Memory device application of a conjugated polymer: role of space charges

Conjugated polymers have been used in data-storage devices. A ‘‘state’’
has been written by applying a voltage pulse. The state of the device has
been ‘‘read’’ from the current under a small probe voltage ~0.2 V!. The
polymer retained the state for more than 1 h which can be refreshed or
erased at will. The stored space charges under a voltage pulse have been
found to control the charge injection and hence the device current. Their
slow relaxation process has resulted in the use of conjugated polymers in
memory device applications. Hysteresis-type behavior has been observed in
the current–voltage characteristics. The density of stored charges at the
polymer layer near the metal/polymer interface has been found to depend
on the voltage amplitude.
The relaxation of the stored charges has been studied by applying two
voltage pulses. By varying the delay between the two pulses, during which
the space charges relax or redistribute, the time constant for charge
relaxation has been calculated. The time constant was found to be
independent of the density of the space charges or of the pace at which
they were stored.