Nonvolatile memory cell using microelectromechanical device

• US 6,054,745 A
• Filed: 01/04/1999
• Issued: 04/25/2000
• Est. Priority Date: 01/04/1999
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Nakos, James S., Williams, Richard Q.
• Primary Examiner(s): WOJCIECHOWICZ, EDWARD JOSEPH
• Application Number:
  US09/225,071
• Time in Patent Office: 477 Days
• Field of Search: 257/296, 257/347, 257/350, 257/415, 257/401, 438/52
• US Class Current: 257/415
• CPC Class Codes: H01H 59/0009 making use of micromechanics
• CPC Class Codes: H10B 41/40 characterised by the peripheral circuit region
• CPC Class Codes: H10B 43/30 characterised by the memory core region

Abstract

A nonvolatile memory cell comprises a conductive cantilever beam having a free end in a first charge state, a first FET having a conductive gate in a second charge state and a pull-in electrode adapted to bring the cantilever beam into electrical contact with the gate to effect a charge state change in the gate. A pull-in electrode input is connected to the electrode, a cantilever input is connected to the cantilever, a column select input is connected to the first FET and a row select input is connected to the first FET. The nonvolatile memory cell is selected by signals applied to the row select input and the column select input. The cell also includes a second FET connected between the cantilever beam and the cantilever input for controlling the passage of signals from the cantilever input to the cantilever beam and a third FET connected between the pull-in electrode and the pull-in electrode input for controlling the passage of signals from the pull-in electrode input to the electrode. The second FET and third FET have gates connected to the row select input. The row select input turns on the second FET and the third FET to allow the passage of signals from the pull-in electrode input to the pull-in electrode and from the cantilever input to the cantilever beam when the nonvolatile memory cell is selected.

Claims

1. A nonvolatile memory cell comprising:

an insulating layer fabricated on a substrate;

an electrically conductive cantilever on said insulating layer, said cantilever supported near a first end thereof and having a second end thereof free for movement;

an electrical conductor in contact with said cantilever near said first end; and

a contact region comprising an FET gate on said substrate near said second end of said cantilever, said contact region adapted to receive and store a charge therein when contacted by said second end of said cantilever.

2. The nonvolatile memory cell of claim 1 further including sensing means near said contact region for sensing a charge state of said contact region.

3. The nonvolatile memory cell of claim 2 wherein said sensing means includes a field-effect transistor and said contact region is adapted to act as a gate for the field-effect transistor.

4. The nonvolatile memory cell of claim 3 wherein said field-effect transistor comprises an n-channel field-effect transistor.

5. The nonvolatile memory cell of claim 1 further including an electrode on said insulating layer for causing said cantilever second end to contact said contact region.

6. The nonvolatile memory cell of claim 1 wherein said insulating layer comprises silicon dioxide.

7. The nonvolatile memory cell of claim 1 further including a protective layer over said an insulating layer covering said cantilever and said contact region.

8. The nonvolatile memory cell of claim 7 wherein said protective layer comprises silicon nitride.

9. The nonvolatile memory cell of claim 7 wherein said electrical conductor comprises a support for said cantilever.

10. A nonvolatile memory cell comprising:

a first conductive element comprising a cantilever beam in a first charge state;

a second conductive element comprising an FET gate in a second charge state;

means for bringing the first and second conductive elements into electrical contact to effect a charge state change in one of said first and second conductive elements; and

means for sensing the charge state in said one of said first and second conductive elements.

11. The nonvolatile memory cell of claim 10 wherein the means for bringing the first and second conductive elements into electrical contact to effect a charge state change comprises an electrode which applies an electrostatic attractive force to said first conductive element.

12. The nonvolatile memory cell of claim 10 wherein the means for sensing the charge state comprises a FET.

13. The nonvolatile memory cell of claim 10 wherein said memory cell is fabricated on a silicon dioxide insulating layer.

