Nanoelectromechanical bistable cantilever device

• US 7,612,424 B1
• Filed: 03/21/2006
• Issued: 11/03/2009
• Est. Priority Date: 07/22/2005
• Status: Active Grant

• Current Assignee: Northwestern University
• Original Assignee: Northwestern University
• Inventors: Ke, Changhong, Espinosa, Horacio D.
• Primary Examiner(s): Nguyen; Dao H
• Application Number:
  US11/385,970
• Time in Patent Office: 1,323 Days
• Field of Search: 257/312, 257/415, 257/419, 257/595, 361/278, 361/290, 361/298.5, 200/181
• US Class Current: 257/415
• CPC Class Codes: B81B 2201/038 Microengines and actuators not provided for in B81B2201/031 - B81B2201/037
• CPC Class Codes: B81B 2201/07 Data storage devices, static or dynamic memories
• CPC Class Codes: B81B 2201/12 STM or AFM microtips
• CPC Class Codes: B81B 2203/0118 Cantilevers
• CPC Class Codes: B81B 3/0054 For holding or placing an element in a given position
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: G11B 9/1445 switching at least one head in operating function; Controlling the relative spacing to keep the head operative, e.g. for allowing a tunnel current flow
• CPC Class Codes: G11C 13/025 using fullerenes, e.g. C60, or nanotubes, e.g. carbon or silicon nanotubes
• CPC Class Codes: G11C 23/00 Digital stores characterised by movement of mechanical parts to effect storage, e.g. using balls; Storage elements therefor
• CPC Class Codes: H01H 1/0094 Switches making use of nanoelectromechanical systems [NEMS]
• CPC Class Codes: H01H 59/0009 making use of micromechanics

Abstract

Nano-electromechanical device having an electrically conductive nano-cantilever wherein the nano-cantilever has a free end that is movable relative to an electrically conductive substrate such as an electrode of a circuit. The circuit includes a power source connected to the electrode and to the nano-cantilever for providing a pull-in or pull-out voltage therebetween to effect bending movement of the nano-cantilever relative to the electrode. Feedback control is provided for varying the voltage between the electrode and the nano-cantilever in response to the position of the cantilever relative to the electrode. The device provides two stable positions of the nano-cantilever and a hysteresis loop in the current-voltage space between the pull-in voltage and the pull-out voltage. A first stable position of the nano-cantilever is provided at sub-nanometer gap between the free end of the nano-cantilever and the electrode with a pull-in voltage applied and with a stable tunneling electrical current present in the circuit. A second stable position of the nano-cantilever is provided with a pull-out voltage between the cantilever and the electrode with little or no tunneling electrical current present in the circuit. The nano-electromechanical device can be used in a scanning probe microscope, ultrasonic wave detection sensor, NEMS switch, random access memory element, gap sensor, logic device, and a bio-sensor when the nano-cantilever is functionalized with biomolecules that interact with species present in the ambient environment be them in air or aqueous solutions. In the latest case, the NEMS needs to be integrated with a microfluidic system.

Claims

1. Electromechanical device having an electrically conductive or semiconducting nano-cantilever wherein the nano-cantilever has a free end that is movable relative to an electrically conductive substrate of a circuit, a power source connected in the circuit for providing a voltage between the substrate and the nano-cantilever to effect bending movement of the nano-cantilever relative to the substrate, and a feedback control for varying the voltage between the substrate and the nano-cantilever in response to the position of the nano-cantilever relative to the substrate wherein two stable positions of the nano-cantilever and a hystersis loop in the current voltage space between a pull-in voltage and a pull-out voltage are provided.

2. The device of claim 1 having a first stable position of the nano-cantilever at a sub-nanometer gap between the free end of the nano-cantilever and the substrate with a pull-in voltage applied and with a stable tunneling electrical current present in the circuit.

3. The device of claim 2 wherein at the first stable position, the elastic force generated in the nano-cantilever from bending movement is equal to the electrostatic force at a stable tunneling current and the inter-atomic van der Waals force.

4. The device of claim 2 wherein the carbon nanotube has an exterior diameter in the range of about 1 nm to about 100 nm.

5. The device of claim 2 wherein the metallic nanowire has a diameter of about 3 nm to about 100 nm.

6. The device of claim 1 having a second stable position of the nano-cantilever with a pull-out voltage between the cantilever and the substrate with little or no tunneling electrical current present in the circuit.

7. The device of claim 6 wherein at the second stable position, the elastic force generated in the nano-cantilever from bending movement is equal to the electrostatic force with little or no tunneling current in the circuit and mostly negligible inter-atomic van der Waals force.

8. The device of claim 1 wherein the nano-cantilever comprises a carbon nanotube or a metallic nanowire.

9. The device of claim 1 wherein the feedback control comprises a resistor connected in the circuit between the power source and the substrate or the nano-cantilever wherein the resistor has a resistance value greater than that of the nano-cantilever and wherein the resistor functions to reduce the voltage in response to the free end of the cantilever moving toward the substrate and to increase the voltage in response to the free end of the cantilever moving away from the substrate.

