Publications by authors named "David Wei Zhang"

109 Publications

Wafer-scale functional circuits based on two dimensional semiconductors with fabrication optimized by machine learning.

Nat Commun 2021 Oct 12;12(1):5953. Epub 2021 Oct 12.

Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117583, Singapore.

Triggered by the pioneering research on graphene, the family of two-dimensional layered materials (2DLMs) has been investigated for more than a decade, and appealing functionalities have been demonstrated. However, there are still challenges inhibiting high-quality growth and circuit-level integration, and results from previous studies are still far from complying with industrial standards. Here, we overcome these challenges by utilizing machine-learning (ML) algorithms to evaluate key process parameters that impact the electrical characteristics of MoS top-gated field-effect transistors (FETs). The wafer-scale fabrication processes are then guided by ML combined with grid searching to co-optimize device performance, including mobility, threshold voltage and subthreshold swing. A 62-level SPICE modeling was implemented for MoS FETs and further used to construct functional digital, analog, and photodetection circuits. Finally, we present wafer-scale test FET arrays and a 4-bit full adder employing industry-standard design flows and processes. Taken together, these results experimentally validate the application potential of ML-assisted fabrication optimization for beyond-silicon electronic materials.
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http://dx.doi.org/10.1038/s41467-021-26230-xDOI Listing
October 2021

CMOS back-end compatible memristors for digital and neuromorphic computing applications.

Mater Horiz 2021 Oct 12. Epub 2021 Oct 12.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China.

In-memory logic calculations and brain-inspired artificial synaptic neuromorphic computing are expected to solve the limitations of the traditional von Neumann computing architecture. The data processing efficiency of the traditional von Neumann architecture is inherently limited by its physically separated processing and storage units, and thus data transmission besides calculation leads to a limited calculation speed and additional high-power consumption. In addition, traditional digital logic calculations and analog calculations have greater limitations in conversion. Herein, we report a flexible two-terminal memristor based on SiCO:H, which is a porous low- back-end complementary metal-oxide-semiconductor (CMOS)-compatible material. Due to its low operating voltage (200 mV) and fast response speed (100 ns), it could perform digital memory calculation and neuromorphic calculation simultaneously. The memristor could realize a transition from short-term to long-term plasticity in the process of enhancement and inhibition during neuromorphic calculation, with high biological reality. In digital logic calculations, IMP-based and MAGIC-based logic calculations were verified. In neuromorphic computing, an Ag ion-based conductive filament was introduced. The relationship between the temporal dynamics of the conductance evolution and the diffusive dynamics of the Ag active metal could be modulated by the external programming electric field strength. The synapses and neuron dynamics in biology were faithfully simulated, realizing a transition from short-term to long-term plasticity in the process of enhancement and inhibition, which has high compatibility and scalability, proposing a novel solution for the next generation of computer architectures.
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http://dx.doi.org/10.1039/d1mh01257fDOI Listing
October 2021

Reversing the Polarity of MoS with PTFE.

ACS Appl Mater Interfaces 2021 Sep 16;13(38):46117-46124. Epub 2021 Sep 16.

Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, P. R. China.

Pristine monolayer molybdenum disulfide (MoS) demonstrates predominant and persistent n-type semiconducting polarity due to the natural sulfur vacancy, which hinders its electronic and optoelectronic applications in the rich bipolarity area of semiconductors. Current doping strategies in single-layer MoS are either too mild to reverse the heavily n-doped polarity or too volatile to create a robust electronic device meeting the requirements of both a long lifetime and compatibility for mass production. Herein, we demonstrate that MoS can be transferred onto polytetrafluoroethylene (PTFE), one of the most electronegative substrates. After transfer, the MoS photoluminescence exhibits an obvious blueshift from 1.83 to 1.89 eV and a prolonged lifetime, from 0.13 to 3.19 ns. The Fermi level of MoS experiences a remarkable 510 meV decrease, transforming its electronic structure into that of a hole-rich p-type semiconductor. Our work reveals a strong p-doping effect and charge transfer between MoS and PTFE, shedding light on a new nonvolatile strategy to fabricate p-type MoS devices.
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http://dx.doi.org/10.1021/acsami.1c11328DOI Listing
September 2021

Spectrum projection with a bandgap-gradient perovskite cell for colour perception.

Light Sci Appl 2020 Sep 15;9(1):162. Epub 2020 Sep 15.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433, China.

Optoelectronic devices for light or spectral signal detection are desired for use in a wide range of applications, including sensing, imaging, optical communications, and in situ characterization. However, existing photodetectors indicate only light intensities, whereas multiphotosensor spectrometers require at least a chip-level assembly and can generate redundant signals for applications that do not need detailed spectral information. Inspired by human visual and psychological light perceptions, the compression of spectral information into representative intensities and colours may simplify spectrum processing at the device level. Here, we propose a concept of spectrum projection using a bandgap-gradient semiconductor cell for intensity and colour perception. Bandgap-gradient perovskites, prepared by a halide-exchanging method via dipping in a solution, are developed as the photoactive layer of the cell. The fabricated cell produces two output signals: one shows linear responses to both photon energy and flux, while the other depends on only photon flux. Thus, by combining the two signals, the single device can project the monochromatic and broadband spectra into the total photon fluxes and average photon energies (i.e., intensities and hues), which are in good agreement with those obtained from a commercial photodetector and spectrometer. Under changing illumination in real time, the prepared device can instantaneously provide intensity and hue results. In addition, the flexibility and chemical/bio-sensing of the device via colour comparison are demonstrated. Therefore, this work shows a human visual-like method of spectrum projection and colour perception based on a single device, providing a paradigm for high-efficiency spectrum-processing applications.
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http://dx.doi.org/10.1038/s41377-020-00400-wDOI Listing
September 2020

Hollow MXene Sphere-Based Flexible E-Skin for Multiplex Tactile Detection.

