This paper proposes an effective method of fabricating top contact organic field effect transistors by using a pho-tolithographic process.The semiconductor layer is protected by a passivation layer.Through photolithographic and etching processes,parts of the passivation layer are etched off to form source/drain electrode patterns.Combined with conventional evaporation and lift-off techniques,organic field effect transistors with a top contact are fabricated suc-cessfully,whose properties are comparable to those prepared with the shadow mask method and one order of magnitude higher than the bottom contact devices fabricated by using a photolithographic process.
This paper reports that the organic field-effect transistors with hybrid contact geometry were fabricated,in which the top electrodes and the bottom electrodes were combined in parallel resistances within one transistor.With the facility of the novel structure,the difference of contact resistance between the top contact geometry and the bottom contact geometry was studied.The hybrid contact devices showed similar characteristics with the top contact configuration devices,which provide helpful evidence on the lower contact resistance of the top contact configuration device.The origin of the different contact resistance between the top contact device and the bottom contact device was discussed.
Low voltage operating organic devices and circuits have been realized using atomic layer deposition deposited aluminum oxide thin film as dielectric layer. The dielectric film has per unit area capacitance of 165 nF/cm2 and leakage current of 1 nA/cm2 at 1 MV/cm. The devices and circuits use the small-molecule hydrocarbon pentacene as the active semiconductor material. Transistors,inverters,and ring oscillators with operating voltage lower than 5 V were obtained. The mobility of organic field-effect transistors was extracted to be 0.16 cm2/Vs in saturation range,the threshold voltage is 0.3 V,and the on/off current ratio is larger than 105. The gain of inverters is estimated to be 12 at -5 V supply voltage,and the propagation delay is 0.25 ms per stage in 5-stage ring oscillators.
SHANG LiWei JI ZhuoYu CHEN YingPin WANG Hong LIU Xin HAN MaiXin LIU Ming
Among the many possible device configurations for organic memory devices,organic field-effect transistor (OFET) memory is an emerging technology with the potential to realize lightweight,low-cost,flexible charge storage media.In this feature article,the recent progress in the classes of OFET-based memory,including floating gate OFET memory,polymer electret OFET memory,ferroelectric OFET memory and several other kinds of OFET memories with unique configurations,are introduced.Finally,the prospects and problems of OFETs memory are discussed.
WANG HongPENG YingQuanJI ZhuoYuLIU MingSHANG LiWeiLIU XingHua
To isolate the active layer from air,double organic layer organic field-effect transistors have been fabricated,based on a two-step vacuum-deposition process.Pentacene acted as the active layer,and subsequently,CuPc was deposited above the pentacene and served as a protecting layer for the active layer.Due to the same electrical characteristics but different morphologies,the bilayer structure was effective in decreasing the contamination ofimpurities and gas,and then improved the device stability in air.
