Showing papers on "Biasing published in 2005"

High performance n-type carbon nanotube field-effect transistors with chemically doped contacts.

Abstract: Short channel (80 nm) n-type single-walled carbon nanotube (SWNT) field-effect transistors (FETs) with potassium (K) doped source and drain regions and high-K gate dielectrics (ALD HfO2) are obtained. For nanotubes with diameter 1.6 nm and band gap 0.55 eV, we obtain n-MOSFET-like devices exhibiting high on-currents due to chemically suppressed Schottky barriers at the contacts, subthreshold swing of 70 mV/decade, negligible ambipolar conduction, and high on/off ratios up to 106 at a bias voltage of 0.5 V. The results compare favorably with the state-of-the-art silicon n-MOSFETs and demonstrate the potential of SWNTs for future complementary electronics. The effects of doping level on the electrical characteristics of the nanotube devices are discussed. Single-walled carbon nanotubes (SWNTs) are promising for future high performance electronics such as field effect transistors (FETs) owing to their various unique properties including ballistic transport with relatively long mean free paths and high compatibility with high- dielectrics imparted by their unique chemical bonding and surface stability. 1-12 While much has been done to achieve high performance p-type nanotube FETs through contact optimization, dielectric integration and lateral scaling, progress on n-FETs has been slow partly due to the difficulty in affording low Schottky (SB) contacts for high on-states and at the same time achieving high on/off ratios with small diameter (or large band gap) tubes. 7 Here, by invoking chemical doping, high- dielectrics, and new device design, we demonstrate n-type SWNT FETs with performance matching or approaching the best p-type nanotube FETs and surpassing the state-of-the-art Si n-MOSFET.

A single-molecule diode

Abstract: We have designed and synthesized a molecular rod that consists of two weakly coupled electronic π -systems with mutually shifted energy levels. The asymmetry thus implied manifests itself in a current–voltage characteristic with pronounced dependence on the sign of the bias voltage, which makes the molecule a prototype for a molecular diode. The individual molecules were immobilized by sulfur–gold bonds between both electrodes of a mechanically controlled break junction, and their electronic transport properties have been investigated. The results indeed show diode-like current–voltage characteristics. In contrast to that, control experiments with symmetric molecular rods consisting of two identical π -systems did not show significant asymmetries in the transport properties. To investigate the underlying transport mechanism, phenomenological arguments are combined with calculations based on density functional theory. The theoretical analysis suggests that the bias dependence of the polarizability of the molecule feeds back into the current leading to an asymmetric shape of the current–voltage characteristics, similar to the phenomena in a semiconductor diode.

Semiconductor substrate process using a low temperature-deposited carbon-containing hard mask

Abstract: A method of processing a thin film structure on a semiconductor substrate using an optically writable mask includes placing the substrate in a reactor chamber, the substrate having on its surface a target layer to be etched in accordance with a predetermined pattern, and depositing a carbon-containing hard mask layer on the substrate by (a) introducing a carbon-containing process gas into the chamber, (b) generating a reentrant toroidal RF plasma current in a reentrant path that includes a process zone overlying the workpiece by coupling plasma RF source power to an external portion of the reentrant path, and (c) coupling RF plasma bias power or bias voltage to the workpiece. The method further includes photolithographically defining the predetermined pattern in the carbon-containing hard mask layer, and etching the target layer in the presence of the hard mask layer.

Low temperature plasma deposition process for carbon layer deposition

Abstract: A method of depositing a carbon layer on a workpiece includes placing the workpiece in a reactor chamber, introducing a carbon-containing process gas into the chamber, generating a reentrant toroidal RF plasma current in a reentrant path that includes a process zone overlying the workpiece by coupling plasma RF source power to an external portion of the reentrant path, and coupling RF plasma bias power or bias voltage to the workpiece.

