Tae Soo Jung

Low-cost label-free electrical detection of artificial DNA nanostructures using solution-processed oxide thin-film transistors.

A high-sensitivity, label-free method for detecting deoxyribonucleic acid (DNA) using solution-processed oxide thin-film transistors (TFTs) was developed. Double-crossover (DX) DNA nanostructures with different concentrations of divalent Cu ion (Cu(2+)) were immobilized on an In-Ga-Zn-O (IGZO) back-channel surface, which changed the electrical performance of the IGZO TFTs. The detection mechanism of the IGZO TFT-based DNA biosensor is attributed to electron trapping and electrostatic interactions caused by negatively charged phosphate groups on the DNA backbone. Furthermore, Cu(2+) in DX DNA nanostructures generates a current path when a gate bias is applied. The direct effect on the electrical response implies that solution-processed IGZO TFTs could be used to realize low-cost and high-sensitivity DNA biosensors.

Recent advances in low-temperature solution-processed oxide backplanes

Applicable flexible electronics, particularly flexible displays, have been developed for next-generation devices in recent years. Sol–gel processing, for example, which uses low-temperature annealing, is a promising technique. This review article focuses on recent advances in achieving low-temperature, solution-processed oxide thin-film transistors (TFTs) through chemical and physical approaches. First, chemical approaches were overviewed in terms of solute and solvent engineering. Second, physical approaches were summarized that some researchers added energy resources except heat on the conventional sol–gel process. The additional energy sources involve microwave annealing, high-pressure annealing, and ultraviolet irradiation. This review article offers an overview of these techniques introduced in details. From these efforts, metal-oxide TFTs can be fabricated at 150°C maintaining their device performance.

High-pressure Gas Activation for Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors at 100 °C

We investigated the use of high-pressure gases as an activation energy source for amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs). High-pressure annealing (HPA) in nitrogen (N2) and oxygen (O2) gases was applied to activate a-IGZO TFTs at 100 °C at pressures in the range from 0.5 to 4 MPa. Activation of the a-IGZO TFTs during HPA is attributed to the effect of the high-pressure environment, so that the activation energy is supplied from the kinetic energy of the gas molecules. We reduced the activation temperature from 300 °C to 100 °C via the use of HPA. The electrical characteristics of a-IGZO TFTs annealed in O2 at 2 MPa were superior to those annealed in N2 at 4 MPa, despite the lower pressure. For O2 HPA under 2 MPa at 100 °C, the field effect mobility and the threshold voltage shift under positive bias stress were improved by 9.00 to 10.58 cm2/V.s and 3.89 to 2.64 V, respectively. This is attributed to not only the effects of the pressurizing effect but also the metal-oxide construction effect which assists to facilitate the formation of channel layer and reduces oxygen vacancies, served as electron trap sites.

Reduction of activation temperature at 150°C for IGZO films with improved electrical performance via UV-thermal treatment

ABSTRACT Activation using the simultaneous UV-thermal (U-T) treatment of sputter-processed InGaZnO (IGZO) thin-film transistors (TFTs) is suggested. This treatment was performed to lower the activation temperature from 300°C (thermal activation alone) to 150°C as well as to improve the electrical characteristics and stability. Despite the low temperature, the U-T-treated devices showed superior electrical characteristics and stability compared to the devices that were only thermally activated (300°C): the mobility improved from 5.19 ± 1.8 to 16.20 ± 1.5 cm2/Vs, the on-off ratio increased from (5.58 ± 3.21) × 108 to (2.50 ± 2.23) × 109, and the threshold voltage shift (under positive bias stress for 1000 s) decreased from 7.1 to 2.2 V. These improvements are attributed to the following two contributions: (1) generation of reactive oxygen radical at a low temperature and (2) decomposition-rearrangement of the metal oxide (MO) bonds in the IGZO active layer. Contributions (1) and (2) effectively increased the MO bonds and decreased the defect-site-related oxygen vacancies.

Electric Field-aided Selective Activation for Indium-Gallium-Zinc-Oxide Thin Film Transistors

A new technique is proposed for the activation of low temperature amorphous InGaZnO thin film transistor (a-IGZO TFT) backplanes through application of a bias voltage and annealing at 130 °C simultaneously. In this ‘electrical activation’, the effects of annealing under bias are selectively focused in the channel region. Therefore, electrical activation can be an effective method for lower backplane processing temperatures from 280 °C to 130 °C. Devices fabricated with this method exhibit equivalent electrical properties to those of conventionally-fabricated samples. These results are analyzed electrically and thermodynamically using infrared microthermography. Various bias voltages are applied to the gate, source, and drain electrodes while samples are annealed at 130 °C for 1 hour. Without conventional high temperature annealing or electrical activation, current-voltage curves do not show transfer characteristics. However, electrically activated a-IGZO TFTs show superior electrical characteristics, comparable to the reference TFTs annealed at 280 °C for 1 hour. This effect is a result of the lower activation energy, and efficient transfer of electrical and thermal energy to a-IGZO TFTs. With this approach, superior low-temperature a-IGZO TFTs are fabricated successfully.

