High Device Yield Research Articles

Linearly programmable two-dimensional halide perovskite memristor arrays for neuromorphic computing.

The exotic properties of three-dimensional halide perovskites, such as mixed ionic-electronic conductivity and feasible ion migration, have enabled them to challenge traditional memristive materials. However, the poor moisture stability and difficulty in controlling ion transport due to their polycrystalline nature have hindered their use as a neuromorphic hardware. Recently, two-dimensional (2D) halide perovskites have emerged as promising artificial synapses owing to their phase versatility, microstructural anisotropy in electrical and optoelectronic properties, and excellent moisture resistance. However, their asymmetrical and nonlinear conductance changes still limit the efficiency of training and accuracy of inference. Here we achieve highly linear and symmetrical conductance changes in Dion-Jacobson 2D perovskites. We further build a 7 × 7 crossbar array based on analogue perovskite synapses, achieving a high device yield, low variation with synaptic weight storing capability, multi-level analogue states with long retention, and moisture stability over 7 months. We explore the potential of such devices in large-scale image inference via simulations and show an accuracy within 0.08% of the theoretical limit. The excellent device performance is attributed to the elimination of gaps between inorganic layers, allowing the halide vacancies to migrate homogeneously regardless of grain boundaries. This was confirmed by first-principles calculations and experimental analysis.

P/N-Type Conversion of 2D MoTe2 Controlled by Top Gate Engineering for Logic Circuits.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) are regarded as promising materials for next-generation logic circuits. Top gate field-effect transistors (FETs) have independent gate control ability and can be fabricated directly on TMDC materials without a transfer process. Therefore, it has the merits of device reliability and complementary metal-oxide semiconductor (CMOS) process compatibility, which are demanded in practical circuit-level integration. However, the fabrication of the top gate FET involves depositing an insulating dielectric layer and a gate electrode in sequence on the TMDC channel material, which may affect the device performance. Insightfully investigating the influences of different top-gate-deposition methods on the electrical properties of the TMDC channel and further harnessing these influences to realize a homogeneous CMOS device on an identical 2D TMDC platform are with practice significance. In this work, p/n-type controllable top gate FET arrays based on 2H-MoTe2 are fabricated by using different top-gate-deposition methods. The electron-beam evaporation (EBE) of top metal gate exhibits an obvious n-doping effect on the 2H-MoTe2 channel and converts it from p-type to n-type, whereas the thermal evaporation of top gate affects little to the channel. High-resolution transmission electron microscopy (HR-TEM) analysis reveals that the high-energy metal atoms from the EBE process can penetrate through the 30 nm gate dielectric layers (including 10 nm Al2O3 seeding layer), leading to multiple atomic defects in both MoTe2 and the interface between MoTe2 and Al2O3. Furthermore, by utilizing the top gate engineering, a large-scale double-top-gate MoTe2 homogeneous CMOS inverter array is fabricated. The CMOS inverters exhibit clear logic swing, negligible hysteresis, and high device yield (∼93%), indicating high device reliability and stability. Notably, the fabrication process is facile, free from transfer procedure, and compatible with traditional silicon technology. This work promotes the application of 2D TMDCs in nanoelectronics integration.

50‐3: Invited Paper: An Active‐Matrix High‐Channel‐Count Neurostimulation System Enabled by Flexible Thin‐Film Transistors

Advanced neurostimulation systems require intimate interface with brain or peripheral nervous system to provide a therapeutic modulation for patients experiencing neural function loss. To achieve these, it requires stimulators with high‐channel counts and mechanical flexibility. In this invited paper, we showed a 4T1C neurostimulation pixel circuit with an active‐matrix architecture, offering the opportunity for high‐channel counts. In addition, a 4‐mask photolithographic process for highly uniform organic thin‐film transistor (OTFT) integrated system was demonstrated for mechanical flexibility, which shows a high device yield of 100% (50/50) and small device variation in threshold voltage of 0.64 V and in mobility of 4.9%. By implementing OTFTs to this novel neurostimulation architecture, we fabricated an OTFT‐based high‐channel‐count neurostimulation system, showing a high stimulator yield of 71.0% and small variation of 15.6% for the output stimulation currents among pixels.

