Method for writing in a MRAM-based memory device with reduced power consumption
View Patent ↗A method of writing in a memory device comprising a plurality of MRAM cells, each cell including a magnetic tunnel junction having a resistance that can be varied during a write operation when heated at a high threshold temperature; a plurality of word lines connecting cells along a row; and a plurality of bit lines connecting cells along a column; the method comprising supplying a bit line voltage to one of the bit lines and a word line voltage to one of the word lines for passing a heating current through the magnetic tunnel junction of a selected cell; said word line voltage is a word line overdrive voltage being higher than the core operating voltage of the cells such that the heating current has a magnitude that is high enough for heating the magnetic tunnel junction at the predetermined high threshold temperature. The memory device can be written with low power consumption.
1. A method of writing in a memory device comprising a plurality of magnetoresistive random access memory (MRAM) cells arranged in rows and columns, each MRAM cell to be written by using a thermally-assisted switching (TAS) write operation, including a magnetic tunnel junction having a resistance that can be varied during a write operation when the magnetic tunnel junction is heated at a high threshold temperature, and a select transistor electrically coupled to the magnetic tunnel junction; a plurality of word lines connecting MRAM cells along a row; and a plurality of bit lines connecting MRAM cells along a column; comprising, during the write operation:
supplying a bit line voltage to one of the bit lines and a word line voltage to one of the word lines for passing a heating current through the magnetic tunnel junction of a selected MRAM cell;
once the magnetic tunnel junction has reached the high threshold temperature, varying the resistance of the magnetic tunnel junction; and
cooling the magnetic tunnel junction such as to freeze said resistance in its written value;
said word line voltage is a word line overdrive voltage being higher than the core operating voltage of the MRAM cells such that the heating current has a magnitude that is high enough for heating the magnetic tunnel junction at the predetermined high threshold temperature.
2. The method according to claim 1 , wherein the word line overdrive voltage is a voltage pulse with a pulse duration being equal to or smaller than about 15 ns.
3. The method according to claim 1 , wherein the word line overdrive voltage is generated by a charge pump or by a regulable external voltage provided by an input-output port.
4. The method according to claim 1 , wherein the memory device further comprises a sense amplifier circuitry, and wherein the pulse duration of the word line overdrive voltage is controlled by the sense amplifier circuitry.
5. The method according to claim 1 , wherein the select transistor is a high power transistor having a low threshold voltage.
6. The method according to claim 1 , wherein the memory device further comprises a plurality of source lines connecting MRAM cells along a row, via the drain of their respective select transistor, and wherein the method further comprises supplying a source line overdrive voltage to the source line.
7. The method according to claim 6 , wherein the source line overdrive voltage has a value substantially equal to the threshold voltage of the select transistor.
8. The method according to claim 6 , further comprising a read operation including measuring the resistance of the magnetic tunnel junction, and supplying the source line overdrive voltage to the source line.