Self-rectifying ZnO thin film memristor and preparation method thereof

Abstract

The application discloses a self-rectifying ZnO thin film memristor and a preparation method thereof. The device resistance change layer is composed of binary metal oxide ZnO, the bottom electrode is composed of ITO, and the metal top electrode is composed of W. The ZnO thin film resistance change layer of the device is prepared by using a simple and efficient glue uniformity method process, and the top electrode of the device is designed by using a magnetron sputtering film coating technology. The application has important application potential in the high-density three-dimensional integration of the device in the aspect of the device architecture physical layer without additionally introducing a series rectifier device and a nonlinear resistor. In the aspect of the device performance, the high-density storage of the multi-resistance state of a single device storage unit can be realized by orderly regulating an applied physical field, and the self-rectifying multi-value resistance change storage has the characteristics of high stability and non-volatility, and therefore has important application prospects in the next generation of non-volatile high-density memories.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microelectronic devices, and particularly relates to a self-rectifying ZnO thin film memristor and a preparation method thereof. BACKGROUND

[0002] The memristor is the fourth basic circuit element besides the capacitor, the inductor and the resistor, and has a series of advantages such as simple structure, low power consumption, high speed, realization of non-volatile high-density storage and miniaturization, and is considered to be one of the strong competitors of the next generation of non-volatile memories. Based on the simple "sandwich device structure" of the memristor, the integrated structure of the nano-structured memristor can adopt the cross array device structure with the highest theoretical integration degree of 4F 2 . However, the cross array device structure often has a serious crosstalk current problem, which will cause information misreading of the device. In order to overcome the adverse effects of the crosstalk current on the stability of the device, the 1R structure storage unit integrated process with the self-rectifying characteristic is simpler and more economical, and the adverse effects of the crosstalk current can be overcome without additionally introducing a series rectifier and a nonlinear resistor, which avoids the interference of the introduction of external devices on the performance and miniaturized integrated application of the device. These advantages make the self-rectifying memristor have important development potential in high-density three-dimensional integrated applications. As the third generation semiconductor material, the binary metal oxide ZnO has important application prospects in the fields of photoelectric technology and high-density information storage due to its simple preparation process, high temperature resistance and small toxicity. However, how to realize the controllable design of the self-rectifying multi-value storage of the ZnO memristor is still a problem to be solved at present.

[0003] Yan Xiaobing et al. of Hebei University disclosed a "memristor based on zinc oxide and a preparation method thereof (CN109461814A)", which prepared a middle ZnO medium resistance layer and a W top electrode by a magnetron sputtering method, and designed a zinc oxide memristor. The device is composed of an FTO bottom electrode, a ZnO middle medium layer and a W top electrode. Wang Jingrui et al. of Ningbo Institute of Technology disclosed a "full-solution preparation method of an oxide memristor", with the authorization announcement number CN107946459B. The AZO bottom electrode layer was prepared by a sol-gel method, the middle ZnO medium layer was prepared by a sol-gel method, and the graphene top electrode layer was deposited by a vacuum filtration method, and an oxide memristor was designed. The device is composed of an AZO substrate, a ZnO middle medium layer and a graphene top electrode. The above disclosed contents have relatively complex preparation processes, which is not conducive to the cost control and commercial application of the device. Secondly, the resistance switching of the device is relatively low, unstable and has low reliability; the device does not realize the self-rectifying characteristic and the regulation and control of high-density multi-value storage.

[0004] Based on the above analysis, a memristor with high resistance switching, stability and reliability, and can realize self-rectifying characteristics and high-density multi-value storage control is currently in urgent need in the industry. SUMMARY

[0005] In view of the above shortcomings, the application discloses a self-rectifying ZnO thin film memristor and a preparation and multi-value storage control method thereof. The self-rectifying device adopts a W / ZnO / ITO device structure, and realizes controllable modulation of self-rectifying multi-value resistance change storage of the device through an ordered modulation bias voltage excitation mode, and has important application prospects in the field of next-generation nonvolatile high-density storage.

[0006] The application is realized through the following technical means:

[0007] The application relates to a self-rectifying ZnO thin film memristor, and realizes controllable modulation of multi-value resistance change storage of the device. The resistance change layer of the device is composed of a binary metal oxide ZnO, the bottom electrode is composed of ITO, and the metal top electrode is composed of W. The ZnO thin film resistance change layer of the device is prepared by using a simple and efficient glue uniformization process, and the top electrode of the device is designed by using a magnetron sputtering film coating technology.

