Field-effect Mobility μFE Research Articles

(Invited) Advanced Transistors for High Frequency Applications

The growing interest for 5G radios pushes technology development towards low-cost and high-performance solutions for operating at microwave and mm-wave. Downscaling CMOS technology has allowed the integration of high-speed transceivers on silicon chips, but high-power amplifiers rely on III-V technologies to deliver the power and efficiency levels required by modern radios.In this work, we motivate the interest of non-Si technologies to meet 5G requirements, and we explore two routes to enable the fabrication of compound semiconductor devices on a large-scale manufacturable Si platform [1,2]. We provide insight on the potential of these new technologies for the design of advanced front-end modules, including modelling and reliability challenges.In the first route (Figure 1(a)), we report on Al(Ga,In)N HEMTs, MISHEMTs and MOSFETs integrated on 200 mm Si wafers using Au-free processing in standard Si CMOS tools, and discuss the performance trade-offs, limitations and solutions. State-of-the-art contact resistance of 0.14 Ω.mm is demonstrated for a non-Au, low thermal budget (<600 oC) contact scheme, as well as a high vertical breakdown voltage (VBD) of >300 V. We show that MISHEMTs, which feature the highest field effect mobility (μFE), >2000 cm2/V.s, and the best 1/f noise performance, have the potential to outperform the other device types in terms of device scalability for high frequency operation. The GaN-on-Si substrate optimization for low RF losses and nonlinear distortion is further discussed.The second route (Figure 1(b)) includes the formation of HBT on Si wafer by selective epitaxy. We demonstrate GaAs/InGaP HBTs grown on a 300 mm Si substrate. A DC current gain of ~112 and breakdown voltage, BVCBO, of 10 V is achieved. The emitter-base and base-collector diodes show an ideality factor of ~1.2 and ~1.4, respectively. This demonstration shows the potential for enabling a hybrid III-V CMOS/ technology for 5G and mm-wave applications, not limited to GaAs but which can also be extended to InGaAs on a 300 mm Si substrate. Figure 1

Mobility Improvement of Amorphous Indium-gallium-zinc Oxide Thin Film Transistor by Roll-to-roll Compatible Plasma Treatment

For the mobility enhancement of amorphous indium-gallium-zinc oxide thin film transistor (a-IGZO TFT), Ar plasma treatment was proposed at room temperature under air as an economic and continuous process. Through the suggested method, the field effect mobility (μFE) improves significantly from 1.69 cm²/V·s to 4.20 cm²/V·s. The increase of oxygen vacancy (VO) and decrease of metal-oxide bonding are observed in the plasma treated device by X-ray photoelectron spectroscopy (XPS) analysis. The increased VO is thought to enhance the carrier concentration and mobility. Some of VO, however, will be an inactive and deep state in the forbidden energy gap of IGZO and deteriorate the electrical stability. To avoid this side effect, the selective Ar plasma treatment was also adapted on source/drain (S/D) contact region and threshold voltage shift under the constant positive gate bias stress was measured to decrease from 6.2 V to 4.8 V, which is similar with the untreated device of 4.4 V. In the contract region plasma device, the μFE improves also by 39.6 % to 2.35 cm²/V·s mainly due to the reduction of S/D contact resistance extracted by the transmission line method (TLM).

A novel TFT with organic-inorganic hybrid perovskite channel layer

Abstract Thin-film field-effect transistors (TFTs) are an essential part of a variety of modern electronics. Interestingly, organic-inorganic hybrid perovskite (OHP) material combines the excellent carrier mobility of inorganic semiconductors and the fabricability of organic materials. Herein a thin-film field-effect transistor using CH3NH3PbI3 as the semiconducting channel was demonstrated. A feasible strategy was presented by modifying the gold electrode with 4-fluorobenzenethiol to eliminate the hole injection barrier between the electrode and CH3NH3PbI3. In addition, we also improved the interfacial characteristics between the gold electrode and the perovskite film by using molybdenum oxide (MoO3) buffer layer. Finally, high-k alumina (Al2O3) was utilized to substitute silicon oxide (SiO2) as the dielectric layer to reach low operating voltage in OHP TFTs. The representative TFT showed superior performance with the subthreshold swing (SS), on/off current ratio and linear field-effect mobility (μFE) values of 0.49 V/dec, 104 and 21.41 cm2/V, respectively. Simple low-temperature processing technology and prominent device performance made this OHP TFT have broad prospects for low-cost, large-area, and flexible applications. The device performance is supposed to be further enhanced through molecular engineering in the organic and inorganic components of the hybrid perovskite to fulfil high speed applications.

