Measuring and testing – Surface and cutting edge testing – Roughness
Patent
1997-03-05
1998-07-14
Williams, Hezron E.
Measuring and testing
Surface and cutting edge testing
Roughness
7351421, 7351434, 7351436, 257415, 257417, G01H 1106, G01L 900
Patent
active
057807272
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an electromechanical transducer comprising a flexible element and an amplifier, wherein the transducer generates an electrical output in sympathy with the movement of the flexible element. The present invention also relates such a transducer employed as a cantilever in local probe microscopes, as sensors, or as oscillators.
BACKGROUND OF THE INVENTION
Electromechanical transducers are found In a broad range of technical fields. They are applied as parts of oscillating circuits, vibrators, sensors, microactuators, or local probe devices, such as the atomic force microscope (AFM). The following presents a variety of known devices taken from different technical fields. These devices emphasize the broad applicability of electromechanical transducers.
An integrated force sensor is described by R. H. Taylor and D. J. Webb in IBM's Technical Disclosure Bulletin, Vol. 25, No. 12, May 1983 on pages 6424/5. This sensor consists of a piezoelectric layer coupled to an elongated gate of an associated field-effect transistor. Pressure on the piezoelectric layer charges the gate electrode and thus modulates the channel conductance of the field-effect transistor.
Another known device is presented by H. C. Nathanson et al. in the IEEE Transactions on Electron Devices, Vol. ED-14, No. 3, March 1967, pp. 117-133, as "resonant gate transistor (RGT)". The RGT employs a beam-shaped electrode suspended over the drain and source of a MOS-type field effect transistor. The oscillations of the (charged) beam vary the channel of the transistor. With an appropriate feedback circuit, the RGT can be forced to oscillate with a constant frequency.
The use of an electromechanical transducer as a "dual direction switch" is demonstrated in U.S. Pat. No. 5,034,648. In this document a piezoelectric rod is attached to the gates of two field-effect transistors.
A piezoelectric actuator for micromechanical devices is further described in Sensors and Actuators, A21-A23 (1990), pp. 226-228 by F. R. Blom et al. The actuator is formed by a multilayered cantilever which consists of a SiO.sub.2 layer and a ZnO layer, both sandwiched between two metal layers. Any voltage applied to the metal layers gives rise to a deflection of the cantilever. Unimorphous or bimorphous piezoelectric cantilevers have also found entry in the field of atomic force microscopy (AFM). Atomic force microscopy is a specific variant of the so-called "local probe methods", all of which involve the use of a tip with an apex having a curvature in the range of 10 to 100 nm. The tip or probe is brought into proximity of a sample to be investigated by means of piezoelectric transducers. In AFM and related techniques, the tip is attached to a piezoelectric cantilever. Numerous proposals are known to exploit the piezoelectric material of the cantilever in order to control its deflection when approaching the surface to the sample. Examples of these proposals are found in the European patent application EP-A-0 492 915, showing several ways of producing cantilever probes with several piezoelectric layers and an appropriate number of electrodes to apply a voltage to the piezoelectric layers. U.S. Pat. No. 4,906,840 discloses a similarly layered cantilever structure with a piezoelectric bimorphous layer allowing the cantilever beam to be bent in opposite directions from its rest position. In some embodiments, the control circuitry necessary to load the piezoelectric bimorph is proposed to be integrated into the substrate from which the cantilever is etched.
Another attempt to produce small Integrated cantilevers for atomic force microscopy Is known from: M. Tortonese et al., Appl. Phys. Lett. 62 (8), 22. Feb. 1993, pp. 834-836. The described bending detection scheme uses a piezoresistive strain sensor. The deflection of the cantilever can be measured directly from the resistivity of a piezoresistive layer within the cantilever beam. This resistivity is determined by an external Wheatstone bridge. The base material silicon itself serves as the piezoresistiv
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Schellin et al., "A Monolithically-Integrated Transistor Microphone: Modelling and Theoretical Behavior", Sensors and Actuators A, vol. a37-a38, Jun.-Aug. 1993, pp. 66-673.
Gimzewski James K.
Schlittler Rato R.
Welland Mark E.
International Business Machines - Corporation
Larkin Daniel S.
Murray James E.
Williams Hezron E.
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