A doped bismuth ferrite memristor with synaptic characteristics and a preparation method thereof

Abstract

The present invention belongs to the technical field of semiconductor memory devices and specifically discloses a doped bismuth ferrite memristor with synaptic properties and a preparation method thereof. The memristor sequentially comprises a substrate, a bottom electrode, a functional layer, and a top electrode; the functional layer is a doped bismuth ferrite film made of bismuth ferrite that is singly doped at the A site, singly doped at the B site, or co-doped at both the A and B sites, the A-site doping element being at least one of a rare earth metal element and an alkaline earth metal element, and the B-site doping element being a 3d transition metal element. By doping the bismuth ferrite, the memristor of the present invention possesses multiple resistance states. Under pulse modulation, it can achieve both stable binary storage and continuously adjustable conductance, fulfilling functions similar to those of biological synapses and having wide application in neural network research.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor memory devices, and more particularly, relates to a doped bismuth ferrite memristor with synaptic characteristics and a preparation method thereof. Background Art

[0002] With the rapid advancement of technology, information exchange and communication are becoming increasingly frequent, and data is experiencing explosive growth. Faced with increasingly complex data processing challenges, information systems must continuously strive for higher and higher data processing efficiency. However, in traditional computers based on the von Neumann architecture, the processor and memory are separated and connected by a bus. This architecture suffers from the so-called von Neumann bottleneck: data exchange between the processor and memory via the bus. While the processor's computing speed and memory access requirements can both be met, the limited bus transmission rate constrains both. Compared to von Neumann computers, the human brain's neural information activity features massive parallelism, distributed storage and processing, self-organization, self-adaptation, and self-learning. Therefore, learning from the human brain and building a new computer architecture that integrates information storage and processing, similar to the human neural system, is considered an effective way to overcome the von Neumann bottleneck.

[0003] Currently, traditional artificial neural networks typically use complementary metal oxide semiconductor (CMOS) circuits and nonlinear circuits to simulate neuronal discharges. However, these approaches require dozens of transistors, capacitors, and adders to simulate just one neuron or synapse, making them impractical for building neural networks in terms of both integration density and power consumption. Due to their small size, low power consumption, high speed, and ease of integration, memristors have been proposed as the basic unit of artificial neural networks to build highly parallel, fault-tolerant, and efficient computer systems.

[0004] In recent years, bismuth ferrite (BiFeO3), a ferroelectric memristor, has emerged as a prominent example of perovskite-type materials, boasting high resistance-to-switching ratios, fast switching speeds, excellent durability, and low power consumption. In a metal / ferroelectric / metal sandwich structure, the ferroelectric polarization direction can be flipped by applying an external voltage bias. Simultaneously, changes in the ferroelectric polarization value can be used to adjust the synaptic weight within the memristor. Previous research has shown that in the distorted perovskite lattice of BFO, the bismuth ferrite (BiFeO3) element, which occupies the A site, is easily volatilized, and the Fe element, which occupies the B site, easily switches from trivalent to divalent. This leads to numerous defects and vacancies in the bismuth ferrite film, significantly affecting the device's cycling stability and significantly compromising its performance in synaptic neural networks. Summary of the Invention

[0005] In response to the defects of the prior art, the purpose of the present invention is to provide a doped bismuth ferrite memristor with synaptic characteristics and a preparation method thereof, aiming to solve the problem of poor performance of the existing ferroelectric memristor in synaptic neural networks due to the presence of many defects and vacancies in the bismuth ferrite film.

[0006] To achieve the above-mentioned object, the present invention provides a doped bismuth ferrite memristor with synaptic characteristics, which comprises a substrate, a bottom electrode, a functional layer and a top electrode in sequence;

[0007] The functional layer is a doped bismuth ferrite film, the material of the doped bismuth ferrite film is bismuth ferrite that is single-doped at the A site, single-doped at the B site, or co-doped at the A site and the B site, the doping element at the A site is at least one of a rare earth metal element and an alkaline earth metal element, and the doping element at the B site is a 3d transition metal element.

[0008] Preferably, the A-site doping element is at least one of Er, Ho, Mg, Ca, Sr, Gd, Sm, La, Dy, Ce, Pr, Y and Ba, and the B-site doping element is at least one of Cr, Mn, Zn, Co, Ni, Nb and Ti.

[0009] Preferably, the material of the doped bismuth ferrite film is B-site single-doped bismuth ferrite, the B-site doping element is Mn, and the doping concentration of the Mn element is less than or equal to 20 at %.

[0010] Preferably, the doping concentration of the Mn element is 6 at % to 20 at %.

