Optoelectronic synaptic device, corresponding preparation method and working method

Abstract

The present invention relates to semiconductor technology and discloses a photoelectric neural synaptic device, a corresponding preparation method, and an operating method. The photoelectric neural synaptic device comprises: a semiconductor substrate, a GaN layer located on the surface of the semiconductor substrate, an AlGaN layer located on the surface of the GaN layer, an amorphous SiNx layer located on the surface of the AlGaN layer, and a gate electrode located on the surface of the amorphous SiNx layer, wherein the GaN layer, AlGaN layer, and amorphous SiNx layer form a floating gate structure, and a source electrode and a drain electrode are located on the surface of the AlGaN layer. The present invention introduces the amorphous SiNx layer as a charge storage layer, allowing photogenerated carriers to separate through the heterojunction polarization field and then enter the charge storage layer, thereby achieving the purpose of preserving photocurrent, ultimately achieving a photoelectric neural synaptic device with high sensitivity, good reliability, and a memory time of greater than 10 years.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a photoelectric neural synapse device, a corresponding preparation method and a working method. Background Art

[0002] Neuromorphic computing, which mimics the behavior of biological neural networks, is considered the most promising next-generation computer for resolving the von Neumann bottleneck. Synapses are the fundamental structures of biological neural networks for information transmission, processing, and storage. Developing synaptic devices that mimic synaptic behavior is key to achieving neuromorphic computing. Based on the principle that biological neurons transmit information via electrical signals, researchers have developed electrically stimulated synaptic devices, such as memristors, transistors, and atomic switches. These devices use electrical signals to simulate synaptic plasticity, but face a bandwidth-connection density trade-off, limiting the speed of electrically stimulated neural networks and potentially leading to significant interconnect issues such as latency and power loss. Compared to electrical signals, optical signals offer advantages such as high bandwidth, low crosstalk, low energy consumption, and no resistance-capacitance delay. Research on optically stimulated optoelectronic synaptic devices could improve the data processing speed and reduce energy consumption of neuromorphic computing. Optical stimulation plays a crucial role in biological perception systems. For example, humans acquire over 70% of their external information through the visual nervous system. Research on optically stimulated optoelectronic synaptic devices also lays the foundation for simulating human visual behavior and addressing the data redundancy issues currently faced by visual biomimetic systems. Therefore, introducing optical signals to construct optoelectronic synaptic devices has become a research hotspot in recent years.

[0003] Optoelectronic synaptic devices integrate sensing, computing, and storage. To ensure data storage reliability, the device's memory should be greater than 10 years. Currently, the memory time of optoelectronic synaptic devices ranges from a few seconds to several thousand seconds, and there is still a lack of optoelectronic synaptic devices with long-term memory. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems in the background technology and to propose a photoelectric neural synaptic device, a corresponding preparation method and a working method, which can enable the device to maintain long-term plasticity (LTP) for more than 10 years.

[0005] The present invention proposes a photoelectric neural synapse device, comprising: a semiconductor substrate, a GaN layer located on the surface of the semiconductor substrate, an AlGaN layer located on the surface of the GaN layer, an amorphous SiNx layer located on the surface of the AlGaN layer, and a gate electrode located on the surface of the amorphous SiNx layer, wherein the GaN layer, the AlGaN layer, and the amorphous SiNx layer constitute a floating gate structure, and a source electrode and a drain electrode are located on the surface of the AlGaN layer.

[0006] Optionally, the semiconductor substrate includes one of sapphire, Si, SiC, and GaN.

[0007] Optionally, an AlN layer is further provided between the semiconductor substrate and the GaN layer.

[0008] Optionally, the specific process for forming the amorphous SiNx material layer corresponding to the amorphous SiNx layer is: preparing a defect-rich amorphous SiNx material layer by PECVD, wherein the growth temperature is 75-100° C. and the ratio of Si / N source gas is 1:1.

[0009] An embodiment of the present invention provides a method for preparing a photoelectric neural synapse device, comprising:

[0010] Providing a semiconductor substrate, forming a GaN layer on the surface of the semiconductor substrate, forming an AlGaN layer on the surface of the GaN layer, and forming an amorphous SiNx layer on the surface of the AlGaN layer, wherein the GaN layer, the AlGaN layer, and the amorphous SiNx layer constitute a floating gate structure;

[0011] The amorphous SiNx layer is etched until the AlGaN layer is exposed, a source electrode and a drain electrode are formed on the surface of the exposed AlGaN layer, and a gate electrode is formed on the surface of the amorphous SiNx layer.

