Patent Publication Number: US-2023165171-A1

Title: Selector with superlattice-like structure and preparation method thereof

Description:
TECHNICAL FIELD 
     The disclosure relates to the technical field of micro-nano electronics, and in particular to a selector with a superlattice-like structure and a preparation method thereof. 
     DESCRIPTION OF RELATED ART 
     With the vigorous development of big data, cloud computing, and Internet of Things industries, along with the explosive growth of massive information and the ever-expanding market demand, the efficient storage and the convenient transmission of data are strict requirements for storage technology at present. Various new high-performance storage technologies have also emerged accordingly. The phase change memory technology is widely recognized in the industry due to characteristics such as relatively mature material system, simple preparation process, good compatibility with CMOS, high device reliability, and advantages in terms of speed and service life. 
     There is the issue of leakage current in the phase change memory. The gate current may flow through the surrounding units, thereby affecting the reliability of the device. Therefore, each memory unit must be connected to a selector. The transition of the phase change material from crystalline to amorphous requires the selector to provide a sufficiently large reset current to heat the phase change material to a specific temperature, and during the process, atoms in the chalcogenide material with gating property in the gating tube may experience atomic drift due to high temperature, thereby causing the failure of the selector. 
     SUMMARY 
     In order to improve the temperature stability of a selector, the embodiments of the disclosure provide a selector with a superlattice-like structure and a preparation method thereof. The technical solutions are as follows. 
     In one aspect, an embodiment of the disclosure provides a selector with a superlattice-like structure. The selector includes a substrate, and a first metal electrode layer, a superlattice-like layer, and a second metal electrode layer sequentially stacked on the substrate. The superlattice-like layer includes n+1 first sublayers and n second sublayers alternately stacked periodically. A material of the first sublayer is amorphous carbon, and a material of the second sublayer is a chalcogenide with gating property. 
     Optionally, a thickness of the first sublayer is 5 to 30 nm. 
     Optionally, a thickness of the second sublayer is 5 to 20 nm. 
     Optionally, an alternate stacking periodic number n of the first sublayers and the second sublayers is 5 to 20. 
     Optionally, the first metal electrode layer and the second metal electrode layer are both inert electrodes, and a material of the inert metal electrode layer includes at least one of Pt, Ti, W, Au, Ru, Al, TiW, TiN, TaN, IrO 2 , ITO, and IZO, or an alloy material composed of any two or more of Pt, Ti, W, Au, Ru, Al, TiW, TiN, TaN, IrO 2 , ITO, and IZO. 
     In another aspect, an embodiment of the disclosure also provides a preparation method of a selector with a superlattice-like structure, which includes: 
     providing a substrate; 
     preparing a first metal electrode layer on the substrate; 
     preparing a superlattice-like layer on the first metal electrode layer, the superlattice-like layer includes n+1 first sublayers and n second sublayers alternately stacked periodically, a material of the first sublayer is amorphous carbon, and a material of the second sublayer is a chalcogenide with gating property; and preparing a second metal electrode layer on the superlattice-like layer. 
     Optionally, preparing the superlattice-like layer on the first metal electrode layer includes: 
     depositing the first sublayers and the second sublayers sequentially on the first metal electrode layer until an alternate stacking periodic number n is completed. 
     Optionally, the depositing includes adopting a physical vapor deposition, a chemical vapor deposition, a molecular beam epitaxy, an atomic layer deposition, or a metal organic deposition. 
     Optionally, a thickness of the first sublayer is 5 to 30 nm. 
     Optionally, a thickness of the second sublayer is 5 to 20 nm. 
     The beneficial effects of the technical solutions according to the embodiments of the disclosure include at least the following. 
     (1) The amorphous carbon of the first sublayer is in contact with the first metal electrode layer and the second metal electrode layer as a buffer layer. Since the radius of carbon atoms in the amorphous carbon is very small, the bond length formed between the carbon atoms is very small and is smaller than the diameter of atoms in the chalcogenide, the atoms in the chalcogenide cannot pass through the amorphous carbon layer, thereby preventing atomic drift in the chalcogenide material with gating property due to high temperature, and also avoiding cross contamination due to the introduction of new materials. At the same time, compared to the selector with switching material of the same thickness, due to the low thermal conductivity of the amorphous carbon, the selector of the disclosure can not only ensure that the threshold voltage of the selector is not affected, but also enable the heat diffused to the selector unit when the phase change material melts to be smaller after integration with the phase change memory unit. 
     (2) Due to the inhibition of crystallization, the thinner the thickness of the chalcogenide, the more stable the bond formation thereof. The insertion of the amorphous carbon layer of the first sublayer separates the chalcogenide with gating property in the thickness direction, so that the thickness of the second sublayer  132  is only 5 to 20 nm, so that the chalcogenide of the second sublayer has very good temperature stability, thereby improving the temperature stability of the entire selector unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to illustrate the technical solutions in the embodiments of the disclosure more clearly, the following briefly introduces the drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the disclosure. For persons skilled in the art, other drawings may also be obtained from the drawings without innovative effort. 
         FIG.  1    is a schematic structural diagram of a selector with a superlattice-like structure according to an embodiment of the disclosure. 
