Thin Film Transistor Array Research Articles

Retina-Inspired X-Ray Optoelectronic Synapse Using Amorphous Ga2O3 Thin Film.

Machine vision techniques are widely applied for object identification in daily life and industrial production, where images are captured and processed by sensors, memories, and processing units sequentially. Neuromorphic optoelectronic synapses, as a preferable option to promote the efficiency of image recognition, are hotly pursued in non-ionizing radiation range, but rarely in ionizing radiation including X-rays. Here, the study proposes an X-ray optoelectronic synapse using amorphous Ga2O3 (a-Ga2O3) thin film. Boosted by the interfacial VO 2+ defects and its slow neutralization rate, the enhanced electron tunneling process at metal/a-Ga2O3 interface produces remarkable X-ray-induced post-synaptic current, contributing to a sensitivity of 20.5, 64.3, 164.1 µC mGy-1 cm-2 for the 1st, 5th, and 10th excitation periods, respectively. Further, a 64×64 imaging sensor is constructed on a commercial amorphous Si (a-Si) thin film transistor (TFT) array. The image contrast can be apparently improved under a series of X-ray pulses due to an outstanding long-term plasticity of the single pixel, which is beneficial to the subsequent image recognition and classification based on artificial neural network. The merits of large-scale production ability and good compatibility with modern microelectronic techniques belonging to amorphous oxide semiconductors may promote the development of neuro-inspired X-ray imagers and corresponding machine vision systems.

Perovskite Thin-Film Transistors for Ultra-Low-Voltage Neuromorphic Visions.

Perovskite thin-film transistors (TFTs) simultaneously possessing exceptional carrier transport capabilities, nonvolatile memory effects, and photosensitivity have recently attracted attention in fields of both complementary circuits and neuromorphic computing. Despite continuous performance improvements through additive and composition engineering of the channel materials, the equally crucial dielectric/channel interfaces of perovskite TFTs have remained underexplored. Here, it is demonstrated that engineering the dielectric/channel interface in 2D tin perovskite TFTs not only enhances the performance and operational stability for their utilization in complementary circuits but also enables efficient synaptic behaviors (optical information sensing and storage) under an extremely low operating voltage of -1mV at the same time. The interface-engineered TFT arrays operating at -1mV are then demonstrated as the preprocessing hardware for neuromorphic visions with pattern recognition accuracy of 92.2% and long-term memory capability. Such a low operating voltage provides operational feasibility to the design of large-scale-integrated and wearable/implantable neuromorphic hardware.

Fabrication of carbon nanotube neuromorphic thin film transistor arrays and their applications for flexible olfactory-visual multisensory synergy recognition

Abstract Artificial multisensory devices play a key role for the human-computer interaction in the field of artificial intelligence (AI). In this work, we have designed and constructed a novel olfactory-visual bimodal neuromorphic carbon nanotube thin film transistor (TFT) arrays for artificial olfactory-visual multisensory synergy recognition with the ultralow single-pulse power consumption of 25 aJ, employing semiconducting single-walled carbon nanotubes (sc-SWCNTs) as channel materials and gas sensitive materials, and poly[[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl]-2,5-thiophenediyl-[5,7-bis(2-ethylhexyl)-4,8-dioxo-4H,8H-benzo[1,2-c:4,5-c0]dithio-phene-1,3-diyl]] (PBDB-T) as the photosensitive material. It is noted that it is the first time to realize the simulation of olfactory and visual senses (from 280 nm to 650 nm) with the wide operating temperature range (0-150 °C) in a single SWCNT TFT device and successfully simulate the recovery of olfactory senses after COVID-19 by olfactory-visual synergy. Furthermore, our SWCNT neuromorphic TFT devices with high Ion/Ioff ratio (up to 106) at a low operating voltage (-2-0.5 V) can mimic not only the basic biological synaptic functions of olfaction and vision (such as paired-pulse facilitation, short-term plasticity, and long-term plasticity), but also optical wireless communication by Morse code. The proposed multisensory, broadband light-responsive, low-power synaptic devices provide great potential for developing AI robots to face complex external environments.

Efficient Sorting of Semiconducting Single-Walled Carbon Nanotubes in Bio-Renewable Solvents Through Main-Chain Engineering of Conjugated Polymers.

