N-channel Operation Research Articles

Novel fabrication process of charge transfer complex thin films for large area by thermal diffusion and their n-channel organic transistor operation

We have proposed a new fabrication process of donor and acceptor charge transfer complex thin films using thermal diffusion. 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) was vacuum-deposited on 2,7-didecylbenzothienobenzothiophene (C10-BTBT) thin films fabricated by spin-coating, and F4-TCNQ molecules were diffused into C10-BTBT thin films by thermally annealing. The X-ray diffraction pattern and field effect transistor of thermally annealed thin films indicated the crystal structure of the charge transfer complex of C10-BTBT and F4-TCNQ and n-channel operation in air, respectively. We conclude that it is good process to use the thermal diffusion for the fabrication of the large area thin films of charge transfer complex.

Nonvolatile operation of vertical ferroelectric gate-all-around nanowire transistors

Ferroelectric gate-all-around (GAA) transistors with a nanowire (NW) channel standing vertically on the substrate would be a potential breakthrough to overcome limitations in the high-integration of ferroelectric memories. In the present study, we fabricated vertical ferroelectric GAA NW transistors (VFGAANWTs) with ZnO NWs (average diameters: 53–193 nm) as the channel, (Hf,Zr)O2 film (average thicknesses: 9.3–58 nm) as the gate ferroelectric, and Ti as the gate electrode. The channel length was 100–300 nm. The VFGAANWTs showed n-channel operation with on/off ratios of ∼10, and their on/off states were retained for at least 2 min by the ferroelectric polarization of (Hf,Zr)O2 after the gate bias was removed, demonstrating the nonvolatile electric field effect in the VFGAANWTs. The results confirm the strong potential of the VFGAANWTs in high-density ferroelectric memory applications.

Light-Emitting Transistors with High Color Purity Using Perovskite Quantum Dot Emitters.

The class of organic-inorganic lead halides with perovskite crystal structures has recently emerged as promising materials for a variety of practical optoelectronic applications. In particular, hybrid halide perovskite quantum dots possess excellent intrinsic optoelectronic properties such as high color purity (full width at half-maximum of 24.59 nm) and photoluminescence quantum yields (92.7%). In this work, we demonstrate the use of perovskite quantum dot materials as an emissive layer of hybrid light-emitting transistors. To investigate the working mechanism of perovskite quantum dots in light-emitting transistors, we investigated the electrical and optical characteristics under both p-channel and n-channel operation. Using these materials, we have achieved perovskite quantum dot light-emitting transistors with high electron mobilities of up to 12.06 cm2·V-1 s-1, high brightness of up to 1.41 × 104 cd m-2, and enhanced external quantum efficiencies of up to 1.79% operating at a source-drain potential of 40 V.

Facile synthesis of picenes incorporating imide moieties at both edges of the molecule and their application to n-channel field-effect transistors.

Picene derivatives incorporating imide moieties along the long-axis direction of the picene core (Cn-PicDIs) were conveniently synthesized through a four-step synthesis. Photochemical cyclization of dinaphthylethenes was used as the key step for constructing the picene skeleton. Field-effect transistor (FET) devices of Cn-PicDIs were fabricated by using ZrO2 as a gate substrate and their FET characteristics were investigated. The FET devices showed normally-off n-channel operation; the averaged electron mobility (μ) was evaluated to be 2(1) × 10−4, 1.0(6) × 10−1 and 1.4(3) × 10−2 cm2 V−1 s−1 for C4-PicDI, C8-PicDI and C12-PicDI, respectively. The maximum μ value as high as 2.0 × 10−1 cm2 V−1 s−1 was observed for C8-PicDI. The electronic spectra of Cn-PicDIs in solution showed the same profiles irrespective of the alkyl chain lengths. In contrast, in thin films, the UV absorption and photoelectron yield spectroscopy (PYS) indicated that the lowest unoccupied molecular orbital (LUMO) level of Cn-PicDIs gradually lowered upon the elongation of the alkyl chains, suggesting that the alkyl chains modify intermolecular interactions between the Cn-PicDI molecules in thin films. The present results provide a new strategy for constructing a high performance n-channel organic semiconductor material by utilizing the electronic features of phenacenes.

Electrical properties of In2O3 and ITO thin films formed by solution process using In(acac)3 precursors

Indium oxide (In2O3) and indium tin oxide (ITO) films were prepared by the solution process using an indium acetylacetonate [In(acac)3] precursor, and their electrical properties were also characterized. Rapid thermal annealing (RTA) of In2O3 and ITO precursor-gel films was performed in O2 by varying the annealing temperature and time. The obtained Hall mobility of In2O3 films is as high as 42.7 cm2 V−1 s−1, while resistivity as low as 2.5 × 10−3 Ωcm is obtained for 1 wt% ITO with a Hall mobility and a carrier concentration of 24.1 cm2 V−1 s−1 and 1.0 × 1020 cm−3, respectively. The ITO was prepared using two different Sn precursors—one was SnCl2 and the other was Sn(acac)2—to compare its electrical properties—and it was found that the Hall mobility was higher in the ITO prepared using Sn(acac)2 as the Sn precursor. Using the solution-processed In2O3 as a channel, a thin film transistor was also fabricated and n-channel transistor operation was confirmed.