Oxygen Vacancy Controlled SiZnSnO Thin‐Film Inverters with High Gain

Amorphous SiZnSnO (a‐SZTO) thin films are successfully deposited to control the electrical characteristics by changing the oxygen partial pressure [p(O2)] ratio during the deposition. As the p(O2) ratio increases, the on current, off current, and the field effect mobility (μFE) decrease and the threshold voltage (Vth) shift to the positive direction gradually. This phenomenon occurs because the oxygen vacancies (VO) in the channel are suppressed due to the effect of oxygen injected during the deposition. To explore the possibility that the device can be applied to integrated thin‐film circuit and operate well in the application, the n‐type only inverters are fabricated using VO controlled thin‐film transistors (TFTs). All inverters have clear voltage transfer characteristics (VTCs) and well operate in the range of 3–15 V of VDD. When Vth shifts to positive direction in enhancement mode (E‐mode), the voltage transition region (Vtr) of the inverter also shifts to positive direction. The highest voltage gain is measured to be about 26.554 V/V at 15 V of VDD. It is proposed to be able to fabricate the inverters and control the transition value of VTCs of the inverter simply by changing p(O2) ratio of E‐mode TFT.

Quantum Confinement Effect in Amorphous In-Ga-Zn-O Heterojunction Channels for Thin-Film Transistors.

Electrical and carrier transport properties in In–Ga–Zn–O thin-film transistors (IGZO TFTs) with a heterojunction channel were investigated. For the heterojunction IGZO channel, a high-In composition IGZO layer (IGZO-high-In) was deposited on a typical compositions IGZO layer (IGZO-111). From the optical properties and photoelectron yield spectroscopy measurements, the heterojunction channel was expected to have the type–II energy band diagram which possesses a conduction band offset (ΔEc) of ~0.4 eV. A depth profile of background charge density indicated that a steep ΔEc is formed even in the amorphous IGZO heterojunction interface deposited by sputtering. A field effect mobility (μFE) of bottom gate structured IGZO TFTs with the heterojunction channel (hetero-IGZO TFTs) improved to ~20 cm2 V−1 s−1, although a channel/gate insulator interface was formed by an IGZO−111 (μFE = ~12 cm2 V−1 s−1). Device simulation analysis revealed that the improvement of μFE in the hetero-IGZO TFTs was originated by a quantum confinement effect for electrons at the heterojunction interface owing to a formation of steep ΔEc. Thus, we believe that heterojunction IGZO channel is an effective method to improve electrical properties of the TFTs.

Electron-spin-resonance and electrically detected-magnetic-resonance characterization on PbC center in various 4H-SiC(0001)/SiO2 interfaces

We characterized an intrinsic interface defect, called the “PbC center,” formed at 4H-SiC(0001)/SiO2 interfaces by means of electron-spin-resonance (ESR) and electrically detected-magnetic-resonance (EDMR) spectroscopies. The formation of the PbC center was observed with a spin density of 3–4 × 1012 cm−2 after standard thermal oxidation. This center could be effectively removed by the NO post-oxidation-anneal (POA) process or ultra-high-temperature oxidation and could be passivated by H atoms via the H2 POA process. There was a clear correlation between the PbC center and field-effect mobility (μFE) of 4H-SiC(0001) metal–oxide–semiconductor field effect transistors (MOSFETs). The PbC center decreased μFE because this center acts as electron traps, reducing the free-carrier density in the inversion channel of 4H-SiC(0001) MOSFET. We also examined the counter doping effect of NO POA by introducing 15N impurities; however, the counter doping of 15N donors was not detectable by ESR (much lower than 2 × 1011 cm−2). Highly sensitive EDMR measurements revealed that the PbC center has two isotropic hyperfine (HF) interactions at 1.3 and 6.8 mT and suggested that its main 13C HF interaction should be larger than 14 mT. Based on the present experimental data, the origin of the PbC center was ascribed as a carbon-related interface defect that forms a C–H bond after hydrogen passivation. This feature is similar to that of the porous-PbC centers (carbon dangling-bond centers) found in porous-SiC/SiO2 systems. However, their HF signatures indicated that the PbC center at 4H-SiC(0001)/SiO2 interfaces and the porous-PbC centers in porous-SiC should be different centers associated with different wave functions.

