Optoelectronic synapse device with photoactive layer containing quantum dot-transition metal dichalcogenide heterojunction

Abstract

To provide a photoelectron synapse element having an optical active layer indicating a neuromorphic feature as well as enabling an optical responce of an infrared wavelength in order to be a recognition of a correct event, and provide a manufacturing method of them.SOLUTION: A photoelectron synapse element comprises an optical active layer in which a heterogeneous bonding is formed by contacting an inorganic quantum dot with a transition metal dichalcogenide of a secondary semiconductor material indicating a synapse characteristic by a light stimulus. Thus, a synapse reaction in responce to an optical signal of a near infrared wavelength can be made. By realizing a visual-brain function toe function of a human indicating the neuromorphic feature by an optical responce (a visual reaction) of the infrared wavelength in a single element with an optical detection feature that it is sensitively reacted at a high speed in the infrared wavelength signal, it can be easily adopted in an autonomous traveling mobility field.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to optoelectronic synapse devices, and more particularly to optoelectronic synapse devices having a photoactive layer including a quantum dot-transition metal dichalcogenide heterojunction. [Background technology]

[0002] Research into autonomous driving began in the 1970s, and in the 2010s, technological developments have been accelerating with the emergence of deep learning technology. Even amid the challenging times of the COVID-19 pandemic, autonomous driving-related technologies are advancing at an even faster pace. To address the core technologies of "artificial intelligence" and "safety" in the future smart mobility industry, the importance of artificial neural network processing devices equipped with sensory element technology that recognizes lanes and obstacles ahead of the vehicle, and neuromorphic technology that processes information simultaneously and in parallel between cognition, perception, and computation, similar to the neuronal structure and behavior of the human brain, is maximizing.

[0003] Currently, mobility systems rely on optical signals (LiDAR, Light Detection and Ranging) or electromagnetic waves (RADAR, Radio Detection and Ranging) to avoid hazards and detect hazards in autonomous driving. However, while LiDAR is based on InGaAs and is specialized for the 900 nm wavelength range, it suffers from a problem of reduced recognition rate due to interference with visible light. Therefore, there is an increasing need for photodetectors that are sensitive and responsive to infrared wavelength signals above 900 nm to avoid interference from visible light in normal atmospheric environments and ensure accurate recognition. Furthermore, to ensure the safety of passengers and cargo and achieve stable autonomous operation, the entire process of hazard recognition, calculation, judgment, and response must be carried out at ultra-high speed. Furthermore, to improve the efficiency of mobility systems, it is necessary to develop a single device capable of performing this process with low power consumption. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been created to solve the above-mentioned problems, and its purpose is to provide an optoelectronic synapse element having a photoactive layer that is capable of responding to light at infrared wavelengths for accurate recognition of objects and exhibits neuromorphic properties, and a method for manufacturing the same. [Means for solving the problem]

[0005] To achieve the above object, an optoelectronic synapse element according to a preferred embodiment of the present invention may include a photoactive layer provided on a substrate and including inorganic quantum dots and a two-dimensional semiconductor material, and a plurality of electrodes provided on the photoactive layer and spaced apart from each other.

[0006] The inorganic quantum dots and the two-dimensional semiconductor material may be in direct contact with each other to form a heterojunction.

[0007] The wavelength of light acceptable to the photoactive layer may include the wavelength range from visible light to near infrared light.

[0008] The two-dimensional semiconductor material may be a single layer or a multi-layer structure of two or more layers.

[0009] The two-dimensional semiconductor material may include a transition metal dichalcogenide.

[0010] The transition metal dichalcogenide is represented by the chemical formula MX2, where M is a transition metal element and may include Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc, Re, Ru, Co, Pd, Pt, Cu, Ga, In, Sn, Ge, Pb, or a combination of two or more selected from these, and X is a chalcogen element and may include S, Se, Te, or a combination of two or more selected from these.

[0011] The transition metal dichalcogenide may include MoS2, MoSe2, MoTe2, WS2, WSe2, WTe2, ZrS2, ZrSe2, HfS2, HfSe2, NbSe2, ReSe2, PdTe2, or a combination of two or more selected from these.

