A method for realizing memristor memristance based on ion diffusion and phase change mechanism

Abstract

This invention belongs to the field of semiconductor storage technology and proposes a method for achieving memristor memristance based on ion diffusion and phase change mechanisms. The memristor structure comprises upper and lower electrode layers and a middle functional layer of Ag2Te semiconductor. The method is characterized by applying an ultra-low voltage to the memristor, inducing phase change and ion diffusion in the Ag2Te semiconductor, which in turn induces a resistive change to achieve memristor memristance. The invention employs a unidirectional positive pulse voltage signal input mode, which achieves stable resistive switching, avoiding the drawbacks of ion diffusion and enabling controllable switching of the memristor's resistance between high and low resistance states.

Description

Technical Field

[0001] This embodiment belongs to the technical field related to semiconductor storage, and specifically relates to a method for realizing memristor memristance based on ion diffusion and phase change mechanisms. Background Art

[0002] A memristor, or memory resistor, is a circuit device that represents the relationship between magnetic flux and charge. Based on the material's resistance transition properties, it enables 0 / 1 information storage, logical operations, and brain-inspired neuromorphic computing. Simply put, a memristor is a nonlinear resistor with memory. Its resistance value can be altered by controlling current flow. If a high resistance value is defined as "1" and a low resistance value as "0," this resistor can store data. Furthermore, the memristor has a simple "MIM" (metal / insulator / metal) structure, making it compatible with CMOS processes. It also offers advantages such as high speed, low power consumption, and ease of integration. This has led to its increasing interest among researchers and rapid development in the fields of storage and computing.

[0003] Currently reported memristors are mostly based on electrochemical metallization, valence state transition, and thermochemical mechanisms occurring within memristive materials. These mechanisms primarily involve the formation and fusing of metal or oxygen vacancy conductive filaments within the materials, which in turn determine the memristive properties of the device. The formation and fracturing of conductive filaments within the materials involve ion migration and redox reactions. The random nature of filament formation reduces the response speed of memristive devices and increases their power consumption. Therefore, identifying novel memristive mechanisms and materials, and developing new memristive device fabrication technologies, are essential. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned existing technologies and provide a method for realizing memristor memristance based on ion diffusion and phase change mechanisms. The present invention designs a unidirectional positive pulse voltage signal input mode, which can achieve stable resistance switching, not only avoiding the shortcomings of ion diffusion, but also enabling the controllable switching of the resistance of the memristor between high and low resistance states.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is:

[0006] A method for realizing memristor memristance based on ion diffusion and phase change mechanism, wherein the structure of the memristor includes upper and lower electrode layers and an intermediate functional layer made of Ag2Te semiconductor material. The method is characterized in that an ultra-low voltage is applied to the memristor to cause phase change and ion diffusion in the Ag2Te semiconductor, thereby causing a resistive change to realize the memristor memristance.

[0007] According to the above scheme, the ultra-low voltage is between 0.35-0.5V, and the voltage is applied in a pulse mode.

[0008] Furthermore, when applying ultra-low voltage, a unidirectional positive pulse voltage signal input mode is adopted. In this mode, the pulse width is 0.2V, the pulse time can be 1-10 seconds, and the interval time can be 1-10 seconds.

[0009] Furthermore, the pulse mode of the applied voltage can be selected as a continuous pulse mode or a square (rectangular) pulse mode. In the continuous pulse mode, the reference voltage can be set to 0V, the amplitude voltage to 0.4V, the amplitude to positive and negative modes, and the rate setting is preferably 0.6V / min; in the square (rectangular) pulse mode, the reference voltage can be set to 0.2V, the amplitude voltage to 0.2V, the amplitude to positive mode, and the pulse time and interval time can be set to 1s.

[0010] According to the above scheme, the ion diffusion is Ag + Diffusion; the phase transition is from monoclinic Ag2Te phase ( α=γ=90°,β=124.153°) transforms into cubic Ag2Te phase ( α=β=γ=90°). The above materials with different crystal structures have different electrical transport properties, so that the memristive material switches between high and low resistance states to realize the memristive function.

