Showing papers on "Biasing published in 2007"

Ga2O3 thin film growth on c-plane sapphire substrates by molecular beam epitaxy for deep-ultraviolet photodetectors

Abstract: (201)-oriented β-Ga2O3 thin films were grown on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. In-plane X-ray diffraction measurements revealed the inclusion of α-Ga2O3 and rotational domains. However, the film grown under the optimized growth conditions exhibited a sharp absorption edge at around 5.0 eV, which is in the deep-ultraviolet region. An ohmic-type metal–semiconductor–metal photodetector showed a high resistance of around 6 GΩ with a small dark current of 1.2 nA at the 10 V bias voltage. Under 254 nm light illumination and 10 V bias voltage, the photoresponsivity was 0.037 A/W, which corresponded to a quantum efficiency of 18%.

Fully transparent thin-film transistor devices based on SnO2 nanowires.

Abstract: We report on studies of field-effect transistor (FET) and transparent thin-film transistor (TFT) devices based on lightly Ta-doped SnO2 nano-wires. The nanowire-based devices exhibit uniform characteristics with average field-effect mobilities exceeding 100 cm2/V x s. Prototype nano-wire-based TFT (NW-TFT) devices on glass substrates showed excellent optical transparency and transistor performance in terms of transconductance, bias voltage range, and on/off ratio. High on-currents and field-effect mobilities were obtained from the NW-TFT devices even at low nanowire coverage. The SnO2 nanowire-based TFT approach offers a number of desirable properties such as low growth cost, high electron mobility, and optical transparency and low operation voltage, and may lead to large-scale applications of transparent electronics on diverse substrates.

Adaptive Frequency and Biasing Techniques for Tolerance to Dynamic Temperature-Voltage Variations and Aging

Abstract: Temperature, voltage, and current sensors monitor the operation of a TCP/IP offload accelerator engine fabricated in 90nm CMOS, and a control unit dynamically changes frequency, voltage, and body bias for optimum performance and energy efficiency. Fast response to droops and temperature changes is enabled by a multi-PLL clocking unit and on-chip body bias. Adaptive techniques are also used to compensate performance degradation due to device aging, reducing the aging guardband.

Submicrometer Inversion-Type Enhancement-Mode InGaAs MOSFET With Atomic-Layer-Deposited $\hbox{Al}_{2}\hbox{O}_{3}$ as Gate Dielectric

Abstract: High-performance inversion-type enhancement-mode n-channel In053Ga047As MOSFETs with atomic-layer-deposited (ALD) Al2O3 as gate dielectric are demonstrated The ALD process on III-V compound semiconductors enables the formation of high-quality gate oxides and unpinning of Fermi level on compound semiconductors in general A 05-mum gate-length MOSFET with an Al2O3 gate oxide thickness of 8 nm shows a gate leakage current less than 10-4 A/cm2 at 3-V gate bias, a threshold voltage of 025 V, a maximum drain current of 367 mA/mm, and a transconductance of 130 mS/mm at drain voltage of 2 V The midgap interface trap density of regrown Al2O3 on In053Ga047As is ~14 x 1012/cm2 ldr eV which is determined by low-and high-frequency capacitance-voltage method The peak effective mobility is ~1100 cm2 / V ldr s from dc measurement, ~2200 cm2/ V ldr s after interface trap correction, and with about a factor of two to three higher than Si universal mobility in the range of 05-10-MV/cm effective electric field

Low temperature CVD process with selected stress of the CVD layer on CMOS devices

Abstract: Device-enhancing coatings are deposited on CMOS devices by successively masking with photoresist each one of the sets of N-channel and P-channel devices while unmasking or leaving unmasked the other set, and after each step of successively masking one of the sets of devices, carrying out low temperature CVD steps with a toroidal RF plasma current while applying an RF plasma bias voltage. The temperature of the workpiece is held below a threshold photoresist removal temperature. The RF bias voltage is held at a level at which the coating is deposited with a first stress when the unmasked set consists of the P-channel devices and with a second stress when the unmasked set consists of N-channel devices.

