Conductive bridge type threshold switching device and electronic equipment

Abstract

The invention belongs to the technical field of microelectronic devices, and particularly discloses a conductive bridge type threshold switching device and electronic equipment. According to the invention, the selenide layer is two-dimensional NbSe2, the oxide layer is Nb2O5, a two-dimensional NbSe2-Nb2O5 heterogeneous double-layer film structure is formed, and compared with a vanadium-selenium-oxygen mixture layer (VSe2-xOx), the resistivity is less than 1.1 * 10 < 4 > S / cm), the Nb2O5 has a larger forbidden band width, and the resistivity is improved by 7-8 orders of magnitude, so that the high-resistance-state resistance value of the device is higher, and the leakage current is at least reduced by 3 orders of magnitude.

Description

Technical Field

[0001] The present application belongs to the technical field of microelectronic devices, and more specifically, relates to a conductive bridge type threshold switch device and an electronic device. Background Art

[0002] Threshold switching devices have the advantages of low power consumption and fast read and write speeds, making them one of the most promising devices for neuromorphic computing. However, for conductive bridge threshold switching devices (CBTS), active metals are usually required as electrode materials, and the resistance switching performance depends on the formation and breaking of conductive filaments composed of active metal ions in the functional layer. However, active metals such as silver or copper have strong diffusion capabilities. During the operation of the device, a large amount of active metal ions will diffuse throughout the functional layer, making the conductive filaments thicker and eventually unable to break, resulting in device failure. And because the growth of conductive filaments is random, the threshold switching voltage of the device is also random. How to constrain the randomness of the growth of conductive filaments is also a factor restricting the development of CBTS.

[0003] But at the same time, CBTS has great application potential due to its simple structure, low energy consumption, good stability and compatibility with CMOS back-end processes. By exploring new material systems, the shortcomings of CBTS devices mentioned above can be overcome. In particular, two-dimensional materials can be used to optimize the traditional device structure, which is expected to overcome the above shortcomings and achieve better performance.

[0004] Patent CN117769347A discloses a threshold conversion device, which includes, from bottom to top: a bottom electrode, a selenide layer, an oxidation product layer and a top electrode; the selenide layer and the oxidation product layer are a whole, and the total thickness of the whole is about 10nm to 100nm, and the thickness of the selenide layer is slightly greater than the thickness of the oxidation product layer, which depends on the degree of oxidation; the selenide layer is a two-dimensional VS2 layer, and the oxidation product layer is a vanadium selenium oxygen mixture layer (VSe 2-x O x ).

[0005] However, this patent has the following defects and shortcomings: high leakage current, and high overall thickness resulting in high randomness in the growth of conductive filaments, which in turn affects the consistency of threshold voltage. Summary of the invention

[0006] In view of the defects of the prior art, the purpose of the present application is to provide a conductive bridge type threshold switch device and an electronic device, aiming to solve the problems of high leakage current and high randomness of conductive filament growth.

[0007] To achieve the above-mentioned object, in a first aspect, the present application provides a conductive bridge type threshold switch device, which comprises, from bottom to top, an active bottom electrode, a two-dimensional niobium diselenide layer, a niobium pentoxide oxide layer and an inert top electrode;

[0008] The niobium pentoxide oxide layer is grown on the two-dimensional niobium diselenide layer by oxidation to form a two-dimensional NbSe2-Nb2O5 heterogeneous double-layer film structure;

[0009] The two-dimensional niobium diselenide layer serves as an active ion barrier layer and an interface contact buffer layer;

[0010] The niobium pentoxide oxide layer serves as a threshold switch functional layer.

[0011] Preferably, the thickness of the niobium pentoxide oxide layer is less than 2 nm.

[0012] It should be noted that the ultra-thin design of the oxide layer thickness in the present application plays the following role: on the one hand, the randomness of the growth of the conductive filaments depends on the growth path. When the growth path is extremely short (due to the ultra-thin oxide layer), the growth path of the conductive filaments becomes unique, that is, the randomness is reduced and the consistency is improved; on the other hand, it works together with the blocking of active ions by the selenide layer of the present application to improve the consistency of the threshold voltage.

[0013] Preferably, the thickness of the two-dimensional niobium diselenide layer is greater than the thickness of the niobium pentoxide oxide layer.

[0014] Preferably, the two-dimensional niobium diselenide layer has a thickness of 2nm-8nm.

[0015] Preferably, the niobium pentoxide oxide layer is grown on the two-dimensional niobium diselenide layer by intrinsic oxidation.

