A unipolar porphyrin copper memristor and a control method thereof

Abstract

The present invention discloses a unipolar porphyrin copper memristor and a control method thereof. The memristor structure of the present invention is, from bottom to top, a bottom electrode indium tin oxide ITO, an organic functional layer, an inorganic resistive layer non-stoichiometric oxide, and a top electrode metal. The inorganic resistive layer is a non-stoichiometric oxide prepared by thermal atomic layer deposition thin film. The present invention obtains a high-quality controllable non-stoichiometric oxide film by introducing a thermal atomic layer deposition process, realizes unipolar voltage control, and provides the possibility for biological function simulation and neuromorphic computing.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology and neuromorphic hardware, and specifically relates to a unipolar porphyrin copper memristor and a control method thereof. Background Art

[0002] At present, with the advent of the digital age, people have an increasing demand for real-time data processing. The traditional Moore's Law is increasingly unable to meet the needs of people's work and life. Memristors are brain-like chips based on storage and computing, which are expected to break through the Moore's limit and are one of the most promising technologies for building analog neural networks for neuromorphic computing.

[0003] Organic materials are rich in functional groups and are lightweight, mechanically flexible, and ductile. Compared with traditional inorganic memristors, memristors made of organic materials offer the possibility of multifunctional applications. People usually regulate the movement of carriers inside memristors by regulating the magnitude of voltage, which provides a basis for multifunctional applications. Traditionally, slow-varying memristors focus on changes in conductance values, and use bidirectional polarity voltages to regulate the growth of conductive filaments or the rate of ion migration, thereby achieving the functions of storage writing and erasing, and further simulating synaptic functions.

[0004] In recent years, researchers have tended to study organic-inorganic hybrid memristors, and have made significant achievements in the exploration of bipolar voltage regulation. For example, organic-inorganic hybrid perovskite memristors achieve voltage modulation under bipolarity by preparing multilayer memristors (Adv. Mater. 2018, 30, 1805454.). There are also a few memristors that have achieved unipolar voltage regulation (Adv. Mater. 2021, 33, 2104370.), but their operating voltage is too large to meet the requirements of low power consumption. Unipolar regulation not only has advantages in simulating biological synapses, but is also widely involved in neuromorphic computing and intelligent applications. Therefore, it is particularly important to develop memristor devices suitable for unipolar low-voltage regulation. Summary of the invention

[0005] The present invention aims at the problems existing in the prior art and provides a unipolar porphyrin copper memristor and a control method thereof. The porphyrin copper memristor is controlled by a unipolar voltage to realize multi-level switching characteristics, which can be used for storage function applications and present low power consumption characteristics. The memristor can simulate the excitation and inhibition process of biological synapses, and the unipolarity indicates that the unipolar voltage can be used to control the synaptic weight in the positive direction.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0007] A unipolar porphyrin copper memristor comprises a four-layer structure, which comprises, from bottom to top, a bottom electrode, an organic functional layer, an inorganic resistive switching layer and a metal top electrode.

[0008] Wherein, the organic functional layer is a porphyrin copper film prepared by vacuum coating method, which serves as an ion transport layer. The organic functional layer is a metal porphyrin copper film, which is taken out immediately after being prepared by vacuum coating equipment, placed in the air for 12 to 24 hours, and then placed in an atomic layer deposition system for preparation. The purpose is to increase the hydrophilicity of the porphyrin copper film, make it easier to transport oxygen ions, reduce the operating voltage of the device, and enable the aluminum oxide film in the atomic layer deposition system to have good contact with the porphyrin copper film.

[0009] Preferably, the inorganic resistive switching layer material is a non-stoichiometric oxide. The inorganic resistive switching layer material is a non-stoichiometric aluminum oxide film with a thickness of 4 to 20 nm.

[0010] The stoichiometric ratio of the number of oxygen atoms and aluminum atoms in the aluminum oxide film, that is, the oxygen-to-aluminum ratio, is 1.2 to 1.3, serving as an ion supply layer.

