Showing papers on "Field-effect transistor published in 2007"

Tunneling Field-Effect Transistors (TFETs) With Subthreshold Swing (SS) Less Than 60 mV/dec

Abstract: We have demonstrated a 70-nm n-channel tunneling field-effect transistor (TFET) which has a subthreshold swing (SS) of 52.8 mV/dec at room temperature. It is the first experimental result that shows a sub-60-mV/dec SS in the silicon-based TFETs. Based on simulation results, the gate oxide and silicon-on-insulator layer thicknesses were scaled down to 2 and 70 nm, respectively. However, the ON/ OFF current ratio of the TFET was still lower than that of the MOSFET. In order to increase the on current further, the following approaches can be considered: reduction of effective gate oxide thickness, increase in the steepness of the gradient of the source to channel doping profile, and utilization of a lower bandgap channel material

Graphene nano-ribbon electronics

Abstract: We have fabricated graphene nano-ribbon field-effect transistor devices and investigated their electrical properties as a function of ribbon width. Our experiments show that the resistivity of a ribbon increases as its width decreases, indicating the impact of edge states. Analysis of temperature-dependent measurements suggests a finite quantum confinement gap opening in narrow ribbons. The electrical current noise of the graphene ribbon devices at low frequency is found to be dominated by the 1/f noise.

Double-Gate Tunnel FET With High- $\kappa$ Gate Dielectric

Abstract: In this paper, we propose and validate a novel design for a double-gate tunnel field-effect transistor (DG tunnel FET), for which the simulations show significant improvements compared with single-gate devices using a gate dielectric. For the first time, DG tunnel FET devices, which are using a high-gate dielectric, are explored using realistic design parameters, showing an on-current as high as 0.23 mA for a gate voltage of 1.8 V, an off-current of less than 1 fA (neglecting gate leakage), an improved average subthreshold swing of 57 mV/dec, and a minimum point slope of 11 mV/dec. The 2D nature of tunnel FET current flow is studied, demonstrating that the current is not confined to a channel at the gate-dielectric surface. When varying temperature, tunnel FETs with a high-kappa gate dielectric have a smaller threshold voltage shift than those using SiO2, while the subthreshold slope for fixed values of Vg remains nearly unchanged, in contrast with the traditional MOSFET. Moreover, an Ion/Ioff ratio of more than 2 times 1011 is shown for simulated devices with a gate length (over the intrinsic region) of 50 nm, which indicates that the tunnel FET is a promising candidate to achieve better-than-ITRS low-standby-power switch performance.

Structure with transistor

Abstract: A structure with a transistor is disclosed comprising a substrate, a gas barrier layer on the substrate, and a transistor on the gas barrier layer. The transistor can include an oxide semiconductor layer. The oxide semiconductor layers can comprise In—Ga—Zn—O. A display, such as a liquid crystal display, can have such a structure.

Gate Injection Transistor (GIT)—A Normally-Off AlGaN/GaN Power Transistor Using Conductivity Modulation

Abstract: We have developed a normally-off GaN-based transistor using conductivity modulation, which we call a gate injection transistor (GIT). This new device principle utilizes hole-injection from the p-AlGaN to the AlGaN/GaN heterojunction, which simultaneously increases the electron density in the channel, resulting in a dramatic increase of the drain current owing to the conductivity modulation. The fabricated GIT exhibits a threshold voltage of 1.0 V with a maximum drain current of 200 mA/mm, in which a forward gate voltage of up to 6 V can be applied. The obtained specific ON-state resistance (RON . A) and the OFF-state breakdown voltage (BV ds) are 2.6 mOmega . cm2 and 800 V, respectively. The developed GIT is advantageous for power switching applications.

Importance of the Debye screening length on nanowire field effect transistor sensors.

Abstract: Nanowire field effect transistors (NW-FETs) can serve as ultrasensitive detectors for label-free reagents. The NW-FET sensing mechanism assumes a controlled modification in the local channel electric field created by the binding of charged molecules to the nanowire surface. Careful control of the solution Debye length is critical for unambiguous selective detection of macromolecules. Here we show the appropriate conditions under which the selective binding of macromolecules is accurately sensed with NW-FET sensors.