Highly spin-polarized tunneling in fully epitaxial Co2Cr0.6Fe0.4Al∕MgO∕Co50Fe50 magnetic tunnel junctions with exchange biasing

Abstract: Fully epitaxial magnetic tunnel junctions (MTJs) with exchange biasing were fabricated with a full-Heusler alloy Co2Cr06Fe04Al (CCFA) thin film and a MgO tunnel barrier, where a Co50Fe50 upper electrode was used in a synthetic ferrimagnetic Co50Fe50∕Ru∕Co90Fe10 trilayer exchange-biased with an IrMn layer through the Co90Fe10∕IrMn interface The fabricated MTJs exhibited clear exchange-biased tunnel magnetoresistance (TMR) characteristics with high TMR ratios of 109% at room temperature and 317% at 42K A high tunneling spin polarization of 088 at 42K was estimated for epitaxial CCFA films with the B2 structure

Setting an operating bias current for a magnetoresistive head by computing a target operating voltage

Abstract: A disk drive is disclosed having a disk, and a head actuated over the disk, the head comprising a magnetoresistive (MR) element. Control circuitry within the disk drive sets an operating bias current for the MR element by computing a target voltage for the MR element, applying a bias current to the MR element, measuring a voltage across the MR element corresponding to the bias current, and adjusting the bias current applied to the MR element until the measured voltage substantially equals the target voltage.

Setting an operating bias current for a magnetoresistive head using ratio of target voltage and measured voltage

Abstract: A method is disclosed for setting an operating bias current for a magnetoresistive (MR) element. A bias current is applied to the MR element, and a voltage across the MR element is measured corresponding to the bias current. The bias current is then adjusted in response to the bias current multiplied by a ratio of a target voltage and the measured voltage. The adjusted bias current is then applied to the MR element. In one embodiment, the bias current is adjusted until the measured voltage substantially equals the target voltage.

Mitigating Parameter Variation with Dynamic Fine-Grain Body Biasing

Abstract: Parameter variation is detrimental to a processor's frequency and leakage power. One proposed technique to mitigate it is Fine-Grain Body Biasing (FGBB), where different parts of the processor chip are given a voltage bias that changes the speed and leakage proper- ties of their transistors. This technique has been proposed for static application, with the bias voltages being programmed at manufac- turing time for worst-case conditions. In this paper, we introduce Dynamic FGBB (D-FGBB), which allows the continuous re-evaluation of the bias voltages to adapt to dynamic conditions. Our results show that D-FGBB is very versa- tile and effective. Specifically, with the processor working in nor- mal mode at fixed frequency, D-FGBB reduces the leakage power of the chip by an average of 28 42% compared to static FGBB. Alternatively, with the processor working in a high-performance mode, D-FGBB increases the processor frequency by an average of 7 9% compared to static FGBB -- or 7 16% compared to no body biasing. Finally, we also show that D-FGBB can be syner- gistically combined with Dynamic Voltage and Frequency Scaling (DVFS), creating an effective means to manage power.

Negative capacitance in organic semiconductor devices: Bipolar injection and charge recombination mechanism

Abstract: The authors report negative capacitance at low frequencies in organic semiconductor based diodes and show that it appears only under bipolar injection conditions. They account quantitatively for this phenomenon by the recombination current due to electron-hole annihilation. Simple addition of the recombination current to the well established model of space charge limited current in the presence of traps yields excellent fits to the experimentally measured admittance data. The dependence of the extracted characteristic recombination time on the bias voltage is indicative of a recombination process which is mediated by localized traps.

Structural and electrical characteristics of atomic layer deposited high κ HfO2 on GaN

Abstract: High κ HfO2 was deposited on n-type GaN (0001) using atomic layer deposition with Hf(NCH3C2H5)4 and H2O as the precursors. Excellent electrical properties of TiN∕HfO2∕GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8nm were obtained, in terms of low electrical leakage current density (∼10−6A∕cm2 at VFB+1V), well behaved capacitance-voltage (C-V) curves having a low interfacial density of states of 2×1011cm−2eV−1 at the midgap, and a high dielectric constant of 16.5. C-V curves with clear accumulation and depletion behaviors were shown, along with negligible frequency dispersion and hysteresis with sweeping biasing voltages. The structural properties studied by high-resolution transmission electron microscopy and x-ray reflectivity show an atomically smooth oxide/GaN interface, with an interfacial layer of GaON ∼1.8nm thick, as probed using x-ray photoelectron spectroscopy.