[0011] Preferably, the bottom electrode is indium tin oxide (ITO), which is used for inputting external power supply electrical signals.

[0012] The preparation method of the above-mentioned unipolar porphyrin copper memristor further specifically comprises the following steps:

[0013] S1: The bottom electrode indium tin oxide is cleaned in an ultrasonic cleaning machine for 5-15 minutes using acetone, anhydrous ethanol and deionized water;

[0014] S2: After cleaning, blow dry with nitrogen;

[0015] S3: putting the dried indium tin oxide into an electric air drying oven for drying for 30-60 minutes;

[0016] S4: treating the dried indium tin oxide bottom electrode with ozone for 6-10 minutes;

[0017] S5: Load the treated indium tin oxide bottom electrode into the vacuum evaporation equipment and wait until the vacuum degree in the chamber is lower than 5×10 -4 After pa, evaporation began, the rate of evaporation of porphyrin zinc was about 0.1Å / S, and the thickness was controlled at 10-25nm by a quartz crystal oscillator. The thickness of the film was determined by a step profiler.

[0018] S7: An inorganic resistive layer is prepared on the organic functional layer using a thermal atomic deposition thin film preparation system, wherein the temperature of the coating chamber in the thermal atomic deposition thin film preparation system is 80°C-250°C; the purpose is to rapidly form a film of aluminum oxide by high temperature annealing, and the oxygen ion content is higher than that during low temperature annealing, which facilitates oxygen ion migration.

[0019] S8: introducing the trimethylaluminum precursor source in the thermal atomic deposition thin film preparation system through a trimethylaluminum precursor atomic layer deposition valve (i.e., an ALD valve) onto the surface of the thin film placed in step S7 to obtain a trimethylaluminum precursor;

[0020] S9: using inert gas nitrogen to clean the trimethylaluminum precursor described in step S8;

[0021] S10: introducing the deionized water precursor in the deionized water precursor source bottle in the thermal atomic deposition thin film preparation system onto the trimethylaluminum precursor through the deionized water precursor ALD valve to preliminarily form an oxide film;

[0022] S11: Using the vacuum evaporation device, wait until the vacuum degree in the chamber is lower than 5×10 -4 After pa, a metal top electrode with a thickness of about 90-150nm was evaporated on the above film.

[0023] S12: After the evaporation is completed, the top electrode of step S11 is placed in a vacuum of less than 5×10 -4 Cool to room temperature in an environment of pa;

[0024] S13: Perform relevant electrical control on the device.

[0025] The control method of the above-mentioned unipolar porphyrin copper memristor further specifically includes the following steps:

[0026] S1: Scan the memristor unit with 0V voltage as the starting voltage and 4V or less as the stopping voltage in the forward I / V voltage scan, keep the scan point interval between 0.5-2S, and the step voltage between 0.005-0.1V. By regulating the migration of oxygen vacancies, ion coupling is formed, and the ion transport and electron transmission functions are completed under the external electric field.

[0027] S2: Scan the memristor unit with 0V voltage as the starting voltage and 5V or higher voltage as the stopping voltage in the forward I / V voltage scan, keep the scan point interval between 0.5-2S, and the step voltage between 0.005-0.1V. By regulating the migration of oxygen vacancies, ion coupling is formed, and the ion transport and electron transmission functions are completed under the external electric field.

[0028] The technical solution of the present invention can produce the following technical effects:

[0029] 1. The unipolar porphyrin copper memristor provided by the present invention can form a unipolar voltage regulation characteristic in one direction, realize the storage performance of write-first and erase-later, and is expected to be applied to artificial intelligence, new information technology, Internet of Things, computer, bioelectronics and other fields.