[0016] Preferably, the oxidation conditions of the intrinsic oxidation are: temperature of 90° C.-110° C., and time of 60 min-80 min.

[0017] Preferably, the two-dimensional niobium diselenide layer establishes an ohmic contact between the active bottom electrode and the niobium pentoxide oxide layer.

[0018] To achieve the above objective, in a second aspect, the present application provides an electronic device, comprising the conductive bridge type threshold switch device as described in the first aspect.

[0019] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art:

[0020] The present application provides a conductive bridge type threshold switch device and an electronic device, wherein the selenide layer is two-dimensional NbSe2, the oxide layer is Nb2O5, and a two-dimensional NbSe2-Nb2O5 heterogeneous double-layer film structure is formed. Compared with the vanadium selenium oxygen mixture layer (VSe 2-x O x The resistivity is less than 1.1×10 4S / cm), the bandgap of Nb2O5 is wider, and the resistivity is increased by 7-8 orders of magnitude, which makes the high-resistance state resistance of the device higher and reduces the leakage current by at least 3 orders of magnitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of a conductive bridge type threshold switch device provided in an embodiment of the present application.

[0022] Figure 2 It is a flow chart of the method for preparing a conductive bridge type threshold switch device provided in an embodiment of the present application.

[0023] Figure 3 It is the XRD characterization spectrum diagram of the two-dimensional NbSe2 material provided in the embodiment of the present application, wherein (a) is the XRD diffraction pattern of the two-dimensional material under the condition of controlling the oxidation temperature to 100°C and different oxidation times, and (b) is an enlargement of the main peak part of (a).

[0024] Figure 4 It is a TEM cross-sectional view of a conductive bridge type threshold switch device provided in an embodiment of the present application.

[0025] Figure 5 : is an electrical DC characteristic diagram of a conductive bridge type threshold switch device provided in an embodiment of the present application, wherein (a), (b), (c), and (d) correspond to the limiting current I of the DC cycle, respectively. CC 600fA, 800fA, 1pA, and 10pA.

[0026] Figure 6 It is the opening time of the conductive bridge type threshold switch device provided in the embodiment of the present application under a pulse.

[0027] Figure 7 It is a DC cycle diagram of a conductive bridge type threshold switch device provided in an embodiment of the present application under a limiting current of 10nA and a probability distribution statistical diagram of its threshold voltage.

[0028] Figure 8 This is a diagram of the electrical durability characteristics of a conductive bridge type threshold switch device provided in an embodiment of the present application.

[0029] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0030] 1-active bottom electrode, 2-two-dimensional niobium diselenide layer, 3-metallic conductive filaments, 4-niobium pentoxide oxide layer, 5-inert top electrode. DETAILED DESCRIPTION

[0031] For ease of understanding, the English abbreviations and related technical terms involved in the embodiments of the present application are explained and described below.

[0032] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0033] like Figure 1 As shown, the present application provides a conductive bridge type threshold switch device, which includes, from bottom to top: an active bottom electrode 1, a two-dimensional niobium diselenide layer 2, a niobium pentoxide oxide layer 4 and an inert top electrode 5; the niobium pentoxide oxide layer 4 is grown on the two-dimensional niobium diselenide layer 2 by oxidation to form a two-dimensional NbSe2-Nb2O5 heterogeneous double-layer thin film structure; the two-dimensional niobium diselenide layer 2 serves as an active ion barrier layer and an interface contact buffer layer; the niobium pentoxide oxide layer 4 serves as a threshold switch functional layer.

[0034] The material of the threshold switch functional layer is derived from the ultra-thin Nb2O5 oxide layer formed by the intrinsic oxidation of NbSe2. The oxide layer is located above the NbSe2 two-dimensional material layer. The metal conductive filament 3 connects the two-dimensional selenide layer 2 and the top electrode 5 through its intrinsic oxide layer. The metal conductive filament 3 is constantly broken and linked in the oxide layer as the applied stimulus changes, thereby causing the resistance state conversion to show the threshold switch performance.

[0035] The resistivity of the NbSe2 two-dimensional material layer itself (1.1×10 4 S / cm) is low, the bandgap width (0eV) is very small, and it has good metallic properties, so that it can establish ohmic contact between the oxidation product layer and the external electrode; at the same time, the two-dimensional material layer blocks the ions of the active bottom electrode, preventing a large number of active metal ions from diffusing into the oxide layer Nb2O5, avoiding the large-scale diffusion of metal ions, affecting the thickness of the conductive filament growth, thereby increasing the high-resistance state resistance of the device and reducing the leakage current of the device.