14. The nonvolatile memory cell of claim 10 further including a protective layer over said insulating layer covering said first and second conductive elements.

15. The nonvolatile memory cell of claim 14 wherein said protective layer comprises silicon nitride.

16. A nonvolatile memory cell comprising:

a conductive cantilever beam having a free end in a first charge state;

a sensing element comprising an FET having a conductive element in a second charge state, said sensing element adapted to sense the charge state in said conductive element; and

an electrode adapted to bring the cantilever beam into electrical contact with the conductive element to effect a charge state change in said conductive element.

17. The nonvolatile memory cell of claim 16 wherein the cantilever beam is electrically conductive over its entire length.

18. The nonvolatile memory cell of claim 16 wherein the electrode is adapted to apply an electrostatic attractive force to said cantilever beam.

19. The nonvolatile memory cell of claim 16 further including a protective layer over said insulating layer covering said cantilever beam, electrode and sensing element.

20. The nonvolatile memory cell of claim 19 wherein said protective layer comprises silicon nitride.

21. The nonvolatile memory cell of claim 16 wherein said cantilever beam comprises polysilicon.

22. The nonvolatile memory cell of claim 16 wherein said electrode comprises polysilicon.

23. A method of creating and sensing a charge state in a nonvolatile memory cell comprising the steps of:

a) providing a first conductive element comprising a cantilever beam in a first charge state;

b) providing a second conductive element comprising an FET gate in a second charge state;

c) electrically contacting the first and second conductive elements to effect a charge state change in one of said first and second conductive elements; and

d) sensing the charge state in said one of said first and second conductive elements.

24. A process for fabricating a nonvolatile memory cell comprising the steps of:

a) providing an insulating layer on a substrate;

b) creating on said substrate a sensing element, a support and an electrode;

c) depositing a removable layer over said sensing element, support and electrode;

d) depositing over said removable, nonconductive layer an electrically conductive layer in contact with said support; and

e) removing said removable layer such that said electrically conductive layer comprises a cantilever supported by said support and having a movable free end over said sensing element, said sensing element being adapted to receive and store a charge therein when said sensing element is at a predetermined potential and a bias is applied to said electrode to pull said cantilever toward the electrode to cause said free end of said cantilever to contact said sensing element.

25. The process of claim 24 wherein in step (b) said electrode is created between said sensing element and support.

26. The process of claim 24 wherein in step (b) said sensing element is created between said electrode and support.

27. The process of claim 24 wherein step (b) comprises creating on said substrate an FET, a support and an electrode.

28. A nonvolatile memory cell comprising:

a conductive cantilever beam having a free end in a first charge state;

a first sensing element comprising an FET having a conductive element in a second charge state;

a pull-in electrode adapted to bring the cantilever beam into electrical contact with the conductive element to effect a charge state change in said conductive element;

a pull-in electrode input (PI) connected to said electrode;

a cantilever input (CL) connected to said cantilever;

a column select input (CS) connected to said first sensing element;

a row select input (RS) connected to said first sensing element, the nonvolatile memory cell being selected by signals applied to the row select input and the column select input;

a second control element connected between said cantilever beam and the cantilever input for controlling the passage of signals from the cantilever input to the cantilever beam; and

a third control element connected between said pull-in electrode and the pull-in electrode input for controlling the passage of signals from the pull-in electrode input to the electrode.

29. The nonvolatile memory cell of claim 28 wherein the second and third control elements each comprise an FET.

30. The nonvolatile memory cell of claim 28 wherein the second FET and third FET have gates connected to the row select input, the row select input turning on the second FET and the third FET to allow the passage of signals from the pull-in electrode input to the electrode and from the cantilever input to the cantilever beam when the nonvolatile memory cell is selected.

31. The nonvolatile memory cell of claim 28 wherein a one is written to the cell when the cantilever electrode is at a one bias and the pull-down electrode is at a zero bias, and a zero is written to the cell when the cantilever electrode is at a zero bias and the pull-down electrode is at a high bias.