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Our body is a multiple perception learning system. Bionic application of perception cognitive functions based on neuromorphic electronics would endow artificial intelligence new intension. In particular, electrolyte-gated transistors have been suggested for neuromorphic platform applications. Due to the fundamental limitations for ionic liquid and ionic gel-based electrolyte, it would be interesting to obtain solid-state electrolytes through a vacuum free system. Thus, in the present work, a simple aqueous solution-processed mesoporous silica coating-gated oxide photo-perception neuromorphic transistors have been proposed. The neuromorphic transistors exhibit good electrical performances. A resistor-loaded inverter is built, exhibiting typical inverter operation at low working voltage. ‘Selective potentiation and depression’ behaviors have been mimicked on the neuromorphic transistor. In addition, the proposed neuromorphic transistor shows optical and electrical synergic response behaviors. Neurological behavior of conditioned taste aversion learning has been mimicked. Thus, the single photo-perception neuromorphic transistor could integrate the functions of perception and neuromorphic algorithm. The proposed photo-perception neuromorphic transistors could have potentials in artificial perception learning systems.

The neural system is a multifunctional perceptual learning system. Our brain can perceive different kinds of information to form senses, including touch, sight, hearing, and so on. Mimicking such perceptual learning systems is critical for neuromorphic platform applications. Here, an artificial tactile perceptual neuron is realized by utilizing electronic skins (E-skin) with oxide neuromorphic transistors, and this artificial tactile perceptual neuron successfully simulates biological tactile afferent nerves. First, the E-skin device is constructed using microstructured polydimethylsiloxane membranes coated with Ag/indium tin oxide (ITO) layers, exhibiting good sensitivities of ∼2.1 kPa-1 and fast response time of tens of milliseconds. Then, the chitosan-based electrolyte-gated ITO neuromorphic transistor is fabricated and exhibits high performance and synaptic responses. Finally, the integrated artificial tactile perceptual neuron demonstrates pressure excitatory postsynaptic current and paired-pulse facilitation. The artificial tactile perceptual neuron is featured with low energy consumption as low as ∼0.7 nJ. Moreover, it can mimic acute and chronic pain and nociceptive characteristics of allodynia and hyperalgesia in biological nociceptors. Interestingly, the artificial tactile perceptual neuron can employ "Morse code" pressure-interpreting scheme. This simple and low-cost approach has excellent potential for applications including but not limited to intelligent humanoid robots and replacement neuroprosthetics.

Recently, realizing artificial perception learning systems at the hardware level based on neuromorphic devices has become a new research branch in artificial intelligence technology. Here, we report multi-functional starch-based bio-polysaccharide electrolyte gated photoelectronic synergic coupled indium–gallium–zinc oxide (IGZO) neuromorphic transistors. Both light illumination and voltage biasing will modulate the channel conductance. Thanks to strong electrical-double-layer (EDL) coupling behaviors of the starch-based bio-polysaccharide electrolyte, the neuromorphic transistor can operate at low voltages. Interestingly, the neuromorphic transistor exhibits long-term memory response behaviors under light stimuli. Moreover, photoelectric synergic spatiotemporal integration behaviors are demonstrated by introducing a light spike stimulus and voltage spike stimulus in a temporal and spatial manner. Furthermore, connections between electric spikes and light spikes have been established, which results in the demonstration of the Pavlovian classical condition. The proposed photoelectric synergic neuromorphic transistors would have potential applications in brain-inspired multifunction intelligent perception system applications.

In recent years, neuromorphic computing has attracted close attention. Simulating synaptic plasticity on neuromorphic devices is an important step in hardware based neuromorphic computing. Metaplasticity is a higher-order form of synaptic plasticity. It can regulate the ability of synapse to generate plasticity. Here, chitosan based electrolyte gated protonic/electronic coupled indium-tin-oxide (ITO) neuromorphic transistors are fabricated. The transistor exhibits unique interfacial ionic coupling effects and interfacial electrochemical doping abilities. Thus, metaplastic excitatory postsynaptic current and metaplastic paired-pulses response are achieved on the chitosan gated ITO neuromorphic transistor. Transitions between paired-pulse facilitation and paired-pulse depression are observed. In addition, metaplastic facilitation of long-term potentiation and metaplastic inhibition of long-term potentiation are also successfully imitated. The present work may expand the applications of solid-state electrolyte gated transistors in neuromorphic platforms.