ACS Appl Mater Interfaces 2021 Sep 14;13(38):45924-45934. Epub 2021 Sep 14.

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, Shanghai 200433, China.

Skin-like electronics that can provide comprehensively tactile sensing is required for applications such as soft robotics, health monitoring, medical treatment, and human-machine interfaces. In particular, the capacity to monitor the contact parameters such as the magnitude, direction, and contact location of external forces is crucial for skin-like tactile sensing devices. Herein, a flexible electronic skin which can measure and discriminate the contact parameters in real time is designed. It is fabricated by integrating the three-dimensional (3D) hollow MXene spheres/Ag NW hybrid nanocomposite-based embedded stretchable electrodes and T-ZnOw/PDMS film-based capacitive pressure sensors. To the best of our knowledge, it is the first stretchable electrode to utilize the 3D hollow MXene spheres with the essential characteristic, which can effectively avoid the drawbacks of stress concentration and shedding of the conductive layer. The strain-resistance module and the pressure-capacitance module show the excellent sensing performance in stability and response time, respectively. Moreover, a 6 × 6 sensor array is used as a demonstration to prove that it can realize the multiplex detection of random external force stimuli without mutual interference, illustrating its potential applications in biomimetic soft wearable devices, object recognition, and robotic manipulation.
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http://dx.doi.org/10.1021/acsami.1c06993DOI Listing
September 2021

High optoelectronic performance of a local-back-gate ReS/ReSe heterojunction phototransistor with hafnium oxide dielectric.

Nanoscale 2021 Sep 2;13(34):14435-14441. Epub 2021 Sep 2.

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, Shanghai 200433, China.

A high optoelectronic performance ReS/ReSe van der Waals (vdW) heterojunction phototransistor utilizing thin hafnium oxide (HfO) as a local-back-gate dielectric layer was prepared and studied. The heterojunction-based phototransistor exhibits a superior electrical performance with a large rectification ratio of ∼10. Furthermore, unlike diode-like heterojunction devices, the innovative introduction of a local-back-gate in this phototransistor provides an outstanding gate-tunable capability with an ultra-low off-state current of 433 fA and a high on/off current ratio of over 10. And under optical excitation of a wide spectrum from 400 to 633 nm, an excellent photodetection responsivity at the 10 A W level and the maximum normalized detectivity of 1.8 × 10 Jones @ 633 nm have been demonstrated. Such high performances are attributed to the band alignment of the type-II heterojunction and the suppression of dark current by the local-back-gate. This work provides a promising reference for two-dimensional (2D) Re-based heterojunction optoelectronic devices.
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http://dx.doi.org/10.1039/d1nr02728jDOI Listing
September 2021

Ultrathin Multibridge Channel Transistor Enabled by van der Waals Assembly.

Adv Mater 2021 Sep 1;33(37):e2102201. Epub 2021 Aug 1.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433, China.

Multibridge channel field-effect transistors (MBCFETs) enable improved gate control and flow of a large drive current and they are regarded as promising candidates for next-generation transistor architecture. However, in achieving a larger drive current with a thinner channel, limitations arise from the decrease in mobility when the thickness of the Si nanosheet is less than 5 nm. In addition, an increase in the leakage current is unavoidable when a large number of channels are stacked. Here, a 2D ultrathin MBCFET is demonstrate, constructed based on 2 nm/2 nm MoS channels. The normalized drive current (23.11 µA*µm µm ) in each level channel of this MBCFET exceeds that of the latest seven-level-stacked Si MBCFET, while the leakage current is only 0.4% of this value, with the subthreshold swing reaching 60 mV dec and an on/off ratio reaching up to 4 × 10 at room temperature. Furthermore, the drive current of this 2D ultrathin MBCFET can be further increased by regulating the polarity of the operation voltage to reduce the injection barrier. The combination of 2D materials and an MBC structure has the potential for use in high-performance and low-power-consumption electronics.
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http://dx.doi.org/10.1002/adma.202102201DOI Listing
September 2021

An in-memory computing architecture based on two-dimensional semiconductors for multiply-accumulate operations.

Nat Commun 2021 06 7;12(1):3347. Epub 2021 Jun 7.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, China.