[0012] The inorganic quantum dots may have a band gap of 1.2 eV or less.

[0013] The inorganic quantum dots may include InAs, PbS, CdS, GaAs, InGaAs, InP, GaInP, or a combination of two or more selected from these.

[0014] The electrode includes a metal or a metal compound, and the metal or metal compound may include a metal element including Ti, Ni, Cr / Au, Ag, or a combination of two or more selected from these.

[0015] In order to achieve the above object, a method for manufacturing an optoelectronic synapse device according to a preferred embodiment of the present invention may include the steps of: synthesizing a two-dimensional semiconductor material on a silicon oxide substrate; transferring the two-dimensional semiconductor material onto another semiconductor substrate to form a two-dimensional semiconductor material layer; forming an electrode layer by depositing a plurality of metal layers spaced apart from one another on a portion of the two-dimensional semiconductor material layer; and applying an inorganic quantum dot colloid solution and a ligand solution to a surface of another portion of the two-dimensional semiconductor material layer, coating the surface, and then drying to form a photoactive layer.

[0016] The two-dimensional semiconductor material layer may be a single layer or a multi-layer structure of two or more layers.

[0017] The transfer step may be a wet transfer.

[0018] The ligand solution is a mixed solution of an organic ligand and an organic solvent, and the organic ligand material may have a short carbon chain or ring of C1 to C8 and may include at least one functional group selected from a thiol group, an amine group, a carboxyl group, and combinations thereof.

[0019] The organic ligand may include thiol-based ligands such as 1,2-ethanedithiol (EDT), 3-mercaptopropionic acid (MPA), and benzenedithiol (BZT); amine-based ligands such as ethylenediamine (EDA) and ammonium thiocyanate (SCN); and a combination of at least two or more selected from these.

[0020] The step of forming the photoactive layer may be performed at room temperature. [Effects of the Invention]

[0021] According to the present invention, an optoelectronic synapse device according to a preferred embodiment of the present invention includes an optically active layer in which inorganic quantum dots that accept near-infrared optical signals and transition metal dichalcogenide, a two-dimensional semiconductor material that exhibits synaptic properties in response to optical stimulation, are in direct contact with each other to form a heterojunction, thereby enabling a synaptic response to optical signals in the near-infrared wavelength range. Therefore, by realizing in a single device the photodetection characteristics of responding sensitively and quickly to not only visible light signals but also infrared wavelength signals for accurate recognition, as well as the function of mimicking human visual and brain functions, which exhibits neuromorphic properties due to optical response (visual response) to infrared wavelengths, the device can be easily applied in the field of autonomous mobility.

[0022] The effects of the present invention are not limited to the effects mentioned above, and include other effects not explicitly mentioned, which are clearly understandable to those skilled in the art from the description throughout the specification. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic diagram showing a cross section of an optoelectronic synapse device according to one embodiment of the present invention. [Figure 2] 1A and 1B are a transmission electron microscope (TEM) image and an X-ray diffraction (XRD) graph, respectively, of inorganic quantum dots included in a photoactive layer of an integrated structure for sensing an optical signal according to an embodiment of the present invention. [Figure 3] 1A is a schematic diagram of an optoelectronic synapse device according to one embodiment of the present invention; FIG. 1B is a graph of the responsivity and detectivity of the device with a 1060 nm wavelength laser output; and FIG. 1D is an IV graph of the device. [Figure 4]1 shows the results of (a) and (d) conductance as a function of pulse number, (b) and (c) PPF index, (e) nonlinearity as a function of laser output depending on the presence or absence of a quantum dot-two-dimensional semiconductor heterojunction, and (f) synaptic weight as a function of pulse number for an optoelectronic synapse element according to one embodiment of the present invention. [Figure 5] FIG. 1 shows (a) a schematic diagram of an optoelectronic synapse device according to one embodiment of the present invention, (b) an IV graph in response to ON / OFF of light, and (c) graphs measuring memory / learning (potentiation) and forgetting (depression) characteristics in response to application of optical pulses. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. The advantages and features of the present invention, as well as methods for achieving them, will become more apparent with reference to the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the technical idea of the present invention is in no way limited to the embodiments disclosed below, and can be embodied in various different forms. The following embodiments are merely provided to fully convey the technical idea of the present invention and to fully convey the scope of the present invention to those skilled in the art to which the present invention pertains. The present invention is only defined by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