Scalable and efficient grating couplers on low-index photonic platforms enabled by cryogenic deep silicon etching

Efficient fiber-to-chip couplers for multi-port access to photonic integrated circuits are paramount for a broad class of applications, ranging, e.g., from telecommunication to photonic computing and quantum technologies. Grating-based approaches are often desirable for providing out-of-plane access to the photonic circuits. However, on photonic platforms characterized by a refractive index ≃ 2 at telecom wavelength, such as silicon nitride or thin-film lithium niobate, the limited scattering strength has thus far hindered the achievement of coupling efficiencies comparable to the ones attainable in silicon photonics. Here we present a flexible strategy for the realization of highly efficient grating couplers on such low-index photonic platforms. To simultaneously reach a high scattering efficiency and a near-unitary modal overlap with optical fibers, we make use of self-imaging gratings designed with a negative diffraction angle. To ensure high directionality of the diffracted light, we take advantage of a metal back-reflector patterned underneath the grating structure by cryogenic deep reactive ion etching of the silicon handle. Using silicon nitride as a testbed material, we experimentally demonstrate coupling efficiency up to − 0.55 dB in the telecom C-band with high chip-scale device yield.

6-20 GHz 30% ScAlN Lateral Field-Excited Cross-Sectional Lamé Mode Resonators for Future Mobile RF Front Ends.

This article reports on 30% scandium-doped AlN (ScAlN) lateral field-excited (LFE) cross-sectional Lame' mode resonators (CLMRs) with unprecedented performance in the 6-20 GHz range. By combining high-crystallinity 30% ScAlN piezoelectric thin films, a lithographic tunability of the resonance frequency, and a simple three-mask post-CMOS compatible fabrication process, we propose a technology platform that can enable the mass production of low-loss, wideband, and compact microacoustic filtering devices spanning a wide spectrum portion on the same chip for the next-generation radio frequency front ends (RFFEs) of handsets. This article demonstrates a successful scaling of the microacoustic technology well beyond the sub-6-GHz fifth-generation (5G) band, as well as the outstanding capabilities of high-crystallinity 30% ScAlN piezoelectric layers in delivering high-quality factor ( Q ) and high-electromechanical coupling ( kt2 ) resonators, notably exceeding the state of the art in terms of relevant figures of merit (FOMs). Furthermore, we experimentally investigate the impact of geometrical parameters, such as tethering configuration and width-over-length ratio on the devices' 3-dB quality factor ( [Formula: see text]), power linearity (PL), and temperature coefficient of frequency (TCF). By adopting a statistical approach for data analysis, we determine the optimal geometry to maximize the Q value. Moreover, we experimentally demonstrate that a fully tethered device's configuration ensures superior PL, lower TCF, and higher device yield and select that as the best design tradeoff between all the variables under consideration. Finally, we discuss a further scaling of LFE CLMRs, both in terms of higher doping levels in the piezoelectric layer, in order to enhance the performance of microacoustic filters, and in terms of higher operation frequencies, in order to reach and cover the mm-wave spectrum.

Large‐Scale N‐Type FET and Homogeneous CMOS Inverter Array Based on Few‐Layer MoTe2

