For Field-effect Transistors Research Articles

Modeling of Gan Hemt by Using an Improved K-Nearest Neighbors Algorithm

A novel black-box modeling method for field effect transistor (FET) based on an improved K-Nearest Neighbors algorithm is proposed in this paper. K-Nearest Neighbors algorithm, which has simple algorithm structure and high accuracy, has shown great potential in regression application. A Taylor series expansion method is employed in nonlinear elements modeling of FET to improve the physical meaning of black-box model. A GaN HEMT power device is used to demonstrate the proposed method. And the experimentation shows that the calculated results using improved K-Nearest Neighbors algorithm based model fit the measurement results well.

A Nonvolatile Memory Device Made of a Ferroelectric Polymer Gate Nanodot and a Single-Walled Carbon Nanotube

We demonstrate a field-effect nonvolatile memory device made of a ferroelectric copolymer gate nanodot and a single-walled carbon nanotube (SW-CNT). A position-controlled dip-pen nanolithography was performed to deposit a poly(vinylidene fluoride-ran-trifluoroethylene) (PVDF-TrFE) nanodot onto the SW-CNT channel with both a source and drain for field-effect transistor (FET) function. PVDF-TrFE was chosen as a gate dielectric nanodot in order to efficiently exploit its bipolar chemical nature. A piezoelectric force microscopy study confirmed the canonical ferroelectric responses of the PVDF-TrFE nanodot fabricated at the center of the SW-CNT channel. The two distinct ferroelectric polarization states with the stable current retention and fatigue-resistant characteristics make the present PVDF-TrFE-based FET suitable for nonvolatile memory applications.

(Invited) Graphene FETs: Promises and Challenges

We present a critical review of graphene for field-effect transistor (FET) application. By using graphene sheet as the channel material, the new FET is expected offer significant advantages in certain aspects over and above that of the present Si-based counterpart. There are many challenges as well since the overall operating principle of the FET channel is different. We present our perspective with regard to these challenges. And we also demonstrate the ability of synthesizing monolayer graphene on Cu foils and placing it on insulator surfaces.

A Knowledge-Based Approach to Online Fault Diagnosis of FET Biosensors

Real-time diagnosis of insulator-semiconductor field-effect transistor (ISFET)-based biosensor systems aims at promptly correcting errors caused by insufficient function; insufficiency is judged by the operational behavior of the sensor, i.e., the data that it produces. Ultimately, a complete failure of the system (i.e., a “dead” sensor) should easily be recognized. Much more difficult is the recognition of a gradual malfunction of this complex system, which may be attributed to faults or failures in one or more of its subsystems. Evidently, the identification of the possible fault modes and their symptoms requires in-depth knowledge of sensor's design and operation, both from the biochemical and electrical/electronic points of view, along with tackling uncertain, incomplete, or imprecise information. In this paper, a novel real-time diagnostic expert scheme for field-effect transistor (FET)-based biosensing is proposed. This paper 1) investigates the causes of sensor misfunction by means of fault tree analysis (FTA) relying on fuzzy reasoning to account for uncertainty and 2) proposes a computer-aided method for diagnosing biosensor failure during operation through an algorithmic procedure that is based on a nested loop mechanism. The tree (dendritic) structure (built using the information provided by the biosensor components and their intrarelations/interrelations on a surface- and a deep-knowledge level) serves as the knowledge base (KB), and the fuzzy-rules-based decision mechanism is the inference engine for fault detection and isolation.

The surface energy-dictated initial growth of a pentacene film on a polymeric adhesion layer for field-effect transistors

We describe how the surface energy of a polymeric adhesion layer affects the initial growth of a pentacene film for field-effect transistors (FETs). Three types of adhesion layers having different surface energies and morphologies were produced with varying the composition ratio of two different polyimides. For the pentacene film of 0.4 nm thick, the monolayer coverage of pentacene grains increases from 26.3% to 64.9% with increasing the surface energy of the underlying adhesion layer from 12.9 to 25.8 mJ/m 2. The surface energy of the adhesion layer is found to play a more dominant role on the initial growth of a pentacene film than the surface roughness. The field-effect mobility in the pentacene FET depends strongly on the monolayer growth of pentacene grains.

