Abstract:
A resistive memory device includes a first metallic layer comprising a source of positive metallic ions, a switching media having an upper surface and a lower surface, wherein the upper surface is adjacent to the first metallic layer, wherein the switching media comprises conductive filaments comprising positive metallic ions from the source of positive metallic ions formed from the upper surface towards the lower surface, a semiconductor substrate, a second metallic layer disposed above the semiconductor substrate, a non-metallic conductive layer disposed above the second metallic layer, and an interface region between the non-metallic conductive layer and the switching media having a negative ionic charge.

Description:
BACKGROUND 
     The present invention is related to memory devices. More particularly, the present invention discloses non-volatile resistive switch memory devices having improved operational characteristics, fabrication techniques, as well as apparatus including such memories. 
     The inventors of the present invention have recognized the success of semiconductor devices has been mainly driven by an intensive transistor down-scaling process. However, as field effect transistors (FETs) approach sizes less than 100 nm, physical problems such as short channel effect begin to hinder proper device operation. For transistor based memories, such as those commonly known as Flash memories, other performance degradations or problems may occur as device sizes shrink. With Flash memories, a high voltage is usually required for programming of such memories, however, as device sizes shrink, the high programming voltage can result in dielectric breakdown and other problems. Similar problems can occur with other types of non-volatile memory devices other than Flash memories. 
     The inventors of the present invention recognize that many other types of non-volatile random access memory (RAM) devices have been explored as next generation memory devices, such as: ferroelectric RAM (Fe RAM); magneto-resistive RAM (MRAM); organic RAM (ORAM); phase change RAM (PCRAM); and others. 
     A common drawback with these memory devices include that they often require new materials that are incompatible with typical CMOS manufacturing. As an example of this, Organic RAM or ORAM requires organic chemicals that are currently incompatible with large volume silicon-based fabrication techniques and foundries. As another example of this, Fe-RAM and MRAM devices typically require materials using a high temperature anneal step, and thus such devices cannot be normally be incorporated with large volume silicon-based fabrication techniques. 
     Additional drawbacks with these devices include that such memory cells often lack one or more key attributes required of non-volatile memories. As an example of this, Fe-RAM and MRAM devices typically have fast switching (e.g. “0” to “1”) characteristics and good programming endurance, however, such memory cells are difficult to scale to small sizes. In another example of this, for ORAM devices reliability of such memories is often poor. As yet another example of this, switching of PCRAM devices typically include Joules heating and undesirably require high power consumption. 
     From the above, improved semiconductor memory devices that can scale to smaller dimensions with reduced drawbacks are therefore desirable. 
     SUMMARY 
     The present invention is related to memory devices. More particularly, embodiments according to the present invention disclose memory (e.g. switching) devices having improved data retention characteristics and methods for forming such devices. Embodiments are described with respect to non-volatile memory devices; however, embodiments may also be applied to a broader range of memory devices, processing devices, and the like. 
     Various embodiments of the present invention include the formation and use of a highly doped intermediate region between an undoped amorphous silicon layer (switching layer) and a doped polysilicon or doped silicon germanium layer. In various embodiments, the doped polysilicon or doped silicon germanium (SiGe) layer is disposed on top of a metal layer, and one or more metal layers (e.g. silver and aluminum) are disposed on top of the undoped amorphous silicon (a-Si) layer. 
     In various embodiments, the materials described above form a basic switching device: Top metal, Ag (filament metal), amorphous Si, doped intermediate material, doped polysilicon or SiGe, Bottom metal. In other embodiments, any number of additional layers may be used in such a device, for example, to promote adhesion, or the like. In various embodiments, the basic switching device may be formed as a back-end process for a CMOS device (e.g. stacked upon other CMOS devices). 