Abstract2D MoTe2 is regarded as a favorable candidate for semiconductor nanoelectronics integration. Chemical‐vapor‐deposition‐grown MoTe2 usually presents p‐type characteristics. In order to realize basic electronic units like complementary metal‐oxide‐semiconductor (CMOS) inverter, controllable fabrication of p‐ and n‐type transistors at large scale is of vital importance. Here, large‐scale MoTe2 n‐channel field‐effect transistor (n‐FET) arrays are successfully fabricated with seamless coplanar metallic 1T′‐WTe2 contacts to reduce contact resistance. High‐k HfO2 serves as a gate dielectric and its atomic‐layer‐deposition (ALD) process causes an n‐doping effect on the 2H‐MoTe2 channel. The FETs perform typical n‐type characteristics with average electron density and on/off ratio of ≈1.7 × 1013 cm−2 and 2.1 × 104, respectively. Furthermore, large‐scale homogeneous CMOS inverter arrays are fabricated, showing clear logic swing with low power consumption (≈0.4 nW) and high device yield (≈92%). Notably, their voltage transfer characteristics exhibit small hysteresis, and they work well after being kept in air for 16 months, indicating high device stability. The statistical results show that both the n‐FETs and CMOS inverters have high uniformity and reliability in performance. Significantly, this fabrication method is free from transfer processes and compatible with traditional silicon technology. This work paves the way for the application of few‐layer MoTe2 in semiconductor nanoelectronics integration.

Centimeter-Transferable III-Nitride Membrane Enabled by Interfacial Adhesion Control for a Flexible Photosensitive Device.

Flexible III-nitride-based optoelectronic devices are crucial for the next-generation foldable/wearable lighting sterilization and sensor working in the ultraviolet (UV) region. However, the strong bonding effect at the epitaxial interface of III-nitride and bare sapphire substrate makes it difficult for epilayer separation and flexible applications. Although the emerging van der Waals epitaxy (vdWE) with graphene insertion layer offers a feasible route for weakening the interfacial adhesion, the intact centimeter-transferable III-nitride membrane still remains challenging. The spontaneous delamination occurs due to the too weak interfacial adhesion of pure vdW force, and on the contrary, the structural damage of graphene by high-temperature hydrogen etching during the III-nitride growth might also cause separation failure. Up to now, the efficient control of vdWE interfacial adhesion is still an on-going research hotspot. Herein, we demonstrate the interfacial adhesion control of III-nitride vdWE by utilizing graded high-temperature nitridation treatment of the graphene insertion layer, which generates defects and N doping in different levels. The corresponding epitaxial modes of pure-vdWE, quasi-vdWE, and mixed epitaxy are achieved according to the interfacial adhesion difference. It reveals that the quasi-vdWE enabled by small graphene defects and proper N doping triggers the low formation energy for AlN nucleation; meanwhile, the proper interfacial adhesion ensures the growth integrality and intact separation of III-nitride membrane in the centimeter scale. The UV resin-assisted bonding technique is proposed for the successful transfer of III-nitride onto a flexible substrate. The flexible photodetector is fabricated by using a graphene monolayer as the photocarrier transport channel, and it achieves a high device yield of 90%, retaining ∼60% of its initial performance after 250 bending cycles. This work offers the promising strategy for controlling vdWE interfacial adhesion, and the separable and transferable III-nitride membrane lays the foundation for advances of future UV foldable and wearable devices.

Analogue Artificial Synaptic Performance of Self‐Rectifying Resistive Switching Device

AbstractThe immense increase of unstructured data require novel computing systems that can process the input data with low power and parallel processing. This functionality is similar to that of human brains that are composed of numerous neurons, synapses, and their complex connections. To mimic the functionality of the human brain with an electronic device, the resistive switching device and crossbar array has attracted considerable attention for artificial synaptic devices and integrated systems, respectively. For this purpose, the self‐rectifying resistive switching cell based on the Si:ZrOx thin film is developed and its reliability characteristics are tested. Four achievements are highlighted in this study. 1) The retention characteristic is improved by the adoption of TaOx thin film as an oxygen reservoir layer. 2) The asymmetric electrodes can make the self‐rectifying resistive cell (SRC) have sufficient rectifying characteristic. 3) The linearity of conductance update has a dominant effect on the inference performance compared to that of the conductance range variation. 4) The device of the interface‐type resistive switching shows a high enough device yield in the crossbar array device and exhibits reliable multiply‐and‐accumulate operations in the crossbar array to mimic the human brain‐inspired computing system.