Conventionally, oxide phototransistors operate at high voltage due to the limited electrostatic modulation behaviors of traditional gate dielectrics. In the present work, we report low-voltage driven chitosan-gated indium tin oxide (ITO) phototransistors with protonic/photonic synergic coupling effects. Due to strong proton gating effects of chitosan, the phototransistor can operate at low voltage of below 1.5 V. Under illumination with light wavelength of 400 nm, the phototransistor exhibits high photoresponsivity up to ∼300 A/W and optical gain up to ∼5000 at low gate bias of −0.45 V. The photoresponses are related to activation of trapped electrons at the interface, which negatively drifts the threshold voltage. Due to the inherent protonic/photonic synergic coupling effects, the phototransistors also demonstrate synaptic functions, including excitatory postsynaptic current and paired-pulse facilitation. Protonic/photonic synergic coupled oxide phototransistors may have potential applications in portable electronics and visual neuromorphic platforms.

Recently, flexible neuromorphic devices have attracted extensive attention for the construction of perception cognitive systems with the ultimate objective to achieve robust computation, efficient learning, and adaptability to evolutionary changes. In particular, the design of flexible neuromorphic devices with data processing and arithmetic capabilities is highly desirable for wearable cognitive platforms. Here, an albumen-based protein-gated flexible indium tin oxide (ITO) ionotronic neuromorphic transistor was proposed. First, the transistor demonstrates excellent mechanical robustness against bending stress. Moreover, spike-duration-dependent synaptic plasticity and spike-amplitude-dependent synaptic plasticity behaviors are not affected by bending stress. With the unique protonic gating behaviors, neurotransmission processes in biological synapses are emulated, exhibiting three characteristics in neurotransmitter release, including quantal release, stochastic release, and excitatory or inhibitory release. In addition, three types of spike-timing-dependent plasticity learning rules are mimicked on the ITO ionotronic neuromorphic transistor. Most interestingly, algebraic arithmetic operations, including addition, subtraction, multiplication, and division, are implemented on the protein gated neuromorphic transistor for the first time. The present work would open a promising biorealistic avenue to the scientific community to control and design wearable "green" cognitive platforms, with potential applications including but not limited to intelligent humanoid robots and replacement neuroprosthetics.

Recently, neuromorphic devices have been receiving increasing interest in the field of artificial intelligence (AI). Realization of fundamental synaptic plasticities on hard-ware devices would endow new intensions for neuromorphic devices. Spike-rate-dependent plasticity (SRDP) is one of the most important synaptic learning mechanisms in brain cognitive behaviors. It is thus interesting to mimic the SRDP behaviors on solid-state neuromorphic devices. In the present work, nanogranular phosphorus silicate glass (PSG)-based proton conductive electrolyte-gated oxide neuromorphic transistors have been proposed. The oxide neuromorphic transistors have good transistor performances and frequency-dependent synaptic plasticity behavior. Moreover, the neuromorphic transistor exhibits SRDP activities. Interestingly, by introducing priming synaptic stimuli, the modulation of threshold frequency value distinguishing synaptic potentiation from synaptic depression is realized for the first time on an electrolyte-gated neuromorphic transistor. Such a mechanism can be well understood with interfacial proton gating effects of the nanogranular PSG-based electrolyte. Furthermore, the effects of SRDP learning rules on pattern learning and memory behaviors have been conceptually demonstrated. The proposed neuromorphic transistors have potential applications in neuromorphic engineering.

Brain-inspired neuromorphic devices have been attracted increasing attentions for artificial intelligent applications. Designing neuromorphic devices that could mimic essential synapse-like functions is of great importance for brain-inspired computation. Ionic-conducting electrolytes possess unique interfacial ionic/electronic coupling effects. Ionic-conducting electrolyte gate transistor could operate at electrostatic modulation mode and at electrochemical mode. At electrostatic modulation mode, channel conductance experiences a volatile change, similar to the short-term plasticity behaviors observed in biological synapses. While at electrochemical mode, the transistor channel conductance always experiences a nonvolatile change, similar to the long-term plasticity behaviors observed in biological synapses. Interestingly, two operation modes will shift from one to another under certain biasing conditions, which means cognitive behaviors can be modulated through certain stimuli or training. Thus, such devices have strong potential applications in brain-inspired artificial synapse devices and neuromorphic systems. Here, we review recently progresses in electrolyte gate transistor-based neuromorphic system.