[0011] Preferably, the material of the substrate is Si / SiO2, glass or SrTiO3; the material of the bottom electrode is TiN, Nb:SrTiO3, SrRuO3, La 0.3 Sr 0.7 At least one of MnO3 and Pt; the material of the top electrode is at least one of Au, Pt, Ag, Cu, Al, W and Ti.

[0012] According to another aspect of the present invention, a method for preparing a doped bismuth ferrite memristor having synaptic characteristics is provided, comprising the following steps:

[0013] growing a bottom electrode on a substrate by magnetron sputtering or pulsed laser deposition;

[0014] growing a doped bismuth ferrite film on the bottom electrode by magnetron sputtering, pulsed laser deposition or sol-gel method;

[0015] performing photolithographic development on the doped bismuth ferrite film;

[0016] A top electrode is grown on the developed doped bismuth ferrite film by magnetron sputtering or electron beam evaporation.

[0017] Preferably, the method of growing the doped bismuth ferrite film by magnetron sputtering specifically includes the following steps:

[0018] S1. Adjust the distance between substrate and target to 80mm~150mm, and the background vacuum degree is equal to or greater than 5.0×10 -3 Pa, wherein the substrate is a substrate with a bottom electrode grown on one side thereof, and the target material is a doped bismuth ferrite ceramic target material;

[0019] S2, heating the substrate and keeping it warm;

[0020] S3. Sputtering coating is performed on the substrate after heat preservation, with the working gas being argon and oxygen, the argon-oxygen ratio being 3:(8-30), the sputtering power being 80W-150W, and the sputtering time being 30min-120min;

[0021] S4. The substrate is in-situ annealed in an argon atmosphere and then naturally cooled to room temperature.

[0022] Preferably, in step S2, the heating temperature is 500°C to 670°C, and the holding time is 30 min to 120 min; in step S4, the annealing is maintained at 500°C to 670°C for 30 min to 60 min.

[0023] Preferably, the photolithography development includes pre-baking at 97° C. for 2 to 3 minutes, with a pre-exposure time of 1.2 to 2 seconds, and post-baking at 115° C. for 2 to 3 minutes, with a post-exposure time of 1 to 12 seconds.

[0024] Preferably, DC magnetron sputtering is used to grow the top electrode. The process conditions of DC magnetron sputtering are as follows: the working gas is argon, the working pressure is 0.5Pa to 3Pa, the target-substrate distance is 80mm to 150mm, the sputtering power is 80W to 150W, the sputtering time is 500s to 2000s, and the background vacuum is equal to or greater than 8×10 -4 Pa.

[0025] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0026] (1) The present invention reduces the internal defects of the bismuth ferrite film by doping bismuth ferrite, effectively improving the problem of unstable valence of iron ions, thereby reducing leakage current and improving the electromagnetic properties of the bismuth ferrite film, so that the doped bismuth ferrite memristive device has two resistive switching characteristics: sudden digital and gradual analog. The device has good activity timing dependent plasticity (STDP) and frequency dependent plasticity (SRDP), and good cyclic stability, laying the foundation for the application of the device in synaptic neural networks.

[0027] (2) The present invention adjusts the Mn doping concentration in the bismuth ferrite film to form a certain amount of MnO2 clusters in the bismuth ferrite. When an external electric field is applied, the conductive filaments formed by oxygen vacancies are thin and dispersed. When disconnected, the conductive filaments can be broken one by one in an orderly manner, causing the device resistance value to change continuously, thereby achieving the performance of simulating synapses, such as long-term potentiation (LTP) and long-term depression (LTD).

[0028] (3) The preparation method of the doped bismuth ferrite memristor provided by the present invention is simple and fast, with strong reliability and high repeatability. The prepared memristor device has low operating voltage, long data retention capability, and good operational repeatability. Moreover, under pulse modulation, it can achieve both stable binary storage and continuously adjustable conductivity characteristics, and can realize functions similar to biological synapses, providing a feasible way to construct memristor neural networks. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of a doped bismuth ferrite memristor device provided in an embodiment of the present invention, wherein: 101 - substrate, 102 - bottom electrode, 103 - functional layer, 104 - top electrode;

[0030] Figure 2 A 100-cycle DC voltage-current cycle curve of the doped bismuth ferrite memristor provided in Example 1 of the present invention;

[0031] Figure 3 LTP and LTD diagrams of the doped bismuth ferrite memristor provided in Example 1 of the present invention;

[0032] Figure 4 A 100-cycle DC voltage-current cycle curve of the doped bismuth ferrite memristor provided in Example 2 of the present invention;

