A nonvolatile memory based on elemental tellurium thin film and a preparation method thereof

Abstract

The application aims to provide a single-element tellurium thin film based nonvolatile memory and a preparation method thereof, and belongs to the technical field of ferroelectric memories. The core area of the nonvolatile memory adopts tellurene which has extremely strong stability in air, greatly improves the stability of the memory, and reduces the difficulty of preparing the memory at room temperature, and solves the problem that the traditional two-dimensional material as a memory unit will appear element segregation in a long cycle process, resulting in device failure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ferroelectric memory, and particularly relates to a nonvolatile memory based on elemental tellurium thin film and a preparation method thereof. BACKGROUND

[0002] Nonvolatile memory units are the main components of digital, portable, independent electronics, and are attracting more and more attention due to their miniaturization, low power consumption and reliable data storage, which are very suitable for solving the problems of large data capacity and integration. Memory based on ultrathin two-dimensional materials has been studied and reported (Nature Electronics, 2021, 4, 399-404.; Nature Electronics, 2022, 5, 248-254.), which has great development potential due to its excellent electrical properties and storage density. Among them, the memory device based on two-dimensional ferroelectric material has high storage density, low power consumption, high storage speed, anti-radiation and non-destructive reading, etc., and is considered as the development trend of the next generation of new memory (Nature Electronics, 2020, 3, 581.). The traditional ferroelectric memory structure generally includes a substrate, a conductive layer, a channel material, a ferroelectric thin film layer, an electrode layer, and a complex gate layer, a variable resistance layer, a protective layer, etc. (Nature Electronics, 2020, 3, 588-597.); but the structure is complex, the process is complicated, the process is difficult, the energy pinning and contact problems between different layers, which poses great challenges to the stability, extreme environment adaptability and cost of the whole memory.

[0003] The stability of the device is particularly important in future development. Inspired by the human brain and neurotransmitter transmission structure, scientists take the process of neuron and synaptic stimulation, information integration, pulse emission, etc. as the design inspiration to construct a series of brain-inspired computing models, device prototypes and integrated architecture, i.e. brain-like computing or neuromorphic computing, which injects strong driving force for the development of future artificial intelligence. Brain-like computing has already shown its potential in autonomous driving, artificial intelligence, etc. due to its high efficiency, low power consumption, parallel computing and high fault tolerance. The further development of brain-like computing is strongly dependent on the improvement of hardware foundation. In the process of brain-like computing, each stimulation will bring new weight distribution. In the process of hundreds of millions of times of calculation, the accuracy of weight update is a key step to determine the accuracy of calculation. Therefore, the non-volatile storage structure as the basic hardware unit must maintain strong stability under the stimulation of hundreds of millions of times (Advanced Materials, 2020, 32, 2004659.). Unfortunately, for almost all types of non-volatile memory, the change of composition and crystal structure of the memory material caused by element segregation under high-intensity stimulation for hundreds of millions of times of cycles will cause the failure of the device (Science, 2021, 374(6573): 1321-1322.; Science, 2021, 374(6573): 1390-1394.), which is a difficulty that must be solved for the next generation of high-speed memory.

[0004] Therefore, it is the development direction of the next generation of high-performance storage and computing integrated devices to find a new material and design a non-volatile memory with simple structure and good stability. SUMMARY

[0005] In view of the problems in the background art, the purpose of the present application is to provide a non-volatile memory based on a single tellurium thin film and a preparation method thereof. The core area of the non-volatile memory of the present application adopts tellurene which has strong stability in air, greatly improving the stability of the memory and reducing the difficulty of preparing the memory at room temperature, solving the problem that traditional materials and two-dimensional materials as memory units will all appear element segregation in the long cycle process, leading to device failure.

[0006] To achieve the above purpose, the technical scheme of the present application is as follows:

[0007] A non-volatile memory based on a single tellurium thin film, from bottom to top, is a substrate, a semiconductor channel layer and an electrode layer; the material of the semiconductor channel layer is a single tellurium thin film with a thickness of 0.4 nm-20 nm.

[0008] Further, the substrate material is silicon / silicon dioxide, flexible film, HfO2 film, aluminum oxide film, etc.

[0009] Further, the electrode material is Cr / Au.

