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Self-Controlled Micromechanical Scanning Tunneling Microscopy Sensor

IP.com Disclosure Number: IPCOM000100538D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 108K

Publishing Venue

IBM

Related People

Joachim, R: AUTHOR [+3]

Abstract

The proposed sensor automatically keeps a tunneling tip in the tunneling mode without any external control means. It merely requires a voltage connection, with the displacement of the tip being directly measured as function of a resistance. The sensor is also suitable for use as a measuring head for AFM (atomic force microscopy) and, generally, for measuring accelerations and temperatures, as well as for frequency-selective microphones and the like. A chief application is the building of large sensor arrays, such as those used in future memory technologies.

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Self-Controlled Micromechanical Scanning Tunneling Microscopy Sensor

       The proposed sensor automatically keeps a tunneling tip
in the tunneling mode without any external control means.  It merely
requires a voltage connection, with the displacement of the tip being
directly measured as function of a resistance.  The sensor is also
suitable for use as a measuring head for AFM (atomic force
microscopy) and, generally, for measuring accelerations and
temperatures, as well as for frequency-selective microphones and the
like.  A chief application is the building of large sensor arrays,
such as those used in future memory technologies.

      The sensor according to the invention uses a unilaterally
suspended conductive cantilever beam 1 with an integrated tunneling
tip 2 at its free end.  The opposite end is provided with a second
electrode 3 arranged at a short spacing from the first (Fig. 1).  The
beam along with the tip is preferably made of highly doped P+
silicon. Beams and tips of other materials are equally conceivable.
The counterelectrode may be readily attached by a DURAN* glass block
4 which (for the electrode spacing) is etched several mm deep in the
beam area and on which metal is evaporated.  Glass block and silicon
beam are fixed to each other by "Mallory" bonding.

      In contrast to known arrangements, counterelectrode 23 is used
for the self-control of the sensor.  For this purpose, an ohmic
resistance 25 is applied between the two electrodes 21, 23.  For the
highly doped P+ silicon beam and DURAN glass block 4, the resistance
may be generated by N- diffusion in the silicon surface (Fig. 2).
The tunneling voltage for the tip is not applied between probe 35 and
tip 32 but between probe 35 and counterelectrode 33 (Fig. 3). In such
an arrangement, a current-dependent voltage is generated on the
capacitor Si beam/counterelectrode 31, 33 and, thus, a
current-dependent electrostatic force on the Si beam.  This simple
arrangement is capable of keeping the tip at a stable self-controlled
spacing from the sample and allows a fine-approach of sample and tip.

      If the spacing is great, there is no current flow, and the Si
beam is in the undeflected state.  When the tip approaches the
sample, tunneling current starts to flow between sample and tip, and
the voltage drop between the counterelectrode and the beam electrode
produces an electrostatic force which retracts the Si beam.  As the
tip scans across the surface of the sample (during tunneling), the
force on the...