Abstract:
The present invention pertains to the technical field of semi-conductor memory. More particularly, the invention relates to a resistive memory based on TaO x  containing Ru doping. The resistive memory comprises an upper electrode, a lower electrode and a TaO x  based storage medium layer containing Ru doping and provided between the upper electrode and the lower electrode. In the storage medium layer based on TaO x  containing Ru doping, the position at which conductive filaments are formed in the storage medium layer based on TaO x  and their number can be effectively controlled through the distributed Ru element, thus avoiding the possibility of random formation. Therefore, the storage performance is more stable and fluctuation of device characteristic parameter is small. Meanwhile, an integration with copper interconnection process at or below 32 nm is made easier.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains to the technical field of semi-conductor memory, and relates to a resistive memory based on metal oxide TaO x  (2≦x≦3) containing Ru doping and method of preparing the same. More particularly, the invention relates to a resistive memory which uses TaO x  matrix containing Ru doping as storage medium, and a method of preparing the resistive memory. 
       BACKGROUND 
       [0002]    Memories have possessed an important position in the market of semiconductors. Due to increasing popularity of portable electronic devices, non-volatile memories have occupied a larger and larger share in the whole market of memory, wherein over 90% shares are held by FLASH. However, due to requirements on storage charge, the floating gate of FLASH cannot be made thinner limitlessly with the development of technology generations. It is reported that the limit of FLASH technology is predicted to be at around 32 nm. Thus, it is urgent to seek a next generation of non-volatile memory having a more superior performance. Recently, resistive switching memory has drawn high degree of attention due to such characteristics as high density, low cost, and being able to break through limitations on development of technical generations. Materials used by resistive switching memory comprises phase-change material, doped SrZrO 3 , Ferroelectric material PbZrTiO 3 , Ferromagnetic material Pr 1-x Ca x MnO 3 , binary metal oxide material, organic material, etc. 
         [0003]    Resistive memory switches between a high resistance state (HRS) and a low resistance state (LRS) in a reversible manner under the effect of electrical signal, thereby realizing storage function. The storage medium material used by resistive memory can be various semiconductor metal oxide materials such as Copper oxide, Titanium dioxide, Tungsten oxide, etc. 
         [0004]    TaO x  (1&lt;x≦3) is one of the binary metal oxide materials. The resistance switching characteristic has been reported by Z. Wei et al. in Panasonic Corporation in a document entitled “Highly reliable TaOx ReRAM and Direct Evidence of Redox Reaction Mechanism”, IEDM, 2008. Therefore, TaO x  can be used as storage medium for resistive memory. As can be seen from the document, the Gibbs free energy ΔG of TaO x  is small and therefore its switching between LRS and HRS is fast, up to the order of nanosecond. Thus, the problem of applying resistive memory in high speed memory has been solved. 
         [0005]    Furthermore, with the development of semiconductor process technology, key sizes are being reduced continuously, and it is necessary that resistive memory technology extends post 45 nm process node. Due to limitations of grain size, corresponding oxides of materials of Cu, W, etc., when used as storage medium, will result in a large leak current, thus increasing power consumption and making it impossible to replace FLASH effectively in the process node of 45 nm and 32 nm. Moreover, at the process node of 32 nm, it is required to reduce the thickness of barrier layer in copper interconnection structure to be 3.6 nm and further increase the ration between depth and width. Traditional Ti/TiN, Ta/TaN, etc., can not meet such requirements. In addition, due to decrease of process sizes, process fluctuation is also more significant, and the problem of electrical characteristic fluctuation of resistive memory based on TaO x  becomes more prominent. 
         [0006]    S. M. Rossnagel, et al., in IBM Corporation points out in a document entitled “Interconnect issues post 45 nm, S. M. Rossnagel” (IEEE INTERNATIONAL ELECTRON DEVICES MEETING 2005, TECHNICAL DIGEST, p 95-97, 2005) that copper diffusion barrier layer material will adopt Ru/TaN complex layer material when post 32 nm process node. 
