Short-term and long-term coupled storage mode artificial neuromorphic devices

Abstract

This invention discloses an artificial neuromorphic device with short-term and long-term coupled memory modes. The device comprises, from bottom to top, a silicon substrate, an HfO2 layer, a SiO2 layer, and a C8-BTBT organic semiconductor layer; two Au electrodes are disposed on the C8-BTBT organic semiconductor layer. Based on a back-to-back Schottky diode synaptic device and incorporating the tunneling behavior of electrons in the SiO2 / HfO2 heterodielectric layer, this invention develops an artificial neuromorphic device coupling short-term and long-term memory modes, providing insights for further creating artificial neural systems that mimic human memory characteristics. This invention couples short-term and long-term memory modes, utilizing tunneling characteristics to adaptively modulate the capture mode. The resulting dual-mode coupled capture achieves long-term memory through the blocking effect of the tunnel layer. The feasibility of this strategy has been fully demonstrated in theory and experiments. Clear mode changes can be produced in tests with different pulse modes.

Description

Technical Field

[0001] This invention belongs to the field of neuromorphic devices, and particularly relates to an artificial neuromorphic device with short-term and long-term coupled storage modes. Background Technology

[0002] In the human brain, there are two fundamentally different memory mechanisms: short-term memory (STM) and long-term memory (LTM). STM (sometimes called working memory) lasts only a few seconds and is responsible for conscious thought and behavior; while LTM lasts for over an hour and is the origin of association. The transition from STM to LTM is a complex function of stimulus intensity and pattern, achievable by enhancing synaptic connectivity. This plasticity of memory and the global parallelism between memory and computation are key mechanisms for achieving high-tolerance, high-precision, and low-power adaptive spike computing, enabling complex recognition and reasoning. Inspired by these mechanisms, building in-memory computing (CIM) architectures on-device to achieve in-situ adaptive computing can overcome the inherent efficiency limitations of traditional von Neumann architectures. Recent research has utilized non-volatile conductance to simulate synaptic weights, thereby manipulating synaptic-like behavior, resulting in devices called synaptic devices. Some of these devices do indeed exhibit pulse pattern-dependent plasticity. Notably, these reported synapses appear promising for adaptive neuromorphic computing. However, further research is needed to combine long-term memory models with short-term memory models to realistically simulate long-term cognition. Utility Model Content

[0003] Purpose of this utility model: The purpose of this utility model is to provide an artificial neuromorphic device with short-term and long-term coupled storage modes. Based on back-to-back Schottky diode synaptic devices and combined with the tunneling behavior of electrons in the SiO2 / HfO2 heterodielectric layer, an artificial neuromorphic device coupling short-term and long-term storage modes is developed, providing ideas for further creating artificial neural systems that mimic human memory characteristics.

[0004] Technical solution: The present invention provides an artificial neuromorphic device with short-term and long-term coupled storage modes, comprising, from bottom to top, a silicon substrate, an HfO2 layer, a SiO2 layer, and a C8-BTBT organic semiconductor layer; two Au electrodes are provided on the C8-BTBT organic semiconductor layer.

[0005] Furthermore, the thickness of the HfO2 layer is 50-150 nm.

[0006] Furthermore, the thickness of the SiO2 layer is 2-4 nm.

[0007] Furthermore, the thickness of the C8-BTBT organic semiconductor layer is 2-3 layers (5-9 nm).

[0008] Furthermore, the Au electrode has dimensions of 40μm × 80μm, and the device channel width and length are 70-90μm and 10-20μm, respectively.

[0009] This utility model also discloses a method for fabricating an artificial neuromorphic device with short-term and long-term coupled storage modes, comprising the following steps:

[0010] Step 1: Clean the silicon substrate and dry the surface moisture.

[0011] Step 2: Grow an HfO2 layer on a silicon substrate using magnetron sputtering;

[0012] Step 3: Grow a SiO2 layer on the HfO2 layer using chemical vapor deposition;

[0013] Step 4: Prepare a C8-BTBT organic semiconductor layer on the SiO2 layer;

[0014] Step 5: Transfer two Au electrodes of the same size to the surface of the C8-BTBT organic semiconductor layer by physical transfer method;

[0015] Step 6: Place the device on the probe stage for testing. Use pulsed light to irradiate the device surface to simulate external stimulation. By adjusting the pulse mode, including different pulse widths or different pulse intensities, the device can be dynamically transitioned from STM to LTM.

[0016] Furthermore, step 1 specifically includes the following steps:

[0017] Step 1.1: Sonicate the substrate in acetone, ethanol, and deionized water for 10-15 minutes each in sequence to remove oil and organic matter from the surface of the epitaxial wafer.

[0018] Step 1.2: Heat the substrate in a solution of H2SO4:H2O2 = 3:1 for 10-15 minutes, then rinse thoroughly with deionized water to remove organic matter from the substrate surface.