[0033] Figure 5 A 200-cycle DC voltage-current cycle curve of the doped bismuth ferrite memristor provided in Example 3 of the present invention;

[0034] Figure 6LTP and LTD diagrams of the doped bismuth ferrite memristor provided in Example 3 of the present invention;

[0035] Figure 7 This is a graph showing the 1000-cycle pulse fatigue resistance characteristics of the doped bismuth ferrite memristor provided in Example 3 of the present invention;

[0036] Figure 8 A 200-cycle DC voltage-current cycle curve of the doped bismuth ferrite memristor provided in Example 6 of the present invention;

[0037] Figure 9 LTP and LTD diagrams of the doped bismuth ferrite memristor provided in Example 6 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] like Figure 1 As shown, the present invention provides a doped bismuth ferrite memristor with synaptic characteristics, which includes a substrate 101, a bottom electrode 102, a functional layer 103 and a top electrode 104 in sequence;

[0040] The functional layer 103 is a doped bismuth ferrite film, the material of which is bismuth ferrite that is single-doped at the A site, single-doped at the B site, or co-doped at the A site and the B site. The doping element at the A site is at least one of a rare earth metal element and an alkaline earth metal element, and the doping element at the B site is a 3d transition metal element.

[0041] The present invention dopes the bismuth ferrite thin film in the ferroelectric memristor. The doped elements form byproducts that restrict the position of the conductive filaments in the oxygen vacancies in the functional layer, causing the conductive filaments to connect and disconnect one by one. Different numbers of conductive filaments correspond to different resistance states, resulting in the device having multiple resistance values. Multiple resistance values ​​are a prerequisite for synaptic plasticity, so this doped bismuth ferrite memristor easily develops synaptic properties. In contrast, in an undoped memristor, since there are no restrictions on the internal conductive filament paths, the formation and disconnection of many conductive filaments occur simultaneously, resulting in only two resistance states and being unable to simulate synaptic properties.

[0042] In some embodiments, the A-site doping element may be at least one of Er, La, Ho, Mg, Ca, Sr, Gd, Sm, Dy, Ce, Pr, Y, and Ba, and the B-site doping element may be at least one of Cr, Mn, Zn, Co, Ni, Nb, and Ti.

[0043] In some embodiments, the material of the doped bismuth ferrite film is bismuth ferrite doped at the B site, wherein the B-site doping element is Mn, wherein the doping concentration of the Mn element is less than or equal to 20 at%. B-site Mn doping can effectively improve the unstable valence state of the iron element in BFO. In addition, due to the presence of MnO2 clusters, when an external electric field is applied to the Mn-doped BFMO device, the oxygen vacancies form conductive filaments. The conductive filaments are very thin and dispersed, and are more likely to break one by one in a regular manner when disconnected. Therefore, the device resistance value can change continuously, thereby giving the device synaptic characteristics.

[0044] Preferably, the Mn doping concentration is 6 to 20 at%, more preferably 10 to 20 at%, and most preferably 15 at%. The resulting memristor can better mimic synaptic behavior and exhibit improved performance. If the Mn doping level is too low, too little MnO2 is formed, and the MnO2 clusters have little effect on the memristive device.

[0045] In some embodiments, the material of the substrate 101 is Si / SiO2, glass or SrTiO3; the material of the bottom electrode 102 is TiN, strontium titanate doped with niobium (Nb:SrTiO3), strontium ruthenate (SrRuO3), strontium lanthanum manganate (La 0.3 Sr 0.7 The material of the top electrode 104 is at least one of Au, Pt, Ag, Cu, Al, W and Ti.

[0046] On the other hand, the present invention also provides a method for preparing a doped bismuth ferrite memristor with synaptic characteristics, comprising the following steps:

[0047] growing a bottom electrode on a substrate by magnetron sputtering or pulsed laser deposition;

[0048] growing a doped bismuth ferrite film on the bottom electrode by magnetron sputtering, pulsed laser deposition or sol-gel method;

[0049] performing photolithographic development on the doped bismuth ferrite film;

[0050] A top electrode is grown on the developed doped bismuth ferrite film by magnetron sputtering or electron beam evaporation.

[0051] Specifically, the method of growing a doped bismuth ferrite film by magnetron sputtering includes the following steps:

[0052] S1. Adjust the distance between substrate and target to 80mm~150mm, and the background vacuum degree is equal to or greater than 5.0×10 -3 Pa, wherein the substrate is a substrate with a bottom electrode grown on one side thereof, and the target material is a doped bismuth ferrite ceramic target material;

[0053] S2, heating the substrate and keeping it warm;

[0054] S3. Sputtering coating is performed on the substrate after heat preservation, with the working gas being argon and oxygen, the argon-oxygen ratio being 3:(8-30), the sputtering power being 80W-150W, and the sputtering time being 30min-120min;

[0055] S4. The substrate is in-situ annealed in an argon atmosphere and then naturally cooled to room temperature.