Comprehensive Review on Amorphous Oxide Semiconductor Thin Film Transistor

Oxide materials are one of the most advanced key technology in the thin film transistors (TFTs) for the high-end of device applications. Amorphous oxide semiconductors (AOSs) have leading technique for flat panel display, active matrix organic light emitting display, active matrix liquid crystal display as well as thin film electronic devices due to their excellent electrical characteristics, such as field effect mobility (μFE), subthreshold swing (SS) and threshold voltage (Vth). Researchers from various fields have studied and considered ways to improve µFE of AOS TFT, which has been studied for 16 years since 2004. Since 2004, mobility has been increased by using various methods, such as designing novel amorphous oxide materials, changing device structures, or adopting new post-treatment. The development of field effect mobility as well as the stability enhancement has been comprehensively reviewed in this report.

Electric field thermopower modulation analyses of the operation mechanism of transparent amorphous SnO2 thin-film transistor

Transparent amorphous oxide semiconductors (TAOSs) based transparent thin-film transistors (TTFTs) with high field effect mobility (μFE) are essential for developing advanced flat panel displays. Among TAOSs, amorphous (a-) SnO2 has several advantages against current a-InGaZnO4 such as higher μFE and being indium-free. Although a-SnO2 TTFT has been demonstrated several times, the operation mechanism has not been clarified thus far due to the strong gas sensing characteristics of SnO2. Here we clarify the operation mechanism of a-SnO2 TTFT by electric field thermopower modulation analyses. We prepared a bottom-gate top-contact type TTFT using 4.2-nm-thick a-SnO2 as the channel without any surface passivation. The effective thickness of the conducting channel was ∼1.7 ± 0.4 nm in air and in vacuum, but a large threshold gate voltage shift occurred in different atmospheres; this is attributed to carrier depletion near at the top surface (∼2.5 nm) of the a-SnO2 due to its interaction with the gas molecules and the resulting shift in the Fermi energy. The present results would provide a fundamental design concept to develop a-SnO2 TTFT.

Effects of hydrogen plasma treatment on the electrical performances and reliability of InGaZnO thin-film transistors

In this work, we have investigated the effects of hydrogen (H) plasma treatment on the electrical performances and reliability of amorphous InGaZnO (a-IGZO) thin film transistors (TFTs). By optimizing the H plasma treatment time, the a-IGZO TFT with H plasma treatment time of 1 min exhibits excellent electrical performances and reliability, such as high field-effect mobility (μFE) of 26.5 cm2/V s and small threshold voltage shifts (ΔVth) value of 2.5 V and −2.3 V under positive gate bias stress (PBS) and negative gate bias stress (NBS) measurements without any passivation layers. The increased performance relies that the H plasma treatment not only could increase the carrier concentration (Ne) but also reduce the surface defects of channel layer and interface trap density of a-IGZO TFTs. The X-ray photo-electron spectroscopy measurement reveals that the H treatment passivated the oxygen vacancy (VO) defects and formed center-bonded complex states (HO or VO-H) in the a-IGZO films, which act as a shallow donor in a-IGZO films. Therefore, the high performances and excellent reliability of a-IGZO TFTs is suggesting that H is a very promising treatment for TFTs to be used for flexible thin film electronic applications.

Mobility of Air-Stable p-type Polythiophene Field-Effect Transistors Fabricated Using Oxidative Chemical Vapor Deposition

Air-stable organic field-effect transistors (FETs) based on an unsubstituted polythiophene (PT) channel, processed using oxidative chemical vapor deposition (oCVD), have been investigated. The intrinsic properties of PT, including its rigid backbone structure and resistance to reactions with water and oxygen, lead to excellent air stability of oCVD PT-based FET devices. The effect of the channel/metalization contact resistance on the field-effect mobility (μFE) of PT-based FETs has also been investigated. Due to the channel/metallization contact resistance, the actual voltages applied to the channel are found to be significantly lower than the intended drain bias because of the voltage drops that occur at the source/drain contacts. Transmission-line measurements reveal that more than 30% of the intended drain bias is lost at all gate voltages applied to the channel. Reconstructed output characteristics excluding the contact effect allow the extraction of a corrected μFE, which is approximately 40% higher than that with contact resistance.

