Properties of rf-sputtered indium-tin-oxynitride thin films

Indium-tin-oxide (ITO) and indium-tin-oxynitride (ITON) thin films have been fabricated by rf-sputtering in plasma containing Ar or a mixture of Ar and N-2, respectively. The structural, electrical and optical properties of ITON films were examined and compared with those of ITO films. The microstructure of ITON films was found to be dependent on the nitrogen concentration in the plasma. Increasing the amount of nitrogen in the plasma increased the resistivity and reduced the carrier concentration and mobility of the films. The electrical properties of the ITON films improved after annealing. The absorption edge of the ITON films deposited in pure N-2 plasma was shifted towards higher energies and showed reduced infrared reflectance compared to the respective properties of ITO films. The potential of indium-tin-oxynitride films for use as a transparent conductive material for optoelectronic devices is addressed

Vibrational properties of SrCu2O2 studied via Density Functional Theory calculations and compared to Raman and infrared spectroscopy measurements

International audienceThe SrCu2O2 material is a p-type transparent conductive oxide. A theoretical study of the SrCu2O2 crystal is performed with a state of the art implementation of the Density Functional Theory. The simulated crystal structure is compared with available X-ray diffraction data and previous theoretical modeling. Density Functional Perturbation Theory is used to study the vibrational properties of the SrCu2O2 crystal. A symmetry analysis of the optical phonon eigenvectors at the Brillouin zone center is proposed. The Raman spectra simulated using the derivatives of the dielectric susceptibility, show a good agreement with Raman scattering experimental results

Electron scattering mechanisms in fluorine-doped SnO2 thin films

Polycrystalline fluorine-doped SnO2 (FTO) thin films have been grown by ultrasonic spray pyrolysis on glass substrate. By varying growth conditions, several FTO specimens have been deposited and the study of their structural, electrical, and optical properties has been carried out. By systematically investigating the mobility as a function of carrier density, grain size, and crystallite size, the contribution of each physical mechanism involved in the electron scattering has been derived. A thorough comparison of experimental data and calculations allows to disentangle these different mechanisms and to deduce their relative importance. In particular, the roles of extended structural defects such as grain or twin boundaries as revealed by electron microscopy or x-ray diffraction along with ionized impurities are discussed. As a consequence, based on the quantitative analysis presented here, an experimental methodology leading to the improvement of the electro-optical properties of FTO thin films is reported. FTO thin films assuming an electrical resistivity as low as 3.7 center dot 10(-4)Omega cm (square sheet resistance of 8 Omega/square) while retaining good transmittance up to 86% (including substrate effect) in the visible range have been obtained. (c) 2013 AIP Publishing LLC

Very large phase shift of microwave signals in a 6 nm Hf x Zr 1− x O 2 ferroelectric at ±3 V

In this letter, we report for the first time very large phase shifts of microwaves in the 1–10 GHz range, in a 1 mm long gold coplanar interdigitated structure deposited over a 6 nm Hf x Zr1−x O2 ferroelectric grown directly on a high resistivity silicon substrate. The phase shift is larger than 60° at 1 GHz and 13° at 10 GHz at maximum applied DC voltages of ±3 V, which can be supplied by a simple commercial battery. In this way, we demonstrate experimentally that the new ferroelectrics based on HfO2 could play an important role in the future development of wireless communication systems for very low power applications

Reconfigurable horizontal-vertical carrier transport in graphene/HfZrO field-effect transistors

We have fabricated at wafer level field-effect-transistors (FETs) having as channel graphene monolayers transferred on a HfZrO ferroelectric, grown by atomic layer deposition on a doped Si (100) substrate. These FETs display either horizontal or vertical carrier transport behavior, depending on the applied gate polarity. In one polarity, the FETs behave as a graphene FET where the transport is horizontal between two contacts (drain and grounded source) and is modulated by a back-gate. Changing the polarity, the transport is vertical between the drain and the back-gate and, irrespective of the metallic contact type, Ti/Au or Cr/Au, the source-drain bias modulates the height of the potential barrier between HfZrO and the doped Si substrate, the carrier transport being described by a Schottky mechanism at high gate voltages and by a space-charge limited mechanism low gate voltages. Vertical transport is required by three-dimensional integration technologies for increasing the density of transistors on chip

Electromagnetic energy harvesting based on HfZrO tunneling junctions

HfZrO ferroelectrics with a thickness of 6 nm were grown directly on Si using atomic layer deposition, top and bottom metallic electrodes being subsequently deposited by electron-beam metallization techniques. Depending on the polarity of the ±10 V poling voltages, the current–voltage dependence of these tunneling diodes shows a rectifying behavior for different polarizations, the ON–OFF ratio being about 104. Because the currents are at mA level, the HfZrO tunneling diodes coupled to an antenna array can harvest electromagnetic energy at 26 GHz (a bandwidth designated for internet of things), with a responsivity of 63 V W−1 and a NEP of 4 nW/Hz0.5

Dispersion force for materials relevant for micro and nanodevices fabrication

The dispersion (van der Waals and Casimir) force between two semi-spaces are calculated using the Lifshitz theory for different materials relevant for micro and nanodevices fabrication, namely, gold, silicon, gallium arsenide, diamond and two types of diamond-like carbon (DLC), silicon carbide, silicon nitride and silicon dioxide. The calculations were performed using recent experimental optical data available in the literature, usually ranging from the far infrared up to the extreme ultraviolet bands of the electromagnetic spectrum. The results are presented in the form of a correction factor to the Casimir force predicted between perfect conductors, for the separation between the semi-spaces varying from 1 nanometre up to 1 micrometre. The relative importance of the contributions to the dispersion force of the optical properties in different spectral ranges is analyzed. The role of the temperature for semiconductors and insulators is also addressed. The results are meant to be useful for the estimation of the impact of the Casimir and van der Waals forces on the operational parameters of micro and nanodevices

Aluminum interdiffusion into LiCoO2 using atomic layer deposition for high rate lithium ion batteries

Here, as with previous work, atomic layer deposition (ALD) has been used to deposit Al2O3 on positive electrode active materials, LiCoO2, to create a protective barrier layer, suppress the high potential phase transition, and thus reduce the subsequent Co dissolution. However, in this study it was found that it also resulted in the reduction of the charge transfer resistance at the positive electrode–electrolyte interface, thus enhancing the performance of the battery. Energy-dispersive X-ray spectroscopy, in conjunction with transmission electron microscopy, shows that a discrete Al2O3 shell was not formed under the selected growth conditions and that the Al diffused into the bulk LiCoO2. The resulting active oxide material, which was significantly thicker than the nominally ALD growth rate would predict, is proposed to be of the form LiCoO2:Al with amorphous and crystalline regions depending on the Al content. The cells consisting of the modified electrodes were found to have good cycling stability and discharge capacities of ∼110 mA h g–1 (0.12 mA h cm–2) and ∼35 mA h g–1 (0.04 mA h cm–2) at 50 and 100 C, respectively