[0056] In some embodiments, the substrate may be a TiN substrate, a SrRuO3 substrate, a Nb:SrTiO3 substrate, and the like. Specifically, the TiN substrate includes a Si / SiO2 substrate and a TiN bottom electrode, and the substrate can be obtained by growing a TiN bottom electrode on a Si / SiO2 substrate using magnetron sputtering. A commercial SrRuO3 substrate includes a SrTiO3 substrate and a SrRuO3 bottom electrode grown on a SrTiO3 substrate. A commercial Nb:SrTiO3 substrate is a whole piece of Nb:SrTiO3 material, which is both a substrate and a bottom electrode. The target material used is a Mn-doped bismuth ferrite ceramic target prepared by a solid-phase reaction method, and the Mn element doping concentration is 0 to 20 at% (the molecular formula of the target material can be expressed as Bi 1.1 Fe 1-x Mn x O3, wherein x=0, 0.05, 0.1, 0.15 or 0.2). Preferably, the doping concentration of the Mn element is 10 at% to 20 at%.

[0057] In some embodiments, in step S2, the heating temperature is 500°C to 670°C, and the holding time is 30 minutes to 120 minutes. The purpose of heating the substrate is to expand the substrate lattice, so that the sputtered functional layer can better grow along the bottom electrode direction and reduce the stress between the functional layer and the bottom electrode.

[0058] In step S3, in order to ensure the reliability and stability of sputtering coating, pre-sputtering is performed on the baffle before sputtering coating. The working gases are argon and oxygen, the argon-oxygen ratio is 3:(8~30), the pre-sputtering power is 80W~150W, and the pre-sputtering time is 5min~20min.

[0059] In step S4, the annealing is carried out at 500° C. to 670° C. for 30 min to 60 min.

[0060] In some embodiments, the photolithography development includes pre-baking at 97° C. for 2 to 3 minutes, with a pre-exposure time of 1.2 to 2 seconds, and post-baking at 115° C. for 2 to 3 minutes, with a post-exposure time of 1 to 12 seconds.

[0061] In some embodiments, DC magnetron sputtering is used to grow the top electrode, and the material of the top electrode is at least one of Au, Pt, Ag, Cu, Al, and Ti. The process conditions of DC magnetron sputtering are: the working gas is argon, the working pressure is 0.5 Pa to 3 Pa, the target substrate distance is 80 mm to 150 mm, the sputtering power is 80 W to 150 W, the sputtering time is 500 s to 2000 s, and the background vacuum is equal to or greater than 8×10 -4 Pa.

[0062] The above technical solution is described in detail below in conjunction with specific embodiments.

[0063] Example 1

[0064] In this embodiment, a 5at% Mn-doped bismuth ferrite memristor with TiN as the bottom electrode was prepared. The specific steps are as follows:

[0065] (1) Clean the TiN substrate using deionized water, acetone, and anhydrous ethanol in an ultrasonic environment for 5 minutes, and then blow dry with a nitrogen gun;

[0066] (2) Place the cleaned substrate on the sample stage and install the target, which is a 5at% Mn-doped bismuth ferrite ceramic target. Adjust the distance between the sample stage and the target to 80 mm, turn on the molecular pump and mechanical pump to evacuate the vacuum chamber to 5.0×10 -3 Pa;

[0067] (3) Heat the substrate to 500°C and keep it warm for 60 minutes. Fill the vacuum chamber with working gases of argon and oxygen, with a ratio of argon to oxygen of 1:10.

[0068] (4) Turn on the RF power supply, rotate the baffle to the top of the substrate, and perform pre-sputtering. The pre-sputtering time is 5 minutes and the pre-sputtering power is 80W.

[0069] (5) After the above step (4) is completed, the baffle is removed and sputtering is carried out for 30 minutes at a sputtering power of 80W;

[0070] (6) After the sputtering is completed, the oxygen gas is turned off and the sample is in-situ annealed in an argon atmosphere at 500°C for 40 minutes. The sample is then naturally cooled to room temperature to obtain a bismuth ferrite film.

