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Organic Molecular Rectifiers

IP.com Disclosure Number: IPCOM000112505D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 111K

Publishing Venue

IBM

Related People

Aviram, A: AUTHOR [+2]

Abstract

The present method of fabrication of large scale integrated circuits involves the deposition of layers of materials by the repeated use of masks to define the positions of the various materials. This becomes increasingly difficult as the dimensions of the circuits become smaller. Thus it is desirable to reduce the number of times in which masks must be applied and aligned. We describe an implementation of this goal for the case of electrical rectifiers, by depositing molecules that can produce this desirable electrical function and requires few masking operations.

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Organic Molecular Rectifiers

      The present method of fabrication of large scale integrated
circuits involves the deposition of layers of materials by the
repeated use of masks to define the positions of the various
materials.  This becomes increasingly difficult as the dimensions of
the circuits become smaller.  Thus it is desirable to reduce the
number of times in which masks must be applied and aligned.  We
describe an implementation of this goal for the case of electrical
rectifiers, by depositing molecules that can produce this desirable
electrical function and requires few masking operations.

      Referring to Fig. 1, electrodes on a substrate are shown.  To
the electrodes, molecules are attached by a chemical reaction that is
specific to the molecule and the electrode material, and not with the
substrate material.  We shall give examples of such binding reactions
later.  The molecules are chosen to have electronic energy levels
close to the Fermi level of the electrode.  More specification of the
molecules will be given below.  To the exposed end of the molecules a
second electrode is attached.

      The device shown in Fig. 1 will produce electrical
rectification if it is structurally asymmetrical.  This can be
achieved either by making the molecules asymmetrical, or by employing
different metals for the electrode material, or both.  An important
feature that we describe here is the relation between the molecule
and the electrode material.  The molecules should be chosen so that
their electronic energy levels have an energy difference to the Fermi
level of the electrode material that is approximately equal to the
voltage at which the rectifier is to exhibit its high-conductivity
state.  Thus the rectifier is designed with consideration of the
electrode material and the molecular energy levels.

      As an example, but not exclusive, of an appropriate pair of
molecule and electrode we show, in Fig. 2, Cu 4,4',4'',4''' tetra
aza-29H, 31H-phthalocyanine, which we shall abbreviate to "CuTAP",
attached to graphite.  The highest occupied energy levels of
phthalocyanine are known to lie about 5.5 eV below the vacuum level
and the work function of graphite is about 4.6 eV.  The difference in
these energies, about 1 eV, sets the scale of applied voltage at
which the highly conductive state may be achieved.  The actual value
of applied voltage will differ from this estimate because of
interaction of the molecules with the electrodes, which changes their
properties compared to their values in isolation.  These changes,
however, are often relatively small.  In the case given above, we
have observed the onset of rectification, using a scanning tunneling
microscope, at an applied voltage of about 0.6 V.  The criterion of
differences in energy levels thus can be a useful guide in t...