[0010] Further, the nonvolatile memory based on the elemental tellurium thin film is excited by an in-plane electric field or an out-of-plane electric field to realize storage writing and reading.

[0011] The application further provides a preparation method of the nonvolatile memory based on the elemental tellurium thin film, comprising the following steps:

[0012] Step 1. Dropping a solution containing the elemental tellurium thin film on the surface of a substrate, spin coating, and heating and drying to prepare a semiconductor channel layer of the elemental tellurium thin film on the surface of the substrate;

[0013] Step 2. Preparing an electrode layer to obtain the nonvolatile memory based on the elemental tellurium thin film;

[0014] The electrode layer is prepared on both sides or upper and lower surfaces of the elemental tellurium thin film, and is a planar diode structure electrode or a vertical diode structure electrode.

[0015] Further, the solution of the elemental tellurium thin film in step 1 is prepared by dissolving the elemental tellurium thin film into a dispersion solvent to form a tellurium-rich dispersion liquid, wherein the dispersion solvent is an inorganic or organic solvent, preferably deionized water, anhydrous ethanol, acetone, isopropanol, chloroform, N,N-dimethylformamide, etc., and the concentration of the tellurium thin film in the solution of the elemental tellurium thin film is 3.68 mg / mL to 0.0184 mg / mL.

[0016] Further, the spin coating parameters in step 1 are as follows: first maintaining 50-100 revolutions per second for 5-10 seconds, then maintaining 300-500 revolutions per second for 20-30 seconds, and the heating temperature is 80-100 DEG C.

[0017] The mechanism of the application is as follows: the nonvolatile ferroelectric memory is constructed based on the elemental two-dimensional material for the first time in the application, the elemental tellurium has in-plane and out-of-plane ferroelectricity, and has a high mobility of up to 700 cm 2 V -1 S -1 The original polarization state of the elemental tellurium is reversed by applying an in-plane or out-of-plane electric field, thereby changing the Schottky barrier between the material and the electrode, rapidly reducing / rising the overall conductivity, and forming a storage window; at the same time, the elemental tellurium has excellent conductivity and oxidation resistance, so that a complex gate layer, a variable resistance layer, and a protective layer are not needed, and the ferroelectric thin film layer and the conductive material layer are both elemental tellurium thin films; in addition, the elemental tellurium material can realize element non-segregation in the process of more than 100 million cycles, avoiding the failure of the memory.

[0018] As described above, the application has the following beneficial effects due to the adoption of the above technical solutions:

[0019] 1. The non-volatile memory based on elemental tellurium thin film of the present application has simple structure, does not need additional material layers such as ferroelectric thin film layer, top gate layer, floating gate layer and the like, and only uses elemental tellurium thin film to replace the traditional device function to form a semiconductor channel layer, thereby overcoming the defects of complex structure and large size of the traditional ferroelectric memory; meanwhile, the device preparation process is simple, and only two steps are needed to prepare the memory with storage and operation functions.

[0020] 2. The non-volatile memory of the present application has a very small ferroelectric thickness, i.e. a ferroelectric characteristic size, which is only 0.4 nm, thereby improving the storage density of the ferroelectric memory; the ferroelectric memory has a large current density (36.6 microamperes / micron), a large storage window (~7 orders of magnitude), a large on-off ratio (~7 orders of magnitude), and a small write voltage (source-drain voltage 50 mV, gate voltage 1 V).

[0021] 3. The non-volatile memory of the present application has strong stability in air, and the ferroelectric memory of the 0.4 nm thick device can be maintained for 16.8 hours in air at room temperature, and the ferroelectric programmable state can be maintained for 10 months; the device can be cycled for more than 10 times without segregation of the elements of the memory unit, thereby greatly improving the accuracy and cycle life of the memory. 8 BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 FIG. 1 is a structural schematic diagram of the non-volatile memory based on elemental tellurium thin film of the present application.

[0023] Figure 2 FIG. 2 is a ferroelectric butterfly curve diagram of the elemental tellurium thin film in the non-volatile memory of the present application.

[0024] Figure 3 FIG. 3 is a storage performance diagram of the non-volatile memory obtained in Example 1 of the present application.

