A conductive bridge type threshold switching device and electronic apparatus

Abstract

The application belongs to the technical field of microelectronic devices, and specifically discloses a conductive bridge type threshold switching device and an electronic device. According to the application, the selenium compound layer is two-dimensional NbSe2, the oxide layer is Nb2O5, a two-dimensional NbSe2-Nb2O5 hetero-bilayer film structure is formed, and the resistivity of the vanadium selenium oxygen mixture layer (VSe 2‑x O x is less than 1.1*10 4 S / cm. The band gap of Nb2O5 is larger, and the resistivity is improved by 7-8 orders of magnitude, so that the resistance value of the device in the high resistance state 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 particularly, relates to a conductive bridge type threshold switching device and an electronic device. BACKGROUND

[0002] Threshold switching devices have the advantages of low power consumption and fast read-write speed, making them one of the most promising devices for neuromorphic computing. However, for conductive bridge type threshold switching devices (CBTS), they usually need to use active metals as electrode materials, and the resistance switching performance depends on the formation and rupture of conductive filaments composed of active metal ions in the functional layer. However, active metals such as silver or copper have strong diffusion ability. During the operation of the device, a large number of active metal ions will diffuse throughout the functional layer, making the conductive filaments thicker and ultimately unable to rupture, leading to device failure. Moreover, due to the randomness of the growth of conductive filaments, the threshold switching voltage of the device also has randomness, and how to constrain the randomness of the growth of conductive filaments is also a factor restricting the development of CBTS.

[0003] However, 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 the CBTS device mentioned earlier can be overcome. In particular, two-dimensional materials can be used to optimize the structure of traditional devices, which is expected to overcome the above shortcomings and achieve superior performance.

[0004] Patent CN117769347A discloses a threshold switching 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 one whole, and the total thickness of the whole is about 10nm-100nm, while the thickness of the selenide layer is slightly larger than that of the oxidation product layer, which is determined by the degree of oxidation; the selenide layer is a two-dimensional VS2 layer, and the oxidation product layer is a vanadium selenide-oxygen mixture layer (VSe 2-x O x ).

[0005] However, this patent has the following defects and deficiencies: high leakage current, high overall thickness leading to high randomness of conductive filament growth, and thus affecting the consistency of threshold voltage. SUMMARY

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

[0007] To achieve the above-mentioned purpose, in a first aspect, the present application provides a conductive bridge type threshold switching device, which includes, from bottom to top: an active bottom electrode, a two-dimensional niobium diselenide layer, a niobium pentoxide oxidation layer, and an inert top electrode.

[0008] The Nb2O5 oxide layer is grown on the two-dimensional NbSe2 layer by oxidation, forming a two-dimensional NbSe2-Nb2O5 hetero-bilayer thin film structure.

[0009] The two-dimensional NbSe2 layer acts as an active ion barrier layer and an interface contact buffer layer.

[0010] The Nb2O5 oxide layer acts as a threshold switching functional layer.

[0011] Preferably, the thickness of the Nb2O5 oxide layer is less than 2 nm.

[0012] It should be noted that the ultra-thin design of the oxide layer in the present application plays the following roles: on the one hand, the randomness of the growth of conductive filaments depends on the growth path. When the growth path is extremely short (due to the ultra-thin oxide layer), the conductive filament growth path becomes unique, that is, the randomness decreases and the consistency increases. On the other hand, together with the blocking of the selenium compound layer to active ions, the consistency of the threshold voltage is improved.

[0013] Preferably, the thickness of the two-dimensional NbSe2 layer is greater than the thickness of the Nb2O5 oxide layer.

[0014] Preferably, the thickness of the two-dimensional NbSe2 layer is 2 nm-8 nm.

[0015] Preferably, the Nb2O5 oxide layer is grown on the two-dimensional NbSe2 layer by intrinsic oxidation.

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

[0017] Preferably, the two-dimensional NbSe2 layer establishes an ohmic contact between the active bottom electrode and the Nb2O5 oxide layer.