         FIG.  2    is a flowchart of a preparation method of a selector with a superlattice-like structure according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
     In order for the objectives, the technical solutions, and the advantages of the disclosure to be clearer, the embodiments of the disclosure will be further described in detail below with reference to the drawings. 
     An embodiment of the disclosure provides a selector with a superlattice-like structure.  FIG.  1    is a schematic structural diagram of a selector with a superlattice-like structure according to an embodiment of the disclosure, as shown in  FIG.  1   . 
     For a selector with a superlattice-like structure, the selector includes a substrate  110 , and a first metal electrode layer  120 , a superlattice-like layer  130 , and a second metal electrode layer  140  sequentially stacked on the substrate  110 . The superlattice-like layer  130  includes n+1 first sublayers  131  and n second sublayers  132  alternately stacked periodically. The material of the first sublayer  131  is amorphous carbon, and the material of the second sublayer  132  is a chalcogenide with gating property. 
     The amorphous carbon of the first sublayer is in contact with the first metal electrode layer and the second metal electrode layer as a buffer layer. Since the radius of carbon atoms in the amorphous carbon is very small, the bond length formed between the carbon atoms is very small and is smaller than the diameter of atoms in the chalcogenide, the atoms in the chalcogenide cannot pass through the amorphous carbon layer, thereby preventing atomic drift in the chalcogenide material with gating property due to high temperature, and also avoiding cross contamination due to the introduction of new materials. At the same time, compared to the selector with switching material of the same thickness, due to the low thermal conductivity of the amorphous carbon, the selector of the disclosure can not only ensure that the threshold voltage of the selector is not affected, but also enable the heat diffused to the selector unit when the phase change material melts to be smaller during integration with the phase change memory unit. 
     It can be understood that the chalcogenide with gating property in the second sublayer refers to a chalcogenide that can implement instantaneous transition from a high resistance state to a low resistance state under an electrical signal operation, and spontaneously return to the high resistance state instantaneously when the electrical signal operation is removed. 
     In some implementations, the chalcogenide with gating property may be a compound composed of one of the first elements (Si, Ge, Sn) combined with one or two of the second elements (S, Se, Te). Specifically, GeTe, GeS, SiTe, SnTe, SnSe, GeSeTe, etc. may be included. 
     Optionally, the thickness of the first sublayer  131  may be 5 to 30 nm to obtain a better buffer effect and prevent atomic drift in the chalcogenide material with gating property due to high temperature. 
     Optionally, an alternate stacking periodic number n of the first sublayers and the second sublayers is 5 to 20. 
     Optionally, the thickness of the second sublayer  132  may be 5 to 20 nm. Due to the inhibition of crystallization, the thinner the thickness of the chalcogenide, the more stable the bond formation thereof. The insertion of the amorphous carbon layer of the first sublayer  131  separates the chalcogenide with gating property in the thickness direction, so that the thickness of the second sublayer  132  is only 2 to 20 nm, so that the chalcogenide of the second sublayer has very good temperature stability, thereby improving the temperature stability of the entire selector unit. 
     Optionally, the thickness of the first sublayer  131  is greater than the thickness of the second sublayer  132 , so as to better physically separate and thermally separate the chalcogenide with gating property. 
     Optionally, the alternate stacking periodic number n of the first sublayers  131  and the second sublayers  132  is 5 to 20. In this way, the coupling between adjacent wells is stronger, and periodic quantum potential wells are formed in the superlattice-like layer  130 , so that the discrete energy levels in each quantum well are expanded into energy bands, thereby reducing the width of the bandgap, so that the threshold voltage of the selector with the superlattice-like layer  130  is lowered, which can not only reduce power consumption, but also better integrate with the memory device unit. 
     Optionally, the first metal electrode layer  120  and the second metal electrode layer  140  are both inert metal electrode layers. Since in the inert metal electrode layer, it is difficult for the inert metal to combine with other elements, active metal conductive particles in the superlattice-like layer  130  can be effectively prevented from diffusing into the electrode on the one hand, thereby improving the cycle characteristic of the device; device failure due to oxidation or erosion of the inert metal electrode layer can also be effectively prevented on the other hand. 
     Preferably, the material of the inert metal electrode layer includes at least one of Pt, Ti, W, Au, Ru, Al, TiW, TiN, TaN, IrO 2 , ITO, and IZO, or an alloy material composed of any two or more of Pt, Ti, W, Au, Ru, Al, TiW, TiN, TaN, IrO 2 , ITO, and IZO. 
     An embodiment of the disclosure provides a preparation method of a selector with a superlattice-like structure.  FIG.  2    is a flowchart of a preparation method of a selector with a superlattice-like structure according to an embodiment of the disclosure. As shown in  FIG.  2   , the method includes: 
     providing a substrate; 
     preparing a first metal electrode layer on the substrate; 
     preparing a superlattice-like layer on the first metal electrode layer, the superlattice-like layer includes n+1 first sublayers and n second sublayers alternately stacked periodically, a material of the first sublayer is amorphous carbon, and a material of the second sublayer is a chalcogenide with gating property; and preparing a second metal electrode layer on the superlattice-like layer. 
