MULTI-TIME PROGRAMMABLE MEMORY DEVICES AND METHODS
An apparatus is provided that includes a memory cell including a reversible resistance-switching memory element coupled in series with a selector element. The memory cell may be selectively configured as either a re-writeable memory cell or a multi-time programmable memory cell. The selector element includes a first switch resistance and a second switch resistance. The resistance-switching memory element includes a first memory element resistance and a second memory element resistance. The memory cell functions as a multi-time programmable memory cell regardless of whether the resistance-switching memory element has the first memory element resistance or the second memory element resistance.
1 . An apparatus comprising:
a memory cell comprising a reversible resistance-switching memory element coupled in series with a selector element, wherein:
the memory cell may be selectively configured as either a re-writeable memory cell or a multi-time programmable memory cell;
the selector element comprises a first switch resistance and a second switch resistance;
the resistance-switching memory element comprises a first memory element resistance and a second memory element resistance; and
the memory cell functions as a multi-time programmable memory cell regardless of whether the resistance-switching memory element has the first memory element resistance or the second memory element resistance.
2 . The apparatus of claim 1 , wherein the first switch resistance is a resistance of the selector element as fabricated.
3 . The apparatus of claim 1 , wherein the selector element is configured to irreversibly switch from the first switch resistance to the second switch resistance in response to a forming operation performed on the selector element.
4 . The apparatus of claim 1 , wherein the memory cell is configured to be programmed a first time by applying one or more pulses comprising a first voltage.
5 . The apparatus of claim 4 , wherein the first voltage comprises a forming voltage of the selector element.
6 . The apparatus of claim 4 , wherein the memory cell is configured to be programmed a second time by applying one or more pulses comprising a second voltage greater than the first voltage.
7 . The apparatus of claim 6 , wherein the memory cell is configured to be programmed a third time by applying one or more pulses comprising a third voltage greater than the second voltage.
8 . The apparatus of claim 1 , wherein:
the memory cell is configured as a multi-time programmable memory cell that may have a first resistance and a second resistance,
wherein the first resistance comprises the first switch resistance and the second resistance comprises the second switch resistance.
9 . The apparatus of claim 8 , wherein the second resistance further comprises the first memory element resistance or the second memory element resistance.
10 . The apparatus of claim 8 , wherein the memory cell is configured as a multi-time programmable memory cell that may have a third resistance that comprises the second switch resistance.
11 . The apparatus of claim 8 , wherein the third resistance further comprises a third memory element resistance lower than the first memory element resistance and the second memory element resistance.
12 . The apparatus of claim 8 , wherein the memory cell is configured as a multi-time programmable memory cell that may have a fourth resistance that comprises an open circuit resistance of the resistance-switching memory element and the selector element.
13 . The apparatus of claim 1 , wherein the reversible resistance-switching memory element comprises a magnetic tunnel junction memory element.
14 . The apparatus of claim 1 , wherein the selector element comprises an ovonic threshold switch.
15 . An apparatus comprising:
a cross-point memory array comprising a plurality of memory cells, each memory cell comprising a magnetic tunnel junction memory element coupled in series with a selector element,
wherein each memory cell in the cross-point memory array may be selectively configured as either a re-writeable memory cell or a multi-time programmable memory cell that may be programmed a first time, a second time and a third time.
16 . The apparatus of claim 15 , wherein the selector element comprises an ovonic threshold switch.
17 . The apparatus of claim 15 , wherein:
each selector element comprises a first switch resistance and a second switch resistance;
each magnetic tunnel junction memory element is configured to reversibly switch between a first memory element resistance and a second memory element resistance; and
each memory cell configured as a multi-time programmable memory cell that functions regardless of whether the magnetic tunnel junction memory element has the first memory element resistance or the second memory element resistance.
18 . The apparatus of claim 15 , wherein:
each memory cell is configured to be programmed a first time by applying one or more pulses comprising a first voltage;
each memory cell is configured to be programmed a second time by applying one or more pulses comprising a second voltage greater than the first voltage; and
each memory cell is configured to be programmed a third time by applying one or more pulses comprising a third voltage greater than the second voltage.
19 . A method comprising:
forming first memory cells and second memory cells using a same fabrication process, each first memory cell and each second memory cell comprising a same structure comprising a magnetic tunnel junction memory element coupled in series with an ovonic threshold switch, the first memory cells comprising a first resistance;
programming the first memory cells a first time by applying one or more pulses comprising a magnitude of a first voltage, the first time programmed first memory cells comprising a second resistance lower than the first resistance;
programming the first memory cells a second time by applying one or more pulses comprising a magnitude of a second voltage greater than the magnitude of the first voltage, the second time programmed first memory cells comprising a third resistance lower than the second resistance; and
programming the first memory cells a third time by applying one or more pulses comprising a magnitude of a third voltage greater than the magnitude of the second voltage, the third time programmed first memory cells comprising a fourth resistance greater than the first resistance,
wherein the first memory cells comprise multi-time programmable memory cells and the second memory cells comprise re-writeable memory cells.
20 . The method of claim 19 , wherein the first memory cells and the second memory cells comprise a cross-point memory array.