Recently, there are increasing interests in eco-friendly electronics. In the present work, water degradable indium-tin-oxide synaptic transistor was proposed. Solution processed starch-based electrolyte acted as gate dielectric. The starch-based electrolyte exhibits extremely strong electrostatic modulation behavior with electric-double-layer (EDL) capacitance of ∼1.6 μF/cm2. The synaptic transistor exhibits a high on/off ratio of ∼1.9 × 107, a small subthreshold swing of ∼99.7 mV/decade and a high field effect mobility of ∼14.9 cm2/Vs, respectively. The oxide synaptic transistor exhibits high stabilities in synaptic responses. Both short-term and long-term synaptic plasticities were mimicked. The proposed oxide synaptic transistors have potential applications in “green” neuromorphic platforms.

Eco-friendly “green” electronics are attracting increasing interests in recent years. Here, biodegradable organic/inorganic hybrid indium-tin-oxide electric double layer (EDL) transistors were fabricated on plastic substrates. Solution processed chitosan based polysaccharide films were used as gate dielectrics. Due to extremely high EDL capacitances of the chitosan-based electrolytes, the oxide EDL transistors exhibit good performances. Resistor loaded inverters were also built, exhibiting full-swing characteristics and high voltage gains at low operation voltages. Wave-type conversions were realized including conversions from sinusoid waves into rectangular waves and from noise signals into two-bit outputs. Furthermore, the organic/inorganic hybrid transistors can be dissolved in water easily. The proposed organic/inorganic hybrid oxide transistors may have potential applications in “green” portable devices.

New functional materials that are constantly introduced into carrier-selective contacts (CSCs), which allow one type of carrier passing through while blocking the other type via energy band alignment at contact region, promote the fabrication of crystalline silicon (c-Si) solar cells towards low-temperature and dopant-free. Here, electron-beam-evaporated molybdenum oxide (MoO x ) and magnesium oxide (MgO x ) are directly deposited upon the front and rear surface of c-Si substrates, respectively, to form CSCs with asymmetric band offset for holes and electrons. Contact resistivity, passivation effect, interfacial structures and chemical states for both MoO x /c-Si and MgO x /c-Si are systematically characterized. Considering good carrier-selectivity at the front and the rear side, the optimum thickness in terms of contact resistivity and photovoltaic performance is 10 nm for MoO x and 1.5 nm for MgO x , respectively. Finally, an efficiency over 14% for the planar MoO x /c-Si/MgO x heterojunction solar cells is achieved, demonstrating huge economic potential in fabrication procedure over conventional high-temperature diffused homojunction solar cells.

Indium-tin-oxide synaptic transistors using proton conducting nanogranular phosphorosilicate glass as gate dielectric are fabricated. Humidity-dependent proton gating behaviors are observed. Moreover, synaptic plasticities are mimicked on the proton gated oxide synaptic transistors. Interestingly, enhanced synaptic facilitation is observed at higher relative humidity originated from the strengthened proton gating. An oxide synaptic transistor with humidity-dependent synaptic plasticities may find potential applications in neuromorphic platforms.

Indium-zinc-oxide thin-film transistors (TFTs) using chitosan-based bio-polysaccharide electrolytes as the gate dielectric are fabricated. The TFTs show a good electrical performance with a very low operation voltage of ~1.0 V. Specific gate capacitance of the electrolyte film and electrical performance of the TFTs can be effectively modulated by the coplanar modulatory terminal due to synergic proton gating effects. Furthermore, a resistor-loaded inverter is investigated, and balanced noise margin is obtained. Such oxide-based TFTs with additional modulatory terminal may find potential applications in portable electronics.

