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Short-Term Synaptic Plasticity Regulation in Solution-Gated Indium-Gallium-Zinc-Oxide Electric-Double-Layer Transistors Changjin Wan, Yang Hui Liu, Li Qiang Zhu, Ping Feng, Yi Shi, and Qing Wan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b12726 • Publication Date (Web): 23 Mar 2016 Downloaded from http://pubs.acs.org on March 28, 2016

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ACS Applied Materials & Interfaces

Short-Term Synaptic Plasticity Regulation in Solution-Gated Indium-Gallium-Zinc-Oxide Electric-Double-Layer Transistors Chang Jin Wan†, ‡, Yang Hui Liu‡, Li Qiang Zhu‡, Ping Feng†, Yi Shi† & Qing Wan*, †, ‡ †

School of Electronic Science & Engineering, and Collaborative Innovation Center of Advanced

Microstructures, Nanjing University, Nanjing 210093, China ‡

Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences,

Ningbo 315201, China KEYWORDS: Solution gated transistors; Electric-double-layer modulation; Artificial synapses; Synaptic plasticity regulation; Neuromorphic systems ABSTRACT:

In biological nervous system, synaptic plasticity regulation is based on the

modulation of ionic fluxes, and such regulation was regarded as the fundamental mechanism underling memory and learning. Inspired by such biological strategies, indium-gallium-zincoxide (IGZO) electric-double-layer (EDL) transistors gated by aqueous solutions were proposed for synaptic behavior emulations. Short-term synaptic plasticity, such as paired-pulse facilitation, high-pass filtering and orientation tuning were experimentally emulated in these EDL transistors. Most importantly, we found that such short-term synaptic plasticity can be effectively regulated by alcohol (ethyl alcohol) and salt (potassium chloride) additives. Our results suggest that solution gated oxide-based EDL transistors could act as the platforms for short-term synaptic plasticity emulation.

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1. INTRODUCTION Electric-double-layer (EDL) modulation due to the interfacial ion accumulation or electrochemical doping provides a novel strategy for tuning the properties of solid-state materials and new-concept device fabrication.1,

2

Among these new-concept devices, EDL transistors

provide an extremely strong capacitance coupling for high-density charge accumulation under a very low voltage bias.

3, 4

For example, Schmitt triggers were realized based on an ionic liquid

gated ZnO transistor.5 Such device combines a solid state material and a liquid interface that connects ion kinetics and electrochemistry beneficially. It was also reported that water-gated transistors could be used as the transducers for sampling waterborne analytes, with applications to biomedical detection and environmental monitoring. 6-9 Recently, it was also reported that the ionic conductivities of water gate dielectric could be enhanced for more than two orders of magnitude by dissolving a biocompatible polyelectrolyte (metal-substituted salmon sperm DNAs) into the water, and finally the operation frequency of a graphene transistor gated by such water-gel could be improved to above 1.0 MHz. 9 Inspired by biological neural systems, artificial synaptic devices are highly desirable for neuromorphic information processing systems. Thanks to the progresses achieved in nanoelectronics, synaptic behaviors were implemented in a broad spectrum of devices, such as memristors and atom switches.10-18 It was reported that the conductance of a memristor could be precisely modulated by controlling the charge flux through it, which enables the emulation of synapse-like memory through programming the patterns and timing of the applied voltage.

10, 12

Recently, electrolyte-gated EDL transistors were also reported to act as the promising candidates for artificial synapses.

15, 16

Such devices can be regarded as “synaptic transistor” if the gate

electrode is regarded as the presynaptic terminal, and the channel with source/drain electrode is