Synthesis and characterization of pyrene-centered oligothiophenes

A series of materials for field effect transistors (FETs), with pyrene at the core and four substituted thiophene arms of different lengths (1–3 thiophene units) have been synthesized using Suzuki cross-coupling reactions and characterized by 1H NMR, 13C NMR, UV–vis absorption, emission spectroscopy, and in one case by X-ray crystallography.

Conducting polymer 1-dimensional nanostructures for FET sensors

In this review we have highlighted advantages of 1-dimensional nanostructures for field effect transistor (FET)/chemiresistor based sensors and advantages of conducting polymer as material of construction over other nanomaterials. Here we have ensembled different techniques used for the fabrication, assembly/alignment, functionalization and sensing applications of conducting polymer nanowire/tube/junction based FET sensors for gas and biomolecule detection. The advantages and disadvantages of various fabrication, functionalization, and assembling techniques are discussed. We evaluate how such devices have enabled the achievement of improved sensor performance in terms of high sensitivity, selectivity and low detection limits. Finally, we conclude by highlighting overall merits of different techniques and challenges researchers face in the field of conducting polymer 1-dimensional nanostructures-based sensors and also predict the future direction in which research efforts are likely to flourish.

Phenacyl–Thiophene and Quinone Semiconductors Designed for Solution Processability and Air‐Stability in High Mobility n‐Channel Field‐Effect Transistors

Electron-transporting organic semiconductors (n-channel) for field-effect transistors (FETs) that are processable in common organic solvents or exhibit air-stable operation are rare. This investigation addresses both these challenges through rational molecular design and computational predictions of n-channel FET air-stability. A series of seven phenacyl-thiophene-based materials are reported incorporating systematic variations in molecular structure and reduction potential. These compounds are as follows: 5,5'''-bis(perfluorophenylcarbonyl)-2,2':5',- 2'':5'',2'''-quaterthiophene (1), 5,5'''-bis(phenacyl)-2,2':5',2'': 5'',2'''-quaterthiophene (2), poly[5,5'''-(perfluorophenac-2-yl)-4',4''-dioctyl-2,2':5',2'':5'',2'''-quaterthiophene) (3), 5,5'''-bis(perfluorophenacyl)-4,4'''-dioctyl-2,2':5',2'':5'',2'''-quaterthiophene (4), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (5), 2,7-bis[(5-phenacyl)thiophen-2-yl]-9,10-phenanthrenequinone (6), and 2,7-bis(thiophen-2-yl)-9,10-phenanthrenequinone, (7). Optical and electrochemical data reveal that phenacyl functionalization significantly depresses the LUMO energies, and introduction of the quinone fragment results in even greater LUMO stabilization. FET measurements reveal that the films of materials 1, 3, 5, and 6 exhibit n-channel activity. Notably, oligomer 1 exhibits one of the highest mu(e) (up to approximately = 0.3 cm(2) V(-1) s(-1)) values reported to date for a solution-cast organic semiconductor; one of the first n-channel polymers, 3, exhibits mu(e) approximately = 10(-6) cm(2) V(-1) s(-1) in spin-cast films (mu(e)=0.02 cm(2) V(-1) s(-1) for drop-cast 1:3 blend films); and rare air-stable n-channel material 5 exhibits n-channel FET operation with mu(e)=0.015 cm(2) V(-1) s(-1), while maintaining a large I(on:off)=10(6) for a period greater than one year in air. The crystal structures of 1 and 2 reveal close herringbone interplanar pi-stacking distances (3.50 and 3.43 A, respectively), whereas the structure of the model quinone compound, 7, exhibits 3.48 A cofacial pi-stacking in a slipped, donor-acceptor motif.

Polymer stabilized ZnO nanoparticles for low-temperature and solution-processed field-effect transistors

