Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2003-03-27
2003-12-23
Tran, Andrew Q. (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S173000, C365S171000, C365S230070, C365S225500
Reexamination Certificate
active
06667899
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to Magnetoresistive Random Access Memories (MRAMs), and more particularly to programming of MRAMs.
BACKGROUND OF THE INVENTION
A magnetoresistive RAM (hereinafter referred to as “MRAM”) is a magnetic memory device. A memory state in an MRAM is not maintained by electrical power, but rather by the direction of the magnetic polarization of magnetic materials. Storing data is accomplished by applying magnetic fields and causing a magnetic material in a MRAM device to be magnetized into either of two possible memory states. Reading data from the memory is accomplished by sensing the resistance differences in the MRAM device between the two states. The magnetic fields for writing are created by passing currents through metal lines external to the magnetic structure. Some MRAMs are toggle memories that are programmed by either reversing the state of the memory cells or leaving them in the same logic state. In order to determine which of these is chosen, the logic state to be written must be compared to the state that is already present. If the outcome of the comparison is that the logic state must be reversed, the write sequence is performed. If the logic state is to stay the same, a write sequence is not performed.
A write or program operation of MRAM bits requires high current densities through the metal lines to create magnetic fields external to the magnetic structure. With extended use, high current densities result in significant movement of atoms in the metal lines leaving resulting atomic voids. The presence of increased holes changes the resistivity of the metal lines thereby resulting in electromigration (EM) failures. The result is a modification of the operation of the MRAM and the likelihood of failed operation.
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U.S. patent application Ser. No. 09/978,859 entitled “A Method of Writing to a Scalable Magnetoresistance Random Access Memory Element,” filed Oct. 16, 2001 and assigned to assignee hereof.
U.S. patent application Ser. No. 10/186,141 entitled “Circuit and Method of Writing a Toggle Memory,” filed Jun. 28, 2002 and assigned to assignee hereof.
U.S. patent application Ser. No. 10/185,868 entitled “MRAM Architecture with Electrically Isolated Read and Write Circuitry,” filed Jun. 28, 2002 and assigned to assignee hereof.
Andre Thomas W.
Nahas Joseph J.
Subramanian Chitra K.
King Robert L.
Motorola Inc.
Tran Andrew Q.
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