Showing papers on "Transistor published in 2009"

Operation of Graphene Transistors at Gigahertz Frequencies

Abstract: Top-gated graphene transistors operating at high frequencies (gigahertz) have been fabricated and their characteristics analyzed. The measured intrinsic current gain shows an ideal 1/f frequency dependence, indicating a FET-like behavior for graphene transistors. The cutoff frequency fT is found to be proportional to the dc transconductance gm of the device, consistent with the relation fT = gm/(2πCG). The peak fT increases with a reduced gate length, and fT as high as 26 GHz is measured for a graphene transistor with a gate length of 150 nm. The work represents a significant step toward the realization of graphene-based electronics for high-frequency applications.

Realization of a High Mobility Dual-gated Graphene Field Effect Transistor with Al2O3 Dielectric

Abstract: We fabricate and characterize dual-gated graphene field-effect transistors (FETs) using Al2O3 as top-gate dielectric. We use a thin Al film as a nucleation layer to enable the atomic layer deposition of Al2O3. Our devices show mobility values of over 8,000 cm2/Vs at room temperature, a finding which indicates that the top-gate stack does not significantly increase the carrier scattering, and consequently degrade the device characteristics. We propose a device model to fit the experimental data using a single mobility value.

Realization of a high mobility dual-gated graphene field-effect transistor with Al2O3 dielectric

Abstract: We fabricate and characterize dual-gated graphene field-effect transistors using Al2O3 as top-gate dielectric. We use a thin Al film as a nucleation layer to enable the atomic layer deposition of Al2O3. Our devices show mobility values of over 8000 cm2/V s at room temperature, a finding which indicates that the top-gate stack does not significantly increase the carrier scattering and consequently degrade the device characteristics. We propose a device model to fit the experimental data using a single mobility value.

Junctionless multigate field-effect transistor

Abstract: This paper describes a metal-oxide-semiconductor MOS transistor concept in which there are no junctions. The channel doping is equal in concentration and type to the source and drain extension doping. The proposed device is a thin and narrow multigate field-effect transistor, which can be fully depleted and turned off by the gate. Since this device has no junctions, it has simpler fabrication process, less variability, and better electrical properties than classical MOS devices with source and drain PN junctions.

Organic Nonvolatile Memory Transistors for Flexible Sensor Arrays

Abstract: Using organic transistors with a floating gate embedded in hybrid dielectrics that comprise a 2-nanometer-thick molecular self-assembled monolayer and a 4-nanometer-thick plasma-grown metal oxide, we have realized nonvolatile memory arrays on flexible plastic substrates. The small thickness of the dielectrics allows very small program and erase voltages (≤6 volts) to produce a large, nonvolatile, reversible threshold-voltage shift. The transistors endure more than 1000 program and erase cycles, which is within two orders of magnitude of silicon-based floating-gate transistors widely employed in flash memory. By integrating a flexible array of organic floating-gate transistors with a pressure-sensitive rubber sheet, we have realized a sensor matrix that detects the spatial distribution of applied mechanical pressure and stores the analog sensor input as a two-dimensional image over long periods of time.

Observation of molecular orbital gating.

Abstract: The ultimate in electronic device miniaturization would be the creation of circuit elements consisting of an individual molecule. A single-molecule transistor exploiting the electrostatic modulation of a molecule's orbital energy is a theoretical possibility. Now Hyunwook Song and colleagues report the successful realization of such a device, a proof of concept that should enhance the practical prospects for molecularly engineered electronics. A longstanding aim in molecular-scale electronics is to create a true transistor analogue in which charge transport through a molecule is directly controlled by external modulation of the molecular orbitals. The observation of such a solid-state molecular device is now reported. The data demonstrate that true molecular transistors can be created, and clear the way for molecularly engineered electronic devices. The control of charge transport in an active electronic device depends intimately on the modulation of the internal charge density by an external node1. For example, a field-effect transistor relies on the gated electrostatic modulation of the channel charge produced by changing the relative position of the conduction and valence bands with respect to the electrodes. In molecular-scale devices2,3,4,5,6,7,8,9,10, a longstanding challenge has been to create a true three-terminal device that operates in this manner (that is, by modifying orbital energy). Here we report the observation of such a solid-state molecular device, in which transport current is directly modulated by an external gate voltage. Resonance-enhanced coupling to the nearest molecular orbital is revealed by electron tunnelling spectroscopy, demonstrating direct molecular orbital gating in an electronic device. Our findings demonstrate that true molecular transistors can be created, and so enhance the prospects for molecularly engineered electronic devices.

