Ion liquid DEME-TFSI memristor with analog biological synapse function and preparation method thereof

Abstract

The application provides an ionic liquid DEME-TFSI memristor with a biological synapse function, comprising a bottom electrode, an ionic liquid layer and a top electrode layer; wherein the bottom electrode is arranged at the bottommost position; the ionic liquid layer is arranged above the bottom electrode; and the top electrode layer is arranged above the ionic liquid layer. The DEME-TFSI memristor with the biological synapse function belongs to a typical nonvolatile memristor, has the advantages of low cost, simple preparation condition, easy design of the structure of the whole memristor, simple process, stable performance and the like, and successfully simulates the characteristics of the biological synapse function, such as LTP / LTD, PPF, STDP and the like, which indicates that the DEME-TFSI memristor has application potential as a high-performance nonvolatile memory and in future computer systems and neuromorphic computing.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of memory, and particularly relates to an ion liquid DEME-TFSI memristor with a simulated biological synapse function and a preparation method thereof. BACKGROUND

[0002] Biological synapses are the basic part of signal transmission between neurons. Each biological synapse is composed of presynaptic / postsynaptic membrane and synaptic cleft. The realization of synapse characteristics depends on the transmission of neurotransmitters in the synapse connecting two neurons. In a neural network, neurons are the basic elements connected to each other through synapses, and have the functions of regulation and information processing. In order to realize the function of adaptive neural network, neuromorphic hardware composed of electronic devices has attracted wide attention. These electronic devices have adjustable and storable conductive states, and can spontaneously generate and regulate neural signals. Among them, the memristor as a new high-efficiency device has become an important research object to realize the function of neural network.

[0003] The dispersion of threshold voltage and high-low resistance value of the memristor is the main problem encountered at present, which may cause false read-write operation and even make the device invalid. In order to improve the performance stability, researchers have proposed various methods, including adding interface layer, doping, adding nanocrystals, improving preparation process and improving operation mode, etc. At present, a large number of reported memristor materials are binary oxides such as NiO, SiOX, NbOX, and chalcogenide semiconductors. There are few memristors based on ion body as intermediate layer. As a new type of polar solvent, ionic liquid has almost no vapor pressure, has non-flammable, non-volatile, good chemical and thermal stability, can be recycled and is environmentally friendly. Therefore, they are called "green" chemical solvents, which can replace traditional volatile and toxic solvents. In addition, due to the unique characteristics of ionic liquid, it is widely used in memristor. Early research focused on using ionic liquid as electrolyte medium to realize the resistance switching function of memristor. With the in-depth research, researchers began to explore the potential of ionic liquid in constructing artificial optoelectronic synapses. An organic polymer doped ionic liquid memristor was developed to realize low-voltage artificial optoelectronic synapses. This kind of memristor obtains rich conductance states through light field regulation at millivolt level voltage, and exhibits short-term and long-term synaptic plasticity functions, including EPSC, PPF, PPD, LTP, LTD, etc., as well as learning-forgetting-relearning characteristics [1] . DEME-TFSI ionic liquid has some unique characteristics. It can provide high ionic conductivity, which is very important for fast ion migration in electronic devices such as memristor, and DEME-TFSI ionic liquid has a wide electrochemical window, which makes it stable in a wider potential range, which helps to improve the reliability and performance of electronic devices. SUMMARY

[0004] The present application aims to overcome the defects of the prior art. An ionic liquid DEME-TFSI memristor with the function of simulating biological synapses and a preparation method thereof are provided.

[0005] The technical scheme of the present application is as follows:

[0006] The first aspect of the present application provides an ionic liquid DEME-TFSI memristor with the function of simulating biological synapses, characterized in that it comprises a bottom electrode, an ionic liquid layer and a top electrode layer.

[0007] The bottom electrode is arranged at the bottommost position.

[0008] The ionic liquid layer is arranged above the bottom electrode.

[0009] The top electrode is arranged above the ionic liquid layer.

[0010] Preferably, the bottom electrode is one of ITO conductive glass, fluorine-doped tin dioxide (FTO) conductive substrate or aluminum-doped zinc oxide (AZO) conductive substrate.

[0011] More preferably, the bottom electrode is fluorine-doped tin dioxide (FTO) conductive substrate.

[0012] The electrode layer is one of active electrodes such as silver, copper, aluminum, zinc, magnesium and iron.

[0013] More preferably, the electrode layer is an active electrode of aluminum.

[0014] Preferably, the thickness of the electrode is 150-350 nm, more preferably 150-300 nm, and further preferably 150-200 nm.

[0015] The thickness of the ionic liquid layer is 50-300 nm, preferably 100-250 nm, and more preferably 150-200 nm.

[0016] The ionic liquid layer is arranged above the bottom electrode.

