Mechanism of O2-anneal induced Vfb shifts of Ru gated stacks

A systematic study of the flat-band voltage (V_fb) shift of Ru gated metal-oxide-semiconductor (MOS) capacitors subjected to thermal treatment in O₂ has been performed. The dependence of the V_fb shift on the thickness of Ru, anneal temperature and time is studied. The V_fb shift is ascribed to the shift of metal gates’ work function (WF), and is not significantly dependent on the type of dielectric (HfO₂ or SiO₂). From time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement, it was found that after thermal treatment in ¹⁸O₂, ¹⁸O penetrated through Ru and was incorporated in the Ru/dielectric interface region. We believe that the formation of the thin interfacial RuO_x layer is responsible for the V_fb shift.     

Direct modulation of widely tunable twin-guide lasers

The possibility to directly modulate widely tunable lasers up to several gigahertz is desirable in telecom applications. We discuss the dynamic properties of the recently proposed widely tunable twin-guide laser concept. It has promising prospects with a maximum theoretical bandwidth above 20 GHz and the 3-dB bandwidth at 250 mA indicates that an actual bandwidth of 12 GHz should be possible. The current lasers were not designed for high-speed modulation, so only 1-GHz modulation can be reached at the moment.     

Ultra-low temperature sensitive deep-well quantum cascade lasers (λ - 4.8 μm) via uptapering conduction band edge of injector region

A new design feature for deep-well quantum cascade (QC) lasers, in which the conduction band edge of the injector region is uptapered, results in virtual suppression of carrier leakage out of the active regions of 4.8 mm emitting devices. For heatsink temperatures in the 20?90°C range the characteristic temperature coefficients for threshold, T₀, and slope efficiency, T₁, reach values as high as 278 and 285 K, respectively, which are nearly twice the values for conventional QC lasers. At 20°C, the threshold current density for uncoated, 30 period, 3 mm-long devices is only ~1.8 kA/cm².     

A Scalable System Architecture for High-Throughput Turbo-Decoders

The need for higher data rates is ever rising as wireless communications standards move from the third to the fourth generation. Turbo-Codes are the prevalent channel codes for wireless systems due to their excellent forward error correction capability. So far research has mainly focused on components of high throughput Turbo-Decoders. In this paper we explore the Turbo-Decoder design space anew, both under system design and deep-submicron implementation aspects. Our approach incorporates all levels of design, from I/O behavior down to floorplaning taking deep-submicron effects into account. Its scalability allows to derive optimized architectures tailored to the given throughput and target technology. We present results for 3GPP compliant Turbo-Decoders beyond 100 Mbit/s synthesized on a 0.18 μm standard cell library.     

High-Power Single-Mode Distributed-Feedback Interband Cascade Lasers for the Midwave-Infrared

A single-mode output power of 41 mW has been obtained at T=120 K and lambdaap3.44 mum from a narrow-ridge interband cascade laser patterned with a Ge distributed-feedback grating. The sidemode suppression ratio at the maximum power is 23 dB, and the linewidth of 0.1 nm is instrument-limited. An alternate contacting geometry yielded robust single-mode output over a broad range of currents and temperatures, and current tuning of the wavelength by up to 17 nm     

Design optimization for high-brightness surface-emitting photonic-crystal distributed-feedback lasers

A new time-domain Fourier-Galerkin (TDFG) theory is developed to simulate the near-field, far-field and spectral characteristics of surface-emitting photonic-crystal distributed-feedback (SE PCDFB) lasers. It is found that a properly-designed two-dimensional hexagonal or square-lattice grating should efficiently couple the output into a single SE mode that retains coherence for aperture diameters of up to /spl ap/1 mm. We identify lattice structures and precise conditions under which all components of the transverse electric or transverse magnetic polarized optical fields constructively interfere to produce a single-lobed, near-diffraction-limited circular output beam. The TDFG simulations predict that quantum efficiencies as high as 30% (60% if reflectors are built into the waveguide structure) should be attainable. A surprising conclusion is that diffractive coupling into the surface-emitting direction must be relatively weak, in order to assure selection of the desired symmetric in-phase mode. Furthermore, gain media with a moderate linewidth enhancement factor should produce the best SE PCDFB performance, whereas edge emitters nearly always benefit from a very small value.     

Influence of device engineering on the analog and RF performances of SOI MOSFETs

This work presents a systematic comparative study of the influence of various process options on the analog and RF properties of fully depleted (FD) silicon-on-insulator (SOI), partially depleted (PD) SOI, and bulk MOSFET's with gate lengths down to 0.08 /spl mu/m. We introduce the transconductance-over-drain current ratio and Early voltage as key figures of merits for the analog MOS performance and the gain and the transition and maximum frequencies for RF performances and link them to device engineering. Specifically, we investigate the effects of HALO implantation in FD, PD, and bulk devices, of film thickness in FD, of substrate doping in SOI, and of nonstandard channel engineering (i.e., asymmetric Graded-channel MOSFETs and gate-body contacted DTMOS).     

Implementation of an Aerostat Positioning System With Cable Control

The capabilities of a multi-tethered aerostat positioning system are investigated using experimental and simulation results. The system consists of a platform supported by a helium-filled aerostat and attached to three anchored ground tethers actuated using computer-controlled winches. The experimental system was designed to perform a proof-of-concept study of a novel large-scale radio telescope requiring a receiver to be positioned accurately at an altitude of up to 500 m. Results from a series of flight tests are presented with a comparison between the passive response of the system and the response using proportional, integral, and derivative (PID) controllers with a position feedback. The motion of the platform is smaller for all cases using the feedback control. To improve on the PID results, a dynamics model of the system is used to develop and simulate optimal and feedforward (FF) control strategies. The optimal linear quadratic Gaussian (LQG) controller offers a 50% improvement over the PID controller, and both the LQG and the PID feedback controllers were shown to benefit considerably from the addition of a FF control term that exploits the measurements of the system's main disturbance force     

Dynamic resource allocation in OFDM systems: an overview of cross-layer optimization principles and techniques

Recently, a lot of research effort has been spent on cross-layer system design. It has been shown that cross-layer mechanisms (i.e., policies) potentially provide significant performance gains for various systems. In this article we review several aspects of cross-layer system optimization regarding wireless OFDM systems. We discuss basic optimization models and present selected heuristic approaches realizing cross-layer policies by means of dynamic resource allocation. Two specific areas are treated separately: models and dynamic approaches for single transmitter/receiver pairs (i.e., a point-to-point communication scenario) as well as models and approaches for point-to-multipoint communication scenarios (e.g., the downlink of a wireless cell). This article provides basic knowledge in order to investigate future OFDM cross-layer-optimization issues     

Finding the dominant source of distortion in two-stage op-amps

Although non-linear distortion is an important specification for op-amps, it is only determined at the end of the design in classical design flows, leaving the designers without a clue about its origin. Recently, the Best Linear Approximation (BLA) has been introduced to approximate non-linear systems. It allows to describe the behaviour of a non-linear system as a linear Frequency Response Function combined with a coloured noise source to describe respectively the wanted linear response and the distortion. To determine the dominant source of non-linear distortion, we combine the BLA with a classical noise analysis in this paper. The paper explains the BLA-based noise analysis and shows the result of this simulation-based analysis when applied to various op-amp architectures. The analysis pinpoints the non-linear hot-spots in an efficient way, without the use of special simulations, manual analytical calculations or modified transistor models.