         [0007]    In view of the above prior art, it is necessary to propose a novel resistive type resistance memory. 
       SUMMARY OF THE INVENTION 
       [0008]    The objective of the invention is to provide a TaO x  based resistive memory and a method of preparing the same so as to solve the problem of fluctuation of device performance parameters and the problem that prior resistive memory are not easily compatible with copper interconnection process at or below 32 nm process node. 
         [0009]    In order to achieve the above objective or other objectives, the invention provides the following technical solution. 
         [0010]    According to one aspect of the invention, a TaO x  based resistive memory is provided comprising an upper electrode, a lower electrode and a TaO x  based storage medium layer containing Ru doping and provided between the upper electrode and the lower electrode. 
         [0011]    According to a preferred technical solution, the storage medium layer is formed by performing annealing diffusion doping of Ru on a TaO x  thin film layer, wherein 2≦x≦3. 
         [0012]    According to another preferred technical solution, the storage medium layer is formed by performing ion implantation doping of Ru on a TaO x  thin film layer, wherein 2≦x≦3. 
         [0013]    Preferably, the thickness range of the storage medium layer is from 1 nm to 200 nm. 
         [0014]    According to an embodiment of the TaO x  based resistive memory of the invention, the TaO x  based resistive memory further comprises a first dielectric layer located above the lower electrode and apertures formed through the first dielectric layer, the storage medium layer being located at the bottom of the aperture. 
         [0015]    According to another embodiment of the TaO x  based resistive memory of the invention, the lower electrode is copper wire formed in channel in a copper interconnection back-end structure, the storage medium layer being formed at the bottom of copper plug. 
         [0016]    According to yet another embodiment of the TaO x  based resistive memory of the invention, the lower electrode is copper plug in a copper interconnection back-end structure, the storage medium layer being formed at the top of copper plug. 
         [0017]    Preferably, the copper interconnection back-end structure is a copper interconnection back-end structure at or below 32 nm process node, wherein copper diffusion barrier layer is Ru/TaN complex layer. 
         [0018]    In the storage medium layer, the atomic percentage of Ru element in the storage medium layer is 0.001%-20%. 
         [0019]    In the storage medium layer, Ru element exists in the storage medium layer in the form of nano crystal. 
         [0020]    The upper electrode is a metal layer of Ta, TaN, Ti, TiN, W, Ni, Al, Co, Cu or Ru, or a complex layer structure formed by any combination of these metal layers. 
         [0021]    According to another aspect of the invention, a method of preparing the above TaO x  based resistive memory is provided, the method comprising the following steps: 
         [0022]    (1) pattern-forming a lower electrode; 
         [0023]    (2) pattern-forming a storage medium layer based on TaO x  containing Ru doping on the lower electrode; and 
         [0024]    (3) pattern-forming an upper electrode on the storage medium layer. 
         [0025]    According to an embodiment of the method of preparing the TaO x  based resistive memory of the invention, said step (2) comprises the following steps: 
         [0026]    (2a) forming a TaO x  thin film layer on the lower electrode, wherein 2≦x≦3; 
         [0027]    (2b) depositing a Ru metal thin film layer or a Ru oxide layer on the TaO x  thin film layer; 
         [0028]    (2c) forming a storage medium layer based on TaO x  containing Ru doping by annealing diffusion doping. 
         [0029]    According to another embodiment of the method of preparing the TaO x  based resistive memory of the invention, said step (2) comprises the following steps: 
         [0030]    (2a′) forming a Ru metal thin film layer or a Ru oxide layer on the lower electrode; 
         [0031]    (2b′) depositing a TaO x  thin film layer on the Ru metal thin film layer, wherein 2≦x≦3; 
         [0032]    (2c′) forming a storage medium layer based on TaO x  containing Ru doping by annealing diffusion doping. 
