologies. fMAX as high as 188 and 135 GHz with minimum noise figure, NFmin as low as 0.3 and 0.5 dB at 2.5 GHz are reported, respectively, for n- and p-MODFET with gatelength from 100 to 130 nm. Experimental data and physical simulations of optimized structures show that fMAX of 70 nm gatelength n-MODFET could reach 360 GHz.

In order to show the potential interest of SrBi 2 Nb 2 O 9 (SBN) ferroelectric films to develop microwave agile devices, we have undertaken the radiofrequency characterization of structures patterned in Au/SBN bilayers deposited on LaAlO 3 and MgO single-crystals. Both coplanar waveguide transmission lines and 10 GHz half-wavelength resonators were characterized in the 100 kHz to 10 GHz frequency range and in the 300 K to 100 K temperature range.

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.

Resume En imagerie de la peau par resonance magnetique nucleaire a 1,5 teslas, le bruit propre d'une antenne en cuivre a la temperature ambiante limite entierement le rapport signal sur bruit (RSB) de l'image. Pour cette application, l'utilisation d'une antenne supraconductrice refroidie a 77 K laisse alors envisager une amelioration significative du RSB. Dans ce but, nous avons effectue une caracterisation preliminaire du RSB que l'on peut obtenir avec une antenne supraconductrice destinee a la microscopie de la peau a 1,5 teslas. Cette caracterisation, realisee sans experience d'imagerie, a montre que le RSB peut etre ameliore d'un facteur 3 a 5 suivant la region anatomique observee. Nous avons de plus mis en evidence l'existence d'une distance antenne-sujet optimale, non nulle, pour laquelle le RSB est maximal. Nous avons ensuite realise les premieres images de la peau in vivo avec une antenne supraconductrice a 1,5 T. Le RSB obtenu est ameliore d'un facteur 3 et l'on peut observer des structures de quelques micrometres qui ne sont pas visibles si l'on utilise une antenne en cuivre a la temperature ambiante. La resolution spatiale associee a la valeur elevee du RSB n'avait encore jamais ete atteinte dans un appareil d'imagerie corps entier.

In conjunction with a remote-controlled smart-sensors project (Villegas M, Bildstein P and Nicole P 1997 Translateur de frequence micro-ondes pour capteur intelligent autonome Proc. 10eme Journees Nationales Microondes (St Malo, 21-23 May 1997) pp 270-1), this study concerns the validation of a radio-frequency microelectromechanical system combining micromechanical capacitive functions and microwave data communication functions. In this project, we have focused on the back-modulation function used for data re-emission. We decided to develop this function with a microelectromechanical mixer made as a passive microwave frequency shifter using an integrated silicon micromechanical capacitive structure. The principles, together with electromechanical considerations, the technology of the silicon implantation, and some first experimental results are described in this paper. The main interest lies in the characterization of the device: both electrical and mechanical properties are tested in parallel to assist us in improving the system and defining a new micromechanical frequency-translator prototype.

Properties of YBaCuO thin films are evaluated in two distinct frequency ranges using different patterns made during the same process on LaAlO/sub 3/ substrate. Microwave superconducting properties in the range 1-45 GHz are determined by S-parameters measurement of a superconducting coplanar waveguide in the range 53-95 K. We obtain a surface resistance of 0.4 m/spl Omega/ at 10.8 GHz and 77 K. Radio-frequency properties are obtained by measuring the Q-factor of a superconducting resonator (YBCO multiturn transmission lines separated by a sapphire sheet) dedicated to surface magnetic resonance imaging. At 52 MHz and 77 K we measure a Q-factor of 33180. The extraction of the radio-frequency surface resistance from Q-factor measurements in the 64-95 K range takes into account external loss mechanisms and nonuniform normal current distribution and leads to a 0.0093-/spl mu//spl Omega/ surface resistance at 52 MHz and 77 K, in good agreement with the value extrapolated from microwave measurements assuming an /spl omega//sup 2/ frequency dependence. The evaluation of /spl lambda//sub 0/ is carried out by using several models for X/sub L/(t). Least squares fits to data in the microwave and radio-frequency domain are performed using the Gorter-Casimir expression for X/sub L/(t) and give the same /spl lambda//sub 0/ value for both devices.

We demonstrate a reduction of loss and group velocity dispersion (GVD) of THz plasmonic waveguides by using a low-loss thin flexible substrate. We present a numerical calculation of the effect of the substrate thickness on the GVD. We show experimentally low absorption and weak distortion of the propagated THz pulses along a THz plasmonic waveguide on a flexible 58μm-thick polyimide substrate.

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)

The ac electrical impedance of a 400-nm-thick La0.67Sr0.33MnO3 thin film (on MgO) has been measured in the frequency range from 30 MHz up to 6 GHz using etched strips. The impedance is found to be nearly a constant resistance that is equal to the dc resistance. The only deviations, in the order of their magnitude, are: (i) the contact pad impedance at low frequency, (ii) a small inductive part in the impedance of the material, and (iii) a low decrease of the resistance above 3 GHz.

The bias dependence of the single-port microwave reflection gain of 15 /spl mu/m-diameter Si Esaki tunnel diodes, grown by molecular beam epitaxy, was studied as a function of frequency. A simple equivalent circuit accurately modeled the data and yielded the forward-bias junction capacitance, which cannot be obtained by conventional low frequency capacitance-voltage techniques. The diodes were highly-doped step p-i-n junctions and exhibited a peak current density of 16 kA/cm/sup 2/. The microwave reflection gain and cut-off frequency were 12 dB land 1.6 GHz, respectively, with a speed index (slew rate) of 7.1 V/ns.

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.

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 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.

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.

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.

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