Multi-bit phase-change random access memory (PRAM) with diameter-controlled contacts and methods of fabricating and programming the same

Abstract

A phase-change random-access memory (PRAM) device includes a chalcogenide element, the chalcogenide element comprising a material which can assume a crystalline state or an amorphous state upon application of a heating current. A first contact is connected to a first region of the chalcogenide element and has a first cross-sectional area. A second contact is connected to a second region of the chalcogenide element and having a second cross-sectional area. A first programmable volume of the chalcogenide material is defined in the first region of the chalcogenide element, a state of the first programmable volume being programmable according to a resistance associated with the first contact. A second programmable volume of the chalcogenide material is defined in the second region of the chalcogenide element, a state of the second programmable volume being programmable according to a second resistance associated with the second contact.

1 . A phase-change random-access memory (PRAM) device, comprising:
 a chalcogenide element, the chalcogenide element comprising a material which can assume a crystalline state or an amorphous state upon application of a heating current;   a first contact connected to a first region of the chalcogenide element and having a first cross-sectional area; and   a second contact connected to a second region of the chalcogenide element and having a second cross-sectional area, wherein:.   a first programmable volume of the chalcogenide material is defined in the first region of the chalcogenide element, a state of the first programmable volume being programmable according to a resistance associated with the first contact; and   a second programmable volume of the chalcogenide material is defined in the second region of the chalcogenide element, a state of the second programmable volume being programmable according to a second resistance associated with the second contact.   
     
     
         2 . The PRAM device of  claim 1 , wherein a resistivity of a material of which the first contact is formed is different from that of a material of which the second contact is formed. 
     
     
         3 . The PRAM device of  claim 1 , wherein a resistivity of a material of which the first contact is formed is substantially the same as a material of which the second contact is formed. 
     
     
         4 . The PRAM device of  claim 1 , wherein the first and second contacts are made of different materials. 
     
     
         5 . The PRAM device of  claim 1 , wherein the first and second contacts are made of substantially the same materials. 
     
     
         6 . The PRAM device of  claim 1 , further comprising a second chalcogenide element, the second chalcogenide element comprising a third programmable volume defined in a third region of the second chalcogenide element. 
     
     
         7 . The PRAM device of  claim 6 , wherein one of the first and second contacts is connected to the third region of the second chalcogenide element, a state of the third programmable volume being programmable according to the resistance associated with the one of the first and second contacts connected to the third region. 
     
     
         8 . The PRAM device of  claim 7 , wherein a resistivity of a material of which the first contact is formed is different from that of a material of which the second contact is formed. 
     
     
         9 . The PRAM device of  claim 7 , wherein the first and second contacts are made of different materials. 
     
     
         10 . The PRAM device of  claim 7 , wherein at least one of the first and second contacts has more than one cross-sectional area. 
     
     
         11 . The PRAM device of  claim 7 , wherein at least one of the first and second contacts has a tapered shape. 
     
     
         12 . The PRAM device of  claim 6 , wherein a resistivity of a material of which the first contact is formed is different from that of a material from which the second contact is formed. 
     
     
         13 . The PRAM device of  claim 6 , wherein the first and second contacts are made of different materials. 
     
     
         14 . The PRAM device of  claim 6 , further comprising a third contact having a third cross-sectional area and being connected to a fourth region of the second chalcogenide element, the fourth region of the second chalcogenide element comprising a fourth programmable volume, a state of the fourth programmable volume being programmable according to a resistance associated with the third contact connected to the fourth region. 
     
     
         15 . The PRAM device of  claim 14 , wherein the third cross-sectional area is the same as one of the first and second cross-sectional areas. 
     
     
         16 . The PRAM device of  claim 14 , wherein the third cross-sectional area is different than one of the first and second cross-sectional areas. 
     
     
         17 . The PRAM device of  claim 14 , wherein a resistivity of a material of which the third contact is formed is different from that of a material of which at least one of the first and second contacts is formed. 
     
     
         18 . The PRAM device of  claim 14 , wherein the third contact and at least one of the first and second contacts are made of different materials. 
     
     
         19 . The PRAM device of  claim 14 , wherein the third contact has more than one cross-sectional area. 
     
     
         20 . The PRAM device of  claim 14 , wherein the third contact has a tapered shape. 
     
     
         21 . The PRAM device of  claim 1 , wherein the PRAM device can store data that can have one of more than two values. 
     
     
         22 . A phase-change random-access memory (PRAM) device, comprising:
 a chalcogenide element, the chalcogenide element comprising a material which can assume a crystalline state or an amorphous state upon application of a heating current;   a first contact connected to a first region of the chalcogenide element and having a first cross-sectional area; and   a second contact connected to a second region of the chalcogenide element and having a second cross-sectional area different than the first cross-sectional area, wherein: a first programmable volume of the chalcogenide material is defined in the first region of   the chalcogenide element, a state of the first programmable volume being programmable according to a resistance associated with the first contact; and   a second programmable volume of the chalcogenide material is defined in the second region of the chalcogenide element, a state of the second programmable volume being programmable according to a second resistance associated with the second contact.   
     
