Double-gate CMOS: symmetrical- versus asymmetrical-gate devices

Numerical device-simulation results, supplemented by analytical characterizations, are presented to argue that asymmetrical double-gate (DG) CMOS, utilizing n⁺ and p⁺ polysilicon gates, can be superior to symmetrical-gate counterparts for several reasons, only one of which is its previously noted threshold-voltage control. The most noteworthy result is that asymmetrical DG MOSFETs, optimally designed with only one predominant channel, yield comparable, and even higher drive currents at low supply voltages. The simulations further give good physical insight pertaining to the design of DG devices with channel lengths of 50 nm and less     

A 1-GHz charge-packet replicator/subtractor circuit for GaAs CCDsignal processing

A novel charge-packet replicator/subtractor circuit based on GaAs charge-coupled device (CCD) technology is described. The circuit exhibits linear gain of 0.989 operating at 1-GHz replication frequency, while consuming only several milliwatts of dynamic power. Experimental results for a prototype circuit operating over the frequency range of 1 MHz to 1 GHz are presented. Due to the low parasitic capacitance of the GaAs semi-insulating substrate, the gain is linear and nearly unity. The chip area required for the circuit consists of several CCD gates and a small MESFET. Based on C-V measurements, the dynamic power consumed for the replication/subtraction process (operating with 5-V clock swings) is estimated to be on the order of several milliwatts at 1 GHz where the operation takes place in 1 ns. Design constraints are outlined and compared to experimental results in an effort to explore the tradeoff between speed and gain. The circuit is shown to be relatively insensitive to the precise voltages used during operation     

Physical subthreshold MOSFET modeling applied to viable design ofdeep-submicrometer fully depleted SOI low-voltage CMOS technology

An insightful study of the subthreshold characteristics of deep-submicrometer fully depleted SOI MOSFET's, based on two-dimensional numerical (PISCES) device simulations, shows that the gate swing and off-state current are governed by gate bias-dependent source/drain charge sharing, which controls back-channel as well as front-channel conduction. The insight from this study guides the development of a physical, two-dimensional analytic model for the subthreshold current and charge, which is linked to our strong-inversion formalism in SOISPICE for circuit simulation. The model is verified by PISCES simulations of scaled devices. The utility of the model in SOISPICE is demonstrated by using it to define a viable design for deep-submicrometer fully depleted SOI CMOS technology based on simulated speed and static power in low-voltage digital circuits     

CMOS active pixel sensor star tracker with regional electronicshutter

A 64×64 element CMOS active pixel sensor (APS) for star tracker applications is reported. The chip features an innovative regional electronic shutter through the use of an individual pixel reset architecture. Using the regional electronic shutter, each star in the field of view can have its own integration period. This way, simultaneous capture of bright stars with dim stars is accommodated, enabling a large increase in tracker capability. The chip achieves 80 dB dynamic range, 50 e-rms read noise, low dark current, and excellent electronic shutter linearity     

Comparison of threshold-voltage shifts for uniaxial and biaxial tensile-stressed n-MOSFETs

Large differences in the experimentally observed strain-induced threshold-voltage shifts for uniaxial and biaxial tensile-stressed silicon (Si) n-channel MOSFETs are explained and quantified. Using the deformation potential theory, key quantities that affect threshold-voltage (electron affinity, bandgap, and valence band density of states) are expressed as a function of strain. The calculated threshold-voltage shift is in agreement with uniaxial wafer bending and published biaxial strained-Si on relaxed-Si/sub 1-x/Ge/sub x/ experimental data , and explains the technologically important observation of a significantly larger (>4x) threshold-voltage shift for biaxial relative to uniaxial stressed MOSFETs. The large threshold shift for biaxial stress is shown to result from the stress-induced change in the Si channel electron affinity and bandgap. The small threshold-voltage shift for uniaxial process tensile stress is shown to result from the n/sup +/ poly-Si gate in addition to the Si channel being strained and significantly less bandgap narrowing.     