In-memory computing may enable multiply-accumulate (MAC) operations, which are the primary calculations used in artificial intelligence (AI). Performing MAC operations with high capacity in a small area with high energy efficiency remains a challenge. In this work, we propose a circuit architecture that integrates monolayer MoS transistors in a two-transistor-one-capacitor (2T-1C) configuration. In this structure, the memory portion is similar to a 1T-1C Dynamic Random Access Memory (DRAM) so that theoretically the cycling endurance and erase/write speed inherit the merits of DRAM. Besides, the ultralow leakage current of the MoS transistor enables the storage of multi-level voltages on the capacitor with a long retention time. The electrical characteristics of a single MoS transistor also allow analog computation by multiplying the drain voltage by the stored voltage on the capacitor. The sum-of-product is then obtained by converging the currents from multiple 2T-1C units. Based on our experiment results, a neural network is ex-situ trained for image recognition with 90.3% accuracy. In the future, such 2T-1C units can potentially be integrated into three-dimensional (3D) circuits with dense logic and memory layers for low power in-situ training of neural networks in hardware.
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http://dx.doi.org/10.1038/s41467-021-23719-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8184885PMC
June 2021

Ultrafast non-volatile flash memory based on van der Waals heterostructures.

Nat Nanotechnol 2021 08 3;16(8):874-881. Epub 2021 Jun 3.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, China.

Flash memory has become a ubiquitous solid-state memory device widely used in portable digital devices, computers and enterprise applications. The development of the information age has demanded improvements in memory speed and retention performance. Here we demonstrate an ultrafast non-volatile flash memory based on MoS/hBN/multilayer graphene van der Waals heterostructures, which achieves an ultrafast writing/erasing speed of 20 ns through two-triangle-barrier modified Fowler-Nordheim tunnelling. Using detailed theoretical analysis and experimental verification, we postulate that a suitable barrier height, gate coupling ratio and clean interface are the main reasons for the breakthrough writing/erasing speed of our flash memory devices. Because of its non-volatility this ultrafast flash memory could provide the foundation for the next generation of high-speed non-volatile memory.
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http://dx.doi.org/10.1038/s41565-021-00921-4DOI Listing
August 2021

Corilagin prevents SARS-CoV-2 infection by targeting RBD-ACE2 binding.

Phytomedicine 2021 Jul 5;87:153591. Epub 2021 May 5.

Dr. Neher's Biophysics Laboratory for Innovative Drug Discovery, State Key Laboratory of Quality Research in Chinese Medicine, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau, China. Electronic address:

Background: The outbreak of coronavirus (SARS-CoV-2) disease caused more than 100,000,000 people get infected and over 2,200,000 people being killed worldwide. However, the current developed vaccines or drugs may be not effective in preventing the pandemic of COVID-19 due to the mutations of coronavirus and the severe side effects of the newly developed vaccines. Chinese herbal medicines and their active components play important antiviral activities. Corilagin exhibited antiviral effect on human immunodeficiency virus (HIV), hepatitis C virus (HCV) and Epstein-Barr virus (EBV). However, whether it blocks the interaction between SARS-CoV-2 RBD and hACE2 has not been elucidated.

Purpose: To characterize an active compound, corilagin derived from Phyllanthus urinaria as potential SARS-CoV-2 entry inhibitors for its possible preventive application in daily anti-virus hygienic products.

Methods: Computational docking coupled with bio-layer interferometry, BLI were adopted to screen more than 1800 natural compounds for the identification of SARS-CoV-2 spike-RBD inhibitors. Corilagin was confirmed to have a strong binding affinity with SARS-CoV-2-RBD or human ACE2 (hACE2) protein by the BLI, ELISA and immunocytochemistry (ICC) assay. Furthermore, the inhibitory effect of viral infection of corilagin was assessed by in vitro pseudovirus system. Finally, the toxicity of corilagin was examined by using MTT assay and maximal tolerated dose (MTD) studies in C57BL/6 mice.

Results: Corilagin preferentially binds to a pocket that contains residues Cys 336 to Phe 374 of spike-RBD with a relatively low binding energy of -9.4 kcal/mol. BLI assay further confirmed that corilagin exhibits a relatively strong binding affinity to SARS-CoV-2-RBD and hACE2 protein. In addition, corilagin dose-dependently blocks SARS-CoV-2-RBD binding and abolishes the infectious property of RBD-pseudotyped lentivirus in hACE2 overexpressing HEK293 cells, which mimicked the entry of SARS-CoV-2 virus in human host cells. Finally, in vivo studies revealed that up to 300 mg/kg/day of corilagin was safe in C57BL/6 mice. Our findings suggest that corilagin could be a safe and potential antiviral agent against the COVID-19 acting through the blockade of the fusion of SARS-CoV-2 spike-RBD to hACE2 receptors.

Conclusion: Corilagin could be considered as a safe and environmental friendly anti-SARS-CoV-2 agent for its potential preventive application in daily anti-virus hygienic products.
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http://dx.doi.org/10.1016/j.phymed.2021.153591DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8098048PMC
July 2021

Spider Web-like Flexible Tactile Sensor for Pressure-Strain Simultaneous Detection.

ACS Appl Mater Interfaces 2021 Mar 16;13(8):10428-10436. Epub 2021 Feb 16.

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, Shanghai 200433, China.