Enhanced piezoelectric tactile sensing behaviors of high-density and low-damage CF4-plasma-treated IGZO thin-film transistors coated by P(VDF-TrFE) copolymers

Piezoelectric pressure sensing behaviors of high-density and low-damage CF4-plasma-treated indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) coated by poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) films have been investigated. The CF4 plasma treatment was performed on the IGZO channel by using an inductively coupled plasma (ICP) system with a quartz filter. Prior to the fabrication of devices, X-ray diffractometer (XRD) and atomic force microscopy (AFM) were applied to identify the enhancement in the crystallinity of P(VDF-TrFE) films on the plasma-fluorinated IGZO films. With the analyses of X-ray photoelectron spectroscopy (XPS), it is proved that the fluorine radicals reacted with the metal-oxygen bonds will increase the oxygen vacancies in IGZO films, contributing to an enhancement in field effect mobility (μFE) and drain current (IDS) of IGZO TFTs. Furthermore, the fluorine atoms diffused from the IGZO channel into the bottom SiO2 layer were confirmed by secondary ion-mass spectroscopy (SIMS), reducing the interfacial and oxide charges of the devices for a negative shift in threshold voltage (Vt). Under a 0.5-kg applied force press/release cyclic test, a 4.8-fold increase in drain current response of 1-min CF4-plasma-treated piezoelectric pressure sensors was optimized, because of the enhanced electrical behaviors of IGZO TFTs and an increase in aligned dipole moments of P(VDF-TrFE) copolymers. The promising results make the piezoelectric pressure sensors with high-density and low-damage CF4-plasma-treated IGZO TFTs coated by P(VDF-TrFE) copolymer suitable for future high-performance tactile sensing applications.

Numerical Analysis on Effective Mass and Traps Density Dependence of Electrical Characteristics of a-IGZO Thin-Film Transistors

We have investigated the effect of electron effective mass (me*) and tail acceptor-like edge traps density (NTA) on the electrical characteristics of amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) through numerical simulation. To examine the credibility of our simulation, we found that by adjusting me* to 0.34 of the free electron mass (mo), we can preferentially derive the experimentally obtained electrical properties of conventional a-IGZO TFTs through our simulation. Our initial simulation considered the effect of me* on the electrical characteristics independent of NTA. We varied the me* value while not changing the other variables related to traps density not dependent on it. As me* was incremented to 0.44 mo, the field-effect mobility (µfe) and the on-state current (Ion) decreased due to the higher sub-gap scattering based on electron capture behavior. However, the threshold voltage (Vth) was not significantly changed due to fixed effective acceptor-like traps (NTA). In reality, since the magnitude of NTA was affected by the magnitude of me*, we controlled me* together with NTA value as a secondary simulation. As the magnitude of both me* and NTA increased, µfe and Ion deceased showing the same phenomena as the first simulation. The magnitude of Vth was higher when compared to the first simulation due to the lower conductivity in the channel. In this regard, our simulation methods showed that controlling me* and NTA simultaneously would be expected to predict and optimize the electrical characteristics of a-IGZO TFTs more precisely.

Physical Modeling of p-Type Fluorinated Al-Doped Tin-Oxide Thin Film Transistors

Fabrication, physical modeling and dynamic response of p-type Al-doped SnOx active channel thin film transistors (TFTs) are presented for the potential application of ultra-high definition (UHD) displays. After deposition of Al-doped SnOx active layer using reactive co-sputtering, the channel was treated with plasma fluorination which improve the device performance of high ION/IOFF ratio of > 106, low subthreshold swing of ~100 mV/dec and high field-effect mobility (μFE) of 4.8 cm 2 V -1 s -1 . To understand the origin of such high performance, physical modeling and numerical simulations were performed using density of state (DOS) model of defects/traps of oxide semiconductor. This model describes the modifications of donor-like tail states and acceptor-like Gaussian defect states due to Al doping on SnO x and fluorine treatment. To evaluate the device performance for UHD large scale displays, the dynamic responses of p-type TFT pixel circuit for various requirements are simulated with physical models. These results suggest that the Al-doped SnO x TFTs are potential candidates for future high-definition displays and many applications in transparent electronics.

