Ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction and preparation method thereof

Abstract

The present invention provides a GaN-GaO heterojunction-based UV synaptic device and a preparation method thereof, which relates to the field of microelectronic technology. The GaN-GaO heterojunction-based UV synaptic device is extremely sensitive to UV light and has successfully simulated various characteristics of biological synapses, including persistent photoconductivity effect (PPC), double pulse facilitation (PPF), and plasticity of transition from short-term memory (STM) to long-term memory (LTM); moreover, the GaN-GaO heterojunction structure can extend the light sensing mechanism, reduce the energy consumption of synaptic events, and increase synaptic plasticity. In addition, the UV synaptic device has the advantages of simple preparation, high sensitivity, good stability, etc., and is very suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the field of microelectronics technology, in particular to a synaptic device, and in particular to an ultraviolet synaptic device based on a gallium nitride-gallium oxide heterojunction and a preparation method thereof. Background Art

[0002] Computing technology based on the von Neumann architecture has achieved great success, but there is an inherent delay in the data transmission between computer processing and memory units, which limits the processing speed and increases energy consumption, namely the von Neumann bottleneck. In the current era of big data, overcoming this bottleneck is crucial to meet the growing demand for data-intensive tasks. Neuromorphic computing, which mimics the energy-saving and highly parallel operation of the biological brain, is one of the most promising platforms to solve this bottleneck. In the biological brain, synapses are reconfigurable connections between neurons and play a vital role in the formation of learning and memory. Therefore, it is generally believed that creating artificial synaptic devices with biological-like functions is a key step in the hardware realization of neuromorphic computing.

[0003] Artificial synaptic devices are developing rapidly. In terms of stimulation signals, the two most widely reported synaptic devices are electrical stimulation synaptic devices and optical stimulation synaptic devices. Compared with electrical stimulation synaptic devices, optical stimulation synaptic devices have the following advantages: low crosstalk, high bandwidth, and the ability to mimic the human visual system for information perception, processing, and memory. Therefore, they are receiving more and more attention.

[0004] Gallium nitride materials have become attractive candidate materials for the development of light-stimulated synaptic devices due to their room temperature PPC behavior and other advantages such as tunable direct band gap, high chemical and thermal properties. For example, CN117766603A discloses a gallium nitride ultraviolet synaptic device and a preparation method thereof, wherein the gallium nitride ultraviolet synaptic device includes a substrate layer, a gallium nitride doped light-absorbing layer and a patterned electrode arranged in sequence from bottom to top; the gallium nitride doped light-absorbing layer is used to generate photogenerated carriers under the stimulation of ultraviolet light signals, and the patterned electrode is used to collect the photogenerated carriers and output electrical signals. The gallium nitride ultraviolet synaptic device described in this technical solution is extremely sensitive to ultraviolet light, and the performance of the neuromorphic device can be optimized by adjusting the doping concentration and type of the gallium nitride doped light-absorbing layer, so that the gallium nitride ultraviolet synaptic device successfully exhibits various properties of biological synapses.

[0005] Currently, researchers are improving the performance of optical synaptic devices by setting up heterojunction structures. Based on this, developing a two-terminal optical synaptic device based on gallium nitride-gallium oxide, so that the gallium oxide-gallium nitride heterostructure can extend the light sensing mechanism, reduce the energy consumption of synaptic events, and increase synaptic plasticity, has important significance for promoting the application in human visual behavior. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a UV synaptic device based on gallium nitride-gallium oxide heterojunction and a preparation method. The UV synaptic device based on gallium nitride-gallium oxide heterojunction is extremely sensitive to ultraviolet light and has successfully simulated various characteristics of biological synapses, including persistent photoconductivity effect (PPC), double pulse facilitation (PPF), and plasticity of transition from short-term memory (STM) to long-term memory (LTM); moreover, the gallium nitride-gallium oxide heterojunction structure can prolong the light sensing mechanism, reduce the energy consumption of synaptic events, and increase synaptic plasticity. In addition, the UV synaptic device has the advantages of simple preparation, high sensitivity, good stability, etc., and is very suitable for industrial production.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] One of the purposes of the present invention is to provide an ultraviolet light synapse device based on a gallium nitride-gallium oxide heterojunction, comprising a substrate layer, a gallium nitride layer and a gallium oxide light absorbing layer stacked in sequence, and a patterned electrode is arranged on the surface of the gallium oxide light absorbing layer; a heterojunction is formed between the gallium nitride layer and the gallium oxide light absorbing layer.