Conjugated polymer sorting is recognized as an efficient and scalable method for the selective extraction of semiconducting single-walled carbon nanotubes (s-SWCNTs). However, this process typically requires the use of nonpolar and aromatic solvents as the dispersion medium, which are petroleum-based and carry significant production hazards. Moreover, there is still potential for improving the efficiency of batch purification. Here, this study presents fluorene-based conjugated polymer that integrates diamines containing ethylene glycol chains (ODA) as linkers within the main chain, to effectively extract s-SWCNTs in bio-renewable solvents. The introduction of ODA segments enhances the solubility in bio-renewable solvents, facilitating effective wrapping of s-SWCNTs in polar environments. Additionally, the ODA within the main chain enhances affinity to s-SWCNTs, thereby contributing to increased yields and purity. The polymer achieves a high sorting yield of 55% and a purity of 99.6% in dispersion of s-SWCNTs in 2-Methyltetrahydrofuran. Thin-film transistor arrays fabricated with sorted s-SWCNTs solution through slot-die coating exhibit average charge carrier mobilities of 20-23 cm2V⁻¹ s⁻¹ and high on/off current ratios exceeding 105 together with high spatial uniformity. This study highlights the viability of bio-renewable solvents in the sorting process, paving the way for the eco-friendly approach to the purification of SWCNTs.

Photoprogrammed Multifunctional Optoelectronic Synaptic Transistor Arrays Based on Photosensitive Polymer-Sorted Semiconducting Single-Walled Carbon Nanotubes for Image Recognition.

The development of neuromorphic optoelectronic systems opens up the possibility of the next generation of artificial vision. In this work, the novel broadband (from 365 to 940nm) and multilevel storage optoelectronic synaptic thin-film transistor (TFT) arrays are reported using the photosensitive conjugated polymer (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(bithiophene)], F8T2) sorted semiconducting single-walled carbon nanotubes (sc-SWCNTs) as channel materials. The broadband synaptic responses are inherited to absorption from both photosensitive F8T2 and sorted sc-SWCNTs, and the excellent optoelectronic synaptic behaviors with 200 linearly increasing conductance states and long retention time >103s are attributed to the superior charge trapping at the AlOx dielectric layer grown by atomic layer deposition. Furthermore, the synaptic TFTs can achieve IOn/IOff ratios up to 106 and optoelectronic synaptic plasticity with the low power consumption (59aJ per single pulse), which can simulate not only basic biological synaptic functions but also optical write and electrical erase, multilevel storage, and image recognition. Further, a novel Spiking Neural Network algorithm based on hardware characteristics is designed for the recognition task of Caltech 101 dataset and multiple features of the images are successfully extracted with higher accuracy (97.92%) of the recognition task from the multi-frequency curves of the optoelectronic synaptic devices.

Monolithic integration of perovskite heterojunction on TFT backplanes through vapor deposition for sensitive and stable x-ray imaging.

Metal halide perovskites exhibit substantial potential for advancing next-generation x-ray detection. However, fabricating high-performance pixelated imaging arrays remains challenging due to the substantial dark current density and stability issues associated with common organic-inorganic hybrid perovskites. Here, we develop a vapor deposition method to create the first all-inorganic perovskite heterojunction film. The heterojunction introduction effectively reduces the dark current density of detectors to about 0.8 nA·cm-2, satisfying thin-film transistor (TFT) integration standards, while also increases sensitivity to above 2.6 × 104 μC·Gyair-1·cm-2, thus giving rise to a record low detection limit of <1 nGyair·s-1 among all polycrystalline perovskite-based x-ray detectors. The devices also demonstrate remarkable stability across multifarious demanding working conditions. Last, through monolithic integration of the heterojunction film with a 64 × 64 pixelated TFT array, we have achieved high-resolution real-time x-ray imaging, which paves the way for the application of all-inorganic perovskite in low-dose flat-panel x-ray detection.