[0012] Optionally, a specific process for forming the floating gate structure includes:

[0013] forming a GaN material layer on the surface of the semiconductor substrate through an epitaxial process, and forming an AlGaN material layer on the surface of the GaN material layer;

[0014] forming an amorphous SiNx material layer on the surface of the AlGaN material layer;

[0015] The amorphous SiNx material layer, the AlGaN material layer and a GaN material layer of a certain thickness are etched, and the remaining GaN layer, the AlGaN layer and the amorphous SiNx layer form a floating gate structure.

[0016] Optionally, the process for forming the amorphous SiNx material layer is: preparing a defect-rich amorphous SiNx material layer by using a PECVD method, wherein the growth temperature is 75° C.-100° C. and the ratio of Si / N source gas is 1:1.

[0017] Optionally, the amorphous SiNx layer is a defect-rich amorphous SiNx layer.

[0018] Optionally, the method further includes forming an AlN layer between the semiconductor substrate and the GaN layer.

[0019] An embodiment of the present invention further provides a method for operating the above-mentioned optoelectronic neural synapse device, including:

[0020] First, a gate voltage lower than the threshold voltage is applied to the gate electrode, which increases the material barrier under the device gate electrode, depletes the two-dimensional electron gas in the AlGaN / GaN channel layer, and turns off the device.

[0021] The device is then irradiated with ultraviolet light below the AlGaN band gap. Under the excitation of ultraviolet light below the AlGaN band gap, the GaN layer absorbs light to generate photogenerated carriers. Under the action of the strong polarization field formed by the AlGaN / GaN heterojunction, the photogenerated carriers separate. Under the action of the gate voltage, the photogenerated electrons tunnel into the amorphous SiNx layer and are captured by the high-density defect states in the amorphous SiNx layer, which lowers the potential barrier of the amorphous SiNx layer originally raised by the gate voltage. The two-dimensional electron gas that was depleted due to the increased potential barrier reappears, and the device is turned on. That is, the electrons captured by the SiNx layer change the threshold voltage of the device, realizing the storage function.

[0022] Beneficial effects of the present invention:

[0023] The present invention forms a floating gate structure by combining a GaN layer, an AlGaN layer and an amorphous SiNx layer, forms a source electrode and a drain electrode on the surface of the AlGaN layer, and forms a gate electrode on the surface of the amorphous SiNx layer. When the device is operating, a gate voltage lower than the threshold voltage is first applied to the gate electrode, which raises the potential barrier of the material below the gate electrode of the device, depletes the two-dimensional electron gas in the AlGaN / GaN channel layer, and turns off the device. The device is then irradiated with ultraviolet light below the AlGaN bandgap. Under the excitation of ultraviolet light below the AlGaN bandgap, the GaN layer absorbs light to generate photogenerated carriers. Under the action of the strong polarization field formed by the AlGaN / GaN heterojunction, the photogenerated carriers are separated. Under the action of the gate voltage, the photogenerated electrons tunnel into the amorphous SiNx layer and are captured by the high-density defect states in the amorphous SiNx layer, lowering the potential barrier of the amorphous SiNx layer originally raised by the gate voltage. The two-dimensional electron gas depleted due to the increased potential barrier reappears, and the device is turned on. That is, the electrons captured by the SiNx layer change the threshold voltage of the device, realizing the storage function. The present invention introduces an amorphous SiNx layer as a charge storage layer, so that the photogenerated carriers enter the charge storage layer after being separated by the heterojunction polarization field, thereby achieving the purpose of preserving the photocurrent, and ultimately obtaining a photoelectric neural synapse device with high sensitivity, good reliability and a memory time of more than 10 years. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the cross-sectional structure of the optoelectronic neural synapse device according to an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of excitatory postsynaptic current of the optoelectronic neural synaptic device according to an embodiment of the present invention in response to light stimulation with a wavelength of 375 nm and a pulse width of 50 ms.