Bonded planar double-metal-gate NMOS transistors down to 10 nm

Abstract: Thanks to bonding, metal-gate etching without any out-of-gate Si consumption, and self-aligned transfer of alignment marks, we have processed the first 10-nm-gate-length DG MOS transistors with metal gates. These devices exhibit excellent short-channel effects control and high-performance characteristics. Their saturation current is very sensitive to the access resistance increase caused by film thinning required to respect the scaling rules. Moreover, their electrical properties can be tuned between LSTP and HP by independently biasing the two gates.

Ab initio analysis of electron-phonon coupling in molecular devices.

Abstract: We report a first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. Using a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two aluminum leads as an example, we analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. We find that the low-lying modes are most important. As a function of bias voltage, the electron-phonon coupling strength can change drastically while the vibrational spectrum changes at a few percent level.

Method for manufacturing semiconductor devices

Abstract: A method for manufacturing semiconductor devices includes a step of etching a sample including an interlayer insulating layer containing Al2O3 and a polysilicon or SiO2 layer in contact with the interlayer insulating layer using a plasma etching system. The interlayer insulating layer is etched with a gas mixture containing BCl3, Ar, and CH4 or He. The gas mixture further contains Cl2. The interlayer insulating layer is etched in such a manner that a time-modulated high-frequency bias voltage is applied to the sample. The interlayer insulating layer is etched in such a manner that the sample is maintained at a temperature of 100° C. to 200° C. The interlayer insulating layer and the polysilicon or SiO2 layer are separately etched in different chambers.

Bistable resistive switching of a sputter-deposited Cr-doped SrZrO/sub 3/ memory film

Abstract: Sputter-deposited Cr-doped SrZrO/sub 3/-based metal-insulator-metal structures exhibited bistable resistive reversible switching as observed under bias voltage and voltage pulse. The ratio of resistance of the two leakage states (high-H, low-L) was about five orders of magnitude. The conduction of the L-state satisfied Frenkel-Poole emission and that of the H-state followed ohmic mechanism, causing the resistance ratio to decrease with increasing bias voltage. The transition time of H- to L-state was five orders of magnitude higher than that of L- to H-state. The transition from H- to L-state was the restricted part for reversible switching operation. The difference in transition time of the two states should be related to the respective conduction mechanisms.

Highly Reliable 250 W GaN High Electron Mobility Transistor Power Amplifier

Abstract: A state-of-the-art highly reliable 250 W AlGaN/GaN high electron mobility transistor (HEMT) push-pull transmitter amplifier operated at a drain bias voltage of 50 V is described. The amplifier, combined with a digital predistortion (DPD) system, also achieved an adjacent channel leakage power ratio (ACLR) of less than -50 dBc for 4-carrier wideband code division multiple access (W-CDMA) signals with a drain supply voltage of 50 V. I also demonstrate its stable operation under RF stress testing for 1000 h at a drain bias voltage of 60 V. Stable gate-leakage current for high-temperature operation was verified. Device fabrications on 4 inch sapphire and 3 inch semi-insulating (S.I.) SiC substrates were also addressed. These performances clarify that an AlGaN/GaN HEMTs amplifier is suitable for 3G W-CDMA systems.

Bias Current Generators with Wide Dynamic Range

Abstract: Mixed-signal or analog chips often require a wide range of biasing currents that are independent of process and supply voltage and that are proportional to absolute temperature. This paper describes CMOS circuits that we use to generate a set of fixed bias currents typically spanning six decades at room temperature down to a few times the transistor off-current. A bootstrapped current reference with a new startup and power-control mechanism generates a master current, which is successively divided by a current splitter to generate the desired reference currents. These references are nondestructively copied to form the chip's biases. Measurements of behavior, including temperature effects from 1.6 and 0.35 ? implementations, are presented and nonidealities are investigated. Temperature dependence of the transistor off-current is investigated because it determines the lower limit for generated currents. Readers are directed to a design kit that allows easy generation of the complete layout for a bias generator with a set of desired currents for scalable MOSIS CMOS processes.

