Abstract:
A method and apparatus are disclosed for inhibiting diffusion of mobile atoms from an antiferromagnetic layer toward a tunnel oxide layer and through a ferromagnetic layer which is pinned by the antiferromagnetic layer. Diffusion of the mobile atoms is inhibited by an oxide layer provided between the anti-ferromagnetic layer and the ferromagnetic layer. Alternatively, the ferromagnetic layer can have boron atoms located on or in the layer to fill interstices.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to an MRAM (magnetic random access memory) cell which inhibits the undesirable diffusion of mobile materials such as manganese.  
         BACKGROUND OF THE INVENTION  
         [0002]    Production of MRAM devices requires high-temperature processing which in some cases can exceed 200° C. During such processing, it is possible for mobile materials such as manganese (Mn) which is used in an antiferromagnetic layer to diffuse along grain boundaries to a tunnel oxide region. Such diffusion lowers reliability and performance of the MRAM device. Consequently, a method for producing MRAM devices which inhibits the diffusion of mobile materials is desired.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    In one aspect, the invention provides an MRAM device having upper and lower conducting layers, an anti-ferromagnetic layer connected to the upper conducting layer, a first ferromagnetic layer connected to the anti-ferromagnetic layer, wherein the first ferromagnetic layer is a pinned layer, a tunnel layer connected to the pinned layer; and a second ferromagnetic layer connected to said tunnel layer and to the lower conducting layer, where the second ferromagnetic layer is a free layer and an barrier layer is introduced between the antiferromagnetic layer and the tunnel layer, or introduced within the ferromagnetic layers. In another aspect of the invention, the first and second ferromagnetic layers are infused with boron. In yet another aspect of the invention, a method of fabricating the above components is disclosed.  
           [0004]    These and other features and advantages of the invention will be more clearly seen from the following detailed description of the invention which is provided in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a block diagram of a conventional MRAM memory cell;  
         [0006]    [0006]FIG. 2 is a block diagram of an MRAM memory cell of the present invention;  
         [0007]    [0007]FIG. 3 is a block diagram of a further modification to the MRAM memory cell of FIG. 1;  
         [0008]    [0008]FIG. 4 is a block diagram of another MRAM cell of the present invention;  
         [0009]    [0009]FIG. 5 is a block diagram of a modification to the MRAM cell of FIG. 4;  
         [0010]    [0010]FIG. 6 is a schematic diagram of the present invention employed within a processor circuit; and  
         [0011]    [0011]FIG. 7 is a block diagram of an MRAM memory cell of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    A conventional MRAM memory cell  100  is shown in FIG. 1, in which a magnetic structure  112  of the cell  100  has upper and lower conduits layers  104  and  108 , which are shown as being composed of tantalum (Ta), although other conductive materials may also be used. The magnetic structure  112  includes a ferromagnetic pinned layer  116  which is “pinned” by an anti-ferromagnetic layer  120  in contact with ferromagnetic layer  116 . The pinned layer has a magnetic field which is always fixed (or pinned) in a single direction by the anti-ferromagnetic layer  120 . The pinned layer  116  is shown in FIG. 1 as being composed of NiFe (Nickel Ferrite); however, it could also be composed of CoFe (Ferrous Cobalt), or CrFe (Chromium Ferrite). An anti-ferromagnetic layer  120  is located near the pinned layer  116 . The memory cell  100  also includes a tunnel oxide layer  124 , typically formed of aluminum oxide (Al 2 O 3 ) in contact with ferromagnetic layer  100  and a second ferromagnetic layer  128  in contrast with the tunnel oxide layer  124 . The second ferromagnetic layer can flip, or change magnetic orientation, which is how the memory cell  100  is programmed to store a ‘1’ or a ‘0’ logic state. The resistance of the cell  100  changes depending on the direction of orientation of the ferromagnetic layer  128 , which is also known as the ‘free’ or ‘sense’ layer. Write currents are applied to the conduction layers  104  and  108  to flip the sense layer  128  to a particular magnetic orientation. The sense layer  128  will hold its orientation until additional write currents are applied, so that the MRAM cell  100  holds a binary value indefinitely, and does not require refresh and is nonvolatile.  