[0026] Figure 3The photoelectric synaptic device of the embodiment of the present invention is subjected to 50 light stimulations and the excitatory postsynaptic current is maintained for more than 10 4 s;

[0027] Figure 4 This is the surface morphology of the amorphous SiNx material layer formed using the PECVD process. DETAILED DESCRIPTION

[0028] The features and advantages of the present invention will be described in detail through embodiments with reference to the accompanying drawings.

[0029] Please refer to Figure 1 The present invention proposes a photoelectric neural synaptic device, comprising: a semiconductor substrate 10, an AlN layer located on the surface of the semiconductor substrate 10, a GaN layer 30 located on the surface of the AlN layer, an AlGaN layer 40 located on the surface of the GaN layer, an amorphous SiNx layer 50 located on the surface of the AlGaN layer 40, a gate electrode 63 located on the surface of the amorphous SiNx layer 50, and a source electrode 61 and a drain electrode 62 located on the surface of the AlGaN layer 40, wherein the GaN layer, the AlGaN layer, and the amorphous SiNx layer constitute a floating gate structure.

[0030] The semiconductor substrate includes one of sapphire, Si, SiC, and GaN.

[0031] In this embodiment, the semiconductor substrate is a SiC substrate, and an AlN layer 20 is provided between the semiconductor substrate and the GaN layer. The AlN layer is used to alleviate the lattice mismatch between the substrate and the GaN layer and to solve the problem of poor wettability of Ga atoms on the SiC substrate.

[0032] Since GaN-based materials are direct bandgap semiconductors with continuously adjustable band gaps from 0.6eV to 6.2eV, they have advantages such as large light absorption coefficient, high electron saturation drift velocity, and good thermal and chemical stability. Photodetectors prepared based on this material can realize single-photon detection and self-driven detection, and have many advantages such as high sensitivity, fast response speed, good reliability, and applicability to extreme environments. Applying nitride materials to optoelectronic synaptic devices can obtain highly responsive and reliable devices.

[0033] However, detectors made from GaN materials have a fast response speed, and achieving non-volatility is a major challenge in applying nitride materials to non-volatile neural synaptic devices. In this embodiment, the structure of the GaN-based optoelectronic neural synaptic device includes a light absorption layer design and a charge storage layer design. The GaN layer is used as the light absorption layer, and the polarization effect of the GaN-based material is utilized to construct an AlGaN / GaN heterojunction to form a polarization field, promote the separation of photogenerated carriers, reduce their recombination rate, increase the carrier lifetime, and enhance the GaN-based non-volatile optoelectronic neural synaptic device's ability to sense weak signals and reduce information acquisition errors.

[0034] In an embodiment of the present invention, the amorphous SiNx layer is defect-rich. Because SiNx does not absorb light at 375nm, the use of an amorphous SiNx layer does not cause carrier recombination. Furthermore, the amorphous SiNx layer is rich in defects and can capture sufficient photogenerated electrons. The present invention incorporates the amorphous SiNx layer as a charge storage layer, allowing photogenerated carriers to separate through the heterojunction polarization field and then enter the charge storage layer, thereby preserving the photocurrent. Ultimately, a photoelectric synaptic device with high sensitivity, good reliability, and a memory time exceeding 10 years is obtained.

[0035] Please refer to Figure 2 and Figure 3 ,in Figure 2 Schematic diagram of excitatory postsynaptic current of the optoelectronic neural synaptic device according to an embodiment of the present invention in response to light stimulation with a wavelength of 375 nm and a pulse width of 50 ms. Figure 3 The photoelectric synaptic device of the embodiment of the present invention is subjected to 50 light stimulations and the excitatory postsynaptic current is obtained. The light stimulation wavelength is 375nm, the pulse width is 50ms, and the time interval between two light stimulations is 950ms. The photocurrent is maintained for more than 10 4 Schematic diagram of excitatory postsynaptic current of s.