[0017] The second aspect of the present application provides a method for preparing the ionic liquid DEME-TFSI memristor of the first aspect, which comprises the following steps:

[0018] Step 1: sequentially clean the conductive substrate with water + detergent, deionized water, acetone and alcohol using an ultrasonic instrument, dry the conductive substrate in a drying box after cleaning, and then perform ozone treatment on the conductive substrate before spin coating to obtain the bottom electrode.

[0019] Step 2: spin-coat DEME-TFSI on the bottom electrode, and heat-treat to form an ionic liquid layer;

[0020] Step 3: grow a top electrode on the ionic liquid layer by vacuum thermal evaporation, to obtain the ionic liquid memristor.

[0021] According to the method of the second aspect of the application, the step (1) further comprises the following steps:

[0022] The fluorine-doped tin dioxide (FTO) conductive substrate is sequentially subjected to ultrasonic cleaning using water + detergent, deionized water, acetone, alcohol and other solvents, each solvent is repeated once, and after ultrasonic cleaning, the fluorine-doped tin dioxide (FTO) is dried in a drying oven, and the fluorine-doped tin dioxide (FTO) is subjected to ozone operation before spin coating;

[0023] Preferably, the ultrasonic cleaning time is 25 min-100 min, more preferably 25 min-60 min, and further preferably 25 min-40 min;

[0024] Preferably, the drying temperature is 55℃-100℃, more preferably 55℃-75℃, and further preferably 60℃.

[0025] Preferably, the drying time is 4h-10h, more preferably 4h-8h, and further preferably 4h-6h;

[0026] Preferably, the ozone time is 25min-60min, more preferably 25min-45mim, and further preferably 25min-35min.

[0027] According to the method of the second aspect of the application, the step (2) further comprises the following steps:

[0028] After ozone, the fluorine-doped tin dioxide (FTO) is drop-coated with an ionic liquid, and after drop-coating, a rapid annealing instrument is used to anneal to obtain an ionic liquid layer;

[0029] Preferably, the drop-coating capacity is 150μL-300μL, more preferably 150μL-250μL, and further preferably 150μL-200μL;

[0030] Preferably, the drop-coating rotation speed is 2500rpm-4000rpm, more preferably 2500rpm-3500rpm, and most preferably 3000rpm, and the drop-coating time is 30min;

[0031] Preferably, the baking temperature is 150℃-400℃, more preferably 150℃-300℃, and further preferably 180℃-250℃;

[0032] Preferably, the time of the roasting is 5 min to 20 min, more preferably 5 min to 15 min, most preferably 10 min.

[0033] Compared with the prior art, the present application has the following advantages:

[0034] The present application uses the unique properties of ionic liquids, through different operation modes, the device I-V cycle characteristics, long-term enhancement / inhibition (LTP / LTD), short-term potentiation (PPF), pulse timing-dependent plasticity (STDP) and the like, which show that the device has better repeated resistance switching behavior and potential application in the nervous system. The handwritten digital recognition analysis based on artificial neural network is made, and after 200 times of training, the recognition accuracy can reach 89%, which shows that the Al / DEME-TFSI / FTO device has application potential as a high-performance non-volatile memory in future computer systems and neuromorphic computing. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the application and together with the description, serve to explain the principles of the application. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Such embodiments are illustrative rather than restrictive and are exemplary and not intended as exhaustive or exclusive embodiments of the present device or method.

[0036] Figure 1 : device structure diagram;

[0037] Figure 2 (a): device single cycle I-V characteristic diagram;

[0038] Figure 2 (b): high-low configuration distribution under 100 cycles of I-V cycle characteristics of the device read at 0.2V voltage;

[0039] Figure 3 : conductance modulation illustration diagram;

[0040] Figure 4 : two-pulse differentiation PPF;

[0041] Figure 5 : long-term potentiation LTP and long-term depression LTD;

[0042] Figure 6 : pulse time-dependent plasticity STDP;

[0043] Figure 7 : artificial neural network model and accuracy. DETAILED DESCRIPTION

[0044] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other in the case of no conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0045] Embodiment 1

[0046] The present example is used to illustrate the ion liquid DEME-TFSI memristor with the function of simulating biological synapses and the preparation method.

[0047] Figure 1 The structure schematic diagram of the ion liquid DEME-TFSI memristor based on the ion liquid DEME-TFSI memristor in the embodiment of the present application is shown. The ion liquid layer is the middle layer 2, and the ion liquid layer is grown on the bottom electrode 1. The ion liquid layer is a transparent material containing water molecules. The hydrogen ions and the cations DEME+ of itself decomposed under the negative gate voltage are accumulated at the junction of the top electrode layer 3 and the ion liquid layer 2, thereby enhancing the Schottky barrier at the junction, so that the device occurs configuration switching. 4 is two probes of Keithley B1500A semiconductor parameter analyzer. One probe is pressed on the top electrode layer 3, and the other probe is pressed on the bottom electrode 1. The configuration resistance state of the device is changed by applying different parameters of voltage on the probe of the top electrode layer 3, so as to realize the function of simulating biological synapses.