         [0013]    When one or more IrMn (iridium manganese) layers are used to pin layer  116 , manganese atoms tend to diffuse through the pinned layer  116  to the tunnel region  124  during high temperature processing of a wafer containing memory cell  100 . This diffusion, shown by the arrows in FIG. 1, changes the electrical switching characteristics of the MRAM memory cell  100  during a read operation.  
         [0014]    As shown in FIG. 2, a slight oxidation layer  204  is formed on top of the pinning layer  116 , which serves as a barrier to mobile Mn atoms. Alternatively, as shown in FIG. 7, a slight oxidation layer  204  may be formed within the pinning layer  116 . An oxide layer  204  which is 2-5 Angstroms thick is sufficient to stop the movement of Mn along grain boundaries to the tunnel oxide layer  124 . Such an oxide would not need to be uniform in consistency, but should be thin enough so as to not consume too much of the ferromagnetic film  208 . Making the oxide  204  too thick will affect the coupling between the pinned layer  116  and the anti-ferromagnetic layer  120 . The oxide  204  can be produced from a nickel iron oxide or cobalt iron oxide by either an exposure to oxygen or with the aid of plasma. The antiferromagnetic layer  120  can then be deposited on the thin oxide barrier  204  and provide pinning for the underlying ferromagnetic layer  116 .  
         [0015]    The advantage of oxidizing the ferromagnetic layer  116  is that such layers will remain ferromagnetic or become slightly antiferromagnetic upon oxidation, and thus will not drastically reduce the coupling of the antiferromagnetic layers with the ferromagnetic layers.  
         [0016]    Another embodiment of the invention is shown in FIG. 3. In this embodiment, the diffusion of Mn along grain boundaries is blocked by materials which are added to the ferromagnetic material and bond to those grain boundaries and thereby effectively plug up the interstices. As shown in FIG. 3, boron (B) is one element that can accomplish such plugging. Boron can be applied to the layer  304  by sputtering, annealing, or by implanting the layer  304  with Boron ions. Boron has the advantage that small amounts can be added to ferromagnetic materials without changing their magnetic behavior. Boron also assists in making the ferromagnetic material amorphous. Consequently, the addition of a thin oxide at the ferromagnetic interface such as the oxide  204  shown in the FIG. 2 embodiment is not necessary. Because the thin oxide  204  need not be employed, the magnetic coupling between the antiferromagnetic  120  and ferromagnetic  116  layers remains consistent.  
         [0017]    Another type of MRAM cell  400  (FIG. 4) uses a Ruthinium layer  408  for “fine-tuning” the magnetic properties of the pinned layer  404 . With this structure, exchange coupling between the two ferromagnetic layers  412  and  414  occurs. Through application of the Ru layer  408 , the exchange coupling can be adjusted and calibrated. Also, the strong coupling through the Ruthenium forces the ferromagnetic layers  412  and  414  to be antiparallel thus forming an antiferromagnet from the Ruthenium layer  408 .  
         [0018]    The oxide layer can also be employed in the FIG. 4 structure, in the manner shown in FIG. 5. Thus, an oxide layer  504  is added to the MRAM cell  400  to inhibit diffusion of Mn atoms toward oxide layer  124 . Although FIG. 5 shows the oxide layer  504  being located between the layers  412  and  408 , the oxide layer  504  could alternatively be located between layers as shown by arrows A, C, and D. Additionally, the oxide layer could be located within the ferromagnetic layers  412 ,  414  as shown by the arrows E and F.  