[0025] Figure 4 FIG. 4 is a storage performance diagram of the non-volatile memory with HfO2 substrate obtained in Example 2 of the present application.

[0026] Figure 5 FIG. 5 is a storage performance diagram of the non-volatile memory with Al2O3 substrate obtained in Example 2 of the present application.

[0027] Figure 6 FIG. 6 is a ferroelectric memory maintenance time sequence diagram of the single-layer tellurium thin film in the PET substrate non-volatile memory obtained in Example 2 of the present application.

[0028] Figure 7 FIG. 7 is a ferroelectric reprogramming memory diagram of the single-layer tellurium thin film in the PET substrate non-volatile memory obtained in Example 2 of the present application after being placed in air for 10 months. DETAILED DESCRIPTION

[0029] ​In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments and drawings.

[0030] A non-volatile memory based on elemental tellurium thin film, a structural schematic diagram of which is shown in Figure 1 from bottom to top, a substrate, a semiconductor channel layer and an electrode layer; the material of the semiconductor channel layer is elemental tellurium thin film, and the thickness is 0.4nm-20nm; the material of the substrate is silicon / silicon dioxide, flexible film, HfO2 thin film, aluminum oxide thin film, etc., and the material of the electrode is Cr / Au.

[0031] Embodiment 1

[0032] A preparation method of a non-volatile memory based on elemental tellurium thin film, comprising the following steps:

[0033] Step 1. Selecting Si / SiO2 as a substrate, wherein the thickness of SiO2 is 280nm, and the substrate is cleaned with acetone and anhydrous ethanol in sequence;

[0034] Step 2. Dissolving 3.68mg of elemental tellurium thin film in 10mL of water solvent, stirring and mixing uniformly to obtain an elemental tellurium thin film solution, then dropping the elemental tellurium thin film solution on the surface of the Si / SiO2 substrate cleaned in step 1, and spin-coating, wherein the spin-coating process is 100rps for 10s and 500rps for 30s, and after spin-coating, the substrate is placed on a baking table and heated and dried at 100℃;

[0035] Step 3. Preparing a Cr / Au electrode layer on both sides of the elemental tellurium thin film obtained in step 2 by using an evaporation method, and the electrode layer comprises 2nm of Cr and 20nm of Au, thereby obtaining a non-volatile memory.

[0036] The non-volatile memory prepared in this embodiment is subjected to storage performance test by using a digital source table, and a cycle gate voltage scanning operation is performed on the gate voltage, wherein the device is in a low resistance state, which is equivalent to writing “1” operation; the device is in a high resistance state, which is equivalent to writing “0” operation; and a small voltage of 10mV is used for data reading.

[0037] The ferroelectric butterfly curve diagram of the tellurium thin film in the silicon oxide substrate device of this embodiment is shown in Figure 2 , wherein the spherical curve is a phase change diagram, and the star-shaped curve is an intensity change diagram; from the spherical curve, it can be seen that the phase is reversed by 180 degrees with the voltage, which indicates that the elemental tellurium thin film has reversible ferroelectric polarization; and from the star-shaped curve, it can be seen that the piezoelectric coefficient of the elemental tellurium thin film is 20pm / V.

[0038] The storage performance diagram of the silicon oxide substrate device is shown in Figure 3 , wherein the vertical coordinate is the reading current (ID ), the horizontal axis is the voltage applied to the gate electrode (V GS ). Gate voltage (V GS ) During the cycle from -60V to 60V and then back to -60V, two hysteresis curves (1-2, 3-4) clearly appear due to the change in polarization state. At the same time, it can be seen from the figure that the device of the present invention has a storage window with a storage performance of 7000, which can achieve storage and reading with high error tolerance.

[0039] Example 2

[0040] A nonvolatile memory was prepared according to the steps of Example 1, except that the Si / SiO2 substrate in step 1 was adjusted to a 10 nm thick HfO2 substrate, a 10 nm thick Al2O3 substrate, and a 20 μm thick PET substrate, while the other steps remained unchanged.

[0041] The device composed of HfO2 substrate and Al2O3 substrate has source and drain electrodes prepared on both sides of the single-element tellurium film, and a bottom electrode prepared on the back side of the substrate.

