Switching device having a non-linear element

Abstract

Method for a memory including a first, second, third and fourth cells include applying a read, program, or erase voltage, the first and second cells coupled to a first top interconnect, the third and fourth cells coupled to a second top interconnect, the first and third cells coupled to a first bottom interconnect, the second and fourth cells are to a second bottom interconnect, each cell includes a switching material overlying a non-linear element (NLE), the resistive switching material is associated with a first conductive threshold voltage, the NLE is associated with a lower, second conductive threshold voltage, comprising applying the read voltage between the first top and the first bottom electrode to switch the NLE of the first cell to conductive, while the NLEs of the second, third, and the fourth cells remain non-conductive, and detecting a read current across the first cell in response to the read voltage.

We claim: 
     
       1. Method for operating a memory comprising:
 applying a read voltage to the memory, wherein the memory comprising a plurality of cells including at least a first cell, a second cell, a third cell, and a fourth cell, 
 wherein the first cell and the second cell are coupled to a first top electrode, 
 wherein the third cell and the fourth cell are coupled to a second top electrode, 
 wherein the first cell and the third cell are coupled to a first bottom electrode, 
 wherein the second cell and the fourth cell are coupled to a second bottom electrode, 
 wherein each cell of the plurality of cells comprises a resistive switching material stack comprising a resistive switching material overlying a non-linear switching element material, 
 wherein the resistive switching material is characterized by a first voltage associated with switching from a non-conductive state to a conductive state, 
 wherein the non-linear switching element material is characterized by a second voltage associated with switching from a non-conductive state to a conductive state, 
 wherein the second voltage is less than the first voltage, 
 wherein the read voltage is between the first voltage and the second voltage, and 
 wherein applying the read voltage to the memory comprises applying the read voltage to the first top electrode while grounding the first bottom electrode to thereby cause non-linear switching element material of the first cell to be in the conductive state, while maintaining non-linear switching element material of the second cell, the third cell, and the fourth cell to remain in the non-conductive state; and 
 detecting a read current across the first cell in response to the read voltage.; 
 wherein the resistive switching material is characterized by a third voltage associated with switching from the conductive state to the non-conductive state; 
 wherein the non-linear switching element material is characterized by a fourth voltage associated with switching from the non-conductive state to the conductive state; and 
 wherein the third voltage is less than the fourth voltage. 
 
     
     
       2. The method of  claim 1  wherein a resistance of the non-conductive state is related to a resistance of the conductive state in a range of ratios selected from a group consisting of: about 100 to about 500 times greater, about 500 to about 1000 times greater, about 1000 times to about 10,000 times greater. 
     
     
       3. The method of  claim 1  wherein while applying the read voltage to the first top electrode while grounding the first bottom electrode, a voltage across the second cell is maintained at less than the second voltage. 
     
     
       4. The method of  claim 1   wherein the resistive switching material is characterized by a third voltage associated with switching from the conductive state to the non-conductive state;   wherein the non-linear switching element material is characterized by a fourth voltage associated with switching from the non-conductive state to the conductive state; and   wherein the third voltage is less than the fourth voltage.   
     
     
       5. The method of claim  4  1 wherein while applying the read voltage to the first top electrode while grounding the first bottom electrode, a voltage across the fourth cell is maintained at greater than the fourth voltage to thereby maintain the non-linear switching element material of the third cell in the non-conductive state. 
     
     
       6. The method of claim  4  1 wherein while applying the read voltage to the first top electrode while grounding the first bottom electrode, the method further comprises applying a fifth voltage between ground and the read voltage to the second bottom electrode. 
     
     
       7. The method of  claim 6  wherein while applying the read voltage to the first top electrode while grounding the first bottom electrode, the method further comprises applying a sixth voltage between ground and the read voltage to the second top electrode. 
     
     
       8. The method of  claim 7  wherein a difference between the sixth voltage and the fifth voltage is greater than the fourth voltage. 
     
     
       9. The method of  claim 1  further comprising:
 applying a write voltage to the memory, wherein the write voltage exceeds the first voltage, wherein applying the write voltage to the memory comprises applying the write voltage to the first top electrode while grounding the first bottom electrode to thereby cause the resistive switching material of the first cell to be in the conductive state. 
 
     
     
       10. The method of  claim 9  wherein applying the write voltage to the first top electrode comprises applying the write voltage to the first top electrode while grounding the first bottom electrode to thereby cause the non-linear switching element material of the first cell to switch from the non-conductive state to the conductive state. 
     