Electronic and Optoelectronic Monolayer WSe2 Devices via Transfer-Free Fabrication Method.

Monolayer transition metal dichalcogenides (TMDs) have drawn significant attention for their potential applications in electronics and optoelectronics. To achieve consistent electronic properties and high device yield, uniform large monolayer crystals are crucial. In this report, we describe the growth of high-quality and uniform monolayer WSe2 film using chemical vapor deposition on polycrystalline Au substrates. This method allows for the fabrication of continuous large-area WSe2 film with large-size domains. Additionally, a novel transfer-free method is used to fabricate field-effect transistors (FETs) based on the as-grown WSe2. The exceptional metal/semiconductor interfaces achieved through this fabrication method result in monolayer WSe2 FETs with extraordinary electrical performance comparable to those with thermal deposition electrodes, with a high mobility of up to ≈62.95 cm2 V-1 s-1 at room temperature. In addition, the as-fabricated transfer-free devices can maintain their original performance after weeks without obvious device decay. The transfer-free WSe2-based photodetectors exhibit prominent photoresponse with a high photoresponsivity of ~1.7 × 104 A W-1 at Vds = 1 V and Vg = -60 V and a maximum detectivity value of ~1.2 × 1013 Jones. Our study presents a robust pathway for the growth of high-quality monolayer TMDs thin films and large-scale device fabrication.

Graphene Strain-Effect Transistor with Colossal ON/OFF Current Ratio Enabled by Reversible Nanocrack Formation in Metal Electrodes on Piezoelectric Substrates

Extraordinarily high carrier mobility in graphene has led to many remarkable discoveries in physics and at the same time invoked great interest in graphene-based electronic devices and sensors. However, the poor ON/OFF current ratio observed in graphene field-effect transistors has stymied its use in many applications. Here, we introduce a graphene strain-effect transistor (GSET) with a colossal ON/OFF current ratio in excess of 107 by exploiting strain-induced reversible nanocrack formation in the source/drain metal contacts with the help of a piezoelectric gate stack. GSETs also exhibit steep switching with a subthreshold swing (SS) < 1 mV/decade averaged over ∼6 orders of magnitude change in the source-to-drain current for both electron and hole branch amidst a finite hysteresis window. We also demonstrate high device yield and strain endurance for GSETs. We believe that GSETs can significantly expand the application space for graphene-based technologies beyond what is currently envisioned.

High-Performance CMOS Inverter Array with Monolithic 3D Architecture Based on CVD-Grown n-MoS2 and p-MoTe2.

In thiswork, monolithic three-dimensional complementary metal oxide semiconductor (CMOS) inverter array has been fabricated, based on large-scale n-MoS2 and p-MoTe2 grown by the chemical vapor deposition method. In the CMOS device, the n- and p-channel field-effect transistors (FETs) stack vertically and share the same gate electrode. High k HfO2 is used as the gate dielectric. An Al2 O3 seed layer is used to protect the MoS2 from heavily n-doping in the later-on atomic layer deposition process. P-MoTe2 FET is intentionally designed as the upper layer. Because p-doping of MoTe2 results from oxygen and water in the air, this design can guarantee a higher hole density of MoTe2 . An HfO2 capping layer is employed to further balance the transfer curves of n- and p-channel FETs and improve the performance of the inverter. The typical gain and power consumption of the CMOS devices are about 4.2 and 0.11 nW, respectively, at VDD of 1V. The statistical results show that the CMOS array is with high device yield (60%) and an average voltage gain value of about 3.6 at VDD of 1 V. This work demonstrates the advantage of two-dimensional semi-conductive transition metal dichalcogenides in fabricating high-density integrated circuits.

Memory characteristics of anthracene-based polyimides in non-volatile resistive memory devices

Two anthracene-containing polyimides were synthesized and compared as an active layer in non-volatile resistive memory devices. The 6FDA-AMDA PI-based devices showed WORM behavior with an on/off ratio of up to 106 and a high device yield of 80%.