Neuromorphic devices and systems with ultralow power consumption are important in building artificial intelligent systems. Here, indium tin oxide (ITO)-based oxide neuromorphic transistors are fabricated using poly(vinyl alcohol) (PVA)-based proton-conducting electrolytes as gate dielectrics. The electrical performances of the transistors can be modulated with the ITO channel thickness. Fundamental synaptic functions, including excitatory postsynaptic current, paired-pulse facilitation, and multistore memory, are successfully emulated. Most importantly, the PVA-gated neuromorphic devices demonstrate ultralow energy consumption of ∼1.16 fJ with ultrahigh sensitivity of ∼5.4 dB, as is very important for neuromorphic engineering applications. Because of the inherent environmental-friendly characteristics of PVA, the devices possess security biocompatibility. Thus, the proposed PVA-gated oxide neuromorphic transistors may find potential applications in "green" ultrasensitive neuromorphic systems and efficient electronic biological interfaces.

Neuromorphic devices are of great significance for capturing the computation power of the neural network with ultralow energy consumption and extremely high efficiency. Here, multigate indium-zinc-oxide-based neuron thin film transistors laterally coupled by sodium alginate electrolyte films were fabricated polyethylene terephthalate substrates for neuromorphic system application. The dynamic range of the synaptic response can be effectively modulated by the third modulatory input. More importantly, multiplicative operation was realized successfully based on the rate-coding mode. Such laterally coupled oxide-based neuron transistors could be used as the potential building block in neuromorphic systems.

Ion-conducting materials have received considerable attention for their applications in fuel cells, electrochemical devices, and sensors. Here, flexible indium zinc oxide (InZnO) synaptic transistors with multiple presynaptic inputs gated by proton-conducting phosphorosilicate glass-based electrolyte films are fabricated on ultrathin Si membranes. Transient characteristics of the proton gated InZnO synaptic transistors are investigated, indicating stable proton-gating behaviors. Short-term synaptic plasticities are mimicked on the proposed proton-gated synaptic transistors. Furthermore, synaptic integration regulations are mimicked on the proposed synaptic transistor networks. Spiking logic modulations are realized based on the transition between superlinear and sublinear synaptic integration. The multigates coupled flexible proton-gated oxide synaptic transistors may be interesting for neuroinspired platforms with sophisticated spatiotemporal information processing.

Flexible metal oxide/graphene oxide hybrid multi-gate neuromorphic transistors are fabricated on flexible conducting graphene substrates. Dendritic integrations in both spatial and temporal modes are emulated, and spatiotemporal correlated logics are obtained. A proof-of-principle visual system model for emulating Lobula Giant Motion Detector neuron is also investigated. The results are of great significance for flexible sensors and neuromorphic cognitive systems.

A low-voltage depletion-load inverter consisting of oxide transistors gated by nanogranular phosphorosilicate glass electrolytes has been fabricated. An indium-zinc–oxide electric-double-layer (EDL) transistor shows a threshold voltage ( $V_{\mathrm {th}}$ ) of approximately −0.1 V and acts as a load. An indium-gallium–zinc-oxide EDL transistor shows a $V_{\mathrm {th}}$ of $\sim 0.3$ V and acts as a driver. The depletion-load inverter shows a high voltage gain of $>40$ and a narrow transition width of $ V at low supply voltage of 2 V. The proposed low-voltage inverter may find potential applications in portable electronics and biosensors.

In the biological nervous system, synaptic plasticity regulation is based on the modulation of ionic fluxes, and such regulation was regarded as the fundamental mechanism underlying memory and learning. Inspired by such biological strategies, indium-gallium-zinc-oxide (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, was 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.

Ion gated electric-double-layer (EDL) transistors provide promising strategies to achieve electrostatic modulation for solid-state materials. Here, proton gated indium-zinc-oxide (IZO) EDL transistors were fabricated by using nanogranular phosphorosilicate glass (PSG) based electrolytes as gate dielectrics. A high proton conductivity of ∼3.9 × 10−4 S cm−1 and an extremely big EDL capacitance of ∼4.4 μF cm−2 were observed for the PSG based electrolyte. The IZO EDL transistors could operate at a low voltage of 1.5 V. Furthermore, resistor-loaded inverters were built, demonstrating modulatable electrical performances by a modulatable operation mode of the driving IZO transistor. Full-swing inverter characteristics were observed at a low supply voltage of 1.5 V, exhibiting a high voltage gain of above 7. The inverters were also used for decreasing the noises of input signals. The proton gated oxide EDL transistors have potential applications in biochemical sensors and portable electronics.