A Compact SPICE Model for Carbon-Nanotube Field-Effect Transistors Including Nonidealities and Its Application—Part II: Full Device Model and Circuit Performance Benchmarking

Abstract: This paper presents a complete circuit-compatible compact model for single-walled carbon-nanotube field-effect transistors (CNFETs) as an extension to Part 1 of this two-part paper. For the first time, a universal circuit-compatible CNFET model including the practical device nonidealities is implemented with HSPICE. In addition to the nonidealities included in the companion paper, this paper includes the elastic scattering in the channel region, the resistive source/drain (S/D), the Schottky-barrier resistance, and the parasitic gate capacitances. More than one nanotube per device can be modeled. Compared to silicon technology, the CNFETs show much better device performance based on the intrinsic gate-delay metric (six times for nFET and 14 times for pFET) than the MOSFET device at the 32-nm node, even with device nonidealities. This large speed improvement is significantly degraded (by a factor of five to eight) by interconnect capacitance in a real circuit environment. We performed circuit-performance comparison with all the standard digital library cells between CMOS random logic and CNFET random logic with HSPICE simulation. Compared to CMOS circuits, the CNFET circuits with one to ten carbon nanotubes per device is about two to ten times faster, the energy consumption per cycle is about seven to two times lower, and the energy-delay product is about 15-20 times lower, considering the realistic layout pattern and the interconnect wiring capacitance.

Layer-by-layer assembly of nanowires for three-dimensional, multifunctional electronics.

Abstract: We report a general approach for three-dimensional (3D) multifunctional electronics based on the layer-by-layer assembly of nanowire (NW) building blocks. Using germanium/silicon (Ge/Si) core/shell NWs as a representative example, ten vertically stacked layers of multi-NW field-effect transistors (FETs) were fabricated. Transport measurements demonstrate that the Ge/Si NW FETs have reproducible high-performance device characteristics within a given device layer, that the FET characteristics are not affected by sequential stacking, and importantly, that uniform performance is achieved in sequential layers 1 through 10 of the 3D structure. Five-layer single-NW FET structures were also prepared by printing Ge/Si NWs from lower density growth substrates, and transport measurements showed similar high-performance characteristics for the FETs in layers 1 and 5. In addition, 3D multifunctional circuitry was demonstrated on plastic substrates with sequential layers of inverter logical gates and floating gate memory elements. Notably, electrical characterization studies show stable writing and erasing of the NW floating gate memory elements and demonstrate signal inversion with larger than unity gain for frequencies up to at least 50 MHz. The ability to assemble reproducibly sequential layers of distinct types of NW-based devices coupled with the breadth of NW building blocks should enable the assembly of increasing complex multilayer and multifunctional 3D electronics in the future.

Intrinsic Current−Voltage Characteristics of Graphene Nanoribbon Transistors and Effect of Edge Doping

Abstract: We demonstrate that the electronic devices built on patterned graphene nanoribbons (GNRs) can be made with atomic-perfect-interface junctions and controlled doping via manipulation of edge terminations. Using first-principles transport calculations, we show that the GNR field effect transistors can achieve high performance levels similar to those made from single-walled carbon nanotubes, with ON/OFF ratios on the order of 103−104, subthreshold swing of 60 meV per decade, and transconductance of 9.5 × 103 Sm-1.

Fabrication of fully transparent nanowire transistors for transparent and flexible electronics

Abstract: The development of optically transparent and mechanically flexible electronic circuitry is an essential step in the effort to develop next-generation display technologies, including 'see-through' and conformable products. Nanowire transistors (NWTs) are of particular interest for future display devices because of their high carrier mobilities compared with bulk or thin-film transistors made from the same materials, the prospect of processing at low temperatures compatible with plastic substrates, as well as their optical transparency and inherent mechanical flexibility. Here we report fully transparent In(2)O(3) and ZnO NWTs fabricated on both glass and flexible plastic substrates, exhibiting high-performance n-type transistor characteristics with approximately 82% optical transparency. These NWTs should be attractive as pixel-switching and driving transistors in active-matrix organic light-emitting diode (AMOLED) displays. The transparency of the entire pixel area should significantly enhance aperture ratio efficiency in active-matrix arrays and thus substantially decrease power consumption.