Rf transmitter with variably biased rf power amplifer and method therefor

Abstract: An RF transmitter (30) includes an RF power amplifier (32) for which the power input bias voltage (40) and signal input bias voltage (80) are controlled within feedback loops. A peak detector (44) generates a lowered-spectrum, peak-tracking signal (34) that follows the largest amplitude peaks of a wide bandwidth communication signal (16) but exhibits a lower bandwidth. This signal (34) is scaled in response to the operation of a drain bias tracking loop (146) then used to control a switching power supply (36) that generates the power input bias voltage. The tracking loop (146) is responsive to out-of-band power detected in a portion of the amplified RF communication signal (16'). A ratio of out-of-band power (128) to in-band power (126) is manipulated in the tracking loop (146) so that the power input bias voltage is modulated in a way that holds the out-of-band power at a desired predetermined level.

p-n Semiconductor membrane for electrically tunable ion current rectification and filtering.

Abstract: We show that a semiconductor membrane made of two thin layers of opposite (n- and p-) doping can perform electrically tunable ion current rectification and filtering in a nanopore Our model is based on the solution of the 3D Poisson equation for the electrostatic potential in a double-cone nanopore combined with a transport model It predicts that, for appropriate biasing of the membrane−electrolyte system, transitions from ohmic behavior to sharp rectification with vanishing leakage current are achievable Furthermore, ion current rectifying and filtering regimes of the nanopore correspond to different charge states in the p−n membrane, which can be tuned with appropriate biasing of the n- and p- layers

A novel voltage-clamped CMOS ISFET sensor interface

Abstract: This paper presents a novel interface for ion-sensitive field effect transistors (ISFET) in which operation at a fixed electrical bias is achieved by voltage clamping. The chosen topology provides pH-dependent current and voltage output signals to drive an appropriate output stage. The circuit can be operated in either strong or weak inversion, depending on the requirements of the application with a pseudo-differential ISFET-REFET topology to allow use of an on-chip reference electrode. Simulation results are shown herein for single-ended and differential implementations. For a single-ended front-end with 1nA bias current, the strong inversion implementation at 2.5V supply has a power consumption of 0.185mW at pH 7 and the weak inversion implementation at 1.5V supply has a power consumption of 13nW at pH 7. The circuit and ISFET-REFET pair have been fabricated in the UMC 0.25mum CMOS technology.

Super Class-AB OTAs With Adaptive Biasing and Dynamic Output Current Scaling

Abstract: A new family of single-stage super Class-AB operational transconductance amplifiers (OTAs) suitable for low-voltage operation and low power consumption is presented. Three novel topologies are proposed featuring simplicity and compactness. They are based on the combination of adaptive biasing techniques for the differential input stage and nonlinear current mirrors for the active load that provide additional dynamic current boosting. The OTAs have been fabricated in a standard 0.5-mum CMOS process. Experimental results show a greatly improved slew rate by factors 30-60 and gain-bandwidth product by factors 11.5-17 when compared to a classical Class-A OTA. The circuits are operated at plusmn1-V supply voltage with only 10 muA of bias current

Generation of Terahertz Radiation by Hot Electrons in Carbon Nanotubes

Abstract: We demonstrate theoretically that quasi-metallic carbon nanotubes emit terahertz radiation induced by an applied voltage. It is shown that in the ballistic transport regime their spontaneous emission spectra have a universal frequency and bias voltage dependence, which raises the possibility of utilizing this effect for high-frequency nanoelectronic devices.