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regarded as the postsynaptic terminal.18 In biological neural system, synaptic plasticity is much complicated than the memory in digital computer, and it can be divided into short-term plasticity and long-term plasticity. In EDL transistors, the volatile changes in the conductivities of channel layers due to the electrostatic modulation at low gate voltage are favorable for short-term synaptic plasticity emulation. When the gate voltage is higher than a critical value, nonvolatile memory due to interfacial electrochemical reaction may occur, which is favorable for long-term synaptic plasticity emulation. Since water is the primary and natural electrolyte in biological systems and can be used as gate dielectrics in bio-compatible transistor, aqueous solution gated transistors have potential for neuromorphic system application. In this work, aqueous solution gated indium-gallium-zinc-oxide (IGZO) EDL transistors were fabricated. Essential short-term synaptic plasticity, including paired-pulse facilitation (PPF) and high-pass filtering, was experimentally demonstrated. Orientation tuning was also emulated by a simplified visual system model based on the high-pass filtering function. Most importantly, we found that alcohol (ethyl alcohol) and salt (KCl) can regulate the short-term synaptic plasticity of the solution gated EDL transistors. 2. RESULTS AND DISCUSSION Figure 1a shows the schematic diagram of an aqueous solution gated IGZO-based transistor on glass substrate. First, 150-nm-thick patterned indium-zinc-oxide (IZO) films used as drain and source electrodes were deposited on glass substrate by magnetron sputtering with a nickel shadow mask. Then, 50-nm-thick IGZO pattern (1.0 mm  10 mm) was deposited between drain and source electrodes by using magnetron sputtering. The IGZO channel width and length are 1000 m and 80 m, respectively. For gating, solution droplets (deionized (DI) water, alcohol solution and KCl solution) with fixed volume of ~5.0 L was dropped on the channel region


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using a micro-syringe. The geometry of the aqueous solution is approximated to hemisphere and the radius of the droplet is estimated to 1.33 mm. One tungsten (W) probe was bended and penetrated into the electrolyte solution as the top gate electrode. Thus, aqueous solution gated IGZO-based transistors were obtained, and the unpassivated regions of the source/drain electrodes are not in directly contact with the aqueous solution. The detailed parameters of the device are shown in Figure S1 in supporting information. Ionic conductivities and frequency dependent specific capacitances of these aqueous electrolytes were characterized by Solartron 1260A Impedance/Gain-Phase Analyzer. Transistor performance and synaptic emulation were experimentally studied by semiconductor parameter analyzer (Keithley 4200 SCS) at room temperature in air ambient with a relative humidity of 60%.

Figure 1 (a) Schematic diagram of an IGZO-based EDL transistor gated by aqueous solution on glass substrate. (b) Output characteristics of a water gated IGZO transistor. (c) Transfer characteristics of a water gated IGZO-based EDL transistor with VDS fixed at 1.5 V. (d) Schematic diagram of a biological synapse.


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Figure 1b shows the output characteristics (IDS vs VDS) of DI water gated IGZO-based EDL transistor with VGS varied from 0 to 1.5 V in 0.25 V steps. The curves exhibit good current saturation behaviors at high VDS and linear characteristics at low VDS. Figure 1c shows the transfer characteristics (IDS vs VGS) of a DI water gated IGZO-based EDL transistor with VDS fixed at 1.5 V. The gate voltage is swept from -1.0 V to 2.0 V and then back. A clockwise hysteresis of ~0.5 V is observed, which is likely due to the existences of mobile hydronium ions and hydroxyl ions within DI water and electrochemical reaction/doping at the IGZO surface.

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The channel current on/off ratio is estimated to be ~1.6105. The leakage current is shown in Figure S2 in supporting information, and the leakage currents are measured to be 0.35 A and 0.72 A when VGS=2.0 and -1.0 V, respectively. Figure 1d schematically illustrates a biological synapse, where ion species (e. g. Na+, K+, and Ca2+) play essential roles in synaptic transmission and plasticity.

19, 20

As an analogy, the alcohol (ethyl alcohol) and salt (potassium chloride)

additives were explored to modulate synaptic behaviors of water gated IGZO-based EDL transistors.


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Figure 2 (a) Specific capacitances vs frequency for 25% alcohol solutions, DI water, 0.25 mM KCl solutions, respectively. (b) Specific capacitance values obtained at 100 Hz as a function of ionic conductivity for different aqueous solutions (alcohol solution with concentrations of 50% and 25%, DI water, and KCl solutions with concentrations of 0.25 and 0.5 mM, respectively). Solid line: fitting curve as guide to the eyes. (c) A typical EPSC recorded from a water gated IGZO-based EDL transistor with a presynaptic spike (0.5 V, 10ms). (d) EPSCs measured from the IGZO-based EDL transistor when different aqueous solutions are provided. Figure 2a shows the frequency-dependent specific capacitance of aqueous solution including DI water, alcohol (volume concentration of 25 %) and KCl solution (molar concentration of 0.25 mM), respectively. The capacitances were measured with a conducting IZO/solution/W probe sandwich structure. Figure S3 in supporting information presents the reproducibility of the frequency-dependent specific capacitance of the solutions. It is observed that the specific capacitances are getting saturated with frequency below ~10 Hz for all three aqueous solutions. A maximum specific capacitance of ~2.0 μF/cm2 is obtained at 1.0 Hz for all solutions. The value here is almost the same as that for pure water containing only hydronium (H3O+) ions and hydroxide (OH-) ions. Pure water has a minimum ion concentration of hydronium ions and hydroxyl ions of ~10-7 M due to self-ionization: 2H2OH3O++OH-. The results here indicate that the alcohol molecules (or salt ions) will not significantly reduce or enlarge the packing density of constituent ions for EDL at low frequency.