[0048] In the present embodiment, the fluorine-doped tin dioxide (FTO) conductive substrate is used as the bottom electrode, and the aluminum is used as the electrode layer, and the preparation method of the ion liquid DEME-TFSI memristor with the function of simulating biological synapses provided by the present application is described.

[0049] Detailed description:

[0050] The specific steps of the ion liquid DEME-TFSI memristor of the present application are as follows:

[0051] 1. Clean the fluorine-doped tin dioxide (FTO) conductive substrate

[0052] Step one: Place the FTO to be cleaned on the cleaning rack and put it in a beaker, and prepare a rubber ring and a plastic film.

[0053] Step two: Add a small amount of cleaning agent and water that submerges the FTO into the beaker containing the FTO, and put it into the ultrasonic instrument for ultrasonic cleaning for 30 minutes.

[0054] Step three: All the liquid in the beaker after step two is introduced into the waste liquid barrel, then deionized water is added to submerge the FTO and put into the ultrasonic instrument for ultrasonic cleaning for 30 minutes.

[0055] Step four: All the liquid in the beaker after step three is introduced into the waste liquid barrel, then acetone is added to submerge the FTO and put into the ultrasonic instrument for ultrasonic cleaning for 30 minutes.

[0056] Step five: All the liquid in the beaker after step four is transferred to the waste liquid tank, then alcohol is added to submerge the FTO and placed in the ultrasonic instrument for 30 minutes, and then placed in the 60°C drying box for 4 hours.

[0057] 2. Preparation of ionic liquid DEME-TFSI liquid layer

[0058] Step one: test the conductivity of FTO with a multimeter, and select the side with conductivity.

[0059] Step two: attach conductive glue to the edge of the FTO with conductivity, and treat with ultraviolet ozone for 30 minutes.

[0060] Step three: place the ozone-treated FTO on the drop coating instrument.

[0061] Step four: use a pipette to draw 200 uL of ionic liquid DEME-TFSI and drop it on the FTO from the previous step.

[0062] Step five: set the drop coating speed to 3000 rpm.

[0063] Step six: set the drop coating time to 30 seconds.

[0064] Step seven: place the drop-coated FTO in a rapid annealing furnace.

[0065] Step eight: evacuate the growth chamber to 1 x 10-6 Torr.

[0066] Step nine: heat the growth chamber to 200°C.

[0067] Step ten: anneal for 10 minutes to form the ionic liquid liquid layer.

[0068] 3. Growth of electrode layer

[0069] Step one: remove the conductive glue under the ionic liquid layer.

[0070] Step two: place a clean mask on top of the ionic liquid layer.

[0071] Step three: use new conductive glue to attach to the top of the mask in the previous step.

[0072] Step four: place the piece from the previous step into the evaporation instrument to evaporate the electrode layer of aluminum.

[0073] Step five: remove the conductive glue and mask from the device after evaporation in the previous step.

[0074] The ionic liquid DEME-TFSI memristor is complete.

[0075] Example 2

[0076] This example is used to illustrate the I-V cycle characteristics of the device and the stability of the device.

[0077] Figure 2 The single cycle I-V characteristic curve of the device prepared in Example 1 and the high-low resistance state distribution map read at 0.2V voltage for 100 cycles. The FTO is grounded during testing, and the voltage is applied on the aluminum electrode with a step of 0.025V. In Figure 2 In (a), "1" refers to the curve of the 0―-2V scanning process, "2" refers to the curve of the -2V―0V scanning process, "3" refers to the curve of the 0V―2.5V scanning process, and the limiting current is 1mA, and "4" refers to the curve of the 2.5V―0V scanning process. Among the curves 1-4, "1" and "2" are the processes of the memristor switching from the low resistance state to the high resistance state, i.e. the erasing process of information. "3" and "4" are the processes of the memristor switching from the high resistance state to the low resistance state, i.e. the writing process of information. Figure 2 (a) shows that the Al / DEME-TFSI / FTO structure of the memristor prepared in Example 1 has typical non-volatile resistance switching characteristics. Figure 2 (b) is the durability test of the device prepared in Example 1, and the test results show that the device has good stability under 100 cycles of I-V cycle characteristics, and the ON / OFF ratio is about 1.5 orders of magnitude.