One-Dimensional orthorhombic CsPbI3 polycrystalline thick film for efficient and highly stable direct X-ray detection and imaging

An ideal direct X-ray detector should convert a low dose of X-ray photons into large quantity of electrical signals, coupled with sustained long-term stability. Nevertheless, a notable conflict arises between X-ray absorption efficiency and carrier transport in thick polycrystalline perovskite films. Moreover, conventional perovskite materials exhibit inherent challenges regarding the stability of their crystal phase and the consistency of the photocurrent. To circumvent these limitations, a polycrystalline perovskite thick film is proposed using orthorhombic CsPbI3 (δ-CsPbI3) as a highly stable active material. Combined with the liquid epitaxy process, δ-CsPbI3 prefers one-dimensional growth along the carrier transportation direction, which suppresses the formation of grain boundaries, enabling high carrier mobility while maintaining X-ray absorption for a thick polycrystalline film. Consequently, the polycrystalline δ-CsPbI3 based detector exhibits a highest sensitivity of 1768.46 μC Gyair-1 cm−2 at an electric field of 432 V mm−1 which is 88.42-fold higher than α-Se based detectors and 190-fold higher than the single crystalline δ-CsPbI3 based detector, respectively. The sensitivity maintains 91.34 % of its initial state after 7 days exposure in the air. Combing with a thin-film transistor array, the detector achieves 8-bit imaging within a 64 × 64 matrix. This work provides a feasible method for commercialized production of high-performance direct X-ray detectors.

Integrated 2T1C pixel circuit with a-Si TFT and NMOS for active matrix mini-LED displays

The 2T1C pixel driver circuit for mini-LED direct display has been proposed, which separates the switching transistor and the driver transistor from the same display substrate, replaces the driver transistor with n-metal oxide semiconductor (NMOS), and combines printed circuit board substrate and thin-film transistor (TFT) substrate to improve the driving capability of the circuit. The NMOS was soldered with mini-LEDs simultaneously onto a substrate which connects to the a-Si TFT array. Two driving modes for a 32-level gray-scale display panel were investigated to compare the voltage-current and optical characteristics. The results demonstrated that the drain-driving mode is better suited for high brightness and high-power display application scenarios as it supports higher-driven currents, but the source-driving mode is more appropriate for precision gray-scale applications due to the higher current linearity of the mode.

Intrinsically Antifouling, soft and conformal bioelectronic from scalable fabrication of Thin-Film OECT arrays by zwitterionic polymers

Thin-film bioelectronic arrays, emerging as a new medical tool, offers significant opportunities for health monitoring, medical diagnosis, medical treatment, life science studies, etc. Thin film devices face several challenges, including biofouling which hinders targeted electrocoupling in complex biological environments, high surface Young's modulus that causes mechanical mismatches with biological matter, and poor surface adhesion that makes it difficult to conform to undeveloped biosurfaces. Here, we developed a universal lithography fabrication platform with high yield, uniformity, and precision to prepare a biomimetic thin-film organic electrochemical transistor (OECT) array featuring intrinsic biofouling resistance, tissue-like surface softness, and strong adhesion to undeveloped surfaces. This fabrication platform is based on the photolithography fabrication of zwitterionic-polymer-based conducting channels and hermetic encapsulation systems without compromising their electrical properties and low permeability. The all-zwitterionic feature softens the surface and helps prevent proteins and cells from approaching the encapsulation and channel surface, thus protecting the OECT array from interference from nonspecific protein and cell interactions. The strong capillary force from the hydrated zwitterions drives the thin-film device to conform well on nonplanar surfaces. Utilizing this biomimetic device, we successfully demonstrated cell-selective electrocoupling in the presence of white blood cells (WBCs) and simultaneously realized close and stable on-skin electrocardiogram (ECG) monitoring via good skin contact and robust epidermal surface lipid resistance. We envision that our process would provide a versatile platform for producing antifouling and flexible bioelectronic devices that seamlessly integrate with biological systems, and promote the practical application of thin-film bioelectronic arrays in real-life scenarios.

Improved temporal performance and optical quantum efficiency of avalanche amorphous selenium for low dose medical imaging.