Homogeneous, smooth and densely-packed nanoparticulate ZnO films for field-effect transistors (FETs) are formed by spin-coating suspensions of ZnO nanoparticles in an organic solvent, followed by baking at 150 °C. The morphology of the films is strongly dependent on the type and amount of surfactant polymers that are employed to cap ZnO nanoparticles and stabilize the suspensions. Infrared spectroscopy, atomic force microscopy, electron microscopy and electrical characterization reveal that a certain amount of surfactant is needed to make the size of the agglomerates small enough to form such nanoparticulate films; however, an excess amount of surfactant results in an increase in the resistivity of the nanoparticulate films owing to the electrically semi-insulating nature of the surfactants. FETs composed of the nanoparticulate ZnO films in the bottom gate configuration operate in the n-channel enhancement mode with a clear saturation current at higher drain voltages. The field-effect mobility of the FETs varies by more than three orders of magnitude dependent on the type and amount of surfactants, exhibiting the highest value of 8 × 10−3 cm2 V−1 s−1. This clearly indicates that the appropriate development and synthesis of surfactants for inorganic nanocrystal suspensions are highly important for low-temperature and solution-processed FETs, compatible with plastic substrates, towards printable electronics.

Synthesis of thieno[3,2-b]thiophene derived conjugated oligomers for field-effect transistors applications

A novel series of soluble thieno[3,2-b]thiophene (TT) oligomers with alternating TT and bithiophene or fluorene triad architectures have been synthesized for field-effect transistor (FET) applications. Their optical, thermal and electronic properties were investigated using UV-Vis and photoluminescence spectroscopy, thermal gravimetric analysis, and cyclic voltammetry. Compared with α,α′-dihexylsexithiophene (D6HT), these oligomers exhibit blue-shifted absorption spectra, 0.1 eV to 0.3 eV lower than the highest occupied molecular orbital (HOMO) energy levels and accordingly higher ambient stability. Their crystallinity and morphology features of these oligomers were further investigated with X-ray diffraction and atomic force microscopy using vacuum-deposited thin film on Si/SiO2 substrate. Symmetrically structured TT-oligomers including HT2TT, HTTT2, HTTTT and DDFTT exhibit ordered film morphology and promising FET performance with devices fabricated by either vacuum deposition or solution processing techniques. Interestingly, HTTT2 shows interconnected terrace island morphology, which is often observed for pentacene. All p-type transistors show promising performance, with HT2TT demonstrating a hole mobility up to 0.025 cm2V−1s−1 and an on/off current ration ∼1.2 × 103 with vacuum sublimated film deposited on 70 °C substrate.

Organic semiconductors for field-effect transistors (FETs): tuning of spectroscopic, electrochemical, electronic and structural properties of naphthalene bisimides via substituents containing alkylthienyl moieties

A series of new naphthalene bisimides containing alkylthienyl groups as a part of their N-substituents have been prepared. Two synthetic routes were used. In the first one appropriate alkylthienyl anilines were synthesized from bromoalkylthiophene derivatives and then condensed with 1,4,5,8-naphthalenetetracarboxylic acid bisanhydride. The second route involved condensation of thienylmethylamine with the same bisanhydride, followed by bromination of the product and its Suzuki-type coupling with alkylthiophene. UV-vis and FTIR spectroscopic investigations showed that the extent of the conjugation in the substituents is very sensitive to their regiochemical arrangement. The presence of alkylthienyl groups lowers the bisimide LUMO level to −3.94 eV with respect to the vacuum level. This property combined with their solution processibility makes the new bisimides excellent candidates for their application as active layers in all-organic field-effect transistors, fabricated by solution processing (spin coating or printing techniques). X-Ray diffraction measurements have shown that the bisimide molecules, deposited on either polyethylene naphthalate (PEN) or untreated Si 〈100〉 substrates, adopt regular arrangements giving rise to crystalline domains, which, in their overwhelming part, are highly oriented respectively to the substrate with the long period of their structure being in a plane perpendicular to the substrate. As a result a tendency to align π-stacked moieties in a direction parallel to the substrate can clearly be observed. Bottom contact staggered organic field-effect transistors have been fabricated and tested in air environment. All layers, except the source and drain electrodes, have been deposited from solution. The obtained transistors exhibit charge carriers mobility approaching 10−2 cm2 V−1 s−1 and the on/off ratio exceeding 105, indicating that this new class of bisimide semiconductors can be considered as promising solution processible materials for n-channel transistors.

