Recent advances in fabrication and functions of neuromorphic system based on organic field effect transistor

The development of various artificial electronics and machines would explosively increase the amount of information and data,which need to be processed via in-situ remediation.Bioinspired synapse devices can store and process signals in a parallel way,thus improving fault tolerance and decreasing the power consumption of artificial systems.The organic field effect transistor(OFET)is a promising component for bioinspired neuromorphic systems because it is suitable for large-scale integrated circuits and flexible devices.In this review,the organic semiconductor materials,structures and fabrication,and different artificial sensory perception systems functions based on neuromorphic OFET devices are summarized.Subsequently,a summary and challenges of neuromorphic OFET devices are provided.This review presents a detailed introduction to the recent progress of neuromorphic OFET devices from semiconductor materials to perception systems,which would serve as a reference for the development of neuromorphic systems in future bioinspired electronics.

High-performance vertical GaN field-effect transistor with an integrated self-adapted channel diode for reverse conduction

A vertical GaN field-effect transistor with an integrated self-adapted channel diode(CD-FET)is proposed to improve the reverse conduction performance.It features a channel diode(CD)formed between a trench source on the insulator and a P-type barrier layer(PBL),together with a P-shield layer under the trench gate.At forward conduction,the CD is pinched off due to depletion effects caused by both the PBL and the metal-insulator-semiconductor structure from the trench source,without influencing the on-state characteristic of the CD-FET.At reverse conduction,the depletion region narrows and thus the CD turns on to achieve a very low turn-on voltage(V_(F)),preventing the inherent body diode from turning on.Meanwhile,the PBL and P-shield layer can modulate the electric field distribution to improve the off-state breakdown voltage(BV).Moreover,the P-shield not only shields the gate from a high electric field but also transforms part of C_(GD)to CGS so as to significantly reduce the gate charge(Q_(GD)),leading to a low switching loss(E_(switch)).Consequently,the proposed CD-FET achieves a low V_(F)of 1.65 V and a high BV of 1446 V,and V_(F),Q_(GD)and E_(switch)of the CD-FET are decreased by 49%,55%and 80%,respectively,compared with those of a conventional metal-oxide-semiconductor field-effect transistor(MOSFET).

Si–Ge based vertical tunnel field-effect transistor of junction-less structure with improved sensitivity using dielectric modulation for biosensing applications

A dielectric modulation strategy for gate oxide material that enhances the sensing performance of biosensors in junction-less vertical tunnel field effect transistors(TFETs)is reported.The junction-less technique,in which metals with specific work functions are deposited on the source region to modulate the channel conductivity,is used to provide the necessary doping for the proper functioning of the device.TCAD simulation studies of the proposed structure and junction structure have been compared,and showed an enhanced rectification of 10^(4) times.The proposed structure is designed to have a nanocavity of length 10 nm on the left-and right-hand sides of the fixed gate dielectric,which improves the biosensor capture area,and hence the sensitivity.By considering neutral and charged biomolecules with different dielectric constants,TCAD simulation studies were compared for their sensitivities.The off-state current IOFFcan be used as a suitable sensing parameter because it has been observed that the proposed sensor exhibits a significant variation in drain current.Additionally,it has been investigated how positively and negatively charged biomolecules affect the drain current and threshold voltage.To explore the device performance when the nanogaps are fully filled,half filled and unevenly filled,extensive TCAD simulations have been run.The proposed TFET structure is further benchmarked to other structures to show its better sensing capabilities.

A non-quasi-static model for nanowire gate-all-around tunneling field-effect transistors

Nanowires with gate-all-around(GAA) structures are widely considered as the most promising candidate for 3-nm technology with the best ability of suppressing the short channel effects,and tunneling field effect transistors(TFETs)based on GAA structures also present improved performance.In this paper,a non-quasi-static(NQS) device model is developed for nanowire GAA TFETs.The model can predict the transient current and capacitance varying with operation frequency,which is beyond the ability of the quasi-static(QS) model published before.Excellent agreements between the model results and numerical simulations are obtained.Moreover,the NQS model is derived from the published QS model including the current-voltage(I-V) and capacitance-voltage(C-V) characteristics.Therefore,the NQS model is compatible with the QS model for giving comprehensive understanding of GAA TFETs and would be helpful for further study of TFET circuits based on nanowire GAA structure.