[0019] Step 1.3: Place the epitaxial wafer in a water bath at 80°C for 10-15 minutes in a volume ratio of NH4OH:H2O2:H2O = 1:1:5, and then clean it with deionized water to remove dust, organic matter and some metal contaminants adsorbed on the surface.

[0020] Step 1.4: Place the substrate in a water bath at 80°C for 10-15 minutes in a volume ratio of HCl:H2O2:H2O = 1:1:6, and then clean it with deionized water to remove metal from the surface of the material.

[0021] Step 1.5: Immerse the substrate in a diluted hydrofluoric acid solution for 2-5 minutes, then rinse it with deionized water to remove the oxide layer on the material surface.

[0022] Step 1.6: Finally, dry with N2 and bake on a hot plate for 5-10 minutes to remove moisture from the substrate surface.

[0023] Further, step 4 specifically involves dissolving 10g of C8-BTBT in a mixed solvent of 98.5wt% anisole and 0.5wt% p-anisaldehyde, then dropping 3μL of the growth solution onto the substrate, using an air pump to generate airflow, and dragging the droplet to move rapidly, thereby quickly forming an organic thin film on the substrate.

[0024] Furthermore, in step 6, the pulsed light is a 365nm pulsed light.

[0025] Beneficial Effects: Compared with existing technologies, this invention has the following significant advantages: This invention proposes a novel device strategy to couple short-time and long-time memory modes, utilizing tunneling characteristics to adaptively modulate the capture mode. The resulting dual-mode coupled capture achieves long-term memory through the blocking effect of the tunnel layer. The feasibility of this strategy has been fully demonstrated in theory and experiments. Clear mode changes can be produced in tests with different pulse modes. Specific beneficial effects are as follows:

[0026] (1) A novel mechanism is employed: the physical separation of electron capture positions using a tunneling mechanism allows for adaptive coupling of dual-mode capture, thereby generating storage modes with different timescales in a single device. Under a weak electric field, electron capture occurs at the SiO2 interface. In this case, the state is relatively volatile because electron capture and decapture occur simultaneously. Before capture and decapture reach equilibrium, stimulation can enhance the state, but after capture and decapture reach equilibrium, stimulation has no enhancing effect, and the device remains in STM mode. If there is a large amount of electron capture at the SiO2 interface, i.e., if there are enough holes in the channel, the energy band of C8-BTBT will bend upward, thereby establishing a sufficiently low tunneling barrier for electrons. In other words, the increase in the electric field of the gratings on both sides of SiO2 caused by capture can lower its tunneling barrier for electrons. Therefore, some electrons will tunnel through SiO2 to the SiO2 / HfO2 interface, accompanied by an increase in the electron return barrier. By combining the high reflow barrier of SiO2 and the high tunneling barrier of HfO2, electrons can be stably blocked at the SiO2 / HfO2 interface, enabling the device to achieve LTM mode. Therefore, the tunneling / capture / blocking structure can generate deep electron trapping, thus ensuring non-volatile storage. Here, this seamless fusion of dual-mode trapping is used to modulate memory modes with long short-term plasticity.

[0027] (2) Novel device behavior: There are few reports on the coupling of short-time and long-time dual-mode memory in single-synaptic devices. This invention controls the electron capture mode by rationally designing the SiO2 / HfO2 heterodielectric layer structure. By adjusting the pulse mode, including different pulse widths and different pulse intensities, the device can dynamically transition from STM to LTM.

[0028] (3) Simple device structure: Based on the back-to-back Schottky diode structure, the present invention grows a SiO2 / HfO2 heterodielectric layer on the Si substrate as the key structure for short-time and long-time dual-mode memory modulation, grows a two-dimensional organic semiconductor layer on the tunneling layer, and finally transfers the Au electrode. The device structure is simple and easy to realize. Attached Figure Description

[0029] Figure 1 This is a cross-sectional view of an artificial neuromorphic device with short-term and long-term storage modes; in the figure, 1 is a silicon substrate, 2 is a 100nm HfO2 layer, 3 is a 3nm SiO2 layer, 4 is a C8-BTBT organic semiconductor layer, and 5 is an Au electrode.

[0030] Figure 2 The mode switching process programmed for different pulse widths;

[0031] Figure 3 The mode switching process programmed for different pulse intensities; Detailed Implementation

[0032] The technical solution of this utility model will be further described below with reference to the accompanying drawings.

[0033] like Figure 1 As shown, the present invention discloses a short-term and long-term coupled storage mode artificial neuromorphic device, which, from bottom to top, includes a silicon substrate, an HfO2 layer, a SiO2 layer, and a C8-BTBT organic semiconductor layer; two Au electrodes are provided on the C8-BTBT organic semiconductor layer.