[0009] In the ultraviolet light synaptic device based on gallium nitride-gallium oxide heterojunction described in the present invention, the gallium nitride layer can alleviate the lattice mismatch and thermal mismatch between the substrate layer and the gallium oxide light absorbing layer, and is used to control the morphology and growth quality of the gallium oxide film and optimize the growth of the gallium oxide light absorbing layer. Secondly, the energy band structure between the heterojunctions can optimize the recombination path of photogenerated carriers, reduce device power consumption, and increase the plasticity of the synaptic device; the gallium oxide light absorbing layer is used to generate photogenerated carriers under the stimulation of ultraviolet light signals, and the patterned electrodes are used to collect the photogenerated carriers and output electrical signals.

[0010] The ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in the present invention is extremely sensitive to ultraviolet light and has successfully simulated various characteristics of biological synapses, including persistent photoconductivity effect (PPC), double pulse facilitation (PPF), and plasticity of transition from short-term memory (STM) to long-term memory (LTM); moreover, the gallium nitride-gallium oxide heterojunction structure can prolong the light sensing mechanism, reduce the energy consumption of synaptic events, and increase synaptic plasticity. In addition, the ultraviolet synaptic device has the advantages of simple preparation, high sensitivity, good stability, etc., and is very suitable for industrial production.

[0011] As a preferred technical solution of the present invention, the substrate layer is made of a material selected from any one of silicon, silicon carbide, sapphire or gallium nitride, and the substrate layer is made of an insulating material.

[0012] As a preferred technical solution of the present invention, the thickness of the gallium nitride layer is 100-5000nm, for example, 100nm, 300nm, 500nm, 1000nm, 1100nm, 1500nm, 2000nm, 2500nm, 3000nm, 3500nm, 4000nm, 4500nm or 5000nm, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0013] As a preferred technical solution of the present invention, the gallium oxide light absorbing layer is an ε-Ga2O3 light absorbing layer and has oxygen vacancy defects.

[0014] It should be noted that the gallium oxide light absorbing layer of the present invention is an ε-Ga2O3 light absorbing layer. Although the β-Ga2O3 light absorbing layer has been studied more, its deposition temperature is relatively high and it is not easy to mass produce. Relatively speaking, although the ε-Ga2O3 light absorbing layer has been studied less, scientists have recently discovered that it has many excellent properties. First, the structure is highly symmetrical and is a hexahedral structure, which has good matching with the GaN direct structure; secondly, it has the largest bandgap width and the highest theoretical breakdown field strength, and has epitaxial growth conditions at a lower temperature; in addition, it is particularly important that ε-Ga2O3 has unique ferroelectric properties, which make ε-Ga2O3 have broad application prospects in neural photoelectric devices. The heterojunction structure of the gallium nitride layer and ε-Ga2O3 designed by the present invention is mainly because GaN can alleviate the lattice mismatch and thermal mismatch between the substrate layer and the gallium oxide light absorbing layer, which is used to control the morphology and growth quality of the gallium oxide film and optimize the growth of the gallium oxide light absorbing layer. Secondly, the energy band structure between heterojunctions can optimize the recombination path of photogenerated carriers, reduce device power consumption, and increase the plasticity of synaptic devices. In addition, GaN material is relatively stable, and provides stable support and environment for the ε-Ga2O3 light-absorbing layer thereon, thereby improving the stability of ε-Ga2O3 and helping to maintain the stable performance of the light-absorbing layer.

[0015] It should be noted that the ε-Ga2O3 light-absorbing layer is designed to be oxygen-deficient and has oxygen vacancy defects, so that the oxygen vacancy defects can be used to achieve the persistent photoconductivity effect (PPC).

[0016] As a preferred technical solution of the present invention, the thickness of the gallium oxide light absorbing layer is 5-1000nm, for example, 5nm, 10nm, 50nm, 100nm, 300nm, 500nm, 700nm, 800nm ​​or 1000nm, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0017] As a preferred technical solution of the present invention, the wavelength range of ultraviolet light to which the gallium oxide light absorbing layer can respond is 200-400nm, such as 254, 265nm, 360nm, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0018] As a preferred technical solution of the present invention, the material for preparing the patterned electrode includes any one of Ag, Pt, Au, Al, Ni, Cu or ITO or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of Ti and Au metal superposition, a combination of Cr and Au metal superposition, a combination of Ti and Pt metal superposition, etc.