[0030] 2. The porphyrin copper memristor provided by the present invention is deposited by a thermal atomic deposition device, and the aluminum oxygen content of aluminum oxide can be adjusted, so that the organic material and the inorganic material can be better coupled, providing favorable conditions for low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a unipolar porphyrin copper memristor device structure described in the present invention; wherein 1 is a metal electrode, 2 is a metal oxide, 3 is porphyrin copper, 4 is indium tin oxide, and 5 is a glass substrate;

[0032] Figure 2 It is a continuous current-voltage curve of a unipolar porphyrin copper memristor described in the present invention when a positive voltage of 4V and a negative voltage of -4V are applied;

[0033] Figure 3 It is a continuous current-voltage curve of a unipolar porphyrin copper memristor described in the present invention when a positive voltage of 5V and a negative voltage of -5V are applied;

[0034] Figure 4 The present invention discloses a continuous current-voltage curve of a unipolar porphyrin copper memristor when a positive voltage of 4V and a negative voltage of 5V are applied. DETAILED DESCRIPTION

[0035] The present invention is further described below by means of specific examples. However, it should be noted that these embodiments are not intended to limit the present invention.

[0036] In the preparation method of the unipolar porphyrin copper memristor of the present invention, a specific device is designed and prepared by using a layer-by-layer stacking method, and the preparation steps include: preparing an organic functional layer on the indium tin oxide bottom electrode, then preparing an inorganic resistive layer metal oxide on the organic functional layer, and finally preparing a metal top electrode on the inorganic resistive layer. Figure 1 Device structure diagram for preparing unipolar porphyrin copper memristor.

[0037] In the control method of the unipolar porphyrin copper memristor of the present invention, the migration of oxygen vacancies is modulated to change the ionic coupling between the organic functional layer and the inorganic resistive layer, so that as the voltage increases, the memristor realizes the characteristic of first writing and then erasing. Compared with the porphyrin zinc memristor, the porphyrin copper memristor has a smaller control voltage and a smaller operating current, meeting the characteristics of low power consumption.

[0038] In a specific embodiment of the present application, the specific implementation steps of a unipolar porphyrin copper memristor are as follows:

[0039] 1. Environmental conditions

[0040] (1) During the actual preparation, the laboratory room temperature is maintained at 5-30℃ and the indoor humidity is maintained at 20%-60%.

[0041] 2. Pretreatment of substrate

[0042] (1) First, the indium tin oxide bottom electrode is cleaned by using acetone, ethanol, and deionized water to clean the substrate, that is, oscillating in an ultrasonic cleaning machine at 100 kHz, 70% power, and a temperature of 0-20°C for 5-15 minutes;

[0043] (2) After cleaning, use a nitrogen gun to blow the indium tin oxide substrate until the surface moisture is dried;

[0044] (3) Place the substrate dried with a nitrogen gun in an electric hot air drying oven and dry it at a temperature of 90-120°C for 20-40 minutes;

[0045] (4) Place the dried substrate in a UV-ozone cleaning machine for 5-15 minutes;

[0046] 3. Preparation of organic functional layer thin film by vacuum coating method

[0047] (1) Place the processed substrate into a vacuum evaporation device and place it under a vacuum pressure of less than 5×10 -4 After pa, the organic resistive layer is evaporated.

[0048] (2) The material of the organic resistive layer is porphyrin copper, the evaporation rate is 0.1Å / S, and the thickness of the porphyrin copper layer is about 25nm.

[0049] (3) While maintaining the original vacuum pressure, wait for the porphyrin copper film to cool to room temperature after evaporation.

[0050] 4. Preparation of Inorganic Resistive Layer Thin Film by Atomic Layer Deposition System

[0051] (1) Place the porphyrin copper film prepared in step 3 in the air for 12 to 24 hours to increase the hydrophilicity of the porphyrin copper film. The purpose is to increase the hydrophilicity of the porphyrin copper film, make it easier for oxygen ions to transport, reduce the device operating voltage, and enable the aluminum oxide film in the atomic layer deposition system to have good contact with the porphyrin copper film. If it is not placed in the air to increase its hydrophilicity, the oxygen ion transport will slow down, the operating voltage will be too high, and it will not meet the requirements of low power consumption.