Photocurrent imaging and efficient photon detection in a graphene transistor

Abstract: We measure the channel potential of a graphene transistor using a scanning photocurrent imaging technique. We show that at a certain gate bias, the impact of the metal on the channel potential profile extends into the channel for more than one-third of the total channel length from both source and drain sides; hence, most of the channel is affected by the metal. The potential barrier between the metal-controlled graphene and bulk graphene channel is also measured at various gate biases. As the gate bias exceeds the Dirac point voltage, VDirac, the original p-type graphene channel turns into a p-n-p channel. When light is focused on the p-n junctions, an impressive external responsivity of 0.001 A/W is achieved, given that only a single layer of atoms are involved in photon detection.

High‐Density Carrier Accumulation in ZnO Field‐Effect Transistors Gated by Electric Double Layers of Ionic Liquids

Abstract: Very recently, electric-field-induced superconductivity in an insulator was realized by tuning charge carrier to a high density level (1 × 1014 cm−2). To increase the maximum attainable carrier density for electrostatic tuning of electronic states in semiconductor field-effect transistors is a hot issue but a big challenge. Here, ultrahigh density carrier accumulation is reported, in particular at low temperature, in a ZnO field-effect transistor gated by electric double layers of ionic liquid (IL). This transistor, called an electric double layer transistor (EDLT), is found to exhibit very high transconductance and an ultrahigh carrier density in a fast, reversible, and reproducible manner. The room temperature capacitance of EDLTs is found to be as large as 34 µF cm−2, deduced from Hall-effect measurements, and is mainly responsible for the carrier density modulation in a very wide range. Importantly, the IL dielectric, with a supercooling property, is found to have charge-accumulation capability even at low temperatures, reaching an ultrahigh carrier density of 8×1014 cm−2 at 220 K and maintaining a density of 5.5×1014 cm−2 at 1.8 K. This high carrier density of EDLTs is of great importance not only in practical device applications but also in fundamental research; for example, in the search for novel electronic phenomena, such as superconductivity, in oxide systems.

High-performance crosslinked colloidal quantum-dot light-emitting diodes

Abstract: Colloidal quantum-dot light-emitting diodes have recently received considerable attention due to their ease of colour tunability, high brightness and narrow emission bandwidth. Although there have been rapid advances in luminance, efficiency and lifetime, device performance is still limited by the large energy barriers for hole and electron injection into the quantum-dot layer. Here, we show that by crosslinking the colloidal quantum-dot layer, the charge injection barrier in a red-light-emitting quantum-dot light-emitting diode may be considerably reduced by using a sol–gel TiO2 layer for electron transport. The device architecture is compatible with all-solution device fabrication and the resulting device shows a high luminance (12,380 cd m−2), low turn-on voltage (1.9 V) and high power efficiency (2.41 lm W−1). Incorporation of the technology into a display device with an active matrix drive backplane suggests that the approach has promise for use in high-performance, easy-to-fabricate, large-area displays and illumination sources. Bright, efficient and low-drive-voltage colloidal quantum-dot LEDs that have a crosslinked-polymer quantum-dot layer, and use a sol–gel titanium oxide layer for electron transport, are reported. Integrating the QD-LEDs with a silicon thin-film transistor backplane results in a QD-LED display.