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

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

[0020] The present application provides a conductive bridge type threshold switching device and an electronic device, the selenium compound layer is two-dimensional NbSe2, the oxide layer is Nb2O5, forming a two-dimensional NbSe2-Nb2O5 hetero-bilayer thin film structure, and the resistivity of the VSe 2-x O x is less than 1.1×10 4The band gap of Nb2O5 is larger, and the resistivity is increased by 7-8 orders of magnitude, so that the resistance of the device in the high resistance state is higher, and the leakage current is reduced by at least 3 orders of magnitude. BRIEF DESCRIPTION OF DRAWINGS

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

[0022] Figure 2 is a flow chart of a preparation method of a conductive bridge type threshold switching device provided by an embodiment of the present application.

[0023] Figure 3 is an XRD characterization spectrum line diagram of a two-dimensional NbSe2 material provided by an embodiment of the present application, wherein (a) is an XRD diffraction pattern of the two-dimensional material under different oxidation times under the condition that the control oxidation temperature is 100℃, and (b) is an enlargement of the main peak part of the (a) diagram.

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

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

[0026] Figure 6 is the turn-on time of a conductive bridge type threshold switching device provided by an embodiment of the present application under a pulse.

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

[0028] Figure 8 is an electrical endurance characteristic diagram of a conductive bridge type threshold switching device provided by an embodiment of the present application.

[0029] In all the drawings, the same reference signs are used to represent the same elements or structures.

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

[0031] For the convenience 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 will be described below with reference to the accompanying drawings.

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

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

[0035] The resistivity of the NbSe2 two-dimensional material layer itself is low (1.1×10 4 S / cm), the band gap is small (0 eV), and it has good metal properties to establish ohmic contact between the oxide 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 amount of active metal ions from diffusing into the oxide layer Nb2O5, avoiding the influence of the diffusion of a large amount of metal ions on the thickness of the conductive filament growth, thereby improving the high resistance value of the device and reducing the leakage current of the device.

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

[0037] The resistance value of the oxide Nb2O5 (10 -11 -10 -12 S / cm) is very high, which can greatly increase the high resistance of the device, thereby reducing the leakage current. Moreover, due to the very thin thickness (less than 2 nm) of the oxide layer, the growth of the conductive filament can be limited in the thin layer, reducing the randomness and improving the consistency of the threshold voltage of the device.

[0038] The oxidation product Nb2O5 of the two-dimensional NbSe2 has a higher resistivity than the oxidation products of other transition metal selenides, which can reduce the operating current after being prepared into a threshold switch device, so that the device has the threshold switch characteristics of low leakage current. ​

[0039] The two-dimensional niobium diselenide layer and the two-dimensional niobium pentoxide layer form a two-dimensional NbSe2-Nb2O5 hetero-bilayer thin film structure, which utilizes the advantages of low resistivity of two-dimensional NbSe2 and easy integration of van der Waals layered structure, and the advantages of large resistivity of intrinsic oxide Nb2O5 and threshold switching function, and the advantages of controllable oxidation of two-dimensional layer to achieve an ultrathin oxide layer (<2nm), so that the threshold switching device prepared has the advantages of good interface contact, low operating current and good consistency.

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

[0041] It should be noted that the ultrathin design of the oxide layer in the present application plays the following roles: on the one hand, the randomness of the growth of the conductive filament depends on the growth path, and when the growth path is extremely short (due to the ultrathin oxide layer), the conductive filament growth path becomes unique, that is, the randomness is reduced and the consistency is improved; on the other hand, in combination with the selection of the selenide layer, the threshold voltage consistency of the prepared device is good.

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

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

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

[0045] Preferably, the oxidation conditions of the intrinsic oxidation are as follows: the temperature is 90℃-110℃, and the time is 60min-80min.

[0046] Specifically, the present application provides a preparation method of the conductive bridge type threshold switching device described above, 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 in an atmospheric environment at 90℃-110℃ for 60min-80min to obtain an oxidation product layer. (At the same time, the selenide layer can also be oxidized by plasma, and then vacuum annealing is performed, specifically, oxidation is performed under the condition of 30W 5min plasma oxidation);

[0050] S4: preparing 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 layer.