     In some embodiments, the dopant concentration of the highly doped intermediate region may be on the order of two or more magnitudes higher than the dopant concentration of the doped poly/SiGe. Additionally, these layers may be doped using the same type dopant (e.g. p+, Boron, etc.). In various embodiments, the intermediate region may be on the order of about 100 angstroms, or less. In some embodiments, when the highly doped intermediate region is placed in contact with the lower doped poly/SiGe, dopant impurities from the highly doped region typically migrate to the lower doped region. The migration of holes from the intermediate region, in various embodiments, result in the intermediate region having a negative charge. 
     In various embodiments, to cause the switching device to switch, a positive voltage is applied across the Top metal and Bottom metal causing an electrical field to form across the amorphous silicon. In response to the electrical field, positive metal (e.g. silver) ions from the silver metal migrate into the amorphous silicon. If enough silver icons migrate into the a-Si, a silver “filament” is formed, similar to a short-circuit through the a-Si. Accordingly, a measured resistance between the top and bottom metal will measurably drop, and the resistive memory device would have switched from a high resistance state to a lower resistance state. 
     In various embodiments, because the intermediate region becomes negatively charged, the silver ions (positive) in the amorphous silicon are attracted to the negatively charged region. Accordingly, the metallic (Ag) filament will be maintained through the amorphous silicon layer. The inventors of the present invention believe that this attraction mechanism will increase the longevity of the metallic filament, and thus will increase the retention time of the resistive memory device. 
     According to one aspect of the present invention, a resistive memory device is described. One device includes a first metallic layer comprising a source of positive metallic ions, and a switching media having an upper surface and a lower surface, wherein the upper surface is adjacent to the first metallic layer, wherein the switching media comprises conductive filaments comprising positive metallic ions from the source of positive metallic ions formed from the upper surface towards the lower surface. A device may include a semiconductor substrate, and a second metallic layer disposed above the semiconductor substrate. Various devices may include a non-metallic conductive layer disposed above the second metallic layer, and an interface region between the non-metallic conductive layer and the switching media having a negative ionic charge. 
     According to another aspect of the present invention, a method for forming a resistive memory device is described. One technique include disposing a first metallic layer above a semiconductor substrate, disposing a non-metallic conductive layer above the first metallic layer, and forming an interface region above and adjacent to the non-metallic conductive layer having a negative ionic charge. A process may include disposing a switching media above and adjacent to the interface region, where the switching media includes an upper surface and a lower surface, and disposing a second metallic layer comprising a source of positive metallic ions above and adjacent to the switching media. 
     According to yet another aspect of the present invention, a resistive memory device manufactured according to the following process is described. The process may include disposing a first metallic layer above a semiconductor substrate (e.g. disposing the first metallic layer on an insulating layer that is on top of a semiconductor substrate), disposing a non-metallic conductive layer above the first metallic layer, and forming an interface region above and adjacent to the non-metallic conductive layer having a negative ionic charge, disposing a switching media above and adjacent to the interface region, where the switching media includes an upper surface and a lower surface, and disposing a second metallic layer comprising a source of positive metallic ions above and adjacent to the switching media. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more fully understand the present invention, reference is made to the accompanying drawings. Understanding that these drawings are not to be considered limitations in the scope of the invention, the presently described embodiments and the presently understood best mode of the invention are described with additional detail through use of the accompanying drawings in which: 
         FIG. 1  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 2  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 3  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 4  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 5  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 6  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 7  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 8  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 9  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 10  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 11  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 12  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 13  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 14  illustrates a perspective view of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 15  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 16  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; 
         FIG. 17  illustrates a cross-section of a process step for forming a switching device according to various embodiments of the present invention; and 
         FIG. 18  illustrates a cross-section of a device structure of a switching device according to various embodiments of the present invention; 
         FIGS. 19A-D  illustrate cross-sections of a device structure of a switching device according to various embodiments of the present invention; 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is generally related to a memory (switching) device and an apparatus including a memory device. More particularly, embodiments of the present invention provide structures and a method for forming one or more resistive switching devices each having improved memory retention characteristics. The embodiments described herein are described with respect to fabrication of high density non-volatile memory devices. However, one of ordinary skill in the art will recognize that these devices may be applied to a broad range of applications, such as processing devices, computing devices, or the like. 
