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Ultrafast Nonvolatile Ferroelectric Information Storage Device

IP.com Disclosure Number: IPCOM000114176D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 139K

Publishing Venue

IBM

Related People

Coufal, HJ: AUTHOR [+2]

Abstract

Disclosed are devices for ultrafast nonvolatile information storage with ferroelectric polymers as the active storage elements. Preferred embodiments utilize Poly(vinylidene fluoride) (PVDF) or PVDF-Trifluoroethylene (PVDF-TrFE) copolymers as the ferroelectric material since these polymers can be obtained as very thin films and can have response times of better than 350 picoseconds.

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Ultrafast Nonvolatile Ferroelectric Information Storage Device

      Disclosed are devices for ultrafast nonvolatile information
storage with ferroelectric polymers as the active storage elements.
Preferred embodiments utilize Poly(vinylidene fluoride) (PVDF) or
PVDF-Trifluoroethylene (PVDF-TrFE) copolymers as the ferroelectric
material since these polymers can be obtained as very thin films and
can have response times of better than 350 picoseconds.

      The ferroelectric polymer can be used in the gate of a standard
dynamic or static RAM device (1,2), for storage of real or
polarization charges in the gate capacitor of a RAM device (3), or as
a shadow RAM in a conventional RAM device (4).  The most basic
information storage device, however, (Fig. 1) consists of a thin
pyroelectric film with a set of parallel conducting electrodes
deposited on one side and an orthogonal set of conducting electrodes
deposited on the other side (5).  The individual storage cells are
formed at the junctures of the opposing electrodes.  A stack of these
two-dimensional arrays can be manufactured by alternately depositing
conducting strips and pyroelectric material to build up a three
dimensional array of ferroelectric capacitors which could be easily
stacked vertically on an integrated circuit with the addressing logic
and sense amplifiers.

      Very thin films of monolayer or bilayer thickness (0.5 to 1.0
nm) can be achieved using Langmuir-Blodgett techniques.  With films
of 25 nanometer thickness, the polarization can be switched in PVDF
with a 2.5V power supply making it compatible with standard
semiconductor memory voltage levels.  Furthermore, the storage
densities that can be obtained by patterning of devices with
nanometer dimensions are orders of magnitude higher than with
existing technologies.  By using the PVDF itself as the photoresist
additional steps in the manufacturing process can be eliminated.
These advantages allow the fabrication of devices with memory
densities many orders of magnitude greater than with present day
technologies.

      To attain high density memories and to be able to read and
write individual bits at high data rates requires that these thin
films also be able to support very narrow charge and/or polarization
depth profiles.  Fig. 2 shows the photothermal response of a thin
PVDF film excited by a 20 picosecond pulse from an Excimer-Dye laser
system (6,7).  This pyroelectric response indicates that the charge
distribution in this electret is only 20 nanometers in depth, an
electret this thick could be switched with a standard 2.5 volt
semiconductor power supply.  Speed of switching is also important and
Fig. 3 shows the pyroelectric response of a thin PVDF
electret-preamplifier combination with a time response of better than
350 picoseconds.  This ultrafast response can only result if the
charge or polarization distribution is uniform to within 7 nanometers
of the electret surface and...