     
         23 . The PRAM device of  claim 22 , wherein a resistivity of a material of which the first contact is formed is different from that of a material from which the second contact is formed. 
     
     
         24 . The PRAM device of  claim 22 , wherein the first and second contacts are made of different materials. 
     
     
         25 . The PRAM device of  claim 22 , further comprising a second chalcogenide element, the second chalcogenide element comprising a third programmable volume defined in a third region of the second chalcogenide element. 
     
     
         26 . The PRAM device of  claim 25 , wherein one of the first and second contacts is connected to the third region of the second chalcogenide element, a state of the third programmable volume being programmable according to the resistance associated with the one of the first and second contacts connected to the third region. 
     
     
         27 . The PRAM device of  claim 26 , wherein a resistivity of a material of which the first contact is formed is different from that of a material from which the second contact is formed. 
     
     
         28 . The PRAM device of  claim 26 , wherein the first and second contacts are made of different materials. 
     
     
         29 . The PRAM device of  claim 26 , wherein at least one of the first and second contacts has more than one cross-sectional area. 
     
     
         30 . The PRAM device of  claim 26 , wherein at least one of the first and second contacts has a tapered shape. 
     
     
         31 . The PRAM device of  claim 25 , wherein a resistivity of a material of which the first contact is formed is different from that of a material from which the second contact is formed. 
     
     
         32 . The PRAM device of  claim 25 , wherein the first and second contacts are made of different materials. 
     
     
         33 . The PRAM device of  claim 25 , further comprising a third contact having a third cross-sectional area and being connected to a fourth region of the second chalcogenide element, the fourth region of the second chalcogenide element comprising a fourth programmable volume, a state of the fourth programmable volume being programmable according to a resistance associated with the third contact connected to the fourth region. 
     
     
         34 . The PRAM device of  claim 33 , wherein the third cross-sectional area is the same as one of the first and second cross-sectional areas. 
     
     
         35 . The PRAM device of  claim 33 , wherein the third cross-sectional area is different than one of the first and second cross-sectional areas. 
     
     
         36 . The PRAM device of  claim 33 , wherein a resistivity of a material of which the third contact is formed is different from that of a material of which at least one of the first and second contacts is formed. 
     
     
         37 . The PRAM device of  claim 33 , wherein the third contact and at least one of the first and second contacts are made of different materials. 
     
     
         38 . The PRAM device of  claim 33 , wherein the third contact has more than one cross-sectional area. 
     
     
         39 . The PRAM device of  claim 33 , wherein the third contact has a tapered shape. 
     
     
         40 . The PRAM device of  claim 22 , wherein the PRAM device can store data that can have one of more than two values. 
     
     
         41 . A phase-change random-access memory (PRAM) device, comprising:
 a chalcogenide element, the chalcogenide element comprising a material which can assume a crystalline state or an amorphous state upon application of a heating current;   a first contact connected to a first region of the chalcogenide element and having a first cross-sectional area; and   a second contact connected to a second region of the chalcogenide element and having a second cross-sectional area substantially the same as the first cross-sectional area, wherein:   a first programmable volume of the chalcogenide material is defined in the first region of the chalcogenide element, a state of the first programmable volume being programmable according to a resistance associated with the first contact; and   a second programmable volume of the chalcogenide material is defined in the second region of the chalcogenide element, a state of the second programmable volume being programmable according to a second resistance associated with the second contact.   
     
     
         42 . The PRAM device of  claim 41 , wherein a resistivity of a material of which the first contact is formed is different from that of a material from which the second contact is formed. 
     
     
         43 . The PRAM device of  claim 41 , wherein the first and second contacts are made of different materials. 
     
     
         44 . The PRAM device of  claim 41 , further comprising a second chalcogenide element, the second chalcogenide element comprising a third programmable volume defined in a third region of the second chalcogenide element. 
     
     
         45 . The PRAM device of  claim 44 , wherein one of the first and second contacts is connected to the third region of the second chalcogenide element, a state of the third programmable volume being programmable according to the resistance associated with the one of the first and second contacts connected to the third region. 
     
     
         46 . The PRAM device of  claim 45 , wherein a resistivity of a material of which the first contact is formed is different from that of a material from which the second contact is formed. 
     
     
         47 . The PRAM device of  claim 45 , wherein the first and second contacts are made of different materials. 
     
     
         48 . The PRAM device of  claim 45 , wherein at least one of the first and second contacts has more than one cross-sectional area. 
     
     
         49 . The PRAM device of  claim 45 , wherein at least one of the first and second contacts has a tapered shape. 
     
     
         50 . The PRAM device of  claim 44 , wherein a resistivity of a material of which the first contact is formed is different from that of a material from which the second contact is formed. 
     
     
         51 . The PRAM device of  claim 44 , wherein the first and second contacts are made of different materials. 
     