Polarity control of carrier injection for nanowire feedback field-effect transistors

We present polarity control of the carrier injection for a feedback field-effect transistor (FBFET) with a selectively thinned p+-i-n+ Si nanowire (SiNW) channel and two separate gates. The SiNW FBFET can be reconfigured in the p- or n-channel operation modes via simple control of electric signals. The two separate gates induce potential barriers in the SiNW channel for selective control of the carrier injection. In contrast to previously reported reconfigurable transistors, our transistor features symmetry of the electrical characteristics for the p- and n-channel operation modes. Positive-feedback operation of the SiNW FBFET provides superior switching characteristics for the p- and n-type configurations, including the on/off ratios (∼ 105) and subthreshold swings (1.36-1.78 mV/dec). This novel transistor is a promising candidate for reconfigurable electronics.

Lightly doped n-type tensile-strained single-crystalline GeSn-on-insulator structures formed by lateral liquid-phase crystallization

A tensile-strained single-crystalline n-type GeSn-on-insulator structure was demonstrated by lateral liquid-phase crystallization of an Sb-doped GeSn layer, and the diffusion and activation behaviors of Sb atoms in a liquid-phase-grown GeSn wire were investigated. A photoluminescence-based study revealed that a substantial amount of Sb was swept out during the liquid-phase growth of the GeSn wire. A thin-film transistor based on an Sb-doped GeSn wire on a quartz substrate exhibited n-channel accumulation-mode operation, and the temperature dependence of field-effect mobility revealed that the single-crystalline GeSn wire is a lightly doped n-type (∼1017 cm−3). The combination of Sb-doped n-type and undoped p-type GeSn wires would be an ideal platform for GeSn-based optoelectronic integration.

Integrating Poly-Silicon and InGaZnO Thin-Film Transistors for CMOS Inverters

The applications of a-InGaZnO thin-film transistors (TFTs) to logic circuits have been limited owing to the intrinsic n-channel operation. In this paper, we demonstrated a hybrid inverter constructed by p-channel low-temperature poly-silicon (LTPS) TFTs and n-channel amorphous-indium–gallium–zinc–oxide (a-IGZO) TFTs. Hydrogenated LTPS TFTs and a-IGZO TFTs have been successfully fabricated on the same panel, followed by a rapid thermal annealing treatment to remove the hydrogens in the a-IGZO TFTs. The resulted hybrid inverter exhibits large noise margin closed to ${V}_{\textsf {DD}}/\textsf {2}$ and a high voltage gain as 68.3. Due to the complementary configurations in the static state, the inverter shows small current and thus consumes low power in hundreds of picowatts. As all the fabrication processes are compatible with conventional techniques, the reported results may open new opportunities in circuit design and applications for oxide TFTs.

High-performance PbS quantum dot vertical field-effect phototransistor using graphene as a transparent electrode

Solution processed photoactive PbS quantum dots (QDs) were used as channel in high-performance near-infrared vertical field-effect phototransistor (VFEpT) where monolayer graphene embedded as transparent electrode. In this vertical architecture, the PbS QD channel was sandwiched and naturally protected between the drain and source electrodes, which made the device ultrashort channel length (110 nm) simply the thickness of the channel layer. The VFEpT exhibited ambipolar operation with high mobilities of μe = 3.5 cm2/V s in n-channel operation and μh = 3.3 cm2/V s in p-channel operation at low operation voltages. By using the photoactive PbS QDs as channel material, the VFEpT exhibited good photoresponse properties with a responsivity of 4.2 × 102 A/W, an external quantum efficiency of 6.4 × 104% and a photodetectivity of 2.1 × 109 Jones at the light irradiance of 36 mW/cm2. Additionally, the VFEpT showed excellent on/off switching with good stability and reproducibility and fast response speed with a short rise time of 12 ms in n-channel operation and 10.6 ms in p-channel operation. These high mobilities, good photoresponse properties and simplistic fabrication of our VFEpTs provided a facile route to the high-performance inorganic photodetectors.