Photolithography-Based Microfabrication of Biodegradable Flexible and Stretchable Sensors.

Biodegradable sensors based on integrating conductive layers with polymeric materials in flexible and stretchable forms have been established. However, the lack of a generalized microfabrication method results in large-sized, low spatial density, and low device yield compared to the silicon-based devices manufactured via batch-compatible microfabrication processes. Here, a batch fabrication-compatible photolithography-based microfabrication approach for biodegradable and highly miniaturized essential sensor components is presented on flexible and stretchable substrates. Up to 1600 devices are fabricated within a 1 cm2 footprint and then the functionality of various biodegradable passive electrical components, mechanical sensors, and chemical sensors is demonstrated on flexible and stretchable substrates. The results are highly repeatable and consistent, proving the proposed method's high device yield and high-density potential. This simple, innovative, and robust fabrication recipe allows complete freedom over the applicability of various biodegradable materials with different properties toward the unique application of interests. The process offers a route to utilize standard micro-fabrication procedures toward scalable fabrication of highly miniaturized flexible and stretchable transient sensors and electronics.

High‐Performance and Environmentally Robust Multilevel Lead‐Free Organotin Halide Perovskite Memristors

AbstractWith a striking explosion of digital information, organic–inorganic halide perovskite (OHP) memristors have been regarded as a promising solution to break the von Neumann bottleneck as the nonvolatile computing‐in‐memory architecture. However, toxicity and stability under ambient conditions are two critical issues for practical applications. Here, lead‐free MASnI3 (MASI) perovskites are reported with improved resistive switching (RS) performance via defects passivating by introducing PEACl. In‐Sn/PEACl‐MASI/PEDOT:PSS/ITO memristor arrays (10 × 10) exhibit reproducible RS with low SET/RESET voltage (VSET/VRESET, +0.58/−0.49 V), ultrahigh ON/OFF ratio (8.5 × 103), stable endurance (2 × 103 cycles), excellent retention (2 × 104 s), high device yield (88%), and multilevel storage. RS remains robust in harsh environments, including high temperature and humidity, long‐term light irradiation, and open‐air conditions. Importantly, a complete physical simulation model that quantitatively and accurately describes RS in vacancy concentration, temperature, and electric potential is proposed originating from conductive filaments formation/rupture. Additionally, PEACl‐MASI memristors are successfully fabricated on polyethylene terephthalate (PET) and Si substrates to explore the potential for large‐scale application on different substrates. The PEACl‐MASI memristors provide an opportunity to develop the next generation of high‐performance and environmentally robust multilevel information storage devices.

(Digital Presentation) Micro-Surface Engineering of Integrated Silicon Microtechnologies for the Development of Sensing and Biosensing Platforms