     
         52 . The PRAM device of  claim 44 , further comprising a third contact having a third cross-sectional area and being connected to a fourth region of the second chalcogenide element, the fourth region of the second chalcogenide element comprising a fourth programmable volume, a state of the fourth programmable volume being programmable according to a resistance associated with the third contact connected to the fourth region. 
     
     
         53 . The PRAM device of  claim 52 , wherein the third cross-sectional area is the same as one of the first and second cross-sectional areas. 
     
     
         54 . The PRAM device of  claim 52 , wherein the third cross-sectional area is different than one of the first and second cross-sectional areas. 
     
     
         55 . The PRAM device of  claim 52 , wherein a resistivity of a material of which the third contact is formed is different from that of a material of which at least one of the first and second contacts is formed. 
     
     
         56 . The PRAM device of  claim 52 , wherein the third contact and at least one of the first and second contacts are made of different materials. 
     
     
         57 . The PRAM device of  claim 52 , wherein the third contact has more than one cross-sectional area. 
     
     
         58 . The PRAM device of  claim 52 , wherein the third contact has a tapered shape. 
     
     
         59 . The PRAM device of  claim 41 , wherein the PRAM device can store data that can have one of more than two values. 
     
     
         60 . A method of making a phase-change random-access memory (PRAM) device, comprising:
 providing a chalcogenide element, the chalcogenide element comprising a material which can assume a crystalline state or an amorphous state upon application of a heating current;   forming a first contact connected to a first region of the chalcogenide element and having a first cross-sectional area; and   forming a second contact connected to a second region of the chalcogenide element and having a second cross-sectional area, wherein:   a first programmable volume of the chalcogenide material is defined in the first region of the chalcogenide element, a state of the first programmable volume being programmable according to a resistance associated with the first contact; and   a second programmable volume of the chalcogenide material is defined in the second region of the chalcogenide element, a state of the second programmable volume being programmable according to a second resistance associated with the second contact.   
     
     
         61 . The method of  claim 60 , wherein the first and second cross-sectional areas are substantially the same. 
     
     
         62 . The method of  claim 60 , wherein the first and second cross-sectional areas are different. 
     
     
         63 . The method of  claim 60 , wherein a resistivity of a material of which the first contact is formed is different from that of a material of which the second contact is formed. 
     
     
         64 . The method of  claim 60 , wherein a resistivity of a material of which the first contact is formed is substantially the same as a material of which the second contact is formed. 
     
     
         65 . The method of  claim 60 , wherein the first and second contacts are made of different materials. 
     
     
         66 . The method of  claim 60 , wherein the first and second contacts are made of substantially the same materials. 
     
     
         67 . The method of  claim 60 , further comprising forming a second chalcogenide element, the second chalcogenide element comprising a third programmable volume defined in a third region of the second chalcogenide element. 
     
     
         68 . The method of  claim 67 , wherein one of the first and second contacts is connected to the third region of the second chalcogenide element, a state of the third programmable volume being programmable according to the resistance associated with the one of the first and second contacts connected to the third region. 
     
     
         69 . The method of  claim 68 , wherein a resistivity of a material of which the first contact is formed is different from that of a material of which the second contact is formed. 
     
     
         70 . The method of  claim 68 , wherein the first and second contacts are made of different materials. 
     
     
         71 . The method of  claim 68 , wherein at least one of the first and second contacts is formed to have more than one cross-sectional area. 
     
     
         72 . The method of  claim 68 , wherein at least one of the first and second contacts is formed to have a tapered shape. 
     
     
         73 . The method of  claim 67 , wherein a resistivity of a material of which the first contact is formed is different from that of a material from which the second contact is formed. 
     
     
         74 . The method of  claim 67 , wherein the first and second contacts are made of different materials. 
     
     
         75 . The method of  claim 67 , further comprising forming a third contact having a third cross-sectional area and being connected to a fourth region of the second chalcogenide element, the fourth region of the second chalcogenide element comprising a fourth programmable volume, a state of the fourth programmable volume being programmable according to a resistance associated with the third contact connected to the fourth region. 
     
     
         76 . The method of  claim 75 , wherein the third cross-sectional area is the same as one of the first and second cross-sectional areas. 
     
     
         77 . The method of  claim 75 , wherein the third cross-sectional area is different than one of the first and second cross-sectional areas. 
     
     
         78 . The method of  claim 75 , wherein a resistivity of a material of which the third contact is formed is different from that of a material of which at least one of the first and second contacts is formed. 
     
     
         79 . The method of  claim 75 , wherein the third contact and at least one of the first and second contacts are made of different materials. 
     
     
         80 . The method of  claim 75 , wherein the third contact is formed to have more than one cross-sectional area. 
     
     
         81 . The method of  claim 75 , wherein the third contact is formed to have a tapered shape. 
     
     
         82 . The method of  claim 60 , wherein the PRAM device can store data that can have one of more than two values.