Active matrix flat panel imagers (AMFPIs) with thin-film transistor arrays experience image quality degradation by electronic noise in low-dose radiography and fluoroscopy. One potential solution is to overcome electronic noise using avalanche gain in an amorphous selenium (a-Se) (HARP) photoconductor in indirect AMFPI. In this work, we aim to improve temporal performance of HARP using a novel composite hole blocking layer (HBL) structure and increase optical quantum efficiency (OQE) to CsI:Tl scintillators by tellurium (Te) doping. Two different HARP structures were fabricated: Composite HBL samples and Te-doped samples. Dark current and optical sensitivity measurements were performed on the composite HBL samples to evaluate avalanche gain and temporal performance. The OQE and temporal performance of the Te-doped samples were characterized by optical sensitivity measurements. A charge transport model was used to investigate the hole mobility and lifetime of the Te-doped samples in combination with time-of-flight measurements. The composite HBL has excellent temporal performance, with ghosting below 3% at 10mR equivalent exposure. Furthermore, the composite HBL samples have dark current and achieved an avalanche gain of 16. Te-doped samples increased OQE from 0.018 to 0.43 for 532nm light. The addition of Te resulted in 2.1% first-frame lag, attributed to hole trapping within the layer. The composite HBL and Te-doping can be utilized to improve upon the limitations of previously developed indirect HARP imagers, showing excellent temporal performance and increased OQE, respectively.

Active pixel image sensor array for dual vision using large‐area bilayer WS2

AbstractTransition metal dichalcogenides (TMDs) are a promising candidate for developing advanced sensors, particularly for day and night vision systems in vehicles, drones, and security surveillance. While traditional systems rely on separate sensors for different lighting conditions, TMDs can absorb light across a broad‐spectrum range. In this study, a dual vision active pixel image sensor array based on bilayer WS2 phototransistors was implemented. The bilayer WS2 film was synthesized using a combined process of radio‐frequency sputtering and chemical vapor deposition. The WS2‐based thin‐film transistors (TFTs) exhibit high average mobility, excellent Ion/Ioff, and uniform electrical properties. The optoelectronic properties of the TFTs array exhibited consistent behavior and can detect visible to near‐infrared light with the highest responsivity of 1821 A W−1 (at a wavelength of 405 nm) owing to the photogating effect. Finally, red, green, blue, and near‐infrared image sensing capabilities of active pixel image sensor array utilizing light stencil projection were demonstrated. The proposed image sensor array utilizing WS2 phototransistors has the potential to revolutionize the field of vision sensing, which could lead to a range of new opportunities in various applications, including night vision, pedestrian detection, various surveillance, and security systems.image

UV-converted heterogeneous wettability surface for the realization of printed micro-scale conductive circuits

Achieving high precision in the fabrication of electronic circuits through additive manufacturing requires breaking the resolution limit of traditional printing processes. To address this challenge, we have developed a novel approach that involves preparing a heterogeneous wetting surface using a light-sensitive NBE-acrylate resin. By creating differences in surface energy on the substrate, we can limit the spread of the ink and surpass the limitations of conventional processes, achieving a printing resolution of 5 μm. The NBE-acrylate resin can be cross-linked under white LED light illumination (with λ > 400 nm) to yield a hydrophobic surface, which can be converted to a hydrophilic surface by UV light illumination (λ = 254 nm). The photochemical reaction of the NBE-acrylate resin under different light irradiation was confirmed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscope (AFM) microforce measurements. In combination with a photomask, patterned heterogeneous wettability surfaces were prepared, which can be utilized for printing precision electronic circuits. Micrometer-scale printed circuits with a low line-to-space (L/S) of 5/50 and 10/10 μm were successfully achieved by optimizing the ink formulation, which is significantly beyond the printing resolution. In the end, fully printed thin film transistor arrays based on semi-conducting carbon nanotubes were achieved, which showed higher charge carrier mobilities of 1.89–4.31 cm2 s−1 V−1 depending on the channel width, demonstrating the application of this precision printed technique.

Ultrathin, Flexible, and Reusable Silicon Shadow Masks Manipulated via Transfer Printing

Stencil lithography is a facile patterning technique that offers a potential solution to the limitations of conventional photolithography. However, several critical factors such as enhanced pattern resolution, ability to pattern on nonplanar surfaces, and multilayer patterning should further be addressed to extend the applications of stencil lithography. This study presents a novel ultrathin silicon shadow mask which is flexible, reusable, and able to be precisely aligned and manipulated through transfer printing. The small thickness of the silicon shadow mask inherently provides it with the enhanced resolution patterning on both planar and nonplanar surfaces. To highlight these attractive benefits, substrates are patterned with metal deposition as well as by etching in a multilayer configuration. Moreover, it is found that the pattern resolution which is degraded as the shadow mask is repeatedly coated with metal and becomes warped can be restored after the mask cleaning procedure, demonstrating its effective reusability. Finally, as a device‐level application, top contact/bottom gate organic thin film transistor arrays are fabricated on both planar and curved surfaces using the shadow mask. These results show the promise of stencil lithography as a versatile and reliable high resolution patterning method for various applications by exploiting the presented ultrathin silicon shadow mask.

