Zhenguo Lin

Coffee-Ring Defined Short Channels for Inkjet-Printed Metal Oxide Thin-Film Transistors

Short-channel electronic devices several micrometers in length are difficult to implement by direct inkjet printing due to the limitation of position accuracy of the common inkjet printer system and the spread of functional ink on substrates. In this report, metal oxide thin-film transistors (TFTs) with channel lengths of 3.5 ± 0.7 μm were successfully fabricated with a common inkjet printer without any photolithography steps. Hydrophobic CYTOP coffee stripes, made by inkjet-printing and plasma-treating processes, were utilized to define the channel area of TFTs with channel lengths as short as ∼3.5 μm by dewetting the inks of the source/drain (S/D) precursors. Furthermore, by introduction of an ultrathin layer of PVA to modify the S/D surfaces, the spreading of precursor ink of the InOx semiconductor layer was well-controlled. The inkjet-printed short-channel TFTs exhibited a maximum mobility of 4.9 cm(2) V(-1) s(-1) and an on/off ratio of larger than 10(9). This approach of fabricating short-channel TFTs by inkjet printing will promote the large-area fabrication of short-channel TFTs in a cost-effective manner.

InGaZnO thin-film transistors with back channel modification by organic self-assembled monolayers

InGaZnO (IGZO) thin-film transistors (TFTs) with back channel modified by different kinds of self-assembled monolayers (SAMs) were fabricated. The mobility and electrical stability of the IGZO-TFTs were greatly improved after SAM-modification, owing to the good interface coupling and less water adsorption-desorption effect on the IGZO surface. Meanwhile, the octadecyltriethoxysilane (OTES) treated IGZO-TFT exhibited a higher mobility of 26.6 cm2 V−1 s−1 and better electrical stability compared to the octadecanethiol (ODT) treated one, which was attributed to the formation of a more compact and steady SAM on the IGZO surface after OTES treatment.

High-mobility thin film transistors with neodymium-substituted indium oxide active layer

Thin-film transistors (TFTs) with neodymium-substituted indium oxide (InNdO) channel layer were demonstrated. The structural properties of the InNdO films as a function of annealing temperature have been analyzed using X-ray diffraction and transmission electron microscopy. The InNdO thin films showed polycrystalline nature when annealed at 450 °C with a lattice parameter (cubic cell) of 10.255 A, which is larger than the cubic In2O3 film (10.117 A). The high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy showed that no Nd2O3 clusters were found in the InNdO film, implying that Nd was incorporated into the In2O3 lattice. The InNdO TFTs annealed at 450 °C exhibited more excellent electrical properties with a high mobility of 20.4 cm2 V−1 s−1 and better electric bias stability compared to those annealed at 300 °C, which was attributed to the reduction of the scattering centers and/or charge traps due to the decrease of the |Nd3d5/254f4O2p−1⟩ electron configuration.

All Inkjet-Printed Metal-Oxide Thin-Film Transistor Array with Good Stability and Uniformity Using Surface-Energy Patterns

An array of inkjet-printed metal-oxide thin-film transistors (TFTs) is demonstrated for the first time with the assistance of surface-energy patterns prepared by printing pure solvent to etch the ultrathin hydrophobic layer. The surface-energy patterns not only restrained the spreading of inks but also provided a facile way to regulate the morphology of metal oxide films without optimizing ink formulation. The fully printed InGaO TFT devices in the array exhibited excellent electron transport characteristics with a maximum mobility of 11.7 cm2 V-1 s-1, negligible hysteresis, good uniformity, and good stability under bias stress. The new route lights a general way toward fully inkjet-printed metal-oxide TFT arrays.

Flexible organic field-effect transistors with high-reliability gate insulators prepared by a room-temperature, electrochemical-oxidation process

Flexible organic field-effect transistors (OFETs) with electrochemically oxidized gate insulators (AlOx:Nd) covered by a thin layer of hydroxyl-free poly(perfluorobutenylvinylether) known as Cytop were fabricated on a polyethylene naphthalate (PEN) substrate. The AlOx:Nd/Cytop bilayer insulator exhibited excellent insulating properties with low leakage current, high dielectric constant, high breakdown field, and low surface roughness. The pentacene film on AlOx:Nd without Cytop consisted of small grains, while the one on AlOx:Nd with Cytop exhibited a dendritic structure with a larger average grain size of ∼350 nm. The pentacene OFET with Cytop exhibited higher mobility (0.75 cm2 V−1 s−1) and better electrical stability under gate-bias-stress (in air condition) compared to that without Cytop. In addition, the flexible OFET was able to maintain a relatively stable performance under a certain degree of bending.