[0052] Embodiment 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. As shown in the figure, the entire preparation process is roughly divided into four steps, which will be described one by one. Figure 2

[0054] First, the bottom electrode is prepared on the silicon substrate for subsequent two-dimensional material transfer. Specifically, the substrate is a Si substrate with a 300 nm silicon oxide epitaxial layer, which is cleaned with acetone, ethanol and deionized water. AZ5214 photoresist is dropped on the silicon wafer, and then spin-coated with a spin coater. Then, it is placed on a hot plate at 97°C for two minutes for pre-baking. Then, the electrode pattern on the mask is transferred to the photoresist by photolithography, and the pre-exposure time is 1.1 seconds. Then, the silicon wafer treated as above is placed on a hot plate at 115°C for 2 minutes for post-exposure. Then, the wafer is placed under the lithography machine for post-exposure, and the time is 11 seconds. Then, the AZ5214 special developing solution is used for developing, and the time is 30 seconds to obtain the expected pattern. Finally, electron beam evaporation is used for metallization, and then the excess metal is peeled off to obtain the bottom electrode. It should be noted that the bottom electrode should not be too thick, generally less than 40 nm, otherwise it will affect the transfer of the two-dimensional material and is not conducive to the preparation of the device. After this step, the bottom electrode corresponding to No. 1 in the figure is formed. Figure 1

[0055] Second, the two-dimensional material is transferred. The material used in this application is 2H-NbSe2. NbSe2 has multiple crystal forms, and 2H-NbSe2 is one of the metallic forms of NbSe2.

[0056] Specifically, the two-dimensional material single crystal block is mechanically peeled off to obtain a single crystal NbSe2 film with a thickness of less than 10 nm, and then a metallographic microscope is used for point transfer, which is to transfer the film to the position of the bottom electrode prepared before, i.e. the tip portion of the 5 μm wide metal strip electrode. After this step, the first layer of two-dimensional material corresponding to No. 2 in the figure is formed. Figure 1 The first layer of two-dimensional material is also a selenide layer, which plays three roles: first, it has good metallic properties to establish an ohmic contact between the functional layer and the electrode; second, it can be oxidized to form an ultra-thin Nb2O5 functional layer; and third, the layer of two-dimensional material can effectively block the diffusion of silver ions from the bottom electrode, avoiding a large amount of silver ions entering the oxide layer, thereby improving the durability and service life of the device.​​

[0057] The third step is oxidation annealing. Specifically, in this embodiment, annealing under atmospheric conditions is taken as an example. The oxidation temperature remains constant, and a series of oxidation time gradients are set to obtain, as shown below. Figure 3 The XRD patterns shown are as follows: (a) is the XRD pattern of the two-dimensional material at different oxidation times under controlled oxidation temperature of 100℃. 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 degree of oxidation. (b) is a magnification of the main peak in (a). To better compare the changes in peak intensity, it can be observed that the peak intensity weakens significantly in the oxidation time range of 50 minutes to 60 minutes, indicating that the two-dimensional NbSe2 layer begins to oxidize at 60 minutes. It is known that after the oxidation time exceeds 60 minutes, the main peak intensity begins to decrease, which means that the degree of oxidation of the two-dimensional layer is further deepened. Therefore, to obtain a thin oxide layer, under the premise of oxidation in an atmospheric environment, the oxidation annealing conditions to be used are 100℃ and annealing in an atmospheric environment for 70 minutes. If plasma oxidation is used, the oxidation conditions are: gas flow rate 100 sccm; oxidation power 30W; oxidation time 5 min. This step is to oxidize the surface layer of the two-dimensional thin film material transferred to the bottom electrode to obtain the corresponding oxide layer with threshold switching characteristics. After this step, it was formed Figure 1 In the middle, the oxidation product layer corresponding to part number 4.

[0058] The fourth step is to fabricate the top electrode, forming a crossbar structure and thus a complete threshold switching device. This step is the same as the bottom electrode fabrication step described above, except that the electrode thickness is not strictly required; an appropriate thickness is sufficient. After this step, a complete threshold switching device is formed. Figure 1 The top electrode corresponding to number 5 in the middle.

[0059] TEM section analysis of the device yielded the following results: Figure 4 As shown, its oxide layer thickness is only 0.71 nm, which restricts the growth of conductive filaments within this thin layer and improves the consistency of the device threshold voltage.