[0019] As a preferred technical solution of the present invention, the patterned electrode includes any one of periodic square electrodes, periodic circular electrodes or periodic interdigitated electrodes, or a combination of at least two of them.

[0020] Preferably, the side length of the periodic square electrode is 1-1000μm, for example 1μm, 10μm, 30μm, 50μm, 70μm, 100μm, 300μm, 500μm, 800μm or 1000μm, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0021] Preferably, the diameter of the periodic circular electrode is 1-1000μm, for example 1μm, 10μm, 30μm, 50μm, 70μm, 100μm, 300μm, 500μm, 800μm or 1000μm, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0022] Preferably, the interdigitated electrode has an interdigitated width of 1-3000 μm, such as 1 μm, 10 μm, 30 μm, 50 μm, 70 μm, 100 μm, 300 μm, 500 μm, 800 μm, 1000 μm, 1500 μm, 2000 μm, 2500 μm or 3000 μm, etc., and a spacing of 1-3000 μm, such as 1 μm, 10 μm, 50 μm, 100 μm, 300 μm, 500 μm, 700 μm. , 1000μm, 1300μm, 1500μm, 2000μm, 2500μm, 2800μm or 3000μm, etc., the number of finger pairs is 3-300 pairs, for example, 3 pairs, 5 pairs, 10 pairs, 30 pairs, 50 pairs, 80 pairs, 100 pairs, 130 pairs, 150 pairs, 180 pairs, 200 pairs, 230 pairs, 250 pairs, 280 pairs or 300 pairs, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0023] The second object of the present invention is to provide a method for preparing a gallium nitride-gallium oxide heterojunction-based ultraviolet synapse device according to the first object, the preparation method comprising the following steps:

[0024] A substrate layer is prepared, a gallium nitride layer is deposited on the substrate layer, a gallium oxide light absorbing layer is deposited on the surface of the gallium nitride layer, and a patterned electrode is prepared on the surface of the gallium oxide light absorbing layer; wherein the deposition includes any one of metal organic chemical vapor deposition, magnetron sputtering or atomic layer deposition.

[0025] As a preferred technical solution of the present invention, the oxygen flow rate range used in the deposition process of the gallium oxide light absorbing layer is 170-350sccm, for example, 170sccm, 200sccm, 230sccm, 250sccm, 280sccm, 300sccm, 310sccm or 350sccm. In the deposition process of the gallium oxide light absorbing layer, the present invention uses an oxygen flow rate lower than the standard oxygen flow rate of 440sccm to increase the oxygen vacancy defects in the ε-Ga2O3 light absorbing layer.

[0026] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0027] (1) The GaN-GaO heterojunction-based UV synaptic device described in the present invention is extremely sensitive to UV light and has successfully simulated various characteristics of biological synapses, including persistent photoconductivity (PPC), double pulse facilitation (PPF), and plasticity in the transition from short-term memory (STM) to long-term memory (LTM); moreover, the GaN-GaO heterojunction structure can prolong the light sensing mechanism, reduce the energy consumption of synaptic events, and increase synaptic plasticity;

[0028] (2) The ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in the present invention has the advantages of simple preparation, high sensitivity, good stability, etc., and is very suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic structural diagram of the ultraviolet synapse device based on gallium nitride-gallium oxide heterojunction according to Example 1 of the present invention;

[0030] In the figure: 101 - substrate layer; 102 - gallium nitride layer; 103 - gallium oxide light absorbing layer; 104 - patterned electrode;

[0031] Figure 2 is a PPC curve of the ultraviolet synapse device based on gallium nitride-gallium oxide heterojunction described in Example 1 of the present invention;

[0032] Figure 3is a PPF curve of the ultraviolet synapse device based on gallium nitride-gallium oxide heterojunction described in Example 1 of the present invention;

[0033] Figure 4 is a transition curve from STM to LTM caused by the ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in Example 1 of the present invention under different light intensities;

