Wood-Derived Nanopaper Dielectrics for Organic Synaptic Transistors

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Organic Electronic Devices

Wood-Derived Nanopaper Dielectrics for Organic Synaptic Transistors Shilei Dai, Yan Wang, Junyao Zhang, Yiwei Zhao, Feipeng Xiao, Dapeng Liu, Tengrui Wang, and Jia Huang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b15063 • Publication Date (Web): 01 Nov 2018 Downloaded from http://pubs.acs.org on November 2, 2018

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ACS Applied Materials & Interfaces

Wood-Derived Nanopaper Dielectrics for Organic Synaptic Transistors Shilei Dai,1 Yan Wang,1 Junyao Zhang,1 Yiwei Zhao,1 Feipeng Xiao,2 Dapeng Liu,1 Tengrui Wang1 and Jia Huang1,2* 1

Interdisciplinary Materials Research Center, School of Materials Science and Engineering, Tongji University, Shanghai, 201804, P. R. China. 2

Key Laboratory of Road and Traffic Engineering of Ministry of Education, Tongji University, Shanghai, 201804, P.R. China. KEYWORDS. Green electronics; Nanopapers; Synaptic transistors; Dielectric materials; Organic electronics ABSTRACT: The use of biocompatible and biodegradable materials in electronic devices can be an important trend in the development of the next-generation green electronics. In addition, by integrating the advantages of low power consumption, low-cost processing and flexibility, organic synaptic devices will be promising elements for the construction of brain-inspired computers. However, previously reported electrolyte-gated synaptic transistors are mainly made of non-biocompatible and non-biodegradable electrolytes. Woods are widely considered as one kind of sustainable and renewable materials. We found that wood-derived cellulose nanopapers have ionic conductivity, and therefore can be used as dielectric materials for organic synaptic transistors. The fabricated wood-derived cellulose nanopapers exhibit decent ionic conductivity of 7.3×10-4 S/m and a high lateral coupling effective capacitance of 18.65 nF cm-2 at 30 Hz. The laterally coupled organic synaptic transistors using wood-derived cellulose nanopapers as the dielectric layer present excellent transistor performances at operating voltage below 1.5 V. More significantly, some important synaptic behaviors, such as excitatory post-synaptic current (EPSC), signal filtering characteristics and dendritic integration are successfully simulated in our synaptic transistors. Since the development of electronic devices with biocompatible and biodegradable materials is essential, this work may inspire new directions for the development of "green" neuromorphic electronics.

INTRODUCTION Electronic products are indispensable consumer goods and have become an important symbol of modern life. However, increasing performance requirements have significantly reduced the life expectancy of consumer electronics, leading to the rapid growth of electronic-wastes (ewastes).1-2 According to a report released by the UN Environment Program, more than 50 million tons of electronic wastes are produced and disposed each year.3 These ewastes are usually made of non-biocompatible or non-biodegradable materials or even toxic materials, which may cause adverse effects on human health and lead to serious environmental pollution.1-2, 4 In addition, due to the complexity of the devices structures and the diversity of materials contained in electronic devices, the recovery of these e-wastes is facing tremendous difficulties. Therefore, the use of biocompatible and biodegradable materials in electronic devices is highly recommended in the development of the next-generation “green” electronics.4-10 In addition, with the arrival of the big data era, people have to handle mountains of complex (or unstructured) information and data. However, traditional von Neumann computers cannot efficiently deal with the unstructured

information due to the physical separation of processing and storage units, which is also referred to as the “von Neumann bottleneck”.11-14 Unlike the traditional von Neumann computer, the human brain is a highly parallel and reconfigurable neural network system that can simultaneously calculate and store information.8, 15-16 Biological synapse, which is the special junction between two neurons, dominates the architecture of human brain. Long-term changes in the characteristics of synaptic transmission provide a physiological basis for learning and memory, while shortterm changes support various neuromorphic computations.17 Therefore, hardware implementation of the synaptic functions will be a significant step in the development of efficient brain-like computers.18-23 Until now, various types of electronic devices, such as memristors,24-26 atomswitch memories,27 spintronic devices,28 phase-change memories29 and synaptic transistors18, 30-38 have been utilized to simulate synaptic functions. In addition, recent studies have shown that some phototransistors or photodetectors can also be used to fabricate photonic synapses because of their adjustable photoresponse behavior and