[0052] (2) A non-stoichiometric oxide film is obtained as an inorganic resistive layer by a thermal atomic layer deposition film preparation system. The atomic layer deposition film is first degassed, and then the coating chamber is heated to 20-100°C, and the film formed in step 3 is placed in the coating chamber.

[0053] (3) After the film is placed in the coating chamber, heat the chamber to 80-250°C and wait for 30-60 minutes until the temperature jump stabilizes;

[0054] (4) The trimethylaluminum precursor source in the thermal atomic deposition device is deposited onto the substrate surface through the trimethylaluminum precursor ALD valve for 10-20 ms to obtain a trimethylaluminum precursor.

[0055] (5) Use inert gas nitrogen to purge the trimethylaluminum precursor for 15-20 seconds.

[0056] (6) introducing the deionized water precursor in the deionized water precursor source bottle in the thermal atomic deposition device into the trimethylaluminum precursor through the deionized water precursor ALD valve for 15 ms to obtain a non-stoichiometric aluminum oxide film with a thickness of 0.010-0.015 nm;

[0057] (7) Use inert gas nitrogen to clean the deionized water precursor for 15-20 seconds.

[0058] (8) Repeat the above steps 70-90 times to obtain a non-stoichiometric film with a thickness of about 4-20 nm;

[0059] (9) High temperature annealing for 30-60 minutes while maintaining the chamber temperature at 150°C. High temperature annealing makes it easier for aluminum oxide film to form and accelerates oxygen ion transport.

[0060] (10) After annealing is completed, the temperature of the coating chamber is lowered to 20-100°C and the temperature is stabilized;

[0061] (11) Remove the film and turn off the atomic layer deposition system.

[0062] 5. Preparation of top electrode by vacuum evaporation coating technology

[0063] (1) Place the thin film formed in step 4 into a vacuum evaporation coating device and add a metal source;

[0064] (2) The vacuum degree of the vacuum evaporation equipment is controlled at 5×10 -4 pa, the evaporation rate is 0.4-0.5Å / S, and the aluminum electrode with a thickness of about 90-150nm is obtained by evaporating the metal and using a stripe pattern mask;

[0065] (3) Complete the top electrode film annealing treatment while maintaining the original vacuum pressure, and the annealing time is 20-50 minutes;

[0066] (4) The substrate is taken out from the vacuum evaporation coating device to obtain a porphyrin copper memristor of the present invention.

[0067] The unipolar porphyrin copper memristor control method of the present invention induces oxygen vacancy migration through voltage control, completes coupling through ion transport, and realizes unipolar voltage control of the porphyrin copper memristor. The voltage control is to use an I / V voltage scanning method to control the forward voltage of the memristor unit.

[0068] The following is a method for controlling the forward voltage of the porphyrin copper memristor prepared in Example 1 by using an I / V voltage scanning method, which specifically includes the following steps:

[0069] (1) Select a memristor unit and insert two probes into the top electrode and bottom electrode regions respectively. The probe connected to the top electrode is grounded and the probe connected to the bottom electrode is applied with a positive voltage. The forward voltage scanning range is 0 to 10 V and the limiting current is Icc = 1 nA-20 mA.

[0070] (2) The memristor unit is subjected to 10 forward I / V scans with a scan range of 0 V to 4 V, a step voltage of 0.05 V, and a forward scan limit current of Icc = 1 μA.

[0071] (3) The memristor unit is subjected to 10 forward I / V scans with a scan range of 0 V to 5 V, a step voltage of 0.05 V, and a forward scan limit current of Icc = 100 μA.

[0072] (4) The memristor unit is subjected to 10 negative I / V scans with a scan range of 0 V to (-4) V, a step voltage of 0.05 V, and a positive scan limit current of Icc = 1 μA.