         [0033]    According to yet another embodiment of the method of preparing the TaO x  based resistive memory of the invention, said step (2) comprises the following steps: 
         [0034]    (2A) forming a first Ru metal thin film layer or a first Ru oxide layer on the lower electrode; 
         [0035]    (2B) depositing a TaO x  thin film layer on the first Ru metal thin film layer, wherein 2≦x≦3; 
         [0036]    (2C) depositing a second Ru metal thin film layer or a second Ru oxide layer on the TaO x  thin film layer; 
         [0037]    (2D) forming a storage medium layer based on TaO x  containing Ru doping by annealing diffusion doping. 
         [0038]    According to still another embodiment of the method of preparing the TaO x  based resistive memory of the invention, said step (2) comprises the following steps: 
         [0039]    (2A′) forming a first TaO x  thin film layer on the lower electrode, wherein 2≦x≦3; 
         [0040]    (2B′) depositing a Ru metal thin film layer or a Ru oxide layer on the TaO x  thin film layer; 
         [0041]    (2C′) forming a second TaO x  thin film layer on the Ru metal thin film layer; 
         [0042]    (2D′) forming a storage medium layer based on TaO x  containing Ru doping by annealing diffusion doping. 
         [0043]    Preferably, the thickness range of the Ru metal thin film layer is from about 0.3nm to about 150 nm; the thickness range of the Ru oxide layer is from about 0.3 nm to about 10 nm. The thickness range of the TaO x  thin film layer is from about 1 nm to about 200 nm. 
         [0044]    The TaO x  thin film layer is formed by oxidizing Ta metal; said oxidizing is an oxidizing in oxygen containing gas at high temperature, an oxidizing in oxygen plasma at high temperature or wet oxidizing. 
         [0045]    The Ru oxide layer is RuO 2 ; when in annealing, a temperature range between 400° C. to 900° C. is selected, wherein the following decomposition reaction occurs on RuO 2 :RuO 2 →Ru+O 2    
         [0046]    The technical effect brought about by the invention lies in that in the storage medium layer based on TaO x  containing Ru doping, the position at which conductive filaments are formed in the storage medium layer based on TaO x  and their number can be effectively controlled through the distributed Ru element, thus avoiding the possibility of random formation. Therefore, the storage performance is made more stable and fluctuation of device characteristic parameter is small. Meanwhile, an integration with copper interconnection process at or below 32 nm is made easier. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]    The above and other objectives and advantages of the invention will become more fully apparent from the following detailed description with reference to accompanying drawings, wherein identical or similar elements are denoted by identical signs. 
           [0048]      FIG. 1  is a schematic structure view of a TaO x  based resistive memory according to a first embodiment of the invention; 
           [0049]      FIG. 2  is a schematic view explaining functional model of the TaO x  based resistive memory shown in  FIG. 1 ; 
           [0050]      FIG. 3  is a schematic structure view of a TaO x  based resistive memory according to a second embodiment of the invention; 
           [0051]      FIG. 4  is a schematic view showing the first embodiment of the method of preparing the TaO x  based resistive memory shown in  FIG. 3 ; 
           [0052]      FIG. 5  is a schematic view showing the second embodiment of the method of preparing the TaO x  based resistive memory shown in  FIG. 3 ; 
           [0053]      FIG. 6  is a schematic view showing the third embodiment of the method of preparing the TaO x  based resistive memory shown in  FIG. 3 ; 
           [0054]      FIG. 7  is a schematic view showing the fourth embodiment of the method of preparing the TaO x  based resistive memory shown in  FIG. 3 ; 
           [0055]      FIGS. 8 to 11  are schematic structure views showing dope forming (TaO x :Ru) storage medium layer with Ru oxide layer as diffusion doping layer; 
           [0056]      FIG. 12  is a schematic principal view of annealing diffusion with Ru oxide layer as diffusion doping layer; 
           [0057]      FIG. 13  is a schematic structure view of a TaO x  based resistive memory according to a third embodiment of the invention; 
           [0058]      FIG. 14  is a schematic structure view of a TaO x  based resistive memory according to a fourth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0059]    The invention will be more fully described in exemplary embodiments with reference to accompanying drawings hereinafter. While the invention provides preferred embodiments, it is not intended that the invention is limited to the described embodiments. For clarity, the thicknesses of layers and regions have been exaggerated in the drawings. However, it should not be construed that these schematic views strictly reflect proportional relationship between geometrical dimensions. 
