A threshold transition device and a preparation method thereof

Abstract

The present invention belongs to the field of semiconductor devices, and discloses a threshold switching device and a preparation method thereof. The threshold switching device includes a bottom electrode, a top electrode, and a functional layer located between the bottom electrode and the top electrode; the functional layer is a binary or multi-metal oxide modified by ion implantation, and active metal nanoparticles are formed inside or on the surface of the functional layer after ion implantation modification; the ion concentration implanted in the functional layer after ion implantation modification shows a nearly Gaussian distribution along the depth of the functional layer; the active metal nanoparticles limit the region where the redox reaction occurs, reduce the randomness of the growth of conductive filaments, and improve the consistency of the threshold switching device; and the nano-scale active electrode region enables the conductive channel to still maintain the characteristic of spontaneous breaking under a large current limit, improving the on-state current density of the threshold switching device.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor devices, and more particularly, relates to a threshold switching (TS) device based on a metal conductive filament and a preparation method thereof. Background Art

[0002] In recent years, resistive memories (RRAM, PCM, etc.) have been favored by researchers due to their advantages of high speed, small feature size, and great potential for three-dimensional stacking. However, during read and write operations, the problem of leakage current crosstalk will be faced. Therefore, a select transistor is integrated into the memory array to solve the crosstalk problem. Among them, the threshold switching (TS) memristor based on a metal conductive filament, as a two-terminal select transistor, not only has a large on-off ratio and extremely low leakage current, but also has the advantages of simple structure, easy integration, and high CMOS process compatibility, becoming a research hotspot in the field of select transistor technology.

[0003] The traditional metal conductive filament TS device uses an active metal thin film (such as Ag or Cu) as the top electrode, and an oxidation-reduction reaction occurs under the action of an electric field. When the applied voltage is greater than V th , a metal conductive channel is formed in the dielectric layer, and the device switches to the low resistance state; when the applied voltage is less than V h , the metal conductive channel spontaneously breaks, and the device returns to the high resistance state. However, due to the strong randomness of the growth of the metal conductive filament, the device consistency is poor. At the same time, in order to maintain the ability of the metal conductive filament to spontaneously break, the on-state current of the device is small (<100 μA), which is difficult to drive the memory connected in series therewith. In addition, the stability of the device is also poor. These problems have hindered the application of TS devices in large-scale memory chips. Summary of the Invention

[0004] Aiming at the defects of the prior art, the purpose of the present invention is to provide a threshold switching device, aiming to solve the problems of poor device consistency and stability and small on-state current density caused by the randomness of the growth of the metal conductive filament in the prior art.

[0005] The present invention provides a threshold switching device, comprising a bottom electrode, a top electrode, and a functional layer located between the bottom electrode and the top electrode; the functional layer is a binary or multi-metal oxide modified by ion implantation, and active metal nanoparticles are formed inside or on the surface of the functional layer after ion implantation modification; the ion concentration implanted in the functional layer after ion implantation modification shows a nearly Gaussian distribution along the depth of the functional layer; the active metal nanoparticles limit the region where the redox reaction occurs, reduce the randomness of the growth of conductive filaments, and improve the consistency of the threshold switching device; and the nano-scale active electrode region enables the conductive channel to still maintain the characteristic of spontaneous rupture under a large current limit, thereby improving the on-state current of the threshold switching device.

[0006] Among them, both the bottom electrode and the top electrode are inert metals, such as Pt, Pd, Au, Ru, W, TiN, TaN, doped Si, etc., and are deposited on the substrate by methods such as magnetron sputtering, thermal evaporation, or electron beam evaporation.

[0007] Furthermore, the material of the functional layer is HfO2, Al2O3, ZrO2, SiO2, Ta2O5, MgO, TiO2, HfAlO x or HfZrO x .

[0008] As an embodiment of the present invention, the functional layer is a single-layer structure or a multi-layer structure; the thickness of the functional layer is 5 nm to 20 nm.