Microfabrication techniques used in semiconductor industry deliver high yield of devices and silicon microtechnologies undoubtedly have a reputation of a well-established platform for manufacture. A Silicon-wafer is the most commonly used substrate due to its low-cost; therefore for decades several protocols have been developed in order to process this particular material for micro-nano electronics. Today, it is possible to manufacture ultramicro-nano scale devices with multiple steps of lithography, deposition, and lift-off. Clearly, such progress of microsystems has been one of the major interests of biology-based research fields due to the need for small-reproducible devices with appropriate interface features, in particular for biosensing-applications.Biosensing technologies have an important contribution to a daily basis life with the examples of glucometers, pregnancy tests, Covid-19 tests, etc. Microtechnologies combined with sensing systems are clearly a rising-star due to several benefits of microfabrication protocols such as excellent reproducibility, miniaturization capabilities, low-cost and design flexibility for device fabrication.Establishment of a successful fabrication route of ultramicro devices with high reproducibility is a challenge. Figure1 shows an example fabrication-flow of one of our devices. We have developed several successful fabrication flows for device manufacturing and we have developed several designs of gold chips based on band-electrode-array[1], disk-electrode-array[2], and multiplexing[3] for varying (bio)sensing applications. Figure2 shows a series of SEM images of designed, fabricated and foam-modified devices.One of the significant key of using such tiny devices is the electrochemical reproducibility of the gold surfaces to establish a successful sensing platform. Therefore we assessed the effect of several cleaning protocols on the electrochemical characteristics of ultramicro-electrode-devices. As an example, Figure3a shows one of the 6-sensing-electrodes on a multiplexed-device(1µm-width,45µm-length). After the cleaning protocol of chip, we studied cyclic voltammetry in a redox probe(5mM Fe(CN)6 3–/4– in 1M KCl). Clearly, applied protocol provides reproducible redox-active sensing-electrode surfaces therefore; we obtained overlapping voltammograms of 6-electrode-on-chip(Figure3b). We also investigated the surface morphology of the gold surface(Figure3c). We discovered that the cleaning protocol increases surface-roughness which may lead a redox-active surface.One another key aspect of our study is the application of these tiny devices. We in particular studied miniaturization of hydrogen-bubble template with chips to explore scaling-down limits of in situ template. Figure2 represents many of designs applied with in situ template studied in highly acidic solution under high negative voltages. We explored the electro-catalytic activity of these foam deposits. For example, Figure3d shows one of the sensing electrodes on multiplexed-device after Cufoam deposition. This device is capable of oxidizing glucose in 0.1M NaOH[1a, 4] at a voltage of +0.8V(Figure3e). Therefore we assessed the linear-range between glucose concentration and device response(Figure3f). One of the parameters we have studied was reusability of multiplexed device and Figure3g shows 10-subsequest measurements studied with a single device. We have shown the application of such devices in whole serum samples and also river water for chemical oxygen demand concentration determination.The other application we have been developing via multiplexing is immunosensor development for animal health. We have developed a simple anti-fouling matrix which allowed us to study in a complex matrix. Figure 4a summarizes the development protocol of antifouling matrix which was studied with CV after fresh antifouling coating and after incubation with either 5% BSA or serum overnight. Figure 4b shows the SEM image of one of the sensing electrode on chip after the gold deposition. We use these needle-like gold depositions as a high surface area substrate where we apply the antifouling matrix. Then, via carbodiimide chemistry we immobilized anti-Haptoglobin antibodies onto surface which is specific to haptoglobin protein (one of the immunosensors on chip). With this study we are aiming to detect several biomarkers from milk of cow after calving. This publication has emanated from research conducted with the financial support of Science Foundation Ireland (SFI) and the Department of Agriculture, Food and Marine on behalf of the Government of Ireland under Grant Numbers [16/RC/3835), DAFM stimulus AgriSense II Grant Number 17/RD/US-ROI/56, and EU Horizon 2020 (DEMETER 857202). [1] aV. B. Juska, A. Walcarius, M. E. Pemble, Acs Appl Nano Mater 2019, 2, 5878-5889; bV. B. Juska, M. E. Pemble, Analyst 2020, 145, 402-414. [2] V. Buk, M. E. Pemble, Electrochimica Acta 2019, 298, 97-105. [3] aL. A. Wasiewska, I. Seymour, B. Patella, R. Inguanta, C. M. Burgess, G. Duffy, A. O'Riordan, Sensors and Actuators B: Chemical 2021, 333, 129531; bB. O'Sullivan, B. Patella, R. Daly, I. Seymour, C. Robinson, P. Lovera, J. Rohan, R. Inguanta, A. O'Riordan, Electrochimica Acta 2021, 395. [4] V. B. Juska, G. Juska, J Chem Technol Biot 2021, 96, 1086-1095. Figure 1

The facile implementing ternary resistive memory in graphite-like melamine-cyanuric acid hydrogen-bonded organic framework with high ternary yield and environmental tolerance