Biodegradable oxide synaptic transistors were fabricated on a graphene coated PET substrate. An acid doped chitosan-based biopolymer electrolyte is used as the gate dielectric. With the acid doping, a high proton conductivity of ∼7.6 × 10−4 S cm−1 and a big electric-double-layer capacitance of ∼1.0 μF cm−2 are observed for the biopolymer electrolyte. The fabricated oxide synaptic transistor exhibits good transistor performances, such as a low operation voltage of 1.0 V, a high field-effect mobility of ∼5.4 cm2 V−1 s−1, a high on/off ratio of ∼3.1 × 106 and a low subthreshold swing of ∼80 mV decade−1. With the unique proton gating behaviors, synaptic functions, such as excitatory post-synaptic current, paired-pulse facilitation and synaptic filtering were mimicked. Furthermore, the proposed oxide synaptic transistor could be dissolved in water in a short time. We believe that the proposed biodegradable synaptic transistors could provide new opportunities for low cost, portable “green” neuromorphic electronics.

Mimicking synaptic activities on solid-state electrolyte gated oxide transistors can lay a concrete foundation for the future of artificial intelligence. Renewable natural materials have the advantages of being abundant, inexpensive, biodegradable and ecologically benign. In the present work, we have proposed a biodegradable pectin electrolyte based proton conductor gated “green” electronic synapse. With the unique proton gating activities, the pectin gated transistor exhibits good electrical performances at low operation voltage. Thus, a low-voltage driven resistor-loaded inverter is fabricated. The devices exhibit neuromorphic functions including excitatory post-synaptic current (EPSC), adjustable synaptic weights and transitions from short-term plasticity (STP) to long-term plasticity (LTP). Interestingly, BCM learning rules have also been mimicked on the proposed synaptic transistor, including spike-rate-dependent plasticity (SRDP) and a sliding frequency threshold (fθ). Bio-realistic implementation of important synaptic plasticities with BCM learning acitivites would improve the efficiency of hardware based neural network for the artificial intelligent system.

Recently, environment-friendly electronic devices are attracting increasing interest. "Green" artificial synapses with learning abilities are also interesting for neuromorphic platforms. Here, solution-processed chitosan-based polysaccharide electrolyte-gated indium tin oxide (ITO) synaptic transistors are fabricated on polyethylene terephthalate substrate. Good transistor performances against mechanical stress are observed. Short-term synaptic plasticities are mimicked on the proposed ITO synaptic transistor. When applying presynaptic and postsynaptic spikes on gate electrode and drain electrode respectively, spike-timing-dependent plasticity function is mimicked on the synaptic transistor. Transitions from sensory memory to short-term memory (STM) and from STM to long-term memory are also mimicked, demonstrating a "multistore model" brain memory. Furthermore, the flexible ITO synaptic transistor can be dissolved in deionized water easily, indicating potential green neuromorphic platform applications.

Recently, synaptic electronics are attracting increasing attention in neuromorphic engineering. Here, inhibitory synapses are proposed based on nanogranular phosphorous silicate glass gated indium tin oxide transistors operated in pseudodiode mode. Activity dependent inhibitory synaptic behaviors are mimicked on the proposed pseudodiode, including paired pulse depression and depression adaptation behaviors. Interestingly, the proposed inhibitory synapse demonstrates low power dissipation as low as ≈16 fJ for triggering a postsynaptic current with high signal‐to‐noise ratio of ≈2.2. Moreover, the inhibitory synapse demonstrates zero resting power dissipation. The proposed pseudodiode‐based inhibitory artificial synapses may find potential applications in neuromorphic platforms. Accepted version

Sensory neurons within skin form an interface between the external physical reality and the inner tactile perception. This interface enables sensory information to be organized identified, and interpreted through perceptual learning-the process whereby the sensing abilities improve through experience. Here, an artificial sensory neuron that can integrate and differentiate the spatiotemporal features of touched patterns for recognition is shown. The system comprises sensing, transmitting, and processing components that are parallel to those found in a sensory neuron. A resistive pressure sensor converts pressure stimuli into electric signals, which are transmitted to a synaptic transistor through interfacial ionic/electronic coupling via a soft ionic conductor. Furthermore, the recognition error rate can be dramatically decreased from 44% to 0.4% by integrating with the machine learning method. This work represents a step toward the design and use of neuromorphic electronic skin with artificial intelligence for robotics and prosthetics. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

The control and detection over processing, transport and delivery of chemical species is of great importance in sensors and biological systems. The transient characteristics of the migration of chemical species reflect the basic properties in the processings of chemical species. Here, we observed the field-configurable proton effects in a laterally coupled transistor gated by phosphorosilicate glass (PSG). The bias on the lateral gate would modulate the interplay between protons and electrons at the PSG/indium-zinc-oxide (IZO) channel interface. Due to the modulation of protons flux within the PSG films, the IZO channel current would be modified correspondingly. The characteristic time for the proton gating is estimated to be on the order of 20 ms. Such laterally coupled oxide based transistors with proton gating are promising for low-cost portable biosensors and neuromorphic system applications.