         [0060]    Herein, the reference views are schematic views of idealized embodiments of the invention. The illustrated embodiments of the invention should not be considered to be merely limited to the particular shapes of regions shown in the drawings. Rather, the invention comprises various shapes that can be derived, such as deviations caused during manufacture. For example, a profile obtained by dry etching generally has such characteristics of being curved or rounded, however, they are all represented by a rectangle in the drawings of embodiments of the invention. The illustrations in the drawings are schematic and should not be construed as limiting the scope of invention. 
         [0061]      FIG. 1  is a schematic structure view of a TaO x  based resistive memory according to a first embodiment of the invention. As shown in  FIG. 1 , the resistive memory  10  comprises an upper electrode  130 , a lower electrode  110  and a storage medium layer  120  of TaO x  containing Ru doping (TaO x :Ru) provided between the upper electrode and the lower electrode, wherein 2≦x≦3. The amount of doped Ru can be selected according to specific requirements on storage characteristics. Specifically, according to a preferred scope of doped amount, the atomic percentage of Ru element in the storage medium layer is 0.001%-20%, such as 0.5% or 2%. The form in which Ru element exists in the storage medium layer  120  is not restricted by the invention. For example, Ru can exist in the form of separate Ru element, or in the form of RuO or RuO 2 , or in the form of any combination of the above three forms. In structure, Ru, RuO or RuO 2  can exist in the form of nano crystal. Moreover, oxygen element can be distributed in the storage medium layer  120  in an even or uneven manner. For example, it can be distributed in such a way that it decreases gradually from top to bottom in the storage medium layer  120 . The specific content of oxygen element and specific distribution form are related to the method of oxidizing and process conditions. The thickness of the storage medium layer  120  is not restricted by the invention. Preferably, the thickness range can be from about 1 nm to about 200 nm. 
         [0062]    An electrical signal, such as a voltage pulse signal and a current pulse signal, is applied between the upper electrode  130  and the lower electrode  110 . (TaO x :Ru) storage medium layer  120  can be switched between a high resistance state and a low resistance state, wherein the switch from high resistance state to low resistance state is defined as Set operation, and the switch from low resistance state to high resistance state is defined as Reset operation. According to the principle of resistive memory, the switch of storage medium layer between a high resistance state and a low resistance state is realized by a formation and disconnect of filament in the storage medium layer. After TaO x  is doped with Ru, the storage characteristic of device is more stable as compared with prior resistive memory in which TaO x  is used as storage medium layer. For example, the distribution in high resistance state or low resistance state is more even. Therefore, the resistive memory  10  can effectively prevent fluctuation of characteristic parameters of device 
         [0063]      FIG. 2  is a schematic view explaining functional model of the TaO x  based resistive memory shown in  FIG. 1 . As shown in  FIG. 2 , the resistive memory is in the low resistance state. Several conductive filaments  122  are formed in the (TaO x :Ru) storage medium layer  120 . The conductive filaments  122  have a relatively lower resistance, thus conducting the upper electrode  130  and the lower electrode. The filaments are typically formed by oxygen vacancies. After Ru is doped, the conductive Ru or Ru oxide are distributed in the storage medium layer  120 . When the Set operation is performed, filaments are more prone to be formed at positions where Ru element is distributed, thus effectively controlling the positions where conductive filaments  122  are formed and the number thereof and avoiding the possibility of random formation. Therefore, the storage characteristic can be made more stable. In the illustrated embodiment, each filament is distributed with doped Ru  121  which exists in the form of nano crystal. 