4, 9

In fact, Helmholtz layer at the

IGZO/water and tungsten/water interface predominantly consists of small hydronium/hydroxide ions and water molecules.

4

Above a certain frequency, the specific capacitance values roll off

gradually, which could be attributed to the limited ionic conductivities of the aqueous solutions. 21

In other words, the ion motion within the electrolyte could not respond promptly to form the

EDL at electrode/electrolyte interfaces when frequencies beyond its polarization time were applied. 4, 9 This frequency for water is higher than that for alcohol solutions, while is lower than that for KCl solutions. Accordingly, the KCl solution exhibits the highest capacitance value and


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the alcohol solution exhibits the lowest capacitance at all frequencies. Figure 2b shows the specific capacitances of different aqueous solutions at 100 Hz as a function of ionic conductivities which were estimated by impedance measurements from Cole-Cole plots as shown in Figure S4 in supporting information. A positive correlation can be observed between the measured capacitance at this frequency and the ionic conductance. The results indicate that alcohol molecule can inhibit the delivery of hydronium and hydroxide ions to form the EDL while the salt ions (K+ and Cl-) can facilitate such processes. 22 Potential pulse (spike) from presynaptic neuron can trigger an excitatory postsynaptic current (EPSC) in postsynaptic neuron through a synapse. This enables the postsynaptic neuron to collectively process such ionic current and establish spatial and temporal correlated functions.23 In our case, the aqueous solution gated IGZO-based transistor could act as an artificial synapse. When a positive gate pulse (0.5 V, 10 ms) and a fixed reading voltage (VDS=0.2 V) are applied, a response channel current with a quick increase followed by a slow decay can be observed, as shown in Figure 2c. Thus, the gate pulse can be analogous to the presynaptic spike and the induced channel current can be analogous to the EPSC. The absolute EPSC amplitude is estimated to be ~175 nA. Figure 2d shows the EPSCs responses from the IGZO-based synaptic transistor when different aqueous solutions are provided. Each EPSC was triggered by a presynaptic spike of 0.5 V in amplitude and 10 ms in duration. Interestingly, the EPSC amplitude of the alcohol solution gated synaptic transistor decreases when the alcohol concentration increases, while the EPSC amplitude of the KCl solution gated synaptic transistor increases when the KCl concentration increases. A minimum EPSC value of ~97 nA is obtained for IGZO synaptic transistor gated by 50% alcohol, and a maximum EPSC value of ~838 nA is obtained for IGZO synaptic transistor gated by 0.5 mM KCl solution. A reasonable explanation is


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provided here. When a positive spike is applied on the gate electrode (W probe), cations and anions will migrate to the solution/IGZO and solution/tungsten interfaces to form EDLs, respectively.

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The formation of EDL at the solution/IGZO interface will induce electrons in

IGZO channel layer due to the huge EDL capacitance coupling, which induces an EPSC in IGZO channel as a result. When the spike is finished, ions will gradually drift back to their equilibrium positions within the solution, which induces the gradual reduction in EPSC. Because the delivery of hydronium and hydroxide ions can be inhibited (facilitated) by the alcohol molecules (salt ions), less (more) ions can be triggered by the same presynaptic spike in an alcohol (KCl) solution gated IGZO-based synaptic transistor than in a water-gated IGZO-based synaptic transistor. In other word, the EPSC amplitude should be positively correlated with ionic conductivities. Such results are consistent with the capacitance behaviors observed above. Therefore, our results indicate that EPSC amplitude can be modulated by ion conductivities in the solution-based gate dielectrics. As a comparison, EPSC amplitude modulated by the amplitude of presynaptic spike was shown in Figure S5 in supporting information.