Local spectroscopy and atomic imaging of tunneling current, forces, and dissipation on graphite.

Abstract: Theory predicts that the currents in scanning tunneling microscopy (STM) and the attractive forces measured in atomic force microscopy (AFM) are directly related. Atomic images obtained in an attractive AFM mode should therefore be redundant because they should be similar to STM. Here, we show that while the distance dependence of current and force is similar for graphite, constant-height AFM and STM images differ substantially depending on the distance and bias voltage. We perform spectroscopy of the tunneling current, the frequency shift, and the damping signal at high-symmetry lattice sites of the graphite (0001) surface. The dissipation signal is about twice as sensitive to distance as the frequency shift, explained by the Prandtl-Tomlinson model of atomic friction.

Signal Processing Circuit Comprising Ion Sensitive Field Effect Transistor and Method of Monitoring a Property of a Fluid

Abstract: A signal processing circuit comprising one or more ion sensitive field effect transistors, ISFETs, and a biasing circuit for biasing the or each ion sensitive field effect transistor to operate in the weak inversion region. A method of monitoring a property of a medium using an ion sensitive field effect transistor, the method comprising: biasing the ion sensitive field effect transistor in the weak inversion region, exposing the ion sensitive field effect transistor to said medium, and analysing an output of the ion sensitive field effect transistor which varies in dependence upon said property.

Body bias compensation for aged transistors

Abstract: Embodiments of the invention include on-chip transistor degradation detection and compensation. In one embodiment of the invention, an integrated circuit is provided including a circuit with a body bias terminal coupled to a body of one or more transistors to receive a body bias voltage; a programmable degradation monitor to detect aging of transistors, and a body bias voltage generator coupled to the circuit and the programmable degradation monitor. The body bias voltage generator to adjust the body bias voltage coupled into the circuit in response to transistor aging detected by the programmable degradation monitor. The programmable degradation monitor includes a reference ring oscillator, an aged ring oscillator, and a comparison circuit. The comparison circuit to compare data delays in the reference ring oscillator and the aged ring oscillator to detect transistor aging within the integrated circuit.

Silicon columnar microstructures induced by an SF6/O2 plasma

Abstract: An inductively coupled SF6/O2 plasma is used to form a columnar microstructure (CMS) on silicon samples cooled at very low temperature (~ −100 °C). The formation of this CMS is studied as a function of bias voltage, temperature, RF power and gas pressure. The characteristic mean diameter and mean height of the microstructure are evaluated by image processing tools from SEM micrographs. A crystallographic effect is also observed at very low temperature, which induces a needle-shaped structure. A physical mechanism is proposed to explain the formation of this CMS.

Effect of direct-current biasing on the dielectric properties of barium strontium titanate

Abstract: Ba 1-x Sr x TiO 3 (BST, x = 0 to x = 1) ferroelectric ceramics doped with 1.0 mol% MgO and 0.05 mol% MnO 2 were prepared with a rate-controlled sintering profile. As the strontium molar fraction x increased, the average grain size decreased from 14 μm for x = 0 to 2 μm for x = 1. Temperature dependence of the dielectric properties was measured as a function of dc biasing. At 10°C above the Curie temperature, the changes of dielectric constant at 5000 V/ cm were 28%, 17%, 26%, and 36% for x = 0, 0.25, 0.5, and 0.75, respectively. The reduction of dielectric constant by the applied dc biasing was fitted by a phenomenological equation that was based on Devonshire's theory. From this phenomenological equation, an anharmonic coefficient, which was an order parameter of the anharmonic interactions, was calculated for each composition. As the strontium molar fraction increased, these coefficients increased from 2.45 x 10 -19 cm 2 .V -2 for x = 0 to 5.90 x 10 -19 cm 2 .V -2 for x = 0.75. A similar trend was observed on the dc field dependence of the dielectric loss, except at high field for x = 0, of which a high loss was obtained. A two-element circuit model was proposed to explain the effect of high dc biasing on the dielectric loss.