[0073] (5) The memristor unit is subjected to 10 negative I / V scans with a scan range of 0 V to (-5) V, a step voltage of 0.05 V, and a positive scan limit current of Icc = 100 μA.

[0074] The present invention regulates the transport of oxygen vacancies in the inorganic resistive layer and the organic functional layer, and regulates the ion coupling characteristics to obtain a unipolar porphyrin copper memristor, with a current level of nanoamperes, reflecting the characteristics of low power consumption. The memristor regulates the ions of the organic functional layer and the inorganic resistive layer based on the voltage, and can accurately regulate the transport of oxygen vacancies in the functional layer through simple voltage regulation, so that the porphyrin copper memristor can simulate the storage function, and as the voltage increases, it is written first and then erased.

[0075] The following is a comparison between the porphyrin copper memristor prepared in Example 1 and the porphyrin zinc memristor prepared in the prior art, which specifically includes the following improvements:

[0076] (1) The porphyrin copper memristor has a smaller write-state control voltage. The porphyrin zinc memristor prepared by the prior art has a storage write-state control voltage of 10V, while the porphyrin copper memristor provided by the present invention has a storage write control voltage of only 4V. The porphyrin copper memristor can better meet the demand for low power consumption.

[0077] (2) The porphyrin copper memristor has a smaller erase state control voltage. The erase state control voltage of the porphyrin zinc memristor prepared by the prior art is 6V, while the erase state control voltage of the porphyrin copper memristor provided by the present invention is only 5V. The porphyrin copper memristor can better meet the demand for low power consumption.

[0078] (3) Porphyrin copper memristor has a smaller operating current. The operating current of porphyrin zinc memristor is 100-500 microamperes, while the operating current level of porphyrin copper memristor is 0.1-600 nanoamperes. The current level is reduced by three orders of magnitude, which better meets the demand for low power consumption.

[0079] Figure 1 The device structure of the unipolar porphyrin copper memristor comprises, from bottom to top, a bottom electrode ITO, a porphyrin copper organic functional layer, an inorganic resistive switching layer metal oxide and a top electrode metal.

[0080] Memristors are usually used to simulate synaptic functions, that is, the upper and lower electrodes act as the front and rear synapses respectively, and the working current of the device acts as the synaptic weight for signal transmission. In other words, memristors can simulate the excitation and inhibition process of biological synapses. The unipolarity indicates that the unipolar voltage can be used to regulate the synaptic weight in the positive direction.

[0081] Figure 2 This is a continuous current-voltage curve of a unipolar porphyrin copper memristor described in the present invention when a positive 4V voltage and a negative -4V voltage are applied; under a positive 4V voltage scan, it can be found that as the number of scans increases, the current level of the device gradually increases, showing a multi-level switching characteristic. After 10 4V positive voltage scans, the current level is 5-20nA, and the current-voltage curve is stable, and the current level is at the nanoampere level, indicating that the device has the characteristics of low power consumption.

[0082] Figure 3 The continuous current-voltage curve of a unipolar porphyrin copper memristor described in the present invention with a positive 5V voltage and a negative -5V voltage applied, it can be seen that the device has no sudden increase in the current level, and as the number of scans increases, the current level of the device gradually decreases, showing a multi-level switching characteristic. After 10 5V positive voltage scans, the current level is 200-1000nA, and the current-voltage curve is stable, and the current level is at the nanoampere level, indicating that the device has the characteristics of low power consumption.

[0083] Figure 4The present invention discloses a continuous current-voltage curve of a unipolar porphyrin copper memristor when a forward voltage of 4V and a forward voltage of 5V are applied. As the number of scans increases, the device exhibits a unipolar characteristic.

[0084] It can be concluded that the device can simulate the excitation characteristics of biological synapses under a forward voltage of 4V, and can simulate the inhibition characteristics of biological synapses under a forward voltage of 5V, thereby achieving forward unipolar voltage regulation.

[0085] In summary, the device can achieve unipolar voltage regulation with low power consumption.

