Method, Apparatus and Computer Program Product for Stepped Reset Programming Process on Programmable Resistive Memory Cell

A method for resetting a phase change memory cell having a memory cell threshold voltage, the memory cell threshold voltage being a voltage at which at least a portion of the amorphous phase change material of the memory cell starts to break down, the memory cell coupled to an access device having an access device threshold voltage, comprising:

• reading a first resistance of the memory cell by (a) applying a voltage, smaller than the memory cell threshold voltage, to a bit line coupled to the memory cell, and by (b) applying a voltage, larger than the access device threshold voltage, to a word line coupled to the access device;
• if the first resistance is larger than a chosen resistance, end the resetting of the memory cell;
• if the first resistance is not larger than the chosen resistance, then proceed by:
• applying a voltage, larger than the memory cell threshold voltage, to the bit line, and applying a voltage VWL, larger than the access device threshold voltage, to the word line;
• reading a second resistance of the memory cell by (a) applying a voltage, smaller than the memory cell threshold voltage, to the bit line, and (b) applying a voltage, larger than the access device threshold voltage, to the word line;
• if the second resistance is larger than the chosen resistance, end the resetting of the memory cell;
• and
• if the second resistance is not larger than the chosen resistance, then proceed by:
• applying a voltage, larger than the memory cell threshold voltage, to the bit line, increasing voltage VWL to obtain an increased voltage VWL, and applying the increased voltage VWL to the word line.

A method for resetting a phase change memory cell having a memory cell threshold voltage, the memory cell threshold voltage being a voltage at which at least a portion of the amorphous phase change material of the memory cell starts to break down, the memory cell coupled to a pair of MOSFETs having an access device threshold voltage, comprising:

• applying a first voltage to a bit line coupled with the memory cell, wherein the first voltage is lower than the memory cell threshold voltage, and applying a second voltage to a pair of word lines coupled to the pair of MOSFETs, so as to read a first resistance of the memory cell, the second voltage being greater than the access device threshold voltage;
• if the first resistance is larger than a chosen resistance, end the resetting of the memory cell, and if not then proceed by:
• applying a third voltage to the bit line, wherein the third voltage is higher than the memory cell threshold voltage, and applying a fourth voltage to the pair of word lines so as to program the memory cell, the fourth voltage being greater than the access device threshold voltage;
• applying the first voltage to the bit line and applying the second voltage to the pair of word lines, so as to read a second resistance of the memory cell;
• and
• if the second resistance is larger than a chosen resistance, end the resetting of the memory cell, and if not then proceed by:
• applying the third voltage to the bit line and applying a fifth voltage to the pair of word lines so as to program the memory cell, the fifth voltage being the sum of the fourth voltage and a predetermined voltage.

A programmable resistive memory system, comprising:

• a memory cell device comprising a plurality of programmable resistive memory cells, wherein each memory cell has a memory cell threshold voltage, the memory cell threshold voltage being a voltage at which at least a portion of the amorphous phase change material of the memory cell starts to break down, and wherein each memory cell is coupled to an access device having an access device threshold voltage;
• and
• a controller for programming the memory cell device, the controller configured for resetting a memory cell by:
• selecting a voltage VWL, voltage VWL being larger than the access device threshold voltage;
• reading a resistance of the memory cell by (a) applying a voltage, smaller than the memory cell threshold voltage, to a bit line coupled to the memory cell, and by (b) applying a voltage, larger than the access device threshold voltage, to a word line coupled to the access device;
• if the resistance is larger than a chosen resistance, end the resetting of the memory cell;
• if the resistance is not larger than the chosen resistance, then proceed by:
• applying a voltage, larger than the memory cell threshold voltage, to the bit line;
• and
• applying voltage VWL to the word line to reset the memory cell;
• reading the resistance of the memory cell by (a) applying a voltage, smaller than the memory cell threshold voltage, to the bit line coupled to the memory cell, and by (b) applying a voltage, larger than the access device threshold voltage, to the word line;
• if the resistance is larger than the chosen resistance, end the resetting of the memory cell;
• if the resistance is not larger than the chosen resistance, then proceed by:
• applying a voltage, larger than the memory cell threshold voltage, to the bit line;
• increasing voltage VWL by a voltage ΔV;
• and
• applying increased voltage VWL to the word line to reset the memory cell;
• and
• return to the second reading step.

A computer program product including computer instructions for programming a memory cell device comprising a plurality of programmable resistive memory cells, wherein each memory cell has a memory cell threshold voltage, the memory cell threshold voltage being a voltage at which at least a portion of the amorphous phase change material of the memory cell starts to break down, and wherein each memory cell is coupled to an access device having an access device threshold voltage, the computer instructions including instructions for executing the following for resetting a memory cell:

• selecting a voltage VWL, voltage VWL being larger than the access device threshold voltage;
• reading a first resistance of the memory cell by (a) applying a voltage, smaller than the memory cell threshold voltage, to a bit line coupled to the memory cell, and by (b) applying a voltage, larger than the access device threshold voltage, to a word line coupled to the access device;
• if the resistance is larger than a chosen resistance, end the resetting of the memory cell;
• if the resistance is not larger than the chosen resistance, then proceed by:
• applying a voltage, larger than the memory cell threshold voltage, to the bit line;
• and
• applying voltage VWL to the word line to reset the memory cell;
• reading the resistance of the memory cell by (a) applying a voltage, smaller than the memory cell threshold voltage, to the bit line coupled to the memory cell, and by (b) applying a voltage, larger than the access device threshold voltage, to the word line;
• if the resistance is larger than the chosen resistance, end the resetting of the memory cell;
• if the resistance is not larger than the chosen resistance, then proceed by:
• applying a voltage, larger than the memory cell threshold voltage, to the bit line;
• increasing voltage VWL by a voltage ΔV;
• and
• applying increased voltage VWL to the word line to reset the memory cell;
• and
• return to the second reading step.