1. A circuit comprising:
a magneto-resistive random access memory (MRAM) cell; and
a control circuit electrically coupled to the MRAM cell, wherein the control circuit comprises:
a current source configured to provide a first writing pulse to write a value into the MRAM cell; and
a read circuit configured to measure a status of the MRAM cell, wherein the control circuit is further configured to verify whether a successful writing is achieved through the first writing pulse.
2. The circuit of claim 1, wherein the control circuit is further configured to:
when the status of the MRAM cell indicates a successful writing by the first writing pulse, stop writing the value to the MRAM cell; and
when the status of the MRAM cell indicates an unsuccessful writing by the first writing pulse, provide a second writing pulse to write the value to the MRAM cell.
3. The circuit of claim 2, wherein the control circuit is further configured to:
verify an additional status of the MRAM cell by the second writing pulse;
when the additional status of the MRAM cell indicates a successful writing by the second writing pulse, stop writing the value to the MRAM cell; and
when the additional status of the MRAM cell indicates an unsuccessful writing by the second writing pulse, provide a third writing pulse to write the value to the MRAM cell.
4. The circuit of claim 2, wherein the current source is configured to control the second writing pulse to be substantially identical to the first writing pulse.
5. The circuit of claim 2, wherein the current source is configured to control the second writing pulse to be different from the first writing pulse.
6. The circuit of claim 1, wherein an intended one-write-probability of the first writing pulse is less than 100 percent.
7. The circuit of claim 6, wherein the intended one-write-probability of the first writing pulse is less than about 99 percent.
8. The circuit of claim 7, wherein the intended one-write-probability of the first writing pulse is less than about 70 percent.
9. The circuit of claim 1, wherein the control circuit is configured to verify the status of the MRAM cell within about 50 nanoseconds after the current source provides the first writing pulse to the MRAM cell.
10. A circuit comprising:
a magneto-resistive random access memory (MRAM) cell; and
a control circuit electrically coupled to the MRAM cell, wherein the control circuit comprises:
a current source configured to provide a plurality of writing pulses to write a same value to the MRAM cell, wherein an intended one-write-probability of each of the plurality of writing pulses is less than 100 percent; and
a read circuit configured to read a status of the MRAM cell, wherein the control circuit is configured to control the read circuit to read the status of the MRAM cell after each of the plurality of writing pulses is provided to the MRAM cell.
11. The circuit of claim 10, wherein the control circuit is further configured to stop writing to the MRAM cell when a pre-determined number of writing pulses is provided to the MRAM cell, and when the read circuit indicates that the same value is not successfully written into the MRAM cell.
12. The circuit of claim 10, wherein the control circuit is further configured to control the current source to increase a pulse length of a subsequent one of the plurality of writing pulses when the read circuit verifies that the MRAM cell fails to be written into in a preceding one of the plurality of writing pulses.
13. The circuit of claim 10, wherein the control circuit is further configured to control the current source to increase a pulse magnitude of a subsequent one of the plurality of writing pulses when the read circuit verifies that the MRAM cell fails to be written into in a preceding one of the plurality of writing pulses.
14. The circuit of claim 10, wherein the current source is configured to control the plurality of writing pulses to be identical to each other.
15. The circuit of claim 10, wherein the control circuit, the current source, and the read circuit are controlled not to write into and read from any additional MRAM cell in a same MRAM array before the plurality of writing pulses is finished.
16. The circuit of claim 10, wherein the intended one-write-probability of each of the plurality of writing pulse is less than about 90 percent.
17. A circuit comprising:
a magneto-resistive random access memory (MRAM) cell; and
a control circuit electrically coupled to the MRAM cell, wherein the control circuit is configured to provide a plurality of write-verification cycles, wherein each of the plurality of write-verification cycles comprises a writing step and a verification step, and wherein an intended one-write-probability of the writing step in each of the plurality of write-verification cycles is less than 100 percent.
18. The circuit of claim 17, wherein the control circuit is configured to stop writing to the MRAM cell when a verification result of a verification step indicates a previous writing step results in a successful writing into the MRAM cell.
19. The circuit of claim 17, wherein the control circuit is configured to stop writing to the MRAM cell when all of the plurality of write-verification cycles fails to result in a successful writing into the MRAM cell.
20. The circuit of claim 17, wherein a pulse length of each of a subsequent one of the plurality of write-verification cycles is greater than a pulse length of a preceding one of the plurality of write-verification cycles.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method of carburizing ferrous metal parts comprising the steps of:
(a) providing a furnace for heating the metal parts and a process chamber;
(b) purging an air atmosphere from the process chamber and heating said process chamber to a temperature of at least 1100\xb0 F.;
(c) feeding a fuel gas to the process chamber and a source of air at a constant flow rate to the process chamber;
(d) boosting the process chamber by feeding an enriching gas to the process chamber to create a carbon potential of at least 0.5%;
(e) cleaning the process chamber by decreasing the flow of enriching gas to the process chamber to create a carbon potential of less than about 0.25%;
(f) repeating the boosting step (d) after performing said cleaning step (e); and
(g) repeating the cleaning step(e) after performing said repeated boosting step (f).