[0036] The bandgap width is positively correlated with the resistance value, and the bandgap width of Nb2O5 is 3.4~5.3eV, VSe 2-x O x The band gap width is less than 1.5eV, so the resistance value of Nb2O5 is higher.

[0037] Oxide Nb2O5 resistance (10 -11 ~10 -12 S / cm) is very high, which can greatly increase the high resistance of the device and thus reduce the leakage current. Moreover, due to its thin thickness (less than 2nm), it can limit the growth of conductive filaments in this thin layer, reduce randomness, and improve the consistency of the device threshold voltage.

[0038] The oxidation product Nb2O5 of two-dimensional NbSe2 has a higher resistivity than the oxidation products of other transition metal selenides. After being prepared into a threshold switching device, the operating current can be reduced, making the device have a threshold switching characteristic with low leakage current.

[0039] The two-dimensional niobium diselenide layer and the niobium pentoxide oxide layer form a two-dimensional NbSe2-Nb2O5 heterogeneous double-layer thin film structure. This structure not only utilizes the advantages of the two-dimensional NbSe2's low resistivity and easy integration of the van der Waals layered structure, but also utilizes the advantages of its intrinsic oxide Nb2O5's large resistivity and threshold switching function. At the same time, it utilizes the controllable oxidation of the two-dimensional layer to achieve an ultra-thin oxide layer (<2nm), so that the prepared threshold switching device has the advantages of good interface contact, low operating current and good consistency.

[0040] Preferably, the thickness of the niobium pentoxide oxide layer is less than 2 nm.

[0041] It should be noted that the ultra-thin design of the oxide layer thickness in the present application plays the following roles: on the one hand, the randomness of the growth of the conductive filaments depends on the growth path. When the growth path is extremely short (due to the ultra-thin oxide layer), the growth path of the conductive filaments becomes unique, that is, the randomness is reduced and the consistency is improved; on the other hand, together with the selection of the selenide layer of the present application, the threshold voltage of the prepared device has better consistency.

[0042] Preferably, the thickness of the two-dimensional niobium diselenide layer is greater than the thickness of the niobium pentoxide oxide layer.

[0043] Preferably, the two-dimensional niobium diselenide layer has a thickness of 2nm-8nm.

[0044] Preferably, the niobium pentoxide oxide layer is grown on the two-dimensional niobium diselenide layer by intrinsic oxidation.

[0045] Preferably, the oxidation conditions of the intrinsic oxidation are: temperature of 90° C.-110° C., and time of 60 min-80 min.

[0046] Specifically, the present application provides a method for preparing the above-mentioned conductive bridge type threshold switch device, which comprises the following steps:

[0047] S1: preparing a bottom electrode on a substrate;

[0048] S2: disposing selenide on the bottom electrode prepared in step S1 to form a selenide layer;

[0049] S3: performing oxidation annealing on the selenide layer, specifically, first oxidizing at 90°C to 110°C in an atmosphere for 60min to 80min to obtain an oxidation product layer. (Also, the selenide layer can be oxidized by plasma, and then vacuum annealing is performed, specifically, oxidation is performed under plasma oxidation conditions of 30W for 5min);

[0050] S4: Prepare a top electrode on the two-dimensional material layer.

[0051] Preferably, the two-dimensional niobium diselenide layer establishes an ohmic contact between the active bottom electrode and the niobium pentoxide oxide layer.

[0052] Example 1

[0053] In this embodiment, the material of the bottom electrode is Ag, and the material of the top electrode is Ti / Au, wherein Ti is an adhesion layer. Figure 2 As shown, the whole preparation process is roughly divided into four steps, which will be explained in turn below.

[0054] The first step is to prepare a bottom electrode on a silicon substrate for subsequent two-dimensional material transfer. Specifically, the substrate selected is a Si substrate with a 300nm silicon oxide epitaxial layer. After cleaning with acetone, ethanol and deionized water, AZ5214 photoresist is dripped on the silicon wafer, spin-coated with a glue spreader, and then placed on a 97°C hot plate for pre-baking for two minutes. Then, photolithography is performed to transfer the electrode pattern on the mask to the photoresist, and the pre-exposure takes 1.1 seconds. Then, the silicon wafer treated as above is placed on a hot plate at 115°C for post-exposure, which takes 2 minutes. Then, the wafer is placed under a photolithography machine for post-exposure, which takes 11 seconds. Then, AZ5214's special developer is used for development, which takes 30 seconds to obtain the expected pattern. Finally, electron beam evaporation is used for metallization, and then the excess metal is stripped off to obtain the bottom electrode. It should be noted that the bottom electrode should not be too thick, generally less than 40nm. Too thick will affect the transfer of two-dimensional materials and is not conducive to the preparation of devices. After this step, the following is formed. Figure 1 In the figure, the bottom electrode corresponding to number 1 is generally an electrode material containing an adhesion layer to prevent it from falling off.