[0034] This invention discloses a method for fabricating short-term and long-term memory-mode artificial neuromorphic devices. The device is fabricated on a silicon substrate, with a 100nm HfO2 layer grown from bottom to top, followed by a 3nm SiO2 layer. A two-dimensional organic semiconductor layer is grown on the SiO2 layer using a liquid-phase process. Two metal electrodes are constructed on the two-dimensional organic semiconductor layer. The key component of the structure is the SiO2 / HfO2 heterodielectric layer. This structure utilizes the tunneling properties of silicon dioxide to control the capture mode of the device operation, namely single-mode capture and dual-mode coupled capture. In dual-mode capture, the charge captured by HfO2 can be cleverly blocked by SiO2, allowing the state to be maintained for a long time. Therefore, by adjusting the pulse mode, the capture mode can be adaptively modulated by the internal field in real time, and the device macroscopically exhibits a transition in memory mode. The steps are as follows:

[0035] S1. The silicon substrate is cleaned using a standard cleaning process. The specific steps are as follows: (1) Sonic cleaning in acetone, ethanol and deionized water for 10 minutes in sequence; (2) Heating in a solution of H2SO4:H2O2 = 3:1 for 10 minutes, and then rinsing thoroughly with deionized water; (3) Water bath at 80°C for 10 minutes in NH4OH:H2O2:H2O = 1:1:5 (volume ratio), and then rinsing thoroughly with deionized water; (4) Water bath at 80°C for 10 minutes in HCl:H2O2:H2O = 1:1:6 (volume ratio), and then rinsing thoroughly with deionized water; (5) Soaking in a diluted hydrofluoric acid solution for 2 minutes, and then rinsing thoroughly with deionized water; (6) Drying with N2 and baking on a hot plate for 5 minutes.

[0036] S2. The HfO2 layer is grown by magnetron sputtering, and the optimal thickness of the HfO2 layer is 100 nm.

[0037] S3. A SiO2 layer is grown on the HfO2 layer. The SiO2 is grown by chemical vapor deposition, and the optimal thickness of the SiO2 layer is 3 nm.

[0038] S4. A two-dimensional organic semiconductor layer C8-BTBT is prepared on the SiO2 layer. The optimal thickness of C8-BTBT is a bilayer (5.3 nm). The preparation method is to dissolve 10 g of C8-BTBT in a mixed solvent of anisole (98.5 wt%) and p-anisaldehyde (0.5 wt%), and then drop 3 μL of the mixed solution onto the substrate. An air pump is used to generate airflow to drag the droplet to move quickly, thereby rapidly forming an organic thin film on the substrate.

[0039] S5. Transfer two Au electrodes of the same size to the thin film surface by physical transfer method.

[0040] S6. During testing, the device is placed on the probe stage, and 365nm pulsed light is used to irradiate the surface of the device to simulate external stimulation. By adjusting the pulse mode, including different pulse widths and different pulse intensities, the device is dynamically transitioned from STM to LTM.

[0041] To demonstrate the device's short-time and long-time storage modes, a 365nm single-pulse light was applied to the device, and the STM and LTM operating modes were achieved by adjusting the pulse width or pulse intensity, respectively.

[0042] Figure 2 The mode switching process is programmed for different pulse widths. When using a 1s pulse width, a rapid decay process can be observed, which is the STM mode. When the pulse width exceeds 2s, due to the control of dual-mode coupling capture, the signal will not completely fade away, but will remain above the baseline level for a long time, which is the LTM mode.

[0043] Figure 3 The mode switching process is programmed for different pulse intensities, using 0.9 μW / cm. 2 The lower pulse programmable short-term plasticity, i.e., STM mode; but when using 1μW / cm 2 When pulsed, the mode changes to LTM mode. Therefore, these results demonstrate the mode coupling of STM and LTM in the present invention, and that mode transitions can be generated by adjusting the pulse mode.

Claims

1. A short-time and long-time coupled storage mode neuromorphic device, characterized in that, From bottom to top, it includes a silicon substrate (1), an HfO2 layer (2), a SiO2 layer (3), and a C8-BTBT organic semiconductor layer (4); two Au electrodes (5) are provided on the C8-BTBT organic semiconductor layer (4).

2. The short and long coupled memory mode neuromorphic device of claim 1, wherein, The thickness of the HfO2 layer (2) is 50-150 nm.

3. The artificial neuromorphic device with short-term and long-term coupled storage modes according to claim 1, characterized in that, The thickness of the SiO2 layer (3) is 2-4 nm.

4. The artificial neuromorphic device with short-term and long-term coupled storage modes according to claim 1, characterized in that, The thickness of the C8-BTBT organic semiconductor layer (4) is 2-3 layers, i.e. 5-9 nm.

5. The artificial neuromorphic device with short-term and long-term coupled storage modes according to claim 1, characterized in that, The Au electrode (5) has a size of 40μm×80μm, and the device channel width and length are 70-90μm and 10-20μm, respectively.

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