[0025] Furthermore, unless otherwise specified in this specification or clearly contradictory to the context, all terms used in this disclosure, including technical and scientific terms, can be used in the same meaning as commonly understood by those of ordinary skill in the art to which this invention belongs. In addition, commonly used terms and dictionary-defined terms should not be construed as ideal or overly formal unless explicitly defined in this application. The terms used in this specification are merely used to describe the embodiments and are not intended to limit the present invention. In this specification, singular expressions include plural terms unless clearly indicated otherwise in the context.

[0026] Where used in this specification, terms such as "comprises" and / or "comprising" do not exclude the presence or addition of stated components, steps, operations and / or elements.

[0027] Optoelectronic synapse devices with photoactive layers containing inorganic quantum dot-two-dimensional semiconductor heterojunctions

[0028] FIG. 1 is a schematic diagram showing a cross section of an optoelectronic synapse device according to one embodiment of the present invention.

[0029] Referring to FIG. 1, an optoelectronic synapse device 100 may include a photoactive layer 40 provided on a substrate 10 and including inorganic quantum dots 20 and a two-dimensional semiconductor material 30, and a plurality of electrodes 50 provided on the photoactive layer 40 and spaced apart from one another.

[0030] The substrate 10 can be a semiconductor substrate made of a semiconductor material such as silicon or SOI (Silicon-on-insulator). It can also be a semiconductor substrate with a wide bandgap (WBG) such as silicon carbide (SiC), gallium nitride (GaN), or gallium oxide (Ga2O3). The substrate 10 can also be doped with a dopant.

[0031] The electrode 50 may include a metal or a metal compound. The metal or metal compound may include metal elements such as Ti, Ni, Cr / Au, Ag, and combinations of two or more selected from these. Any metal or metal compound containing a metal element suitable for use in electronic devices such as a metal electrode or metal interconnection may be used without limitation.

[0032] The photoactive layer 40 may include inorganic quantum dots 20 and a two-dimensional semiconductor material 30 as a light-receiving layer that receives an applied optical signal. In particular, the photoactive layer 40 can be easily used as a channel layer of an optoelectronic synapse device that can respond to optical signals including near-infrared wavelengths, since the inorganic quantum dots 20 that receive near-infrared optical signals and the two-dimensional semiconductor material 30 that exhibits synaptic properties in response to optical stimulation are in direct contact with each other to form a heterojunction.

[0033] Specifically, when an infrared optical signal is irradiated onto the inorganic quantum dots 20 layer of the photoactive layer 40, charges are excited from the valence band to the conduction band of the quantum dots. The excited charges are then transferred to the channel layer of the two-dimensional semiconductor material 30 in contact with the quantum dots, allowing current to flow through the semiconductor channel layer. At this time, a portion of the charges is trapped / detrapped at the interface between the transition inorganic quantum dots 20 and the two-dimensional semiconductor material 30, allowing the conductivity of the semiconductor channel to be reversibly controlled. This allows the conductivity of the channel of the two-dimensional semiconductor material 30 to be controlled by applying an infrared signal, thereby variably controlling the concentration of trapped charges, thereby realizing memory, learning, and forgetting characteristics related to infrared stimulation. In particular, the optoelectronic synapse element according to a preferred embodiment of the present invention employs a vertical heterojunction structure between an infrared-sensitive zero-dimensional material (inorganic quantum dots 20) and a two-dimensional semiconductor material 30 in the semiconductor channel layer, thereby making it possible to reversibly control the charge trapping / detrapping behavior at the junction interface between the light (infrared) sensitive layer and the semiconductor channel layer, and thus enabling the realization of even higher memory and learning capabilities than neural network elements based on a single material that do not form a heterojunction structure.

