Memory device applications 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.