       FIG. 1  illustrates a substrate  102  having a surface region  104 . In various embodiments, the substrate  102  can be a semiconductor substrate, such as: a single crystal silicon wafer, a silicon germanium wafer, a silicon-on-insulator substrate, commonly known as SOI, and the like. Depending on the specific embodiment, the processes described herein are back-end CMOS processes, i.e. processes limited to certain temperature ranges, and the like, that can be performed upon substrates having existing CMOS devices. Accordingly, the substrate  102  may include one or more transistor devices, conductors, or the like, formed therein (not shown). In various embodiments, the one or more devices may be operationally coupled to the switching device, e.g. a driver; may include processing or other computational logic; may include one or more physical sensors; or the like. 
       FIG. 2  illustrates a resulting cross-section after a first dielectric material  202  is disposed overlying the surface region  104  of the semiconductor substrate  102 . The first dielectric material can be a suitable dielectric material such as silicon oxide, silicon nitride or combinations thereof depending on the embodiment. The first dielectric material can be deposited using techniques such as chemical vapor deposition (CVD) process including plasma enhanced chemical vapor deposition or low pressure chemical vapor deposition depending on the application. For example, silicon oxide may be formed using silane, disilane, a suitable chlorosilane or TEOS and other suitable silicon bearing materials, depending on the embodiment. 
       FIG. 3  illustrates a first adhesion layer  302  may be formed overlying the first dielectric material. The first adhesion layer can be titanium, titanium nitride, tantalum, tantalum nitride, tungsten, or tungsten nitride or a combination of these. The first adhesion layer  302  may be deposited using a physical vapor deposition process such as a sputtering process in a specific embodiment. Techniques such as a chemical vapor deposition using a suitable precursor may also be used. For example, adhesion layer  302  may be formed by first depositing a titanium metal on the first dielectric material, following by sputtering a titanium nitride material. 
     Referring to  FIG. 4 , some embodiments include a first wiring material  402  formed overlying the first adhesion layer  302 . The first wiring material  402  can be tungsten, copper, aluminum or other suitable metal materials including alloys thereof. In various embodiments, the first wiring material  402  can be deposited using techniques such as physical vapor deposition, evaporation, chemical vapor deposition, electrochemical methods such as electroplating or electrode-less deposition from a liquid medium, or other suitable deposition techniques including a combination. In certain embodiments, the first wiring material  402  can be a doped semiconductor material such as a doped silicon material. In a specific embodiment, the first adhesion layer  302  functions as a glue layer between the first wiring material  402  and the first dielectric layer  202 . In a specific embodiment, tungsten is formed by sputtering on top of layer  302  to form layer  402 . In various embodiments, the tungsten may have a thickness of between 100 nm and 1000 nm thick, and sometimes between 200 nm and 500 nm thick. 
     The method performs a first pattern and etch process  506  to form a first (or bottom) wiring structure  502  as shown in  FIG. 5 . In some embodiments, the first wiring structure  502  includes the first wiring material  402  and the first adhesion material  302 . As shown, the first wiring structure is characterized by a width  504 , and extends in a first direction (e.g. into the page). In various embodiments, the first pattern and etch process includes forming a masking layer overlying the first wiring material  402  followed by an etching process  506 . The masking layer can be an organic photo resist material, a hard mask, or the like depending on the application. In one example, where tungsten is the first wiring material  402 , the first adhesion layer  302  can be titanium nitride, or a tungsten-bearing material; and the etching process can use a fluorine bearing species such as CF 4  etchant, or the like. In some embodiments, the first wiring structure  502  can have a width ranging from about 5 nm to about 1200 nm. In other embodiments, the width can range from about 30 nm to about 100 nm. Of course one skilled in the art would recognize other variations, modifications, and alternatives, depending upon desired feature size. 