[0036] from Figure 2 and Figure 3 It can be shown that the photoelectric synaptic device of the present invention is subjected to 50 light stimulations to generate an excitatory postsynaptic current, the light stimulation wavelength is 375nm, the pulse width is 50ms, and the time interval between two light stimulations is 950ms. The excitatory postsynaptic current is maintained for more than 10 4s, by exponentially fitting the photocurrent decay curve, and using the fitting function to extrapolate the postsynaptic current decay after 10 years, the postsynaptic current was maintained for more than 10 years, and the storage time was comparable to that of a memory device. That is, after multiple light stimulations, the optoelectronic neural synaptic device of the present invention can transform from short-term plasticity (STP) to long-term plasticity (LTP). The reason why the device achieves long-term memory is that photogenerated electrons tunnel into the SiNx layer and are captured by defects in the SiNx layer and fixed in the SiNx layer. The tunneling probability is proportional to the carrier concentration. The pulse duration of the pulsed light selected for the test was 50ms, and the light stimulation time was short, resulting in a limited concentration of photogenerated carriers. However, under multiple light stimulations, photogenerated carriers accumulate, the probability of photogenerated electron tunneling increases, and a significant tunneling effect occurs.

[0037] An embodiment of the present invention further provides a method for preparing a photoelectric neural synapse device, comprising:

[0038] Step S100, providing a semiconductor substrate, forming a GaN layer on the surface of the semiconductor substrate, forming an AlGaN layer on the surface of the GaN layer, and forming an amorphous SiNx layer on the surface of the AlGaN layer, wherein the GaN layer, the AlGaN layer, and the amorphous SiNx layer constitute a floating gate structure;

[0039] In step S200 , the amorphous SiNx layer is etched until the AlGaN layer is exposed, a source electrode and a drain electrode are formed on the surface of the exposed AlGaN layer, and a gate electrode is formed on the surface of the amorphous SiNx layer.

[0040] The specific process of forming the floating gate structure includes:

[0041] forming a GaN material layer on the surface of the semiconductor substrate through an epitaxial process, and forming an AlGaN material layer on the surface of the GaN material layer;

[0042] forming an amorphous SiNx material layer on the surface of the AlGaN material layer;

[0043] The amorphous SiNx material layer, the AlGaN material layer and a GaN material layer of a certain thickness are etched to form an isolation structure, and the remaining GaN layer, the AlGaN layer and the SiNx layer constitute a floating gate structure.

[0044] The amorphous SiNx material layer is formed by PECVD, and the amorphous SiNx layer is a defect-rich amorphous SiNx layer.

[0045] The process for forming a defect-rich amorphous SiNx material layer using PECVD is as follows: growth temperature is 75-100°C, and the ratio of Si / N source gas is 1:1. Since the growth temperature is very low, 75-100°C, the grown amorphous SiNx material layer is rich in defects, which is conducive to the defects of the amorphous SiNx layer capturing photogenerated electrons and fixing them in the SiNx layer. Please refer to Figure 4 , is a surface morphology image of an amorphous SiNx material layer formed using a PECVD process according to an embodiment of the present invention. It can also be seen from the morphology image that the amorphous SiNx material layer has a low film density and many defects.

[0046] The process of forming the GaN material layer and the AlGaN material layer is MOCVD.

[0047] In this embodiment, the source electrode, drain electrode, and gate electrode can be formed using the same metal deposition process. That is, the source and drain electrodes are formed on the exposed surface of the AlGaN layer using electron beam deposition and rapid annealing, and the gate electrode is formed on the surface of the amorphous SiNx layer using photolithography and electron beam deposition.

[0048] In other embodiments, the gate electrode may not be formed in the same metal deposition process as the source electrode and the drain electrode.

[0049] An embodiment of the present invention further provides a method for operating a photoelectric neural synapse device, including:

[0050] First, a gate voltage lower than the threshold voltage is applied to the gate electrode, which increases the material barrier below the gate electrode of the device, depletes the two-dimensional electron gas in the AlGaN / GaN channel layer, and turns off the device.

[0051] The device is then irradiated with ultraviolet light below the AlGaN band gap. Under the excitation of ultraviolet light below the AlGaN band gap, the GaN layer absorbs light to generate photogenerated carriers. Under the action of the strong polarization field formed by the AlGaN / GaN heterojunction, the photogenerated carriers separate. Under the action of the gate voltage, the photogenerated electrons tunnel into the amorphous SiNx layer and are captured by the high-density defect states in the amorphous SiNx layer, which lowers the potential barrier of the amorphous SiNx layer originally raised by the gate voltage. The two-dimensional electron gas that was depleted due to the increased potential barrier reappears, and the device is turned on. That is, the electrons captured by the SiNx layer change the threshold voltage of the device, realizing the storage function.