[0071] (7) The bismuth ferrite film prepared in step (6) was subjected to photolithographic development using AZ5214 negative photoresist, pre-baked at 97°C for 3 minutes, pre-exposure time of 1.5 seconds, and post-baked at 115°C for 3 minutes, post-exposure time of 1 second;

[0072] (8) The top electrode was prepared by DC magnetron sputtering. The target material was Pt target, and the background vacuum of the vacuum chamber was 8.0×10 -4 Pa, the sputtering gas is argon, the pressure is 2 Pa, the target-substrate distance is 80 mm, the sputtering power is 80 W, and the sputtering time is 500 s.

[0073] Figure 2 The 100-cycle DC IV curve of 5% Mn-doped BFO shows a large resistive switching window and good fatigue resistance consistency, indicating that doping can improve the resistive switching characteristics of BFO. Figure 3 The long-term potentiation (LTP) and long-term depression (LTD) of 5% Mn-doped BFO indicate that the device has synaptic characteristics, but its linearity is poor, and the overlap of multiple resistance states in LTP is more serious.

[0074] Example 2

[0075] In this embodiment, a 10 at% Mn-doped bismuth ferrite memristor with TiN as the bottom electrode is prepared. The specific steps are as follows:

[0076] (1) Clean the TiN substrate using deionized water, acetone, and anhydrous ethanol in an ultrasonic environment for 5 minutes, and then blow dry with a nitrogen gun;

[0077] (2) Place the cleaned substrate on the sample stage and install the target, which is a 10 at% Mn-doped bismuth ferrite ceramic target. Adjust the distance between the sample stage and the target to 100 mm, turn on the molecular pump and mechanical pump to evacuate the vacuum chamber to 5.0 × 10 -3 Pa;

[0078] (3) Heat the substrate and keep it warm at 640°C for 30 minutes. Fill the vacuum chamber with working gases of argon and oxygen, with a ratio of argon to oxygen of 1:4.

[0079] (4) Turn on the RF power supply, rotate the baffle to the top of the substrate, and perform pre-sputtering. The pre-sputtering time is 15 minutes and the pre-sputtering power is 100W.

[0080] (5) After the above step (4) is completed, the baffle is removed and sputtering is performed. The sputtering time is 60 minutes and the sputtering power is 100W.

[0081] (6) After the sputtering is completed, the oxygen gas is turned off and the sample is in-situ annealed in an argon atmosphere at 640°C for 30 minutes. The sample is then naturally cooled to room temperature to obtain a bismuth ferrite film.

[0082] (7) The bismuth ferrite film prepared in step (6) was subjected to photolithographic development using AZ5214 negative photoresist, pre-baked at 97°C for 2 min, pre-exposure time of 1.2 s, and post-baked at 115°C for 2 min, post-exposure time of 2 s;

[0083] (8) The top electrode was prepared by DC magnetron sputtering. The target material was Pt target, and the background vacuum of the vacuum chamber was 8.0×10 -4 Pa, the sputtering gas is argon, the pressure is 0.5 Pa, the target-substrate distance is 100 mm, the sputtering power is 150 W, and the sputtering time is 1000 s.

[0084] Figure 4 The 100-cycle DC IV curve for 10% Mn-doped BFO shows a distinct resistance window and a gradual reset curve, indicating multiple resistance states. Furthermore, long-term potentiation (LTP) and depression (LTD) pulse experiments on synaptic efficacy demonstrate that the memristor fabricated in this example exhibits excellent synaptic properties.

[0085] Example 3

[0086] In this embodiment, a 15 at % Mn-doped bismuth ferrite memristor with TiN as the bottom electrode is prepared. The specific steps are as follows:

[0087] (1) Clean the TiN substrate using deionized water, acetone, and anhydrous ethanol in an ultrasonic environment for 5 minutes, and then blow dry with a nitrogen gun;

[0088] (2) Place the cleaned substrate on the sample stage and install the target, which is a 15 at% Mn-doped bismuth ferrite ceramic target. Adjust the distance between the sample stage and the target to 100 mm, turn on the molecular pump and mechanical pump to evacuate the vacuum chamber to 5.0 × 10 -3 Pa;

[0089] (3) Heat the substrate and keep it warm at 640°C for 30 minutes. Fill the vacuum chamber with working gases of argon and oxygen, with a ratio of argon to oxygen of 1:4.

[0090] (4) Turn on the RF power supply, rotate the baffle to the top of the substrate, and perform pre-sputtering. The pre-sputtering time is 15 minutes and the sputtering power is 100W.

[0091] (5) After the above step (4) is completed, the baffle is removed and sputtering is performed. The sputtering time is 60 minutes and the sputtering power is 100W.

[0092] (6) After the sputtering is completed, the oxygen gas is turned off and the sample is in-situ annealed in an argon atmosphere at 640°C for 30 minutes. The sample is then naturally cooled to room temperature to obtain a bismuth ferrite film.

