Scanning magnectic microscope having improved magnetic sensor

• US 20040207396A1
• Filed: 04/28/2004
• Published: 10/21/2004
• Est. Priority Date: 08/16/2002
• Status: Active Grant

• Current Assignee: Brown University
• Original Assignee: Brown University
• Inventors: Xiao, Gang
• Granted Patent: US 7,145,330 B2
• Time in Patent Office: Days
• US Class Current: 324/244
• CPC Class Codes: G01Q 10/04 Fine scanning or positioning
• CPC Class Codes: G01Q 30/04 Display or data processing devices
• CPC Class Codes: G01Q 60/54 Probes, their manufacture, or their related instrumentation, e.g. holders
• CPC Class Codes: G01R 33/0385 in relation with magnetic force measurements magnetic force microscopes G01Q60/50

Abstract

A scanning magnetic microscope SMM (20) includes a sensor (10) for sensing a magnetic field generated by a specimen (78), the sensor including one of a MTJ, a GMR, or an EHE sensor; translation apparatus (22A-C, 52) for translating the sensor relative to a surface of sad specimen; and a data processor (50), having an input coupled to an output of said sensor, for constructing an image of said magnetic field. The sensor preferably includes one to three sensing units each defining a sensing axis for sensing a component of a magnetic field from a specimen, the sensing units disposed such that the sensing axes are orthogonal to one another. Pluralities of such sensors can be disposed in two or three dimensional arrays. The SMM can be used for examining the current flow in ICs, electromigration, magnetic data storage media, biomagnetic systems and magnetic ink used to print currency.

Claims

11. A scanning magnetic microscope, comprising:

a plurality of N magnetic sensors for sensing a magnetic field generated by a specimen;

said N magnetic sensors disposed transversely with respect to a measurement axis, whereby said magnetic field may be sensed at N locations simultaneously, N being an integer greater than one; and

translation means for translating at least one of said magnetic sensor and said specimen along a measurement axis relative to a surface of said specimen.

12. The scanning magnetic microscope of claim 11 wherein each of the N magnetic sensors comprise at least two magnetic sensing units each defining a sensing axis, said sensing axes of each magnetic sensor being disposed orthogonally to one another.

13. The scanning magnetic microscope of claim 12 wherein each of the N magnetic sensors comprise three magnetic sensing units each defining a sensing axis, said sensing axes of each magnetic sensor being disposed orthogonally to one another.

14. A microscope according to claim 11, in which said set of N magnetic sensors are disposed at about equal distances from one another along a transverse axis that is perpendicular to said measurement axis, and wherein the translation means further comprises means for stepping one of said specimen and at least one of said sensors transversely with respect to said measurement axis.

15. A microscope according to claim 11, further comprising a height control apparatus for actively maintaining at least one of said magnetic sensors at a measurement offset distance from a surface of said specimen during measurement.

16. A microscope according to claim 11, further comprising a system for maintaining at least one of said magnetic sensors in contact with a surface of said specimen during measurement.

17. A microscope according to claim 16, further comprising a wear-resistant coating on a contact surface of said sensors.

18. A microscope according to claim 17, in which said wear-resistant coating is selected from the group comprising amorphous carbon and synthetic diamond.

19. A microscope according to claim 16, further comprising a coating of lubricant between said sensor and said sample.

20. A microscope according to claim 11 further comprising a data processor, having an input coupled to an output of said magnetic sensor, for constructing an image of said magnetic field.

21. A microscope according to claim 11 further comprising a lubricant reservoir that is translated with said magnetic sensor.

22. A scanning magnetic microscope, comprising:

at least one magnetic sensor for sensing a magnetic field generated by a specimen;

translation means for translating at least one of said magnetic sensor and said specimen along a measurement axis relative to one another; and

active sensor height control means for maintaining said at least one magnetic sensor at a predetermined height above the surface of said specimen during operation of said translation means.

23. A scanning magnetic microscope according to claim 22, in which said translation means translates said at least one sensor along said measurement axis with respect to a fixed specimen.

24. A scanning magnetic microscope according to claim 22, in which said translation means translates said specimen along said measurement axis with respect to said at least one sensor.

25. A scanning magnetic microscope according to claim 22, in which said translation means translates both said specimen and said at least one sensor along said measurement axis.

26. A scanning magnetic microscope according to claim 22 further comprising a data processor, having an input coupled to an output of said magnetic sensor, for constructing a three dimensional image of said magnetic field.

27. A microscope according to claim 22 further comprising a lubricant reservoir that is translated with said magnetic sensor.

28. A scanning magnetic microscope, comprising:

a magnetic sensor for sensing a magnetic field generated by a specimen, said sensor being protected from electrostatic discharge by at least two low-forward voltage diodes connected in parallel with said sensor with opposite polarity; and

translation means for translating one of said sensor and said specimen along a measurement axis relative to a surface of said specimen.

29. A microscope according to claim 28 further comprising a data processor, having an input coupled to an output of said sensor, for constructing an image of said magnetic field.

30. A microscope according to claim 28 further comprising a lubricant reservoir that is translated with said magnetic sensor.

31. A magnetic sensor comprising at least two of:

a first magnetic sensing unit defining a first sensing axis,

a second magnetic sensing unit defining a second sensing axis, and

a third magnetic sensing unit defining a third sensing axis,

each of said at least two sensing units disposed such their respective sensing axes are orthogonal to one another.

32. The magnetic sensor of claim 31 wherein each of said magnetic sensing units defines a multilayer structure.

33. A magnetic sensor according to claim 31 further comprising translation means for translating the sensor and a specimen relative to one another along a measurement axis that is substantially parallel to one of the sensing axes.