Replacement and Rearrangement of an Oxide Lattice by Germanium Doping in Solution-Processed Indium–Zinc-Oxide Thin-Film Transistors

Germanium (Ge) doping effects on solution-processed indium-zinc-oxide (IZO) thin-film transistors (TFTs) were investigated. Ge doping increased the carrier concentration of Ge-doped IZO (Ge:IZO) thin films from 3.32 × 1014 to 3.13 × 1015 cm3 by Ge substitution for zinc (Zn). Ge easily substituted for Zn in the IZO active layer, due to its comparably small atomic radius. By this substitution, Ge doping provided additional valence electrons to the active layer, resulting in a value for the field-effect mobility of a Ge:IZO TFT that was almost two times greater than that of a pristine IZO TFT. Consequently, despite the Ge:IZO TFT being a quaternary system, it displayed a better electrical performance and stability at low processing temperatures, thus demonstrating the feasibility of this device for flexible displays.

Hall transport of divalent metal ion modified DNA lattices

We investigate the Hall transport characteristics of double-crossover divalent metal ion (Cu2+, Ni2+, Zn2+, and Co2+)-modified DNA (M-DNA) lattices grown on silica via substrate-assisted growth. The electronic characteristics of the M-DNA lattices are investigated by varying the concentration of the metal ions and then conducting Hall measurements, including resistivity, Hall mobility, carrier concentration, and magneto resistance. The tendency of the resistivity and Hall mobility was to initially decrease as the ion concentration increased, until reaching the saturation concentration (Cs) of each metal ion, and then to increase as the ion concentration increased further. On the other hand, the carrier concentration revealed the opposite tendency as the resistivity and Hall mobility. The specific binding (≤Cs) and the nonspecific aggregates (>Cs) of the ions into the DNA lattices were significantly affected by the Hall characteristics. The numerical ranges of the Hall parameters revealed that the M-DNA la...

Low-temperature activation under 150°C for amorphous IGZO TFTs using voltage bias

ABSTRACT Proposed herein is a new technique of activation for the backplane of low-temperature amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) by applying a bias voltage to gate, source, and drain electrodes and simultaneously annealing them at 150°C. This ‘voltage bias activation’ can be an effective method of reducing the backplane processing temperature from 300°C to 150°C. Compared with the reference a-IGZO TFTs fabricated at 300°C, the a-IGZO TFTs fabricated through voltage bias activation showed sufficient switching characteristics: 10.39 cm2/Vs field effect mobility, 0.41 V/decade subthreshold swing, and 3.65 × 107 on/off ratio. These results were analyzed thermodynamically using infrared micro-thermography. In the case of the positive gate voltage bias condition, the maximum temperature of the a-IGZO channel increased to 48°C, and this additional annealing effect and activation energy lowering compensated for the insufficient thermal energy of annealing at a low temperature (150°C). With this approach, a-IGZO TFTs were successfully fabricated at a low temperature.

Interface location-controlled indium gallium zinc oxide thin-film transistors using a solution process

The role of an interface as an electron-trapping layer in double-stacked indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) was investigated and interface location-controlled (ILC) IGZO TFTs were introduced. In the ILC TFTs, the thickness of the top and bottom IGZO layers is controlled to change the location of the interface layer. The system exhibited improved electrical characteristics as the location of the interface layer moved further from the gate insulator: field-effect mobility increased from 0.36 to 2.17 cm2 V−1 s−1, and the on-current increased from 2.43 × 10−5 to 1.33 × 10−4 A. The enhanced electrical characteristics are attributed to the absence of an electron-trapping interface layer in the effective channel layer where electrons are accumulated under positive gate bias voltage.

Enhancement of Switching Characteristic for p-Type Oxide Semiconductors Using Hypochlorous Acid

We explored the effects of hypochlorous acid (HClO) oxidation on p-type oxide semiconductors. HClO generates oxygen radicals (O·) (strong reactive oxygen species) that affect the chemical state of p-type copper oxide (CuO x) thin films by reacting with CuO x. On robust oxidation by HClO, the numbers of Cu-O bonds increased and the numbers of copper vacancies serving as hole carriers decreased. In the modified CuO x thin-film transistors (TFTs), switching was evident. The subthreshold swing was 0.70 V/dec, the on-/off-current ratio was 4.86 × 104, and the field effect mobility was 2.83 × 10-3 cm2/V·s. Pristine CuO x TFTs did not exhibit switching.