Chang-Hung Li

Room-temperature-operated sensitive hybrid gas sensor based on amorphous indium gallium zinc oxide thin-film transistors

An organic sensing layer is capped onto an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) to form a hybrid sensor. The organic layer, served as a second gate, forms a p-n junction with the a-IGZO film. Oxidizing or reducing vapor molecules act like electron acceptors or electron donors to change the potential of the organic layer and the current of a-IGZO TFT. A sensitive and reversible response to 100 ppb ammonia and 100 ppb acetone is obtained at room temperature. This letter opens a route to develop low-cost large-area bio/chemical sensor arrays based on the emerging a-IGZO TFT technology.

Deep ultraviolet laser direct write for patterning sol-gel InGaZnO semiconducting micro/nanowires and improving field-effect mobility

Deep-UV (DUV) laser was used to directly write indium-gallium-zinc-oxide (IGZO) precursor solution and form micro and nanoscale patterns. The directional DUV laser beam avoids the substrate heating and suppresses the diffraction effect. A IGZO precursor solution was also developed to fulfill the requirements for direct photopatterning and for achieving semi-conducting properties with thermal annealing at moderate temperature. The DUV-induced crosslinking of the starting material allows direct write of semi-conducting channels in thin-film transistors but also it improves the field-effect mobility and surface roughness. Material analysis has been carried out by XPS, FTIR, spectroscopic ellipsometry and AFM and the effect of DUV on the final material structure is discussed. The DUV irradiation step results in photolysis and a partial condensation of the inorganic network that freezes the sol-gel layer in a homogeneous distribution, lowering possibilities of thermally induced reorganization at the atomic scale. Laser irradiation allows high-resolution photopatterning and high-enough field-effect mobility, which enables the easy fabrication of oxide nanowires for applications in solar cell, display, flexible electronics, and biomedical sensors.

Sensitive gas sensor embedded in a vertical polymer space-charge-limited transistor

We report a very sensitive gas sensor embedded in a vertical polymer space-charge-limited transistor. The oxidizing and reducing gases act as electron dedoping and electron doping agents on the transistor active layer to change the potential distribution in the vertical channel and hence to change the output current density. With a 30-ppb detection limit to ammonia, the sensor can be used for non-invasive breath monitor in point-of-care applications. The integration of a sensitive gas sensor and a low-operation-voltage transistor in one single device also facilitates the development of low-cost and low-power-consumption sensor array.

Multilayer rapid-drying blade coating for organic solar cells by low boiling point solvents

A bulk heterojunction organic solar cell with poly(3-hexylthiophene) (P3HT) as the donor and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM) as the acceptor is deposited using blade coating on a hot plate at 80 °C with hot air of 70 °C applied from above. In contrast to the 30 min of conventional dichlorobenzene solvent annealing, the rapid-drying blade coating forms a dry film in 1 s. The fabrication throughput is substantially enhanced. The blade-coated film has a smoother surface roughness of 3.5 nm compared with 10.5 nm for solvent annealing; however, the desired phase separation in the 50 nm scale forms despite the rapid drying. A single layer solar cell exhibits power conversion efficiency of 4.1% with blade coating in chlorobenzene, which is the same as solvent annealing device. A multilayer device with carrier blocking layers fabricated entirely of the less toxic toluene also exhibits efficiency of 4.1%.

Achieving saturation in vertical organic transistors for organic light-emitting diode driving by nanorod channel geometric control

When conventional field-effect transistors with short channel length suffer from non-saturated output characteristics, this work proposed a vertical channel transistor to operate like a solid-state vacuum tube and exhibit good saturated curves. We utilized deep ultra-violet interference lithography to produce ordered grid-like metal to control the potential profile in vertical channel. We compared experimental and simulated characteristics to investigate the keys to achieve saturation. Finally, with an optimized design, a vertical organic transistor is used to drive a solution-processed white-light organic light-emitting diode to perform a luminescence control (0–260 cd/m2) with a 3.3-V base potential swing.

High-Current-Drive Dual-Gate a-IGZO TFT With Nanometer Dotlike Doping

In this letter, we use a dual-gate (DG) structure together with nanometer dotlike doping (NDD) in active channel to produce a-IGZO thin-film transistors with very high current drive. With DG operation, the output current increases from 0.14 mA of the conventional device to 0.76 mA of the NDD device. The enhanced lateral field and improved carrier accumulation in DG operation may explain the significantly enlarged drive current. Particularly, simulated electron distribution reveals that high carrier concentration is induced under NDD regions in DG operation. The device without NDD, however, does not exhibit improved drive current in DG operation.

Investigating the gas sensing mechanism of the vertical polymer space-charge-limited transistor

A high-sensitivity gas sensor based on SCLT is demonstrated in this paper. The oxidizing and reducing gases which act as electron dedoping (e-dedoping) and doping (edoping) agents on the transistor active layer is investigated. Dedoping and doping the active layer varies the potential distribution in the vertical channel, and changes the output current density. The lowest detectable concentration of ammonia was 30 ppb at a base-to-emitter voltage as -0.2 V and collector-to-emitter voltage as -1.2 V.