Room-temperature fabrication of flexible oxide TFTs by co-sputtering of IGZO and ITO

Amorphous oxide semiconductors, especially indium gallium zinc oxide (IGZO), have been widely studied and obtained significant progress in flexible thin-film transistors (TFTs) due to the high carrier mobility and low deposition temperature. However, a further annealing step is generally required to activate electrical properties and improve the device performance, which limited their applications in flexible electronics. In this study, we achieved flexible TFTs and arrays using co-sputtered IGZO and indium tin oxide (ITO) as channels deposited at room temperature without post-annealing. It was found that better transistor switching properties could be effectively achieved by regulating the sputtering power of ITO in the co-sputtered deposition. The device performance is comparable to that of the conventional oxide TFTs with high annealing temperatures (⩾300 °C), exhibiting a high saturation mobility (μ sat) of 15.3 cm2 V−1s−1, a small subthreshold swing (SS) of 0.21 V dec−1, and a very high on–off ratio (I on/off) of 1011. In addition, a 12 × 12 flexible TFT array was achieved with uniform performance owing to the low-temperature processing advantage of this technique. The flexible TFTs exhibited robust mechanical flexibility with a minimum bending radius of 5 mm and bending cycles up to 1000. Furthermore, an inverter based on co-sputtered IGZO and ITO was demonstrated with the maximum gain of 22. All these achievements based on the proposed TFTs without post-annealing process are expected to promote the applications in advanced flexible displays and large-area integrated circuits.

Fabrication of Large‐Area Organic Thin Film Transistor Array with Highly Uniform Water‐Borne Polyimide Gate Dielectric via Green Solvent‐Engineered Bar‐Coating Process

AbstractHere, the utilization of a highly uniform water‐borne polyimide (W‐PI) thin film as a gate dielectric layer for large‐scale organic thin film transistors (OTFTs) exceeding 100 cm2 is presented, employing the bar‐coating technique. The W‐PI thin films are obtained uniformly over a large area by systematically manipulating the surface tension of the water‐soluble poly(amic acid) salts (W‐PAAS) solution using alcohol as a co‐solvent in a “Green” process. The thickness of the W‐PI thin film is precisely controlled within the range of tens to hundreds of nanometers by adjusting key parameters, including the concentration of the W‐PAAS solution, wire diameter, and bar‐coating speed. As a result, 500 pentacene‐based OTFTs are successfully fabricated on a 10 × 10 cm2 substrate, utilizing a 280 nm thick W‐PI gate dielectric film. These devices exhibit excellent uniformity, with field‐effect mobility of 0.20 ± 0.02 cm2 V−1 s−1. Furthermore, the fabrication of electronic devices using an environmental‐friendly bar‐coating method on large‐area flexible substrates is demonstrated. This study highlights the considerable potential of eco‐friendly W‐PI thin films as dielectric materials, offering advantages such as cost‐effectiveness and high efficiency for reliable industrial applications.

Effect of Large-Area Exfoliation and Etching on the Electrical Behavior of Transition-Metal Dichalcogenide Field-Effect Transistors

Large-area layer transfer was used to fabricate multilayer transition-metal dichalcogenide (TMDC) thin-film transistor (TFT) arrays with areas of (40 × 40 μm2) from single-crystal flakes. The effects of plasma etching of the TFT backchannel surface and bulk defects in the layers on the electrical performance and stability of the n-channel depletion-mode TFTs were investigated. Few-layer structures (∼3 monolayers) were fabricated using a dry etching process to thin multilayer (∼60–90 nm thick) TMDC structures. The etching improved the threshold voltage of the TFTs, resulting in a positive threshold voltage shift of +40 V after etching the backchannel, correlating to a bulk trap density of approximately 1 × 1016 cm–3 eV–1 per monolayer. Etching the MoS2 surface resulted in a threshold voltage shift of 0.2 V per nanometer of MoS2 removed (for MoS2 thicknesses >15 nm). For MoS2 layers etched to <15 nm, the threshold voltage changed to ∼1.8 V per nanometer. An observed degradation of the carrier transport and electrical stability of these samples were found to be due to the proximity of the etched surface approaching the active channel region of the device. The results reveal the performance trade-offs of fabricating large-area arrays of few-layer TMDC TFTs using a mechanical exfoliation and dry etching approach.

