George Adamopoulos

High‐Mobility Low‐Voltage ZnO and Li‐Doped ZnO Transistors Based on ZrO2 High‐k Dielectric Grown by Spray Pyrolysis in Ambient Air

Sequential layers of the high-k dielectric ZrO2 and the electron transporting semiconductors ZnO and Li-doped ZnO are deposited onto conductive indium tin oxide electrodes using spray pyrolysis. With these structures, thin-film transistors are fabricated with operating voltages below 6 V and maximum electron mobilities on the order of 85 cm(2) V-1 s(-1).

Spray-Deposited Li-Doped ZnO Transistors with Electron Mobility Exceeding 50 cm(2)/Vs

Ambient spray pyrolysis is used for the deposition of high quality polycrystalline ZnO films utilizing blends of precursor solutions based on Zinc and Lithium acetates and the demonstration of n-channel thin-film transistors with electron mobility exceeding 50 cm(2)/Vs (see figure).

Low-voltage ZnO thin-film transistors based on Y2O3 and Al2O3 high-k dielectrics deposited by spray pyrolysis in air

We report the application of ambient spray pyrolysis for the deposition of high-k polycrystalline Y2O3 and amorphous Al2O3 dielectrics and their use in low-voltage ZnO thin-film transistors. The films are studied by means of atomic force microscopy, UV-visible absorption spectroscopy, impedance spectroscopy, and field-effect measurements. ZnO transistors based on spray pyrolysed Y2O3 and Al2O3 dielectrics show low leakage currents, and hysteresis-free operation with a maximum electron mobility of 34 cm2/V s and current on/off ratio on the order of 105. This work is a significant step toward high-performance oxide electronics manufactured using simple and scalable processing methods.

Determination of bonding in amorphous carbons by electron energy loss spectroscopy, Raman scattering and X-ray reflectivity

X-ray reflectivity (XRR) and Raman scattering are developed as non-destructive methods to find the density and sp 3 content of unhydrogenated and hydrogenated amorphous carbon films. An empirical relationship is found to derive the sp 3 fraction from visible Raman spectra, while ultraviolet (UV) Raman is able to directly detect sp 3 sites. The sp 3 fraction and density are linearly correlated in amorphous carbon (a-C) and hydrogenated amorphous carbon (a-C:H) films. ” 2000 Elsevier Science B.V. All rights reserved.

Electronic properties of ZnO field-effect transistors fabricated by spray pyrolysis in ambient air

We report the application of spray pyrolysis (SP) for the deposition of high quality zinc oxide (ZnO) films and the fabrication of thin-film transistors. The chemical, structural, optical, and electronic properties of as-deposited ZnO films are studied using infrared spectroscopy, atomic force microscopy, UV-visible spectroscopic ellipsometry, and field-effect measurements. SP ZnO films are found to be uniform and polycrystalline with a band gap of 3.32 eV. ZnO transistors exhibit n-channel characteristics with electron mobility in the range 10–22 cm2/Vs. Device performance is found to depend on the work function of source/drain metal electrodes and on the device architecture employed.

p-channel thin-film transistors based on spray-coated Cu2O films

Thin films of cuprous oxide (Cu2O) were grown using solution-based spray pyrolysis in ambient air and incorporated into hole-transporting thin-film transistors. The phase of the oxide was confirmed by X-ray diffraction measurements while the optical band gap of the films was determined to be ∼2.57 eV from optical transmission measurements. Electrical characterization of Cu2O films was performed using bottom-gate, bottom-contact transistors based on SiO2 gate dielectric and gold source-drain electrodes. As-prepared devices show clear p-channel operation with field-effect hole mobilities in the range of 10−4–10−3 cm2 V−1 s−1 with some devices exhibiting values close to 1 × 10−2 cm2 V−1 s−1.

Hydrogen content estimation of hydrogenated amorphous carbon by visible Raman spectroscopy

In the present study, we report the hydrogen content estimation of the hydrogenated amorphous carbon (a‐C:H) films using visible Raman spectroscopy in a fast and nondestructive way. Hydrogenated diamondlike carbon films were deposited by the plasma enhanced chemical vapor deposition, plasma beam source, and integrated distributed electron cyclotron resonance techniques. Methane and acetylene were used as source gases resulting in different hydrogen content and sp2∕sp3 fraction. Ultraviolet-visible (UV-Vis) spectroscopic ellipsometry (1.5–5eV) as well as UV-Vis spectroscopy were provided with the optical band gap (Tauc gap). The sp2∕sp3 fraction and the hydrogen content were independently estimated by electron energy loss spectroscopy and elastic recoil detection analysis-Rutherford back scattering, respectively. The Raman spectra that were acquired in the visible region using the 488nm line shows the superposition of Raman features on a photoluminescence (PL) background. The direct relationship of the sp2...

Air-stable solution-processed hybrid transistors with hole and electron mobilities exceeding 2 cm2 V-1 s-1.

An alternative approach for the development of high-performance unipolar and ambipolar thin-film transistors and integrated circuits based on hybrid heterostructures comprising a phase-separated solution processed p-type organic small-molecule:polymer semicondcutor blend and a spray-coated n-type ZnO semiconductor layer is demonstrated.

Ultraviolet Raman characterisation of diamond-like carbon films

Diamond-like carbon (DLC) films with a range of sp(3) fractions have been examined by ultraviolet (UV) spectroscopy with 244 nm excitation. The UV Raman spectra of both hydrogenated and unhydrogenated films show the G peak near 1600 cm(-1) and a broad peak around 1200 cm(-1), which is attributed to C-C stretching vibrations of sp(3) sites. It is found that the ratio of the intensities of the C peak and the 1200 cm(-1) peak follows a universal dependence with the sp(3) content in both hydrogenated and unhydrogenated DLCs. This can be used for non-destructive evaluation of the sp(3) content of any DLC film.

ZnO-based thin film transistors employing aluminum titanate gate dielectrics deposited by spray pyrolysis at ambient air.

The replacement of SiO2 gate dielectrics with metal oxides of higher dielectric constant has led to the investigation of a wide range of materials with superior properties compared with SiO2. Despite their attractive properties, these high-k dielectrics are usually manufactured using costly vacuum-based techniques. To overcome this bottleneck, research has focused on the development of alternative deposition methods based on solution-processable metal oxides. Here we report the application of spray pyrolysis for the deposition and investigation of Al2x-1·TixOy dielectrics as a function of the [Ti(4+)]/[Ti(4+)+2·Al(3+)] ratio and their implementation in thin film transistors (TFTs) employing spray-coated ZnO as the active semiconducting channels. The films are studied by UV-visible absorption spectroscopy, spectroscopic ellipsometry, impedance spectroscopy, atomic force microscopy, X-ray diffraction and field-effect measurements. Analyses reveal amorphous Al2x-1·TixOy dielectrics that exhibit a wide band gap (∼4.5 eV), low roughness (∼0.9 nm), high dielectric constant (k ∼ 13), Schottky pinning factor S of ∼0.44 and very low leakage currents (<5 nA/cm(2)). TFTs employing stoichiometric Al2O3·TiO2 gate dielectrics and ZnO semiconducting channels exhibit excellent electron transport characteristics with low operating voltages (∼10 V), negligible hysteresis, high on/off current modulation ratio of ∼10(6), subthreshold swing (SS) of ∼550 mV/dec and electron mobility of ∼10 cm(2) V(-1) s(-1).