Design and Analysis of Graphene Based Tunnel Field Effect Transistor with Various Ambipolar Reducing Techniques

The fundamental advantages of carbon-based graphene material,such as its high tunnelling probability,symmetric band structure(linear dependence of the energy band on the wave direction),low effective mass,and characteristics of its 2D atomic layers,are the main focus of this research work.The impact of channel thickness,gate under-lap,asymmetric source/drain doping method,workfunction of gate contact,and High-K material on Graphene-based Tunnel Field Effect Transistor(TFET)is analyzed with 20 nm technology.Physical modelling and electrical characteristic performance have been simulated using the Atlas device simulator of SILVACO TCAD with user-defined material syntax for the newly included graphene material in comparison to silicon carbide(SiC).The simulation results in significant suppression of ambipolar current to voltage characteristics of TFET and modelled device exhibits a significant improvement in subthreshold swing(0.0159 V/decade),the ratio of Ion/Ioff(1000),and threshold voltage(-0.2 V with highly doped p-type source and 0.2 V with highly doped n-type drain)with power supply of 0.5 V,which make it useful for low power digital applications.

High Performance of Enhanced Mode Field Effect Transistor and Ultraviolet Sensor Based on ZnO Nanosheet

ZnO nanosheets with thickness of a few nanometers are prepared by vapor transport and condensation method, and their structure and optical properties are well characterized. Field effect transistor （FET） and ultraviolet （UV） sensors are fabricated based on the ZnO nanosheets. Due to the peculiar structure of nanosheet, the FET shows n-type enhanced mode behavior and high electrical performance, and its field-effect mobility and on/off cur- rent ratio can reach 256 cm2/（V.s） and ~10^8, respectively. Moreover, the response of UV sensors can also be remarkably improved to ~3 × 10^8. The results make the ZnO nanosheets be a good material for the applications in nanoelectronic and optoelectronic devices.

Progress of power field effect transistor based on ultra-wide bandgap Ga_2O_3 semiconductor material

As a promising ultra-wide bandgap semiconductor, gallium oxide(Ga_2O_3) has attracted increasing attention in recent years. The high theoretical breakdown electrical field(8 MV/cm), ultra-wide bandgap(～ 4.8 eV) and large Baliga's figure of merit(BFOM) of Ga_2O_3 make it a potential candidate material for next generation high-power electronics, including diode and field effect transistor(FET). In this paper, we introduce the basic physical properties of Ga_2O_3 single crystal, and review the recent research process of Ga_2O_3 based field effect transistors. Furthermore, various structures of FETs have been summarized and compared, and the potential of Ga_2O_3 is preliminary revealed. Finally, the prospect of the Ga_2O_3 based FET for power electronics application is analyzed.

Study of Non-Ideal Effects for Extended Gate Field Effect Transistor Chlorine Ion Sensing Device

We use the extended gate field effect transistor (EGFET)as the structure of the chlorine ion sensor,and the chlorine ion ionophores (ETH9033 and TDDMAC1)are incorporated into solvent polymeric membrane (PVC/DOS),then the chlorine ion selective membrane is formed on the sensing window,and the fabrication of the EGFET chlorine ion sensing device is completed.The surface potential on the sensing membrane of the EGFET chlorine ion sensing device will be changed in the different chlorine ion concentration solutions,then changes further gate voltage and drain current to detect chlorine ion concentration.We will study non-ideal effects such as temperature,hysteresis and drift effects for the EGFET chlorine ion sensing device in this paper,these researches will help us to improve the sensing characteristics of the EGFET chlorine ion sensing device.

Study on Extended Gate Field Effect Transistor with Nano-TiO-2 Sensing Membrane by Sol-Gel Method

The nano-titanium dioxide (nano-TiO_2) sensing membrane,fabricated by sol-gel technology,was used as the pH-sensing layer of the extended gate field effect transistor (EGFET) device.The objective of this research is the preparation of titanium dioxide materials by sol-gel method using Ti(OBu)_4 as the precursor.In this study,we fabricated a nano-titanium dioxide sensing layer on the ITO glass by dip coating.In order to examine the sensitivity of the nano-TiO_2 films applied to the EGFET devices,we adopted the ITO glass as substrate,and measured theⅠ_(DS)-Ⅴ_G curves of the nano-titanium dioxide separative structure EGFET device in the pH buffer solutions that have different pH values by the Keithley 236 Instrument.By the experimental results,we can obtain the pH sensitivities of the EGFET with nano-TiO_2 sensing membrane prepared by sol-gel method,which is 59.86mV/pH from pH 1 to pH 9.