[0009] Furthermore, a single layer of nanoparticles is formed on the surface of the functional layer after ion implantation modification, and the size range of the single layer of nanoparticles is 1 nm to 50 nm.

[0010] In addition, gradient-sized nanoclusters can also be formed inside the functional layer after ion implantation modification, and the gradient size range is 0.1 nm to 10 nm, and the central position d p range is 1 nm to 20 nm.

[0011] The present invention also provides a method for manufacturing the above-mentioned threshold switching device, which successively includes the following steps: bottom electrode deposition, functional layer growth, photolithography, controllable preparation of nanoparticles, and top electrode deposition processes; wherein the controllable preparation process of nanoparticles is realized by an ion implantation process, and the ion beam element type in the ion implantation process is an active metal, the energy range of the implanted ions is 1 keV to 30 keV, the dose range of the implanted ions is 10 13 ~10 17 ions / cm 2 , the ion implantation angle range is -45° to 45°, and the substrate temperature range during implantation is RT to 600 °C.

[0012] In the embodiments of the present invention, due to the mismatch of surface tension, the metal ions injected into the functional layer are not easily bonded to the oxide medium, but tend to bond with themselves to form nanoparticles or nanoclusters. The position, size, and distribution range of the nanoparticles or clusters in the functional layer are strictly controlled by the above process conditions.

[0013] Among them, the ion beam element is a single ion or a double ion; the ion beam element is Ag, Cu, Ni, Ag2Te, Ag2S, Ag2Se, Cu2S, Cu2Se or Cu2Te.

[0014] Through the above technical solutions conceived by the present invention, compared with the prior art, since the active metal nanoparticles prepared by ion implantation can control the region where the redox reaction occurs, the randomness of the growth of the conductive filaments is greatly reduced, and the consistency of the TS devices is significantly improved; at the same time, the nanoscale active electrode region also enables the conductive filaments to maintain the characteristic of spontaneous fracture even under a large limiting current, so that the on-state current of the TS devices is significantly increased, thus making up for its deficiencies in the application of large-scale memory chips.

[0015] In addition, compared with other traditional chemical and physical methods, the preparation method provided by the present invention has the following two advantages: (1) It has extremely high semiconductor process compatibility and simple process steps; (2) Precise controllability, stability, and reliability of the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The content of the present invention can be better understood when reading the following detailed description in conjunction with the accompanying drawings. It should be emphasized that, according to the standard practice in the industry, the various components are not drawn to scale.

[0017] Figure 1 The device structure of the control group provided by the prior art;

[0018] Figure 2 The device structure of Embodiment (I) of the present invention;

[0019] Figure 3 The device structure of Embodiment (II) of the present invention;

[0020] Figure 4 The specific preparation method flow of the TS device based on the ion implantation technology provided by the embodiments of the present invention;

[0021] Figure 5 The cyclic I-V curve diagram of the control group device provided by the prior art;

[0022] Figure 6 The cyclic I-V curve diagram of the device of Embodiment (I) of the present invention;

[0023] Figure 7It is the cyclic I-V curve diagram of the device in Embodiment (II) of the present invention;

[0024] Figure 8 It is the Vth distribution of different devices provided by the embodiments of the present invention.

[0025] Among them, 1 is the substrate, 2 is the bottom electrode, 3 is the functional layer, 4 is the active metal top electrode, 5 is the inert metal top electrode, 6 is the active metal nanoparticles, 7 is the ion implantation protection layer, and 8 is the active metal nanoclusters. Detailed implementation manners

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] Figure 1 It is the structure diagram of the TS device provided by the prior art. As a control group, the specific structure includes a substrate 1 (SiO2 / Si), a bottom electrode 2 (Pt / Ti), a functional layer 3 (HfO2), an active metal top electrode 4 (Ag) and an inert metal top electrode 5 (Pt).