[0034] Figure 5 is a transition curve from STM to LTM caused by the ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in Example 1 of the present invention under different pulse numbers;

[0035] Figure 6 This is the learning curve of the ultraviolet synapse device based on gallium nitride-gallium oxide heterojunction described in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0037] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0038] Example 1

[0039] This embodiment provides a UV synaptic device based on gallium nitride-gallium oxide heterojunction, such as Figure 1 As shown, it includes: a substrate layer 101, a gallium nitride layer 102 and a gallium oxide light absorbing layer 103 stacked in sequence, and a patterned electrode 104 is arranged on the surface of the gallium oxide light absorbing layer 103; a heterojunction is formed between the gallium nitride layer 102 and the gallium oxide light absorbing layer 103.

[0040] This embodiment also provides a method for preparing an ultraviolet synaptic device based on a gallium nitride-gallium oxide heterojunction, the preparation method comprising the following steps:

[0041] (1) Prepare the sapphire substrate layer and clean it with alcohol, deionized water and acetone in sequence;

[0042] (2) Preparation of a gallium nitride layer: After the sapphire substrate layer in step (1), a 4.5 μm non-doped GaN layer is prepared using an MOCVD device. After the process is completed, the MOCVD device is gradually cooled down, and the sample is taken out after the cooling is completed;

[0043] (3) Preparation of gallium oxide light absorbing layer: A 300 nm thick ε-Ga2O3 light absorbing layer is further grown on the GaN layer prepared in step (2) using MOCVD equipment. The TMGa flow rate is 495 sccm, and the O2 flow rate is designed to have a low oxygen content of 350 sccm. The pressure is 20 kPa. The deposition temperature is 500 °C and the deposition time is 35 min.

[0044] (4) Preparing a patterned electrode: On the surface of the gallium oxide light-absorbing layer in step (3), a Ag metal electrode is prepared. The electrode is a periodic interdigitated electrode with an interdigit width of 100 μm, a spacing of 50 μm, and four pairs of interdigits.

[0045] Using a semiconductor parameter measuring instrument and a probe station, a 254nm laser light source was used as the experimental light source, the laser power was set to 0.63mW, the reading voltage was set to 5V, the light pulse duration was set to 10s, and the PPC curve was measured; the laser power was set to 0.63mW, the reading voltage was set to 5V, the single light pulse duration was set to 2s, and the interval time between two light pulses was set to 4s to measure the PPF curve.

[0046] The PPC curve of the ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in Example 1 is as follows: Figure 2 As shown in the figure, it can be seen that when the sample is irradiated with a 254nm light source, the conductivity of the sample increases significantly, and there is a charge capture process. After the illumination ends, the conductivity decreases, but it cannot immediately return to the initial value. The sample has a significant PPC effect. After fitting with a stretched exponential function, it is found that its relaxation time is 63s. Its excellent persistent photoconductivity can be used to construct biological synaptic devices.

[0047] The PPF curve of the ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in Example 1 is as follows: Figure 3 As shown in the figure, it can be seen that after the sample was irradiated with continuous light pulses with a duration of 2s and an interval of 4s, the second current peak was significantly higher than the first peak, resulting in a PPF phenomenon. The ratio of A2 / A1 was 1.47, and the synaptic response was significantly enhanced after two stimulations, indicating short-range plasticity.

[0048] The transition curves of the short-term memory (STM) to long-term memory (LTM) of the ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in Example 1 under different light intensities are as follows: Figure 4 As shown in the figure, it can be clearly seen that when the light intensity increases from 0.6mw / cm 2 Increased to 2.3mw / cm 2 , the corresponding postsynaptic current increases from 0.2μA to 0.63μA. In addition to the gain effect of light intensity on postsynaptic current, the increase in the number of light pulses will also cause the increase of postsynaptic current of the device.

[0049] The transition curves of the ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in Example 1 from short-term memory (STM) to long-term memory (LTM) at different pulse numbers are as follows: Figure 5 As shown in the figure, it can be clearly seen that when the number of light exposures increases from 3 to 50 times, the corresponding postsynaptic current increases from 0.19μA to 0.87μA. The above two situations are consistent with the performance of biological synapses. After the light stimulation conditions change, the device has achieved a transition from STM to LTM.