N-channel field-effect transistors with an organic-inorganic layered perovskite semiconductor

Large electron injection barriers and electrode degradation are serious issues that need to be overcome to obtain n-channel operation in field-effect transistors with an organic-inorganic layered perovskite (C6H5C2H4NH3)2SnI4 semiconductor. By employing low-work-function Al source/drain electrodes and by inserting C60 layers between the perovskite semiconductor and the Al electrodes to reduce the injection barrier and to suppress the electrode degradation, we demonstrate n-channel perovskite transistors with electron mobilities of up to 2.1 cm2/V s, the highest value ever reported in spin-coated perovskite transistors. The n-channel transport properties of these transistors are relatively stable in vacuum but are very sensitive to oxygen, which works as electron traps in perovskite and C60 layers. In addition, grazing-incidence X-ray scattering and thermally stimulated current measurements revealed that crystallite size and electron traps largely affect the n-channel transport properties.

Epitaxial growth of In-rich InGaN on yttria-stabilized zirconia and its application to metal–insulator–semiconductor field-effect transistors

We grew In-rich InxGa1-xN films on yttria-stabilized zirconia (YSZ) substrates at low temperatures by pulsed sputtering deposition. It was found that single-crystal InxGa1-xN (0.63 ≤ x ≤ 0.82) films can be prepared without significant compositional fluctuations at growth temperatures below 500 °C. It was also found that the electrical properties of InGaN are strongly dependent on In composition, growth temperature, and film polarity. N-channel operation of the metal–insulator–semiconductor field-effect transistor (MISFET) with an ultrathin InGaN channel on the YSZ substrates was successfully demonstrated. These results indicate that an InGaN-based MISFET is a promising device for next-generation high-speed electronics.

Organic Semiconductors based on Dyes and Color Pigments.

Organic dyes and pigments constitute a large class of industrial products. The utilization of these compounds in the field of organic electronics is reviewed with particular emphasis on organic field-effect transistors. It is shown that for most major classes of industrial dyes and pigments, i.e., phthalocyanines, perylene and naphthalene diimides, diketopyrrolopyrroles, indigos and isoindigos, squaraines, and merocyanines, charge-carrier mobilities exceeding 1 cm(2) V(-1) s(-1) have been achieved. The most widely investigated molecules due to their n-channel operation are perylene and naphthalene diimides, for which even values close to 10 cm(2) V(-1) s(-1) have been demonstrated. The fact that all of these π-conjugated colorants contain polar substituents leading to strongly quadrupolar or even dipolar molecules suggests that indeed a much larger structural space shows promise for the design of organic semiconductor molecules than was considered in this field traditionally. In particular, because many of these dye and pigment chromophores demonstrate excellent thermal and (photo-)chemical stability in their original applications in dyeing and printing, and are accessible by straightforward synthetic protocols, they bear a particularly high potential for commercial applications in the area of organic electronics.

Band Engineering to Improve Average Subthreshold Swing by Suppressing Low Electric Field Band-to-Band Tunneling With Epitaxial Tunnel Layer Tunnel FET Structure

Tunnel field-effect transistor (FET) is a promising candidate in ultralow-power applications due to its distinct operation mechanism, namely band-to-band tunneling (BTBT). The integration of different low-bandgap materials is explored extensively to improve the ON-state BTBT current of the tunnel FETs. The epitaxial tunnel layer (ETL) tunnel FET integrated with the hetero-material system is a promising structure due to its process compatibility with CMOS technologies. In the scenario of n-channel operation, the concept of the suppression of the low electric field BTBT is proposed. The SiGe/Si hetero-material system is applied to the n-channel ETL tunnel FET to suppress the low electric field BTBT by the ETL band engineering. The optimized ETL tunnel FET exhibits a high ON-state BTBT current due to the low bandgap material in the ETL. The average SS behavior is also further improved by suppressing the low electric field BTBT. In this study, the design concept and the device parameters of the n-channel ETL tunnel FET are discussed in detail. The performances of the complementary ETL tunnel FETs using the SiGe/Si hetero-material system are also provided to enrich the value of the ETL tunnel FET in the circuit applications.

Steep Subthreshold Swing n- and p-Channel Operation of Bendable Feedback Field-Effect Transistors with p(+)-i-n(+) Nanowires by Dual-Top-Gate Voltage Modulation.

In this study, we present the steep switching characteristics of bendable feedback field-effect transistors (FBFETs) consisting of p(+)-i-n(+) Si nanowires (NWs) and dual-top-gate structures. As a result of a positive feedback loop in the intrinsic channel region, our FBFET features the outstanding switching characteristics of an on/off current ratio of approximately 10(6), and point subthreshold swings (SSs) of 18-19 mV/dec in the n-channel operation mode and of 10-23 mV/dec in the p-channel operation mode. Not only can these devices operate in n- or p-channel modes, their switching characteristics can also be modulated by adjusting the gate biases. Moreover, the device maintains its steep SS characteristics, even when the substrate is bent. This study demonstrates the promising potential of bendable NW FBFETs for use as low-power components in integrated circuits or memory devices.