34. A row of N magnetic sensors each according to claim 31 adjacent to one another along the first sensing axis, wherein N is an integer greater than one.

35. A two-dimensional array of rows of N magnetic sensors, each row according to claim 34, said rows adjacent to one another along a row-axis that is perpendicular to the first sensing axis.

36. A three-dimensional array of two-dimensional arrays of sensors, each two-dimensional array according to claim 35, each of the two-dimensional arrays disposed adjacent to one another along an axis that is perpendicular to both the row-axis and the first sensing axis.

37. A row of N magnetic sensors according to claim 34 further comprising translation means for translating the sensor and a specimen relative to one another.

38. The row of N magnetic sensors as in claim 37 wherein said translation means further comprises means for stepping one magnetic sensor relative to another magnetic sensor.

39. The magnetic sensor of claim 31 wherein said magnetic sensor comprises one of a MTJ, a GMR, and an EHE.

40. At magnetic detector apparatus comprising:

a first magnetic sensor comprising at least one magnetic sensing unit defining a first sensing axis; and

a second magnetic sensor comprising at least one magnetic sensing unit defining a second sensing axis;

said first and second sensors disposed adjacent to one another and oriented such that the first and second sensing axes are one of parallel and perpendicular to one another.

41. The magnetic detector apparatus of claim 40 wherein said first and second sensing axes are substantially parallel to one another, and said first and second sensors are disposed along a line that is substantially perpendicular to said first and second sensing axes.

42. A two-dimensional array of N magnetic detector apparatuses each according to claim 41, wherein the line defined by a first magnetic detector apparatus is substantially parallel to a line defined by a second magnetic detector apparatus, wherein N is an integer greater than one.

43. The magnetic detector apparatus of claim 41 further comprising

translation means for translating at least one of the detector apparatus and a specimen relative to one another;

and

a data processor having an input coupled to an output of said magnetic sensor, for constructing an image of a magnetic field sensed by the first and second magnetic sensors.

44. The magnetic detector apparatus of claim 43 wherein the translation means is particularly adapted to translate at least one of the detector apparatus and a document bearing magnetic ink relative to one another.

45. The magnetic detector apparatus of claim 43 wherein the translation means is particularly adapted to translate at least one of the detector apparatus and an integrated circuit chip relative to one another.

46. The magnetic detector apparatus of claim 45 wherein the translation means comprises means to apply a current to an integrated circuit specimen.

47. The magnetic detector apparatus of claim 45 wherein the translation means is particularly adapted to translate at least one of the detector apparatus and an exposed substrate surface of an integrated circuit chip relative to one another.

48. A method of measuring a magnetic field comprising:

providing a scanning magnetic microscope comprising at least one magnetic sensor, said sensor comprising at least two magnetic sensing units each defining a sensing axis, said sensing axes being disposed orthogonally to one another;

applying a sense current to the magnetic sensor;

translating the at least one sensor relative to a surface of a specimen along a measurement axis.

49. The method of claim 48 wherein the scanning magnetic microscope comprises at least two magnetic sensors disposed along a line that is transverse to the measurement axis, and wherein translating comprises translating the at least two sensors simultaneously.

50. The method of claim 49 wherein translating the at least two sensors comprises translating said at least two sensors such that movement of one of said sensors in a height direction is independent of movement of at least one other of said sensors in the height direction, said height direction being perpendicular to said measurement axis.

51. A method of measuring a magnetic field comprising:

providing a scanning magnetic microscope comprising at least one magnetic sensing unit defining a sensing axis;

disposing a specimen such that an exposed surface of a substrate of said specimen is adjacent to said magnetic sensing unit;

applying a sense current to the magnetic sensing unit;

translating the magnetic sensing unit and said specimen relative to one another; and

measuring a magnetic field from the specimen using said sensing unit.

1. A scanning magnetic microscope, comprising:

a magnetic sensor for sensing a magnetic field generated by a specimen;

said magnetic sensor comprising at least two magnetic sensing units each defining a sensing axis, said sensing axes being disposed orthogonally to one another; and

translation means for translating at least one of said magnetic sensor and said specimen relative to one another along a measurement axis that is not parallel to the sensing axis.

2. A microscope according to claim 1, further comprising a set of N magnetic sensors disposed transversely with respect to said measurement axis, wherein N is an integer greater than one.

3. A microscope according to claim 2, in which said set of N magnetic sensors are disposed at about equal distances from one another along a transverse axis that is perpendicular to said measurement axis.

4. A microscope according to claim 1, further comprising a height control apparatus for actively maintaining said magnetic sensor at a measurement offset distance from a surface of said specimen during measurement.

5. A microscope according to claim 1, further comprising a system for maintaining said magnetic sensor in contact with a surface of said specimen during measurement.

6. A microscope according to claim 5, further comprising a wear-resistant coating on a contact surface of said sensors.

7. A microscope according to claim 6, in which said wear-resistant coating is selected from the group comprising amorphous carbon film and synthetic diamond film.

8. A microscope according to claim 5, further comprising a coating of lubricant between said sensor and said sample.

9. A microscope according to claim 1 further comprising a data processor, having an input coupled to an output of said magnetic sensor, for constructing an image of said magnetic field.

10. A microscope according to claim 1 further comprising a lubricant reservoir that is translated with said magnetic sensor.

52. The method of claim 51 wherein disposing a specimen further comprises disposing said specimen such that a plane defined by said exposed surface lies perpendicular to said sensing axis.

53. The method of claim 51 wherein the substrate comprises silicon.

54. The method of claim 51 wherein said specimen is an integrated circuit chip.

52-1. The method of claim 51 wherein translating the magnetic sensing unit and said specimen relative to one another comprises translating while said magnetic sensing unit remains in contact with said exposed surface.