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Figure 1 (a) Cellulose, one of the main components of trees. (b) Photo image of a highly transparent WCN. Red arrows in (b) point to the edge of the WCN. (c) SEM image and (d) AFM image of WCNs. The insert in (d) shows the surface roughness obtained from the line scan (black line) of the AFM image. The average surface roughness is around 1 nm. tunable memory effect.39-45 These studies have made important contributions to the development of synaptic electronics, however, they are mainly focused on achieving effective synaptic functions rather than the environmental impact. Therefore, to achieve “green” neuromorphic devices, new materials which have application prospects in artificial synapses should be developed. Herein, we report the use of wood-derived cellulose nanopapers (WCNs) as the dielectric materials for laterally coupled organic synaptic transistors. Cellulose nanofibers are one of the main components of woods, and thus they have been widely considered as one of the most ubiquitous and abundant biocompatible polymers on earth.6 More importantly, wood cellulose nanofibers exhibit a good thermal stability with a low coefficient of thermal expansion (CTE) of 0.1 ppm/K (crystalline cellulose in the axial direction), excellent mechanical properties (tensile strength of 0.3−1.4 GPa, elastic modulus of 14−27 GPa) and chemical durability.46 These properties of cellulose nanofibers enable them to be used in numerous applications, especially in green electronics. Previously reported nanopaper-based electronics mainly focused on using nanopaper as substrate materials.47 Here, we report using WCNs as dielectric materials for organic synaptic transistors. In addition to the excellent properties of cellulose nanofiber described above, WCNs were chosen as dielectric materials for organic synaptic transistors because they have ultra-smooth surface and ionic conductivity, which are essential for achieving organic synaptic transistors with high performances and low working voltages. The fabricated WCNs exhibit decent ionic conductivity of 7.3×10-4 S/m and a high lateral coupling capacitance of 18.65 nF cm-2 at 30 Hz. In

addition, the fabricated laterally coupled organic synaptic transistors using WCNs as the dielectric layer present excellent transistor performances at operating voltage below 1.5 V. More significantly, some important synaptic behaviors, such as excitatory post-synaptic current (EPSC), signal filtering characteristics and dendritic integration are successfully mimicked in the laterally coupled organic synaptic transistors. Since the production of electronic devices with biocompatible and biodegradable materials is essential, this work may inspire new directions for the development of "green" neuromorphic electronics. RESULTS AND DISCUSSION Wood-derived cellulose nanopaper dielectrics Trees are one of the main natural resources on which human life depends. For the past several millennia, woods from trees have been used primarily for the production of ordinary papers or structural materials. However, recent studies illustrated that the wood fiber possesses mesoporous and hierarchical structures, enabling new applications beyond their traditional use.6, 48 More importantly, trees or woods are sustainable and renewable materials and therefore have potential in the application of green electronics.6 The simplified hierarchical structure of a wood cellulose fiber is presented in Figure 1a. A microfiber contains thousands of nanofibers. WCNs can be made from nanofiber pulp that is produced from wood cellulose fibers by using TEMPO-oxidization and homogenization processes (see Experimental Section). Figure 1b shows the photo image of a highly transparent WCN. The wavelength of light is larger than the dimeter of nanofibers, and therefore light can directly go through WCNs without scattering. The high transparency of WCNs makes them useful as materials


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Figure 2 (a) TEMPO oxidation process in WCN production. (b) The Cole–Cole plot of WCN dielectrics. The insert depicts the test structure. (c) Frequency-dependent effective capacitance. The insert shows the test structure. The test electrode area is 0.024 cm2, while the distance between two test electrodes is kept at 200 μm. for transparent electronics. To investigate the surface morphology of WCNs, scanning electron microscope (SEM) measurement was carried out. No obvious pores were observed in the SEM image (Figure 1c). In addition, the uniform surface flatness of WCNs observed in the SEM image confirms that WCNs have potential as dielectric materials for electronic devices. Besides, atomic force microscopy (AFM) was also employed to study the surface morphology of WCNs. Obviously, WCNs are composed of densely packed nanosized fibers (Figure 1d). The mechanical entanglements and hydrogen bonds between the nanofibers make them closely pack with each other. The average surface roughness of WCNs obtained from AFM image is around 1 nm, which also confirms that WCNs have ultra-smooth surface. The ultra-smooth surface of WCNs makes it possible to build organic electronic devices directly on their surface. Figure 2a shows the TEMPO oxidation process in WCNs production. Hydroxymethyl groups at the glucose C6 position will be partially converted to sodium carboxylates.47 With the help of trace water contained in WCNs, sodium ions can dissociate from carboxylic groups. In addition, WCNs contain a large number of hydrogen bonds which can absorb moisture from the air and thus introduce protons into WCNs. Therefore, the fabricated WCNs may have ionic conductive property. In order to investigate the ionic conductive property of WCNs, the electrochemical impedance spectroscopy measurement was employed. Typical Cole-Cole plot of WCNs was presented

in Figure 2b. The ionic conductivity of the WCNs was determined from the following equation: 𝑑