Class of High-Efficiency Tuned Switching Power Amplifiers

Abstract: The previous literature on tuned power amplifiers has not made clear the fundamental differences between amplifiers in which the output device acts 1) as a current source, or 2) as a switch. Previous circuits have often operated in contradiction to their design assumptions, resulting in the need for “cut-and-try” design. The new class of amplifiers deseribed here is based on a load network synthesized to hWe a transient response which maximizes power efficiency even if the active device switching times are substantial fractions of the ac cycle. The new class of amplifiers, named “Class E; 1 is defined and is iflustnated by a detailed description and a set of design equations for one simple member of the class. For that circuit the authors measured 96 percent transistor efficiency at 3.9 MHr at 26-W output from a pair of Motorola 2N3735 TO-5 transistors. Advantages of Class E are unusually high efficiency, a priori designability, large reduction in second-breakdown stress, low sensitivityy to activedevice characteristics, and potential for high-efficiency operation at higher frequencies than pI eviously published Class-D circuits. Harmonic output and power gain are comparable to those of conventional amplifiers.

High-Efficiency Differential-Drive CMOS Rectifier for UHF RFIDs

Abstract: A high-efficiency CMOS rectifier circuit for UHF RFIDs was developed. The rectifier has a cross-coupled bridge configuration and is driven by a differential RF input. A differential-drive active gate bias mechanism simultaneously enables both low ON-resistance and small reverse leakage of diode-connected MOS transistors, resulting in large power conversion efficiency (PCE), especially under small RF input power conditions. A test circuit of the proposed differential-drive rectifier was fabricated with 0.18 mu m CMOS technology, and the measured performance was compared with those of other types of rectifiers. Dependence of the PCE on the input RF signal frequency, output loading conditions and transistor sizing was also evaluated. At the single-stage configuration, 67.5% of PCE was achieved under conditions of 953 MHz, - 12.5 dBm RF input and 10 KOmega output load. This is twice as large as that of the state-of-the-art rectifier circuit. The peak PCE increases with a decrease in operation frequency and with an increase in output load resistance. In addition, experimental results show the existence of an optimum transistor size in accordance with the output loading conditions. The multi-stage configuration for larger output DC voltage is also presented.

Semiconducting Thienothiophene Copolymers: Design, Synthesis, Morphology, and Performance in Thin‐Film Organic Transistors

Abstract: Organic semiconductors are emerging as a viable alternative to amorphous silicon in a range of thin-film transistor devices. With the possibility to formulate these p-type materials as inks and subsequently print into patterned devices, organic-based transistors offer significant commercial advantages for manufacture, with initial applications such as low performance displays and simple logic being envisaged. Previous limitations of both air stability and electrical performance are now being overcome with a range of both small molecule and polymer-based solution-processable materials, which achieve charge carrier mobilities in excess of 0.5 cm 2 V -1 s -1 , a benchmark value for amorphous silicon semiconductors. Polymer semiconductors based on thienothiophene copolymers have achieved amongst the highest charge carrier mobilities in solution-processed transistor devices. In this Progress Report, we evaluate the advances and limitations of this class of polymer in transistor devices.

Graphene Frequency Multipliers

Abstract: In this letter, the ambipolar transport properties of graphene flakes have been used to fabricate full-wave signal rectifiers and frequency-doubling devices. By correctly biasing an ambipolar graphene field-effect transistor in common-source configuration, a sinusoidal voltage applied to the transistor gate is rectified at the drain electrode. Using this concept, frequency multiplication of a 10-kHz input signal has been experimentally demonstrated. The spectral purity of the 20-kHz output signal is excellent, with more than 90% of the radio-frequency power in the 20-kHz frequency. This high efficiency, combined with the high electron mobility of graphene, makes graphene-based frequency multipliers a very promising option for signal generation at ultrahigh frequencies.

Thin-film transistor

Abstract: A gate-insulated thin film transistor is disclosed. One improvement is that the thin film transistor is formed on a substrate through a blocking layer in between so that it is possible to prevent the transistor from being contaminated with impurities such as alkali ions which exist in the substrate. Also, a halogen is added to either or both of the blocking layer and a gate insulator of the transistor in order that impurities such as alkaline ions, dangling bonds and the like can be neutralized, therefore, the reliability of the device is improved.