[0093] (7) The bismuth ferrite film prepared in step (6) was subjected to photolithographic development using AZ5214 negative photoresist, pre-baked at 97°C for 2 min, pre-exposure time of 1.2 s, and post-baked at 115°C for 2 min, post-exposure time of 2 s;

[0094] (8) The top electrode was prepared by DC magnetron sputtering. The target material was Pt target, and the background vacuum of the vacuum chamber was 8.0×10 -4 Pa, the sputtering gas is argon, the pressure is 0.5 Pa, the target-substrate distance is 100 mm, the sputtering power is 150 W, and the sputtering time is 1000 s.

[0095] Figure 5 The 100-cycle DC IV curve of 15% Mn-doped BFO shows a large resistive switching window, indicating that doping can improve the resistive switching characteristics of BFO. Figure 6 For the long-term potentiation and long-term depression of 15% Mn-doped BFO, except for the overlap of individual LTD resistance states, the remaining LTP and LTD not only have good linearity, that is, each pulse corresponds to a resistance value; but also do not weaken after repeating 5 cycles. Figure 7 The pulse test curve of 15% Mn-doped BFO shows that its switching speed is very fast, only tens of nanoseconds, and it does not decay even after 5000 cycles. The above shows that the memristor prepared in this embodiment has good synaptic properties.

[0096] Example 4

[0097] In this embodiment, a bismuth ferrite memristor with TiN as the bottom electrode and 20 at% Mn doping is prepared. The specific steps are as follows:

[0098] (1) Clean the TiN substrate using deionized water, acetone, and anhydrous ethanol in an ultrasonic environment for 5 minutes, and then blow dry with a nitrogen gun;

[0099] (2) Place the cleaned substrate on the sample stage and install the target, which is a 20 at% Mn-doped bismuth ferrite ceramic target. Adjust the distance between the sample stage and the target to 150 mm, turn on the molecular pump and mechanical pump to evacuate the vacuum chamber to 5.0 × 10 -3 Pa;

[0100] (3) Heat the substrate and keep it warm at 670°C for 120 min. Fill the vacuum chamber with working gases of argon and oxygen at a ratio of 3:8.

[0101] (4) Turn on the RF power supply, rotate the baffle to the top of the substrate, and perform pre-sputtering. The pre-sputtering time is 20 minutes and the sputtering power is 150W.

[0102] (5) After the above step (4) is completed, the baffle is removed and sputtering is performed. The sputtering time is 120 min and the sputtering power is 150 W.

[0103] (6) After the sputtering is completed, the oxygen gas is turned off and the sample is in situ annealed in an argon atmosphere at 670°C for 60 minutes. The sample is then naturally cooled to room temperature to obtain a bismuth ferrite film.

[0104] (7) The bismuth ferrite film prepared in step (6) was subjected to photolithographic development using AZ5214 negative photoresist, pre-baked at 97°C for 2.5 min, pre-exposure time 2 s, and post-baked at 115°C for 2.5 min, post-exposure time 12 s;

[0105] (8) The top electrode was prepared by DC magnetron sputtering. The target material was Pt target, and the background vacuum of the vacuum chamber was 8.0×10 -4 Pa, the sputtering gas is argon, the pressure is 3 Pa, the target-substrate distance is 150 mm, the sputtering power is 100 W, and the sputtering time is 2000 s.

[0106] Through the long-term potentiation (LTP) and long-term depression (LTD) pulse experiments of synaptic efficacy, it was found that the memristor prepared in this embodiment has good synaptic characteristics.

[0107] Example 5

[0108] In this embodiment, a bismuth ferrite memristor with SrRuO3 as the bottom electrode and 15at% Mn doping was prepared. The specific steps are as follows:

[0109] (1) Clean the SrRuO3 substrate using deionized water, acetone, and anhydrous ethanol in an ultrasonic environment for 5 minutes, and then blow dry with a nitrogen gun;

[0110] (2) Place the cleaned substrate on the sample stage and install the target, which is a 15 at% Mn-doped bismuth ferrite ceramic target. Adjust the distance between the sample stage and the target to 100 mm, turn on the molecular pump and mechanical pump to evacuate the vacuum chamber to 5.0 × 10 -3 Pa;

[0111] (3) Heat the substrate and keep it warm at 640°C for 30 minutes. Fill the vacuum chamber with working gases of argon and oxygen, with a ratio of argon to oxygen of 1:4.

[0112] (4) Turn on the RF power supply, rotate the baffle to the top of the substrate, and perform pre-sputtering. The pre-sputtering time is 15 minutes and the pre-sputtering power is 100W.