Bias Voltage Dependence of Tunneling Anisotropic Magnetoresistance in Magnetic Tunnel Junctions with MgO and Al 2 O 3 Tunnel Barriers

Abstract: Tunneling anisotropic magnetoresistance (TAMR) is observed in tunnel junctions with transition metal electrodes as the moments are rotated from in-plane to out-of-plane in sufficiently large magnetic fields that the moments are nearly parallel to one another. A complex angular dependence of the tunneling resistance is found with twofold and fourfold components that vary strongly with bias voltage. Distinctly different TAMR behaviors are obtained for devices formed with highly textured crystalline MgO(001) and amorphous Al2O3 tunnel barriers. A tight-binding model shows that a fourfold angular dependence can be explained by the presence of an interface resonant state that affects the transmission of the contributing tunneling states through a spin-orbit interaction.

Enhanced Magnetotransport at High Bias in Quasimagnetic Tunnel Junctions with EuS Spin-Filter Barriers

Abstract: In quasimagnetic tunnel junctions with a EuS spin-filter tunnel barrier between Al and Co electrodes, we observed large magnetoresistance (MR). The bias dependence shows an abrupt increase of MR ratio in high bias voltage, which is contrary to conventional magnetic tunnel junctions. This behavior can be understood as due to Fowler-Nordheim tunneling through the fully spin-polarized EuS conduction band. The I-V characteristics and bias dependence of MR calculated using tunneling theory show excellent agreement with experiment.

Current–Voltage Characteristics of Long-Channel Nanobundle Thin-Film Transistors: A “Bottom-Up” Perspective

Abstract: By generalizing the classical linear response theory of "stick" percolation to nonlinear regime, we find that the drain-current of a nanobundle thin-film transistor (NB-TFT) is described under a rather general set of conditions by a universal scaling formula ID=A/LSxi(LS/LC,rho SLS 2)timesf(VG,VD ), where A is a technology-specific constant, xi is a function of geometrical factors such as stick length LS, channel length LC, and stick density rhoS, and f is a function of drain VD and gate VG biasing conditions This scaling formula implies that the measurement of the full current-voltage characteristics of a "single" NB-TFT is sufficient to predict the performance characteristics of any other transistor with arbitrary geometrical parameters and biasing conditions

Decoherence and single electron charging in an electronic Mach-Zehnder interferometer

Abstract: We investigate the temperature and voltage dependence of the quantum interference in an electronic Mach-Zehnder interferometer using edge channels in the integer quantum-Hall regime. The amplitude of the interference fringes is significantly smaller than expected from theory; nevertheless the functional dependence of the visibility on temperature and bias voltage agrees very well with theoretical predictions. Superimposed on the Aharonov-Bohm (AB) oscillations, a conductance oscillation with a six times smaller period is observed. The latter depends only on gate voltage and not on the AB phase, and may be related to single electron charging.

Calibrated microelectromechanical microphone

Abstract: A MEMS microphone comprising a MEMS transducer having a back plate and a diaphragm as well as controllable bias voltage generator providing a DC bias voltage between the back plate and the diaphragm. The microphone also has an amplifier with a controllable gain, and a memory for storing information for determining a bias voltage to be provided by the bias voltage generator and the gain of the amplifier.

Band-to-band tunneling in a carbon nanotube metal-oxide-semiconductor field-effect transistor is dominated by phonon-assisted tunneling.

Abstract: Band-to-band tunneling (BTBT) devices have recently gained a lot of interest due to their potential for reducing power dissipation in integrated circuits. We have performed extensive simulations for the BTBT operation of carbon nanotube metal-oxide-semiconductor field-effect transistors (CNT-MOSFETs) using the nonequilibrium Green's function formalism for both ballistic and dissipative quantum transport. In comparison with recently reported experimental data (J. Am. Chem. Soc. 2006, 128, 3518-3519), we have obtained strong evidence that BTBT in CNT-MOSFETs is dominated by optical phonon assisted inelastic transport, which can have important implications on the transistor characteristics. It is shown that, under large biasing conditions, two-phonon scattering may also become important.

Microwave power generated by a spin-torque oscillator in the presence of noise

Abstract: An expression for the microwave power generated by a spin-torque oscillator in the presence of thermal noise is derived. This expression, when used in a subcritical regime, demonstrates that generated power is determined by the noise level and provides a simple way to experimentally determine the threshold current for microwave generation. The same expression gives a good quantitative description of the experimentally measured dependence of the generated power on the bias current in a moderate super-critical range of bias current variation.

