聚酰亚胺为栅绝缘层的并五苯场效应晶体管

以真空蒸发的有机半导体材料并五苯为有源层,以旋涂的聚酰亚胺作为栅绝缘层,以真空蒸发的Al为栅、源和漏电极,成功制作了顶接触式并五苯有机场效应晶体管(OFET).测试表明,在源漏电压为70 V时,器件的载流子迁移率μ为0.079 cm2/V·s,器件的开关电流比为1.7×104.     

SiC（0001）面衬底上自氧化栅介质和自对准形成石墨烯场效应晶体管

A scalable self-aligned approach is employed to fabricate monolayer graphene field-effect transistors on semi-insulated 4H-SiC （0001） substrates. The self-aligned process minimized access resistance and parasitic capacitance. Self-oxidized Al2O3, formed by deposition of 2 nm A1 followed by exposure in air to be oxidized, is used as gate dielectric and shows excellent insulation. An intrinsic cutoff frequency of 34 GHz and maximum oscillation frequency of 36.4 GHz are realized for the monolayer graphene field-effect transistor with a gate length of 0.2 μm. These studies show a pathway to fabricate graphene transistors for future applications in ultra-high frequency circuits.     

Fabrication of pentacene organic field-effect transistors with polyimide gate dielectric layer

The organic field effect transistors had been fabricated using the pentacene by vacuum evaporation as the active layer, the polyimide by spin coating as insulator layer, and aluminum by vacuum evaporation as gate, source and drain electrodes respectively. The field-effect mobility of 0.079 cm2/V.s was tested at Vds=70 V, and on/off radio up to 1.7×104.     

Cardanol-based polymeric gate dielectric for solution-processed organic field-effect transistors on flexible substrates

A cardanol-based polymer, poly(2-hydroxy-3-cardanylpropyl methacrylate) (PHCPM), was utilized as the gate dielectric of an organic field-effect transistor (OFET). PHCPM has good surface properties, appropriate gate dielectric characteristics, and good compatibility with solution-processed semiconducting polymers. The electrical properties of an FET that was prepared with natural resource-based PHCPM as a gate dielectric layer and solution-processed poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) as a semiconducting layer were investigated on flexible substrates. The flexible PBTTT-OFET device with the PCHPM gate dielectric exhibited high mobility and reliable performance, even in the bending state, without significant hysteresis.     

Parylene based bilayer flexible gate dielectric layer for top-gated organic field-effect transistors

In this paper, we report on a bilayer insulating film based on parylene-c for gate dielectric layers in top-gate/bottom-contact inkjet-printed organic field-effect transistors (OFETs) with indacenodithiophene-co-benzothiadiazole (IDTBT) and poly([N,N’-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5’-(2,2’-bitthiophene)) (P(NDI2OD-T2)) as with p- and n-channel semiconductors. The thin parylene-c film (t = 210 nm) show large gate leakage density (2.52 nA/cm² at 25 V) and low breakdown voltage (2.2 MV/cm). In addition, a degraded field-effect mobility (μ) was observed in printed IDTBT and P(NDI2OD-T2) OFETs with the parylene-c single-layered dielectric. X-ray photoelectron spectroscopy (XPS) analysis reveals that the degradation of μ is due to unwanted chemical interaction between parylene-c and the conjugated polymer surface during the parylene-c deposition process. By inserting 50-nm thick poly(methyl-methacrylate) (PMMA) and polystyrene (PS) layer in-between the parylene-c and conjugated polymer film, highly improved gate leakage density and breakdown voltage are achieved. The printed IDTBT and P(NDI2OD-T2) OFETs with a bilayer dielectric compose of parylene-c and PMMA and PS show significantly improved hole and electron μ of 0.47 cm²/Vs and 0.13 cm²/Vs, respectively, and better operation stability. In addition, we demonstrate inkjet-printed polymer complementary inverter with a high voltage gain of 25.7 by applying a PS/parylene-c bilayer dielectric.     