δ = (𝑅−𝑅

0 )𝐴

(1)

where d, R, R0, A stand for the thickness of WCNs, the impedance real value, the resistance of the electrodes and the electrode area, respectively. In our case, d = 30 μm, R = 416 Ω, R0 = 5 Ω and A = 1×10-4 m2. Therefore, δ is estimated to be 7.3×104 S/m, which confirms that WCNs exhibit decent ionic conductivity. The movable ions (sodium ions and protons) in the WCNs will migrate to and accumulate at the interface of WCNs and electrodes under the effect of the electric field, resulting in the formation of an electric-double-layer (EDL).49 The frequency dependent capacitance of WCNs is shown in Figure 2c. Traditionally, the capacitance of a dielectric material is tested in a vertical sandwich structure. However, the capacitance of WCNs here was measured in the lateral structure (see the insert picture in Figure 2c). We chose this lateral structure mainly because our synaptic transistors are all fabricated with the lateral structure which has been proved suitable for multi-gates synaptic transistors.30 The distance between the two electrodes for this test was kept at 200 μm. As the frequency increases, the lateral effective capacitance drops. This phenomenon can be well explained by the slow ion mobility in response to the high electric field frequency. The lateral coupling effective capacitance of WCNs crossing the 200 μm distance at 30 Hz is still as high as 18.65 nF cm-2. The high lateral effective capacitance of WCNs can be attributed to the



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Figure 3 (a) The schematic of lateral coupled C8-BTBT field-effect transistors (b) Optical transmittance of the bare WCN and the WCN covered with C8-BTBT at different wavelengths. (c) Transfer curve and (d) output characteristics of lateral coupled C8-BTBT transistors. formation of EDL at the WCN/electrode interface caused by the migration of movable ions within the WCN. The ionic conductive property of WCNs also makes it possible to construct organic synaptic transistors directly on their surface. Laterally coupled organic field-effect transistors In this study, 2,7-dioctyl [1] benzothieno[3,2-b] [1] benzothiophene (C8-BTBT) was selected as the channel material due to its outstanding semiconductor performance and high transparency. Figure 3a shows the schematic of the laterally coupled field-effect transistors (LCFETs). Figure 3b compares the transmittance of the bare WCN and the WCN covered with C8-BTBT. Compared with the bare WCN, only a slight reduction in the transparency of the WCN covered with C8-BTBT was observed. But, both of them showed high transparency (close to 90 %) in the visible light region. Figure 3c shows transfer characteristics (Id-Vg) of the LCFETs. Thanks to the ionic conductive property of WCNs, the fabricated LCFETs exhibited decent transistor performance at operating voltage below 1.5 V (-1.5 V). The clockwise hysteresis observed in the transfer curve may be attributed to the presence of mobile ions (sodium ions and protons) in WCNs. The hole mobility extracted from the saturation region is estimated to be around 1.25 cm2 V-2 s-1 (calculated at capacitance of 18.65 nF cm-2). Figure 3d shows the typical output curves (Id-Vd) of the LCFETs with excellent pinched-off and saturation regions. The linear region observed in output curves indicates that our devices

exhibited a decent Ohmic contact. To investigate the operating repeatability of the LCFETs, the pulse response measurement was carried out, as shown in Figure S1. It is obvious that the LCFETs exhibit a highly repeatable switch on and switch off behavior in response to the gate voltage pulse, indicating that no obvious electrochemical doping occurs at the interface of OSC/dielectric under the gate voltage of -1 V. Electronic devices with excellent flexibility would enable many novel applications such as wearable systems and foldable displays.25 To investigate the applicability of LCFET as a flexible device, we have measured its transfer curve after 1000 times of bending (Figure S2). Decent OFET transfer curve was observed even after 1000 times of bending, indicating that our devices have decent mechanical flexibility. 2.3 Synaptic performances Biologically, synapses are the sites where neurons are functionally linked and are key parts of information transmission.17 Figure 4a shows the diagram of a biological synapse. The information transmission process of the biological synapse begins with the triggering of action potentials which will alter the permeability of the calcium channel in the presynaptic membrane, allowing the influx of calcium ions and thus resulting in the release of neurotransmitters. Neurotransmitters diffuse in the synaptic cleft and ultimately interact with receptors on the postsynaptic membrane, thereby altering the


