Taeho Jung

Moisture induced surface polarization in a poly(4-vinyl phenol) dielectric in an organic thin-film transistor

Surface polarization in a poly(4-vinyl phenol) (PVP) dielectric induced by water molecules has been qualitatively investigated in pentacene thin-film transistors. The magnitudes of drain currents from devices with PVP dielectrics subject to specific surface treatments increased with humidity, whereas the opposite responses were observed from device with SiO2 dielectrics. The increase in drain current is attributed to the accumulation of extra charge carriers induced by the surface polarization in addition to that by the vertical electric field. Such polarization effects should be carefully considered in characterizing organic and polymer thin-film transistors, particularly those with polymeric gate insulators.

High-mobility bottom-contact n -channel organic transistors and their use in complementary ring oscillators

The electrical characteristics of bottom-contact organic field-effect transistors fabricated with the air-stable n-type semiconductor N,N′-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2) are described. The mobility, threshold voltage, subthreshold swing, and Ion∕Ioff ratio(VDS=40V, VG=0∼40V) are 0.14cm2∕Vs, 1.6V, 2.0V/decade, and 1.2×103, respectively. The effect of electrode/dielectric surface treatment on these devices is also examined, with a combination of 1-octadecanethiol and hexamethyldisilazane. Organic complementary five-stage ring oscillators were fabricated using pentacene and PDI-8CN2, and operated at an oscillation frequency of 34kHz and a propagation delay per stage of 3μs.

Pentacene field-effect transistors with sub-10-nm channel lengths

The field effect in pentacene thin-film transistors was studied using bottom-contact devices with channel lengths below 10nm. To suppress spreading current in these devices, which have a small channel width-to-length (W-L) ratio, we employed a pair of guarding electrodes as close as 20nm to the two sides of the channel. The responses of these nanometer scale transistors exhibit good gate modulation. Mobilities of 0.046cm2∕Vs and on/off ratios of 97 were achieved in sub-10-nm transistors. We find that the device response is strongly influenced by the nature of the metal-semiconductor contact.

Nanoscale n-channel and ambipolar organic field-effect transistors

N-channel and ambipolar organic field-effect transistors (OFETs) with a few tens of nanometer channel length were fabricated and characterized. N,N′-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2) was employed as the active semiconductor and yielded a linear regime electron mobility of 2.3×10−3cm2∕Vs at 5×105V∕cm in an OFET with channel length of 15nm. An ambipolar heterostructure transistor consisting of thin layers of PDI-8CN2 and pentacene was fabricated with channel length of about 23nm. Field-effect hole and electron mobilities of 9.2×10−3 and 4.0×10−3cm2∕Vs, respectively, are obtained at 5×105V∕cm. These results represent the shortest channel length n-channel and ambipolar organic transistors that have been fabricated.

Nanoscale chemical sensors based on conjugated polymer transistors

Nanoscale thin film transistors with conjugated polymers as the active layer were fabricated to investigate their chemical sensing properties. Guarding electrodes as close as 20 nm to the two sides of the channel were employed to eliminate undesirable spreading currents and ensure that the sensor active area is truly nanoscale. The response of drain current exhibited opposite directions in nanoscale sensors compared to large scale devices, for the same analyte-semiconductor combination. The transition in response behavior was observed occurring in a certain interval of channel length. The chemical sensing mechanisms in both microscale and nanoscale transistors are briefly discussed.

Organic transistors: improved performance and fast response

This paper reviews the transport phenomena in pentacene transistors and presents a model of how fast rectifier circuits work. Nanoscale organic and polymer transistor characteristics are also discussed.

Organic complementary circuits using solution deposited active semiconductors

Byungwook Yoo a, Debarshi Basu a, Taeho Jung a, Daniel Fine a, Brooks A. Jones b, Antonio Facchetti b Michael R. Wasielewski b, Tobin J. Marks b, Klaus Dimmler c, and Ananth Dodabalapur a a Department ofElectrical and Computer Engineering, Microelectronics Research Center, The University ofTexas at Austin, 10100 Burnet Rd, Bldg 160, Austin, TX 78758, email: bwyoo(dmail. utexas. edu, ph: 1-512-232-1846 b Department of Chemistry, the Materials Research Center, and the Centerfor Nanofabrication & Molecular SelfAssembly, Northwestern University, 2145 Sheridan Rd, Evanston, IL 60208-3113 cOrganicID, 422 East Vermio Ave, Colorado Springs, CO 80903