[0011] Specifically, when an ultra-low voltage of about 0.35V is applied, the Ag2Te semiconductor material will undergo Ag + Diffusion, this ion diffusion will cause the functional layer material (Ag2Te) of the device to deviate from the 2:1 chemical ratio in the direction of the electric field, and the Ag content will decrease. This ion diffusion can not only affect the resistance of the entire device but also promote the phase change of Ag2Te. When Ag occurs in the Ag2Te semiconductor material, + When the Ag content decreases due to ion diffusion, the threshold voltage for phase transition decreases, allowing phase transition and resistive switching to occur at ultra-low voltages. This ion diffusion is both reversible and unstable. Therefore, the present invention designs a unidirectional positive pulse voltage signal input mode, which can achieve stable resistive switching, avoiding the drawbacks of ion diffusion while also enabling controllable switching of the memristor's resistance between high and low resistance states.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] Unlike conventional memristors based on conductive filaments, where random filament formation reduces device response and increases device power consumption, the present invention provides a method for implementing memristor memristance based on ion diffusion and phase change mechanisms. The ion diffusion and phase change induced by an applied voltage in this invention offer low power consumption and high speed, resulting in a phase transition threshold voltage of only approximately 0.35V. When a rectangular pulse voltage is input, the resistance changes rapidly, and the device can quickly switch between high and low resistance states in response to voltage changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the structure of the memristor based on ion diffusion and phase change mechanism in Example 1.

[0015] Figure 2 Schematic diagram of the structure of the memristor based on ion diffusion and phase change mechanism in Example 2.

[0016] Figure 3 These are scanning transmission electron microscopy (STEM) images and energy dispersive spectroscopy (EDS) images of the silver ion diffusion in the memristor prepared in Example 1 under ultra-low voltage induction.

[0017] Figure 4 This is the electron diffraction of the two phase structures of the memristor prepared in Example 1, the phase change region and the non-phase change region at a voltage of 0.35V.

[0018] Figure 5 The scanning transmission electron microscopy (STEM) images, selected area electron diffraction (SAED) images and structural model of the two phase structures before and after the phase change in the memristor prepared in Example 1 are shown.

[0019] Figure 6 Graph showing the electrical performance of the memristor prepared in Example 1.

[0020] Figure 7 This is a scanning transmission electron microscopy (STEM) image of the interface structure when a phase change occurs in the memristor prepared in Example 2.

[0021] Figure 8 This is the DC IV curve of the memristor prepared in Example 2.

[0022] Figure 9 This is the RV curve of the memristor prepared in Example 2 under rectangular wave pulse voltage.

[0023] Specific embodiment

[0024] In order to better understand the present embodiment, the content of the present embodiment is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present embodiment and are not used to limit the present embodiment.

[0025] In the following embodiments, the memristor comprises, from bottom to top, a substrate, a bottom electrode, a resistive switching layer, and a top electrode. The resistive switching layer is made of Ag2Te semiconductor material and has a thickness of 50-100 nm. The bottom electrode is made of Pt and has a thickness of 500-1000 nm. The top electrode is made of Pt or Ag and has a thickness of 500-1000 nm. The memristor is fabricated by sequentially depositing the bottom electrode, resistive switching layer, and top electrode on the substrate surface using vacuum evaporation or magnetron sputtering.

[0026] In the following embodiments, in order to implement the memristor memristor method, two memristor structures are used as implementation objects. Among them, the memristor structure specifically used in embodiment 1 is as follows: Figure 1 As shown, from bottom to top, it includes a Si substrate, a Pt bottom electrode, a resistive switching layer (Ag2Te), and a Ag top electrode. The bottom electrode is 1000 nm thick, the top electrode is 1000 nm thick, and the resistive switching layer is 100 nm thick. The memristor used in Example 2 differs from the memristor in Example 1 in that the bottom electrode is replaced with Pt. The memristor in Example 1 is labeled Memristor A; the memristor in Example 2 is labeled Memristor B.

