Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-07-15
2004-10-19
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S421000, C257S422000, C438S003000, C438S048000, C438S050000, C365S158000
Reexamination Certificate
active
06806523
ABSTRACT:
TECHNICAL FIELD
The invention pertains to magnetoresistive memory devices, such as, for example, magnetic random access memory (MRAM) devices, and also pertains to methods of forming magnetoresistive memory devices.
BACKGROUND OF THE INVENTION
Numerous types of digital memories are utilized in computer system components, digital processing systems, and other applications for storing and retrieving data. MRAM is a type of digital memory in which digital bits of information comprise alternative states of magnetization of magnetic materials in memory cells. The magnetic materials can be thin ferromagnetic films. Information can be stored and retrieved from the memory devices by inductive sensing to determine a magnetization state of the devices, or by magnetoresistive sensing of the magnetization states of the memory devices. It is noted that the term “magnetoresistive device” characterizes the device and not the access method, and accordingly a magnetoresistive device can be accessed by, for example, either inductive sensing or magnetoresistive sensing methodologies.
A significant amount of research is currently being invested in magnetic digital memories, such as, for example, MRAM's, because such memories are seen to have significant potential advantages relative to the dynamic random access memory (DRAM) components and static random access memory (SRAM) components that are presently in widespread use. For instance, a problem with DRAM is that it relies on power storage within capacitors. Such capacitors leak energy, and must be refreshed at approximately 15 nanosecond intervals. The constant refreshing of DRAM devices can drain energy from batteries utilized to power the devices, and can lead to problems with lost data since information stored in the DRAM devices is lost when power to the devices is shut down.
SRAM devices can avoid some of the problems associated with DRAM devices, in that SRAM devices do not require constant refreshing. Further, SRAM devices are typically faster than DRAM devices. However, SRAM devices take up more semiconductor real estate than do DRAM devices. As continuing efforts are made to increase the density of memory devices, semiconductor real estate becomes increasingly valuable. Accordingly, SRAM technologies are difficult to incorporate as standard memory devices in memory arrays.
MRAM devices have the potential to alleviate the problems associated with DRAM devices and SRAM devices. Specifically, MRAM devices do not require constant refreshing, but instead store data in stable magnetic states. Further, the data stored in MRAM devices can potentially remain within the devices even if power to the devices is shutdown or lost. Additionally, MRAM devices can potentially be formed to utilize less than or equal to the amount of semiconductor real estate associated with DRAM devices, and can accordingly potentially be more economical to incorporate into large memory arrays than are SRAM devices.
Although MRAM devices have potential to be utilized as digital memory devices, they are currently not widely utilized. Several problems associated with MRAM technologies remain to be addressed. It would be desirable to develop methodologies for making MRAM devices in which bits are stable over time and relative to stray magnetic field effects, and in which the bits can be formed by photolithographic processes and scaled as dimensions produced by photolithography decrease. Further, it would be desirable to develop MRAM devices which avoid various shape-related issues associated with some of the currently-produced MRAM devices.
SUMMARY OF THE INVENTION
In one aspect, the invention encompasses a magnetoresistive memory device. The device includes a conductive core, and a first magnetic layer extending at least partially around the conductive core. A non-magnetic material is over at least a portion of the first magnetic layer and separated from the conductive core by at least the first magnetic layer. A second magnetic layer is over the non-magnetic material, and separated from the first magnetic layer by at least the non-magnetic material.
In another aspect, the invention encompasses a method of forming a magnetoresistive memory device. A trench is formed in an insulative material, and partially filled with a first magnetic material to narrow the trench. The narrowed trench is at least partially filled with a conductive material. A second magnetic material is formed over the conductive material. A non-magnetic material is formed over the second magnetic material. A third magnetic material is formed over the non-magnetic material. The first and second magnetic materials are incorporated into a sense portion of a magnetoresistive memory device, together with the conductive material. The third magnetic material is incorporated into a reference portion of the magnetoresistive memory device.
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Micro)n Technology, Inc.
Nelms David
Tran Long
Wells St. John P.S.
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