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Figure 4 (a) The diagram of a biological synapse (b) Typical EPSC behavior of the LCFETs triggered by a presynaptic spike (-0.5 V, 30 ms) which is applied through the gate terminal. (c) Presynaptic spike-intensity-dependent EPSC of the LCFETs. (d) Energy consumption per spike as a function of the presynaptic spike width. The presynaptic spike intensity was kept at -0.1 V. postsynaptic membrane ion permeability. The excitatory current of postsynaptic neurons caused by positive ions entering the postsynaptic membrane is called excitatory postsynaptic current (EPSC). Analogy to biological synapses, the gate terminal of the LCFETs is regarded as the presynaptic membrane while the C8-BTBT channel is regarded as the postsynaptic membrane. In addition, the movable ions within the WCNs can be regarded as neurotransmitters. Figure 4b shows the typical EPSC behavior of the LCFETs triggered by a presynaptic spike (-0.5 V, 30 ms) which is applied through the gate terminal. The EPSC is recorded at a constant drain voltage (Vd) of -0.1 V. At the end of the presynaptic spike, EPSC reached a maximum value of 6.5 nA and then gradually declined to its original resting current. The EPSC behavior observed in the LCFETs is very similar to the EPSC behavior in biological synapses.20 Since the main chains of celluloses are entangled with each other and have a high rigidity, anionic groups attached on the cellulose backbone are not movable. Therefore, only small positive ions (sodium ions and protons) can move under the electric field. When a negative presynaptic spike is applied, positive ions will be attracted toward the gate terminal, resulting in the net negative ions accumulation under the channel area. The accumulated negative ions will induce an increase in channel carriers through the electrostatic coupling effect, resulting in an increase in the channel current. When the presynaptic spike ends, due to the concentration gradient, the accumulated positive ions near the gate terminal will gradually diffuse back to the equilibrium state. This process will cause the channel current to continuously decrease until it stabilizes.

To investigate the temporal response behavior of LCFETs, presynaptic spike-intensity-dependent EPSCs were studied. The intensities of the presynaptic spike were altered from -0.1 to 1.5 V with a constant spike width of 30 ms. The value of EPSC increases with the increase of the presynaptic spike intensity and tends to be saturated at high presynaptic spike, as shown in Figure 4c. It is mainly due to that more and more positive ions will be attracted toward the gate terminal with the increase of the presynaptic spike intensity. Since the number of movable positive ions under the channel layer is limited, the triggered EPSC will eventually saturate. In addition to the presynaptic spike intensity, the presynaptic spike-width-dependent EPSCs were also been investigated (Figure. S3). The EPSC value increases with the increase of the presynaptic spike width and tends to be saturated at large spike width. Therefore, the EPSC values of LCFETs can be modulated by utilizing presynaptic spike intensity and width. Figure 4d presents the energy consumption per spike as a function of the presynaptic spike width. The energy consumption per spike was calculated from the following equation:50-51 𝐸𝑝𝑒𝑟 𝑠𝑝𝑖𝑘𝑒 = 𝐼𝑝𝑒𝑎𝑘 × 𝑡 × 𝑉𝑑

(2)

where t and Ipeak are spike width and the maximum EPSC value, respectively. The minimum energy consumption per spike of the LCFETs was calculated to be 0.19 nJ, which is lower than the energy consumption of artificial synapses based on traditional CMOS circuits and comparable with the energy consumption of recently reported synaptic transistors.21 The en-



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ergy consumption per spike of the LCFETs may be further reduced by decreasing the device size or further reducing the spike width.

Therefore, the sublinear integration has been successfully simulated in the C8-BTBT synaptic transistors with dual inplane gates.