Hydrated bovine serum albumin as the gate dielectric material for organic field-effect transistors

Bovine serum albumin (BSA) is a natural protein with good hydration ability which contains acidic and basic amino acid residues of ca. 34% in total. In vacuum, pentacene organic field-effect transistors (OFETs) with BSA as the gate dielectric exhibits a field-effect mobility value (μ_FE,sat) of 0.3 cm² V⁻¹ s⁻¹ in the saturation regime and a threshold voltage (V_TH) of ca. −16 V. BSA is easy to be hydrated in air ambient. Electrical properties of BSA in vacuum and hydrated BSA in air ambient are characterized. Similar to polyelectrolyte, hydrated BSA may act the gate dielectric with the formation of electric double-layer capacitors (EDLCs) to improve the device performance. In a relative humidity of 47%, the μ_FE,sat value increases to 4.7 cm² V⁻¹ s⁻¹ and the V_TH reduces to −0.7 V. Generation of mobile ions in hydrated BSA and the formation of EDLCs are discussed.     

聚合物栅绝缘层厚度对并五苯有机场效应管性能的影响

采用不同厚度的聚甲基丙烯酸甲酯(PMMA)作为栅绝缘层,制备了并五苯有机场效应晶体管(OFET)。测量了不同厚度的PMMA的介电特性,并详细分析了栅绝缘层厚度对器件性能的影响。其中,采用260nm厚的PMMA栅绝缘层的OFET具有比采用其它厚度的器件更优越的性能,其场效应迁移率、阈值电压与开关电流比分别达到3.39×10-3 cm2/Vs、-19V和103。     

UV assisted non-volatile memory behaviour using Copper (II) phthalocyanine based organic field-effect transistors

In this report, we have demonstrated the optical non-volatile memory characteristics using CuPc OFET. The memory operation was comprehensively demonstrated with different programming conditions. It was found that the programming of CuPc OFET with an electric pulse at the gate terminal under UV-light photo-illumination compared to other programming conditions, could substantially increase the memory window due to massive charge trapping in the polymer electret layer, which causes shift in the device transfer characteristics from low-conduction state (“OFF state”, or logic 0) to high conduction state (“ON state”, or logic 1) at V_GS = 0V. From device operation at −50V, a memory window of greater than 45V could be achieved by applying a programming voltage of +70 V at the gate terminal under UV-light photo-illumination. Moreover, it was completely erased by applying −100 V at the gate terminal in dark.     

Controllable carrier density of pentacene field-effect transistors using polyacrylates as gate dielectrics

We have studied the effect of the chemical structure of dielectrics by evaporating pentacene onto a series of polyacrylates: poly(methylmethacrylate), poly(4-methoxyphenylacrylate), poly(phenylacrylate), and poly(2,2,2-trifluoroethyl methacrylate) in organic thin-film transistors (OTFTs). In top-contact OTFTs, the polyacrylates had a significant effect on field-effect mobilities ranging 0.093 ∼ 0.195 cm² V⁻¹ s⁻¹. This variation neither correlated with the polymer surface morphology nor the observed pentacene crystallite size. This result implies that the PTFMA device generates the local electric field that accumulates holes and significantly shifts the threshold voltage and the turn-on voltage to −8.62 V and 3.5 V, respectively, in comparison with those of PMMA devices.     

Solution-processed natural gelatin was used as a gate dielectric for the fabrication of oxide field-effect transistors

Biocompatible and biodegradable materials are attractive for environmentally safe, flexible and biosustainable devices since they are nontoxic renewable materials with a low cost. Gelatin, a natural protein, is a promising biopolymer for photography, cosmetic manufacturing and food. In this paper, solution-processed natural gelatin was used as a gate dielectric for the fabrication of oxide field-effect transistors (FETs). Similarly to a polyelectrolyte, mobile ions can be generated in gelatin in air environment. A high gate specific capacitance larger than 0.93 μF/cm² was obtained in gelatin processed at low concentrations, due to the formation of electric-double-layers (EDLs). As gelatin films processed at a low concentration of 0.02 g/mL, the fabricated FETs showed excellent electrical performances. The average current on/off ratio and the mobility were estimated to be 1.36 × 10⁵ and 33.2 cm²/V, respectively. The proposed technique may be application in the bioelectronics field, including biosensors and synaptic devices.     

Effects of polar functional groups and roughness topography of polymer gate dielectric layers on pentacene field-effect transistors

The present study analyzed the effects of the polar functional groups and rough topography of the gate dielectric layer on the characteristics of pentacene field-effect transistors. For this purpose, prior to deposition of the organic semiconductor, we introduced polar functional groups and created a rough topography onto the poly(methylmethacrylate)/Al₂O₃ gate dielectric layer using oxygen plasma treatment, and controlled the number of polar groups using an aging process. The mobility decrease observed after oxygen plasma treatment ranged from 0.2 to <0.01 cm²/V s and was related to the many polar functional groups and the rough topography of the gate dielectric, which formed localized trap states in the band gap and created disorder in the crystal structure. In addition, the electric dipole of the polar groups and the fixed interface charges induced a positive shift of the threshold voltage and an increase in the off-state current. After aging of the oxygen plasma-treated gate dielectrics, the reduced number of polar groups led to greatly enhanced charge mobility, a less positive shift of the threshold voltage, a lower off-state current, and lower activation energy compared to layers without aging. However, the mobility still remained lower than for layers without plasma treatment owing to the rough topography of the gate dielectric.     