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

[0061] When no voltage is applied, due to the strong diffusion of silver ions, a small amount of silver ions released from the silver bottom electrode penetrates the two-dimensional layer and enters the ultra-thin oxide layer. Then, under the condition that a positive voltage is applied to the top electrode and the bottom electrode is grounded, due to the effect of the electric field, the silver ions move towards the bottom electrode and accumulate at the two-dimensional material layer. With the increase of the voltage until the threshold voltage is reached, a positive triangular silver conductive filament channel is formed from the bottom electrode to the top electrode, and the device resistance realizes the transition from high resistance to low resistance. At the same time, the silver conductive filament itself will gradually disintegrate due to Joule heat, and when the voltage gradually decreases, the effect of the electric field on the drift of silver ions gradually weakens, and the conductive filament becomes thinner and thinner. When the voltage decreases 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 switching electrical cycle of the threshold switching device.

[0062] Test examples:

[0063] As shown in Figure 5 , it is a direct current cycle electrical characteristic diagram of the threshold switching device prepared according to the above process conditions, wherein (a), (b), (c), (d) respectively correspond to the limiting current I CC of 600fA, 800fA, 1pA, 10pA, HRS represents the high resistance state, and LRS represents the low resistance state. Intuitively, the limiting current during operation is small, and the leakage current is very small, maintained at the order of fA. At the same time, it can be known from Figure 6 that the switching time of the device operating under pulse is 8.2μs, so the opening 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 under a larger current, as shown in Figure 7 , the threshold voltage data of the direct current cycle diagram is counted, and the consistency characteristic parameters [ΔV(2σ) / V mean ] of the opening and holding voltage are obtained, which are 16.87% and 23.17% respectively under the limiting current of 100nA, which is higher in consistency compared with the same type of device.

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

[0066] Figure 8The electrical endurance characteristic diagram of the threshold switch device is shown. It can be seen that the number of operations of the device under pulse can reach 10 6 , which indicates that the endurance performance is good, and the device is not prone to failure.

[0067] It should be understood that expressions such as "include" and "may include" used in the present application indicate the presence 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 "include" and / or "have" can be interpreted to mean that a specific feature, number, operation, constituent element, component or combination thereof is present, but cannot be interpreted to exclude the presence or addition of one or more other features, 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 terms. For example, the expression "A and / or B" can include A, can include B, or can include both A and B.

[0069] In the description of the embodiments of the present application, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be understood broadly, for example, "connection" can be detachable connection, or can be non-detachable connection; can be direct connection, or can be indirect connection through intermediate medium. Among them, "fixed connection" means that the relative positional relationship after connection is unchanged. "Rotary connection" means that the relative rotation after connection is connected. "Sliding connection" means that the relative sliding after connection is connected. The orientation language mentioned in the embodiments of the present application, such as "top", "bottom", "inner", "outer", "left", "right", etc., is only the direction of the drawing, therefore, the orientation language used is to better, more clearly illustrate and understand the embodiments of the present application, and is not indicative or implied that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, therefore, it 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, symmetry, equality, parallel, perpendicular, etc. These limitations are all for the current process level, and are not strictly defined in the mathematical sense, allowing a small amount of deviation, approximately symmetrical, approximately equal, approximately parallel, approximately perpendicular, etc. can be. For example, A is parallel to B, which means that A and B are parallel or approximately parallel, the included angle between A and B can be between 0 degrees and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, the included angle between A and B can be between 80 degrees and 100 degrees.

[0071] The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to 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 intrinsically oxidized and grown on the two-dimensional niobium diselenide layer to form a two-dimensional NbSe2-Nb2O5 heterogeneous bilayer thin film structure. The two-dimensional niobium diselenide layer serves as an active ion blocking layer and an interface contact buffer layer. The niobium pentoxide oxide layer serves as a threshold switching functional layer. The thickness of the niobium pentoxide oxide layer is less than 2 nm.

2. The conductive bridge type threshold switch device as described in 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.

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

4. The conductive bridge type threshold switch device as described in claim 1, characterized in that, The intrinsic oxidation conditions are: temperature 90℃-110℃, time 60min-80min.

5. The conductive bridge type threshold switch device according to any one of claims 1 to 4, characterized in that, The two-dimensional niobium diselenide layer establishes an ohmic contact between the active bottom electrode and the niobium pentoxide oxide layer.

6. An electronic device, characterized in that, Includes the conductive bridge type threshold switch device as described in any one of claims 1 to 5.

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