[0027] The preparation method of memristor A specifically comprises the following steps:

[0028] 1) Ultrasonic cleaning of the silicon substrate with deionized water, ethanol, and acetone for 30 min in sequence, and drying with nitrogen;

[0029] 2) Use vacuum evaporation equipment to deposit Pt as the lower electrode. Pump the vacuum in the coating chamber to a suitable vacuum degree (10 -1 Pa), and pre-heat the substrate and Pt to remove moisture and enhance the film-substrate bonding strength; then continue to vacuum to reach a vacuum degree of 10 -3 Pa or less; when the vacuum degree reaches the requirement, the coating material is pre-melted (1772℃), and then the temperature is increased to reach the evaporation temperature of the coating material (3827℃); during evaporation, the substrate is heated to 300℃ to improve the bonding force between the deposition gas and the substrate.

[0030] 3) Using magnetron sputtering equipment, an Ag2Te thin film was prepared on the Pt electrode. The Ag2Te block prepared by the melt method was fully ground into a disc-shaped target (50 mm in diameter) and loaded into the magnetron sputtering vacuum chamber. The background vacuum of the chamber during magnetron sputtering was 2.5×10 -3 Pa, the working gas is argon, the working pressure is 0.8Pa, and the sputtering power is 150W.

[0031] 4) Use vacuum evaporation equipment to deposit Ag as the top electrode. This process is the same as in step 2). However, due to the different electrode materials, the pre-melting and evaporation temperatures of the coating material are different: 962°C and 2212°C, respectively. During the evaporation process, ensure that the top and bottom electrodes do not touch to prevent short circuits.

[0032] The preparation method of the memristor B specifically comprises the following steps:

[0033] (1) Ultrasonic cleaning of the silicon substrate with deionized water, ethanol, and acetone for 30 min in sequence, and then drying with nitrogen;

[0034] (2) Use magnetron sputtering equipment to deposit Pt as the lower electrode on the silicon substrate. Place the substrate and metal platinum target in (1) into the magnetron sputtering vacuum chamber, and calibrate the deposition rate of metal platinum in the vacuum chamber by quartz crystal oscillator. The vacuum degree of the chamber during magnetron sputtering is 0.5 Pa, and the rate is

[0035] (3) Ag2Te thin film was prepared on the Pt electrode using magnetron sputtering equipment. The Ag2Te block obtained by the melting reaction was fully ground into a disc-shaped target (diameter 50 mm) and loaded into the magnetron sputtering vacuum chamber. The background vacuum of the chamber during magnetron sputtering was 2.5×10 -3 Pa, the working gas is argon, the working pressure is 0.8Pa, and the sputtering power is 150W.

[0036] (4) Using magnetron sputtering equipment to deposit Pt as the upper electrode, this process is consistent with step (2).

[0037] Example 1

[0038] A method for realizing memristor memristance based on ion diffusion and phase change mechanism. The memristor A prepared in this embodiment is placed on a 2H4B-nanochip, and its electrical performance data can be obtained with the help of a sample rod power supply system dedicated to an in-situ transmission electron microscope. During the experiment, first, the voltage is manually increased, that is, it is manually increased from 0V in increments of 0.01V until a resistance change occurs. Based on this, after determining that the threshold voltage of the resistance change is about 0.35, the voltage application mode is changed to a pulse mode. In the pulse mode, continuous pulse mode and square (rectangular) pulse mode can be selected: in the continuous pulse mode, the reference voltage is set to 0V, the amplitude voltage is 0.4V, the amplitude is selected in positive and negative mode, the rate is set to 0.6V / min, the number of cycles is 3, and the results are as follows: Figure 3-6 As shown in a; in square (rectangular) pulse mode, the reference voltage is set to 0.2V, the amplitude voltage is 0.2V, the amplitude is only checked in the forward mode, the pulse time and interval time are both set to 1s, and the number of cycles is 5. The result is as follows Figure 6For safety reasons, all the above voltage application methods have a current limit of 0.01A.