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Figure 3 (a) EPSCs recorded from DI water gated IGZO-based synaptic transistor in response to two successive presynaptic spikes (0.5 V, 10 ms) with time interval of 40 ms. The facilitation ratio (A2/A1) is estimated to ~1.56. (b) EPSCs recorded from 25% alcohol and 0.25 mM KCl solutions gated devices, respectively. The presynaptic spikes are the same as that in (A). A2/A1 is estimated to be ~1.66 and 1.23, respectively. (c) and (d) illustrate the A2/A1 value plotted as a function of time interval (T) for the devices gated by alcohol solutions and KCl solutions with different concentrations, respectively. The PPF values are provided for comparison in each figure. Paired-pulse facilitation (PPF) is an essential short-term plasticity in decoding temporal information in auditory or visual signals.

24, 25

The IGZO-based synaptic transistor gated by

aqueous solution can also mimic such synaptic function. As shown in Figure 3a, when two successive spikes with a time interval (ΔT) of 40 ms are applied on presynaptic terminal of a DI water gated IGZO-based synaptic transistor, two EPSC peaks are observed. The amplitude of the second peak (A2) with amplitude of ~250 nA is obviously larger than that of the first peak (A1) of ~160 nA. Such behavior is similar to the PPF behavior observed in biological synapses.

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Facilitation ratio (A2/A1) is estimated to be ~1.56. Similar behaviors were also observed in IGZO-based synaptic transistor gated by alcohol (25%) and KCl (0.25 mM) solutions, as shown in Figure 3b. The facilitation ratio of the alcohol solution gated synaptic transistor is as high as 1.66, while that of the KCl solution gated synaptic transistor is only ~1.23. Figure 3c and d shows the facilitation ratios plotted as a function of ΔT for the IGZO-based synaptic transistor gated by alcohol and KCl solutions with different concentrations, respectively. The maximum facilitation ratio for each synapse is obtained at ΔT=20 ms. When ΔT increases, the facilitation ratio decreases gradually to approach the value of 1. Here we give a reasonable explanation based on the dynamic process of ion migration. When the second spike is applied, the hydronium ions triggered by the first spike may still partially reside near the solution/IGZO interface. Thus, the hydronium ions triggered by the second spike are augmented with the residual hydronium ions triggered by the first spike, which will induce a PPF observed in the IGZO-based synaptic transistor. The shorter ΔT, the higher PPF facilitation ratio can be obtained. Interestingly, our


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results showed that the facilitation ratios increase with the increase of alcohol concentration at all T, while the facilitation ratios decrease with the increase of KCl concentration. For example, the facilitation ratios at ΔT=40 ms for IGZO-based synaptic transistor gated by 50% and 25% alcohol solutions, DI water, 0.5 mM and 0.25 mM KCl solutions are 1.93, 1.66, 1.56, 1.23 and 1.16, respectively. The delivery of hydronium and hydroxyl ions is inhibited (facilitated) by alcohol molecule (salt ions) as mentioned above. Therefore, when the second spike is triggered, there are more (fewer) residual ions that remain from the first spike, which induces a larger (lower) increment in EPSC amplitude. As a result, the facilitation ratios of alcohol (KCl) solution gated synaptic transistor are much higher (less) than water gated synaptic transistor at the same ΔT. In biological system, synapse with a high (low) initial probability of neurotransmitter release would lead depression (facilitation) of short-term plasticity.

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As an analogy, the alcohol (salt)

can function as a facilitation (depression) modulator in short-term plasticity emulations for the aqueous solution gated IGZO-based synaptic transistor.

Figure 4 (a) EPSCs recorded from a water gated IGZO-based synaptic transistor in responses to the stimulus trains with different frequencies. The stimulus train at each frequency consists of 10 stimulus spikes (0.5V, 10ms). (b) Frequency-dependent EPSCS gain (A10/A1) plotted as a function of presynaptic spike frequency for 25 % alcohol, DI water and 0.25 mM KCl solutions, respectively.