In nerve cells, the branches produced by the extended portion of the cell body are called dendrites, which are the entrances to the incoming information from other neurons. Dendrites are able to collect, integrate, and modulate thousands of presynaptic input signals and then transmit signals through axons to post-synaptic neurons.17, 52 Dendrite integration includes the integration of unsynchronized single events (temporal summation) and the simultaneous integration of single events occurring in different regions (spatial summation).30 Figure 5a presents the schematic diagram of the biological spatial summation from two spatial isolated synaptic inputs. The signals from input 1 and input 2 are summed in the postsynaptic neuron. To mimic this spatial summation function, C8-BTBT synaptic transistors with dual in-plane gates were fabricated (Figure 5b). Figure 5c depicts the protocol for testing spatial summation (dendritic integration) in the dual in-plane gates C8-BTBT synaptic transistors. Firstly, the presynaptic spikes from Gate 1 and Gate 2 are applied separately. Then, they are applied simultaneously. The triggered postsynaptic signals (or EPSCs) are measured at a constant Vd of -0.1 V. Figure 5d and Figure S4 show the postsynaptic signals triggered by Gate 1 and Gate 2, respectively, while Figure 5e presents the postsynaptic signals simultaneously triggered by Gate 1 and Gate 2. Obviously, under a certain presynaptic spike, the postsynaptic signal simultaneously triggered by Gate 1 and Gate 2 is larger than the postsynaptic signal triggered by single gate (Gate 1 or Gate 2). Figure 5f shows the comparison between measured EPSC sum and arithmetic EPSC sum of two EPSCs (EPSC 1 and EPSC 2) at different presynaptic spikes. The measured EPSC sum is lower than the arithmetic EPSC sum.

Biologically, the probability of vesicle release is activity-dependent, and the biological synapses can act as dynamic filters during information transmission.17, 53 Synapses with low vesicle release probabilities have a high-pass filtering effect because high frequency signals are required to trigger vesicle release when the release probability is low. Figure 6a depicts the schematic of a high-pass filter in biological synapses. To investigate the filtering behavior of the LCFETs, a series of presynaptic spike trains with different frequency were applied through the gate electrode. The EPSC values were measured at a constant Vd of -0.1 V. The resulted EPSC values are presented in Figure 6b. The EPSC amplitude remained almost the same after 10 presynaptic spikes at a frequency of 0.5 Hz. But, with the increase of the presynaptic spike frequency, the EPSC amplitude increased dramatically. Figure 6c shows the presynaptic spike-frequency-dependent EPSC gain. The EPSC gain increased from 1.1 to 3.54 when the frequency of presynaptic spikes changed from 0.5 Hz to 2.5 Hz. This behavior is very similar to the high-pass filter behavior observed in the biological synapses. Therefore, the high-pass filter behavior has been successfully mimicked in the LCFETs. The simulated highpass filter behavior is of great significance for the future realization of neuromorphic computing. CONCLUSION We have fabricated laterally coupled organic synaptic transistors based on biocompatible and biodegradable WCNs. The fabricated WCNs exhibit decent ionic conductivity of 7.3×10-4

Figure 5(a) Schematic diagram of the dendrite integration from two inputs. (b) The schematic image of LCFETs with two inplane gates as presynaptic inputs. Gate 1 and Gate 2 stand for Input 1 and Input 2 in (a), respectively. (c) Protocol for testing spatial summation (dendritic integration). Firstly, the presynaptic spikes from Gate 1 and Gate 2 are applied separately. Then, they are applied simultaneously. The triggered postsynaptic signals (or EPSCs) are measured at a constant V d of -0.1 V. (d) EPSC values triggered by Gate 1. (e) EPSC values simultaneously triggered by Gate 1 and Gate 2. The presynaptic spike intensity altered from -0.1 to -1.5 V. (f) Comparison of arithmetic EPSC sum and measured EPSC sum of two EPSCs. The measured EPSC sum is lower than the arithmetic EPSC sum