         [0019]    [0019]FIG. 6 illustrates an exemplary processing system  600  which may utilize an electronic device comprising an MRAM device  100  constructed in accordance with any of the embodiments of the present invention disclosed above in connection with FIGS. 2, 3 and  5 . The processing system  600  includes one or more processors  601  coupled to a local bus  604 . A memory controller  602  and a primary bus bridge  603  are also coupled the local bus  604 . The processing system  600  may include multiple memory controllers  602  and/or multiple primary bus bridges  603 . The memory controller  602  and the primary bus bridge  603  may be integrated as a single device  606 .  
         [0020]    The memory controller  602  is also coupled to one or more memory buses  607 . Each memory bus accepts memory components  608  which include at least one memory device  610  of the present invention. The memory components  608  may be a memory card or a memory module. Examples of memory modules include single inline memory modules (SIMMs) and dual inline memory modules (DIMMs). The memory components  608  may include one or more additional devices  609 . For example, in a SIMM or DIMM, the additional device  609  might be a configuration memory, such as a serial presence detect (SPD) memory. The memory controller  602  may also be coupled to a cache memory  605 . The cache memory  605  may be the only cache memory in the processing system. Alternatively, other devices, for example, processors  601  may also include cache memories, which may form a cache hierarchy with cache memory  605 . If the processing system  600  include peripherals or controllers which are bus masters or which support direct memory access (DMA), the memory controller  602  may implement a cache coherency protocol. If the memory controller  602  is coupled to a plurality of memory buses  616 , each memory bus  616  may be operated in parallel, or different address ranges may be mapped to different memory buses  607 .  
         [0021]    The primary bus bridge  603  is coupled to at least one peripheral bus  610 . Various devices, such as peripherals or additional bus bridges may be coupled to the peripheral bus  610 . These devices may include a storage controller  611 , an miscellaneous I/O device  614 , a secondary bus bridge  615 , a multimedia processor  618 , and an legacy device interface  620 . The primary bus bridge  603  may also coupled to one or more special purpose high speed ports  622 . In a personal computer, for example, the special purpose port might be the Accelerated Graphics Port (AGP), used to couple a high performance video card to the processing system  600 . In addition to memory device  631  which may contain a buffer device of the present invention, any other data input device of FIG. 6 may also utilize a buffer device of the present invention including the CPU  601 .  
         [0022]    The storage controller  611  couples one or more storage devices  613 , via a storage bus  612 , to the peripheral bus  610 . For example, the storage controller  611  may be a SCSI controller and storage devices  613  may be SCSI discs. The I/O device  614  may be any sort of peripheral. For example, the I/O device  614  may be an local area network interface, such as an Ethernet card. The secondary bus bridge may be used to interface additional devices via another bus to the processing system. For example, the secondary bus bridge may be an universal serial port (USB) controller used to couple USB devices  617  via to the processing system  600 . The multimedia processor  618  may be a sound card, a video capture card, or any other type of media interface, which may also be coupled to one additional devices such as speakers  619 . The legacy device interface  620  is used to couple legacy devices, for example, older styled keyboards and mice, to the processing system  600 . In addition to memory device  631  which may contain a buffer device of the invention, any other data input device of FIG. 6 may also utilize a buffer device of the invention, including a CPU  601 .  
         [0023]    The processing system  600  illustrated in FIG. 6 is only one exemplary processing system with which the invention may be used. While FIG. 6 illustrates a processing architecture especially suitable for a general purpose computer, such as a personal computer or a workstation, it should be recognized that well known modifications can be made to configure the processing system  600  to become more suitable for use in a variety of applications. For example, many electronic devices which require processing may be implemented using a simpler architecture which relies on a CPU  601  coupled to memory components  608  and/or memory buffer devices  304 . These electronic devices may include, but are not limited to audio/video processors and recorders, gaming consoles, digital television sets, wired or wireless telephones, navigation devices (including system based on the global positioning system (GPS) and/or inertial navigation), and digital cameras and/or recorders. The modifications may include, for example, elimination of unnecessary components, addition of specialized devices or circuits, and/or integration of a plurality of devices.