Phosphate-dependent DNA Immobilization on Hafnium Oxide for Bio-Sensing Applications

AbstractHafnium(IV) oxide (HfO2) has replaced silicon oxide as a gate dielectric material in leading edge CMOS technology, providing significant improvement in gate performance for field effect transistors (FETs). We are currently exploring this high-k dielectric for its use in nucleic acid-based FET biosensors. Due to its intrinsic negative charge, label-free detection of DNA can be achieved in the gate region of high-sensitivity FET devices. Previous work has shown that phosphates and phosphonates coordinate specifically onto metal oxide substrates including aluminum and titanium oxides. This property can therefore be exploited for direct immobilization of biomolecules such as nucleic acids. Our work demonstrates that 5’ phosphate-terminated single stranded DNA (ssDNA) can be directly immobilized onto HfO2 surfaces, without the need for additional chemical modification or crosslinking. Non-phosphorylated ssDNA does not form stable surface interactions with HfO2, indicating that immobilization is dependent upon the 5’ terminal phosphate. Further work has shown that surface immobilized ssDNA can be hybridized to complementary target DNA and that sequence-based hybridization specificity is preserved. These results suggest that the direct DNA-HfO2 immobilization strategy can enable nucleic acid-based biosensing assays on HfO2 terminated surfaces. This work will further enable high sensitivity electrical detection of biological targets utilizing transistor-based technologies.

Nonlinear and fully distributed field effect transistor modelling procedure using time-domain method

An accurate and efficient modelling approach for field effect transistors (FET) as nonlinear active transmission lines is presented. The nonlinear active multiconductor transmission line (NAMTL) equations are obtained by considering the transistor as three active coupled lines operating in a nonlinear regime. This modelling procedure accurately spots the effect of wave propagation along the device electrodes. This modelling approach is applied to an FET by solving the NAMTL equations using a finite-difference time-domain technique. The results of this model are compared with the semi-distributed (slice) model. This method produces more accurate results than the slice model, especially at high frequencies.

Epitaxial growth of two-dimensional electron gas (2DEG) in strained silicon for research on ultra-low energy electronic processes

We present a review of the progress in the field of 2DEG in strained Si/SiGe heterostructures during the past 20 or so years. We highlight the difference in the key challenges in sample preparation between the samples for low-temperature transport studies and those for field-effect transistor (FET) applications. The requirements of low electron density and high electron mobility for low-temperature electron transport are also discussed. High mobility (> 300,000 cm 2/V s) can be reproducibly achieved recently and low electron sheet density (1.1 × 10 11 cm − 2 ) in modulation-doped samples (as opposed to gated) has also been observed. Magnetotransport measurements provide indications of the mobility limiting factors thereby pointing to the plausible directions for further improvements on the strained Si sample quality.

Direct Growth of Single Walled Carbon Nanotubes for the Characterization of Structural and Electronic Properties

ABSTRACTFabricating horizontally aligned single wall carbon nanotubes (CNTs) with controlled properties has been one of the significant challenges for field-effect transistor (FET) applications. This report demonstrates a novel procedure for the fabrication of horizontally aligned single walled CNTs using the focused ion beam (FIB) and chemical vapor deposition (CVD). This method allows the morphologies, internal structures, and elemental compositions of CNTs to be directly analyzed in the scanning electron microscope (SEM) and transmission electron microscope (TEM) and avoids any sample preparation procedures that might alter the structure of the CNTs. The techniques of electron beam and ion beam induced deposition (EBID and IBID) of Pt electrodes to the CNT ends were compared and both were found to produce metal contamination around the target area. The fabrication of large area electrodes to assist in testing the CNT's electronic properties, including contact resistance and I-V characteristics was investigated. Using this fabrication technique we were able to perform an I-V sweep on a CNT circuit as well as detect the metal contamination on the CNTs which occurred as a result of electrode deposition.

Exclusive-OR gate with a single carbon nanotube

Carbon nanotubes (CNTs) are now well-established as efficient channels for field-effect transistors (FETs). Logic circuitry based on CNTs have until now been demonstrated by replacing the silicon channel of a conventional metal-oxide-semiconducutor FET by a CNT. We propose a circuit design utilizing the ambipolarity of the Schottky-barrier-type CNT-FET to realize an exclusive-OR (XOR) gate using a single CNT. The merits and limitations of such a CNT-XOR gate with respect to conventional XOR gates are discussed.