[0008] A preparation method of a self-rectifying ZnO thin film memristor, and the specific steps are as follows:

[0009] (1) 0.5mM zinc acetate dihydrate is used as a zinc source, 20mL isopropyl alcohol is used as a solvent, and 600ul ethanolamine is used as a stabilizer, the three are mixed and magnetically stirred to obtain a ZnO precursor solution.

[0010] (2) A suitable amount of ZnO precursor solution is taken by using a pipette and dropped on an ITO glass sheet with a size of 1cm*2cm which is placed statically, and a uniform ZnO precursor film is formed by glue uniformization, the spin-coated film sample is dried for 5-20min, and the above glue uniformization step is repeated until the film thickness reaches the experimental requirement, and an ITO sample is obtained.

[0011] Further, the glue uniformization rate is 1000-3500r / min, and the glue uniformization time is 10-30s.

[0012] (3) After the glue uniformization step is completed, the ITO sample is dried and then placed in a muffle furnace for rapid annealing, and after natural cooling to room temperature, the ITO sample is taken out, and a once-annealed ZnO thin film with a uniform surface is obtained.

[0013] Further, the muffle furnace annealing temperature is 350-700 DEG C, and the reaction time is 5-20min.

[0014] (4) again aspirate the ZnO precursor solution in step (1) onto the ZnO thin film sample after the first annealing, so that the uniform coating forms a uniform thin film, and then dry the thin film for 5-20 min, repeat the uniform coating step until the thin film thickness reaches the requirement, to obtain a second uniform coating sample;

[0015] (5) after drying the second uniform coating sample, place it in a muffle furnace for annealing, and then take it out after natural cooling to room temperature, to obtain a ZnO thin film sample after the second annealing;

[0016] (6) take out the ZnO thin film sample after the second annealing, wash it clean with deionized water after natural cooling to room temperature, and then dry it naturally, to obtain a ZnO thin film sample required by the process;

[0017] (7) use a metal mask plate magnetron sputtering film technology to sputter deposit a certain thickness and morphology of a top electrode on the surface of the ZnO thin film sample, to realize the design of the ZnO thin film memristor. According to the structural design requirements of the device, the top electrode of the device can be selected as a metal electrode or a non-metal electrode.

[0018] By orderly regulating the applied bias voltage of the device, controllable modulation of the non-volatile self-rectifying multi-value storage of the device is realized. In addition, the multi-value storage regulation of the device can also use regulation of the limiting current, magnetic field, light field or other physical field excitation to realize controllable modulation of the multi-value resistance change storage.

[0019] The beneficial effects of the present application are as follows:

[0020] 1. At the physical layer of the device architecture, without additional introduction of series rectifier devices and nonlinear resistors, the self-rectifying ZnO thin film memristor can effectively overcome the adverse effects of crosstalk current on the stability of the device, and has important application potential in the high-density three-dimensional integration of the device.

[0021] 2. At the device performance level, through orderly regulation of the applied physical field, high-density storage of the multi-resistance state of a single device storage unit can be realized, which has important application prospects in the next generation of non-volatile high-density memory.

[0022] 3. The self-rectifying ZnO thin film memristor designed in the present application has the characteristics of high stability and non-volatile self-rectifying multi-value resistance change storage, and has potential application advantages as the next generation of non-volatile high-density memory. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Figure 1 is a structural schematic diagram of the device designed in Embodiment 1 of the present application;

[0024] Figure 2The FESEM image of the surface morphology of the ZnO thin film sample prepared in Embodiment 1 of the present application is shown in the figure;

[0025] Figure 3 The FESEM image of the cross-sectional morphology of the ZnO thin film sample prepared in Embodiment 1 of the present application is shown in the figure;

[0026] Figure 4 The XPS image of the surface Zn2p of the ZnO thin film sample prepared in Embodiment 1 of the present application is shown in the figure;

[0027] Figure 5 The XPS image of the surface O1s of the ZnO thin film sample prepared in Embodiment 1 of the present application is shown in the figure;

[0028] Figure 6 The semi-logarithmic I-V curve of the device prepared in Embodiment 2 under 50 cycles of voltage scanning is shown in the figure;

[0029] Figure 7 The semi-logarithmic I-V curve of the device prepared in Embodiment 2 under forward bias voltage regulation is shown in the figure. DETAILED DESCRIPTION

[0030] The present application will be described in detail below with reference to the accompanying drawings.

[0031] Embodiment 1

[0032] Preparation of a self-rectifying ZnO thin film memristor

[0033] The present embodiment is the preparation of a self-rectifying ZnO thin film memristor, and the structure is shown in the figure. Figure 1 The top electrode of the device is a metal W electrode (thickness of about 80 nm), the middle resistive layer is ZnO (thickness of about 100 nm), and the bottom electrode is an ITO substrate.