[0034] First, the inorganic quantum dots 20 may be materials that can respond to optical signals, e.g., optical pulses, and can absorb and emit light in the visible to near-infrared wavelength range, e.g., the wavelength range from 380 nm to 1500 nm. In particular, the wavelength range receptive to the inorganic quantum dot 20 materials according to preferred embodiments of the present invention may include the near-infrared wavelength range, specifically, 800 nm to 1500 nm, and more specifically, the wavelength range from 900 nm to 1200 nm.

[0035] The inorganic quantum dot 20 material is a zero-dimensional (0D) material, which is a uniform circular inorganic particle having a nanoscale diameter, and may have a diameter of 0.1 to 10 nm, specifically, 0.5 to 7 nm, and more specifically, 1 to 5 nm, but is not limited thereto.

[0036] In addition, according to a preferred embodiment of the present invention, the inorganic quantum dot 20 material may be a semiconductor material that absorbs and emits light in the near-infrared region and has a band gap of 1.2 eV or less. The inorganic quantum dot 20 material may include, for example, InAs, PbS, CdS, GaAs, InGaAs, InP, GaInP, or a combination of two or more selected from these. In one embodiment, it may include InAs, but is not limited thereto. In particular, InAs quantum dots as the inorganic quantum dot 20 material are semiconductor materials capable of absorbing and emitting light in the near-infrared wavelength range, comply with the Restriction of Hazardous Substances (RoHS) Directive, and may be a material that can easily replace lead-chalcogenide quantum dots, such as PdS and CdS, which contain highly toxic heavy metals. InAs quantum dots can primarily exhibit n-type characteristics.

[0037] Furthermore, the inorganic quantum dots 20 may be covered with organic ligands, which will be described later, for passivation to prevent charge trapping effects.

[0038] On the other hand, the inorganic quantum dots 20 may be further doped or alloyed to improve the quantum dots' effective light absorption ability, specifically, infrared light absorption ability, or two or more types of inorganic quantum dots may be composited, or may be fabricated in a core-shell structure for effective passivation.

[0039] The two-dimensional (2D) semiconductor material 30 may have a structure in which strong covalent bonds are formed within a single layer and relatively weak van der Waals forces are used between layers. Unlike conventional optoelectronic devices, the two-dimensional semiconductor material 30 has a direct transition property in itself, allowing it to be readily used as a channel layer of an optoelectronic device even as a single material, thereby simplifying the device structure.

[0040] The two-dimensional semiconductor material 30 may be provided in the photoactive layer 40 in the form of an ultrathin film or ultrathin plate-like particles, for example, flakes, having a layered structure, or may be provided as a monolayer or a multilayer of two or more layers. Specifically, the two-dimensional semiconductor material 30 may be provided in a multilayer structure of several layers. The two-dimensional semiconductor material 30 exhibits indirect transition characteristics in a bulk or thin film state with a normal thickness, but exhibits direct transition characteristics when the film thickness is within a single layer or a few layers. It has excellent photoresponsiveness, transparency, and flexibility, and is therefore effectively applicable to optoelectronic devices.

[0041] In addition, the two-dimensional semiconductor material 30 has a layered structure in which each layer has very strong covalent bonds between the constituent atoms, and the layers are bonded by weak van der Waals forces. Since there are no dangling bonds extending outside the layers and there is only two-dimensional interaction between the constituent atoms in principle, carrier transport exhibits ballistic transport, unlike that of ordinary thin films or bulks, making it applicable as a high-mobility, high-speed, and low-power semiconductor.

[0042] In addition, the two-dimensional semiconductor material 30 can be heterogeneously bonded with various materials due to its uniform surface characteristics, making it applicable to synapse elements with bonded structures. In particular, the two-dimensional semiconductor material 30 has the advantage of being capable of photoelectron response sensitive to minute optical stimuli due to its atomic-scale thin layer structure, and therefore, it can respond sensitively to the application of pulsed optical stimuli, thereby enabling the development of memory and learning abilities with increased conductivity and forgetting characteristics due to electrical stimuli.