     In a specific embodiment, the method includes forming a second dielectric material  602  overlying the first wiring structure as illustrated in  FIG. 6 . The second dielectric material  602  can be silicon oxide, silicon nitride, or any suitable dielectric material including a dielectric stack and a combination of various dielectric materials depending on the embodiment. As merely an example, the second dielectric material can be a silicon oxide deposited using a plasma enhanced chemical vapor deposition (PECVD) process using tetra-ethyl oxy-silicate (TEOS) as precursor in a specific embodiment. Other deposition methods such as spin on glass followed by a suitable curing step may be used. Alternatively, a combination of more than one deposition processes may be used depending on the application. 
     Referring to  FIG. 7 , embodiments include performing a planarizing process to form a planarized second dielectric layer surface region  702  and expose a first wiring structure surface  704 . In some embodiments, the planarizing process can be a chemical mechanical polishing (CMP) process using the first wiring (for example, tungsten) structure surface as a polishing stop in a specific embodiment. In other embodiments, the planarizing process can be a selective etch process such as a reactive ion etching using the first wiring (for example, tungsten) structure surface as an etch stop. In other embodiments a combination of chemical and physical processes may be performed to obtain the result illustrated in  FIG. 7 . 
     In some embodiments of the present invention, the process includes deposition of a bottom metallic barrier material  802  overlying the first wiring structure surface  704  as shown in  FIG. 8 . In some embodiments, bottom metallic barrier material  802  can be titanium, titanium nitride, tantalum, tantalum nitride, or tungsten nitride or a combination of these. The bottom metallic barrier material  802  may be deposited using a physical vapor deposition process such as sputtering in a specific embodiment. In other embodiments, techniques such as a chemical vapor deposition using a suitable precursor may also be used. 
     As shown in  FIG. 9 , the method includes depositing a contact layer  902  overlying the bottom metallic barrier material  802 . In certain embodiments, the contact layer  902  serves to control and improve switching capability for the switching device. For example for a switching device using amorphous silicon as the switching material (described below), the contact layer  902  can be a polysilicon material in a specific embodiment. In various embodiments, the polysilicon material may be doped with a p-type dopant, such as a boron bearing species, or the like. In some embodiments, the dopant concentration ranges from about 1E18 per cm 3  to about 1E22 per cm 3 , and in other embodiments, the dopant concentration is on the order of about 1E19 per cm 3 . In some embodiments, the polysilicon material is formed using a plasma enhanced chemical vapor deposition process or a low pressure chemical vapor deposition process and a silicon bearing species such as silane, disilane, a suitable chlorosilane, and others. The impurity species may be doped, in-situ, or ex-situ depending in the embodiment. In various embodiments, deposition temperature ranges from about 300 Degree Celsius to about 550 Degree Celsius may be utilized. 
     In an alternative embodiment, the contact layer  902  may be a polycrystalline silicon germanium material. In such cases, the silicon germanium material may be doped with a p-type dopant, such as a boron bearing species, or the like. In some embodiments, the dopant concentration ranges from about 1E18 per cm 3  to about 1E22 per cm 3 , and in other embodiments, the dopant concentration is on the order of about 1E19 per cm 3 . The polycrystalline silicon germanium material having the p+ impurity characteristic can be formed using a plasma enhanced chemical vapor deposition process, a low pressure chemical vapor deposition process, or others, using a suitable silicon precursor, a suitable germanium precursor, and a suitable p type impurity species. As examples, the silicon precursor can be silane, disilane, a suitable chlorosilane, and others; the germanium precursor can be germane (GeH 4 ), germanium chloride (GeCl 4 ), and other suitable germanium bearing species; and the p+ impurity can be provided using a boron bearing species, an aluminum bearing species, a gallium bearing species, an indium bearing species, and others. The impurity species may be doped, in-situ, or ex-situ, depending in the embodiment. In various embodiments, deposition temperature for the polycrystalline silicon germanium material can range from about 350 Degree Celsius to about 500 Degree Celsius. In such embodiments, the contact layer  902  will typically be polycrystalline in nature without an anneal step. In some embodiments, contact layer  902  may be formed using a technique disclosed in the above-referenced patent application. 