     Specifically, the method may include the following. 
     In step S 11 , providing a substrate. 
     In the embodiment, the substrate may be a semiconductor substrate. Specifically, the semiconductor substrate may be a silicon wafer with a crystal phase of &lt;100&gt; and a layer of silicon dioxide on the surface. 
     During implementation, the substrate may be cleaned first, and the silicon wafers may be sequentially placed in acetone and alcohol for ultrasonic ceaning for about ten minutes; and after the ultrasonication is completed, the residual liquid on the surface is blown and dried with a nitrogen gun for subsequent use. On the cleaned silicon wafer, a dense layer of silicon dioxide is grown using plasma-enhanced chemical vapor deposition or atomic layer deposition. 
     In step S 12 , preparing a first metal electrode layer on the substrate. 
     Specifically, the first metal electrode layer is an inert metal electrode layer, and the material of the inert metal electrode layer includes at least one of Pt, Ti, W, Au, Ru, Al, TiW, TiN, TaN, IrO 2 , ITO, and IZO, or an alloy material composed of any two or more of Pt, Ti, W, Au, Ru, Al, TiW, TiN, TaN, IrO 2 , ITO, and IZO. 
     During implementation, a 100 nm Pt metal layer may be sputtered on the substrate through magnetron as the first metal electrode layer. 
     In step S 13 , depositing a superlattice-like layer on the first metal electrode layer. The superlattice-like layer includes n+1 first sublayers and n second sublayers periodically alternately stacked. The material of the first sublayer is amorphous carbon, and the material of the second sublayer is a chalcogenide with gating property. 
     Specifically, the first sublayers and the second sublayers are sequentially deposited on the first metal electrode layer until an alternate stacking periodic number n is completed, where n is a positive integer. The depositing may include adopting a physical vapor deposition, a chemical vapor deposition, a molecular beam epitaxy, an atomic layer deposition, or a metal organic deposition to form the first sublayer or the second sublayer. 
     It can be understood that the chalcogenide with gating property in the second sublayer refers to a chalcogenide that can implement instantaneous transition from a high resistance state to a low resistance state under an electrical signal operation, and spontaneously return to the high resistance state instantaneously when the electrical signal operation is removed. 
     In some implementations, the chalcogenide with gating property may be a compound composed of one of the first elements (Si, Ge, Sn) combined with one or two of the second elements (S, Se, Te). Specifically, GeTe, GeS, SiTe, SnTe, SnSe, GeSeTe, etc. may be included. 
     Preferably, the alternate stacking periodic number n of the first sublayers and the second sublayers in the superlattice-like layer is 5 to 20. 
     Optionally, the thickness of the first sublayer may be 5 to 30 nm to obtain a better buffer effect and prevent atomic drift in the chalcogenide material with gating property due to high temperature. 
     Optionally, the thickness of the second sublayer may be 5 to 20 nm. The thinner the thickness of the second sublayer, the more stable the bond formation thereof, so that the selector has better temperature stability. The insertion of the amorphous carbon layer in the first sublayer separates the chalcogenide with gating property in the thickness direction, so that the thickness of the second sublayer is only 5 to 20 nm, so that the chalcogenide of the second sublayer has very good temperature stability, thereby improving the temperature stability of the entire selector unit. 
     During implementation, a layer of amorphous carbon material may be deposited on the first metal electrode layer as the first sublayer with a thickness of 5 nm; a layer of GeS material is then grown as the second sublayer with a thickness of 5 nm; an amorphous carbon material layer-a GeS material layer-an amorphous carbon material layer- . . . -GeS-an amorphous carbon material layer are then alternately grown to form the superlattice-like layer. The superlattice-like layer contains n+1 amorphous carbon material layers and n GeS material layers. 
     The amorphous carbon of the first sublayer is in contact with the first metal electrode layer and the second metal electrode layer as a buffer layer, which can prevent atomic drift in the chalcogenide material with gating property due to high temperature, and also avoid cross contamination due to the introduction of new materials. At the same time, compared to the selector with switching material of the same thickness, the selector of the disclosure can not only ensure that the threshold voltage of the selector is not affected, due to the low thermal conductivity of the amorphous carbon, the selector can also enable the heat diffused to the selector unit when the phase change material melts to be smaller during integration with the phase change memory unit. 
     In step S 14 , preparing a second metal electrode layer on the superlattice-like layer. 
     The second metal electrode layer is prepared on the superlattice-like layer. Specifically, the second metal electrode layer is an inert metal electrode layer, and the material of the inert metal electrode layer includes at least one of Pt, Ti, W, Au, Ru, Al, TiW, TiN, TaN, IrO 2 , ITO, and IZO, or an alloy material composed of any two or more of Pt, Ti, W, Au, Ru, Al, TiW, TiN, TaN, IrO 2 , ITO, and IZO. 
     During implementation, a 100 nm W metal layer may be sputtered on the superlattice-like layer through magnetron as the second metal electrode layer. 
     The above are only preferred embodiments of the disclosure and are not intended to limit the disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the disclosure shall all be included in the protection scope of the disclosure.