[0043] The two-dimensional semiconductor material 30 may include a transition metal dichalcogenide (TMD). Specifically, the transition metal dichalcogenide material is represented by the chemical formula MX2, where M is a transition metal element, such as Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc, Re, Ru, Co, Pd, Pt, Cu, Ga, In, Sn, Ge, or Pb, or a combination of two or more selected therefrom, and X is a chalcogen element, such as S, Se, or Te, or a combination of two or more selected therefrom. Specifically, the transition metal dichalcogenide material may include MoS2, MoSe2, MoTe2, WS2, WSe2, WTe2, ZrS2, ZrSe2, HfS2, HfSe2, NbSe2, ReSe2, PdTe2, or a combination of two or more selected from these. More specifically, the transition metal dichalcogenide material may include MoS2, MoSe2, WS2, WSe2, or a combination of two or more selected from these, and in one embodiment, may include WSe2, but is not limited thereto.

[0044] The crystal structure of the transition metal dichalcogenide material has a covalent bond between the transition metal M and the chalcogen element X, and based on this, it can have a hexagonal structure in the planar direction. The crystal structure can also be changed through a further phase change step or doping step.

[0045] Method for manufacturing an optoelectronic synapse device with an optically active layer including a heterojunction of inorganic quantum dots and two-dimensional semiconductor materials

[0046] A method for manufacturing an optoelectronic synapse device according to an embodiment of the present invention may first include the step of providing a two-dimensional semiconductor material on a silicon oxide substrate.

[0047] The step of preparing the two-dimensional semiconductor material may specifically involve a chemical vapor deposition (CVD) method. This may involve arranging quartz boats containing precursor materials at regular intervals in a chemical vapor deposition apparatus having multiple, e.g., two, heating zones, and heating the boats to grow or deposit the two-dimensional semiconductor material on the surface of a silicon oxide substrate. However, the step of preparing the two-dimensional semiconductor material is not limited to the above-described method, and those skilled in the art may manufacture two-dimensional semiconductor materials with desired physical properties or crystallinity by appropriately adjusting or processing experimental conditions according to the purpose.

[0048] Subsequently, a step of transferring the two-dimensional semiconductor material onto another semiconductor substrate to form a two-dimensional semiconductor material layer may be performed. The semiconductor substrate may be a semiconductor substrate such as silicon or SOI (Silicon-on-insulator), which is different from the silicon oxide substrate, which is a bulk insulator. Semiconductor substrates having a wide bandgap (WBG), such as silicon carbide (SiC), gallium nitride (GaN), or gallium oxide (Ga2O3), may also be used. The semiconductor substrate may be doped with a dopant.

[0049] The two-dimensional semiconductor material layer may be in direct contact with the semiconductor substrate to form a van der Waals junction due to van der Waals forces (vdW). Specifically, the junction between the silicon lattice on the surface of the semiconductor substrate and the two-dimensional semiconductor material layer may be formed by bonding due to van der Waals forces. Atoms of each layer may not intersect with each other to intermix or penetrate, but may form a gap between the semiconductor substrate and the two-dimensional semiconductor material layer that physically separates each interface, i.e., a van der Waals gap, between the semiconductor substrate and the two-dimensional semiconductor material layer. In particular, in the manufacturing process of the two-dimensional semiconductor material layer, a transfer process, more specifically a wet transfer process, may be used to minimize physical damage to the surface and form a thin film with a uniform thickness. Furthermore, by providing the two-dimensional semiconductor material layer formed by van der Waals junction, highly reactive dangling bonds on the surface of the semiconductor substrate are removed, and the inherent physical properties of the substrate are preserved, which makes it advantageously applicable to realizing high performance devices.

[0050] Subsequently, a step of forming an electrode layer by depositing a plurality of metal layers spaced apart from one another on a portion of the two-dimensional semiconductor material layer may be performed. The metal layers may include a metal or a metal compound. For example, referring back to FIG. 1 , metal electrodes 50 may be formed on both sides of the two-dimensional semiconductor material layer 30, and inorganic quantum dots 20 (described below) may be formed in the openings where the metal electrodes 50 are not formed. The metal or metal compound may include metal elements such as Ti, Ni, Cr / Au, Ag, and combinations of two or more selected from these. Any type containing a metal element suitable for use in electronic devices such as metal electrodes and metal interconnections may be used, but is not limited thereto.

