Method for magnetic screening of arrays of magnetic memories

A method for testing cells in an MRAM device for abnormal thermal stability factor (delta) using coercivity as a proxy, the MRAM device having a plurality of cells that have a low resistance state and a high resistance state, the plurality of cells having varying coercivity that includes low coercivity cells, normal coercivity cells and high coercivity cells, the method comprising:

• initializing low coercivity cells, normal coercivity cells and high coercivity cells into a first resistance state by applying an externally generated first magnetic field to the MRAM device to force a plurality of the cells into the first resistance state, the first magnetic field having a first strength and a first direction selected to switch low, normal and high coercivity cells into the first resistance state;
• removing the first magnetic field;
• applying an externally generated second magnetic field to the MRAM device, the second magnetic field having a second strength and a second direction selected to only switch normal and low coercivity cells into the second resistance state and to leave the high coercivity cells in the first resistance state;
• removing the second magnetic field;
• and
• determining a failing set of cells as including cells that are in the first resistance state.

A method for testing cells in an MRAM device for abnormal thermal stability factor (delta) using coercivity as a proxy, the MRAM device having a plurality of cells that have a low resistance state and a high resistance state, the plurality of cells having varying coercivity that includes low coercivity cells, normal coercivity cells and high coercivity cells, the method comprising:

• initializing low coercivity cells, normal coercivity cells and high coercivity cells into a first resistance state by applying an externally generated first magnetic field to the MRAM device to force a plurality of the cells into the first resistance state, the first magnetic field having a first strength and a first direction selected to switch low, normal and high coercivity cells into the first resistance state;
• removing the first magnetic field;
• applying an externally generated second magnetic field to the MRAM device, the second magnetic field having a second strength and a second direction selected to only switch normal and low coercivity cells into the second resistance state and to leave the high coercivity cells in the first resistance state;
• removing the second magnetic field;
• applying an externally generated third magnetic field to the MRAM device, the third magnetic field having a third strength and a third direction selected to only switch low coercivity cells into the first resistance state and to leave the normal coercivity cells in the second resistance state;
• and
• determining a failing set of cells as including cells that are in the first resistance state.

A method for testing cells in an MRAM device for abnormal thermal stability factor (delta) using coercivity as a proxy, the MRAM device having a plurality of cells that are switchable between a low resistance state and a high resistance state using electric current generated by circuitry in the MRAM device, the plurality of cells including low coercivity cells, normal coercivity cells and high coercivity cells, the method comprising:

• applying an externally generated first magnetic field to the MRAM device to force a plurality of the cells into a first resistance state, the first magnetic field having a first strength and a first direction selected to switch low, normal and high coercivity cells into the first resistance state;
• removing the first magnetic field;
• driving a selected electric current through each cell using circuitry in the MRAM device to switch a plurality of the cells into the second resistance state;
• applying an externally generated second magnetic field to the MRAM device, the second magnetic field having a second strength and a second direction selected to only switch low coercivity cells into the first resistance state and to leave the normal coercivity cells in the second resistance state;
• and
• determining a failing set of cells as including cells that are in the first resistance state.