[0052] Although the present invention has been disclosed above in terms of preferred embodiments, this is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

Claims

1. A photoelectric synaptic device, characterized in that: include: A semiconductor substrate, a GaN layer located on the surface of the semiconductor substrate, an AlGaN layer located on the surface of the GaN layer, an amorphous SiNx layer located on the surface of the AlGaN layer, and a gate electrode located on the surface of the amorphous SiNx layer, wherein the GaN layer, the AlGaN layer, and the amorphous SiNx layer constitute a floating gate structure, and a source electrode and a drain electrode are located on the surface of the AlGaN layer.

2. The optoelectronic synaptic device according to claim 1, wherein: The semiconductor substrate includes one of sapphire, Si, SiC, and GaN.

3. The optoelectronic synaptic device according to claim 1, wherein: An AlN layer is further provided between the semiconductor substrate and the GaN layer.

4. The optoelectronic synaptic device according to claim 1, wherein: The specific process of forming the amorphous SiNx material layer corresponding to the amorphous SiNx layer is: using the PECVD method to prepare the defect-rich amorphous SiNx material layer, wherein the growth temperature is 75-100° C. and the ratio of Si / N source gas is 1:

1.

5. A method for preparing a photoelectric synaptic device, characterized in that: include: Providing a semiconductor substrate, forming a GaN layer on the surface of the semiconductor substrate, forming an AlGaN layer on the surface of the GaN layer, and forming an amorphous SiNx layer on the surface of the AlGaN layer, wherein the GaN layer, the AlGaN layer, and the amorphous SiNx layer constitute a floating gate structure; The amorphous SiNx layer is etched until the AlGaN layer is exposed, a source electrode and a drain electrode are formed on the surface of the exposed AlGaN layer, and a gate electrode is formed on the surface of the amorphous SiNx layer.

6. The method for preparing the optoelectronic neural synapse device according to claim 5, wherein: The specific process of forming the floating gate structure includes: forming a GaN material layer on the surface of the semiconductor substrate through an epitaxial process, and forming an AlGaN material layer on the surface of the GaN material layer; forming an amorphous SiNx material layer on the surface of the AlGaN material layer; The amorphous SiNx material layer, the AlGaN material layer and the GaN material layer are etched, and the remaining GaN layer, the AlGaN layer and the amorphous SiNx layer form a floating gate structure.

7. The method for preparing the optoelectronic neural synapse device according to claim 5, wherein: The process for forming the amorphous SiNx material layer is as follows: preparing a defect-rich amorphous SiNx material layer by using a PECVD method, wherein the growth temperature is 75-100° C. and the ratio of Si / N source gas is 1:

1.

8. The method for preparing the optoelectronic neural synapse device according to claim 5, wherein: The amorphous SiNx layer is a defect-rich amorphous SiNx layer.

9. The method for preparing the optoelectronic neural synapse device according to claim 5, wherein: The method further includes forming an AlN layer between the semiconductor substrate and the GaN layer.

10. A method for operating the optoelectronic neural synapse device according to claim 1, characterized in that: include: First, a gate voltage lower than the threshold voltage is applied to the gate electrode, which increases the material barrier below the gate electrode of the device, depletes the two-dimensional electron gas in the AlGaN / GaN channel layer, and turns off the device. The device is then irradiated with ultraviolet light below the AlGaN band gap. Under the excitation of ultraviolet light below the AlGaN band gap, the GaN layer absorbs light to generate photogenerated carriers. Under the action of the strong polarization field formed by the AlGaN / GaN heterojunction, the photogenerated carriers separate. Under the action of the gate voltage, the photogenerated electrons tunnel into the amorphous SiNx layer and are captured by the high-density defect states in the amorphous SiNx layer, which lowers the potential barrier of the amorphous SiNx layer originally raised by the gate voltage. The two-dimensional electron gas that was depleted due to the increased potential barrier reappears, and the device is turned on. That is, the electrons captured by the SiNx layer change the threshold voltage of the device, realizing the storage function.

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