[0051] A method for manufacturing an optoelectronic synapse device according to an embodiment of the present invention may include a step of applying an inorganic quantum dot colloid solution and a ligand solution to another surface of the two-dimensional semiconductor material layer, the openings, and then drying the coating to form a photoactive layer.

[0052] The inorganic quantum dots are Optoelectronic synapse devices with photoactive layers containing inorganic quantum dot-two-dimensional semiconductor heterojunctions The inorganic quantum dots 20 may be the same as those used in the above.

[0053] The ligand solution may be a mixed solution of an organic ligand and an organic solvent. The organic ligand may have a short carbon chain or ring of C1 to C8 for effective passivation of the inorganic quantum dots and may include one or more functional groups selected from the group consisting of a thiol group, an amine group, a carboxyl group, and combinations thereof. Specifically, the organic ligand may include thiol-based ligands such as 1,2-ethanedithiol (EDT), 3-mercaptopropionic acid (MPA), and benzenedithiol (BZT); amine-based ligands such as ethylenediamine (EDA) and ammonium thiocyanate (SCN); and combinations of at least two of these. In one embodiment, the organic ligand may be 1,2-ethanedithiol (EDT), but is not limited thereto.

[0054] The photoactive layer may be a channel layer of an optoelectronic device capable of responding to near-infrared wavelength light, and may include a heterojunction formed by direct contact between the inorganic quantum dots and the two-dimensional semiconductor material. The two-dimensional semiconductor material has uniform surface characteristics that allow it to easily form a heterojunction with the inorganic quantum dots, making it applicable to synaptic devices with a zero-dimensional (0D)-two-dimensional (2D) material junction structure. In particular, the two-dimensional semiconductor material has the advantage of enabling photoelectron responses sensitive to even minute optical stimuli due to its atomic-scale thin layer structure. Therefore, by responding sensitively to the application of pulsed optical stimuli, it is possible to exhibit memory and learning abilities with increased conductivity and forgetting characteristics due to electrical stimuli.

[0055] The present invention will be described in more detail below with reference to examples and comparative examples. However, the following examples and comparative examples are merely for the purpose of illustrating the present invention, and the scope of the present invention is not limited thereto.

[0056] Manufacturing example: WSe 2 Synthetic steps of

[0057] To synthesize tungsten selenide (WSe), a chemical vapor deposition (CVD) system with two heating zones was used. First, a silicon oxide (SiO) substrate was used. A quartz boat containing 480 mg of selenium (Se) (99.5%, Sigma-Aldrich) powder was placed in the first heating furnace, and a quartz boat containing a mixed powder of 40 mg of NaCl (99%, Sigma-Aldrich) and 240 mg of tungsten oxide (WO) (99.9%, Sigma-Aldrich) was placed in the second heating furnace. After this, with the distance between the two quartz boats set to 34 cm, Se and WO3 / NaCl were grown in the primary heating furnace at a heating rate of 10.9 °C / min and a growth temperature of 600 °C, and in the secondary heating furnace at a heating rate of 14.5 °C / min and a growth temperature of 600 °C. In the synthesis step, the flow rates of Ar and H2 gases as carrier gases were 100 sccm and 20 sccm, respectively. After synthesis, natural cooling was performed, and finally, a multilayer flake-shaped WSe2 layer with a layer thickness of approximately 50 to 70 nm was obtained.

[0058] Example: QD / WSe 2 Fabrication of optoelectronic synapse devices containing heterojunctions as photoactive layers.