[0028] Such as Figure 2 and Figure 3 As shown, the TS device provided by the embodiment of the present invention includes: a bottom electrode and a top electrode, and a functional layer located between the bottom electrode and the top electrode. The functional layer is modified by ion implantation, and active metal nanoparticles or nanoclusters with a certain size and concentration are distributed inside or on the surface thereof. The preparation method includes processes such as bottom electrode deposition, functional layer growth, photolithography, ion implantation, and top electrode deposition.

[0029] Among them, both the bottom electrode and the top electrode are inert metals, such as Pt, Pd, Au, Ru, W, TiN, TaN, doped Si, etc., and are deposited on the substrate by methods such as magnetron sputtering, thermal evaporation, or electron beam evaporation. The functional layer is a binary or multi-metal oxide, such as HfO2, Al2O3, ZrO2, SiO2, Ta2O5, MgO, TiO2, HfAlO x 、HfZrO x etc., and can be a single-layer or multi-layer structure, and is grown on the bottom electrode by methods such as atomic layer deposition (ALD), magnetron sputtering, pulsed laser deposition, thermal oxidation, evaporation, chemical vapor deposition, etc.

[0030] In the embodiments of the present invention, the functional layer of the TS device adopts a binary or multi-metal oxide material. The purpose is that this material is not easily bonded to active metal ions such as Ag or Cu, and the migration of these metal ions in the functional layer is relatively easy, so that the Ag or Cu conductive filaments can spontaneously break under a very small electric field or no electric field.

[0031] In the ion implantation process of the embodiments of the present invention, active metal elements are used, which can be single-ion or double-ion implantation, to form active metal nanoparticles in the functional layer, such as Ag, Cu, Ni, Ag2Te, Ag2S, Ag2Se, Cu2S, Cu2Se, Cu2Te, etc.; control the energy of the ion beam (a few keV to several hundred keV), and accurately implant the active metal ions into the interface between the functional layer and the top electrode or inside the functional layer, and the implantation depth range in the functional layer is 0-20 nm; control the implantation dose of the ion beam (10 13 ~10 17 ions / cm 2 ), so that the active metal ions form uniformly sized and controllable nanoparticles (a few nm to dozens of nm), and the depth and size distribution of the nanoparticles are accurately controlled by the energy and dose of the ion beam.

[0032] These uniform active metal nanoparticles limit the region where the redox reaction occurs, greatly reducing the randomness of the growth of the conductive filaments, thereby greatly improving the device consistency; at the same time, the nano-scale active electrode region also enables the conductive channel to still maintain the characteristic of spontaneous breakage under a large current limit, thereby significantly increasing the on-state current of the device.

[0033] The present invention can significantly improve the on-state current and consistency of the TS device, making up for its deficiencies in the application of large-scale memory chips.

[0034] As Figure 4 shown, the present invention also provides a method for preparing the above-mentioned threshold switching device, which sequentially includes the following steps: bottom electrode deposition, functional layer growth, lithography, controllable nanoparticle preparation, and top electrode deposition processes; among them, the controllable nanoparticle preparation process is realized by an ion implantation process, and the ion beam element type in the ion implantation process is an active metal, the energy range of the implanted ions is 1 keV to 30 keV, the dose range of the implanted ions is 10 13 ~10 17 ions / cm 2 , the ion implantation angle range is -45° to 45°, and the substrate temperature range during implantation is RT to 600°C.

[0035] Among them, the ion beam element is a single ion or a double ion; the ion beam element can be Ag, Cu, Ni, Ag2Te, Ag2S, Ag2Se, Cu2S, Cu2Se or Cu2Te.

[0036] Compared with other traditional chemical and physical methods, the preparation method provided by the present invention has the following two advantages: (1) It has ultra-high semiconductor process compatibility and simple process steps; (2) Precise controllability, stability and reliability of the process.

[0037] In order to describe in detail the threshold switching device and its preparation method provided by the embodiments of the present invention, the following is a detailed description with reference to the accompanying drawings and specific examples:

[0038] Embodiment (I):

[0039] Figure 2 It is a schematic structural diagram of the TS device provided by Embodiment (I), mainly including a substrate 1, a bottom electrode 2, a single-layer resistive random access memory material 3, active metal nanoparticles 6, an ion implantation protection layer 7 and an inert metal top electrode 5.