High-performance pentacene field-effect transistors using Al2O3 gate dielectrics prepared by atomic layer deposition (ALD)

High-performance pentacene field-effect transistors have been fabricated using Al₂O₃ as a gate dielectric material grown by atomic layer deposition (ALD). Hole mobility values of 1.5 ± 0.2 cm²/V s and 0.9 ± 0.1 cm²/V s were obtained when using heavily n-doped silicon (n⁺-Si) and ITO-coated glass as gate electrodes, respectively. These transistors were operated in enhancement mode with a zero turn-on voltage and exhibited a low threshold voltage (< −10 V) as well as a low sub-threshold slope (<1 V/decade) and an on/off current ratio larger than 10⁶. Atomic force microscopy (AFM) images of pentacene films on Al₂O₃ treated with octadecyltrichlorosilane (OTS) revealed well-ordered island formation, and X-ray diffraction patterns showed characteristics of a “thin film” phase. Low surface trap density and high capacitance density of Al₂O₃ gate insulators also contributed to the high performance of pentacene field-effect transistors.     

Influence of gate-to-source and gate-to-drain recesses on GaAs camel-like gate field-effect transistors

In this article, the characteristics of the GaAs homojunction camel-like gate field-effect transistors with and without the gate-to-source and gate-to-drain recesses structures are first investigated and compared. As to the device without the recesses structure, a second channel within the n ⁺-GaAs cap layer is formed at large gate bias, which could enhance the drain output current and transconductance. Furthermore, a two-stage relationship between drain current (and transconductance) versus gate voltage is observed in the recesses structure. The simulated results exhibit a maximum drain saturation current of 447 (351 mA/mm) and a maximum transconductance of 525 (148 mS/mm) in the studied device without (with) the recesses structure. Consequentially, the demonstration and comparison of the variable structures provide a promise for design in circuit applications.     

Al2O3/TiO2 nanolaminate gate dielectric films with enhanced electrical performances for organic field-effect transistors

Nanolamination has entered the spotlight as a novel process for fabricating highly dense nanoscale inorganic alloy films. OFET commercialization requires, above all, excellent dielectric properties of gate dielectric layer. Here, we describe the fabrication and characterization of Al–O–Ti (AT) nanolaminate gate dielectric films using a PEALD process, and their OFET applications. The AT films exhibited a very smooth surface (R_q < 0.3 nm), a high dielectric constant (17.8), and a low leakage current (8.6 × 10⁻⁹ A/cm² at 2 MV/cm) compared to single Al₂O₃ or TiO₂ films. Importantly, a 50 nm thick AT film dramatically enhanced the value of μFET (0.96 cm²/V) on a pentacene device, and the high off-current level in a single TiO₂ film was effectively reduced. The nanolamination process removes the drawbacks inherent in each single layer so that the AT film provides excellent dielectric properties suitable for fabricating high-performance OFETs. Triethylsilylethynyl anthradithiophene (TES-ADT), a solution-processable semiconductor, was combined with the AT film in an OFET, and the electrical properties of the device were characterized. The excellent dielectric properties of the AT film render nanolamination a powerful strategy for practical OFET applications.     

Facile polymer gate dielectric surface-modification for organic thin-film transistors using self-assembled surfactant layer

We demonstrate facile polymer gate dielectric surface-modification method for organic thin-film transistors (OTFTs). We simply introduce self-assembled surfactant layer onto the top surface of poly(4-vinylphenol) (PVP) dielectric by spin coating PVP solution mixed with sodium dodecyl sulfate and tridecafluorohexane-1-sulfonic acid potassium salt as additive agents. The surfactant-modified PVP layer acquires various merits compared to pristine PVP layer in terms of surface smoothness and hydrophobicity, as confirmed by contact angle measurement, atomic force microscopy analyses, grazing incident X-ray diffraction and near-edge X-ray absorption fine structure spectroscopy. The resulting OTFTs with the conventional semiconducting poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) as the active layer and surfactant-modified PVP as the dielectric layer reveal overall ascendency over the OTFT with pristine PVP, especially in terms of operating hysteresis and reliability. The effects of hydrophobicity of surfactants on the surface properties of PVP as well as the OTFT performances are fully discussed in conjunction with various characterization tools.     

