Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Of transducer assembly mechanism
Reexamination Certificate
1998-12-04
2001-06-12
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Of transducer assembly mechanism
C369S128000
Reexamination Certificate
active
06246652
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device using a sensor for a small rotation angle. More particularly, the invention relates to a device using a sensor capable of detecting a small rotation angle of an object that has a small area for reflecting light.
Since atomic force microscopy was first proposed by G. Binning inPhys. Rev. Letters Vol. 58, No. 9, pp. 930 (1986), a number of improvements have been made on the technology and new applications thereof have been undertaken. Illustratively, European Patent Laid-Open No. 290648 (Nov. 17, 1988) proposes a method for eliminating disadvantages involved in detecting the displacement of a cantilever by use of a tunneling current, the proposed method detecting the cantilever displacement in terms of capacitance or optical interference. In Appl. Phys. Lett. 53(12), Sep. 19, 1988, pp. 1045-1047, G. Meyer et al propose a laser beam deflection detection method under the title of “Novel optical approach to atomic force microscopy.” This method is intended to remove deficiencies stemming from detecting the cantilever displacement by optical interference.
To such advances in atomic force microscopy, the inventors of the present invention have also contributed some improvements that go beyond the traditional scope of atomic force microscope. Specifically, they have proposed, among others, such applications as “Surface observing apparatus” in U.S. Pat. No. 5,436,448, “Scanning probe microscope and method of control error correction” in U.S. Pat. No. 5,467,642, “Precision machining method, precision machining apparatus and data storage apparatus using the same” in U.S. Pat. No. 5,471,064, and “A device for recording information in a size of several tens of nanometers or less by applying the principle of an atomic force microscope” in U.S. patent application Ser. No. 09/142,663.
In the devices proposed above, the displacement of a free end of the cantilever is detected as a small rotation angle through the use of the laser beam deflection detection method proposed by G. Meyer et al. Today, this method is one of the most commonly utilized techniques for detecting a small rotation angle of the cantilever.
The laser beam deflection detection method works primarily as follows: light from a light source is first reflected on a surface of a measuring object. When the measuring object (i.e., its reflecting surface) is rotated by an angle of &thgr;, reflected light is changed in orientation by an angle of 2 &thgr; in the same direction as that of the rotation of the measuring object according to the principle of reflection. If the angle &thgr; is sufficiently small, a beam of reflected light is displaced from its initial position by 2L &thgr; at a distance of L from the reflecting surface. If the distance L is sufficiently long, the displacement of the light beam may be made large enough to allow the rotation angle of the measuring object to be sensed by a detector for detecting light spot displacement.
SUMMARY OF THE INVENTION
In conventional devices incorporating or applying atomic force microscopy, their cantilevers typically measure a few hundred &mgr;m long and tens of &mgr;m wide each. Where the size of a measuring object is on such a small order, a sufficient quantity of reflected light is obtained by having light from a light source focused through a lens onto the measuring object placed at a focal point. Hence the need for limiting the incident light to a sufficiently small light beam. According to the laser beam deflection detection method, the focused laser beam spot typically has a diameter of tens of microns.
Where the head of a recording and reproducing apparatus is implemented in the form of a cantilever, as in the case of the above-cited U.S. Pat. No. 5,471,064 or U.S. patent application Ser. No. 09/142,663, there is a problem: the data read rate is limited by the resonance frequency of the cantilever. To increase the read rate requires enlarging the resonance frequency of the cantilever while keeping its spring constant sufficiently small. This makes it mandatory to reduce the overall size of the cantilever. A cantilever with a resonance frequency on the megahertz order may be fabricated effectively by reducing its total length to 10 microns or less, with some variations allowed depending on the thickness.
Cantilevers as short as 10 microns require that the spot diameter of the laser beam emitted thereto be reduced correspondingly; otherwise reflecting efficiency will suffer. Illustratively, for a cantilever with a total length of 10 microns, the laser beam emitted thereto must have a spot diameter of about 5 microns. In the future, cantilevers are expected to be further reduced in size, i. e., to 1 to 5 microns in overall length.
The operating range of the microscope (i.e., surface observing apparatus) based on atomic force microscopy is also restricted by the resonance frequency of a cantilever used therein, as is the case with recording and reproducing apparatuses. Improving the scanning speed of the cantilever shortens the time it takes the microscope to observe objects; this also requires the use of a cantilever having a high resonance frequency.
Some non-contact scanning type force microscopes function advantageously when utilizing a cantilever with a high resonance frequency. There is a case in which periodically timed potential signals occurring on the surface of a sample are detected directly in terms of deflection of a cantilever, the deflection being caused by electrostatic force acting between the sample surface and the cantilever. In that case, it is obvious that the higher the resonance frequency of the cantilever, the higher the frequency changes that may be detected.
REFERENCES:
patent: 5436448 (1995-07-01), Hosaka et al.
patent: 5467642 (1995-11-01), Hosake et al.
patent: 5471064 (1995-11-01), Koyanagi et al.
patent: 5537372 (1996-07-01), Albrecht et al.
patent: 290648 (1988-11-01), None
patent: 5-079834 (1993-03-01), None
patent: 5-87548 (1993-04-01), None
patent: WO97/35308 (1997-09-01), None
Physical Review Letters, vol. 56, No. 9, Mar. 3, 1986, “Atomic Force Microscope”, G. Binnig et al, pp. 930-933.
Applied Physical Letters, vol. 53, No. 12, Sep. 19, 1988, “Novel Optical Approach to Atomic Force Microscopy”, G. Meyer et al, pp. 1045-1047.
Etoh Kimitoshi
Hosaka Sumio
Kikukawa Atsushi
Koyanagi Hajime
Hitachi , Ltd.
Huber Paul W.
Mattingly Stanger & Malur, P.C.
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