     
       11. A memory operated according to the method described in  claim 1 . 
     
     
       12. A memory comprising:
 a plurality of cells including at least a first cell, a second cell, a third cell, and a fourth cell, wherein each cell of the plurality of cells comprises a resistive switching material stack comprising a resistive switching material overlying a non-linear switching element material, wherein the resistive switching material is characterized by a first voltage associated with switching from a non-conductive state to a conductive state, wherein the non-linear switching element material is characterized by a second voltage associated with switching from a non-conductive state to a conductive state, wherein a second voltage is less than the first voltage; 
 a plurality of top electrodes including a first top electrode and a second top electrode, wherein the first cell and the second cell are coupled to the first top electrode, and wherein the third cell and the fourth cell are coupled to the second top electrode; 
 a plurality of bottom electrodes including a first bottom electrode and a second bottom electrode, wherein the first cell and the third cell are coupled to the first bottom electrode, and wherein the second cell and the fourth cell are coupled to the second bottom electrode, wherein a read current path is associated with the first cell, wherein non-read current paths are associated with the second cell, the third cell, and the fourth cell, wherein the non-linear switching element material of the first cell is configured to reduce resistance of the read current path, and wherein the non-linear switching element material of the second cell, the third cell, and the fourth cell are configured to increase resistance of the non-read current; and 
 a voltage source coupled to the plurality of top electrodes and to the plurality of bottom electrodes, wherein the voltage source is configured to provide a plurality of voltages to the plurality of top electrodes and to the plurality of bottom electrodes.;  
 wherein the resistive switching material is characterized by a third voltage associated with switching from the conductive state to the non-conductive state; 
 wherein the non-linear switching element material is characterized by a fourth voltage associated with switching from the non-conductive state to the conductive state; and 
 wherein the third voltage is less than the fourth voltage. 
 
     
     
       13. The memory of  claim 12 
 wherein the non-linear switching element material of the first cell is configured to be in the conductive state dependent upon a read voltage that is greater than the second voltage but less than the first voltage, that is applied to the first top electrode while grounding the first bottom electrode; and 
 wherein the voltage source is configured to provide the read voltage. 
 
     
     
       14. The memory of  claim 12 
 wherein the non-linear switching element material of the second cell is configured to be in the non-conductive state dependent upon a read voltage that is greater than the second voltage but less than the first voltage, is applied to the first top electrode while grounding the first bottom electrode; and 
 wherein the voltage source is configured to provide the read voltage. 
 
     
     
       15. The memory of  claim 14  wherein when the read voltage is applied to the first top electrode while grounding the first bottom electrode, a voltage greater than ground is applied to the second bottom electrode such that a voltage across the second cell is less than the second voltage. 
     
     
       16. The memory of  claim 12  wherein the resistive switching material is selected from a group consisting of: an amorphous silicon material, a silicon sub-oxide, a silicon germanium sub-oxide. 
     
     
       17. The memory of  claim 12  wherein each of the plurality of bottom electrodes comprises a metal or a conductive silicon material selected from a group consisting of: a doped polysilicon, and a doped silicon germanium material. 
     
     
       18. The memory of  claim 12   wherein the resistive switching material is characterized by a third voltage associated with switching from the conductive state to the non-conductive state;   wherein the non-linear switching element material is characterized by a fourth voltage associated with switching from the non-conductive state to the conductive state; and   wherein the third voltage is less than the fourth voltage.   
     
     
       19. The memory of  claim 12 
 wherein the non-linear switching element material of the fourth cell is configured to be in the non-conductive state dependent upon a read voltage that is greater than the second voltage but less than the first voltage, that is applied to the first top electrode while grounding the first bottom electrode; and 
 wherein a voltage difference greater than the fourth voltage is applied to the fourth cell. 
 
     
     
       20. The memory of  claim 12 
 wherein the voltage source is configured to provide a read voltage to the first top electrode, wherein the voltage source is configured to provide a fifth voltage to the second bottom electrode and a sixth voltage to the second top electrode, wherein a voltage difference between the second top electrode and the second bottom electrode is greater than the fourth voltage. 
 
     
     
       21. The memory of claim 12 wherein a ratio between the resistance of the first cell compared to a resistance of the second cell is greater than 1:1000.  
     
     
       22. The memory cell of claim 12 wherein the non-linear switching material is selected from a group consisting of: a solid electrolyte material and a metal sub-oxide.  
     