Influence of Oxygen Partial Pressure on Radio Frequency Magnetron Sputtered Amorphous InZnSnO Thin Film Transistors.

Amorphous oxide semiconductors (AOS) have been studied extensively for the past decade as a possible alternative to polysilicon thin film transistors (TFTs). One such example is amorphous InZnSnO (IZTO), which was used in this study as an active channel layer for TFTs. A 30 nm-thick IZTO film was deposited using RF magnetron sputtering with various oxygen partial pressures, followed by annealing treatment in air at 350 °C. The resulting films showed good optical properties with high transparency of >85% in the visible spectrum, which is important for realizing transparent devices. The amorphous IZTO TFT device showed good performance with a field-effect mobility (μFE) of 29.1 cm²/Vs, threshold voltage (VT) of 0.70 V, on/off current ratio (Ion/Ioff) of ~108, and subthreshold swing (SS) value of 0.12 V/dec. Oxygen incorporation during deposition of the channel layer affected the overall electrical properties of the TFTs, which is associated with the change of interface trap density.

Defect-creation effects on abnormal on-current under drain bias illumination stress in a-IGZO thin-film transistors

On-current ION and field effect mobility μFE changed abnormally by drain bias illumination stress (DBIS) in amorphous InGaZnO thin-film transistors. First, ION dropped to 35% of its initial value and μFE decreased from 11.8 cm2/(V∙s) to 3.0 cm2/(V∙s) because of acceptor-like tail states ATAIL, which were generated by rupture of weak oxygen bonds near the drain region. The ATAIL trap electrons, and therefore have negative charge, which causes scattering of charged carriers and decrease in μFE. As DBIS time elapsed, ionized oxygen vacancies (VO2+) were generated near the drain region, so ION was re-elevated to 1.57 times as high as its dropped value (i.e., to 55% of its initial value); μFE increased from 3.0 cm2/(V∙s) to 6.9 cm2/(V∙s) (i.e., to 59% of its origin value);. These compensation effects happened when ATAIL and VO2+ occurred in the same place, so generation of VO2+ near drain region was the main cause of the re-elevation.

Layer‐Dependent Optoelectronic Properties of 2D van der Waals SnS Grown by Pulsed Laser Deposition

AbstractLayered metal monochalcogenides have attracted significant interest in the 2D family since they show different unique properties from their bulk counterparts. The comprehensive synthesis, characterization, and optoelectrical applications of 2D‐layered tin monosulfide (SnS) grown by pulsed laser deposition are reported. Few‐layer SnS‐based field‐effect transistors (FETs) and photodetectors are fabricated on Si/SiO2 substrates. The premium 2D SnS FETs yield an on/off ratio of 3.41 × 106, a subthreshold swing of 180 mV dec−1, and a field effect mobility (µFE) of 1.48 cm2 V−1 s−1 in a 14‐monolayer SnS device. The layered SnS photodetectors show a broad photoresponse from ultraviolet to near‐infrared (365–820 nm). In addition, the SnS phototransistors present an improved detectivity of 9.78 × 1010 cm2 Hz1/2 W−1 and rapid response constants of 60 ms for grow‐time constant τg and 10 ms for decay‐time constant τd under extremely weak 365 nm illumination. This study sheds light on layer‐dependent optoelectronic properties of 2D SnS that promise to be important in next‐generation 2D optoelectronic devices.

The role of oxygen in determining the electrical performance of ZnSnO nanofiber field-effect transistors

In recent years, one-dimensional (1D) nanostructures, such as nanotubes, nanowires and nanofibers, have been extensively investigated as potential building blocks in nanoscale devices owing to their excellent physical and chemical properties. In this report, zinc tin oxide (ZnSnO) nanofiber networks (NFNs) were fabricated by electrospinning, and the surface morphologies, crystallinities, grain size distributions, and chemical compositions of the nanofibers annealed in different atmospheres were systematically investigated. To verify the possible applications, field-effect transistors (FETs) based on ZnSnO NFNs/SiO2 were integrated. It is found that the field-effect mobility (µFE) of FETs based on ZnSnO NFNs annealed in oxygen is an order of magnitude higher than those annealed in air. When high-κ ZrOx thin film was employed as gate dielectric, the operating voltage was substantially reduced and a high µFE of 21.58 cm2 V−1 s−1 was achieved for the FETs based on ZnSnO NFNs annealed at 500 °C in oxygen. FETs based on oxygen-annealed ZnSnO NFNs/ZrOx exhibit great potential for applications in low-cost and low-voltage devices.