10. A two dimensional array of devices of claim 1 for multiplexing wherein the nano-cantilevers of a plurality of the devices are connected to a common electrode.

11. The array of claim 10 wherein a common electrically conductive substrate is spaced beneath a plurality of the nano-cantilevers of the devices.

12. The array of claim 10 wherein the devices are arranged in a column and row configuration.

13. Combination of the electromechanical device of claim 1 and a solid state switch in the circuit connected to one or more power sources in a manner that different voltage values can be applied between the nano-cantilever and the electrically conductive substrate to provide first and second stable positions of the nano-cantilever relative to the electrically conductive substrate.

14. The combination of claim 13 wherein at the first stable position, the elastic force generated in the nano-cantilever from bending movement is equal to the electrostatic force at a stable tunneling current and the inter-atomic van der Waals force.

15. The combination of claim 13 wherein the nano-cantilever has a first stable position at the sub-nanometer gap between the end of the nano-cantilever and the substrate with a pull-in voltage applied and with a stable tunneling electrical current present in the circuit.

16. The combination of claim 13 wherein the nano-cantilever has a second stable position with a pull-out voltage applied between the nano-cantilever and the substrate with little or no tunneling electrical current present in the circuit.

17. The combination of claim 16 wherein at the second stable position, the elastic force generated in the nano-cantilever from bending movement is equal to the electrostatic force with little or no tunneling current in the circuit and mostly negligible inter-atomic van der Waals force.

18. The combination of claim 13 wherein the feedback control comprises a resistor connected in the circuit wherein the resistor has a resistance value greater than that of the nano-cantilever, wherein the resistor functions to reduce the voltage in response to the free end of the nano-cantilever moving toward the substrate and to increase the voltage in response to the free end of the nano-cantilever moving away from the substrate, and wherein an output voltage is read from the resistor.

23. A scanning probe microscope, ultrasonic wave detection sensor, NEMS switch, random access memory element, gap sensor, logic device or bio-sensor includes the device of any one of claims 1-22.

19. Electromechanical device, comprising an electrically conductive or semiconducting nano-cantilever comprising a carbon nanotube or metallic nanowire having a free end movable relative to an electrically conductive electrode, a power source connected to the electrode and the nano-cantilever for applying a pull-in voltage between the electrode and the nano-cantilever to effect relative bending movement of the nano-cantilever toward the electrode, and feedback control resistor between the power source and the electrode for reducing the pull-in voltage between the electrode and the nano-cantilever in response to the free end of the nano-cantilever moving closer to the electrode and for increasing the pull-in voltage between the electrode and the nano-cantilever in response to the free end of the nano-cantilever moving away from the electrode wherein two stable positions of the nano-cantilever and a hystersis loop in the current voltage space between the pull-in voltage and the pull-out voltage are provided.

20. The device of claim 19 having a first stable position of the nano-cantilever occurring at a sub-nanometer gap between the free end of the nano-cantilever and the electrode with a pull-in voltage applied and with a stable tunneling electrical current present in the circuit.

21. The device of claim 19 wherein a second stable position of the nano-cantilever is established when the voltage is less than the pull-in voltage.

22. The device of claim 19 wherein the nano-cantilever is functionalized with biomolecules.

24. In a method of moving a free end of an electrically conductive or semiconducting nano-cantilever relative to a conductive substrate of a circuit, the steps of providing a voltage between the substrate and the nano-cantilever to effect bending movement of the nano-cantilever relative to the substrate and varying the voltage between the substrate and the nano-cantilever by feedback control in response to the position of the nano-cantilever relative to the substrate wherein two stable positions of the nano-cantilever and a hystersis loop in the current voltage space between a pull-in voltage and a pull-out voltage are provided.

25. The method of claim 24 having a first stable position of the nano-cantilever at a sub-nanometer gap between the free end of the nano-cantilever and the substrate with a pull-in voltage applied and with a stable tunneling electrical current present in the circuit where, at the first stable position, the elastic force generated in the nano-cantilever from bending movement is equal to the electrostatic force at a stable tunneling current and the inter-atomic van der Waals force.

26. The method of claim 24 having a second stable position of the nano-cantilever with a pull-out voltage between the cantilever and the substrate where, at the second stable position, the elastic force generated in the nano-cantilever from bending movement is equal to the electrostatic force with little or no tunneling current in the circuit and mostly negligible inter-atomic van der Waals force.

27. The method of claim 24 including moving the nano-cantilever that comprises a carbon nanotube or a metallic nanowire.

28. The method of claim 24 wherein the feedback control is provided by connecting a resistor in the circuit, said resistor functioning to reduce the voltage in response to the free end of the nano-cantilever moving toward the substrate and to increase the voltage in response to the free end of the nano-cantilever moving away from the substrate.