2. The method according to claim 1, wherein during said boosting step (d) the enriching gas is supplied to the process chamber at a ratio of from about 0 to about 1.2 cubic feet of enriching gas to every cubic foot of air.
3. The method according to claim 1, wherein during said cleaning step (e) the enriching gas is supplied to the process chamber at a ratio of from about 0 to about 0.35 cubic feet of enriching gas to every cubic foot of air.
4. The method according to claim 1, wherein said boosting step (d) is performed for a period of from about 10 to about 90 minutes.
5. The method according to claim 1, wherein said cleaning step (e) is performed for a period of from about 3 to about 40 minutes.
6. The method according to claim 1, wherein said gas of said step (b) comprises a carrier gas formed by the partial combustion of a fuel gas.
7. The method according to claim 6, wherein during said boosting step (d) and said cleaning step (e) said total air flow comprises a flow rate of X cubic feet per hour, and during said boosting step (d) the maximum enriching gas flow comprises a flow rate of Y cubic feet per hour, and during said boosting step (d) and said cleaning step (e) the fuel gas flow rate used to form the carrier gas comprises a flow rate of Z cubic feet per hour, such that the flow rates of the Y plus Z equals approximately the total air flow rate X.
8. The method according to claim 6, wherein during said steps (d), (e), (f) and (g) said total air flow rate and said fuel gas flow rate is substantially constant.
9. The method according to claim 1, wherein during said purging step (b) the process chamber is purged using a carrier gas.
10. The method according to claim 9, wherein said carrier gas comprises an endothermic carrier gas formed by the partial reaction of the fuel gas and a portion of the air in an externally heated catalyst filled chamber.
11. The method according to claim 10, wherein said externally heated catalyst filled chamber comprises an endothermic gas generator.
12. The method according to claim 1, wherein during said purging step (b) the process chamber is purged using an inert gas.
13. The method according to claim 12, wherein said inert gas comprises nitrogen.
14. The method according to claim 6, wherein said furnace includes a generator device comprising a combustion tube and a radiant heater tube for combusting a source of hydrocarbon fuel and generating a source of heat, a generator tube surrounding at least a portion of said radiant heater tube, said generator tube having an inlet for receiving the air and the fuel gas, and an outlet tube for exhausting partially combusted fuel gas to the process chamber.
15. The method according to claim 6, wherein said enriching gas and said fuel gas both comprise methane (CH4).
16. The method according to claim 14, wherein said generator tube is at least partially isolated from said process chamber.
17. The method according to claim 14, wherein said generator device is mounted such that a substantial portion of the generator tube is not located in the process chamber of the furnace.
18. The method according to claim 14, wherein said enriching gas is inlet for receiving fuel gas and the air.
19. The method according to claim 1, wherein during said boosting step (d) the process chamber is maintained at a temperature of from about 1,500\xb0 F. to about 1,850\xb0 F.
20. The method according to claim 6, wherein said carrier gas is produced externally of the process chamber.
21. The method according to claim 1, wherein said gas of said step (b) is at least one gas selected from the group consisting of a carrier gas, CH4, CO, C2H6, C2H4, C6H6, C4H10, C3H8 and mixtures thereof.
22. The method according to claim 1, wherein said enriching gas is at least one gas selected from the group consisting of CH4, CO, C2H6, C2H4, C6H6, C4H10, C3H8 and mixtures thereof.
23. The method according to claim 1, wherein said furnace comprises a furnace selected from the group consisting of a rotary furnace, a rotary retort furnace, a continuous furnace and a batch furnace.
24. The method according to claim 1, wherein during said boosting step (d) a carbon potential of at least 1.4% is attained in the process chamber.
25. The method according to claim 1, wherein during said boosting steps (d) and (f) and said cleaning steps (e) and (g) a substantially constant total air flow rate is maintained.
26. A method of heat treating ferrous metal parts comprising the steps of:
(a) providing a furnace for heating the metal parts and a process chamber;
(b) purging an air atmosphere from the process chamber and heating said process chamber to a temperature of at least 1100\xb0 F.;
(c) feeding a fuel gas to the process chamber and a source of air;
(d) boosting the process chamber by feeding an enriching gas to the process chamber to create a carbon potential of at least 0.5%;
(e) cleaning the process chamber by decreasing the flow of enriching gas to the process chamber to create a carbon potential of less than about 0.25%;
(f) repeating the boosting step (d) after performing said cleaning step (e);
(g) repeating the cleaning step(e) after performing said repeated boosting step (f);
(h) wherein during said cleaning and boosting steps said fuel gas and said air is fed to the process chamber at a substantially constant flow rate.
27. The method according to claim 26, wherein said fuel gas is partially consumed to form an endothermic carrier gas.