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A Method of Creating Local Transient Programming Current for MRAM by Charge Storage

IP.com Disclosure Number: IPCOM000020221D
Original Publication Date: 2003-Nov-03
Included in the Prior Art Database: 2003-Nov-03
Document File: 2 page(s) / 78K

Publishing Venue

IBM

Abstract

A method of creating local current pulse for writing MRAM cell and associated cell structures are described. The cell structure includes two write lines that traverse the array in generally the same direction. A write transistor and a local write wire is connected in series between these two metal lines for each cell. The write operation starts by charging the two metal lines to different electrical potential. The discharge of capacitors distributed along these lines when one of the write transistors is turned on creates a current pulse that writes the selected cell to the desired state.

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  A Method of Creating Local Transient Programming Current for MRAM by Charge Storage

    One major difficulty in scaling Magnetic-Random-Access-Memory to higher density relates to the size of the required write currents. The write currents are generally higher than 5 milliamperes and must be carried from one edge of the array to the opposite edge. Very large transistors are generally required to switch these large currents, which reduces array efficiency. Large voltage difference required to drive these currents across the array limits the scaling down of the power supply voltage. Passing the write current through the array also subjects large number of cells to one component of the write field (so called half-select condition). This document describes a method of generating the required write currents locally around the selected cell only by charge storage, and eliminating the above difficulties.

LBL RBL

WWL

Write Wire

Write FET

MTJ

Figure 1, one cross-point cell implementation of local write current concept.

    As shown in Figure 1, one possible implementation in the cross-point MRAM array. Small drivers charge all node capacitors on the left BL of the selected cell to the high voltage (or low voltage, depending on the data to be written), while all node capacitors on the right BL of the selected cell to the opposite voltage supply. The write transistor is then quickly turned on. Charges stored on node capacitors surge through the write transistor and the write wire an...