High Capacity Low Cost Multi-State Magnetic Memory

Abstract

One embodiment of the present invention includes multi-state current-switching magnetic memory element including a stack of two or more magnetic tunneling junctions (MTJs), each MTJ having a free layer and being separated from other MTJs in the stack by a seeding layer formed upon an isolation layer, the stack for storing more than one bit of information, wherein different levels of current applied to the memory element causes switching to different states.

1 . A multi-state current-switching magnetic memory element comprising:
 a stack of two or more magnetic tunneling junctions (MTJs), each MTJ having a free layer and being separated from other MTJs in the stack by a seeding layer formed upon an isolation layer, the stack for storing more than one bit of information,   wherein different levels of current applied to the memory element causes switching to different states.   
     
     
         2 . A multi-state current-switching magnetic memory element, as recited in  claim 1 , wherein the free layers of the MTJs each have a unique composition, thereby causing each MTJ to switch states at a unique switching current. 
     
     
         3 . A multi-state current-switching magnetic memory element, as recited in  claim 1 , wherein the free layers of the MTJs each have a unique thickness, thereby causing each MTJ to switch states at a unique switching current. 
     
     
         4 . A multi-state current-switching magnetic memory element, as recited in  claim 1 , wherein the barrier layers of the MTJs each have a unique thickness, thereby causing each MTJ to switch states at a unique switching current. 
     
     
         5 . A multi-state current-switching magnetic memory element, as recited in  claim 4 , wherein the barrier layer of each of the MTJs is made substantially of magnesium oxide (MgO) and may include one or more of the following compounds—aluminum oxide (Al 2 O 3 ), titanium oxide (TiO2), magnesium oxide (MgOx), ruthenium oxide (RuO), strontium oxide (SrO), Zinc oxide (ZnO). 
     
     
         6 . A multi-state current-switching magnetic memory element, as recited in  claim 5 , wherein each of the MTJs includes a fixed layer, and a barrier layer, the barrier layer separating the fixed layer and the free layer. 
     
     
         7 . A multi-state current-switching magnetic memory element, as recited in  claim 6 , wherein the fixed layer of each of the MTJs is made substantially of magnetic material. 
     
     
         8 . A multi-state current-switching magnetic memory element, as recited in  claim 7 , further including a pinning layer formed adjacent to the fixed layer of each of the MTJs. 
     
     
         9 . A multi-state current-switching magnetic memory element, as recited in  claim 8 , further including a bottom electrode on top of which is formed the pinning layer of one of the MTJs. 
     
     
         10 . A multi-state current-switching magnetic memory element, as recited in  claim 9 , further including a top electrode formed on top of the free layer of one of the MTJs. 
     
     
         11 . A multi-state current-switching magnetic memory element comprising:
 A first magnetic tunneling junction (MTJ) formed on top of a bottom electrode;   A second MTJ, formed on top of the first MTJ, and the second MTJ separated from the first MTJ by and a seeding layer formed on top of an insulation layer; and   A top electrode formed on top of the second MTJ;   Wherein different levels of current applied to the memory element causes switching to different states.   
     
     
         12 . A multi-state current-switching magnetic memory element, as recited in  claim 11 , further including a first pinning layer formed between the bottom electrode and the first MTJ. 
     
     
         13 . A multi-state current-switching magnetic memory element, as recited in  claim 12 , further including a second pinning layer formed between the seeding layer formed on top of the insulation layer, and the second MTJ. 
     
     
         14 . A multi-state current-switching magnetic memory element, as recited in  claim 13 , wherein each MTJ includes a fixed layer, and a barrier layer, the barrier layer separating the free layer from the fixed layer. 
     
     
         15 . A multi-state current-switching magnetic memory element, as recited in  claim 14 , wherein the barrier layer of each MTJ is made substantially of magnesium oxide (MgO) and may include one or more of the following compounds—aluminum oxide (Al2O3), titanium oxide (TiO2), magnesium oxide (MgOx), ruthenium oxide (RuO), strontium oxide (SrO), Zinc oxide (ZnO). 
     
     
         16 . A multi-state current-switching magnetic memory element, as recited in  claim 15 , wherein the barrier layer of each MTJ has a unique thickness, thereby causing each MTJ to have a unique resistance. 
     
     
         17 . A multi-state current-switching magnetic memory element, as recited in  claim 16 , wherein the fixed layer of each of the MTJs is made substantially of magnetic material. 
     
     
         18 . A multi-state current-switching magnetic memory element, as recited in  claim 17 , wherein the free layer of each of the MTJs is unique in composition, causing each MTJ to have a unique switching current.