         [0064]      FIG. 3  is a schematic structure view of a TaO x  based resistive memory according to a second embodiment of the invention. Again, the resistive memory  10  comprises a lower electrode  20 , an upper electrode  50 , and a storage medium layer  30  of TaO x  containing Ru doping (TaO x :Ru) formed between the upper electrode  50  and the lower electrode  20 . This embodiment differs from the embodiment shown in  FIG. 1  in that it further comprises a dielectric layer  40  above the lower electrode  20  and apertures formed through the dielectric layer  40 , and the (TaO x :Ru) storage medium layer  30  is formed at the bottom the apertures of the dielectric layer  40 . Therefore, the area of (TaO x :Ru) storage medium layer  30  is defined by the apertures of the dielectric layer. In order to facilitate integrating with copper interconnection process, it is preferred that the lower electrode  20  is selected as copper metal layer, such as copper wire. 
         [0065]    The method process of preparing TaO x  based resistive memory will be further described in combination with the embodiment shown in  FIG. 3  hereinafter. 
         [0066]      FIG. 4  is a schematic view showing the first embodiment of the method of preparing the TaO x  based resistive memory shown in  FIG. 3 . 
         [0067]    As shown in  FIG. 4   a , at step S 10 , a dielectric layer  40  is deposited on the lower electrode  20 ; the lower electrode  20  can be various conductive metal layer such as copper metal layer or Ta metal layer. The thickness of the dielectric layer  40  is selected and determined according to the thickness of the storage medium layer. The material of the dielectric layer  40  can be SiO 2 , Si 3 N 4 , SiOCH, FSG (F doped silicon oxide) HSQ (H doped silicon oxide) or a complex material thereof, or other materials which function as well. The dielectric layer  40  can be formed by sputtering, CVD deposition, etc. 
         [0068]    As shown in  FIG. 4   b , at step S 20 , apertures  21  are formed on the dielectric layer  40  by pattern-etching; the area of apertures  21  is selected and determined according to the area of storage medium layer intended to be formed. The apertures  21  can be formed by conventional lithography etching process. 
         [0069]    As shown in  FIG. 4 ; at step S 30 , a TaO x  thin film layer  31  is formed at the bottom of the apertures. The TaO x  thin film layer is mainly formed by the two following methods: (1) direct depositing; (2) oxidizing Ta metal. When the first method is employed, for example, the TaO x  thin film layer can be formed by reactive sputter deposition in oxygen gas atmosphere. The process conditions of sputter (e.g., flow of oxygen gas, pressure, temperature, etc) determine the ratio of specific components of the TaO x  thin film layer. Those skilled in the art, when enlightened by this application, can determine specific process conditions experimentally. When the second method is employed, there exists two different procedures to form the TaO x  thin film layer: (a) the lower electrode  20  uses Ta metal, and the TaO x  thin film layer  31  is formed by oxidizing part of Ta metal with the dielectric layer  40  as mask; (b) a Ta metal thin film layer is deposited first and the TaO x  thin film layer  31  is then formed by oxidizing Ta metal thin film layer, wherein the methods of oxidizing main includes: (1) oxidizing in gas containing oxygen at high temperature; (2) oxidizing in oxygen plasma at high temperature; (3) wet oxidizing. Taking the oxidizing method in (1) as an example, by exposing Ta metal thin film layer in the apertures  21  to oxygen containing gas at a certain high temperature (300° C.-600° C.) condition, a chemical reaction will occur between the Ta metal and the gas and a TaO x  compound layer will be produces by oxidizing. In this embodiment, the constant gas pressure during the chemical reaction is smaller than 20 Torr. In the produced TaO x  compound layer, 2≦x≦3, the stoichiometric ratio of oxygen and Ta is relevant to the process parameters during formation, such as gas flow, temperature, duration etc, and the ratio of oxygen and Ta in the TaO x  compound layer is not necessarily entirely even. In this embodiment, since Ta on the surface is more easily bonded to gas containing oxygen, the closer it is to the lower electrode  20  in the TaO x  compound layer, the higher the ratio of Ta and oxygen is. The thickness of the TaO x  thin film layer  31  is not restricted by the invention. Preferably, the thickness range can be from about 1 nm to about 40 nm, e.g., 5 nm. 