     
       23. The memory cell of claim 12 wherein the non-linear switching material is bi-polar.  
     
     
       24. The memory cell of claim 12 wherein the non-linear switching material consists of multiple layers of materials.  
     
     
       25. A method for operating a memory comprising:
 applying a program voltage to the memory, wherein the memory comprising a plurality of cells including at least a first cell, a second cell, a third cell, and a fourth cell,
 wherein the first cell and the second cell are coupled to a first top electrode, 
 wherein the third cell and the fourth cell are coupled to a second top electrode, 
 wherein the first cell and the third cell are coupled to a first bottom electrode, 
 wherein the second cell and the fourth cell are coupled to a second bottom electrode, 
 wherein each cell of the plurality of cells comprises a resistive switching material stack comprising a resistive switching material having crystal defect regions and a non-linear switching element material, 
 wherein each cell is characterized by a first first-polarity voltage associated with the resistive switching material switching from a non-conductive state to a conductive state and a first second-polarity voltage associated with the resistive switching material switching from the conductive state to the non-conductive state, 
 wherein each cell is characterized by a second first-polarity voltage and a second second-polarity voltage associated with the non-linear switching element material switching from a second non-conductive state to a second conductive state, 
 wherein the second first-polarity voltage is less than the first first-polarity voltage, 
 wherein the first second-polarity voltage is less than the second second-polarity voltage, 
 wherein the program voltage is greater than or equal to the first first-polarity voltage, and 
 wherein applying the program voltage to the memory comprises applying the program voltage to the second top electrode; 
   grounding the second bottom electrode;   applying a first bias to the first top electrode and applying a second bias to the first bottom electrode;   causing a non-linear switching element material of the fourth cell to enter the conductive state and causing a resistive switching material of the fourth cell to enter the conductive state,   maintaining non-linear switching element materials of the first cell, the second cell, and the third cell in the non-conductive state in response to the applying the program voltage, grounding the second bottom electrode, the applying the first bias and the applying the second bias; and   removing the program voltage from the second top electrode, whereby the non-linear switching element material of the fourth cell returns to the non-conductive state, and wherein the resistive switching material of the fourth cell remains in the conductive state.   
     
     
       26. The method of claim 25
 wherein applying the program voltage to the second top electrode while grounding the second bottom electrode causes metal particles from the second top electrode to diffuse into crystal defect regions of the resistive switching material of the fourth cell; and   wherein after removing the program voltage from the second top electrode, the metal particles from the second top electrode remain trapped in the crystal defect regions of the resistive switching material of the fourth cell.   
     
     
       27. The method of claim 25 wherein while applying the program voltage to the second top electrode while grounding the second bottom electrode, a voltage across the second cell is maintained at less than the second first-polarity voltage. 
     
     
       28. The method of claim 25
 wherein the first and second first-polarity voltages are positive; and   wherein the first and second second-polarity voltage are negative.   
     
     
       29. The method of claim 28 wherein
 applying the first bias to the first top electrode comprises applying a first bias voltage less than the second first-polarity voltage to the first top electrode; and   wherein a voltage across the second cell in response to the applying the first bias voltage is less than the second first-polarity voltage.   
     
     
       30. The method of claim 29
 wherein applying the second bias to the first bottom electrode comprises applying a second bias voltage to the first bottom electrode;   wherein a voltage difference between the program voltage and the second bias voltage is less than the second first-polarity voltage; and   wherein a voltage across the third cell is less than the second first-polarity voltage.   
     
     
       31. The method of claim 30
 wherein a voltage across the first cell comprises a third second-polarity voltage; and   wherein the second second-polarity voltage is less than the third second-polarity voltage.   
     
     
       32. The method of claim 25 wherein a resistance ratio between the second conductive state to the second non-conductive state of the non-linear switching element material is within a range of about 1,000 to about 10,000. 
     
     
       33. The method of claim 25 further comprising:
 applying an erase voltage to the second top electrode;   further grounding the second bottom electrode;   further biasing the first top electrode;   further biasing the first bottom electrode to thereby cause the non-linear switching element material of the fourth cell to enter the conductive state and cause the resistive switching material of the fourth cell to enter the non-conductive state, while maintaining non-linear switching element materials of the first cell, the second cell, and the third cell in the non-conductive state; and   removing the erase voltage from the second top electrode, whereby the non-linear switching element material of the fourth cell returns to the non-conductive state, and wherein the resistive switching material of the fourth cell remains in the non-conductive state.   
     
     
       34. The method of claim 33, wherein:
 the further biasing the first top electrode comprises applying a first bias voltage less than the second first-polarity voltage to the first top electrode; and   a voltage across the second cell in response to the applying the first bias voltage is greater than the second second-polarity voltage and less than the second first-polarity voltage.