A study of dynamic characteristics and simulation of MEMS torsional micromirrors

Abstract: A theoretical model of dynamic characteristics of a torsional micromirror, considering the coupled effect of torsion and bending, is present in this paper. The step response and steady harmonic response of the micromirror are analyzed by the Runge–Kutta method. Various nonlinear phenomena are observed using the numerical simulation. When the bias voltage is applied between the micromirror and electrode plate, both the period and amplitude of the response increase as the applied voltage increases. The larger the applied voltage, the further is the shift of the mean dynamic response to the static equilibrium position. When the micromirror is excited by a harmonic voltage, the resonant frequency decreases with increasing the applied voltage and the shift of the mean harmonic steady response is very different from the step response. The mean dynamic response varies with the amplitude and frequency of the exciting voltages. And this model is verified by comparing the analytical results with ANSYS simulation results with reasonable deviations.

Efficiency of body biasing in 90-nm CMOS for low-power digital circuits

Abstract: The efficiency of body biasing for leakage reduction and performance improvement in a 90-nm CMOS low-power technology with triple-well option is evaluated. Static measurements of single devices and dynamic measurements of ring oscillators and 32-b parallel prefix adders are presented. Whereas forward biasing still provides a significant performance improvement of up to 37% for low-leakage devices with 2.2-nm gate oxide thickness, the application of reverse biasing to reduce subthreshold leakage currents is inefficient due to additional leakage currents such as gate leakage and gate-induced drain leakage. Experimental results confirm that, in 90-nm CMOS circuits, the efficiency of body biasing strongly depends on the device type and operating temperature. Moreover, the impact of the zero-temperature coefficient point on static device and dynamic circuit performance is investigated.

Magnetic random access memory with stacked toggle memory cells having oppositely-directed easy-axis biasing

Abstract: A magnetic random access memory (MRAM) has memory stacks arranged in the X-Y plane on the MRAM substrate, with each memory stack having two memory cells stacked along the Z axis and each memory cell having an associated biasing layer. Each biasing layer reduces the switching field of its associated cell by applying a biasing field along the hard-axis of magnetization of the free layer of its associated cell. The free layers in the two cells in each stack have their in-plane easy axes of magnetization aligned parallel to one another. Each biasing layer has its in-plane magnetization direction oriented perpendicular to the easy axis of magnetization (and thus parallel to the hard axis) of the free layer in its associated cell. The hard-axis biasing fields generated by the two biasing layers are in opposite directions.

Communication by radio waves and optical waveguides

Abstract: The invention relates to improvements to full-duplex bi-directional opto-electrical transducers, primarily for use in radio-over-fiber installations, such as remote-antenna installations for cellular radio apparatus. The transducer is of the kind based on an electroabsorption modulator, and the first improvement consists in biasing it by means of a constant-current source rather than conventionally by directly setting a bias voltage. With appropriate selection of the EAM, a preset constant current source is considered adequate, but its setting may be adjusted to operating conditions by a control algorithm if found desirable. A second improvement consists in increasing the effective load impedance of the EAM by using an inductive load that forms a tuned circuit with the internal capacitance of the EAM, resonant at a frequency in the operating range.

A 950 MHz rectifier circuit for sensor networks with 10 m-distance

Abstract: A high-sensitivity rectifier is fabricated in a 0.3 /spl mu/m CMOS technology. The circuit can rectify an RF signal less than the NMOS threshold voltage by using a bias voltage between the gate and the drain terminals of a transistor. The IC achieves a 950 MHz signal rectification over -14 dBm corresponding to 10 m-distance communication and recharges a 1.2 V secondary battery.

