Characterization of a cantilever with an integrated deflection sensor

doi:10.1016/0040-6090(94)05829-6

Thin Solid Films

Volume 264, Issue 2, 15 August 1995, Pages 159-164

https://doi.org/10.1016/0040-6090(94)05829-6 Get rights and content

Abstract

The atomic force microscope (AFM) is a sensitive and gentle instrument to examine the topography of surfaces. The sensitivity of the AFM depends on the choice of the detector, which is used to measure the vertical motion of the cantilever tip. In this paper, a cantilever with an integrated Wheatstone bridge as a deflection sensor will be introduced. This detection system is based on the piezoresistive effect. We call this sensor the Wheatstone bridge Piezo Lever. The principle set-up of this cantilever is described and a theoretical study as well as experimental investigations of sensor sensitivity are made. Experimental results are in accordance with theoretical predictions. If one uses the ‘lock-in’ technique, the resolution is limited mainly by the thermal vibration of the cantilever. However, this is no limitation to reach atomic resolution. The experimental study shows a voltage-dependable sensitivity resulting from heat generation of the voltage-supplied Wheatstone bridge. Measurements of various test structures are shown and special tip artefacts in the AFM are presented.

References (13)

I.W. Rangelow et al.
Plasma etching for micromechanical sensor applications
Microelectron. Eng.
(1994)
I.W. Rangelow
Sharp silicon tips for AFM and field emission
Microelectron. Eng.
(1994)
E. Meyer
Atomic force microscopy
Surf. Sci.
(1992)
G. Binnig et al.
Atomic force microscope
Phys. Rev. Lett.
(1986)
D. Rugar et al.
Improved fiber-optic interferometer for atomic force microscopy
Appl. Phys. Lett.
(1989)
A.J. den Boef
Scanning force microscopy using a simple low-noise interferometer
Appl. Phys. Lett.
(1989)

There are more references available in the full text version of this article.

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Characterization of a cantilever with an integrated deflection sensor

Abstract

Microelectron. Eng.

Microelectron. Eng.

Surf. Sci.

Atomic force microscope

Phys. Rev. Lett.

Improved fiber-optic interferometer for atomic force microscopy

Appl. Phys. Lett.

Scanning force microscopy using a simple low-noise interferometer

Appl. Phys. Lett.