[0034] The specific steps for designing the ZnO memristor with self-rectifying characteristics are as follows:

[0035] (1) Preparation of ZnO precursor solution: prepare a precursor solution containing 0.5 mM zinc acetate dihydrate, 20 mL isopropyl alcohol, and 600 μL ethanolamine, and place the precursor solution under a magnetic stirrer for stirring to obtain a ZnO precursor solution.

[0036] (2) Use a pipette to take 100 μL of the ZnO precursor solution and drop it on a stationary ITO glass sheet with a size of 1 cm x 2 cm, uniformly coat to form a uniform ZnO precursor film, dry the spin-coated film sample for 5 min, repeat the uniform coating step 4 times to complete the above-mentioned uniform coating step, and obtain an ITO sample. The uniform coating rate is 2000 r / min, and the uniform coating time is 20 s.

[0037] (3) After the uniform coating operation is completed, the ITO sample is dried and then placed in a muffle furnace for rapid annealing. After the sample is naturally cooled to room temperature, it is taken out, and a ZnO thin film sample with a uniformly annealed surface is obtained. The annealing temperature of the muffle furnace is 500°C, and the annealing time is 10 minutes.

[0038] (4) The ZnO precursor solution in step (1) is again taken up to the ZnO thin film sample after the first annealing, so that the uniform coating forms a uniform thin film. The thin film is then dried for 5-20 minutes, and the uniform coating step is repeated until the thin film thickness reaches the required value, and a second uniform coating sample is obtained.

[0039] (5) The second uniform coating sample is dried and then placed in a muffle furnace for annealing. After the sample is naturally cooled to room temperature, it is taken out, and a ZnO thin film sample after the second annealing is obtained.

[0040] (6) The ZnO thin film sample after the second annealing is taken out, washed with deionized water, and naturally air-dried, and a ZnO thin film sample with a thickness of 100 nm is obtained. The surface and cross-sectional morphologies of the sample are shown in Figure 2 and Figure 3 .

[0041] As shown in Figure 2 and Figure 3 , the thickness of the ZnO thin film sample is about 100 nm, and the surface is uniform.

[0042] As shown in Figure 4 , the XPS peak of Zn 2p on the surface of the sample is composed of two spin-orbit coupling energy levels of Zn 2p 3 / 2 and Zn 2p 1 / 2 , which are symmetrical Gaussian-Lorentzian peaks, indicating that the valence state of Zn is relatively single. The binding energy of Zn 2p 1 / 2 is 1022 eV, which is close to the Zn 2p 1 / 2 binding energy (1021.75 eV) of the hexagonal wurtzite bulk structure ZnO, indicating that Zn is in an oxidized state, i.e., the Zn element in the ZnO thin film sample mainly exists in the form of Zn 2+ .

[0043] As shown in Figure 5 , the XPS peak of O 1s on the surface of the sample can be decomposed into three Gaussian fine peaks, i.e., there are three components of O, in which the peak at a binding energy of 529.8 eV corresponds to the lattice oxygen of the sample, and the peaks at binding energies of 531.6 eV and 532.6 eV correspond to the oxygen vacancies on the surface of the sample and the hydroxyl oxygen adsorbed on the surface, respectively.

[0044] (7) Using the metal mask magnetron sputtering film technology, a certain thickness and morphology of metal W top electrode is sputtered and deposited on the surface of the ZnO thin film sample prepared in step (6), so as to realize the design of W / ZnO / ITO structure memristor. Among them, the thickness of the metal W top electrode is about 80 nm, and the diameter is 5 μm.

[0045] Example 2

[0046] Preparation of a self-rectifying ZnO thin film memristor

[0047] The specific steps of designing a ZnO memristor with self-rectifying characteristics are as follows:

[0048] (1) Preparation of ZnO precursor solution. Prepare a precursor solution containing 0.5 mM zinc acetate dihydrate, 20 mL isopropyl alcohol, and 600 μL ethanolamine, and stir the precursor solution under a magnetic stirrer.

[0049] (2) Use a pipette to take 100 μL of the precursor solution in step (1) and drop it on a static ITO glass sheet with a size of 1 cm x 2 cm, and evenly glue to form a uniform ZnO precursor film. Dry the spin-coated film sample for 20 min, and repeat the above glueing step 4 times. The glueing rate is 3500 r / min, and the glueing time is 30 s.

[0050] (3) After the glueing operation is completed, the ITO sample in step (2) is dried and placed in a muffle furnace for rapid annealing. After natural cooling to room temperature, it is taken out to obtain a uniform ZnO thin film sample after one-time annealing. The muffle furnace annealing temperature is 700℃, and the time is 20 min.