[0040] In the embodiment of the present invention, the substrate is Si with a grown SiO2 insulating layer, the single-crystalline silicon orientation is (100), the thickness of the SiO2 insulating layer is 1 μm, and it is ultrasonically cleaned and dried with acetone, absolute ethanol, and deionized water in sequence to remove surface contaminants.

[0041] In the embodiment of the present invention, the bottom electrode is Pt / Ti, where Ti is used as the adhesion layer of the bottom electrode, and Ti and Pt are grown on the substrate by DC magnetron sputtering in sequence. The sputtering power is 30 W, the Ar gas pressure is 0.5 Pa, the sputtering times are 75 s and 1500 s respectively, and the thicknesses of Ti and Pt are 5 nm and 100 nm respectively.

[0042] In the embodiment of the present invention, the functional layer is specifically HfO2 with a thickness of 10 nm, which is prepared by atomic layer deposition (ALD). The specific process of ALD is: the nitrogen gas flow rate is 0.5 sccm, the reaction chamber pressure is 100 - 500 mTorr, the reaction temperature is 250 °C, the reaction precursors are TEMA-Hf and H2O, the reaction rate is 0.1 nm deposited per cycle, and a total of 100 cycles are deposited.

[0043] In this embodiment, ultraviolet lithography is specifically used to prepare the top electrode pattern. The specific process is: the photoresist model is AZ5214, the spin coating time is 45 s, pre-baked at 97 °C for 2 min, the mask plate grid size is 100 μm, the pre-exposure time is 1.8 s, post-baked at 115 °C for 2 min, the post-exposure time is 18 s, and the development time is 35 s.

[0044] In this embodiment, the ion implantation protection layer is specifically Pt with a thickness of 10 nm, which is grown on the functional layer by DC magnetron sputtering, and can avoid damaging the functional layer during the ion implantation process.

[0045] In this embodiment, silver ion implantation is used to form uniform silver nanoparticles (Ag NPs) at the interface between the Pt protection layer and the HfO2 functional layer. The size of the Ag NPs is 5 nm to 10 nm. The ion implantation process is as follows: Using a silver ion source, the vacuum degree of the sample chamber reaches 10 -4 Pa, the implantation energy is 30 keV, and the dose is 10 15 ~10 17 ions / cm 2 , the angle between the sample normal and the ion beam is 45°, the sample tray is at room temperature, and no additional heating device is used.

[0046] In this embodiment, the inert metal top electrode is specifically Pt with a thickness of 40 nm, which is deposited by DC magnetron sputtering.

[0047] After the device preparation is completed, electrical characteristic test and analysis are carried out. As Figure 5 and 6 shown, the I-V curves of the control group device and the device of this embodiment are respectively presented, and the number of cycles is 50 times. The device of this embodiment exhibits obvious threshold transition characteristics near 0.4 V. Figure 8 shows its V th probability distribution. It can be seen that the V th consistency of the device D2 of this embodiment is significantly better than that of the control group device D1, and the fluctuation σ / μ decreases from 16.1% to 7.7%, indicating that the preparation method and process shown in this embodiment can improve the threshold transition consistency of the device.

[0048] Embodiment (II):

[0049] Figure 3 is a schematic structural diagram of the TS device provided by Embodiment (II), which mainly includes a substrate 1, a bottom electrode 2, a single-layer resistive random access memory material 3, nanoclusters 8, and a top electrode 5. Its ALD, magnetron sputtering, and photolithography processes are similar to those of Embodiment 1, and the process flow and specific preparation steps are the same as those of Embodiment (I). After the photolithography electrode pattern process, the ion implantation process of this embodiment is as follows:

[0050] Using a solid electrolyte ion source (SEIS), directly perform ion implantation on the HfO x functional layer without an additional protection layer. The vacuum degree of the sample chamber reaches 10 -4 Pa, the implantation energy is 4 keV, and the dose is 10 13 ~10 15 ions / cm 2, lower than that of Example (I), the ion beam is vertically injected into the sample (the angle between the sample normal and the ion beam is 0°), the sample tray is at room temperature, and no additional heating device is used. Low-energy and low-dose silver ions are injected into HfO x material to dope the functional layer. Silver ions agglomerate to form nanoclusters inside the functional layer. At the same time, due to the low energy and small dose, the functional layer will not be damaged to cause the device to short-circuit and fail.