     As illustrated in  FIG. 9 , an interface layer  1001  may also be specifically formed over the contact layer  902 . In various embodiments, interface layer  1001  may be similar to composition as the switching material  1002  (described below), such as an amorphous silicon material. In various embodiments, the switching material  1002  is not intentionally doped, whereas interface layer  1001  is intentionally doped. Further details regarding formation of the amorphous silicon material is provided below. In various embodiments, the interface layer  1001  is intentionally doped with a p-type dopant, similar to the p-type dopant used in the contact layer  902 . For example, the p-type impurity may be include a boron bearing species, an aluminum bearing species, a gallium bearing species, an indium bearing species, and the like. In contrast to the contact layer  902 , the interface layer  1001  has a substantially higher impurity concentration. In some examples, the contact layer  902  has an impurity concentration on the order of 1E19 per cm 3 , and the interface layer  1001  has a p-type dopant concentration of 1E15 per cm 3  to about 5E22 per cm 3 , or the like. In various embodiments, the doping may be performed in situ, or the like. In various embodiments, the interface layer  1001  may be on the order of about 100 Angstroms, or the like. 
     In other embodiments, the interface layer (interface region)  1001  may be formed as a part or region of the contact layer  902  deposition. In such embodiments, while the polycrystalline material (e.g. polysilicon, silicon germanium) is deposited as the contact layer  902 , the in situ concentration of the dopant material may be modified. As an example, the concentration of Boron, or the like may be greatly increased near the end of the deposition of the contact layer  902  to form the interface layer  1001 . Similar to the embodiments described above, it is contemplated that interface region  1001  may be on the order of about 100 Angstroms, or the like. 
     In various embodiments, based upon the differences in dopant concentrations of interface region  1001  (higher) and the contact layer  902  (lower), it is contemplated that the p+ dopants within the interface region  1001  will tend to migrate (e.g. out-diffuse) to regions of lower p concentration, i.e. the contact layer  902 . In various embodiments, this migration of p+ dopants will tend to give the interface region  1001  a negative ionic charge. As will be described further below, it is believed that the negative ionic charge of the interface region  1001  will tend to attract positively charged metallic ions that may be present within the switching material  1002 . 
     As illustrated in  FIG. 10 , various processes include forming a switching material  1002  overlying the interface layer or region  1001 . In various embodiments, the switching material  1002  can be an intrinsic amorphous silicon material, that is not intentionally doped. The intrinsic amorphous silicon material can be deposited using a chemical deposition method or a physical deposition method depending on the embodiment. The chemical deposition method can include a chemical vapor deposition process using silane, disilane, a suitable chlorosilane, or a suitable silicon-containing gas as a precursor. In a specific embodiment, the intrinsic amorphous silicon material may be deposited using a plasma-assisted chemical deposition method. In various embodiments, the deposition temperature for the amorphous silicon material can range from about 200 Degree Celsius to about 500 Degree Celsius and sometimes at about 350 Degree Celsius to about 400 Degree Celsius. Depending on the embodiment, the amorphous silicon material  1002  can be provided at a thickness ranging from about 5 nm to about 100 nm. In some embodiments, the amorphous silicon material  1002  is provided at a thickness ranging from about 10 nm to about 50 nm. Depending on the application, the amorphous silicon material  1002  may also be deposited using a physical vapor deposition such as sputtering using a suitable silicon target material. brave 
     In some embodiments, the interface layer  1001  may be formed as part or region of the switching material  1002  deposition. In such embodiments, initially while amorphous silicon material is being deposited, a high concentration of p+ dopants may be provided, in situ, to form interface layer  1001 . After the interface layer  1001  of doped amorphous silicon material is formed, p+ dopants may be removed from the chamber, and undoped amorphous silicon material  1002  may be formed above the interface layer  1001 . 