[0051] (4) Take an appropriate amount of ZnO precursor solution in step (1) again to the ZnO thin film sample after one-time annealing, so that the glueing forms a uniform film. Then dry the film for 5-20 min, repeat the glueing step until the film thickness reaches the requirement, and obtain a two-time glueing sample;

[0052] (5) After drying the two-time glueing sample, it is placed in a muffle furnace for annealing. After natural cooling to room temperature, it is taken out to obtain a ZnO thin film sample after two-time annealing;

[0053] (6) The ZnO thin film sample after two-time annealing is taken out, washed with deionized water, and naturally dried to obtain a ZnO thin film sample with a thickness of 150 nm.

[0054] (7) Using the metal mask magnetron sputtering film technology, a certain thickness and morphology of metal W top electrode is sputtered and deposited on the surface of the ZnO thin film sample prepared in step (6), so as to realize the design of W / ZnO / ITO structure memristor. Among them, the thickness of the metal W top electrode is about 80 nm, and the diameter is 5 μm.

[0055] Example 3

[0056] Preparation of a self-rectifying ZnO thin film memristor

[0057] The specific steps of designing a ZnO memristor with self-rectifying characteristics are as follows:

[0058] (1) Preparation of ZnO precursor solution. Prepare a precursor solution containing 0.5 mM zinc acetate dihydrate, 20 mL isopropyl alcohol, and 600 μL ethanolamine, and stir the precursor solution under a magnetic stirrer.

[0059] (2) Use a pipette to take 100 μL of the precursor solution in step (1) and drop it on a static ITO glass sheet with a size of 1 cm x 2 cm, and evenly glue to form a uniform ZnO precursor film. Dry the spin-coated film sample for 15 min, and repeat the above glueing step 4 times. The glueing rate is 1000 r / min, and the glueing time is 10 s.

[0060] (3) After the glueing operation is completed, the ITO sample in step (2) is dried and placed in a muffle furnace for rapid annealing. After natural cooling to room temperature, it is taken out to obtain a uniform ZnO thin film sample after one-time annealing. The muffle furnace annealing temperature is 350℃, and the time is 5 min.

[0061] (4) Take an appropriate amount of ZnO precursor solution in step (1) again to the ZnO thin film sample after one-time annealing, so that the glueing forms a uniform film. Then dry the film for 5-20 min, repeat the glueing step until the film thickness reaches the requirement, and obtain a two-time glueing sample;

[0062] (5) After drying the two-time glueing sample, it is placed in a muffle furnace for annealing. After natural cooling to room temperature, it is taken out to obtain a ZnO thin film sample after two-time annealing;

[0063] (6) The ZnO thin film sample after two-time annealing is taken out, washed with deionized water, and naturally dried to obtain a ZnO thin film sample with a thickness of 60 nm.

[0064] (7) Using the metal mask magnetron sputtering film technology, a certain thickness and morphology of metal W top electrode is sputtered and deposited on the surface of the ZnO thin film sample prepared in step (6), so as to realize the design of W / ZnO / ITO structure memristor. Among them, the thickness of the metal W top electrode is about 80 nm, and the diameter is 5 μm.

[0065] Test Example 1

[0066] A multi-value storage control method of a self-rectifying ZnO thin film memristor

[0067] The embodiment is a multi-value storage control method of a self-rectifying ZnO thin film memristor. Under the optimized process conditions, the upper electrode of the device is a metal W electrode (the thickness is about 80 nm), the middle resistive layer is a ZnO thin film (the thickness is about 100 nm), and the bottom electrode is an ITO conductive glass substrate. In terms of device testing and control, the forward bias voltage of the device is controlled in order to realize the controllable modulation of the multi-value resistive random access memory of the device.

[0068] The specific steps of the multi-value storage control method of the device are as follows:

[0069] 1. Since the device does not need to be electrically activated, as shown in Figure 1 , in order to prevent the device from being broken down, a limiting current of 5 mA is set, and a bias voltage is directly applied to the W top electrode of the device to test and control the resistive random access memory characteristics of the device, while keeping the ITO bottom electrode of the device grounded during the testing and control process.

[0070] 2. Performance test of the device. As shown in Figure 6 , under 50 cycles of voltage scanning (in which the forward bias voltage of the device is set to 3 V), the ZnO thin film memristor shows high stability, high reliability, and non-volatile self-rectifying resistive random access memory characteristics. The set voltage and reset voltage of the device can be stably maintained at about 1 V and -0.2 V, respectively, showing reliable non-volatile resistive random access memory characteristics.