[0051] Figure 7 This is the I-V curve of the device in this embodiment, and the number of cycles is 50 times. It can be seen that the device exhibits threshold switching characteristics near 0.1V, and V th is significantly lower than that of the control group and Example (I). This is because when the ion implantation directly dopes the HfO x functional layer, it will cause an increase in the defect concentration in the HfO x functional layer, which increases the mobility of Ag + ions, thereby reducing the threshold switching voltage V th . In addition, Figure 8 also shows the V th probability distribution. The V th fluctuation σ / μ of the device provided in this embodiment is only 3.5%. Compared with the control group, the device consistency has been significantly improved.

[0052] It is easy for those skilled in the art to understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A threshold switching device, characterized in that, It includes a bottom electrode, a top electrode, and a functional layer located between the bottom electrode and the top electrode; The functional layer is a binary or multi-metal oxide modified by ion implantation, and active metal nanoparticles are formed inside or on the surface of the functional layer after ion implantation modification; the active metal is Ag, Cu, Ni, Ag2Te, Ag2S, Ag2Se, Cu2S, Cu2Se or Cu2Te; In the functional layer after ion implantation modification, the implanted ion concentration shows a nearly Gaussian distribution along the depth of the functional layer; the sizes of the nanoclusters formed inside the functional layer after ion implantation modification show a gradient distribution; The active metal nanoparticles limit the region where the redox reaction occurs, reduce the randomness of the growth of conductive filaments, and improve the consistency of the threshold switching device; moreover, the nano-scale active electrode region enables the conductive channel to still maintain the characteristic of spontaneous rupture under a large current limit, and improves the on-state current density of the threshold switching device.

2. The threshold transition device according to claim 1, characterized in that, The material of the functional layer is HfO2, Al2O3, ZrO2, SiO2, Ta2O5, MgO, TiO2, HfAlO x or HfZrO x .

3. The threshold transition device according to claim 1 or 2, characterized in that, The functional layer is a single-layer structure or a multi-layer structure.

4. The threshold transition device according to any one of claims 1-3, characterized in that, The thickness of the functional layer is 5 nm to 20 nm.

5. The threshold transition device according to any one of claims 1-4, characterized in that, After ion implantation modification, a single layer of nanoparticles is formed on the surface of the functional layer, and the size range of the single layer of nanoparticles is 1 nm to 50 nm.

6. The threshold transition device according to any one of claims 1-5, characterized in that, The functional layer after ion implantation modification forms nano-clusters with gradient sizes inside it, and the gradient size range is 0.1 nm to 10 nm, and the central position d p The range is 1 nm to 20 nm.

7. A method for preparing the threshold switching device according to any one of claims 1-6, characterized in that, It sequentially includes the following steps: bottom electrode deposition, functional layer growth, lithography, controllable preparation of nanoparticles, and top electrode deposition process; Wherein the controllable preparation process of the nanoparticles is realized by an ion implantation process, and the elemental type of the ion beam in the ion implantation process is an active metal. The energy range of the implanted ions is 1 keV to 30 keV, and the dose range of the implanted ions is 10 13 ~10 17 ions / cm 2 , the angular range of ion implantation is -45° to 45°, and the substrate temperature range during implantation is RT to 600 °C.

8. The method according to claim 7, wherein The ion beam element is a single ion or a double ion.

9. The method according to claim 8, wherein, The ion beam element is Ag, Cu, Ni, Ag2Te, Ag2S, Ag2Se, Cu2S, Cu2Se or Cu2Te.

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