Electrically reprogrammable ROM using N-channel memory transistors with floating gate

An electrically reprogrammable read-only-memory (REPROM) device, providing the fully decoded and on-board-writable functions, is described. The device consists of novel N-channel memory transistors with floating gate, non-volatile memory transistors, which enable electrically reprogramming operation. The memory transistor has been through more than 10⁷ rewrite cycles with no gain facto (β) decrease. The memory device has been processed by the flat-MOS and the Si-gate technologies. It has a 2048 bit memory capacity, organized as 256 words of 8 bits. The polycrystalline silicon floating gate is covered with vapor-deposited silicon nitride. This allows selective write and erase operation, giving the memory device a new bit-level reprogrammable function.     

Organic field-effect transistors (OFETs) of highly oriented films of dithiophene-tetrathiafulvalene prepared by zone casting

We report on the preparation of large area coverage of well-oriented films of dithiophene-tetrathiafulvalene (DT-TTF) from solution by using the zone casting technique. The X-ray analysis shows that the molecules are highly ordered in the films with the stacking direction parallel to the substrate. We further demonstrate that it is possible to prepare organic field-effect transistors (OFETs) employing these films. The devices reveal a remarkable OFET mobility with a maximum value of 0.17 cm²/V s. The fact that the films are prepared from solution makes these devices eminently suitable for low-cost electronics.     

Organic field-effect transistor circuits using atomic layer deposited gate dielectrics patterned by reverse stamping

We report on a reverse stamping method to produce via-holes in circuits comprising acene-based top-gate organic field-effect transistors (OFETs) having a CYTOP/Al₂O₃ (by atomic layer deposition) bilayer gate dielectric. This method relies on the weak adhesive force that exists between a small molecule acene film and a polymer to enable easy delamination of the bilayer gate dielectric by using a PDMS stamp. We demonstrate the effectiveness of this method by fabricating simple circuits using top-gate triisopropylsilylethynyl pentacene (TIPS-pentacene)/poly (triarylamine) (PTAA) OFETs.     

A cross-linked poly(methyl methacrylate) gate dielectric by ion-beam irradiation for organic thin-film transistors

The electrical characteristics of pentacene organic thin-film transistors (OTFTs) using cross-linked poly(methyl methacrylate) (PMMA) as the gate dielectric are reported. Ultra-thin films of cross-linked PMMA could be obtained by spin-coating and subsequent irradiation using a 1.515 MeV ⁴He⁺ ion beam. The resulting film, with a thickness of 33 nm, possessed a low leakage current density of about 10^?6 A cm^?2 for fields up to 2 MV cm^?1. OTFTs incorporating the cross-linked dielectric operated at relatively low voltages, <10 V, and exhibited a mobility of 1.1 cm² V^?1 s^?1, a threshold voltage of ?1 V, a sub-threshold slope of 220 mV per decade and an on/off current ratio of 1.0 × 10⁶.     

Pentacene organic field-effect transistors with polymeric dielectric interfaces: Performance and stability

Low-voltage pentacene organic field-effect transistors (OFETs) with different gate dielectric interfaces are studied and their performance in terms of electrical properties and operational stability is compared. Overall high electrical performance is demonstrated at low voltage by using a 100 nm-thick high-κ gate dielectric layer of aluminum oxide (Al₂O₃) fabricated by atomic layer deposition (ALD) and modified with hydroxyl-free low-κ polymers like polystyrene (PS), divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) (Cyclotene™, Dow Chemicals), and as well as with the widely used octadecyl-trichlorosilane (OTS). Devices with PS and BCB dielectric surfaces exhibit almost similar electrical performance with high field-effect mobilities, low subthreshold voltages, and high on/off current ratios. The higher mobility in pentacene transistors with PS can be correlated to the better structural ordering of pentacene films, as demonstrated by atomic force microscopy (AFM) images and X-ray diffraction (XRD). The devices with PS show good electrical stability under bias stress conditions (V_GS = V_DS = −10 V for 1 h), resulting in a negligible drop (2%) in saturation current (I_DS) in comparison to that in devices with OTS (12%), and to a very high decay (30%) for the devices with BCB.