[0039] Figure 3 、 Figure 4 、 Figure 5 and Figure 6 This is a picture of the memristor A prepared in this example taken during the in-situ transmission experiment. As the applied voltage slowly increases (manually controlled, increasing by 0.01V), silver ion diffusion begins to occur in the memristor A prepared in this example. Figure 3 ab. Figure 3 Figure c shows that silver ions diffuse along the direction of applied voltage and form a non-uniform content phenomenon in the region. When the voltage reaches 0.35V, the phase transition occurs first on the silver-less side at the same voltage, as shown in Figure 5. Figure 4 The electron diffraction patterns and structures of the two phase regions before and after the phase transition are as follows: Figure 5 , which shows that after the phase transition, Ag2Te has completely different structures and orientation relationships (α-[0-10] and β-

[110] ). In this embodiment, the diffusion of silver ions changes the defect concentration in different regions of the material, and the increase in silver ion vacancies increases the resistance of the material. At the same time, the two completely different phase structures after the phase transition change the electrical transport properties in the Ag2Te semiconductor material. The interaction between the two makes the memristor A prepared in this embodiment have controllable high and low resistance characteristics under ultra-low voltage induction. However, when a negative voltage is applied, the memristor resistance phenomenon of the memristor prepared in this embodiment is not obvious, as shown in FIG. Figure 6 a, which is due to the reduction of silver ion vacancies caused by negative voltage. Based on this, the memristor A prepared in this embodiment can achieve stable memristive phenomenon by changing the applied voltage to a unidirectional positive pulse voltage with a pulse width of 0.2V, a pulse time of 1s, and an interval time of 1s. Figure 6 b.

[0040] Example 2

[0041] A method for realizing memristor memristance based on ion diffusion and phase change mechanism, wherein the experimental process is consistent with that of Example 1.

[0042] Figure 7 、 Figure 8 and Figure 9 The following are pictures and electrical performance curves of the memristor B prepared in this example, taken during the in-situ transmission experiment. When the voltage is applied to 0.35V, two phases coexist in the memristor B prepared in this example, namely α phase (monoclinic Ag2Te) and β phase (cubic Ag2Te), appear. Figure 7 . Figure 8 and Figure 9 The electrical performance curves are shown when different types of pulse voltages are input. Figure 8In the experiment, when a continuous pulse voltage (-0.4V-0.4V) is applied, the current changes with the voltage and suddenly changes near the threshold voltage, indicating that the resistance of the material suddenly changes.

[0043] Figure 9 This is the sudden change of resistance with voltage when a unidirectional square (rectangular) positive pulse voltage (pulse width 0.2V, pulse time 1-10s, interval time 1-10s) is applied. Figure 8 and Figure 9 Both demonstrate the working performance of the memristor B prepared in this embodiment, which is a reversible transition and is rapidly sensitive to voltage changes.

[0044] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several improvements and changes can be made without departing from the creative concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for realizing the operation of a memristor, wherein the structure of the memristor comprises upper and lower electrode layers and an intermediate functional layer made of Ag2Te semiconductor material, characterized in that: Applying an ultra-low voltage of 0.3-0.5 V to the memristor causes resistance change, and the memristor memristance is realized based on ion diffusion and phase change mechanisms.

2. The operating method according to claim 1, characterized in that: When applying ultra-low voltage, a unidirectional positive pulse voltage signal input mode is used, with the pulse high and low voltages being 0.4 V and 0.2 V respectively, the pulse width being 0.2 V, the pulse time being 1-10 seconds, and the interval time being 1-10 seconds.

3. The operating method according to claim 1, characterized in that: When applying ultra-low voltage, the continuous pulse mode was used, the reference voltage was set to 0 V, the amplitude voltage was set to 0.4 V, the amplitude was selected in positive and negative mode, and the rate was set to 0.6 V / min.

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