Process/physics-based threshold voltage model for nano-scaled double-gate devices

Compact physics/process-based model for threshold voltage in double-gate devices is presented. Predominant short-channel effects for double-gate devices, which are drain-induced barrier lowering (DIBL) and short-channel-induced barrier lowering (SCIBL), are physically analysed and modeled to be applicable to SPICE-compatible circuit simulators. The short-channel models are also developed for bulk-Si device and compared to those of double-gate devices. The validity and predictability of the models are demonstrated and confirmed by numerical device simulation results for extremely scaled L _eff = 25?nm double-gate devices and bulk-Si device.     

Tissue chambers--a useful model for in vivo studies of cytokine production in the pig

An in vivo tissue chamber model was developed to enable studies of local cytokine production and cellular events during inflammatory and immune reactions in the pig. Tissue chambers made of sialistic rubber tubing were surgically implanted in the subcutaneous tissue- and samples of tissue chamber fluid (TCF) and inflammatory cells were collected by aspiration with a syringe. To evaluate the model for local cytokine production, two cytokine inducers, polyribinosinic-polyribocytidylic acid (poly I:C) and fixed Aujeszky's disease virus infected PK15 cells (ADV-PK15), were injected into the tissue chambers and samples of TCF were collected 0, 4, 8, 12, 24 and 48 h post injection. Poly I:C injections induced local production of interferon-alpha (IFN-alpha) as well as tumor necrosis factor (TNF) in the TCF but kinetic differences in the production of the cytokines were noted. Poly I:C also induced an increase in cell numbers in the TCF, mainly due to increased neutrophil numbers. Injections of ADV-PK15 induced local IFN-alpha production in the TCF as long as the pigs were serologically negative to ADV. Immunofluorescence and in situ hybridization techniques could be applied for characterization of TCF cells. Moreover, cells recovered from the tissue chambers were viable and could be used in functional in vitro tests. Taken together, this tissue chamber model could prove very useful in in vivo studies of inflammatory/immune responses and cytokine production in the pig.     

Health of laying hens in an aviary system over five batches of birds

Mortality and health were studied in laying hens kept in an aviary system on a practical scale. All management inputs were done by university staff. Five batches of birds (trials) during a period of 6 years with approximately 4,700 birds per trial were included in the study. The aviary was a three-tiered "Marielund" system divided into 4 pens. Three hybrids, reared on litter with access to perches, were used; Lohmann Selected Leghorn (LSL), Lohmann Brown (LB) and an experimental cross (SLU-1329). The hens were not beak-trimmed. The stocking density was 17 hens/m2 ground floor. Mortality varied between pens and between batches, ranging from normal rates of 3.4% to 7.8%, except in LSL in Trial 2 and LB in Trial 3 where it was much higher (15.6% and 20.9%, respectively). The dominating causes of total mortality were salpingitis and cannibalism. Coccidiosis and lymphoid leucosis contributed significantly to mortality in Trial 2. An infestation with fowl mites (Dermanyssus gallinae) occurred in Trial 1. Feather loss was most severe in LB. Keel bone deviations were recorded at increasing levels by age. Foot abscesses occurred more frequently at 35 weeks than at 55 weeks. LSL was more severely affected than LB and SLU-1329.     

Significant time constants defined by high-current charge dynamicsin advanced silicon-based bipolar transistors

Analytical expressions for the time constants in advanced silicon-based bipolar transistors defined by the charge dynamics in the base-collector junction space-charge region (τ_C) and by the charge modulation in the quasi-neutral base (τ_BM) are derived based on an accounting for the high-current-induced perturbation of the space-charge region. The derivations show that voltage drops in the intrinsic and extrinsic collector regions and in the extrinsic emitter region are important in defining τ_C and τ_BM, and that τ_BM is approximately proportional to collector-current density. Application of the results to an aggressive SiGe-base HBT technology shows that τ_C and τ_BM are comparable to the base transit time, and hence that they are significant in defining high-current speed of the HBT