[0086] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which does not depart from the content of the technical solution of the present invention and still falls within the protection scope of the present invention.

Claims

1. A unipolar porphyrin copper memristor, comprising a four-layer structure, from bottom to top, a bottom electrode, an organic functional layer, an inorganic resistive layer and a top electrode, wherein the inorganic resistive layer is an oxide film, and the top electrode is a noble metal, characterized in that: The organic functional layer is a metal porphyrin copper film, which is taken out immediately after being prepared by vacuum coating equipment, placed in the air for 12 to 24 hours, and then placed in an atomic layer deposition system to continue preparing an inorganic resistive switching layer.

2. The unipolar porphyrin copper memristor according to claim 1, characterized in that: The inorganic resistive switching layer is a non-stoichiometric aluminum oxide film with a thickness of 4 to 20 nm. The ratio of the number of oxygen atoms to aluminum atoms in the non-stoichiometric aluminum oxide film, ie, the oxygen-to-aluminum ratio, is 1.2 to 1.

3.

3. The unipolar porphyrin copper memristor according to claim 1, characterized in that: The inorganic resistive switching layer is prepared by thermal atomic deposition and annealing after atomic layer deposition.

4. The unipolar porphyrin copper memristor according to claim 3, characterized in that: The inorganic resistive switching layer preparation method is specifically as follows: S1: placing the substrate on which the porphyrin copper film has been evaporated in a coating chamber of a thermal atomic deposition film preparation system, wherein the temperature of the coating chamber is set in a range of 80° C. to 250° C.; S2: Depositing trimethylaluminum precursor on the surface of porphyrin copper film; S3: Cleaning the surface of the trimethylaluminum precursor deposited in S2 with nitrogen gas for 10 to 30 seconds; S4: Deionized water is deposited onto the trimethylaluminum precursor to obtain a non-stoichiometric aluminum oxide film with a thickness of about 0.1 nm; S5: Cleaning the 0.1 nm non-stoichiometric aluminum oxide film described in S4 with nitrogen gas for 10 to 30 seconds; S6: After repeating steps S2-S5, a non-stoichiometric aluminum oxide film of 4-20 nm is obtained, and annealed at a high temperature of 150° C. for 30-60 minutes in a chamber, namely the inorganic resistive switching layer.

5. A control method for a unipolar porphyrin copper memristor, using the unipolar porphyrin copper memristor according to any one of claims 1 to 4, characterized in that: By adjusting the voltage and the migration of oxygen vacancies in the inorganic resistive switching layer, erasing with negative voltage, writing with a forward voltage below 4V, and erasing with a forward voltage above 5V can be achieved.

6. The control method of the unipolar porphyrin copper memristor according to claim 5, characterized in that: The method for writing with a forward voltage below 4V is: using 0V voltage as the starting voltage and a voltage less than or equal to 4V as the stopping voltage in the forward I / V voltage scan, keeping the scan point interval between 0.5-2S, and the step voltage between 0.005-0.1V, to scan the memristor unit.

7. The control method of the unipolar porphyrin copper memristor according to claim 5, characterized in that: The method for erasing when the forward voltage is above 5V is as follows: using 0V voltage as the starting voltage and a voltage greater than or equal to 5V as the stopping voltage in the forward I / V voltage scan, keeping the scan point interval between 0.5-2S, and the step voltage between 0.005-0.1V, to scan the memristor unit.

8. The control method of the unipolar porphyrin copper memristor according to claim 5, characterized in that: The negative voltage erasing method is: using 0V voltage as the starting voltage and a voltage less than or equal to 10V as the stopping voltage in the negative I / V voltage scan, keeping the scan point interval between 0.5-2S, and the step voltage between 0.005-0.1V to scan the memristor unit.

9. The control method of the unipolar porphyrin copper memristor according to any one of claims 6 to 8, characterized in that: The current generated under the I / V voltage is at the nanoampere level.

Images