     As illustrated in  FIG. 11 , various embodiments include depositing a conductive material  1102  overlying switching material  1002 . In a specific embodiment, for an amorphous silicon switching material, conductive material  1102  can comprise a silver material, and in other embodiments, materials including silver, platinum, palladium, copper or nickel, or a combination may be used for conductive material  1102 . The conductive material  1102  can be deposited using a physical deposition process such as sputtering or evaporation. The silver material may also be formed using a chemical deposition process such as chemical vapor deposition, electrochemical such as electroplating, electrodeless deposition, or a combination depending on the application. 
     In some embodiments, a thin layer of material may be present prior to the deposition of conductive material  1102 . This thin layer may be within the range of approximately 5 nm to approximately 25 Angstroms, approximately 40 A to 30 A, approximately 30 A, or the like. In some embodiments, the thin layer serves to reduce the diffusion or agglomeration of conductive material  1102  (e.g. silver) into switching material  1102  during fabrication of the disclosed structures. In such embodiments, as back end fabrication steps may include high temperature operations, the thin layer reduces the migration of the metallic ions into the switching material  1002 . In some embodiments, the thin layer also serves to restrict or control where metallic ions migrate into switching material  1002  during operation of the device. In some embodiments, during operation of the device a thin oxide layer is used to control a conductive path from a metallic layer to the switching layer. In various embodiments of the present invention, the thin layer may be a layer of oxide, carbon, or other relative stable material. These materials may be formed via a plasma enhanced chemical vapor deposition process, an atomic layer deposition process, a spin coating process, a plasma oxidation process, a physical vapor deposition process, a naturally occurring growth, or the like. In some embodiments, the formed oxide may be etched until the desired thickness is obtained for the thin layer. In some examples, an Argon etch may be used. In some embodiments, the conductive material  1102  is thus formed or deposited on top of the thin layer that is specifically grown, formed, deposited, or naturally occurring upon the silicon switching material  1002 . 
     The method deposits a top barrier material  1202  overlying the conductive material as shown in  FIG. 12 . Top barrier material  1202  layer can protect the conductive material  1102 . Top barrier material  1202  can also serve as a diffusion barrier between conductive material  1102  and subsequent materials, and forms an electrical contact between conductive material  1102  and subsequent materials. Top barrier material  1202  can also serve as a polish stop material in a subsequent step for a CMP process. Top barrier material  1202  can be titanium, titanium nitride, tantalum or tantalum nitride, tungsten, or tungsten nitride, or any suitable barrier material depending on the embodiment. Depending on the application, top barrier material  1202  can be formed using a chemical deposition such as atomic layer deposition, chemical vapor deposition, and others, or a physical deposition such as sputtering, depending on the application. 
     In a specific embodiment, the method includes subjecting a stack of material comprising the bottom metallic barrier material  802 , the contact material  902 , the interface layer  1001 , the switching material  1002 , the conductive material  1102 , and the top barrier material  1202  to a second pattern and etch process to form a plurality of pillar structures  1302  as shown in  FIG. 13 . The shape of the cross section shape of pillar structures  1302  may be approximately square, rectangularly, circular, hexagonal, or other similar shape. Each of the pillar structure includes the bottom metallic barrier material  802 , the contact material  902 , the interface layer  1001 , the switching material  1002 , the conductive material  1102 , and the top barrier material  1202 . 