Multifunctional CuO nanowire devices: P-type field effect transistors and CO gas sensors

Abstract: We report the properties of a field effect transistor (FET) and a gas sensor based on CuO nanowires. CuO nanowire FETs exhibit p-type behavior. Large-scale p-type CuO nanowire thin-film transistors (104 devices in a 25?mm2 area) are fabricated and we effectively demonstrate their enhanced performance. Furthermore, CuO nanowire exhibits high and fast response to CO gas at 200??C, which makes it a promising candidate for a poisonous gas sensing nanodevice.

High Speed, High Stability and Low Power Sensing Amplifier for MTJ/CMOS Hybrid Logic Circuits

Abstract: Densely embedding Magnetic Tunnel Junctions (MTJ) in CMOS logic circuits is considered as one potentially powerful solution to bring non volatility, instant on/off and low standby power in today's programmable logic circuits, in order to overcome major drawbacks while preserving high operation speed. A critical issue in this process is the integration of MTJ electric signal to CMOS electronics, in particular the requirement of ldquozerordquo read/write error for logic applications. In this paper, we propose a new sense amplifier circuit, called Pre-Charge Sense Amplifier (PCSA). This circuit, comprising 7 CMOS transistors at minimum size, is able to read the magnetic configuration of a pair of magnetic tunnel junctions with opposite configurations at high speed (about 200 ps), with very low power and error rate compared to previously proposed solutions. Simulations using a ST Microelectronics 90 nm design kit and a compact model of MTJ demonstrate the performances of PCSA.

A single-molecule optical transistor

Abstract: Quantum information processing systems and related technologies are likely to involve switching and amplification functions in ultrasmall objects such as nanotubes. In today's electronic devices the transistor performs these functions. A 'quantum age' equivalent of the conventional transistor would, ideally, use photons rather than electrons as information carriers because of their speed and robustness against decoherence. But robustness also stops them being easily controlled. Now a team from optETH and ETH in Zurich demonstrates the realization of a single-molecule optical transistor. In it, a single dye molecule coherently attenuates or amplifies a tightly focused laser beam, depending on the power of a second 'gating' beam. The transistor is the most fundamental building block in present-day technologies. For the purpose of quantum information processing schemes and for the development of a 'quantum computer', photons are attractive information carriers because of their speed and robustness against decoherence. However, their robustness also prevents them from being easily controlled; despite this, experiments now show the realization of a quantum optical transistor. The transistor is one of the most influential inventions of modern times and is ubiquitous in present-day technologies. In the continuing development of increasingly powerful computers as well as alternative technologies based on the prospects of quantum information processing, switching and amplification functionalities are being sought in ultrasmall objects, such as nanotubes, molecules or atoms1,2,3,4,5,6,7,8,9. Among the possible choices of signal carriers, photons are particularly attractive because of their robustness against decoherence, but their control at the nanometre scale poses a significant challenge as conventional nonlinear materials become ineffective. To remedy this shortcoming, resonances in optical emitters can be exploited, and atomic ensembles have been successfully used to mediate weak light beams7. However, single-emitter manipulation of photonic signals has remained elusive and has only been studied in high-finesse microcavities10,11,12,13 or waveguides8,14. Here we demonstrate that a single dye molecule can operate as an optical transistor and coherently attenuate or amplify a tightly focused laser beam, depending on the power of a second ‘gating’ beam that controls the degree of population inversion. Such a quantum optical transistor has also the potential for manipulating non-classical light fields down to the single-photon level. We discuss some of the hurdles along the road towards practical implementations, and their possible solutions.

High Electron Mobility in Vacuum and Ambient for PDIF-CN2 Single-Crystal Transistors

Abstract: Single-crystal field-effect transistors (FETs) based on a fluorocarbon-substituted dicyanoperylene-3,4:9,10-bis(dicarboximide) [PDIF-CN2] were fabricated by lamination of the semiconductor crystal on Si-SiO2/PMMA-Au gate-dielectric-contact substrates. These devices were characterized both in vacuum and in the air, and they exhibit electron mobilities of ca. 6−3 and ca. 3−1 cm2 V−1 s−1, respectively, Ion:Ioff > 103, and near-zero threshold voltage.