The low ternary yield and expensive organic active materials hinder the potential industrialization of organic multi-level resistive memories. Here, facile melamine (M)-cyanuric acid (C) hydrogen-bonded organic framework (M−C HOF) was firstly fabricated as a new type of ternary memorizer. In the M−C HOF, the robust graphite-like planar 2D sheet along ab-plane containing a rosette motif is constructed from nine hydrogen bonds among M and C, and the 2D sheets are stacked into a 3D network through strong π–π stacking interactions. The FTO/M−C/Ag device exhibits a typical ternary memory performance with considerable OFF/ON1/ON2 current ratio of 1:103.1:104.6, relatively low set voltages (1.14 and 1.70 V), good reliability, and high ternary device yield of 74 %. The ternary resistive switching behavior could be ascribed to the filled traps in 2D layer (for ON1 state) and the carriers flowing in 3D network (for ON2 state), which have been verified by quenched fluorescence of isolated M and C, increased (201) lattice plane distance upon external voltages. Besides, this ternary memorizer has superior thermal stability (300 °C) and irradiative tolerance. This attempt of HOF-based ternary memorizer presents a new choice for efficient and facial multi-level resistive material.

Filament Engineering of Two-Dimensional h-BN for a Self-Power Mechano-Nociceptor System.

The switching variability caused by intrinsic stochasticity of the ionic/atomic motions during the conductive filaments (CFs) formation process largely limits the applications of diffusive memristors (DMs), including artificial neurons, neuromorphic computing and artificial sensory systems. In this study, a DM device with improved device uniformity based on well-crystallized two-dimensional (2D) h-BN, which can restrict the CFs formation from three to two dimensions due to the high migration barrier of Ag+ between h-BN interlayer, is developed. The BN-DM has potential arrayable feature with high device yield of 88%, which can be applied for building a reservoir computing system for digital pattern recognition with high accuracy rate of 96%, and used as an artificial nociceptor to sense the external noxious stimuli and mimic the important biological nociceptor properties. By connecting the BN-DM to a self-made triboelectric nanogenerator (TENG), a self-power mechano-nociceptor system, which can successfully mimic the important nociceptor features of "threshold", "relaxation" and "allodynia" is designed.

Highly Reliable Selection Behavior With Controlled Ag Doping of Nano-Polycrystalline ZnO Layer for 3D X-Point Framework

In this letter, a threshold switching (TS) selector with Ag doping-based nano-polycrystalline ZnO switching layer (SL) having (002) preferred orientation has been manifested, without incorporating an active Ag metal layer, using a facile co-sputtering deposition technique. The TS selectors with extremely controlled doping of ~0.14 at. % Ag concentration showed remarkable electroforming (EF)-free selection behavior such as gigantic selectivity (~1011), extreme-low off-current (~10 fA), high on-current density (~1.6 MA/cm2), ultra-steep switching slope (~0.8 mV/decade), satisfactory endurance (>106), fast switch-on speed (~38 ns) and relaxation speed (~64 ns), and high device yield (~90%). Furthermore, selector devices showed reproducible selection behavior with stable threshold voltage (Vth) having merely 8% variances.

Cotrollable growth of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films and their applications in devices