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Frequency-dependent synaptic transmission was considered as one of the fundamental mechanisms that underlies many neural computations such as orientation detection, sound-source localization, etc. 20, 26, 27 As shown in Figure 4a, the stimulus trains with frequency ranged from 4 to 50 Hz are applied on presynaptic terminal of a water-gated IGZO-based EDL transistor. The stimulus train at each frequency consists of 10 presynaptic spikes (0.5 V, 10 ms). The amplitudes of EPSCs increase with the increase of the stimulus frequency. The maximum EPSCs at each frequency increase from ~175 to ~424 nA. The EPSC gain is defined as the ratio between the amplitudes of the tenth EPSC peak (A10) and the first EPSC peak (A1) at each frequency. Figure 4b shows the frequency-dependent EPSC gain plotted as a function of the stimuli frequency for alcohol solution (25%), DI water and KCl solution (0.25 mM), respectively. The gains of all the IGZO synaptic transistors increase with the increase of stimuli frequency, which indicates the high-pass filtering function. The gains are always ~1.0 at 4Hz for the three solutions. Interestingly, the gains at 50 Hz decrease from ~2.7, through ~2.5, to ~1.3 for IGZO-based synaptic transistors gated by 25 % alcohol solution, water and 0.25 mM KCl solution, respectively. Such results suggest that the gain control of such artificial synaptic filter can be achieved through tuning the EDL coupling effect.


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Figure 5 (a) A schematic diagram showing the measurements for orientation tuning experiment. The EPSC recorded from a water gated IGZO-based synaptic transistor when the orientation angle of the panel is (b) 0o and (c) 78.5o. (d) The normalized gain of EPSC responses plotted as function of orientation angle for IGZO-based synaptic transistor gated by alcohol (25%), water and KCl (0.25 mM), respectively.

Neurons in the primary visual cortex respond preferentially to edges with a particular orientation.26,

27

Such orientation selectivity is necessary for encoding of visual images

orientations. In some mammals such as monkey, the orientation tuning curve can be enhanced by attention without causing systematic changes.

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We built a simple model of visual system as

shown in Figure 5a. A photodetector and processing circuit are connected to the gate of an aqueous solution gated IGZO-based synaptic transistor, The coordinate of the photodetector is (x, 0, 0). A square panel with five pairs of black-white grating patterns was moved along y axis in yoz plane. The orientation angle () is defined as the angle between z axis and the grating orientation. For each orientation, the panel is moved from side to side, and the coordinate of the


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center is (0, y, 0). Each time when the edge of the grating pattern move across the coordinate origin is detected by the photodetector, the processing circuit would provide a voltage pulse (0.5 V, 10 ms) to the presynaptic terminal of the water gated IGZO synaptic transistor. The presynaptic spikes corresponding to each orientation were computed by Matlab software and generated by Keithley 4200. The detailed descriptions about the experiments were illustrated in Figure S6 in supporting information. As shown in Figure 5b, when the orientation is 0o, ten presynaptic spikes with frequency of 50 Hz are triggered successively and induces a dramatically increased EPSC with the maximum value of ~500 nA. As shown in Figure 5c, when the orientation angle is 78.5o, only two presynaptic spikes with a frequency of 10 Hz were triggered with the maximum EPSC amplitude of ~284 nA. The visual response is defined as the maximum EPSC amplitude at each orientation angle. Furthermore, the visual responses for alcohol solution (25%) and KCl solution (0.25 mM) gated IGZO-based synaptic transistor are also studied. Figure 5d illustrates the normalized visual responses for alcohol solution (25%), water and KCl solution (0.25 mM) gated IGZO-based synaptic transistor as a function of orientation angle. The experimental data were fitted by Gaussian function. Followed a neuroscience protocol, the halfwidth (WH) of the Gaussian curve measured at half-height were used as criterion of orientation selectivity.28 The WH values for alcohol solution, water and KCl solution gated IGZO-based synaptic transistors are estimated to be 53o, 59o and 63o, respectively. Therefore, the alcohol solution gated synaptic transistor shows the best orientation selectivity. Such result also suggests that control of orientation selectivity of an aqueous solution gated IGZO-based synaptic transistor can be achieved by modifying the concentrations of alcohol or KCl. Such results indicate that the aqueous solution gate IGZO-based synaptic transistors have the potential to mimic complex psychological behaviors.


