Interdigital deflection sensor for microcantilevers

• US 5,908,981 A
• Filed: 09/05/1996
• Issued: 06/01/1999
• Est. Priority Date: 09/05/1996
• Status: Expired due to Term

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Quate, Calvin F., Minne, Stephen C., Manalis, Scott R., Atalar, Abdullah
• Primary Examiner(s): NOLAND, THOMAS
• Application Number:
  US08/708,446
• Time in Patent Office: 999 Days
• Field of Search: 356/354, 356/356, 250/306, 250/307, 73/105
• US Class Current: 73/105
• CPC Class Codes: G01Q 20/02 by optical means
• CPC Class Codes: Y10S 977/87 Optical lever arm for reflecting light
• CPC Class Codes: Y10S 977/873 Tip holder

Abstract

A deflection sensor for a microcantilever includes two sets of interdigitated fingers, one (reference) set being attached to the substrate from which the microcantilever extends and the other (movable) set being attached to the tip of the microcantilever. Together the interdigitated fingers form an optical phase grating. The deflection of the microcantilever is measured by directing a light beam against the optical phase grating and detecting the intensity of the reflected light in the first (or other) component of the resulting diffraction pattern. As the microcantilever deflects, the reference and movable fingers move relative to one another creating large variations in the intensity of the zeroth and first order components of the diffraction pattern. To eliminate "1/f" noise the deflection of the microcantilever can be measured using an AC signal.

Claims

1. A combination comprising:

a cantilever extending from a support and having a free end comprising a tip, said cantilever comprising a phase grating, said phase grating comprising;

a first element having a first surface, the first surface configured to reflect a first portion of a beam of electromagnetic radiation; and

a second element adjacent the first element and having a second surface configured to reflect a second portion of the beam, said first and second elements being separated by a gap wherein relative motion between said first and second elements occurs as a force against said tip varies;

a source of electromagnetic radiation configured to direct the beam onto the phase grating; and

a photodetector configured to receive a part of the beam reflected by the phase grating.

2. The combination of claim 1, wherein the second element is coupled to said support and the first element is coupled to said tip.

3. The combination of claim 1, further comprising an actuator connected to the first element.

4. The combination of claim 3, wherein the actuator is connected to the second element.

5. The combination of claim 1, wherein the first surface is offset from the second surface by a bias distance.

6. The combination of claim 5, wherein the beam has a wavelength λ

, and wherein the bias distance is a multiple of one-eighth the wavelength λ

.

7. The combination of claim 5, further comprising an actuator connected to the first element, the actuator configured to induce the bias distance.

8. The combination of claim 1, wherein the first and second surfaces are specular.

9. The combination of claim 1, wherein the electromagnetic radiation is light having a wavelength of less than 0.5 microns.

10. The combination of claim 1, wherein

the second element is positioned adjacent the first element such that the reflected first and second portions interfere with one another to create a diffraction pattern.

11. The combination of claim 10, wherein the diffraction pattern includes a zero-order component and a plurality of higher-order components, and wherein the portion of the beam reflected by the phase grating is at least one of the components.

12. The combination of claim 1 wherein said combination comprises an atomic force microscope.

13. A combination comprising:

a cantilever having a phase grating and comprising a support, said phase grating comprising;

a first element extending from the support and having a first surface, the first surface configured to reflect a first portion of a beam of electromagnetic radiation; and

a second element adjacent the first element and having a second surface configured to reflect a second portion of the beam, wherein the first element includes a first plurality of fingers and the second element includes a second plurality of fingers interdigitated with the first plurality of fingers;

a source of electromagnetic radiation configured to direct the beam onto the phase grating; and

a photodetector configured to receive a part of the beam reflected by the phase grating.

14. The combination of claim 13, wherein the cantilever has a length and a width, and wherein the first and second pluralities of fingers are perpendicular to the length of the cantilever.

15. The combination of claim 13, wherein the cantilever has a length and a width, and wherein the first and second pluralities of fingers are parallel to the length of the cantilever.

16. The combination of claim 13 wherein said combination comprises an atomic force microscope.

17. The combination of claim 13 wherein said combination further comprises:

a one dimensional array of cantilevers, the one dimensional array of cantilevers comprising said cantilever and a second cantilever, the second cantilever having a second phase grating and comprising a second support, the second phase grating comprising;

a third element extending from the second support and having a third surface, the third surface configured to reflect a third portion of the beam of electromagnetic radiation; and

a fourth element adjacent the third element and having a fourth surface, the fourth surface configured to reflect a fourth portion of the beam, wherein the third element includes a third plurality of fingers and the fourth element includes a fourth plurality of fingers interdigitated with the third plurality of fingers; and

a second photodetector configured to receive a second part of the beam reflected by the second phase grating.

18. The combination of claim 17, where the combination comprises a two dimensional array of cantilevers.

19. The combination of claim 17, wherein the first cantilever has a length and a width, and wherein the first plurality of fingers and the second plurality of fingers are perpendicular to the length of the first cantilever.

20. The combination of claim 19, wherein the second cantilever has a length and a width, and wherein the third plurality of fingers and the fourth plurality of fingers are perpendicular to the length of the second cantilever.

21. The combination of claim 17, wherein the first cantilever has a length and a width, and wherein the first plurality of fingers and the second plurality of fingers are parallel to the length of the first cantilever.

22. The combination of claim 21, wherein the second cantilever has a length and a width, and wherein the third plurality of fingers and the fourth plurality of fingers are perpendicular to the length of the second cantilever.

23. A combination comprising:

a cantilever having a phase grating and comprising a support, the phase grating comprising;

a first element extending from the support and having a first surface, the first surface configured to reflect a first portion of a beam of electromagnetic radiation; and

a second element adjacent the first element and having a second surface configured to reflect a second portion of the beam wherein the second element is a reference element and the first element is a movable element that includes a tip of the cantilever;

a source of electromagnetic radiation configured to direct a beam onto the phase grating; and

a photodetector configured to receive a part of the beam reflected by the phase grating, wherein the phase grating has a first grating period, the cantilever further comprising;

a second phase grating having a second grating period.

24. The combination of claim 23, wherein the first grating period is different from the second grating period.

25. The combination of claim 24, wherein the first and second phase gratings are for measuring torsional displacement of the movable element.

26. The combination of claim 23 wherein said combination comprises an atomic force microscope.