Ultrathin, freestanding polymer hybrid film with macroscopic sizes and molecular thicknesses have received significant interest due to their applications as functional devices, microsensors or nanoactuators. Herein, a 2D Janus hybrid of polymer-grafted carbon nanotubes/graphene oxide (CNTs/GO) thin film is fabricated using microcontact printed CNTs/GO as photo active surface to grow polymer brushes by self-initiated photografting and photopolymerization selectively from one side of CNTs/GO film. This achieved 2D Janus hybrid materials with grafted polymer layer as insulative carpet and supported CNTs/GO thin film as conductive element have the potential application as flexible and miniature electric carpet for heating micro-/nano devices locally.

For photovoltaic applications, low-cost SiNx-coated metallurgical grade silicon (MG-Si) wafers were used as substrates for polycrystalline silicon (poly-Si) thick films deposition at temperatures ranging from 640 to 880 °C by thermal chemical vapor deposition. X-ray diffraction and Raman results indicated that high-quality poly-Si thick films were deposited at 880 °C. To obtain n-type poly-Si, the as-deposited poly-Si films were annealed at 880 °C capped with a phosphosilicate glass. Electrical properties of the n-type poly-Si thick films were investigated by four-probe and Hall measurements. The carrier concentration and electron mobility of the n-type poly-Si film was estimated to be 1.7 × 1019 cm−3 and 68.1 cm2 V−1 s−1, respectively. High-quality poly-Si thick films deposited on MG-Si wafers are very promising for photovoltaic applications.

By doing inside the catalytic combustion furnace with Pd-based honeycomb monoliths of lean natural gas-air mixtures and measuring temperature field and the composition of flue gas, the exhaust gas of Low-carbon catalytic combustion furnace of natural gas can be analyzed and discussed. In addition, the catalytic combustion furnace in the pottery was also investigated, which can reduce the pollutant emission of the product process, and reduce global warming.

Ion coupling has provided an additional method to modulate electric properties for solid-state materials. Here, phosphorosilicate glass (PSG)-based electrolyte gated protonic/electronic coupled indium–tin–oxide electric-double-layer (EDL) transistors are fabricated. The oxide transistor exhibits good electrical performances due to an extremely strong proton gating behavior for the electrolyte. With interfacial electrochemical doping, channel conductances of the oxide EDL transistor can be regulated to different levels, corresponding to different initial synaptic weights. Thus, activity dependent synaptic responses such as excitatory postsynaptic current, paired-pulse facilitation, and high-pass filtering are discussed in detail. The proposed proton conductor gated oxide EDL synaptic transistors with activity dependent synaptic plasticities may act as fundamental building blocks for neuromorphic system applications.

An indiumezinc-oxide (IZO) based ionic/electronic hybrid synaptic transistor gated by field-configurable nanogranular SiO2 films was reported. The devices exhibited a high current ON/OFF ratio of above 107, a high electron mobility of similar to 14 cm(2) V-1 s(-1) and a low subthreshold swing of similar to 80 mV/decade. The gate bias would modulate the interplay between protons and electrons at the channel/dielectric interface. Due to the dynamic modulation of the transient protons flux within the nanogranular SiO2 films, the channel current would be modified dynamically. Short-term synaptic plasticities, such as short-term potentiation and short-term depression, were mimicked on the proposed IZO synaptic transistor. The results indicate that the synaptic transistor proposed here has potential applications in future neuromorphic devices.