Monolayer molybdenum disulfide (MoS&lt;sub&gt;2&lt;/sub&gt;) is an emerging two-dimensional (2D) semiconductor material.The MoS&lt;sub&gt;2&lt;/sub&gt; film has a natural atomic-level thickness, excellent optoelectronic and mechanical properties, and it also has the potential applications in very large-scale integration technology in the future. In this article we summarize the research progress made by our group in the studying of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films in the past few years. The controlled growth of large-size MoS&lt;sub&gt;2&lt;/sub&gt; single crystals is achieved by oxygen-assisted chemical vapor deposition method. By a unique facile multisource CVD growth method, the highly oriented and large domain size ML MoS&lt;sub&gt;2&lt;/sub&gt; films are epitaxially grown on a 4-inch wafer scale. Almost only 0° and 60° oriented domains are present in films, and the average size of MoS&lt;sub&gt;2&lt;/sub&gt; grains ranges from 100 μm to 180 μm . The samples exhibit their best optical and electrical quality ever obtained, as evidenced from their wafer-scale homogeneity, nearly perfect lattice structure, average room-temperature device mobility of ~70 cm&lt;sup&gt;2&lt;/sup&gt;·V&lt;sup&gt;–1&lt;/sup&gt;·s&lt;sup&gt;–1&lt;/sup&gt; and high on/off ratio of ~10&lt;sup&gt;9&lt;/sup&gt; on SiO&lt;sub&gt;2&lt;/sub&gt; substrates. By adjusting the oxygen doping concentration in the MoS&lt;sub&gt;2&lt;/sub&gt; film through using an effective CVD technique, electrical and optical properties can be well modified, thereby greatly improving the carrier mobilities and controllable n-type electronic doping effects resulting from optimized oxygen doping levels of MoS&lt;sub&gt;2–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;O&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; . In terms of MoS&lt;sub&gt;2&lt;/sub&gt; thin film devices and applications, the 4-inch wafer-scale high-quality MoS&lt;sub&gt;2&lt;/sub&gt; monolayers are used to fabricate the transparent MoS&lt;sub&gt;2&lt;/sub&gt;-based transistors and logic circuits on flexible substrates. This large-area flexible FET device shows excellent electrical performance with a high device density (1,518 transistors per cm&lt;sup&gt;2&lt;/sup&gt;) and yield (97%), and exhibits a high on/off ratio (10&lt;sup&gt;10&lt;/sup&gt;), current density (~35 μA·μm&lt;sup&gt;–1&lt;/sup&gt;), mobility (~55 cm&lt;sup&gt;2&lt;/sup&gt;·V&lt;sup&gt;–1&lt;/sup&gt;·s&lt;sup&gt;–1&lt;/sup&gt;) and flexibility. Based on the vertically integrated multilayer device via a layer-by-layer stacking process, an individual layer of all-2D multifunctional FET is successfully achieved with nearly multiplied on-current density, equivalent device mobility, and persevered on/off ratio and subthreshold swing (SS) of the individual layer, the combined performance of the device is fully utilized, and the integration of “sensing-storing-computing” is realized. A two-terminal floating-gate memory (2TFGM) based artificial synapse built from all-2D van der Waals materials is prepared, the 2TFGM synaptic device exhibits excellent linear and symmetric weight update characteristics with high reliability and tunability. A large number of states of up to ≈3000, high switching speed of 40 ns and low energy consumption of 18 fJ for a single pulse are demonstrated experimentally. The introduction of structural domain boundaries in the basal plane of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; can greatly enhance its hydrogen evolution reaction performance by serving as active sites. The progress we have made in the preparation of monolayer MoS&lt;sub&gt;2&lt;/sub&gt; films and the research on device characteristics is of guiding significance for the basic and application research of MoS&lt;sub&gt;2&lt;/sub&gt;, and also is universal and instructive for other 2D transition metal dichalcogenides.

Artificial synapses based on electric stress induced conductance variation in vertical MoReS3 nanosheets

As promising nonvolatile memory devices, memristors based on transition metal dichalcogenides, such as MoS2 and MoTe2, have received much attention for their polymorphism and distinct electronic characteristics. However, state-of-the-art memristors with horizontal placement of sandwiching 2D material layers suffer from poor performance in switching variability and endurance for the preparation and transfer process. Herein, we report a memristor based on vertical MoReS3 nanosheets spread on the surface of carbon fiber cloth. The atomic-scale thickness, combined with the structural transition from the T′ phase to the T″ phase in Janus MoReS3 nanostructures, lowers the spatial (device-to-device) and temporal (cycle-to-cycle) variation and prolongs the lifespan of the device during resistive switching processes. Furthermore, our memristor achieves a high device yield and accurate analogue programming and, thus, exhibits the synapse-like learning behavior such as short-term memory and long-term memory. These results demonstrate the potential of direct modulation of 2D materials with electric stress and motivate further research in implementation of artificial synapses.