[0055] The second step is to transfer two-dimensional materials. The material used in this application is 2H-NbSe2. NbSe2 has multiple crystal forms, and 2H-NbSe2 is a type of NbSe2 with metallic properties.

[0056] Specifically, the two-dimensional material single crystal block was mechanically peeled off to obtain a single crystal NbSe2 film less than 10nm, and then a metallographic microscope was used to perform a fixed-point transfer to the position of the previously prepared bottom electrode, that is, the tip of the 5μm wide metal strip electrode. After this step, a single crystal NbSe2 film with a thickness of less than 10nm was obtained. Figure 1 In the figure, the first layer of two-dimensional material corresponding to number 2 is also a selenide layer. The two-dimensional material of the selenide layer plays three roles: first, it has good metallic properties to establish ohmic contact between the functional layer and the electrode; second, it can be oxidized to form an ultra-thin Nb2O5 functional layer; finally, this two-dimensional layer can effectively block the diffusion of silver ions from the bottom electrode, prevent a large amount of silver ions from entering the oxide layer, thereby improving the durability of the device and increasing the life of the device.

[0057] The third step is to perform oxidation annealing. Specifically, in this embodiment, taking annealing in an atmospheric environment as an example, the oxidation temperature is constant, and a series of oxidation time gradients are set to obtain the following: Figure 3 The XRD spectrum shown in the figure, where (a) is the XRD diffraction pattern of the two-dimensional material under the condition of controlling the oxidation temperature to 100℃ and different oxidation times. Different peak intensities correspond to the amount of two-dimensional material, that is, the greater the peak intensity, the more two-dimensional material remains and the lower the oxidation degree; (b) is an enlargement of the main peak part of (a). In order to better compare the change of peak intensity, it can be observed that the peak intensity decreases significantly in the oxidation time range from 50 minutes to 60 minutes, indicating that the two-dimensional NbSe2 layer begins to oxidize after 60 minutes. It is known that after the oxidation time exceeds 60 minutes, the main peak intensity begins to decrease, which means that the oxidation degree of the two-dimensional layer is further deepened. Therefore, in order to obtain a thin oxide layer, the oxidation annealing conditions to be used under the premise of oxidation in the atmospheric environment are 100℃ and annealing in the atmospheric environment for 70 minutes. If oxidation is performed by plasma, the oxidation conditions are: gas flow rate 100sccm; oxidation power 30W; oxidation time 5min. This step is to oxidize the surface layer of the two-dimensional thin film material transferred to the bottom electrode to obtain a corresponding oxide layer with threshold switching characteristics. After this step, the Figure 1 In the figure, it corresponds to the oxidation product layer of part number 4.

[0058] The fourth step is to make the top electrode, form a crossbar structure, and form a complete threshold switch device. This step is the same as the above bottom electrode production step, except that the electrode thickness is not very strict and can be appropriate. After this step, a Figure 1 The top electrode corresponding to number 5.

[0059] The device was analyzed by TEM slices, and the results are as follows: Figure 4 As shown, the thickness of the oxide layer is only 0.71 nm, which limits the growth of conductive filaments in the thin layer and improves the consistency of the device threshold voltage.

[0060] In this application, the device consists of a bottom electrode, an unoxidized two-dimensional NbSe2 material layer, an intrinsic oxide layer Nb2O5, and a top electrode. The conductive mechanism is described as follows:

[0061] When no voltage is applied, due to the strong diffusion of silver ions, a small amount of silver ions released by the silver bottom electrode will pass through the two-dimensional layer and enter the ultra-thin oxide layer. Then, when a positive voltage is applied to the top electrode and the bottom electrode is grounded, due to the action of the electric field, the silver ions move toward the bottom electrode and accumulate in the two-dimensional material layer. As the voltage increases until the threshold voltage is reached, a equilateral triangle silver conductive filament channel is formed from the bottom electrode to the top electrode, and the device resistance is converted from high resistance to low resistance. At the same time, the silver conductive filament itself will gradually disintegrate due to Joule heat. When the voltage gradually decreases, the effect of the electric field on the drift motion of silver ions gradually weakens, and the conductive filament will become thinner and thinner. When the voltage is reduced to the holding voltage, the conductive channel breaks, and the device changes from low resistance to high resistance. The above two processes describe a complete threshold switch electrical cycle of the threshold switch device.

