Organic fi eld-effect transistors (OFETs) are attractive building blocks for low-cost electronic devices such as radio-frequency identifi cation (RFID) tags, sensors, electronic paper, and backplane circuits for active-matrix displays. [1][2][3][4][5][6] Low-voltage operation of OFETs is necessary for practical applications, hence the need to develop gate dielectrics with a high areal capacitance. [ 7 , 8 ] To this end, ultrathin dielectric layers have been demonstrated based on self-assembled-monolayer (SAM) chemistry. [ 7 , 9-11 ] In these cases, the formation of the dielectric layer relies on specifi c surface chemistries and therefore these approaches may not be suitable for the deposition of blanket layers on arbitrary substrates. For the same reason, the robustness and yield may be problematic due to the critical roles that surface cleanliness and roughness play on binding. On the other hand, inorganic. high-κ metal oxide dielectrics, which are attractive due to their high dielectric constant, have been fabricated by various methods such as metal anodization, [ 10 , 12 ] vacuumbased deposition, [13][14][15] and sol-gel chemistry. [ 16 ] An advantage of an oxide dielectric is the ability to functionalize the surface with a variety of SAMs that are often found to be benefi cial to charge transport in OFETs, or can be used to control the threshold voltage. Although inorganic/SAM hybrid dielectrics provide high capacitance and low leakage current, so far they have either required vacuum processing or relatively hightemperature anneals ( T > 200 ° C), making them incompatible with low-cost solution processing on fl exible substrates. Here, we describe the fabrication of low-voltage polymeric OFETs where the dielectric and the semiconductor are deposited from solution at room temperature. Zirconium oxide (ZrO x ) was deposited via a sol-gel process and fully cured by UV irradiation under ambient conditions, eliminating the need for a hightemperature anneal. In order to reduce the leakage current and make the dielectric compatible with organic semiconductors, the ZrO x fi lm was functionalized with a layer of octadecylphosphonic acid (ODPA). As a result, a high-performance ( μ = 0.2 cm 2 V − 1 s − 1 ), low-voltage ( | V GS | < 3 V), and high-on-off-ratio (10 5 -10 6 ) polymer OFET processed entirely from solution at room temperature is demonstrated using poly(2,5-bis(3-tetradecylthiophen-2yl(thieno[3,2-b]thiophene) (PBTTT-C 14 ) as the semiconductor. The fi eld-effect mobility was exclusively limited by the fact that the processing occurred entirely at room temperature and therefore the semiconductor was not annealed into its most-ideal microstructure. [17][18][19] A staggered, bottom-gate device structure was fabricated ( Figure 1 a ) using ZrO x as the gate dielectric, due to its high dielectric constant ( κ = 25) and wide bandgap ( E g = 5.8 eV). [ 20 ] Typical ZrO x -deposition methods include atomic-layer deposition, [ 21 ] sputtering, [ 22 ] and e-beam evaporation. [ 23 ] These methods, however, require...

We investigate solution based fabrication of high-k ZrO2 thin films for low-voltage-operated organic field effect transistors (OFETs). An alternative UV curing method for the densification of Zr-based gel films, which allows for low-temperature processing, is compared to the conventional thermal annealing method. Elemental and microstructural analysis shows that UV-curing induces the decomposition of organic-metal bonds and causes the densification of the metal oxide film, just as the conventional thermal annealing of gel films does, resulting in a high-k dielectric layer from Zr-based solutions. Furthermore, we found that the low temperature associated with UV-curing prevents the interface layer from intermixing with the substrate. Fabricated ZrO2 films (5–6 nm in thickness) treated with an octadecylphosphonic acid self-assembled monolayer exhibit low leakage current density (below 10–6 to 10–7 A/cm2) at 3 V and high dielectric breakdown strength (V > 4 V). Using this dielectric layer, solution processable polymer OFETs with PBTTT-C-14 as the organic semiconductor function well at low voltage (below −3 V.) The effect of self-assembled monolayers (SAMs) on the morphology and microstructure of the organic semiconductor deposited on the ZrO2 dielectrics are investigated. Finally, we demonstrate solution-processable, low-temperature fabrication of OFETs on a flexible substrate.

Strongly textured organic semiconductor micropatterns made of the small molecule dioctylbenzothienobenzothiophene (C(8)-BTBT) are fabricated by using a method based on capillary force lithography (CFL). This technique provides the C(8)-BTBT solution with nucleation sites for directional growth, and can be used as a scalable way to produce high quality crystalline arrays in desired regions of a substrate for OFET applications.

An organic/inorganic hybrid sensing device is proposed based on a dual-gate organic thin film transistor architecture using polythiophenes as semiconductors and AlOx as the top dielectric. When a polar molecule adsorbs on the top dielectric, the threshold voltage of the bottom gate transistor shifts leading to several orders of magnitude increase of the current at an appropriately chosen gate voltage. The devices are tested by exposing them to a saturated water atmosphere, which leads to a four orders of magnitude current increase within one minute. This sensor design maintains some advantages of organic semiconductors such as low-temperature processing and fabrication on flexible substrates. Finally, it can be operated at low voltages with the potential for extremely low-power operation.

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