A dielectric-modulated field-effect transistor for biosensing

Abstract: Interest in biosensors based on field-effect transistors (FETs), where an electrically operated gate controls the flow of charge through a semiconducting channel, is driven by the prospect of integrating biodetection capabilities into existing semiconductor technology. In a number of proposed FET biosensors, surface interactions with biomolecules in solution affect the operation of the gate or the channel. However, these devices often have limited sensitivity. We show here that a FET biosensor with a vertical gap is sensitive to the specific binding of streptavidin to biotin. The binding of the streptavidin changes the dielectric constant (and capacitance) of the gate, resulting in a large shift in the threshold voltage for operating the FET. The vertical gap is fabricated using simple thin-film deposition and wet-etching techniques. This may be an advantage over planar nanogap FETs, which require lithographic processing. We believe that the dielectric-modulated FET (DMFET) provides a useful approach towards biomolecular detection that could be extended to a number of other systems.

Perylenediimide nanowires and their use in fabricating field-effect transistors and complementary inverters.

Abstract: Perylenetetracarboxyldiimide (PTCDI) nanowires self-assembled from commercially available materials are demonstrated as the n-channel semiconductor in organic field-effect transistors (OFETs) and as a building block in high-performance complementary inverters. Devices based on a network of PTCDI nanowires have electron mobilities and current on/off ratios on the order of 10-2 cm2/Vs and 104, respectively. Complementary inverters based on n-channel PTCDI nanowire transistors and p-channel hexathiapentacene (HTP) nanowire OFETs achieved gains as high as 8. These results demonstrate the first example of the use of one-dimensional organic semiconductors in complementary inverters.

Tunnel field-effect transistor without gate-drain overlap

Abstract: Tunnel field-effect transistors are promising successors of metal-oxide-semiconductor field-effect transistors because of the absence of short-channel effects and of a subthreshold-slope limit. However, the tunnel devices are ambipolar and, depending on device material properties, they may have low on-currents resulting in low switching speed. The authors have generalized the tunnel field-effect transistor configuration by allowing a shorter gate structure. The proposed device is especially attractive for vertical nanowire-based transistors. As illustrated with device simulations, the authors’ more flexible configuration allows of the reduction of ambipolar behavior, the increase of switching speed, and the decrease of processing complexity.

From One- to Three-Dimensional Organic Semiconductors: In Search of the Organic Silicon?

Abstract: Organic semiconductors based on π-conjugated systems are the focus of considerable interest in the emerging area of soft or flexible photonics and electronics. Whereas in recent years the performances of devices such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), or solar cells have undergone considerable progress, a number of technical and fundamental problems related to the low dimensionality of organic semiconductors based on linear π-conjugated systems remain unsatisfactorily resolved. This low dimensionality results in an anisotropy of the optical and charge-transport properties, which in turn implies a control of the material organization/molecular orientation during or after device fabrication. Such a constraint evidently represents a problem when device fabrication by solution-based processes, such as printing techniques, is envisioned. The aim of this short Review is to illustrate possible alternative strategies based on the development of organic semiconductors with higher dimensionality, capable to exhibit isotropic electronic properties.

Simulation of Graphene Nanoribbon Field-Effect Transistors

Abstract: We present an atomistic 3-D simulation of graphene nanoribbon field-effect transistors (GNR-FETs), based on the self consistent solution of the 3-D Poisson and Schrodinger equations with open boundary conditions within the nonequilibrium Green's function formalism and a tight-binding Hamiltonian. With respect to carbon nanotube FETs, GNR-FETs exhibit comparable performance, reduced sensitivity to the variability of channel chirality, and similar leakage problems due to band-to-band tunneling. Acceptable transistor performance requires prohibitive effective nanoribbon width of 1-2 nm and atomistic precision that could in principle be obtained with periodic etch patterns or stress patterns.

Interface‐Controlled, High‐Mobility Organic Transistors

Abstract: The achievement of high mobilities in field-effect transistors (FETs) is one of the main challenges for the widespread application of organic conductors in devices. Good device performance of a single-crystal pentacene FET requires both removal of impurity molecules from the bulk and the manipulation of interface states. A reliable method for fabricating FETs, which involves careful control of the semiconductor/gate interface (see figure), is presented.

