Hsing-Hung Hsieh

Modeling of amorphous InGaZnO4 thin film transistors and their subgap density of states

We report a model of the carrier transport and the subgap density of states in amorphous InGaZnO4 (a-IGZO) for device simulation of a-IGZO thin-film transistors (TFTs) operated in both the depletion mode and the enhancement mode. A simple model using a constant mobility and two-step subgap density of states reproduced well the characteristics of the a-IGZO TFTs. a-IGZO exhibits low densities of tail states and deep gap states, leading to small subthreshold swings and high mobilities.

Amorphous ZnO transparent thin-film transistors fabricated by fully lithographic and etching processes

Oxide-semiconductor-based thin-film transistors (TFTs), particularly the amorphous ones, are becoming an important emerging technology. Since oxide semiconductors easily form polycrystalline phases, usually more complicated oxide mixtures are needed for growing amorphous phases. In this letter, we report that by simply reducing the thickness, ZnO can be intentionally grown into the amorphous phase. Furthermore, both top-gate and bottom-gate amorphous ZnO TFTs of micrometer scales were effectively implemented using fully lithographic and etching processes. Rather high field-effect mobilities of 25 and 4cm2∕Vs and on∕off current ratios of >107 and >106 were achieved for top-gate and bottom-gate configurations, respectively.

A new type of soluble pentacene precursor for organic thin-film transistors

A new type of soluble pentacene precursor is synthesized, which extrudes a unit of CO upon heating at 150 degrees C, to produce pentacene in nearly quantitative yield.

High-Performance Flexible a-IGZO TFTs Adopting Stacked Electrodes and Transparent Polyimide-Based Nanocomposite Substrates

We demonstrated flexible amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) on fully transparent and high-temperature polyimide-based nanocomposite substrates. The flexible nanocomposite substrates were coated on the carrier glass substrates and were debonded after the TFT microfabrication. The adoption of the Ti/IZO stacked electrodes as source/drain/ gain electrodes significantly improved the etching compatibility with other material layers, enabling successful implementation of flexible a-IGZO TFTs onto the transparent nanocomposite substrates by conventional lithographic and etching processes. The flexible a-IGZO TFTs exhibited decent mobility and mechanical bending capability. Field-effect mobility of up to 15.9 cm2/V · s, a subthreshold swing of 0.4 V/dec, a threshold voltage of 0.8 V, and an on/off ratio of >; 108 were extracted from the TFT characteristics. The devices could be bent down to a radius of curvature of 3 mm and yet remained normally functional. Such successful demonstration of flexible oxide TFTs on transparent flexible substrates using fully lithographic and etching processes that are compatible with existing TFT fabrication technologies shall broaden their uses in flexible displays and electronics.

Self-Aligned Top-Gate Coplanar In-Ga-Zn-O Thin-Film Transistors

Self-aligned techniques are often used in conventional CMOS and Si-based thin-film transistors (TFTs) technologies due to various merits. In this paper, we report self-aligned coplanar top-gate InGaZnO TFTs using PECVD a-SiNinfin:H patterned to have low hydrogen content in the channel region and high hydrogen content in the source/drain region. After annealing to induce hydrogen diffusion from a-SiNinfin:H into the oxide semiconductor, the source-drain regions become more conductive and yet the channel region remains suitable for TFT operation, yielding a working self-aligned TFT structure. Such fabrication involves neither back-side exposure nor ion implantation, and thus may be compatible with the typical and cost-effective TFT manufacturing.

Photogeneration and thermal generation of pentacene from soluble precursors for OTFT applications.

A CO adduct of pentacene with an unsymmetrical structure is synthesized; it is soluble and can be spin-coated into thin films. Pentacene is regenerated in near quantitative yield by either thermal or photoinduced elimination of CO. OTFT devices fabricated by this compound exhibit typical FET characteristics.

Fabrication of p-Type SnO Thin-Film Transistors by Sputtering with Practical Metal Electrodes

P-type thin-film transistors using polycrystalline tin monoxide (SnO) active layers were achieved by an industry-compatible sputtering technique with a SnO ceramic target. The SnO films clearly exhibited p-type conduction with the p-type Hall mobilities of 1–4 cm2 V-1 s-1 and hole concentrations of 1017–1018 cm-3. The physical and chemical structures of SnO films were characterized by X-ray diffraction analysis and X-ray photoemission spectroscopy. It is concluded that amorphous and SnO-dominant films were obtained as deposited. Further annealing at ≤300 °C induces crystallization but no major chemical reaction. The transmission line method was adopted to characterize the contact resistance between SnO layers and various metal electrodes. Results show that Mo and Ni could be used as effective electrodes for p-type SnO, avoiding the use of noble metals. Finally, p-type SnO TFTs using practical metal electrodes were fabricated, where a field-effect mobility of up to 1.8 cm2 V-1 s-1 and an on/off current ratio of >103 were achieved.

Sputtering Deposition of P-Type SnO Films with SnO2 Target in Hydrogen-Containing Atmosphere

In this work, we had investigated sputtering deposition of p-type SnO using the widely used and robust SnO2 target in a hydrogen-containing reducing atmosphere. The effects of the hydrogen-containing sputtering gas on structures, compositions, optical, and electrical properties of deposited SnOx films were studied. Results show that polycrystalline and SnO-dominant films could be readily obtained by carefully controlling the hydrogen gas ratio in the sputtering gas and the extent of reduction reaction. P-type conductivity was unambiguously observed for SnO-dominant films with traceable Sn components, exhibiting a p-type Hall mobility of up to ∼3 cm(2) V(-1) s(-1). P-type SnO thin-film transistors using such SnO-dominant films were also demonstrated.

The Influence of Channel Compositions on the Electrical Properties of Solution-Processed Indium-Zinc Oxide Thin-Film Transistors

Electrical properties of indium-zinc oxide (IZO) thin-film-transistors (TFTs) based on solution processes with various channel compositions are investigated in this paper. Amorphous IZO thin films with high transparency and smooth/uniform surfaces are deposited by spin-coating. The In:Zn ratio is varied by adjusting the precursor compositions, and its influences on the electrical properties, such as resistivity, mobility, and threshold voltage, etc., of IZO films and TFTs are studied. The devices showed field effect mobility ranging from 0.07 to 2.13 cm2/Vmiddots with the In component (In/(In + Zn)) varying from 0.2 to 0.5.

Room-temperature-processed flexible n-InGaZnO/p-Cu2O heterojunction diodes and high-frequency diode rectifiers

In this work, we report successful implementation of room-temperature-processed flexible n-InGaZnO/p-Cu2O heterojunction diodes on polyethylene naphthalate (PEN) plastic substrates using the sputtering technique. Using n-type InGaZnO and p-type Cu2O films deposited by sputtering at room temperature, flexible n-InGaZnO/p-Cu2O heterojunction diodes were successfully fabricated on PEN plastic substrates. The didoes on PEN substrates exhibited a low apparent turn-on voltage of 0.44?V, a high rectification ratio of up to 3.4???104 at ?1.2?V, a high forward current of 1?A?cm?2 around 1?V and a decent ideality factor of 1.4, similar to the characteristics of n-InGaZnO/p-Cu2O diodes fabricated on glass substrates. The characterization of the frequency response of the room-temperature-processed flexible n-InGaZnO/p-Cu2O heterojunction diode rectifiers indicated that they are capable of high-frequency operation up to 27?MHz, sufficient for high-frequency (13.56?MHz) applications. Preliminary bending tests on diode characteristics and rectifier frequency responses indicate their promise for applications in flexible electronics.