[0059] The WSe2 prepared by the method of Preparation Example 1 was transferred onto a silicon / silicon oxide (Si / SiO2) substrate for use as a photoactive layer. Then, 50 nm of nickel (Ni) was deposited using an e-beam evaporator to form a metal electrode. This resulted in multiple electrode layers stacked on the WSe2 at a distance from each other, i.e., a metal (Ni) electrode with a WSe2 / Ni interface. Next, an InAs quantum dot colloidal solution was applied to the WSe2 photoactive layer in the openings where no metal electrode was formed, and spin-coated at 2,000 rpm for 30 seconds. A ligand solution, EDT (1,2-ethanedithiol), was then added dropwise and allowed to stand for 30 seconds. The substrate was then rotated at 2,000 rpm for 30 seconds, followed by the application of an acetonitrile solution for 5 seconds (2,000 rpm), which was repeated twice. Finally, the substrate was rotated at 2,000 rpm for 30 seconds, and then baked at 150° C. for 30 minutes under vacuum.

[0060] Comparative example: WSe 2 Manufacture of an optoelectronic synapse element including the above as an optical signal receiving portion

[0061] An optoelectronic synapse device was fabricated in the same manner as in the above example, except that the InAs quantum dot colloidal solution was not applied onto the WSe2 photoactive layer.

[0062] FIG. 2 shows (a) a transmission electron microscope (TEM) image and (b) an X-ray diffraction (XRD) graph of inorganic quantum dots included in a photoactive layer of an integrated structure for optical signal sensing according to one embodiment of the present invention.

[0063] Referring to FIG. 2, it can be seen that in order to apply the inorganic quantum dots InAs as a photoactive layer, uniform circular particles having a diameter of approximately 3 to 4 nm are prepared as a colloidal solution.

[0064] FIG. 3 shows (a) a schematic diagram of an optoelectronic synapse device according to one embodiment of the present invention, (b) the responsivity and detectivity with a laser output of 1060 nm wavelength, and (c) and (d) IV graphs.

[0065] Referring to Figure 3, after applying an infrared laser with a wavelength of 1060 nm to the photoactive layer of the optoelectronic synapse element, the current in the OFF region of the element increased, and the responsivity and detectivity were confirmed. It was confirmed that the dark current characteristics to infrared stimuli were enhanced.

[0066] Figure 4 shows the results of (a) and (d) conductance as a function of pulse number, (b) and (c) PPF index, (e) nonlinearity as a function of laser output depending on the presence or absence of a quantum dot-two-dimensional semiconductor heterojunction, and (f) synaptic weight as a function of pulse number for an optoelectronic synapse device according to one embodiment of the present invention.

[0067] Referring to Figure 4, it can be seen that applying a 1060 nm infrared laser to the photoactive layer of an optoelectronic synapse device achieves memory / learning (potentiation) and forgetting (depression) characteristics. It can also be seen that spike-timing-dependent plasticity (STDP), excitatory postsynaptic current (EPSC), inhibitory postsynaptic current (IPSC), paired-pulse facilitation (PPF), and low-power information forgetting characteristics can be realized, thereby realizing neuromorphic technology. Furthermore, it can be seen that the optoelectronic synapse device of the present invention has the potential to be an in-sensor computing device capable of signal recognition, processing, and calculation in a single device.

[0068] Transfer and output characteristics were measured using a probe station (M5VC, MS TECH, Korea) and a laser oscillator. It was confirmed that N-type characteristics could be obtained from the InAs / WSe2 element compared to the existing P-type WSe2 element. Responsivity and detectivity were measured at a wavelength of 1060 nm and were found to be 2.2 A / W and 9.0 x 10, respectively. 10 Jones was measured, and it was confirmed that when a single pulse was irradiated, the photoresponse current showed a response characteristic that was improved by approximately 60% compared to the comparative example (WSe2).

[0069] To confirm the feasibility of using an InAs / WSe2 heterojunction structure to mimic the human retina, we measured its neuromorphic properties. Using visible and infrared laser wavelengths of 405 nm and 1060 nm, respectively, and a frequency of 0.5 Hz, 100 pulses were applied at 0.5, 1, 2, and 3 mW and 5, 10, and 15 mW, respectively. Potentiation and depression were observed, respectively. Based on this, nonlinearity was analyzed and found to be 5% higher than that of existing WSe2 devices. Furthermore, paired pulse facilitation (PPF) and paired pulse depression (PPD) were observed, confirming the potential for neuromimetic functionality.