[0042] The storage performance of the HfO2-based non-volatile memory prepared in this embodiment is shown in the figure below. Figure 4 As shown, a constant voltage (V DS =0.5V), a voltage change (V GS =-1.0~1.0~-1.0V), at a turn-on voltage of 1V, the ferroelectric storage window is 300, and the switching ratio reaches 7 orders of magnitude; if the source-drain voltage is constant at 50mV and the turn-on voltage is 2V, the ferroelectric storage window is as high as 3 orders of magnitude.

[0043] The storage performance of the non-volatile memory based on Al2O3 is shown in the figure Figure 5 As shown in the figure, the ferroelectric storage window can always maintain 7 orders of magnitude within a voltage range as wide as 60V, enabling high-performance storage architecture.

[0044] The time series diagram of the ferroelectric memory maintenance of a single-layer tellurium thin film in a non-volatile memory on a PET substrate is shown in the figure. Figure 6 As shown in the figure, the device was subjected to PFM (Piezoelectric Force Microscopy) and a 4V voltage was applied to write the square shape. As can be seen from the figure, the readout pattern can maintain the complete result at 195 minutes, and the pattern can still be read out at 990 minutes, indicating that even on a flexible substrate, the non-volatile storage of tellurium memory can reach more than 1000 minutes. The single-layer tellurium thin film ferroelectric reprogramming memory after being placed in the air for 10 months is shown in the figure. Figure 7 As shown in the figure, it can be seen that the ferroelectric memory based on a single-layer tellurium thin film still maintains non-volatile function, indicating the high stability of tellurium-based memory.

[0045] The above merely provides the specific implementation of the present application, any feature disclosed in the specification can be replaced by other equivalent or similar purpose alternative features unless specifically described, and all features disclosed or all steps in the method or process can be combined in any manner except for mutually exclusive features and / or steps.

Claims

1. A non-volatile memory based on a single-element tellurium thin film, characterized in that: From bottom to top, substrate, semiconductor Channel layer and electrode layer; the material of the semiconductor channel layer is a single-element tellurium thin film with in-plane and out-of-plane ferroelectricity, with a thickness of 0.4 nm; and by applying an in-plane or out-of-plane electric field, the original polarization state of the single-element tellurium is reversed, thereby changing The Schottky barrier between the material and the electrode causes the overall conductivity to drop / increase rapidly, forming a storage window; the electrode material is Cr / Au.

2. The nonvolatile memory according to claim 1, wherein: The substrate material is silicon / silicon dioxide, thin film, HfO2 thin film or aluminum oxide thin film.

3. The nonvolatile memory according to claim 2, wherein: The flexible film is a PET film.

4. The nonvolatile memory according to any one of claims 1 to 3, wherein: Based on single-element tellurium thin film The non-volatile memory realizes storage writing and reading through in-plane electric field or out-of-plane electric field excitation.

5. A method for preparing a non-volatile memory according to any one of claims 1 to 3, It is characterized by: The following steps are involved: Step 1. Add a solution containing a single-element tellurium thin film on the substrate surface, spin-coat, heat and dry to prepare a thin film on the substrate surface. Obtaining a semiconductor channel layer of a single-element tellurium thin film; Step 2. Prepare the electrode layer to obtain a non-volatile memory based on a single-element tellurium thin film; The electrode layer is prepared on both sides or upper and lower sides of the single-element tellurium thin film, and is a planar diode structure electrode or a vertical structure Diode structure electrode.

6. The preparation method according to claim 5, characterized in that In step 1, the solution of the elemental tellurium thin film is prepared by The high-quality tellurium film is dissolved in the dispersion solvent to form a tellurium-rich dispersion, wherein the dispersion solvent is deionized water, anhydrous ethanol, propylene glycol, Ketone, isopropyl alcohol, chloroform or N,N-dimethylformamide, the concentration of tellurium thin film in the solution of elemental tellurium thin film is 3.68 mg / m L ~ 0.0184 mg / mL.

7. The preparation method according to claim 5, characterized in that The spin coating parameters in step 1 are: 50~100 rpm Hold for 5~10 seconds, then maintain at 300~500 rpm for 20~30 seconds; the heating temperature is 80~100℃.

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