Temperature-Dependent Opacity of the Gate Field Inside MoS2 Field-Effect Transistors.

The transport behaviors of MoS2 field-effect transistors (FETs) with various channel thicknesses are studied. In a 12 nm thick MoS2 FET, a typical switching behavior is observed with an Ion/Ioff ratio of 106. However, in 70 nm thick MoS2 FETs, the gating effect weakens with a large off-current, resulting from the screening of the gate field by the carriers formed through the ionization of S vacancies at 300 K. Hence, when the latter is dual-gated, two independent conductions develop with different threshold voltage (VTH) and field-effect mobility (μFE) values. When the temperature is lowered for the latter, both the ionization of S vacancies and the gate-field screening reduce, which revives the strong Ion/Ioff ratio and merges the two separate channels into one. Thus, only one each of VTH and μFE are seen from the thick MoS2 FET when the temperature is less than 80 K. The change of the number of conduction channels is attributed to the ionization of S vacancies, which leads to a temperature-dependent intra- and interlayer conductance and the attenuation of the electrostatic gate field. The defect-related transport behavior of thick MoS2 enables us to propose a new device structure that can be further developed to a vertical inverter inside a single MoS2 flake.

Inversion channel mobility and interface state density of diamond MOSFET using N-type body with various phosphorus concentrations

We investigated the phosphorus concentration (NP) dependence of the field-effect mobility μFE and interface state density Dit in inversion channel diamond metal-oxide-semiconductor field-effect transistors (MOSFETs). The inversion channel diamond MOSFETs are potentially applicable in high-frequency, high-current, and high-voltage devices because of the material's excellent properties such as a wide bandgap, high breakdown electric field, high carrier mobility, and high thermal conductivity. However, the influences of device design parameters, such as NP in an n-type body and the oxide layer material, on the electrical characteristics of inversion channel diamond MOSFETs have not yet been reported. In this study, we fabricated inversion channel diamond MOSFETs using n-type bodies with various NP values. For decreased NP in the n-type body, μFE was increased, while Dit was decreased. Using the n-type body with the lowest NP of 2 × 1015 cm−3, the maximum μFE of 20 cm2/V·s and the minimum Dit of 1 × 1013 cm−2·eV−1 were obtained. In addition, an inverse correlation was found between μFE and Dit. Specifically, in the low-gate-voltage region of the drain current–gate voltage characteristics, μFE and Dit were strongly inversely correlated. The high Dit suggests that most holes are trapped in the interface state as strong scattering factors in the low-gate-voltage region. Lower Dit values are therefore important for obtaining higher μFE values, the same as in Si and SiC.

Damage-free mica/MoS2 interface for high-performance multilayer MoS2 field-effect transistors

For top-gated MoS2 field-effect transistors, damaging the MoS2 surface to the MoS2 channel are inevitable due to chemical bonding and/or high-energy metal atoms during the vacuum deposition of gate dielectric, thus leading to degradations of field-effect mobility (μFE) and subthreshold swing (SS). A top-gated MoS2 transistor is fabricated by directly transferring a 9 nm mica flake (as gate dielectric) onto the MoS2 surface without any chemical bonding, and exhibits excellent electrical properties with an on–off ratio of ∼108, a low threshold voltage of ∼0.2 V, a record μFE of 134 cm2 V−1 s−1, a small SS of 72 mV dec−1 and a low interface-state density of 8.8 × 1011 cm−2 eV−1, without relying on electrode-contact engineered and/or phase-engineered MoS2. Although the equivalent oxide thickness of the mica dielectric is in the sub-5 nm regime, enhanced stability characterized by normalized threshold voltage shift (1.2 × 10−2 V MV−1 cm−1) has also been demonstrated for the transistor after a gate-bias stressing at 4.4 MV cm−1 for 103 s. All these improvements should be ascribed to a damage-free MoS2 channel achieved by a dry transfer of gate dielectric and a clean and smooth surface of the mica flake, which greatly decreases the charged-impurity and interface-roughness scatterings. The proposed transistor with low threshold voltage and high stability is highly desirable for low-power electronic applications.