Multiparameter integrated sensors are required for the next generation of flexible wearable electronics. However, mutual interference between detected signals is a technical bottleneck for a flexible tactile sensor to realize pressure-strain monitoring simultaneously and sensitively. Herein, a flexible dual-parameter pressure-strain sensor based on the three-dimensional (3D) tubular graphene sponge (TGS) and spider web-like stretchable electrodes is designed and fabricated. As the pressure-sensitive module, the unique 3D-TGS with an uninterrupted network of tubular graphene and high graphitic degree demonstrates great robust compressibility, supporting compression to ∼20% without shape collapse. The spider web-like stretchable electrodes as the strain-sensitive module are fabricated by a spray-embedded process based on the hierarchical multiscale hybrid nanocomposite of Ag nanowires (NWs) and carbon nanotubes (CNTs) with an optimal mass ratio. By comparing the output signals of spider web-like flexible electrodes, the magnitude and direction of the applied force can be effectively monitored simultaneously. Moreover, the potential applications of the flexible dual-parameter pressure-strain device in human-machine interaction are also explored, showing great promise in artificial intelligence and wearable systems.
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http://dx.doi.org/10.1021/acsami.0c21960DOI Listing
March 2021

A Steep-Slope MoS/Graphene Dirac-Source Field-Effect Transistor with a Large Drive Current.

Nano Lett 2021 Feb 10;21(4):1758-1764. Epub 2021 Feb 10.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China.

In the continuous transistor feature size scaling down, the scaling of the supply voltage is stagnant because of the subthreshold swing (SS) limit. A transistor with a new mechanism is needed to break through the thermionic limit of SS and hold the large drive current at the same time. Here, by adopting the recently proposed Dirac-source field-effect transistor (DSFET) technology, we experimentally demonstrate a MoS/graphene (1.8 nm/0.3 nm) DSFET for the first time, and a steep SS of 37.9 mV/dec at room temperature with nearly free hysteresis is observed. Besides, by bringing in the structure of gate-all-around (GAA), the MoS/graphene DSFET exhibits a steeper SS of 33.5 mV/dec and a 40% increased normalized drive current up to 52.7 μA·μm/μm ( = 1 V) with a current on/off ratio of 10, which shows potential for low-power and high-performance electronics applications.
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http://dx.doi.org/10.1021/acs.nanolett.0c04657DOI Listing
February 2021

Fabrication of 1D Te/2D ReS Mixed-Dimensional van der Waals Heterojunction for High-Performance Phototransistor.

ACS Nano 2021 Feb 5;15(2):3241-3250. Epub 2021 Feb 5.

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, Shanghai 200433, China.

The superior optical and electronic properties of the two-dimensional (2D) rhenium disulfide (ReS) makes it suitable for nanoelectronic and optoelectronic applications. However, the internal defects coupled with with the low mobility and light-absorbing capability of ReS impede its utilization in high-performance photodetectors. Fabrication of mixed-dimensional heterojunctions is an alternative method for designing high-performance hybrid photodetectors. This study proposes a mixed-dimensional van der Waals (vdW) heterojunction photodetector, containing high-performance one-dimensional (1D) -type tellurium (Te) and 2D -type ReS, developed by depositing Te nanowires on ReS nanoflake using the dry transfer method. It can improve the injection and separation efficiency of photoexcited electron-hole pairs due to the type II heterojunction formed at the ReS and Te interface. The proposed heterojunction device is sensitive to visible-light sensitivity (632 nm) with an ultrafast photoresponse (5 ms), high responsivity (180 A/W), and specific detectivity (10), which is superior to the pristine Te and ReS photodetectors. As compared to the ReS device, the responsivity and response speed is better by an order of magnitude. These results demonstrate the fabrication and application potential of Te/ReS mixed-dimensional heterojunction for high-performance optoelectronic devices and sensors.
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http://dx.doi.org/10.1021/acsnano.0c09912DOI Listing
February 2021

Dual-gate MoS2 phototransistor with atomic-layer-deposited HfO2 as top-gate dielectric for ultrahigh photoresponsivity.

Nanotechnology 2021 Feb 3. Epub 2021 Feb 3.

Department of Microelectronics, Fudan University, Key Laboratory of Surface Physics, Shanghai 200433, People's Republic of China,, Shanghai, CHINA.

An asymmetric dual-gate (DG) MoS2 field effective transistor (FET) with ultrahigh electrical performance and optical responsivity using atomic-layer-deposited HfO2 as top-gate (TG) dielectric was fabricated and investigated. The effective DG modulation of MoS2 FET exhibited an outstanding electrical performance with a high on/off current ratio of 6×108. Furthermore, a large threshold voltage modulation could be obtained from -20.5 to -39.3 V as a function of the TG voltage in a DG MoS2 phototransistor. Meanwhile, the optical properties were systematically explored under a series of gate biases and illuminated optical power under the 550 nm laser illumination. And the ultrahigh photoresponsivity of 2.04×105 AW-1 has been demonstrated with the structure of DG MoS2 phototransistor because the electric field formed by DG can separate photogenerated electrons and holes efficiently. So, the DG design for the 2D materials with ultrahigh photoresponsivity gives promising opportunity for the application of optoelectronic devices.
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http://dx.doi.org/10.1088/1361-6528/abe2ccDOI Listing
February 2021

Two-dimensional ferroelectric channel transistors integrating ultra-fast memory and neural computing.

Nat Commun 2021 01 4;12(1):53. Epub 2021 Jan 4.

ASIC & System State Key Lab., School of Microelectronics, Fudan University, Shanghai, 200433, China.