Carbon-Based Field-Effect Transistors for Nanoelectronics

Abstract: In this review, the suitability of the major types of carbon nanostructures as conducting channels of field-effect transistors (FETs) is compared on the basis of the dimensionality and size of their π-conjugated system. For each of these materials, recent progress in its synthesis, electrical and structural characterization, as well as its implementation into various gate configurations is surveyed, with emphasis laid onto nanoscale aspects of the FET design and the attainable device performance. Finally, promising future research directions, such as the integration of different carbon nanostructures into novel device architectures, are outlined.

Field Effect Transistors for Terahertz Detection: Physics and First Imaging Applications

Abstract: Resonant frequencies of the two-dimensional plasma in FETs increase with the reduction of the channel dimensions and can reach the THz range for sub-micron gate lengths. Nonlinear properties of the electron plasma in the transistor channel can be used for the detection and mixing of THz frequencies. At cryogenic temperatures resonant and gate voltage tunable detection related to plasma waves resonances is observed. At room temperature, when plasma oscillations are overdamped, the FET can operate as an efficient broadband THz detector. We present the main theoretical and experimental results on THz detection by FETs in the context of their possible application for THz imaging.

Two-dimensional numerical simulation of radio frequency sputter amorphous In–Ga–Zn–O thin-film transistors

Abstract: We reported on a two-dimensional simulation of electrical properties of the radio frequency (rf) sputter amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs). The a-IGZO TFT used in this work has the following performance: field-effect mobility (μeff) of ∼12 cm2/V s, threshold voltage (Vth) of ∼1.15 V, subthreshold swing (S) of ∼0.13 V/dec, and on/off ratio over 1010. To accurately simulate the measured transistor electrical properties, the density-of-states model is developed. The donorlike states are also proposed to be associated with the oxygen vacancy in a-IGZO. The experimental and calculated results show that the rf sputter a-IGZO TFT has a very sharp conduction band-tail slope distribution (Ea=13 meV) and Ti ohmic-like source/drain contacts with a specific contact resistance lower than 2.7×10−3 Ω cm2.

Bilayer PseudoSpin Field-Effect Transistor (BiSFET): A Proposed New Logic Device

Abstract: We propose a new type of graphene-based transistor intended to allow lower voltage, lower power operation than possible with complementary metal-oxide-semiconductor (CMOS) field-effect transistors. Increased energy efficiency is not only important for its own sake, but is also necessary to allow continued device scaling and the resulting increase in computational power in CMOS-like logic circuits. We describe the basic device structure and physics and predicted current-voltage characteristics. Advantages over CMOS in terms of lower voltage and power are discussed.

Low-Temperature-Grown Transition Metal Oxide Based Storage Materials and Oxide Transistors for High-Density Non-volatile Memory

Abstract: An effective stacked memory concept utilizing all-oxide-based device components for future high-density nonvolatile stacked structure data storage is developed. GaInZnO (GIZO) thin-film transistors, grown at room temperature, are integrated with one-diode (CuO/InZnO)–one-resistor (NiO) (1D–1R) structure oxide storage node elements, fabricated at room temperature. The low growth temperatures and fabrication methods introduced in this paper allow the demonstration of a stackable memory array as well as integrated device characteristics. Benefits provided by low-temperature processes are demonstrated by fabrication of working devices over glass substrates. Here, the device characteristics of each individual component as well as the characteristics of a combined select transistor with a 1D–1R cell are reported. X-ray photoelectron spectroscopy analysis of a NiO resistance layer deposited by sputter and atomic layer deposition confirms the importance of metallic Ni content in NiO for bi-stable resistance switching. The GIZO transistor shows a field-effect mobility of 30 cm2 V−1 s−1, a Vth of +1.2 V, and a drain current on/off ratio of up to 108, while the CuO/InZnO heterojunction oxide diode has forward current densities of 2 × 104 A cm−2. Both of these materials show the performance of state-of-the-art oxide devices.