[0071] 3. In terms of multi-value storage control of the device. As shown in Figure 7 , the reverse bias voltage of the device is fixed at -1.5 V, and the forward bias voltage of the device is sequentially controlled from 3 V, 3.5 V to 4 V, realizing the controllable modulation of the multi-value resistive random access memory of the device in the low resistance state and the high resistance state.

[0072] The above embodiments are only device designs and multi-value storage control methods under optimized process conditions and control methods. Any multi-value storage control method involving the structure of the ZnO thin film memristor, the design and preparation process of the resistive layer, the preparation and equivalent electrode replacement design of the top electrode or bottom electrode, and the replacement of the external physical field to realize the multi-value storage control method all belong to the protection scope of the present patent. Including but not limited to the following cases:

[0073] ①In the structural design of the device, for the bottom electrode of the device, in addition to using ITO bottom electrode, other electrodes can be used to replace, such as using FTO glass substrate or other suitable electrode for uniform coating process.

[0074] ②In the structural design of the device, for the ZnO resistive switching layer of the device, in addition to using uniform coating process, plasma enhanced atomic layer deposition, magnetron sputtering deposition, electron beam evaporation deposition technology, chemical vapor deposition, hydrothermal method and other technologies can be used for preparation. In the preparation of resistive switching material, in addition to using isopropyl alcohol, ethylene glycol methyl ether or ethanol can be used to replace ZnO precursor solution. In addition, in addition to using single layer ZnO thin film, hydroxyl iron or other substances can be grown on ZnO to form heterojunction structure, and organic matter such as PVP(polyvinyl) can be doped in ZnO nanometer thin film structure to achieve the purpose of optimizing the device structure.

[0075] ③In the structural design of the device, for the W top electrode of the device, in addition to using magnetron sputtering deposition, other methods can be selected to prepare metal upper electrode, such as thermal evaporation, chemical vapor deposition, molecular beam epitaxy deposition, etc. In addition, according to the requirements of the structure design of the device, the top electrode of the device can choose other metal electrode, or non-metal electrode.

[0076] ④In the multi-value storage control of the device, in addition to using external bias voltage for multi-value storage control, control limiting current, external light field, magnetic field and other physical field excitation can be used to realize.

Claims

1.A self-rectifying ZnO thin film memristor, comprising: a resistive switching layer, a bottom electrode, and a metal top electrode; the resistive switching layer is composed of binary metal oxide ZnO, the bottom electrode is composed of ITO, and the metal top electrode is composed of W; the resistive switching layer is prepared by a spin coating method and has a thickness of 60-150 nm; the top electrode is prepared by a magnetron sputtering coating technology; and the self-rectifying ZnO thin film memristor is prepared by the following method, comprising: (1) mixing 0.5 mM zinc acetate dihydrate, 20 mL isopropyl alcohol, and 600 μL ethanolamine, and then magnetically stirring to obtain a ZnO precursor solution for standby; (2) taking an appropriate amount of the ZnO precursor solution onto an ITO glass sheet to form a uniform ZnO precursor film by spin coating, and then drying the film for 5-20 min, and repeating the spin coating step until the film thickness reaches the required value to obtain an ITO spin coating sample; (3) drying the ITO spin coating sample and then placing it in a muffle furnace for annealing at a temperature of 350-700 ℃ for 5-20 min; after natural cooling to room temperature, the sample is taken out to obtain a ZnO thin film sample after first annealing for standby; (4) again taking an appropriate amount of the ZnO precursor solution in step (1) onto the ZnO thin film sample after first annealing to form a uniform film by spin coating, and then drying the film for 5-20 min, and repeating the spin coating step until the film thickness reaches the required value to obtain a secondary spin coating sample; (5) drying the secondary spin coating sample and then placing it in a muffle furnace for annealing at a temperature of 350-700 ℃ for 5-20 min; after natural cooling to room temperature, the sample is taken out to obtain a ZnO thin film sample after second annealing; (6) taking out the ZnO thin film sample after second annealing, washing it with deionized water after natural cooling to room temperature, and then naturally air-drying to obtain a ZnO thin film sample meeting the process requirements; (7) sputtering and depositing a top electrode on the surface of the ZnO thin film sample in step (6) by a magnetron sputtering coating technology using a metal mask plate to obtain a self-rectifying ZnO thin film memristor. 2.The self-rectifying ZnO thin film memristor according to claim 1, wherein: the spin coating rate in step (2) is 1000-3500 r / min, and the spin coating time is 10-30 s. 3.The self-rectifying ZnO thin film memristor according to claim 1, wherein: the spin coating rate in step (4) is 1000-3500 r / min, and the spin coating time is 10-30 s.

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