5.1: Invited Paper: Highly Stretchable Metal Oxide Island TFTs array for Deformable Display Applications

Deformable displays are attracting attention for use in various applications because of their high flexibility and stretchability. This paper describes our recent work on the development of flexible and stretchable thin‐film transistor (TFT) backplane technologies for deformable displays. We developed a flexible bezel‐less TFT backplane with through‐plastic‐vias and dome‐shaped stretchable TFT arrays with acrylic adhesive.

Serially connected tantalum and amorphous indium tin oxide for sensing the temperature increase in IGZO thin-film transistor backplanes

A temperature sensor embedded in an In-Ga-Zn oxide (IGZO) TFT was evaluated after fabrication to facilitate monitoring of the temperature distribution on a thin-film transistor (TFT) array. Because the proposed temperature sensor uses the same material as the TFT, no additional process or material is required. Moreover, it can be used as a light shield layer because the temperature sensor is located on a TFT. The temperature sensor used in this study was serially connected to indium tin oxide and a metal. As the temperature increased to 120 °C, the output voltage of the temperature sensor increased to 176.6 mV. The sensitivity, hysteresis, and repeatability were 0.85 mV/°C, 3.56 %, and 0.04 %, respectively. The temperature sensor was integrated into an amorphous IGZO bottom-gate TFT. The TFT exhibited a field-effect mobility of 8.2 cm2V−1·s−1 and threshold voltage of 5.2 V. As the drain current increased from 300 µA to 1.1 mA, the temperature increased from 26 to 32.9 °C, and the output voltages of the temperature sensor augmented from 66 to 76 mV. The integrated temperature sensors enable us to measure the temperature distribution in a display panel and compensate for image deterioration due to increased temperature.

Rapid Uniformity Analysis of Fully Printed SWCNT-Based Thin Film Transistor Arrays via Roll-to-Roll Gravure Process.

The roll-to-roll (R2R) gravure process has the potential for manufacturing single-wall carbon nanotubes (SWCNT)-based thin film transistor (TFT) arrays on a flexible plastic substrate. A significant hurdle toward the commercialization of the R2R-printed SWCNT-TFT array is the lack of a suitable, simple, and rapid method for measuring the uniformity of printed products. We developed a probing instrument for characterizing R2R gravure printed TFT, named PICR2R-TFT, for rapidly characterizing R2R-printed SWCNT-TFT array that can present a geographical distribution profile to pinpoint the failed devices in an SWCNT-TFT array. Using the newly developed PICR2R-TFT instrument, the current-voltage characteristics of the fabricated SWCNT-TFT devices could be correlated to various R2R-printing process parameters, such as channel length, roll printing length, and printing speed. Thus, by introducing a characterization tool that is reliable and fast, one can quickly optimize the R2R gravure printing conditions to enhance product uniformity, thereby maximizing the yield of printed SWCNT-TFT arrays.

SnSe ambipolar thin film transistor arrays with copper-assisted exfoliation

SnSe is a layered metal chalcogenide with potential ambipolar applications. However, the scale of devices is subject to limitation of milli/centi-meter-sized two-dimensinal (2D) flakes. Here, we demonstrate the preparation of wafer-scale SnSe ambipolar thin film transistor (TFT) arrays. The a-axis-oriented SnSe thin films were prepared via atomic layer deposition. The processes of lithography and copper-assisted exfoliation help to peel off unnecessary films to form isolated SnSe flakes. After evaporating nickel as contact electrodes, TFT arrays were successfully fabricated. The on/off current ratios are upgraded from 103 to 104 through annealing at 500 °C to improve the crystalline quality of SnSe, and both hole and electron mobilities increase fivefold to 41.29 and 34.99 cm2 V−1 s−1, respectively. The devices exhibit from symmetric ambipolar to hole-dominated behaviors as SnSe channel thickness increases to 50 nm. The copper-assisted exfoliation method provides an etching technique to make patterned 2D devices.