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High-Density Electrochemical Storage Device

IP.com Disclosure Number: IPCOM000117167D
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 123K

Publishing Venue

IBM

Related People

Delamarche, E: AUTHOR [+3]

Abstract

For any electroactive species (e.g., molecule), the oxidation state is reached when a threshold potential V* is applied. By increasing or decreasing the potential across this threshold, it is possible to oxidize or reduce the electroactive species (Fig. 1). The oxidation (o) or reduction (r) leads to a current produced by the transfer of m charges according to eqno ( 1 ) M% sup n %%% adjust(u 3) adjust(d 3 l 12) M% sup n+m + m e sup - where M is the electroactive molecule, and n denotes the oxidation state. These two reversible states for the system represent a binary information which is suitable for data storage.

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High-Density Electrochemical Storage Device

      For any electroactive species (e.g., molecule), the oxidation
state is reached when a threshold potential V* is applied.  By
increasing or decreasing the potential across this threshold, it is
possible to oxidize or reduce the electroactive species (Fig. 1).
The oxidation (o) or reduction (r) leads to a current produced by the
transfer of m charges according to
                                 eqno ( 1 )
                            M% sup n %%%
                   adjust(u 3) <rarrow overmark o>
                adjust(d 3 l 12) <larrow undermark r>
                       M% sup n+m + m e sup -
  where M is the electroactive molecule, and n denotes the oxidation
state.  These two reversible states for the system represent a binary
information which is suitable for data storage.

      The storage medium is an electroactive single layer of
molecules assembled on a flat substrate, forming a regular lattice
(Fig. 2).  Each point of this lattice, containing several
electroactive molecules, is an independent entity equivalent to one
bit of information.  A lot of molecules, in particular those
containing a transition metal (e.g., Mn, Fe, Ru), show several
successive redox states at higher potential values, corresponding to
the exchange of more than 1 electron (i.e., m = 2, 3, 4 etc.).  This
offers the opportunity to store more than one bit of information in
each storage unit.

      A conductive nanoprobe is used to apply locally the potential
necessary to change the oxidation state of each individual molecule
and thereby performing a read/write operation on the storage medium.
Nanoprobes are known from techniques derived from scanning tunneling
microscopy (STM) and, atomic force microscopy (AFM).  A particular
advantage of AFM and ac-AFM (1, 2) is the higher displacement speed
and the larger distance to the sample.  In comparison with the
potential switching rate of the microelectrode and the electron
transfer rate, the displacement speed of the probe is the limiting
factor of the storage device.  A larger tip-sample distance favors a
better distribution of the applied potential over all molecules
forming a storage unit representing a single bit.  A large
sample-probe distance also enhances the lifetime of the applied
cantilever or tip.  If the STM technique is used, the major part of
the tip must be insulated, leaving the apex as microelectrode (3).
In the case of ac AFM or AFM techniques, it is necessary to coat the
cantilever with some  metallic layer or to couple it with a
microelectrode.

      For the redox reaction, the active monolayer is immersed in an
electrolyte which provides the ionic current to the scanning
microelectrode.  The electrolyte can be a liquid film or a droplet or
meniscus following the scanning microelectrode.  The use of a third
e...