[0050] The learning curve of the ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction described in Example 1 is as follows: Figure 6 As shown, the laser power is set to 0.63mW, the reading voltage is set to 5V, the duration of a single light pulse is set to 2s, and the interval between two light pulses is set to 2s. It can be seen from the figure that the device has learning ability. In the first learning process, the excitatory postsynaptic current increased significantly under 30 consecutive pulse stimulations. After that, after a period of forgetting, when the second learning process was carried out, only 10 consecutive light pulses were used to make the excitatory synaptic current reach the peak current that could only be reached by 19 pulses in the first time. This phenomenon is similar to the learning-forgetting-learning process of the human brain, which further verifies that our device has the learning ability of biological synapses. Since ε-Ga2O3 has a highly symmetrical hexahedral structure, and the common GaN material is a hexagonal crystal fiber-type structure, its crystal structure is compatible with ε-Ga2O3, so that the two can form a high-quality heterostructure during the epitaxial growth process.

[0051] Therefore, combining nitride and ε-Ga2O3 to form a III-oxide / III-nitride heterojunction device structure dedicated to optoelectronic applications has good prospects in optimizing device performance; the use of gallium nitride-gallium oxide heterojunction structure can optimize the compatibility between gallium oxide and substrate materials, reduce the surface roughness of the epitaxial layer, and form an epitaxial layer with higher crystal quality.

[0052] In summary, the GaN-GaO heterojunction-based UV synaptic device is extremely sensitive to UV light and has successfully simulated various characteristics of biological synapses, including persistent photoconductivity (PPC), double pulse facilitation (PPF), and plasticity of transition from short-term memory (STM) to long-term memory (LTM); moreover, the GaN-GaO heterojunction structure can prolong the light sensing mechanism, reduce the energy consumption of synaptic events, and increase synaptic plasticity. In addition, the UV synaptic device has the advantages of simple preparation, high sensitivity, and good stability, and is very suitable for industrial production.

[0053] The present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0054] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0055] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0056] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction, characterized in that: It is composed of a substrate layer, a gallium nitride layer and a gallium oxide light absorbing layer stacked in sequence, and a patterned electrode is arranged on the surface of the gallium oxide light absorbing layer; a heterojunction is formed between the gallium nitride layer and the gallium oxide light absorbing layer; Among them, the gallium nitride layer is a non-doped GaN layer; the gallium oxide light absorption layer is an ε-Ga2O3 light absorption layer, and there are oxygen vacancy defects; the preparation method of the gallium oxide light absorption layer is: using MOCVD equipment to further grow an ε-Ga2O3 light absorption layer on the prepared GaN layer, the TMGa flow rate is 495sccm, the O2 flow rate is designed to have a low oxygen content, 350sccm; the pressure is 20kPa; the deposition temperature is 500°C, and the deposition time is 35min.

2. The ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction according to claim 1, characterized in that: The substrate layer is made of a material selected from any one of silicon, silicon carbide, sapphire or gallium nitride.

3. The ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction according to claim 1, characterized in that: The thickness of the gallium nitride layer is 100-5000nm.

4. The ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction according to claim 1, characterized in that: The thickness of the gallium oxide light absorbing layer is 5-1000nm.

5. The ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction according to claim 1, characterized in that: The wavelength range of ultraviolet light to which the gallium oxide light-absorbing layer can respond is 200-400 nm.

6. The ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction according to claim 1, characterized in that: The material for preparing the patterned electrode includes any one of Ag, Pt, Au, Al, Ni, Cu or ITO, or a combination of at least two of them.

7. The ultraviolet synaptic device based on gallium nitride-gallium oxide heterojunction according to claim 1, characterized in that: The patterned electrode includes any one of a periodic square electrode, a periodic circular electrode or a periodic interdigitated electrode, or a combination of at least two of them.

8. A method for preparing a gallium nitride-gallium oxide heterojunction-based ultraviolet synapse device according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: A substrate layer is prepared, a gallium nitride layer is deposited on the substrate layer, a gallium oxide light absorbing layer is deposited on the surface of the gallium nitride layer, and a patterned electrode is prepared on the surface of the gallium oxide light absorbing layer; wherein the deposition includes any one of metal organic chemical vapor deposition, magnetron sputtering or atomic layer deposition.

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