With the advent of the big data era, applications are more data-centric and energy efficiency issues caused by frequent data interactions, due to the physical separation of memory and computing, will become increasingly severe. Emerging technologies have been proposed to perform analog computing with memory to address the dilemma. Ferroelectric memory has become a promising technology due to field-driven fast switching and non-destructive readout, but endurance and miniaturization are limited. Here, we demonstrate the α-InSe ferroelectric semiconductor channel device that integrates non-volatile memory and neural computation functions. Remarkable performance includes ultra-fast write speed of 40 ns, improved endurance through the internal electric field, flexible adjustment of neural plasticity, ultra-low energy consumption of 234/40 fJ per event for excitation/inhibition, and thermally modulated 94.74% high-precision iris recognition classification simulation. This prototypical demonstration lays the foundation for an integrated memory computing system with high density and energy efficiency.
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http://dx.doi.org/10.1038/s41467-020-20257-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7782550PMC
January 2021

MoS-on-AlN Enables High-Performance MoS Field-Effect Transistors through Strain Engineering.

ACS Appl Mater Interfaces 2020 Dec 30;12(49):54972-54979. Epub 2020 Nov 30.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, People's Republic of China.

Molybdenum disulfide (MoS) has substantial application prospects in the field of electronic devices. The fabrication of devices of excellent quality based on MoS films is an important research direction. In this study, based on the atomic layer deposition technique, large-area MoS films were grown, and top-gate MoS-based field-effect transistor arrays were fabricated on four substrates (AlN, GaN, sapphire, and SiO). It was found that the interface defects that were introduced by lattice mismatch and roughness of the growth substrate could cause an exponential (10) drop in mobility. Because of the small lattice mismatch and excellent surface quality, transistors on the AlN substrate have shown an enhanced mobility (10.45 cm V s) compared to transistors on the other substrates. This study proves that the AlN substrate is a superior substrate for large-area and high-performance MoS film synthesis. This result can also be applied in higher-level microelectronic systems, such as in digital logic circuit design.
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http://dx.doi.org/10.1021/acsami.0c16079DOI Listing
December 2020

Flexible organic field-effect transistor arrays for wearable neuromorphic device applications.

Nanoscale 2020 Nov;12(45):23150-23158

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, P. R. China.

With the advent of wearable microelectronic devices in the interdisciplinary bio-electronics research field, synaptic devices with capability of neuromorphic computing are attracting more and more attention as the building blocks for the next generation computing structure. Conventional flash-like synaptic transistors are built on rigid solid-state substrates, and the inorganic materials and the high-temperature processing steps have severely limited their applications in various flexible electronic devices and systems. Here, flexible organic flash-like synaptic devices have been fabricated on a flexible substrate with the organic C8-BTBT as the conducting channel. The device exhibits a memory window greater than 20 V and excellent synaptic functions including short/long-term synaptic plasticity and spike-timing-dependent plasticity. In addition, even under the bending condition (7 mm bending radius), the transistor can still stably achieve a variety of synaptic functions. This work shows that low-temperature processing technology with the integration of organic materials can pave a promising pathway for the realization of flexible synaptic systems and the future development of wearable electronic devices.
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http://dx.doi.org/10.1039/d0nr06478eDOI Listing
November 2020

High-bandwidth light inputting multilevel photoelectric memory based on thin-film transistor with a floating gate of CsPbBr/CsPbI blend quantum dots.

Nanotechnology 2021 Feb;32(9):095204

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, People's Republic of China.

The electronic-photonic convergent systems can overcome the data transmission bottleneck for microchips by enabling processor and memory chips with high-bandwidth optical input/output. However, current silicon-based electronic-photonic systems require various functional devices/components to convert high-bandwidth optical signals into electrical ones, thus making further integrations of sophisticated systems rather difficult. Here, we demonstrate thin-film transistor-based photoelectric memories employing CsPbBr/CsPbI blend perovskite quantum dots (PQDs) as a floating gate, and multilevel memory cells are achieved under programming and erasing modes, respectively, by imputing high-bandwidth optical signals. For different bandwidth light input (i.e. 500-550, 575-650 and 675-750 nm) with the same intensity, three levels of programming window (i.e. 3.7, 1.9 and 0.8 V) and erasing window (i.e. -1.9, -0.6 and -0.1 V) are obtained under electrical pulses, respectively. This is because the blend PQDs have two different bandgaps, and different amounts of photo-generated carriers can be produced for different wavelength optical inputs. It is noticed that the 675-750 nm light inputs have no effects on both programming and erasing windows because of no photo-carriers generation. Four memory states are demonstrated, showing enough large gaps (1.12-5.61 V) between each other, good data retention and programming/erasing endurance. By inputting different optical signals, different memory states can be switched easily. Therefore, this work directly demonstrates high-bandwidth light inputting multilevel memory cells for novel electronic-photonic systems.
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http://dx.doi.org/10.1088/1361-6528/abc6e0DOI Listing
February 2021

Spectrum projection with a bandgap-gradient perovskite cell for colour perception.

Light Sci Appl 2020 15;9:162. Epub 2020 Sep 15.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, 200433 China.

