K.N. Narayanan Unni

A nonvolatile memory element based on an organic field-effect transistor

Organic field-effect transistors were fabricated with pentacene as the active material and a ferroelectric copolymer poly(vinylidene fluoride–trifluoroethylene) as the gate insulator. As-prepared devices showed normal p-type transistor operation. The ON- and OFF-states could be written to the device by applying appropriate voltages to the gate with respect to short-circuited source and drain electrodes. The devices exhibited excellent memory retention properties.

Improved performance of pentacene field-effect transistors using a polyimide gate dielectric layer

Organic field-effect transistors using pentacene have been fabricated employing polyimide gate dielectric layers. The root-mean square surface roughness of polyimide films is 9 A. Devices with thin polyimide films as gate achieved a mobility of 0.16 cm2 V−1 s−1, threshold voltage −6.4 V, on–off ratio ~ 104 and subthreshold slope 7.5 dec−1 with the gate voltage span between 0 and −30 V. The upper limit of interface trap density has been estimated to be 3.9 × 1012 cm−2 eV−1. The mobility is found to be gate bias dependent.

The memory effect of a pentacene field-effect transistor with a polarizable gate dielectric

The nonvolatile transistor memory element is an interesting topic in organic electronics. In this case a memory cell consists of only one device where the stored information is written as a gate insulator polarization by a gate voltage pulse and read by the channel conductance control with channel voltage pulse without destruction of the stored information. Therefore such transistor could be the base of non-volatile non-destructively readable computer memory of extremely high density. Also devices with polarizable gate dielectrics can function more effectively in certain circuits. The effective threshold voltage Vt can be brought very close to zero, for applications where the available gate voltage is limited. Resonant and adaptive circuits can be tuned insitu by polarizing the gates. Poly(vinylidene fluoride), PVDF and its copolymer with trifluoroethylene P(VDF-TrFE) are among the best known and most widely used ferroelectric polymers. In this manuscript, we report new results of an organic FET, fabricated with pentacene as the active material and P(VDF-TrFE) as the gate insulator. Application of a writing voltage of -50 V for short duration results in significant change in the threshold voltage and remarkable increase in the drain current. The memory effect is retained over a period of 20 hours.