[0062] Test example:

[0063] like Figure 5 As shown in FIG. 1 , it is a DC cycle electrical characteristic diagram of the threshold switch device prepared according to the above process conditions, wherein (a), (b), (c), and (d) correspond to the limiting current I of the DC cycle respectively. CC 600fA, 800fA, 1pA, 10pA, HRS represents high resistance state, LRS represents low resistance state. Intuitively, the limiting current is very small during operation, and the leakage current is very small, maintained at the fA level. Figure 6 It can be seen that the switching time of the device under pulse operation is 8.2μs, from which the turn-on power consumption of the device can be calculated as W = UIt = 0.5V × 0.6 × 10 -12 A×8.2×10 -6 s = 2.46aJ.

[0064] At the same time, the threshold voltage consistency of the device is tested at a larger current, such as Figure 7 As shown in the figure, by statistically analyzing the threshold voltage data of the DC cycle diagram, the consistency characteristic parameters of the turn-on and hold voltages [ΔV(2σ) / V mean ], and are 16.87% and 23.17% respectively at a limiting current of 100nA, which are more consistent than similar devices.

[0065] The present application prepares a double-layer thin film structure of NbSe2-Nb2O5 through several process steps. The Nb2O5 oxide layer induced by intrinsic oxidation has a high resistance, and the growth of conductive filaments is also confined in the ultra-thin oxide layer, which has a significant effect on reducing device leakage current, achieving lower operating current and reducing the randomness of conductive filament growth.

[0066] Figure 8The electrical durability characteristic diagram of the threshold switch device is shown. It can be seen that the device can operate up to 10 times under pulses. 6 , indicating that its durability is good and the device is not prone to failure.

[0067] It should be understood that expressions such as "including" and "may include" that may be used in the present application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In the present application, terms such as "including" and / or "having" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0068] In addition, in the present application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0069] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the relative position relationship after connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0070] In addition, in the embodiments of the present application, the mathematical concepts mentioned are symmetry, equality, parallelism, verticality, etc. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense, and allow a small amount of deviation, approximation to symmetry, approximation to equality, approximation to parallelism, approximation to verticality, etc. are all possible. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0071] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A conductive bridge type threshold switch device, characterized in that: From bottom to top, it includes: an active bottom electrode, a two-dimensional niobium diselenide layer, a niobium pentoxide oxide layer, and an inert top electrode; The niobium pentoxide oxide layer is grown on the two-dimensional niobium diselenide layer by oxidation to form a two-dimensional NbSe2-Nb2O5 heterogeneous double-layer film structure; The two-dimensional niobium diselenide layer serves as an active ion barrier layer and an interface contact buffer layer; The niobium pentoxide oxide layer serves as a threshold switch functional layer.

2. The conductive bridge type threshold switch device according to claim 1, characterized in that: The thickness of the niobium pentoxide oxide layer is less than 2 nm.

3. The conductive bridge type threshold switch device according to claim 1, characterized in that: The thickness of the two-dimensional niobium diselenide layer is greater than the thickness of the niobium pentoxide oxide layer.

4. The conductive bridge type threshold switch device according to claim 3, characterized in that: The thickness of the two-dimensional niobium diselenide layer is 2nm-8nm.

5. The conductive bridge type threshold switch device according to claim 1, characterized in that: The niobium pentoxide oxide layer is grown on the two-dimensional niobium diselenide layer by intrinsic oxidation.

6. The conductive bridge type threshold switch device according to claim 1, characterized in that: The oxidation conditions of the intrinsic oxidation are: temperature of 90° C.-110° C., and time of 60 min-80 min.

7. The conductive bridge type threshold switch device according to any one of claims 1 to 6, characterized in that: The two-dimensional niobium diselenide layer establishes an ohmic contact between the active bottom electrode and the niobium pentoxide oxide layer.

8. An electronic device, characterized in that: It comprises a conductive bridge type threshold switch device as claimed in any one of claims 1 to 7.

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