Surface passivation performances of Al2O3 layers deposited on p-type Czochralski Si wafers by atomic layer deposition (ALD) were investigated as a function of post-deposition annealing conditions. The maximal minority carrier lifetime of ∼4.7 ms was obtained for Al2O3 passivated p-type Si. Surface passivation mechanisms of Al2O3 layers were investigated in terms of interfacial state density (Dit) and negative fixed charge densities (Qfix) through capacitance–voltage (C–V) characterization. High density of Qfix and low density of Dit were needed for high passivation performances, while high density of Dit and low density of Qfix degraded the passivation performances. A low Dit was a prerequisite to benefit from the strong field effect passivation induced by high density of negative fixed charges in the Al2O3 layer.

Al2O3 films were deposited on n-type crystalline Si (c-Si) wafers by atomic layer deposition using Al(CH3)3 and H2O as precursors. Surface anti-reflectance and passivation performances were investigated. Average reflectances between 2.8 and 4.2% were obtained for Al2O3 coated textured Si with Al2O3 thickness ranged between 100 and 70 nm. Wide thickness window for low reflectance between 2.8 and 4.2% indicates its potential anti-reflectance applications. A high minor carrier lifetime of ～4.5 ms is obtained for n-type c-Si wafers passivated by 100 nm Al2O3 films, corresponding to an effective surface recombination velocity of ～4 cm/s. Wide annealing time window and wide annealing temperature window are addressed to obtain good passivation performances with high minor carrier lifetime >3 ms. The passivation performances are related to the released H atoms from Al–OH bonds and the formation of Al vacancies and O interstitials within Al2O3 films. Our results indicate that Al2O3 films show dual functions of anti-reflectance and surface passivation for photovoltaic applications.

Indium–zinc-oxide (IZO) electric-double-layer transistors are fabricated on proton conducting chitosan-based biopolymer electrolyte. Due to the extremely strong proton gating originated from proton migration within the chitosan films, good electrical performances are obtained. Characteristic time for the proton gating is estimated to be on the order of several milliseconds. Furthermore, a resistor loaded inverter is built, showing a high-voltage gain of $\sim 9$ at a low supply voltage of 1.2 V. The proton-gated IZO transistors may find potential applications in portable electronics and synaptic electronics.

Flexible low-voltage indium-gallium-zinc-oxide (IGZO) electric-double-layer transistors are fabricated on polyethylene terephthalate substrates at room temperature and proposed for energy-efficient artificial synapse application. The IGZO channel conductance and the gate voltage pulse are regarded as synaptic weight and synaptic spike, respectively. The energy consumption of our IGZO synaptic transistor is estimated to be as low as $\sim 0.23$ pJ/spike. Short-term synaptic plasticity and high-pass filtering behaviors are also mimicked in an individual IGZO synaptic transistor.

Laterally coupled indium-zinc-oxide electric-double-layer (EDL) transistors gated by solution-processed sodium alginate electrolyte films are self-assembled on glass substrates. Due to the strong EDL effect, a low-operation voltage of 1.5 V, a high-current ON/OFF ratio of $\sim 3.1\times 10^{6}$ and a high-electron mobility of $\sim 8.8$ cm $^{2}$ /Vs are obtained. Furthermore, AND logic operation is demonstrated when two in-plane gate electrodes are used as the input terminals. Such low-voltage laterally coupled oxide EDL transistors have potential applications in portable biosensors and synaptic electronics.

Recent progress in using biomaterials to fabricate functional electronics has got growing attention for the new generation of environmentally friendly and biocompatible electronic devices. As a kind of biological material with rich source, proteins are essential natural component of all organisms. At the same time, artificial synaptic devices are of great significance for neuromorphic systems because they can emulate the signal process and memory behaviors of biological synapses. In this report, natural chicken albumen with high proton conductivity was used as the coupling electrolyte film for organic/inorganic hybrid synaptic devices fabrication. Some important synaptic functions including paired-pulse facilitation, dynamic filtering, short-term to long-term memory transition and spatial summation and shunting inhibition were successfully mimicked. Our results are very interesting for biological friendly artificial neuron networks and neuromorphic systems.

Low-temperature sol-gel processed silica electrolyte films showed a high specific capacitance of 3.0 μF/cm(2) due to the electric-double-layer (EDL) effect. Oxide-based transistors gated by such silica electrolyte films show a high on/off ratio (10(7)) and a very low operation voltage (2.0 V). The proton-related dynamic modulation in these devices makes them ideal candidates for biological synapse emulation. Short-term synaptic plasticity, such as paired pulse facilitation, was successfully emulated. Most importantly, spiking and logic operation were also demonstrated when two lateral in-plane gates were used as the presynaptic inputs. Our oxide-based EDL transistors gated by sol-gel processed silica electrolyte films provide an interesting approach for synaptic behavior emulation, which is interesting for brain-inspired neuromorphic systems.