Temperature-dependent ambipolar electrical characteristics of pentacene-based thin-film transistors: The impact of opposite-sign charge carriers

The temperature-dependent electrical and charge transport characteristics of pentacene-based ambipolar thin-film transistors (TFTs) were investigated at temperatures ranging from 77K to 300K. At room temperature (RT), the pentacene-based TFTs exhibit balanced and high charge mobility with electron (μe) and hole (μh) mobilities, both at about 1.6cm2/Vs. However, at lower temperatures, higher switch-on voltage of n-channel operations, almost absent n-channel characteristics, and strong temperature dependence of μe indicated that electrons were more difficult to release from opposite-signed carriers than that of holes. We observed that μe and μh both followed an Arrhenius-type temperature dependence and exhibited two regimes with a transition temperature at approximately 210–230K. At high temperatures, data were explained by a model in which charge transport was limited by a dual-carrier release and recombination process, which is an electric field-assisted thermal-activated procedure. At T<210K, the observed activation energy is in agreement with unipolar pentacene-based TFTs, suggesting a common multiple trapping and release process-dominated mechanism. Different temperature-induced characteristics between n- and p-channel operations are outlined, thereby providing important insights into the complexity of observing efficient electron transport in comparison with the hole of ambipolar TFTs.

Synthesis and characterization of MgSnO prepared via a ball milling process

Nanocrystalline powders of MgO–SnO2 (MgSnO) were experimentally obtained via a high-energy ball milling process with various operating time and annealing temperatures. The average crystallite size and lattice strain of the MgSnO powder decreased and increased, respectively, with increasing milling time. X-ray diffraction results revealed that the Mg2SnO4 phase formed after calcinations of the as-milled MgSnO powder at temperatures higher than 1000°C. The film annealed at 500°C exhibited a much higher transmittance (~92%) in the visible region than that of a previously reported, non-ball-milled Mg-doped SnO2. The surface morphology of MTO films is dependent on the annealing temperature. The fabricated MgSnO TFT operating in electron-accumulation mode can perform n-channel operations. In addition, the sub-threshold voltage swing value of the device is 0.29V/decade.

23.1: Invited Paper: Jet Printed TFTs and Circuits for Flexible Electronics

AbstractPrinted and flexible devices are potential technologies for future display applications. Progress in printed materials, devices and circuits enables organic TFTs and solution oxides with mobility greater than 1 cm2/Vs, the organic TFTs having n‐channel and p‐channel operation. Simple logic circuits and flexible TFT backplane prototypes will be discussed.

Silicon tunneling field-effect transistors with tunneling in line with the gate field

We present experimental results on the fabrication and characterization of vertical Si tunneling field-effect transistors (TFETs) in a device geometry with tunneling in line with the gate field. Compared to vertical Si TFETs without this geometry modification, on-currents are increased by more than one order of magnitude with ION = 1.1 μA/μm at VDS = 0.5 V and an ION/IOFF ratio of 3.4 ·104 in n-channel operation. We present further suggestions for device improvements.

6,13-Dicyano pentacene-2,3:9,10-bis(dicarboximide) for solution-processed air-stable n-channel field effect transistors and complementary circuit

Aromatic diimides have attracted much attention due to their unique properties and potential applications for n-channel organic field effect transistors (OFETs). In this study, N,N′-dialkyl-6,13-dicyano pentacene-2,3:9,10-bis(dicarboximide) (1) was synthesized and used in n-channel OFETs. The photophysical, electrochemical and thermal properties of 1 were investigated. The low LUMO energy level (−4.15 eV) located within the air stability window ensures air-stable n-channel operation. Solution-processed top-contact thin film transistors based on such linear aromatic dicarboximide showed typical n-channel characteristics with a high electron mobility of up to 0.08 cm2 V−1 s−1 and a high Ion/Ioff ratio of 106 to 107. The devices exhibited good air stability when exposed to air for several months. Complementary inverters based on n-type 1 and p-type TIPS-pentacene were fabricated, which showed a maximum voltage gain (−dVOUT/dVIN) of 57.

Solution-processable n-type and ambipolar semiconductors based on a fused cyclopentadithiophenebis(dicyanovinylene) core

Two fused cyclopentadithiophenebis(dicyanovinylene) derivatives (FCPDT-16 and FCPDT-C24) with a low-lying LUMO energy level (3.88 eV) and a rigid core structurewere successfully synthesized.They have good thermal stability and form highly ordered packing structures both in the bulk solid state and in thin films. The field effect transistors fabricated from a solution of these two compounds showed ambipolar behaviour with major n-channel operation. FCPDT-C16 exhibited electron mobility up to 0.16 cm(2) V(-1) s(-1).