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Figure 6(a) Schematic diagram of a high-pass filter in biological synapses. (b) EPSC signals in response to 10 presynaptic spike trains with different frequencies. Spike width and intensity was kept and 200 ms and -1.5 V, respectively. The EPSC signals were recorded at a constant Vd of -0.1 V. (c) Presynaptic spike-frequency-dependent EPSC gain. The EPSC gain is defined as A10/A1, where A1 and A10 are the EPSC peaks of the first spike and the tenth spike of each frequency, respectively. S/m and a high lateral coupling capacitance of 18.65 nF cm-2 at 30 Hz. Organic synaptic transistors using WCNs acting as dielectrics present excellent transistor performances at operating voltage below 1.5 V. More significantly, some important synaptic behaviors, such as excitatory post-synaptic current (EPSC), signal filtering characteristics and dendritic integration are successfully simulated in LCFETs. These synapse-like behaviors are very vital for future realization of brain-like computing. Since the production of electronic devices with biocompatible and biodegradable materials is essential, this work may inspire new directions for the development of "green" neuromorphic electronics. EXPERIMENTAL SECTION Materials. Sodium hypochlorite (NaClO), (2, 2, 6, 6-tetramethylpiperidin-1-yl) oxidanyl (TEMPO), (Tridecafluoro-1, 1, 2, 2-teterahydrooctyl) trichlorosilane (FOTS) and 2,7-dioctyl [1] benzothieno[3,2-b] [1] benzothiophene (C8-BTBT) were purchased from Shanghai Titan Scientific Co., Ltd., Energy Chemical, Sigma Aldrich and Suna Tech Inc., respectively. Fabrication of wood-derived cellulose nanopapers (WCNs). TEMPO (100 mg) was ultra-sonicated in deionized water (95 mL) to acquire uniform aqueous solution. Then in deionized water (65 mL), sodium bromide (NaBr, 659 mg) was first dissolved and later blended with the uniform solution of TEMPO. Softwood pulp (6.5 g, dry weight) was suspended in deionized water (80 mL) with fierce stir. Afterwards, the mixed TEMPO/NaBr solution and additional aqueous solution of NaClO (38 mL, 12%) were added to the suspension. Using the pH meter (METTLER TOLEDO), the pH value of the mixed solution can be monitored. While at the same time, by adding the sodium hydroxide (NaOH, 0.5 mol/L) solution, the pH value was kept at 10.5 for 3 h. Furthermore, to be purified, the product was washed by deionized water for three times. The purified product was diluted by deionized water and then dispersed in nanofiber by a blender machine. After the high speed centrifugation for 30 min at 10000 rpm, the nanofibers in the dispersion liquid can be separated from the microfibers and thus the supernatant was collected. The supernatant was then tip-sonicated to acquire the ultima uniform cellulose nanopaper pulp for 10 min. Into the culture dishes which have already been pretreated with FOTS, the ultima cellulose nanopaper pulp was added. Then we waited until the pulp naturally

dried in the semiconductor cleanroom. At last, the WCN was obtained, and it was solid-state and could be easily stripped from the culture dishes. Fabrication of laterally coupled organic synaptic transistors. C8-BTBT was thermal evaporated (0.1~0.3 Å s-1, P ≈ 4 × 10-4 Pa) onto the surface of WCNs through shadow mask. Then, Au source-drain and gate electrodes were deposited on the top of C8-BTBT film through shadow mask. The channel length (L) and channel width (W) were 200 μm and 6 mm, respectively. Characterization. The surface morphology of WCNs was investigated by using scanning electron microscope (SEM, Nova NanoSEM 450) and atomic force microscope (AFM, SEIKO SPA-300HV). Ionic conductivity and frequency-dependent effective capacitance of WCNs were characterized using the electrochemical station (Bio-logic SAS, VMP-3) and the LCR meter (Tonghui TH2827C), respectively. The devices performances were tested by using the Keithley 4200-SCS semiconductor Parameter Instruments and the Keithley 2636B System SourceMater at room temperature with a relative humidity of 60~65%.

ASSOCIATED CONTENT SUPPORTING INFORMATION The Supporting Information is available free of charge on the ACS Publications website. 100 times of switch on and off operation of LCFETs; Transfer curve of LCFETs after 1000 times of bending; Presynaptic spike-width-dependent EPSC of the LCFETs; EPSC values triggered by Gate 2.

AUTHOR INFORMATION Corresponding Author * (J. H.). E-mail: [email protected].

Author Contributions All authors have given approval to the final version of the manuscript.



ACKNOWLEDGMENT This work was supported by the Science & Technology Foundation of Shanghai (17JC1404600), the National Natural Science Foundation of China (No. 51741302), the National Key Research and Development Program of China (Nos. 2017YFA0103904), and the Fundamental Research Funds for the Central Universities.

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Graphical Abstract


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Wood-Derived Nanopaper Dielectrics for Organic Synaptic Transistors

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