Inspired by the dendritic integration and spiking operation of a biological neuron, flexible oxide-based neuromorphic transistors with multiple input gates are fabricated on flexible plastic substrates for pH sensor applications. When such device is operated in a quasi-static dual-gate synergic sensing mode, it shows a high pH sensitivity of ~105 mV/pH. Our results also demonstrate that single-spike dynamic mode can remarkably improve pH sensitivity and reduce response/recover time and power consumption. Moreover, we find that an appropriate negative bias applied on the sensing gate electrode can further enhance the pH sensitivity and reduce the power consumption. Our flexible neuromorphic transistors provide a new-concept sensory platform for biochemical detection with high sensitivity, rapid response and ultralow power consumption.

The selective emitter technology is the most effective method to improve the silicon solar cell performance. However, the strict alignment requirements between the Ag gridlines and the selective emitters should be addressed. In the present study, a novel front metal contact patterning scheme for crystalline silicon (c-Si) solar cells is developed. An intersected selective laser doping process is applied. The control experiment indicates that the best efficiency increases for ∼23.8% from ∼14.39% to ∼17.74% after receiving the laser doping process. Moreover, our laser doping process does not affect the open-circuit voltage and short-circuit current significantly and the emitter properties have not been degraded in terms of the emitter saturation current. The improved front metal contact results in the improved energy conversion efficiency. The developed process offers an elegant and reliable approach for the low-cost, high throughput industrial-scale production process.

Free-standing chitosan membranes with high proton conductivity are prepared by a simple coating-peeling process. Laterally coupled flexible indium-zinc oxide electric-double-layer transistors with dual in-plane gates are fabricated on such chitosan membranes for the first time. The operation voltage, subthreshold swing, and field-effect mobility are estimated to be 1.0 V, 119 mV/decade, and 1.2 cm(2)/V s, respectively. Finally, "AND" logic operation is experimentally demonstrated with two in-plane gates as the input terminals. Such free-standing laterally coupled flexible transistors have potential applications in biosensors and biocompatible electronics.

Indium-tin-oxide-based electric-double-layer (EDL) thin-film transistors (TFTs) are used as pH sensors. Such EDL devices show a low operation voltage of ~ 1.5 V and a high field-effect electron mobility (μFE) of ~ 20 cm2·V-1·s-1 when phosphorous-doped nanogranular SiO2-based electrolyte films are used as the gate dielectric. The pH sensor based on such EDL TFT exhibits a high sensitivity of 58.1 mV·pH-1 and a good linearity in the pH range from 2 to 12. In addition, such pH sensors present a low threshold voltage drift rate of 2.2 mV·h-1 and a hysteresis voltage of 8.3 mV after a pH loop of 7→ 4→ 7→ 10→7.

Recently, neuromorphic devices have attracted great attentions in the field of brain-inspired neuromorphic engineering. As an important form of short-term synaptic plasticity, post-tetanic potentiation (PTP) plays a crucial role in the formation of short-term memory in biological nervous system. Here, indium-tin-oxide synaptic transistors were proposed by using solution-processed starch-based biopolymer electrolytes as gate dielectrics, demonstrating good electrical performances at a low operation voltage of 1 V. Short-term plasticities were mimicked on the proposed oxide synaptic transistors. PTP behaviors were demonstrated on the synaptic devices. Furthermore, effects of prior history of synaptic activity on PTP responses have been discussed in detail. The proposed synaptic transistors may have potential applications in neuromorphic system.

The formation of High-k/SiO2 dipole layer is experimentally observed as the flatband voltage shift of MIS capacitors without high-k film thickness dependence. It is also deduced from the band bending of SiO2 and high-k at the interface by using XPS measurements. As a model to explain the driving force to form the dipole, the areal density difference of oxygen atoms at high-k/SiO2 interface is taken account to predict both the direction and magnitude of the dipoles. This is the only model to give a reasonable explanation to the experimentally observed directions of the dipoles.