Pre-conditioning circuits and methods for programmable impedance elements in memory devices

1. A memory device, comprising:

a plurality of programmable impedance elements programmable between a low impedance state in response to a program voltage and a higher impedance state in response to an erase voltage that has a different polarity than the program voltage;

a programming circuit configured to apply the program and erase voltages to selected elements; and

a pre-condition path configured to apply a pre-condition voltage only of the erase voltage polarity to fresh elements in a pre-condition operation; wherein

fresh elements are elements that have not been subject to any programming voltages.

2. The memory device of claim 1 , wherein:

at least some of the elements are in the low impedance state after the pre-condition operation.

3. The memory device of claim 1 , wherein:

the pre-condition path is configured to apply a pre-condition voltage having a different magnitude than the erase voltage.

4. The memory device of claim 1 , wherein:

the pre-condition path is configured to apply a pre-condition current through an element having a magnitude different than currents applied to an element when it is programmed to the low or higher impedance states.

5. The memory device of claim 4 , wherein:

the pre-condition path is configured to apply a pre-condition current through an element that is less than a current applied to an element when it is programmed to the low or high impedance states.

6. The memory device of claim 1 , wherein:

the pre-condition path is configured to apply a pre-condition current of no more than 100 uA.

7. The memory device of claim 1 , wherein:

the erase voltage has a magnitude of no more than 1 volt.

8. The memory device of claim 1 , wherein:

the pre-condition path is configured to apply a pre-condition voltage that ramps from a lower start voltage to a higher end voltage.

9. The memory device of claim 1 , wherein:

the pre-condition path is configured to apply a pre-condition voltage that ramps from a higher start voltage to a lower end voltage.

10. The memory device of claim 1 , further including:

a plurality of memory cells arranged into at least one array, each memory cell including at least one element and an access device that couples the element to a bit line, the access devices of a same row being coupled to a same word line; and

a word line driver circuit coupled to each word line, each word line driver circuit configured to apply a ramping voltage to its corresponding word line.

11. The memory device of claim 1 , wherein:

each element comprises a solid ion conductor material disposed between two electrodes.

12. A memory device, comprising:

a plurality of programmable impedance elements;

circuits configured to apply program electrical conditions to place selected elements into a low impedance state, to apply erase electrical conditions to place selected elements into a higher impedance state, and to apply pre-condition electrical conditions to fresh elements in a pre-condition operation; wherein

fresh elements are elements that have never been subject to the program or erase electrical conditions, and

the pre-condition electrical conditions are selected from the group of: low current high voltage (LCHV) conditions and high voltage high current (HVHC) conditions, wherein

the LCHV conditions apply a lower current and a higher magnitude voltage to elements than the program or erase electrical conditions, and

the HVHC conditions apply a higher magnitude voltage and higher current to elements than the program or erase electrical conditions.

13. The memory device of claim 12 , wherein:

the pre-condition and erase electrical conditions apply a different polarity voltage across the elements as compared to the program electrical conditions.

14. The memory device of claim 12 , wherein:

the pre-condition electrical conditions are the LCHV conditions; and

the circuits are configured to apply a pre-condition current of no more than 10 uA to elements.

15. The memory device of claim 12 , wherein:

the circuits are configured to apply a pre-condition voltage having a different magnitude rate-of-change than voltages of the standard electrical programming conditions.

16. The memory device of claim 12 , wherein:

the pre-condition electrical conditions are the HVHC conditions; and

the circuits are configured to apply a pre-condition voltage across elements of no less than 1.0 V.

17. The memory device of claim 12 , further including:

a plurality of memory cells arranged into at least one array, each memory cell including at least one element and an access device that couples the element to a bit line, the access devices of a same row being coupled to a same word line; and

a word line driver circuit coupled to each word line.

18. The memory device of claim 17 , wherein:

bit lines are pre-charged to a pre-condition voltage while word lines maintain access devices in an off state; and

the word line driver circuit is configured to drive a word line to a select voltage to enable an access device in a pre-condition operation; wherein

the pre-condition electrical conditions are created by the capacitive discharge of the bit line.

19. The memory device of claim 17 , further including:

the word line driver circuit is configured to drive word lines to a standard voltage to read data from the elements and to drive word lines to a boost voltage in the pre-condition operation, the boost voltage having a greater magnitude than the standard voltage.

20. The memory device of claim 12 , wherein:

each element comprises a solid ion conductor material disposed between two electrodes.

21. A method, comprising:

manufacturing a device that programs elements to a low impedance state with first electrical conditions, and programs elements to a higher impedance state with second electrical conditions having a different polarity than the first electrical conditions; and

before programming any elements to the low or higher impedance states, pre-conditioning fresh elements with pre-condition electrical conditions different than at least the first electrical conditions; wherein

the pre-condition electrical conditions include any selected from the group of: single polarity conditions that apply a voltage only of the same polarity as the second electrical conditions; high voltage low current (HVLC) conditions that apply a greater magnitude voltage and smaller current than the first or second electrical conditions; and

(HVHC) conditions that apply a greater magnitude voltage and greater current than the first or second electrical conditions.

22. The method of claim 21 , wherein:

the pre-condition electrical conditions are the HVLC conditions; and

the pre-conditioning of the fresh elements includes limiting a current flow through fresh elements to less than 10 uA.

23. The method of claim 21 , wherein:

the pre-condition electrical conditions are the HVHC conditions; and

pre-conditioning electrical conditions include a voltage across fresh elements of no less than 1.0 volts.

24. The method of claim 21 , wherein:

the pre-conditioning includes applying a ramped voltage to the elements selected from: a ramped voltage that increases over time, a ramped voltage that decreases over time, and a ramped voltage that increases and decreases over time.

25. The methods of claim 24 , wherein:

applying the ramped voltage further includes

charging at least one bit line to a pre-condition voltage, and

turning on an access device of a memory cell to enable the bit line to discharge through an element.

26. The methods of claim 24 , wherein:

applying the ramped voltage includes applying a ramped voltage to a control terminal of access devices coupled to the elements.

27. The methods of claim 21 , wherein:

the pre-conditioning includes applying the pre-condition electrical conditions to a greater number of elements than a number of elements accessible when elements are programmed to the low impedance or higher impedance state.

28. The memory device of claim 21 , wherein:

each element comprises a solid ion conductor material disposed between two electrodes.