Light sensitive display

Abstract: A liquid crystal device includes a front electrode layer, a rear electrode layer, and a liquid crystal material located between the front electrode layer and the rear electrode layer. A first and second transistor each includes three terminals. The first transistor is a photo transistor. The first terminal of the first transistor electrically interconnected to a conductive electrode free from additional electrical elements therebetween. The second terminal of the first transistor is electrically interconnected to the conductive electrode free from additional electrical elements therebetween and the second terminal of the first transistor is maintained at the same potential as the conductive electrode. The first terminal of the first transistor and the second terminal of the first transistor electrically interconnected to one another free from additional electrical elements therebetween and the first terminal of the first transistor and the second terminal of the first transistor are maintained at the same potential. The second terminal of the first transistor is a gate of the first transistor. The third terminal of the first transistor electrically interconnected to the first terminal of the second transistor free from additional electrical elements therebetween and maintained at the same potential. The second transistor provides a readout function for the circuit. The second terminal of the second transistor electrically connected to one of the select electrodes. The second terminal of the second transistor is a gate of the second transistor. The third terminal of the second transistor is electrically interconnected to a readout system. The second transistor is substantially inhibited from receiving ambient light thereon. The first transistor is not substantially inhibited from receiving ambient light thereon. The first transistor and the second transistor being together with the rear electrode layer. The readout system determines a region of the device that experiences a change in the light level impinging on the device.

Organic Light Emitting Field Effect Transistors: Advances and Perspectives†

Abstract: Light emitting field effect transistors based on molecular and polymeric organic semiconductors are multifunctional devices that integrate light emission with the current modulating function of a transistor. The planar geometry of organic light emitting field effect transistors (OLEFETs) offers direct access to the light emission region, providing a unique experimental configuration to investigate fundamental optical and electronic properties in organic semiconductors. OLEFETs show great potential for technological applications such as active matrix full color electroluminescent displays. In this Feature Article we review advances in OLEFETs since their first demonstration in 2003 and we highlight exciting challenges associated with their future development.

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.

Fin Field-Effect Transistors

Abstract: A fin field-effect transistor (finFET) with improved source/drain regions is provided. In an embodiment, the source/drain regions of the fin are removed while spacers adjacent to the fin remain. An angled implant is used to implant the source/drain regions near a gate electrode, thereby allowing for a more uniform lightly doped drain. The fin may be re-formed by either epitaxial growth or a metallization process. In another embodiment, the spacers adjacent the fin in the source/drain regions are removed and the fin is silicided along the sides and the top of the fin. In yet another embodiment, the fin and the spacers are removed in the source/drain regions. The fins are then re-formed via an epitaxial growth process or a metallization process. Combinations of these embodiments may also be used.

Length scaling of the Double Gate Tunnel FET with a high-K gate dielectric

Abstract: In this paper, the length scaling of the silicon Double Gate Tunnel Field Effect Transistor (DG Tunnel FET) is studied. It is found that scaling limits are reached sooner by Tunnel FETs with an SiO 2 gate dielectric, while those with a high-K dielectric can be scaled further before threshold voltage, and average and point subthreshold swing are affected. It is demonstrated that the scaling of the high-K Tunnel FET is completely different than that of conventional MOS transistors. An outstanding feature of the Tunnel FET switch is that length scaling has a much weaker impact on device characteristics than does gate control (e.g. the use of a high-K dielectric), which primarily dictates the tunneling barrier width and consequently, device conduction. This paper demonstrates that while some improvements are observed, the length scaling does not dramatically affect switch figures of merit such as subthreshold slope, Ion and I off down to about 20 nm, and an optimized device design can be extended over a much larger window of sub-micron dimensions, compared to the MOSFET. A discussion of the length dependence of the transconductance, g m , and output conductance, g ds of the Tunnel FET is presented for the first time.

Performance Projections for Ballistic Graphene Nanoribbon Field-Effect Transistors

Abstract: The upper limit performance potential of ballistic carbon nanoribbon MOSFETs (CNR MOSFETs) is examined. Calculation of the bandstructure of nanoribbons using a single pz-orbital tight-binding method and evaluation of the current-voltage characteristics of a nanoribbon MOSFET were used in a semiclassical ballistic model. The authors find that semiconducting ribbons a few nanometers in width behave electronically in a manner similar to carbon nanotubes, achieving similar ON-current performance. The calculations show that semiconducting CNR transistors can be candidates for high-mobility digital switches, with the potential to outperform the silicon MOSFET. Although wide ribbons have small bandgaps, which would increase subthreshold leakage due to band to band tunneling, their ON-current capabilities could still be attractive for certain applications

Polymer electrolyte-gated organic field-effect transistors: low-voltage, high-current switches for organic electronics and testbeds for probing electrical transport at high charge carrier density.