High-sheet-charge–carrier-density AlInN∕GaN field-effect transistors on Si(111)

Al In N ∕ Ga N heterostructures have been proposed to possess advantageous properties for field-effect transistors (FETs) over AlGaN∕GaN [Kuzmík, IEEE Electron Device Lett. 22, 501 (2001); Yamaguchi et al., Phys. Status Solidi A 188, 895 (2001)]. A major advantage of such structures is that AlInN can be grown lattice-matched to GaN while still inducing high charge carrier densities at the heterointerface of around 2.7×1013cm−3 by the differences in spontaneous polarization. Additionally, it offers a higher band offset to GaN than AlGaN. We grew AlInN FET structures on Si(111) substrates by metalorganic chemical vapor phase epitaxy with In concentrations ranging from 9.5% to 24%. Nearly lattice-matched structures show sheet carrier densities of 3.2×1013cm−2 and mobilities of ∼406cm2∕Vs. Such Al0.84In0.16N FETs have maximum dc currents of 1.33A∕mm for devices with 1μm gate length.

Orientation Control and Properties of Pb(Zr, Ti)O3 Thin Films Deposited on Ni–Zn-Ferrite for Novel Ferroelectric/Ferromagnetic Memory Applications

A novel memory with a ferroelectric/ferromagnetic stacked structure was proposed. Multilevel recording is expected for this novel memory. The principle of ferroelectric recording is the same as that for field effect transistor (FET) ferroelectric random access memories (FeRAMs). The principle of magnetic recording is that the source-drain current is modified by the Lorentz force caused by the remanent magnetization of ferromagnetic thin film. It was clarified that the drain current and source-drain voltage (Id–Vd) characteristics of a Si metal-oxide-semiconductor field effect transistor (MOSFET) was actually modified in an external magnetic field. Such modification was also brought about by the remanent magnetization of a ferromagnetic thin film. To achieve high remanent polarization and remanent magnetization at the same time in the ferroelectric/ferromagnetic stacked structure, we prepared Pb(Zr, Ti)O3 (PZT)/(Ni, Zn)Fe2O4 (NZF) thin films with several crystallographic orientations on Si(001) substrates. The orientations of PZT and NZF thin films were controlled by designing buffer layers between the Si(001) substrate and NZF thin film. It was found that (111)-orientatied PZT on (111)-orientated NZF thin film satisfied both high remanent polarization and remanent magnetization at the same time.

Gate Bias Modulated Current Flow Analysis at Organic Semiconductor / Metal Interface for Developing High Performance Organic Fet

ABSTRACTWe have developed a current flow analysis system for Field Effect Transistors (FET) using a conductive cantilever of a probe microscope. Using this analysis system, nanoscale current images were observed on a pentacene active layer grown on a bottom electrode in ordinary FETs. When gold (Au) was employed as a bottom electrode, we found the special region around the electrode edge. The current flow hardly occurred in this region. On the other hand, using a conductive polymer (PEDOT) bottom electrode, such a region was not observed. From the detailed observation around the electrode edge, we concluded that the special region would be caused by diffusion of Au particles that evoked heterogeneous pentacene growth, and then the heterogeneity worked as a contact resistance.

Fabrication and Characterization of Pt/(Bi, La)4Ti3O12/Si3N4/Si Metal Ferroelectric Insulator Semiconductor Structure for FET-Type Ferroelectric Memory Applications

For field effect transistor (FET)-type ferroelectric memories, c-axis oriented (Bi, La)4Ti3O12 films with small remanent polarization Pr of 4 µC/cm2 were investigated. Bi3.25La0.75Ti3O12 films were prepared by the sol-gel method on amorphous Si3N4 layers formed on Si substrates using atomic nitrogen radicals. It was found that the films formed using stoichiometric sol-gel solution did not crystallize even after annealing at 800°C in O2 ambient. Therefore, 2.5 to 7.5% excess-Bi solutions were used and such parameters as pre annealing and crystallization temperatures, film thickness and crystallization ambient were optimized. As a result, the well c-axis-oriented Bi3.25La0.75Ti3O12 films with good crystallinity and good surface morphology were obtained at temperatures higher than 600°C. It was also found in a Pt/100 nm-Bi3.25La0.75Ti3O12/3 nm-Si3N4/Si (metal/ferroelectric/insulator/semiconductor) structure that C–V characteristics showed a hysteresis loop with a memory window of about 1 V and both high and low capacitance values kept at zero bias voltage did not change for more than 3 h.