[0070] Figure 5 shows (a) a schematic diagram of an optoelectronic synapse element according to one embodiment of the present invention, (b) an IV graph in response to ON / OFF of light, and (c) graphs measuring the memory / learning (potentiation) and forgetting (depression) characteristics in response to the application of light pulses.

[0071] Referring to Figure 5, it can be seen that the application of infrared light (1060 nm) as a pulsed stimulus improves the photosensitivity and plasticity of synaptic elements. After applying visible light pulses to the optoelectronic synaptic element of the present invention, the conductivity increased with the application of the pulses, and then electrical depression using the back gate was observed, demonstrating the plasticity of the synaptic element. Therefore, the optoelectronic synaptic element of the present invention was able to demonstrate not only a visual response to optical stimuli but also neuromorphic properties, thereby confirming that it is possible to realize the technical characteristics of visual-brain function replication.

[0072] Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, the above-described embodiments are merely illustrative in all respects and are not limiting. [Explanation of symbols]

[0073] 100: Photoelectron synapse element 10: Circuit board 20: Inorganic quantum dots 30: Two-dimensional semiconductor materials 40: Photoactive layer 50: Electrode

Claims

1. synthesizing a two-dimensional semiconductor material on a silicon oxide substrate; wet-transferring the two-dimensional semiconductor material onto another semiconductor substrate to form a two-dimensional semiconductor material layer; forming an electrode layer by depositing a plurality of metal layers spaced apart from one another on a portion of the two-dimensional semiconductor material layer; forming a photoactive layer by coating a colloidal solution containing inorganic quantum dots and a ligand solution on another surface of the two-dimensional semiconductor material layer, and then drying the coated surface; Including, the inorganic quantum dots and the two-dimensional semiconductor material layer have portions that directly contact each other to form a heterojunction; The ligand solution is a mixed solution in which an organic ligand and an organic solvent are mixed, and the organic ligand has a short carbon chain or ring of C1 to C8 and includes at least one functional group selected from a thiol group, an amine group, a carboxyl group, and combinations thereof; At least a part of the surface of the inorganic quantum dots where the heterojunction is not formed is covered with the organic ligand.

1. A method for manufacturing an optoelectronic synapse element, comprising:

2. The wavelengths of light that are acceptable to the photoactive layer include the visible to near-infrared wavelength range. A method for manufacturing the optoelectronic synapse device according to claim 1.

3. The inorganic quantum dots have a band gap of 1.2 eV or less. A method for manufacturing the optoelectronic synapse device according to claim 1.

4. The inorganic quantum dots include InAs, PbS, CdS, GaAs, InGaAs, InP, GaInP, and combinations of two or more selected from these. A method for manufacturing the optoelectronic synapse device according to claim 1.

5. The two-dimensional semiconductor material includes a transition metal dichalcogenide. A method for manufacturing the optoelectronic synapse device according to claim 1.

6. The transition metal dichalcogenide has the chemical formula MX ２ is expressed as M is a transition metal element and includes Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc, Re, Ru, Co, Pd, Pt, Cu, Ga, In, Sn, Ge, Pb, or a combination of two or more selected from these; The X is a chalcogen element, and includes S, Se, Te, or a combination of two or more selected from the above. A method for manufacturing the optoelectronic synapse element according to claim 5.

7. The two-dimensional semiconductor material layer may be a single layer or a multi-layer of two or more layers. A method for manufacturing the optoelectronic synapse device according to claim 1.

8. The organic ligand includes thiol-based ligands such as 1,2-ethanedithiol (EDT), 3-mercaptopropionic acid (MPA), and benzenedithiol (BZT); amine-based ligands such as ethylenediamine (EDA) and ammonium thiocyanate (SCN); and a combination of at least two of these. A method for manufacturing the optoelectronic synapse device according to claim 1.

9. The step of forming the photoactive layer is performed at room temperature. A method for manufacturing the optoelectronic synapse device according to claim 1.

10. the electrode layer comprises a metal or a metal compound; The metal or metal compound includes a metal element including Ti, Ni, Cr / Au, Ag, and a combination of two or more selected from these. A method for manufacturing the optoelectronic synapse device according to claim 1.

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