Studies on NdxIn1−xO3 semiconducting thin films prepared by rf magnetron sputtering

Neodymium-substituted indium oxide (NdxIn1−xO3, NIO) semiconducting thin films fabricated by rf sputtering were investigated. It was found that the incorporation of Nd atoms would lead to broadening the optical band gap, suppressing the grain growth, and reducing the free carrier concentration. The field-effect transistors with different NIO (5%, 15%, and 25% Nd concentration of the targets) channel layers exhibited similar electrical stability under positive gate-bias-stress, but the ones with 15% and 25% Nd concentration displayed much better stability under negative gate-bias-stress. Detailed studies showed that the content of |Nd3d5/254f4O2p−1> electron configuration decreased as the Nd concentration increased, resulting in the reduction of holes during negative-bias-stress. And the reduction of the |Nd3d5/254f4O2p−1> content as the Nd concentration increased was ascribed to less overlap between the metal and ligand orbitals arose from large lattice expansion.

Solution-processed indium-zinc-oxide thin-film transistors based on anodized aluminum oxide gate insulator modified with zirconium oxide

Solution-processed indium-zinc-oxide (IZO) thin-film transistors (TFTs) based on anodized aluminum oxide gate insulator modified with a zirconium oxide (ZrOx) interlayer were fabricated. By introduction of the ZrOx interlayer, the IZO-TFTs exhibited improved performance with a higher mobility of 7.8 cm2 V−1 s−1, a lower Vth of 4.6 V and a lower SS of 0.21 V dec−1 compared to those without the ZrOx interlayer. Comprehensive studies showed that the Al element easily diffused into the IZO film and formed AlOx clusters which acted as defects to deteriorate TFT performance; and after modification with a ZrOx interlayer, the diffusion of Al was suppressed and the Zr diffusing effect almost could be ignored. These results suggested that the introduction of an interlayer with less diffusing effect as well as an effect of blocking the elements from the gate insulator diffusing into the channel layer could be an effective way to improve the electrical performance for solution-processed oxide TFTs.

High mobility flexible polymer thin-film transistors with an octadecyl-phosphonic acid treated electrochemically oxidized alumina gate insulator

Flexible solution-processed polymer thin-film transistors (PTFTs) with a low band-gap (LBG) donor–acceptor (D–A) conjugated polymer as the active layer and electrochemically oxidized alumina (AlOx:Nd) as the gate insulator are fabricated on polyethylene naphthalate (PEN) substrates. The AlOx:Nd insulator exhibits excellent insulating properties with low leakage current, a high dielectric constant and a high breakdown field. To improve the interface coupling between the polymer active layer and the AlOx:Nd insulator, the AlOx:Nd insulator is treated with octadecyl-phosphonic acid (ODPA), forming self-assembled monolayers (SAMs) on the surface, and great improvement in TFT performance with the highest mobility of 2.88 cm2 V−1 s−1 is attained. The performance improvement is attributed to the smoother surface and lower surface energy of the ODPA-treated AlOx:Nd compared to those of bare AlOx:Nd. In addition, the flexible PTFT exhibits only small shifts in the transfer curves at bending curvatures (R) at 30 mm, but the device shows larger threshold voltage and higher off current (Ioff) after bent at R = 5–20 mm, which may be attributed to the damage in the insulator-semiconductor interface.

Facile patterning of amorphous indium oxide thin films based on a gel-like aqueous precursor for low-temperature, high performance thin-film transistors

A “green precursor” and a “green patterning technique” were used to fabricate low temperature processed indium oxide (InOx) semiconductors. For the InOx precursor, chloride ligand-based indium(III) was dissolved in deionized (DI) water without any additives to form a gel-like precursor. The as-spin-coated precursor films could be facilely patterned using the “green patterning technique”, which requires only ultraviolet (UV) irradiation and DI water. A systematic study was carried out to investigate the chemical reaction of the chloride-based precursor films as well as the semiconductor properties. It was found that UV irradiation and water treatment not only helped to transform In–Cl into In–OH, but also helped to remove the Cl-related impurities. It led to the activation of InOx films at temperatures as low as 180 °C. The mobility of InOx TFTs based on an anodized aluminium oxide (AlOx:Nd) insulator with patterning was improved by more than 1 order compared to that without patterning at an annealing temperature of 280 °C. In addition, flexible InOx TFTs on polyimide (PI) substrates were demonstrated. They showed only a little degradation in the subthreshold region of the transfer curve even at a bending curvature (R) of 5 mm.

High-mobility ZrInO thin-film transistor prepared by an all-DC-sputtering method at room temperature

Thin-film transistors (TFTs) with zirconium-doped indium oxide (ZrInO) semiconductor were successfully fabricated by an all-DC-sputtering method at room temperature. The ZrInO TFT without any intentionally annealing steps exhibited a high saturation mobility of 25.1 cm2V−1s−1. The threshold voltage shift was only 0.35 V for the ZrInO TFT under positive gate bias stress for 1 hour. Detailed studies showed that the room-temperature ZrInO thin film was in the amorphous state with low carrier density because of the strong bonding strength of Zr-O. The room-temperature process is attractive for its compatibility with almost all kinds of the flexible substrates, and the DC sputtering process is good for the production efficiency improvement and the fabrication cost reduction.