     As shown, in one embodiment, each of the pillar structure  1302  including the bottom metallic barrier material maintains a metal-to-metal contact  1304  with the first wiring structure  802 . Depending on the embodiment, the pillar structure  1302  can be aligned to the bottom wiring structure  502  as shown in  FIG. 13   a . The pillar structure  1302  may not necessarily be perfectly aligned to the first wiring structure  502  as shown in  FIG. 13   b  while maintaining the metal-to-metal contact in a specific embodiment. 
     In various embodiments, the pillar structure can have a feature size of less than about 250 nm and preferably about 90 nm, or even 40 nm, depending on the technology node adopted. The bottom wiring structure can have a width of about 90 nm or greater. The pillar structure with a bottom metallic barrier material enables a metal-to-metal contact with the first wiring structure even when there is a mis-alignment of the pillar structure to the first wiring structure during the second pattern and etch process in a specific embodiment. A perspective view of a plurality of pillar structures  1402  on the first wiring structure  1404  is illustrated in  FIG. 14 . 
     After forming the pillar structures  1302 , the method includes depositing a third dielectric material  1502  overlying at least the plurality of pillar structures including exposed regions of the first wiring structures. The third dielectric material can be silicon oxide, silicon nitride, or suitable dielectric material including a dielectric stack with a combination of various dielectric materials depending on the embodiment. As merely an example, the third dielectric material can be a silicon oxide deposited using a plasma enhanced chemical vapor deposition (PECVD) process using tetra-ethyl oxy-silicate as precursor in a specific embodiment. Other deposition method such as spin on glass followed by a suitable curing step may be used. Alternatively, a combination of deposition processes may be used depending on the application. 
     In a specific embodiment, the third dielectric layer is subjected to a planarizing process to form a planarized third dielectric layer surface  1602  and exposing a top surface region  1604  of the pillar structure as shown in  FIG. 16 . The exposed top surface region of the pillar structure includes a surface region of the top barrier material in a specific embodiment. The planarizing process can be a chemical mechanical polishing (CMP) process using the top barrier material as a polishing stop in a specific embodiment. The planarizing process can be a selective etch process such as a reactive ion etching using the top barrier material surface as an etch stop in specific embodiment. Of course one skilled in the art would recognize other modifications, variations, and alternatives. 
     Referring to  FIG. 17 . The method includes depositing a second adhesion material  1702  overlying the planarized third dielectric layer surface and the top surface region of the pillar structure. The second adhesion layer can be titanium, titanium nitride, tantalum, tantalum nitride, or tungsten nitride or a combination of these. The second adhesion material  1702  may be deposited using a physical vapor deposition process such as sputtering in a specific embodiment. 
     Techniques such as a chemical vapor deposition including atomic layer deposition using a suitable precursor may also be used. In a specific embodiment, the method deposits a top wiring material  1704  overlying the second adhesion material  1702 . The second wiring material  1702  can be tungsten, copper, aluminum or other suitable metal materials including alloys. The second wiring material  1702  can be deposited using techniques such as physical vapor deposition, evaporation, chemical vapor deposition, electrochemical methods such as electroplating or electrodeless deposition from a liquid medium, or other suitable deposition techniques including a combination. In certain embodiments, the top wiring material  1702  can be a doped semiconductor material such as a doped silicon material. In a specific embodiment, the second adhesion material  1702  functions as a glue layer between the top wiring material and the third dielectric layer. Taking tungsten as the second wiring material  1704  as an example, tungsten can have a thickness ranging from about 100 nm to about 1000 nm and preferably ranging from about 200 nm to about 500 nm depending on the application. 
     In various embodiments, the method performs a third pattern and etch process to form a top wiring structure  1804  as shown in  FIG. 18 . The top wiring structure  1804  includes the top wiring material  1704  and the second adhesion material  1702  in a specific embodiment. In a specific embodiment, the top wiring structure is formed in a direction  1806  (also  FIG. 14 ) at an angle to the bottom wiring structure direction ( 1807 ,  FIG. 14 ). In certain embodiments, the top wiring structure  1804  is formed orthogonal to the bottom wiring structure  502 . Of course one skilled in the art would recognize other variations (e.g. angles), modifications, and alternatives. 