[0078] Example 3

[0079] This example is used to illustrate that the conductance of the device has continuous adjustable ability, and to prove that it has the potential to simulate biological synapses

[0080] Figure 3 The conductance continuous adjustment map of the device prepared in Example 1. The device is subjected to continuous negative bias sweep, and the stop voltage amplitude increases from -1V to -2.4V, and then subjected to continuous positive voltage sweep, and the Icc value increases from 0.5mA to 10mA. As can be seen from the figure, the conductance of the device is continuously adjustable, showing good conductance modulation characteristics, which shows that the device prepared in Example 1 has the potential to simulate biological synapses.

[0081] Example 4

[0082] This example is used to illustrate that the device has the ability to simulate the behavior of biological synapses.

[0083] Different pulse voltages are applied to the two ends of the Al / DEME-TFSI / FTO device prepared in Example 1, and the functions of biological synapses such as PPF, LTP / LTD and STDP are successfully simulated.

[0084] Figure 4is the PPF simulation of the device prepared in Example 1. The double-pulse heterosynaptic description is the enhancement of the excitatory postsynaptic current (EPSC) of the first pulse by the second pulse when two consecutive pulses are successfully applied on the presynaptic membrane (top electrode). The value of EPSC is closely related to the time interval of the two pulses applied on the presynaptic membrane. The shorter the time interval of the two pulses, the more obvious the enhancement. Figure 4 The PPF properties similar to biology are demonstrated.

[0085] Figure 5 is the LTP / LTD simulation of the device prepared in Example 1. By applying consecutive positive pulses and consecutive negative pulses on the device, the device exhibits good LTP / LTD characteristics, similar to the long-term memory of the human brain.

[0086] Figure 6 is the STDP simulation of the device prepared in Example 1. By designing the spike-shaped pulse using the time-division multiplexing (TDM) method, the device successfully exhibits the STDP characteristics on the device, indicating that the device prepared in Example 1 can simulate the STDP learning rule.

[0087] Example 5

[0088] In this embodiment, a three-layer artificial neural network is constructed using the LTP / LTD results, and an algorithm is used for handwritten digit recognition.

[0089] In this embodiment, an artificial neural network is constructed using the LTP / LTD results of the device prepared in Example 1, and an algorithm is used for simulation, and the results are shown in Figure 7 As can be seen from the figure, with the increase of the number of training, the picture blur degree is reduced, and the recognition accuracy is gradually increased. After 200 training, the recognition accuracy reaches 89%. This result proves that the Al / DEME-TFSI / FTO device has potential application prospects in the field of neuromorphic computing.

[0090] The above description is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any skilled person in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. An ionic liquid DEME-TFSI memristor with mimicking biological synapse function, characterized in that, The bottom electrode, the ionic liquid layer, and the top electrode layer are sequentially arranged. The bottom electrode is arranged at the bottom. The ionic liquid layer is arranged above the bottom electrode. The top electrode is arranged above the ionic liquid layer. The material of the ionic liquid layer is DEME-TFSI.

2. The ionic liquid DEME-TFSI memristor of claim 1, wherein, The bottom electrode is one of ITO conductive glass, fluorine-doped tin dioxide conductive substrate, and aluminum-doped zinc oxide conductive substrate.

3. The ionic liquid DEME-TFSI memristor of claim 1, wherein, The thickness of the ionic liquid layer is 50 nm to 300 nm.

4. The ionic liquid DEME-TFSI memristor of claim 1, wherein, The thickness of the top electrode layer is 150 nm to 350 nm.

5. The ionic liquid DEME-TFSI memristor of claim 1, wherein, The material of the top electrode is one of silver, copper, aluminum, zinc, magnesium, and iron.

6. A method for preparing an ionic liquid DEME-TFSI memristor with the function of simulating biological synapse, characterized in that, The method comprises the following steps: Step 1: sequentially clean the conductive substrate with water + detergent, deionized water, acetone, and alcohol using an ultrasonic instrument, dry the conductive substrate in a drying box after cleaning, and then perform ozone treatment on the conductive substrate before spin coating to obtain the bottom electrode; Step 2: spin coat DEME-TFSI on the bottom electrode and perform heat treatment to form the ionic liquid layer; Step 3: grow the top electrode on the ionic liquid layer by vacuum thermal evaporation to obtain the ionic liquid memristor.

7. The method of claim 6, wherein each cleaning step of the conductive substrate in step 1 lasts for 30 minutes. The drying time of the conductive substrate in step 1 is 4 to 8 hours. The ozone treatment time of the conductive substrate in step 1 is 30 minutes.

8. The method of claim 6, wherein the volume of DEME-TFSI spin coated in step 2 is 150 to 300 μL. The spin coating speed of DEME-TFSI in step 2 is 2500 to 4000 rpm. The spin coating time of DEME-TFSI in step 2 is 30 minutes. The heat treatment temperature in step 2 is 150 to 400°C. The heat treatment time in step 2 is 5 to 20 minutes.

9. The method of claim 6, wherein the thickness of the top electrode grown in step 3 is 150 to 350 nm. ​ ​ ​

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