         [0070]    As shown in  FIG. 4   d , at step S 40 , a Ru metal thin film layer  32  is deposited on the TaO x  thin film layer  31 . The Ru metal thin film layer  32  is mainly used for diffusion doping. Therefore, a thinner thickness is selected for the Ru metal thin film layer  32 . The thickness range of the Ru metal thin film layer  32  can be from about 0.3 nm to about 10 nm. For example, it can be selected as him or 2 nm. The Ru metal thin film layer  32  can be formed by such processes as sputter, ALD (atomic layer deposition), etc. 
         [0071]    As shown in  FIG. 4   e , at step S 50 , the (TaO x :Ru) storage medium layer  30  is formed by annealing diffusion doping. In this embodiment, Ru at the surface layer can be diffused to the TaO x  thin film layer by annealing in certain conditions, so that the (TaO x  : Ru) storage medium layer  30  is formed. Specifically, a quick annealing treatment in vacuum condition can be selected, wherein the annealing temperature is 300° C.-700° C. and the annealing duration is 10-30 minutes. Ru atoms diffuse into the TaO x  thin film layer and exist in the storage medium layer  30  in the form of Ru atoms or RuOz (1≦z≦2) oxides. 
         [0072]    As shown in  FIG. 4   f , at step S 60 , the upper electrode  50  is formed by patterning. The upper electrode  50  and the lower electrode  30  can be of a single layer structure, and can be metal materials such as Ta, TaN, Ti, TiN, W, Ni, Al, Co, Cu or Ru, or a complex layer structure formed by any combination of these single layer structures. For example, when the thickness of the Ru metal thin film layer  32  is thick and Ru does not totally diffuse, the remaining Ru metal (not shown) can be used as a portion of the upper electrode  50 . 
         [0073]    Hitherto, the TaO x  based resistive memory shown in  FIG. 3  is substantially formed. The preparation method shown in  FIG. 4  has many modifications, especially on the structure before forming the (TaO x :Ru) storage medium layer  30  by doping. There can be many modifications on the positions of Ru metal thin film layer and TaO x  thin film layer, which will be described respectively hereinafter. 
         [0074]      FIG. 5  is a schematic view showing the second embodiment of the method of preparing the TaO x  based resistive memory shown in  FIG. 3 . As compared with the embodiment shown in  FIG. 4 , the embodiment shown in  FIG. 5  is different in that it performs step S 40  first before performing step S 50 . As shown in  FIG. 5   c , the Ru metal thin film layer  32  is formed at the bottom of the apertures. Then, as shown in  FIG. 5   d , the TaO x  thin film layer  31  is deposited on the Ru metal thin film layer  32 . During annealing diffusion, Ru is diffusion doped upwardly from the bottom. Other steps are substantially the same as those described above and will not be discussed repeatedly. 
         [0075]      FIG. 6  is a schematic view showing the third embodiment of the method of preparing the TaO x  based resistive memory shown in  FIG. 3 . As compared with the embodiment shown in  FIG. 5 , the embodiment shown in  FIG. 6  is different in that a Ru metal thin film layer  32   b  and  32   a  are formed both above and below the TaO x  thin film layer  32  respectively, and Ru is diffusion doped towards the TaO x  thin film layer  31  simultaneously from the bottom and top of the TaO x  thin film layer  31 . As shown in  FIG. 6   c , a Ru metal thin film layer  32   a  is formed at the bottom of the apertures; as further shown in  FIG. 6   d , a TaO x  thin film layer  31  is deposited on the Ru metal thin film layer  32   a;  then, as shown in  FIG. 6   e , the Ru metal thin film layer  32   b  is deposited on the TaO x  thin film layer  31 . Other steps are substantially the same as those described above with respect to  FIG. 4  and will not be discussed repeatedly. 
