Doo-Hyoung Lee

High-performance, spin-coated zinc tin oxide thin-film transistors

We have developed a general and low-cost, solution-based process that is suitable for the deposition of transparent conducting oxides through spin-coating or inkjet printing under ambient conditions. Highly transparent (-95% in the visible portion) zinc tin oxide semiconducting thin films were deposited by spin coating. The deposited films were found to be smooth and uniform with an amorphous structure. Enhancement-mode metal-insulator-semiconductor field-effect transistors were fabricated showing a field-effect mobility (μ FE ) as high as 16 cm 2 /V s, a turn-on voltage of 2 V, a current on-to-off ratio greater than 10 5 , and a high on-current of 2.25 mA.

The Growth Mechanism of Nickel Oxide Thin Films by Room-Temperature Chemical Bath Deposition

Chemical bath deposition (CBD) is an advantageous thin film deposition technique for depositing compound semiconductors at low temperature. In this paper, nickel oxide thin films were prepared by CBD from an aqueous solution composed of nickel sulfate, potassium persulfate, and ammonia at room temperature. Thin film growth mechanisms were studied by using quartz crystal microbalance, UV-vis absorption, and photon correlation spectroscopy. The data indicate that film growth is strongly dependent upon mixing conditions and competes with homogeneous particle formation. No film formation was observed without the addition of persulfate. A growth mechanism based on the combination of particle sticking and molecule level heterogeneous growth is proposed. The as-deposited film contained α-Ni(OH) 2 and 4Ni(OH) 2 ·NiOOH·xH 2 O and was converted to nickel oxide (NiO) by thermal annealing according to thermogravimetric. X-ray diffraction and X-ray photoelectron spectroscopy measurements.

Inkjet printed high-mobility indium zinc tin oxide thin film transistors

Thin-film transistors based on inkjet printed indium zinc tin oxide (IZTO) channel layers are reported in this paper. The printed IZTO transistor has a high field-effect mobility (µFE = ∼30 cm2V−1 s−1), excellent on-to-off current ratio (>1 × 106) and behaves as an enhancement mode device (turn-on voltage = 2 V). This mobility is an order magnitude higher than previously reported for inkjet printed oxide-based transistors. The printed films are highly transparent in the UV-Visible regime with a transmittance higher than 95%. A transparent thin film transistor using a printed IZTO channel was also demonstrated for the first time.

Inkjet-Printed High Mobility Transparent–Oxide Semiconductors

In this paper, we report a general and low-cost process to fabricate high mobility metal-oxide semiconductors that is suitable for thin-film electronics. This process use simple metal halide precursors dissolved in an organic solvent and is capable of forming uniform and continuous thin films via inkjet-printing or spin-coating process. This process has been demonstrated to deposit a variety of semiconducting metal oxides include binary oxides (ZnO, In2O3 , SnO2 , Ga2O3 ), ternary oxides (ZIO, ITO, ZTO, IGO) and quaternary compounds (IZTO, IGZO). Functional thin film transistors with high field-effect mobility were fabricated successfully using channel layers deposited from this process. This synthetic pathway opens an avenue to form patterned metal oxide semiconductors through a simple and low-cost process and to fabricate high performance transparent thin film electronics via digital fabrication processes on large substrates.

Functional Porous Tin Oxide Thin Films Fabricated by Inkjet Printing Process

The highly transparent SnO 2 thin films were deposited through solution-based inkjet printing using a simple precursor solution. We were able to fabricate porous tin oxide thin film that has a thin nanoporous layer on top and a thicker meso- and macroporous layer beneath the top layer. The thin-film transmittance is over 98% in the visible wavelength range. A mechanism based on gas evolution was proposed to explain the formation of porous structure. A depletion-mode thin-film transistor using the porous tin oxide channel layer was fabricated with a field-effect mobility of 3.62 cm 2 /V s.

Chemical nanoparticle deposition of transparent ZnO thin films

A novel approach to deposit transparent ZnO thin films is reported. This approach uses a continuous-flow microreactor to generate a flux of nanoparticles which then impinge on a heated substrate. The as-deposited film consists of highly transparent nanocrystalline ZnO with a dilated optical bandgap of 4.35 eV. Functional ZnO metal-insulator-semiconductor field-effect-transistors (MISFETs) were successfully fabricated using this technique after a post-air-annealing process. A MISFET with an effective mobility of 0.16 cm 2 /V s and a current on-to-off ratio of ∼10 4 was produced. This approach is promising as a low-cost technique for fabricating nanostructured thin films.

Biogenic silica based Zn2SiO4:Mn2+ and Y2SiO5:Eu3+ phosphor layers patterned by inkjet printing process

We demonstrate herein the fabrication of patterned layers of Zn2SiO4:Mn2+ and Y2SiO5:Eu3+ phosphor materials based on nanostructured diatom biosilicavia the inkjet printing process.

ZnS Thin Films Deposited by a Spin Successive Ionic Layer Adsorption and Reaction Process

In this article, we reported a spin successive ionic layer adsorption and reaction (SILAR) method for the first time. ZnS thin films were deposited by spin SILAR using ZnCl2 and Na2S aqueous precursor solutions at room temperature and atmosphere pressure. The optical, structural, and morphological characterizations of the films were studied by scanning electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV/visible spectroscopy. Smooth (average roughness <3 nm), uniform, and highly transparent ZnS (transmittance of over 90% in the visible band) thin films could be successfully deposited using this technique with shorter cycle time and much less solvent usage.