[0113] (5) After the above step (4) is completed, the baffle is removed and sputtering is performed. The sputtering time is 60 minutes and the sputtering power is 100W.

[0114] (6) After the sputtering is completed, the oxygen gas is turned off and the sample is in-situ annealed in an argon atmosphere at 640°C for 30 minutes. The sample is then naturally cooled to room temperature to obtain a bismuth ferrite film.

[0115] (7) The bismuth ferrite film prepared in step (6) was subjected to photolithographic development using AZ5214 negative photoresist, pre-baked at 97°C for 2 min, pre-exposure time of 1.2 s, and post-baked at 115°C for 2 min, post-exposure time of 2 s;

[0116] (8) The top electrode was prepared by DC magnetron sputtering. The target material was Pt target, and the background vacuum of the vacuum chamber was 8.0×10 -4 Pa, the sputtering gas is argon, the pressure is 0.5 Pa, the target-substrate distance is 100 mm, the sputtering power is 150 W, and the sputtering time is 1000 s.

[0117] Through the long-term potentiation (LTP) and depression (LTD) pulse experiments of synaptic efficacy, it was found that the memristor prepared in this embodiment has synaptic characteristics.

[0118] Example 6

[0119] In this embodiment, a bismuth ferrite memristor with Nb:SrTiO3 material as the bottom electrode and 15at% Mn doping was prepared. The specific steps are as follows:

[0120] (1) Clean the Nb:SrTiO3 substrate using deionized water, acetone, and anhydrous ethanol in an ultrasonic environment for 5 minutes, and then blow dry with a nitrogen gun;

[0121] (2) Place the cleaned substrate on the sample stage and install the target, which is a 15 at% Mn-doped bismuth ferrite ceramic target. Adjust the distance between the sample stage and the target to 100 mm, turn on the molecular pump and mechanical pump to evacuate the vacuum chamber to 5.0 × 10 -3 Pa;

[0122] (3) Heat the substrate and keep it warm at 640°C for 30 minutes. Fill the vacuum chamber with working gases of argon and oxygen, with a ratio of argon to oxygen of 1:4.

[0123] (4) Turn on the RF power supply, rotate the baffle to the top of the substrate, and perform pre-sputtering. The pre-sputtering time is 15 minutes and the pre-sputtering power is 100W.

[0124] (5) After the above step (4) is completed, the baffle is removed and sputtering is performed. The sputtering time is 60 minutes and the sputtering power is 100W.

[0125] (6) After the sputtering is completed, the oxygen gas is turned off and the sample is in-situ annealed in an argon atmosphere at 640°C for 30 minutes. The sample is then naturally cooled to room temperature to obtain a bismuth ferrite film.

[0126] (7) The bismuth ferrite film prepared in step (6) was subjected to photolithographic development using AZ5214 negative photoresist, pre-baked at 97°C for 2 min, pre-exposure time of 1.2 s, and post-baked at 115°C for 2 min, post-exposure time of 2 s;

[0127] (8) The top electrode was prepared by DC magnetron sputtering. The target material was Pt target, and the background vacuum of the vacuum chamber was 8.0×10 -4 Pa, the sputtering gas is argon, the pressure is 0.5 Pa, the target-substrate distance is 100 mm, the sputtering power is 150 W, and the sputtering time is 1000 s.

[0128] Figure 8 The 200-cycle DC IV curve of 15% Mn-doped BFO with Nb:SrTiO3 bottom electrode shows a large resistive switching window, and its set and reset processes are both gradual, indicating that it has multi-value characteristics. Figure 9 The long-term potentiation and long-term depression of 15% Mn-doped BFO are shown. It can be seen that the LTP and LTD of each cycle not only have good linearity, that is, each pulse corresponds to a single resistance value, but also do not decay after three repeated cycles. The above shows that the memristor prepared in this example has good synaptic properties.

[0129] Comparative Example

[0130] In this comparative example, a pure phase bismuth ferrite memristor with TiN material as the bottom electrode was prepared. The specific steps are as follows:

[0131] (1) Clean the TiN substrate using deionized water, acetone, and anhydrous ethanol in an ultrasonic environment for 5 minutes, and then blow dry with a nitrogen gun;

[0132] (2) Place the cleaned substrate on the sample stage and install the target material, which is a pure phase bismuth ferrite ceramic target. Adjust the distance between the sample stage and the target material to 100 mm, turn on the molecular pump and mechanical pump to evacuate the vacuum chamber to 5.0×10 -3 Pa;

[0133] (3) Heat the substrate and keep it warm at 640°C for 30 minutes. Fill the vacuum chamber with working gases of argon and oxygen, with a ratio of argon to oxygen of 1:4.