         [0076]      FIG. 7  is a schematic view showing the fourth embodiment of the method of preparing the TaO x  based resistive memory shown in  FIG. 3 . As compared with the embodiment shown in  FIG. 4 , the embodiment shown in  FIG. 7  is different in that a Ru metal thin film layer  32  is formed between two TaO x  thin film layers  31   a  and  31   b,  and Ru is diffusion doped from the bottom of the TaO x  thin film layer  31   a  and the top of the TaO x  thin film layer  31   b  respectively. As shown in  FIG. 7   c , the TaO x  thin film layer  31   a  is formed at the bottom of the apertures; as further shown in  FIG. 7   d , the Ru metal thin film layer  32  is deposited on the TaO x  thin film layer  31   a;  then, as shown in  FIG. 7   e , another TaO x  thin film layer  31   b  is formed on the Ru metal thin film layer  32 . Other steps are substantially the same as those described above with respect to  FIG. 4  and will not be discussed repeatedly. 
         [0077]    The methods of heat diffusion doping Ru are specifically described in the above embodiments of preparation methods. However, the (TaO x :Ru) storage medium layer  30  shown in  FIG. 4   e  can also be formed by performing Ru ion implantation doping on the TaO x  thin film layer  31  shown in  FIG. 4   c.    
         [0078]    During the course of annealing diffusion doping Ru, the invention is not merely limited to proposing the methods shown in  FIGS. 4-7  for performing diffusion doping using Ru metal thin film layer. A method which uses conductive Ru oxide layer in place of Ru metal thin film layer as the diffusion doping layer is further proposed. 
         [0079]      FIGS. 8 to 11  are schematic structure views showing dope forming (TaO x :Ru) storage medium layer with Ru oxide layer as diffusion doping layer, wherein the structure embodiment shown in  FIG. 8  is used to replace the structure of  FIG. 4   d . As shown in  FIG. 8 , Ru oxide layer  33  is used to replace Ru metal thin film layer  32 . The structure embodiment shown in  FIG. 9  is used to replace the structure of  FIG. 5   d . As shown in  FIG. 9 , Ru oxide layer  33  is used to replace Ru metal thin film layer  32 . The structure embodiment shown in  FIG. 10  is used to replace the structure of  FIG. 6   e . As shown in  FIG. 10 , Ru oxide layers  33   a  and  33   b  are used to replace Ru metal thin film layers  32   a  and  32   b  respectively. The structure embodiment shown in  FIG. 11  is used to replace the structure of  FIG. 7   e . As shown in  FIG. 11 , Ru oxide layer  33  is used to replace Ru metal thin film layer  32 . In the above exemplary structures, the thickness range of Ru oxide layer is preferably from about 0.3 nm to about 10 nm. For example, it can be selected to be 1 nm or 2 nm. The Ru oxide layer can be formed by thin film deposition methods such as reactive sputtering, etc. Preferably, the Ru oxide layer is RuO 2 . When Ru oxide layer is used as diffusion doping layer, those skilled in the art can, during the process of annealing diffusion, select annealing conditions that are different from the method process of the embodiment shown in  FIG. 4  as required. For example, the annealing temperature can be selected to be 400° C.-900° C., and the annealing duration can be selected to be 30 seconds to 30 minutes. It is noted that for the structure shown in  FIG. 10 , such a structure can be employed in other embodiments where one layer is Ru metal thin film layer while the other layer is Ru oxide layer, i.e., Ru metal thin film layer and Ru oxide layer simultaneously serve as diffusion doping layer. 