Abstract: We report the fabrication and extensive characterization of solid polymer electrolyte-gated organic field-effect transistors (PEG-FETs) in which a polyethylene oxide (PEO) film containing a dissolved Li salt is used to modulate the hole conductivity of a polymer semiconductor. The large capacitance (approximately 10 microF/cm2) of the solution-processed polymer electrolyte gate dielectric facilitates polymer semiconductor conductivities on the order of 103 S/cm at low gate voltages ( 3 cm2/V.s. PEG-FETs fabricated with gate electrodes either aligned or intentionally nonaligned to the channel exhibited dramatically different electrical behavior when tested in vacuum or in air. Large differences in ionic diffusivity can explain the dominance of either electrostatic charging (in vacuum) or bulk electrochemical doping (in air) as the device operational mechanism. The use of a larger anion in the polymer electrolyte, bis(trifluoromethanesulfonyl)imide (TFSI-), yielded transistors that showed clear current saturation and square law behavior in the output characteristics, which also points to electrostatic (field-effect) charging. In addition, negative transconductances were observed using the PEO/LiTFSI electrolyte for all three polymer semiconductors at gate voltages larger than -3 V. Bias stress measurements performed with PEO/LiTFSI-gated bottom contact PEG-FETs showed that polymer semiconductors can sustain high ON currents for greater than 10 min without large losses in conductance. Collectively, the results indicate that PEG-FETs may serve as useful devices for high-current/low-voltage applications and as testbeds for probing electrical transport in polymer semiconductors at high charge density.

Gate-defined quantum dots in intrinsic silicon.

Abstract: We report the fabrication and measurement of silicon quantum dots with tunable tunnel barriers in a narrow-channel field-effect transistor. Low-temperature transport spectroscopy is performed in both the many-electron (∼100 electrons) regime and the few-electron (∼10 electrons) regime. Excited states in the bias spectroscopy provide evidence of quantum confinement. These results demonstrate that depletion gates are an effective technique for defining quantum dots in silicon.

Fabrication of Field-Effect Transistors from Hexathiapentacene Single-Crystal Nanowires

Abstract: This paper describes a simple, solution-phase route to the synthesis of bulk quantities of hexathiapentacene (HTP) single-crystal nanowires. These nanowires have also been successfully incorporated as the semiconducting material in field-effect transistors (FETs). For devices based on single nanowires, the carrier mobilities and current on/off ratios could be as high as 0.27 cm2/Vs and >103, respectively. For transistors fabricated from a network of nanowires, the mobilities and current on/off ratios could reach 0.057 cm2/Vs and >104, respectively. We have further demonstrated the use of nanowire networks in fabricating transistors on mechanically flexible substrates. Preliminary results show that these devices could withstand mechanical strain and still remain functional. The results from this study demonstrate the potential of utilizing solution-dispersible, nanostructured organic materials for use in low-cost, flexible electronic applications.

Analysis of the contact resistance in staggered, top-gate organic field-effect transistors

Abstract: Contact resistance effects are significant in many organic field-effect transistors. Here, we present a detailed analysis of the contact resistance in staggered, top-gate conjugated polymer field-effect transistors. A compact physical model based on the current crowding formalism has been developed. It includes gate modulation of the bulk resistivity of the semiconductor to explain the experimentally observed gate voltage dependence of the contact resistance for different thicknesses of the semiconducting film. The contact resistance is found to be Ohmic. For thick semiconducting films, we have observed a significant asymmetry between source and drain contact resistances with the drain resistances increasing more rapidly with thickness than the source resistance, reflecting the importance of diffusion at the drain contact.

Cyanonaphthalene diimide semiconductors for air-stable, flexible, and optically transparent n-channel field-effect transistors

Abstract: Core-cyanated naphthalene diimide organic semiconductors were synthesized for use in field-effect transistors. The unusual combination of wide band gap and high mobility in these materials enables the fabrication of the first flexible, air-stable n-type organic transistors with a transparent channel on conventional overhead transparency film or on ITO/glass substrates.