Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
1999-01-15
2001-05-29
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
Reexamination Certificate
active
06237399
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates cantilevers embedded with sensors on surface and integrated amplification circuitry responding to deflection of the cantilever useable in magnetic disk drives, magnetic force microscopes, magnetic resonance force microscopes, accelerometers, and other systems where a sensing of a mechanical deflection is involved.
2. Brief Description of the Prior Art
A number of cantilever sensors have been patented recently and commercial models of these sensors are now available in microminiature form. All of these cantilever sensors use passive detectors to sense the deflection of the free end of the cantilever. For example, the cantilever magnetometer developed by Naughton and Chaparala (AIP conference proceedings #273, p.407, 1992, “Capacitance Platform Magnetometer for thin film and small crystal superconductor studies and U.S. Pat. N
0
. 5,739,686, the disclosure of which is incorporated herein, by reference, as though recited in full) consists of two capacitor plates, one of which is roughly Five microns thick, and machined out of a silicon wafer. The two plates are glued together to a sample platform with the top plate free to bend as a cantilever. This cantilever design has been used in the sensitive measurements of the magnetic properties of materials in very high fields and over a very broad temperature range. In these measurements, a small piece of a magnetic sample is glued to the free end of the cantilever. Any external magnetic field acts on the magnetic sample and causes the cantilever to deflect and thus change the capacitance. However, this cantilever design and the capacitance method of detecting the deflection of the cantilever suffers from the drawback that it is not possible to determine whether it is the force or the torque acting on the magnetic sample that is causing the deflection of the cantilever tip.
Another example of an existing cantilever sensor is the Atomic Force Microscope (AFM) cantilever of Albrecht et. al. (U.S. Pat. N
0
. 5,483,822), the disclosure of which is incorporated herein, by reference, as though recited in full, and Applied Physics Letters, 62, p.634, 1993, “Atomic Resolution with an Atomic Force Microscope with Piezoresistive Detection”). Here, the deflection of the cantilever is obtained by measuring the change in the resistance of a layer of doped silicon on the cantilever which itself is micromachined from a block of single crystal silicon. This design also suffers from the inability to distinguish between a force and a torque signal and furthermore requires external amplification circuitry to magnify the effects of the change in the resistance of the doped silicon layer.
Additional background as to cantilevers with piezoresistive deflection sensors are found in U.S. Pat. Nos. 5,345,815 and 5,595,942, the disclosures of which are incorporated herein, by reference, as though recited in full.
SUMMARY OF THE INVENTION
It has now been discovered, that improved operation and capabilities of a cantilever measuring device can be achieved through the separate measurement of force and torque contributions to the deflection of the cantilever. Using recent technological improvements in the processing of semiconducting and ferromagnetic materials (Si & Fe), a new type of cantilever sensor with active detectors has been fabricated, which enables the separation of the measurement of the force and torque contributions to the deflection of the cantilever. The active detectors provide an order of magnitude more sensitive than the above described capacitance cantilever sensor. These new sensors utilize the strain dependence in the characteristics of Field Effect Transistors (FETs) placed on the surface of the cantilevers. The FETs have thus been integrated into the cantilever sensor and this has enabled the deflection induced signals to become amplified at the very point of origin. It has also enabled the use of the sensors in environments where low power dissipation is necessary. These sensors are useful in scanning probe magnetic force microscopy MFM), magnetic resonance force microscopy, force and/or torque magnetometry, in reading of all types of magnetic information, including those on disk drives and agglomerates of magnetic molecules and atoms. The use of the new integrated FET sensors, in addition to increasing the sensitivity, has simplified many of the measurement processes by eliminating the number of external components needed. Furthermore, the technology we have developed is modular in nature and several sensor models scaleable for smaller/larger signals have been built.
The present invention is a cantilever arm with a detector (passive or active) at the fixed (base) end of the cantilever and a second similar detector at the free end for use in separating the force and torque contributions to the deflection of the cantilever. Deflection of the free end of the cantilever by a force produces a strain in the base of the cantilever and the deflection of the free end by a torque produces no strain in the base but produces maximum strain at the free end. That difference in the changes of the surface strains produce changes in an appropriate physical property of the detectors in proportion to the cantilever arm's deflection. A voltage measuring apparatus is coupled to the two detectors to generate a signal corresponding to the cantilever arm's deflection.
The cantilever is formed on an appropriate substrate, such as a semiconductor like silicon or gallium arsenide, glass or quartz, or plastics, such as Kapton, polymide etc. A metal layer is deposited over the substrate's surface and patterned to form an electrical connection between the detectors and a voltage measuring circuit. The substrate below said cantilever arm is substantially removed so as to form a cantilevered structure. A magnetic tip is connected to the free end of the cantilever arm to facilitate the structure's use in mapping magnetic features on a surface of interest, such as a magnetic storage disk, and other similar devices.
REFERENCES:
patent: 5345815 (1994-09-01), Albrecht et al.
patent: 5483822 (1996-01-01), Albrecht et al.
patent: 5595942 (1997-01-01), Albrecht et al.
patent: 5723775 (1998-03-01), Watanabe et al.
patent: 5739686 (1998-04-01), Naughton et al.
“Capacitance Platform Magnetometer for Thin Film and Small Cyrstal Superconductor Studies”, M. Chaparala, O. H. Chung, and M. J. Naughton; American Institute of Physics, 1992. AIP Conference proceedings #273, p. 407.
“Atomic Resolution with an Atomic Force Microscope With Piezoresistive Detection”, M. Totonese, R.C. Barrett, and C.F. Quate; Applied Physics Letter, 62, 1993, p. 834.
Chaparala Murali V.
Jones Stephen H.
Shivaram Bellave S.
Larkin Daniel S.
Parker Sheldon H.
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