Compact InAlAs–InGaAs Metal– Semiconductor– Metal Photodetectors Integrated on Silicon-on-Insulator Waveguides

Abstract: We present measurement results of compact and efficient InAlAs-InGaAs metal-semiconductor-metal photodetectors integrated on silicon-on-insulator (SOI) waveguides. These thin-film devices are heterogeneously integrated on the SOI substrate by means of low-temperature die-to-wafer bonding using divinyldisiloxane benzocyclobutene (DVS-BCB). The responsivity of a 30-mum-long detector is 1.0 A/W at a wavelength of 1550 nm and the dark current is 4.5 nA at a bias voltage of 5 V.

Low-Noise CMOS single-photon avalanche diodes with 32 ns dead time

Abstract: The implementation of single-photon avalanche diode detectors (SPAD) in a standard high voltage 0.7-mum CMOS technology is presented. Two different device structures, combined with integrated quenching circuits, have been fabricated and successfully tested. A novel biasing scheme is proposed allowing the reduction of afterpulsing effect and the decrease of minimum device-to-device distance. Good noise performance is obtained for the 100 mum2 active area device where over 50% of the population has a dark count rate below lOOcps and afterpulsing lower than 0.3% with a 4-V excess bias and a 32-ns dead time. The peak photon detection probability is about 30%, while the overall system, upper limit, for the time resolution is 144 ps.

Integrated circuits with adjustable body bias and power supply circuitry

Abstract: An integrated circuit is provided with adjustable transistor body bias circuitry and adjustable power supply circuitry. The adjustable circuitry may be used to selectively apply body bias voltages and power supply voltages to blocks of programmable logic, memory blocks, and other circuit blocks on the integrated circuit. The body bias voltages and power supply voltages may be identified by computer aided design tools. The body bias voltages may be used to reduce leakage currents and power consumption when high speed circuit block operation is not required. Reduced power supply voltages may also be used to reduce power consumption when high speed circuit block operation is not required. To ensure optimum switching speeds, circuit blocks for which high-speed performance is critical can be provided with minimal body bias voltage or no body bias and can be provided with maximum power supply levels.

Josephson-Vortex-Flow Terahertz EmissioninLayeredHigh-Tc SuperconductingSingleCrystals

Abstract: Rapidly increasing applications of the electromagnetic (EM) waves in the terahertz frequency range (� 0:1–30 THz) demand a novel technique of efficient terahertz-wave generation. Semiconductor EM-wave generating elements mainly rely on two operation principles: sinusoidal current oscillation and the transition of electronic states between quantum levels, which are realized by electronic and photonic means, respectively. However, terahertz-range EM-wave technology has remained underdeveloped (often dubbed the ‘‘terahertz gap’’) due to the following reasons: (i) in electronics, the transit of charge carriers in a semiconductor device inherently takes too long to produce the terahertz oscillation, while (ii) in photonics, the terahertz-range photon energy is much lower than the room-temperature ambient thermal energy. In spite of recent progress in assorted generation techniques [1– 4] the terahertz generation remains to be a subject of intensive research efforts. The present Letter describes the direct detection of the Josephson vortex-flow-induced terahertz-wave emission from Bi2Sr2CaCu2O8� x (Bi-2212) stacked intrinsic Josephson junctions (IJJs). Since the size of the superconducting gap in Bi-2212 is higher than the Josephson plasma edge both the emission and the detection are allowed in a terahertz range [5]. In this study, the terahertzwave emission was confirmed by observing Shapiro steps in an on-chip stack of IJJs (detector stack) as it was irradiated by the emission from the oscillator stack. The frequency of the emitted wave was tuned by the bias voltage, while the emission power was controlled by the bias current and switching of the resonating modes. Naturally grown layered high-Tc superconducting Bi2212 single crystals contain IJJs [6], where a 0.3-nm-thick superconducting CuO2 bilayer and a 1.2-nm-thick insulating BiO-SrO layer alternate along the c axis. Since the superconducting electrodes in IJJs are much thinner than ������������