Study on the Carbon Nanotube Separative Structure for the Extended Gate H^+-Ion Sensitive Field Effect Transistor

We use the carbon nanotube (CNT) as the material of the pH sensing layer of the separative structure for the extended gate H^+-ion sensitive field effect transistor (EGFET) device.The CNT paste was prepared with CNT powder,Ag powder,silicagel,the di-n-butyl phthalate and the toluene solvents by appropriate ratio,then immobilized on the silicon substrate to form the carbon nanotube sensing layer.We measured theⅠ_(DS)-Ⅴ_G curves of the carbon nanotube separative structure EGFET device in the different pH buffer solutions by the Keithley 236Ⅰ-Ⅴmeasurement system.According to the experimental results,we can obtain the pH sensitivities of the carbon nanotube separative structure EGFET device,which is 62.54mV/pH from pH1 to pH13.

Effect of depositing PCBM on perovskite-based metal–oxide–semiconductor field effect transistors

In this manuscript,the perovskite-based metal–oxide–semiconductor field effect transistors（MOSFETs） with phenylC61-butyric acid methylester（PCBM） layers are studied.The MOSFETs are fabricated on perovskites,and characterized by photoluminescence spectra（PL）,x-ray diffraction（XRD）,and x-ray photoelectron spectroscopy（XPS）.With PCBM layers,the current–voltage hysteresis phenomenon is effetely inhibited,and both the transfer and output current values increase.The band energy diagrams are proposed,which indicate that the electrons are transferred into the PCBM layer,resulting in the increase of photocurrent.The electron mobility and hole mobility are extracted from the transfer curves,which are about one order of magnitude as large as those of PCBM deposited,which is the reason why the electrons are transferred into the PCBM layer and the holes are still in the perovskites,and the effects of ionized impurity scattering on carrier transport become smaller.

Low-Programmable-Voltage Nonvolatile Memory Devices Based on Omega-shaped Gate Organic Ferroelectric P(VDF-TrFE) Field Effect Transistors Using p-type Silicon Nanowire Channels

A facile approach was demonstrated for fabricating high-performance nonvolatile memory devices based on ferroelectric-gate field effect transistors using a p-type Si nanowire coated with omega-shaped gate organic ferroelectric poly(vinylidene fluoride-trifluoroethylene)(P(VDF-Tr FE)). We overcame the interfacial layer problem by incorporating P(VDF-Tr FE) as a ferroelectric gate using a low-temperature fabrication process. Our memory devices exhibited excellent memory characteristics with a low programming voltage of ±5 V, a large modulation in channel conductance between ON and OFF states exceeding 105, a long retention time greater than 3 9 104 s, and a high endurance of over 105 programming cycles while maintaining an ION/IOFFratio higher than 102.

Review of gallium oxide based field-effect transistors and Schottky barrier diodes

Gallium oxide(Ga_2O_3), a typical ultra wide bandgap semiconductor, with a bandgap of ~4.9 e V, critical breakdown field of 8 MV/cm, and Baliga's figure of merit of 3444, is promising to be used in high-power and high-voltage devices.Recently, a keen interest in employing Ga_2O_3 in power devices has been aroused. Many researches have verified that Ga_2O_3 is an ideal candidate for fabricating power devices. In this review, we summarized the recent progress of field-effect transistors(FETs) and Schottky barrier diodes(SBDs) based on Ga_2O_3, which may provide a guideline for Ga_2O_3 to be preferably used in power devices fabrication.

Two-Dimensional Transition Metal Dichalcogenides and Their Charge Carrier Mobilities in Field-Effect Transistors

Two-dimensional(2D) materials have attracted extensive interest due to their excellent electrical, thermal,mechanical, and optical properties. Graphene has been one of the most explored 2D materials. However, its zero band gap has limited its applications in electronic devices. Transition metal dichalcogenide(TMDC), another kind of 2D material,has a nonzero direct band gap(same charge carrier momentum in valence and conduction band) at monolayer state,promising for the efficient switching devices(e.g., field-effect transistors). This review mainly focuses on the recent advances in charge carrier mobility and the challenges to achieve high mobility in the electronic devices based on 2DTMDC materials and also includes an introduction of 2D materials along with the synthesis techniques. Finally, this review describes the possible methodology and future prospective to enhance the charge carrier mobility for electronic devices.