       FIGS. 19A-D  illustrates operational diagrams according to various embodiments of the present invention.  FIG. 19A  illustrates a close-up view of an embodiment of the switching portion including contact layer  902  (e.g. p-doped polysilicon), interface region  1001  (e.g. p+ doped amorphous silicon), switching material  1002  (e.g. amorphous silicon), and conductive material  1102  (e.g. aluminum). 
       FIG. 19B  illustrates an embodiment when a voltage, e.g. a forming voltage is applied across with switching portion. As illustrated, conductive metal particles (e.g. ions) of the conductive material  1102  migrate into switching material  1002  upon application of a positive voltage. When sufficient numbers of metal ions migrate within conductive material  1102 , a filament-type structure  1904  is formed, as shown. 
     In various embodiments, the filament structure is characterized by a physical length. The length has been found to be dependent on an amplitude and polarity of a voltage applied across to the top wiring structure  1804  and the bottom wiring structure  502 . Formation of this filament  1904  changes the resistance of the switching material  1002  in a specific embodiment. In some embodiments, the conductive material  1102  is silver and the switching material  1002  is amorphous silicon. Then, upon applying a positive voltage to the top wiring structure  1804  with respect to the bottom wiring structure  502 , a plurality of silver particles migrate into regions of the amorphous silicon material. The plurality of silver particles can include a silver filament structure having a length. Subsequently, when a voltage (e.g. a read voltage less than the forming voltage) is applied across the switching portion, the silver filament conducts current through switching material  1002 . Accordingly, the resistance of the resistive memory depends upon the length of the silver filament, in various embodiments. The length of the silver filament structure changes upon applying sufficiently high or low voltages (for example operating voltage such as write voltage or erase voltage), thus changing the resistance (e.g. reducing) of the amorphous silicon material  1002 . 
       FIG. 19C  illustrates an embodiment when no voltage (e.g. a read voltage, a forming voltage, an erase voltage, or the like) is applied across the switching portion starting from the configuration illustrated in  FIG. 19B . As was mentioned above, interface layer  1001  can be a highly doped p material, e.g. amorphous silicon, and contact layer  902  can be a doped p material, e.g. polysilicon. As a result of the differences in doping concentrations, it is envisioned that holes will migrate from interface layer  1001  to contact layer  902 . In various embodiments, the net result of the migration is that the interface layer  1001  becomes negatively charged, as shown. 
     In various embodiments, the conductive metallic particles are envisioned to be positive metallic ions. Within the configuration of  FIG. 19C , the conductive metallic particles become attracted to the negatively biased interface layer  1001 , as shown. Since, the positive metallic ions are attracted to the negatively biased interface layer  1001 , the retention time of the resistive memory device described in the various embodiments is believed to be increased. 
       FIG. 19D  illustrates an embodiment when a voltage, e.g. an erase voltage is applied across switching portion starting from the configuration illustrated in  FIG. 19B . As illustrated, conductive metal particles (e.g. ions) of the conductive material  1102  migrate away from contact layer  902  upon application of a negative voltage. The negative voltage should be sufficient to overcome the attractive forces between the positive metallic ions and the negatively biased interface layer  1001 . When sufficient numbers of metal ions migrate away from contact layer  902 , the filament-type structure  1904  is greatly reduced, as shown. In various embodiments, when a voltage (e.g. a read voltage greater than the erase voltage, but less than the forming voltage) is subsequently applied across the switching portion, the conduction of current through switching material  1002  is greatly reduced, i.e. the resistance is increased. 
     In a specific embodiment, the top wiring structure, the bottom wiring structure and the switching element sandwiched between the first wiring structure and the second wiring structure provide for a switching device for a non-volatile memory device. Of course one skilled in the art would recognize other variations, modifications, and alternatives. It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or alternatives in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.