Solution-deposited zinc oxide and zinc oxide/pentacene bilayer transistors: High mobility n-channel, ambipolar and nonvolatile devices

A solution processed n-channel zinc oxide (ZnO) field effect transistor (FET) was fabricated by simple dip coating and subsequent heat treatment of a zinc acetate film. The field effect mobility of electrons depends on ZnO grain size, controlled by changing the number of coatings and zinc acetate solution concentration. The highest electron mobility achieved by this method is 7.2 cm(2) V-1 s(-1) with On/Off ratio of 70. This electron mobility is higher than for the most recently reported solution processed ZnO transistor. We also fabricated bilayer transistors where the first layer is ZnO, and the second layer is pentacene, a p-channel organic which is deposited by thermal evaporation. By changing the ZnO grain size (or thickness) this type of bilayer transistor shows p-channel, ambipolar and n-channel behavior. For the ambipolar transistor, well balanced electron and hole mobilities are 7.6 x 10(-3) and 6.3 x 10(-3) cm(2) V-1 s(-1) respectively. When the ZnO layer is very thin, the transistor shows p-channel behavior with very high reversible hysteresis. The nonvolatile tuning function of this transistor was investigated.