Reasons for obtaining an optical dielectric constant from the Poole–Frenkel conduction behavior of atomic-layer-deposited HfO2 films

Abstract: The leakage current characteristics of a 16-nm-thick HfO2 film, grown by atomic-layer-deposition using HfCl4 as Hf precursor and O3 as oxidant, were investigated. The electron injection from the Pt top electrode to the HfO2 films was measured at various temperatures. The measured leakage current versus applied bias voltage curves showed the Poole–Frenkel conduction behavior in the high electric field region. However, the estimated dielectric constant from the Poole–Frenkel fitting corresponds to the dielectric constant of the optical frequency region. The quantum mechanical calculation of the electron transition from the metal electrode to the traps in the HfO2 film showed that the transition time was very short (10−14–10−16s) under the applied field. Therefore, the dielectric response of the HfO2 film to the electron conduction by Poole–Frenkel mechanism must be of the optical frequency under steady state current conduction.

Impact of electron-phonon scattering on the performance of carbon nanotube interconnects for GSI

Abstract: While electron mean-free path in carbon nanotubes can be as large as several micrometers for small bias voltages, for large biases electrons get backscattered by optical and zone-boundary phonons and nanotube resistance can increase by more than 100 times. This letter reveals this kind of backscattering has a small impact (error <25%) in most interconnect applications of carbon nanotubes in which adequate numbers of nanotubes are connected in parallel. This is mainly due to relatively small electric fields along nanotubes when they are used as interconnects. This is in sharp contrast with transistor applications of carbon nanotubes in which transconductance degrades considerably by electron-phonon scatterings unless their channels are made ultrashort (/spl sim/10 nm).

Hydrogen and hydrocarbon gas sensing performance of Pt/WO3/SiC MROSiC devices

Abstract: Pt/WO3/SiC devices based Schottky diodes have been fabricated and their hydrogen and hydrocarbon gas sensing performance investigated. The semiconducting metal oxide WO3 films were 100 nm thick and prepared using r.f. magnetron sputtering. A Pt layer was deposited on the top of the WO3 forming the Schottky diode. The I–V characteristics have been analyzed, from which the change in the barrier height, subject to the introduction of the analyte gas, was calculated. The dynamic properties of these sensors were evaluated at constant biasing currents of 9 and 90 μA, at temperatures between 300 and 700 °C. The results show the sensors have extremely stable baseline, with all responses being repeatable. Voltages shifts in excess of 1 V were observed.

Impedance spectroscopy on organic bulk-heterojunction solar cells

Abstract: We measured the electrical impedance spectra of organic bulk-heterojunction solar cells based on an absorber blend of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester. Comparing the spectra of the non-treated device and after two consecutive treatments with applied forward bias voltage at 110 °C, we observed a region in the semiconductor with a low conductivity, which was expanding after the treatments. We concluded that this region is a depletion region at the aluminium contact. This was confirmed by the bias dependence of the impedance spectra. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nonequilibrium electronic transport of 4,4 ' -bipyridine molecular junction

Abstract: The electronic transport properties of a 4,4'-bipyridine molecule sandwiched between two Au(111) surfaces are studied with a fully self-consistent nonequilibrium Green's-function method combined with the density-functional theory. The 4,4'-bipyridine molecule prefers to adsorb near the hollow site of the Au(111) surface and distorts slightly. The modifications on the electronic structure of the molecule due to the presence of the electrodes are described by the renormalized molecular orbitals, which correspond well to the calculated transmission peaks. The average Fermi level lies close to the lowest unoccupied renormalized molecular orbital, which determines the electronic transport property of the molecular junction under a small bias voltage. The total transmission is contributed by a single channel. The transmission peaks shift with the applied bias voltage, and this behavior depends on the spatial distribution of the renormalized molecular orbitals and the voltage drop along the molecular junction. The shape of the calculated conductance curve of the equilibrium geometric configuration reproduces the main feature of the experimental results, but the value is larger than the measured data by about 6 times. Good agreement with the experimental measurements can be obtained by elongating the molecular junction. The electronic transport behaviors depend strongly on the interface configuration.