Semiconductor signal processing device

Abstract: A unit operator cell includes a plurality of SOI (Silicon on Insulator) transistors, write data is stored in a body region of at least two SOI transistors, and the storage SOI transistors are connected in series with each other to a read port or each of the storage SOI transistors is singly connected to the read port. Therefore, an AND operation result or a NOT operation result of data stored in the unit operator cells can be obtained, and operation processing can be performed only by writing and reading data. A semiconductor signal processing device that can perform logic operation processing and arithmetic operation processing at high speed is implemented with low power consumption and a small occupation area.

Precursor Parameter Identification for Insulated Gate Bipolar Transistor (IGBT) Prognostics

Abstract: Precursor parameters have been identified to enable development of a prognostic approach for insulated gate bipolar transistors (IGBT). The IGBT were subjected to thermal overstress tests using a transistor test board until device latch-up. The collector-emitter current, transistor case temperature, transient and steady state gate voltages, and transient and steady state collector-emitter voltages were monitored in-situ during the test. Pre- and post-aging characterization tests were performed on the IGBT. The aged parts were observed to have shifts in capacitance-voltage (C-V) measurements as a result of trapped charge in the gate oxide. The collector-emitter ON voltage VCE(ON) showed a reduction with aging. The reduction in the VCE(ON) was found to be correlated to die attach degradation, as observed by scanning acoustic microscopy (SAM) analysis. The collector-emitter voltage, and transistor turn-off time were observed to be precursor parameters to latch-up. The monitoring of these precursor parameters will enable the development of a prognostic methodology for IGBT failure. The prognostic methodology will involve trending precursor data, and using physics of failure models for prediction of the remaining useful life of these devices.

On Enhanced Miller Capacitance Effect in Interband Tunnel Transistors

Abstract: We compare the transient response of double-gate thin-body-silicon interband tunnel field-effect transistor (TFET) with its metal-oxide-semiconductor field-effect transistor counterpart. Due to the presence of source side tunneling barrier, the silicon TFETs exhibit enhanced Miller capacitance, resulting in large voltage overshoot/undershoot in its large-signal switching characteristics. This adversely impacts the performance of Si TFETs for digital logic applications. It is shown that TFETs based on lower bandgap and lower density of states materials like indium arsenide show significant improvement in switching behavior due to its lower capacitance and higher ON current at reduced voltages.

Semiconductor Device Portion Having Sub-Wavelength-Sized Gate Electrode Conductive Structures Formed from Rectangular Shaped Gate Electrode Layout Features and Having Equal Number of PMOS and NMOS Transistors

Abstract: A semiconductor device is disclosed as having a substrate portion that includes a plurality of diffusion regions that include at least one p-type diffusion region and at least one n-type diffusion region. A gate electrode level region is formed above the substrate portion to include a number of conductive features defined to extend in only a first parallel direction. Each of the conductive features within the gate electrode level region is fabricated from a respective originating rectangular-shaped layout feature. Each of the conductive features within the gate electrode level region has a width less than a wavelength of light used in a photolithography process to fabricate the conductive features. Conductive features within the gate electrode level region form respective PMOS transistor devices and respective NMOS transistor devices. A number of the PMOS transistor devices is equal to a number of the NMOS transistor devices in the gate electrode level region.

CMOS-Analogous Wafer-Scale Nanotube-on-Insulator Approach for Submicrometer Devices and Integrated Circuits Using Aligned Nanotubes

Abstract: Massive aligned carbon nanotubes hold great potential but also face significant integration/assembly challenges for future beyond-silicon nanoelectronics. We report a wafer-scale processing of aligned nanotube devices and integrated circuits, including progress on essential technological components such as wafer-scale synthesis of aligned nanotubes, wafer-scale transfer of nanotubes to silicon wafers, metallic nanotube removal and chemical doping, and defect-tolerant integrated nanotube circuits. We have achieved synthesis of massive aligned nanotubes on complete 4 in. quartz and sapphire substrates, which were then transferred to 4 in. Si/SiO2 wafers. CMOS analogous fabrication was performed to yield transistors and circuits with features down to 0.5 μm, with high current density ∼20 μA/μm and good on/off ratios. In addition, chemical doping has been used to build fully integrated complementary inverter with a gain ∼5, and a defect-tolerant design has been employed for NAND and NOR gates. This full-wafer...