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Recently, obvious dissolution of IGZO film was observed after immersion in water for three days.29 In our experiment, the timescale (generally dozens of seconds) is much shorter than that in such reference, so dissolution of IGZO is not a problem for our fundamental research. At the same time, it was reported that both traditional electrostatic coupling and interface electrochemical doping may occur in liquid-gated EDL transistors depend on the applied gate voltage.4 That is why EDL transistors were sometime called electrochemical transistors. When the gate voltage is higher than 1.23 V, the observed memory-like characteristics (as shown in Fig. 1c) should be mainly originated from the electrochemical reaction at the IGZO surface. Based on this electrochemical doping, long-term memory and plasticity can be emulated by this surface electrochemical reaction. In such sense, electrochemical “instability” is also favorable for longterm plasticity emulation.30 In our experiment, investigations were only focused on the shortterm synaptic behavior emulation, and the gate pulse voltage is only as low as 0.5V, which is much lower than 1.23 V. So electrochemical reaction at the IGZO surface should be suppressed, and repeatable EPSC can be measured under same pulse gate voltage. 3. CONCLUSION In summary, we have experimentally demonstrated a solution gated IGZO-based EDL transistor for short-term synaptic plasticity emulation. Paired-pulse facilitation, high-pass filtering and orientation tuning functions were mimicked. In previous reports, the modulation of synaptic plasticity can be only realized through programming the pattern and/or timing of the applied voltages.

Our results suggested that synaptic plasticity could also be effectively

regulated by alcohol (ethyl alcohol) and salt (potassium chloride) additives.


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4. EXPERIMENTAL SECTION Device Fabrication. First, 150 nm-thick patterned indium-zinc-oxide (IZO) films used as drain and source electrodes were deposited on glass by RF magnetron sputtering with a nickel shadow mask. Then 50 nm-thick indium-gallium-zinc-oxide (IGZO) channel layers were deposited between drain and source using RF magnetron sputtering method. The channel width and length are 1000 and 80 m, respectively. For gating, the fixed volume (~5.0 L) of droplet of deionized (DI) water or the alcohol solution or KCl solutions was applied over the channel region from a microsyringe. The alcohol solutions with volume concentration of 25% and 50% were used in this paper and KCl solutions with molar concentration of 0.25 mM and 0.5 mM were used. The DI water (18 M·cm) was obtained from Millipore purification system. Electrical Characterizations. The ionic conductivities and frequency dependent capacitances of aqueous solution were characterized by a Solartron 1260A Impedance/Gain-Phase Analyzer. In the impedance spectroscopy measurements, the direct-current (DC) voltage and the alternating current (AC) small-signal amplitude are 0 V and 0.1 V, respectively. One bended tungsten probe is penetrated into the aqueous solution as the top gate electrode. To secure the repeatability, the probe was washed by the DI water for several times and then drying by nitrogen gas gun. After that, the probe was washed by the aqueous solution for several times before penetrated into the solution droplet for gating. The filed-effect transistor characteristics and synaptic emulations were carried out using a semiconductor parameter analyzer (Keithley 4200 SCS) at room temperature in dark with a high relative humidity of 60 %.


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ASSOCIATED CONTENT Supporting Information. Side view and top view of the device; Leakage current of the DI water gate dielectric; The reproducibility of the frequency-dependent specific capacitance of 25 % alcohol, DI water, and 0.25 mM KCl solutions; Impedance measurements for 50% and 25% alcohol solution, DI water, and 0.25 and 0.5 mM KCl solutions, respectively; EPSC recorded from a water gated transistors when the voltage of presynaptic spike varied from 0.2 to 1.0 V in 0.2 V steps; The detailed description about the orientation tuning experiments. This material is available free of charge via the Internet at http://pubs.acs.org.” AUTHOR INFORMATION Corresponding Author * Email: [email protected] (Q. W.) Author Contributions Q. W., Y. S. and C. J. W. conceived and designed the experiments; C. J. W., Y. H. L., L. Q. Z, and P. F. fabricated the devices and performed electrical measurements. The manuscript was written by C. J. W., L. Q. Z., and Q. W. Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENT This work was supported by the National Science Foundation for Distinguished Young Scholars of China (61425020), the National Natural Science Foundation of China (11474293) and the Zhejiang Provincial Natural Science Foundation of China (LR13F040001).

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Short-Term Synaptic Plasticity Regulation in ... - ACS Publications

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