         [0080]      FIG. 12  is a schematic principal view of annealing diffusion with Ru oxide layer as diffusion doping layer. As shown in  FIG. 12 , a decomposition reaction: RuO 2 →Ru+O 2  will occur on RuO 2  at a certain temperature, thus producing RuO or Ru nano crystal which diffuses towards TaO x  thin film layer. If the decomposition is incomplete, Ru can also exist in the form of RuO 2  nano crystal. It is further noted that, all of RuO 2 , RuO and Ru are conductive and their resistivities do not differ much from each other. Therefore, even if the decomposition of RuO 2  is incomplete and only RuO or RuO 2  nano crystals exist in TaO x , conductive filaments can be stabilized so that conductive filaments are distributed around RuO or RuO 2  nano crystals. In addition, O −2  produced after decomposition of RuO 2  are diffused into the TaO x  thin film layer and atom-bonded with Ta atoms so that oxygen vacancies are filled in. Therefore, defect concentration in original TaO x  storage medium layer is reduced, resistance in initial resistance state and resistance in low resistance state of (TaO x :Ru) storage medium layer are effectively improved, whereby as compared with the method show in  FIG. 4 , power consumption of device can be more reduced. 
         [0081]    The (TaO x :Ru) storage medium layer formed by the above described method contains tow metal elements, Ta and Ru. According to the prior art, in a copper interconnection structure at or below 32 nm process node, the diffusion barrier layer of copper will employ Ru/TaN complex layer material, which also contains metal elements of Ru and Ta. Therefore, when the resistive memory is integrated with a copper interconnection back-end process structure, no new elements will be introduced. Therefore, process risk is low and the resistive memory can be easily integrated with copper interconnection back-end process at or below 32 nm process node. 
         [0082]    Hereinafter, the embodiment of TaO x  based resistive memory integrated with a copper interconnection back-end structure will be further described. 
         [0083]      FIG. 13  is a schematic structure view of a TaO x  based resistive memory according to a third embodiment of the invention. In this embodiment, the TaO x  based resistive memory  4  can be integrated with a copper interconnection back-end process. The lower electrode of the TaO x  based resistive memory  4  is a copper plug  62  in the copper interconnection, and the (TaO x :Ru) storage medium layer  30  is formed at the top of the copper plug  62 . The TaO x  based resistive memory  4  can be formed by the following method process. 
         [0084]    With reference to  FIG. 13 , copper wire  60  and copper plug  62  on the copper wire  60  are formed by conventional Damascene process or dual Damascene process. Then, a cap layer  81  is formed on the copper plug  62  and inter-layer dielectric layer  71 . Thereafter, the cap layer  81  is pattern-etched so as to open the top of the copper plug  62 . Therefore, the (TaO x :Ru) storage medium layer  30  can be formed in the hole of open copper plug according to the methods of various embodiments described above. Further, an upper electrode (not shown in  FIG. 13 ) can also be formed on the (TaO x :Ru) storage medium layer  30 . 
         [0085]    Preferably, the copper interconnection structure is a copper interconnection structure at or below 32 nm process node, wherein the diffusion barrier layer  90  employs Ru/TaN complex layer. 
         [0086]      FIG. 14  is a schematic structure view of a TaO x  based resistive memory according to a fourth embodiment of the invention. In this embodiment, the TaO x  based resistive memory  5  can be integrated with a copper interconnection back-end process. The lower electrode of the TaO x  based resistive memory  5  is copper wire  60  in the copper interconnection. The (TaO x :Ru) storage medium layer  30  is formed at the bottom of the copper plug  62 . In this embodiment, an upper electrode  50  formed between the (TaO x :Ru) storage medium layer  30  and the copper plug  61  is further included. Also, it is preferred that the copper interconnection structure is a copper interconnection structure at or below 32 nm process node, wherein the diffusion barrier layer  90  employs Ru/TaN complex layer. 
         [0087]    The above embodiments mainly describe the resistive memories of the invention and methods of preparing the same. Though some of the embodiments of the invention have been described, those skilled in the art will understand that the invention can be implemented in many other forms without departing from its spirit and scope. Therefore, the illustrated examples and embodiments should be considered as schematic rather than being limiting. The invention can cover various modifications and substitutes without departing from the spirit and scope of the invention defined by appended claims.