[0134] (4) Turn on the RF power supply, rotate the baffle to the top of the substrate, and perform pre-sputtering. The pre-sputtering time is 15 minutes and the pre-sputtering power is 100W.

[0135] (5) After the above step (4) is completed, the baffle is removed and sputtering is performed. The sputtering time is 60 minutes and the sputtering power is 100W.

[0136] (6) After the sputtering is completed, the oxygen gas is turned off and the sample is in-situ annealed in an argon atmosphere at 640°C for 30 minutes. The sample is then naturally cooled to room temperature to obtain a bismuth ferrite film.

[0137] (7) The bismuth ferrite film prepared in step (6) was subjected to photolithographic development using AZ5214 negative photoresist, pre-baked at 97°C for 2 min, pre-exposure time of 1.2 s, and post-baked at 115°C for 2 min, post-exposure time of 2 s;

[0138] (8) The top electrode was prepared by DC magnetron sputtering. The target material was Pt target, and the background vacuum of the vacuum chamber was 8.0×10 -4 Pa, the sputtering gas is argon, the pressure is 0.5 Pa, the target-substrate distance is 100 mm, the sputtering power is 150 W, and the sputtering time is 1000 s.

[0139] The memristor prepared in this comparative example has only two resistance values ​​and does not have synaptic characteristics.

[0140] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A doped bismuth ferrite memristor with synaptic properties, characterized by: It includes a substrate, a bottom electrode, a functional layer and a top electrode in sequence; The functional layer is a doped bismuth ferrite film. The material of the doped bismuth ferrite film is bismuth ferrite doped with Mn element in the B position, wherein the doping concentration of the Mn element is 6 at% to 20 at%, which can form MnO2 clusters in the bismuth ferrite. When an external electric field is applied, the conductive filaments formed by oxygen vacancies are thin and dispersed. When disconnected, the conductive filaments can be broken one by one in a regular manner, causing the device resistance value to change continuously.

2. The doped bismuth ferrite memristor according to claim 1, characterized in that: The material of the substrate is Si / SiO2, glass or SrTiO3; the material of the bottom electrode is TiN, Nb:SrTiO3, SrRuO3, La 0.3 Sr 0.7 At least one of MnO3 and Pt; the material of the top electrode is at least one of Au, Pt, Ag, Cu, Al, W and Ti.

3. A method for preparing a doped bismuth ferrite memristor according to claim 1 or 2, characterized in that: The steps include: growing a bottom electrode on a substrate by magnetron sputtering or pulsed laser deposition; growing a doped bismuth ferrite film on the bottom electrode by magnetron sputtering, pulsed laser deposition or sol-gel method; performing photolithographic development on the doped bismuth ferrite film; A top electrode is grown on the developed doped bismuth ferrite film by magnetron sputtering or electron beam evaporation.

4. The preparation method according to claim 3, characterized in that The method of growing a doped bismuth ferrite film by magnetron sputtering specifically includes the following steps: S1. Adjust the distance between substrate and target to 80 mm~150 mm, and the background vacuum degree is equal to or greater than 5.0×10 -3 Pa, wherein the substrate is a substrate with a bottom electrode grown on one side thereof, and the target material is a doped bismuth ferrite ceramic target material; S2, heating the substrate and keeping it warm; S3. Sputtering coating is performed on the substrate after insulation, with the working gases being argon and oxygen, the argon-oxygen ratio being 3:(8-30), the sputtering power being 80 W-150 W, and the sputtering time being 30 min-120 min; S4. The substrate is in-situ annealed in an argon atmosphere and then naturally cooled to room temperature.

5. The preparation method according to claim 4, wherein: In step S2, the heating temperature is 500°C to 670°C, and the holding time is 30 min to 120 min; in step S4, the annealing is maintained at 500°C to 670°C for 30 min to 60 min.

6. The preparation method according to claim 3, wherein The photolithography development includes a pre-bake at 97°C for 2 min to 3 min, a pre-exposure time of 1.2 s to 2 s, and a post-bake at 115°C for 2 min to 3 min, and a post-exposure time of 1 s to 12 s.

7. The preparation method according to claim 3, wherein The top electrode was grown by direct current magnetron sputtering. The process conditions of the direct current magnetron sputtering were as follows: the working gas was argon, the working pressure was 0.5 Pa to 3 Pa, the target-substrate distance was 80 mm to 150 mm, the sputtering power was 80 W to 150 W, the sputtering time was 500 s to 2000 s, and the background vacuum was equal to or greater than 8×10 -4 Pa.

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