Optoelectronic devices for light or spectral signal detection are desired for use in a wide range of applications, including sensing, imaging, optical communications, and in situ characterization. However, existing photodetectors indicate only light intensities, whereas multiphotosensor spectrometers require at least a chip-level assembly and can generate redundant signals for applications that do not need detailed spectral information. Inspired by human visual and psychological light perceptions, the compression of spectral information into representative intensities and colours may simplify spectrum processing at the device level. Here, we propose a concept of spectrum projection using a bandgap-gradient semiconductor cell for intensity and colour perception. Bandgap-gradient perovskites, prepared by a halide-exchanging method via dipping in a solution, are developed as the photoactive layer of the cell. The fabricated cell produces two output signals: one shows linear responses to both photon energy and flux, while the other depends on only photon flux. Thus, by combining the two signals, the single device can project the monochromatic and broadband spectra into the total photon fluxes and average photon energies (i.e., intensities and hues), which are in good agreement with those obtained from a commercial photodetector and spectrometer. Under changing illumination in real time, the prepared device can instantaneously provide intensity and hue results. In addition, the flexibility and chemical/bio-sensing of the device via colour comparison are demonstrated. Therefore, this work shows a human visual-like method of spectrum projection and colour perception based on a single device, providing a paradigm for high-efficiency spectrum-processing applications.
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http://dx.doi.org/10.1038/s41377-020-00400-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7492220PMC
September 2020

Two-dimensional materials for next-generation computing technologies.

Nat Nanotechnol 2020 07 9;15(7):545-557. Epub 2020 Jul 9.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai, China.

Rapid digital technology advancement has resulted in a tremendous increase in computing tasks imposing stringent energy efficiency and area efficiency requirements on next-generation computing. To meet the growing data-driven demand, in-memory computing and transistor-based computing have emerged as potent technologies for the implementation of matrix and logic computing. However, to fulfil the future computing requirements new materials are urgently needed to complement the existing Si complementary metal-oxide-semiconductor technology and new technologies must be developed to enable further diversification of electronics and their applications. The abundance and rich variety of electronic properties of two-dimensional materials have endowed them with the potential to enhance computing energy efficiency while enabling continued device downscaling to a feature size below 5 nm. In this Review, from the perspective of matrix and logic computing, we discuss the opportunities, progress and challenges of integrating two-dimensional materials with in-memory computing and transistor-based computing technologies.
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http://dx.doi.org/10.1038/s41565-020-0724-3DOI Listing
July 2020

Ferroelectric domain wall memory with embedded selector realized in LiNbO single crystals integrated on Si wafers.

Nat Mater 2020 Nov 15;19(11):1188-1194. Epub 2020 Jun 15.

Department of Materials Science and Engineering and Inter-University Semiconductor Research Center, Seoul National University, Seoul, Korea.

Interfacial 'dead' layers between metals and ferroelectric thin films generally induce detrimental effects in nanocapacitors, yet their peculiar properties can prove advantageous in other electronic devices. Here, we show that dead layers with low Li concentration located at the surface of LiNbO ferroelectric materials can function as unipolar selectors. LiNbO mesa cells were etched from a single-crystal LiNbO substrate, and Pt metal contacts were deposited on their sides. Poling induced non-volatile switching of ferroelectric domains in the cell, and volatile switching in the domains in the interfacial (dead) layers, with the domain walls created within the substrate being electrically conductive. These features were also confirmed using single-crystal LiNbO thin films bonded to SiO/Si wafers. The fabricated nanoscale mesa-structured memory cell with an embedded interfacial-layer selector shows a high on-to-off ratio (>10) and high switching endurance (~10 cycles), showing potential for the fabrication of crossbar arrays of ferroelectric domain wall memories.
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http://dx.doi.org/10.1038/s41563-020-0702-zDOI Listing
November 2020

Atomic Layer Deposition of GaO/ZnO Composite Films for High-Performance Forming-Free Resistive Switching Memory.

ACS Appl Mater Interfaces 2020 Jul 25;12(27):30538-30547. Epub 2020 Jun 25.

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, Shanghai 200433, China.

The resistive switching behavior in resistive random access memories (RRAMs) using atomic-layer-deposited GaO/ZnO composite film as the dielectric was investigated. By alternatively atomic-layer-depositing GaO and ZnO with different thickness, we can accurately control the oxygen vacancy concentration. When regulating ZnO to ∼31%, the RRAMs exhibit a forming-free property as well as outstanding performance, including the ratio of a high resistance state to the low resistance state of 1000, retention time of more than 1 × 10 s, and the endurance of 100. By preparing RRAMs of different Zn concentration, we carried out a comparative study and explored the physical origin for the forming-free property as well as good performance. Finally, a unified model is proposed to account for the resistive switching and the current conduction mechanism, providing meaningful insights in the development of high-quality and forming-free RRAMs for future memory and neuromorphic applications.
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http://dx.doi.org/10.1021/acsami.0c06476DOI Listing
July 2020

Nonvolatile ferroelectric field-effect transistors.

Nat Commun 2020 Jun 4;11(1):2811. Epub 2020 Jun 4.

State Key Laboratory of ASIC & Systems, School of Microelectronics, Fudan University, 200433, Shanghai, China.