Field-effect transistors based on two-dimensional materials for logic applications

Field-effect transistors （FETs） for logic applications, graphene and MoS2, are discussed. These materials have based on two representative two-dimensional （2D） materials, drastically different properties and require different consider- ations. The unique band structure of graphene necessitates engineering of the Dirac point, including the opening of the bandgap, the doping and the interface, before the graphene can be used in logic applications. On the other hand, MoS2 is a semiconductor, and its electron transport depends heavily on the surface properties, the number of layers, and the carrier density. Finally, we discuss the prospects for the future developments in 2D material transistors.

Electrically Tunable Energy Bandgap in Dual-Gated Ultra-Thin Black Phosphorus Field Effect Transistors

The energy bandgap is an intrinsic character of semiconductors, which largely determines their properties. The ability to continuously and reversibly tune the bandgap of a single device during real time operation is of great importance not only to device physics but also to technological applications. Here we demonstrate a widely tunable bandgap of few-layer black phosphorus （BP） by the application of vertical electric field in dual-gated BP field-effect transistors. A total bandgap reduction of 124 meV is observed when the electrical displacement field is increased from 0.10 V/nm to 0.83 V/nm. Our results suggest appealing potential for few-layer BP as a tunable bandgap material in infrared optoelectronies, thermoelectric power generation and thermal imaging.

Unique Characteristics of Vertical Carbon Nanotube Field-effect Transistors on Silicon

A vertical carbon nanotube field-effect transistor(CNTFET) based on silicon(Si) substrate has been proposed and simulated using a semi-classical theory. A single-walled carbon nanotube(SWNT) and an n-type Si nanowire in series construct the channel of the transistor. The CNTFET presents ambipolar characteristics at positive drain voltage(Vd) and n-type characteristics at negative Vd. The current is significantly influenced by the doping level of n-Si and the SWNT band gap. The n-branch current of the ambipolar characteristics increases with increasing doping level of the n-Si while the p-branch current decreases. The SWNT band gap has the same influence on the p-branch current at a positive Vd and n-type characteristics at negative Vd. The lower the SWNT band gap, the higher the current. However, it has no impact on the n-branch current in the ambipolar characteristics. Thick oxide is found to significantly degrade the current and the subthreshold slope of the CNTFETs.

Mobility enhancement of strained GaSb p-channel metal-oxide-semiconductor field-effect transistors with biaxial compressive strain

Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） are experimentally and theoretically investigated, The biaxial compressive strained GaSb MOSFETs show a high peak mobility of 638 cm2/V.s, which is 3.86 times of the extracted mobility of the fabricated GaSb MOSFETs without strain. Meanwhile, first principles calculations show that the hole effective mass of GaSb depends on the biaxial compressive strain. The biaxiai compressive strain brings a remarkable enhancement of the hole mobility caused by a significant reduction in the hole effective mass due to the modulation of the valence bands.

A high mobility C_(60) field-effect transistor with an ultrathin pentacene passivation layer and bathophenanthroline/metal bilayer electrodes

C60 field-effect transistor （OFET） with a mobility as high as 5.17 cm2/V.s is fabricated. In our experiment, an ultrathin pentacene passivation layer on poly-（methyl methacrylate） （PMMA） insulator and a bathophenanthroline （Bphen）/Ag bilayer electrode are prepared. The OFET shows a significant enhancement of electron mobility compared with the corresponding device with a single PMMA insultor and an Ag electrode. By analysing the C60 film with atomic force microscopy and X-ray diffraction techniques, it is shown that the pentacene passivation layer can contribute to C60 film growth with the large grain size and significantly improve crystallinity. Moreover, the Bphen buffer layer can reduce the electron contact barrier from Ag electrodes to C60 film efficiently.

A review for compact model of graphene field-effect transistors

Graphene has attracted enormous interests due to its unique physical, mechanical, and electrical properties. Specially, graphene-based field-effect transistors （FETs） have evolved rapidly and are now considered as an option for conventional silicon devices. As a critical step in the design cycle of modem IC products, compact model refers to the development of models for integrated semiconductor devices for use in circuit simulations. The purpose of this review is to provide a theoretical description of current compact model of graphene field-effect transistors. Special attention is devoted to the charge sheet model, drift-diffusion model, Boltzmann equation, density of states （DOS）, and surface-potential-based compact model. Finally, an outlook of this field is briefly discussed.