Future data-intensive applications will have integrated circuit architectures combining energy-efficient transistors, high-density data storage and electro-optic sensing arrays in a single chip to perform in situ processing of captured data. The costly dense wire connections in 3D integrated circuits and in conventional packaging and chip-stacking solutions could affect data communication bandwidths, data storage densities, and optical transmission efficiency. Here we investigated all-ferroelectric nonvolatile LiNbO transistors to function through redirection of conducting domain walls between the drain, gate and source electrodes. The transistor operates as a single-pole, double-throw digital switch with complementary on/off source and gate currents controlled using either the gate or source voltages. The conceived device exhibits high wall current density and abrupt off-and-on state switching without subthreshold swing, enabling nonvolatile memory-and-sensor-in-logic and logic-in-memory-and-sensor capabilities with superior energy efficiency, ultrafast operation/communication speeds, and high logic/storage densities.
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http://dx.doi.org/10.1038/s41467-020-16623-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7272614PMC
June 2020

High-energy x-ray radiation effects on the exfoliated quasi-two-dimensional β-GaO nanoflake field-effect transistors.

Nanotechnology 2020 Aug 12;31(34):345206. Epub 2020 May 12.

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, Shanghai 200433, People's Republic of China.

The effects of x-ray irradiation on the mechanically exfoliated quasi-two-dimensional (quasi-2D) β-GaO nanoflake field-effect transistors (FETs) under the condition of biasing voltage were systematically investigated for the first time. It has been revealed that the device experienced two stages during irradiation. At low ionizing doses (<240 krad), the device performance is mainly influenced by the photo-effect and the subsequent persistent photocurrent (PPC) effect as a result of the pre-existing electron traps (e-trap) in the oxides far away from the SiO/β-GaO interface. At larger doses (>240 krad), the device characteristics are dominated by the radiation-induced structural or compositional deterioration. The newly-generated e-traps are found located at the SiO/β-GaO interface. This study shed light on the future radiation-tolerant device fabrication process development, paving a way towards the feasibility and practicability of β-GaO-based devices in extreme-environment applications.
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http://dx.doi.org/10.1088/1361-6528/ab925dDOI Listing
August 2020

Hierarchical highly ordered SnO nanobowl branched ZnO nanowires for ultrasensitive and selective hydrogen sulfide gas sensing.

Microsyst Nanoeng 2020 4;6:30. Epub 2020 May 4.

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, 200433 Shanghai, China.

Highly sensitive and selective hydrogen sulfide (HS) sensors based on hierarchical highly ordered SnO nanobowl branched ZnO nanowires (NWs) were synthesized via a sequential process combining hard template processing, atomic-layer deposition, and hydrothermal processing. The hierarchical sensing materials were prepared in situ on microelectromechanical systems, which are expected to achieve high-performance gas sensors with superior sensitivity, long-term stability and repeatability, as well as low power consumption. Specifically, the hierarchical nanobowl [email protected] NW sensor displayed a high sensitivity of 6.24, a fast response and recovery speed (i.e., 14 s and 39 s, respectively), and an excellent selectivity when detecting 1 ppm HS at 250 °C, whose rate of resistance change (i.e., 5.24) is 2.6 times higher than that of the pristine SnO nanobowl sensor. The improved sensing performance could be attributed to the increased specific surface area, the formation of heterojunctions and homojunctions, as well as the additional reaction between ZnO and HS, which were confirmed by electrochemical characterization and band alignment analysis. Moreover, the well-structured hierarchical sensors maintained stable performance after a month, suggesting excellent stability and repeatability. In summary, such well-designed hierarchical highly ordered nanobowl [email protected] NW gas sensors demonstrate favorable potential for enhanced sensitive and selective HS detection with long-term stability and repeatability.
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http://dx.doi.org/10.1038/s41378-020-0142-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8433378PMC
May 2020

Ultralow Power Wearable Heterosynapse with Photoelectric Synergistic Modulation.

Adv Sci (Weinh) 2020 Apr 16;7(8):1903480. Epub 2020 Mar 16.

State Key Laboratory of ASIC and System School of Microelectronics Fudan University Shanghai 200433 China.

Although the energy consumption of reported neuromorphic computing devices inspired by biological systems has become lower than traditional memory, it still remains greater than bio-synapses (≈10 fJ per spike). Herein, a flexible MoS-based heterosynapse is designed with two modulation modes, an electronic mode and a photoexcited mode. A one-step mechanical exfoliation method on flexible substrate and low-temperature atomic layer deposition process compatible with flexible electronics are developed for fabricating wearable heterosynapses. With a pre-spike of 100 ns, the synaptic device exhibits ultralow energy consumption of 18.3 aJ per spike in long-term potentiation and 28.9 aJ per spike in long-term depression. The ultrafast speed and ultralow power consumption provide a path for a neuromorphic computing system owning more excellent processing ability than the human brain. By adding optical modulation, a modulatory synapse is constructed to dynamically control correlations between pre- and post-synapses and realize complex global neuromodulations. The novel wearable heterosynapse expands the accessible range of synaptic weights (ratio of facilitation ≈228%), providing an insight into the application of wearable 2D highly efficient neuromorphic computing architectures.
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http://dx.doi.org/10.1002/advs.201903480DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7175259PMC
April 2020

Room-temperature developed flexible biomemristor with ultralow switching voltage for array learning.

Nanoscale 2020 Apr;12(16):9116-9123

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China.

As one of the emerging neuromorphic computing devices, memristors may break through the limitation of traditional computers with a von Neumann architecture. However, the development of flexible memristors is limited by the high-temperature fabrication process, large operating voltage and non-uniform distribution of resistance. The room-temperature process has attracted great attention due to its advantages of low thermal dissipation, low cost and excellent compatibility with flexible electronics. Here, we proposed a fully physical vapour deposition (PVD) process for fabricating a memristor without additional heat treatment. The device showed excellent resistive switching characteristics with ultralow set/reset voltages (0.48 V/-0.39 V), uniform distribution (10%/15%), stable retention characteristic, multilevel storage behavior and reliable flexibility (radius of 10 mm). With continuously modulated conductance, typical synaptic plasticities were simulated by our flexible biomemristor, including excitatory post-synaptic current (EPSC), paired-pulse facilitation (PPF), long-term potentiation/depression (LTP/LTD) and learning-forgetting curve. Furthermore, the array learning behavior like that of the human brain was simulated with these trainable biomemristors. This study paves a new way for developing low-cost, wearable, neuromorphic computing electronics at room temperature and expands the applications of artificial synapse arrays.
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http://dx.doi.org/10.1039/d0nr00919aDOI Listing
April 2020

Modification of 1D TiO nanowires with GaON by atomic layer deposition for [email protected] core-shell nanowires with enhanced photoelectrochemical performance.

Nanoscale 2020 Apr;12(13):7159-7173

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, Shanghai 200433, China.

As a well-known semiconductor that can catalyse the oxygen evolution reaction, TiO2 has been extensively investigated for its solar photoelectrochemical water properties. Unmodified TiO2 shows some issues, particularly with respect to its photoelectrochemical performance. In this paper, we present a strategy for the controlled deposition of controlled amounts of GaOxNy cocatalysts on TiO2 1D nanowires ([email protected] core-shell) using atomic layer deposition. We show that this modification significantly enhances the photoelectrochemical performance compared to pure TiO2 NW photoanodes. For our most active [email protected] core-shell nanowires with a GaOxNy thickness of 20 nm, a photocurrent density up to 1.10 mA cm-2 (at 1.23 V vs. RHE) under AM 1.5 G irradiation (100 mW cm-2) has been achieved, which is 14 times higher than that of unmodified TiO2 NWs. Furthermore, the band gap matching with TiO2 enhances the absorption of visible light over unmodified TiO2 and the facile oxygen vacancy formation after the deposition of GaOxNy also provides active sites for water activation. Density functional theory studies of model systems of GaOxNy-modified TiO2 confirm the band gap reduction, high reducibility and ability to activate water. The highly efficient and stable systems of [email protected] core-shell nanowires with ALD deposited GaOxNy demonstrate a good strategy for the fabrication of core-shell structures that enhance the photoelectrochemical performance of readily available photoanodes.
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http://dx.doi.org/10.1039/c9nr10908kDOI Listing
April 2020

Three-Dimensional Nanoscale Flexible Memristor Networks with Ultralow Power for Information Transmission and Processing Application.

Nano Lett 2020 06 23;20(6):4111-4120. Epub 2020 Mar 23.

State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433, China.

To construct an artificial intelligence system with high efficient information integration and computing capability like the human brain, it is necessary to realize the biological neurotransmission and information processing in artificial neural network (ANN), rather than a single electronic synapse as most reports. Because the power consumption of single synaptic event is ∼10 fJ in biology, designing an intelligent memristors-based 3D ANN with energy consumption lower than femtojoule-level (e.g., attojoule-level) and faster operating speed than millisecond-level makes it possible for constructing a higher energy efficient and higher speed computing system than the human brain. In this paper, a flexible 3D crossbar memristor array is presented, exhibiting the multilevel information transmission functionality with the power consumption of 4.28 aJ and the response speed of 50 ns per synaptic event. This work is a significant step toward the development of an ultrahigh efficient and ultrahigh-speed wearable 3D neuromorphic computing system.
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http://dx.doi.org/10.1021/acs.nanolett.9b05271DOI Listing
June 2020

Ultrahigh-Sensitive Finlike Double-Sided E-Skin for Force Direction Detection.

ACS Appl Mater Interfaces 2020 Mar 12;12(12):14136-14144. Epub 2020 Mar 12.

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics & Systems, School of Microelectronics, Fudan University, Shanghai 200433, China.

Flexible pressure sensing is required for the excellent sensing performance and dexterous manipulation of the measured objects in their potential applications. Particularly, the ability to measure and discriminate the direction of force, contact surface, and contact location in real time is crucial for robotics with tactile feedback. Herein, a three-dimensional elastic porous carbon nanotube (CNT) sponge is synthesized by chemical vapor deposition, which is successfully applied in the piezoresistive sensor. scanning electron microscopy study intuitively illustrates the characteristics that the microfibers of the CNT sponge distort and contact with each other under an external force. As a result, new conductive paths are created at the contact points between the CNT microfibers, which provides a basic sensing principle for a piezoresistive sensor. The CNT sponge-based sensor has an ultrahigh sensitivity in a wide pressure range (0-4 kPa for 4015.8 kPa), a rapid response time of 120 ms, and excellent durability over 5000 cycles. Moreover, a finlike flexible double-sided electronic skin (e-skin) is fabricated by a simple method to achieve force direction detection, which has potential applications in intelligent wearable devices and human-machine interaction.
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http://dx.doi.org/10.1021/acsami.9b23110DOI Listing
March 2020
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