Qinwo Shen

Preparation of AlN thin films by nitridation of Al-coated Si substrate

AlN thin films have been grown on Al-coated Si(100) and Si(111) substrates by using nitridation in high-purity nitrogen ambient, where the Al layer was previously deposited on Si by ultra-high vacuum (UHV) electron beam evaporation. The temperature of nitridation was found to play an important role in the formation of AlN films. XRD results showed AlN films formed by nitridation at 1000°C for 30 min exhibited good crystallinity with the preferred orientation of (002) for both Si(111) and Si(100) cases. Other analysis techniques, like Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy have been used to evidence the formation and purity of the AlN films. Scanning electron microscope observations of the films revealed a closely-packed granular texture.

Reactive deposition epitaxial growth of β‐FeSi2 film on Si(111): In situ observation by reflective high energy electron diffraction

Reactive deposition epitaxial growth of β‐FeSi2 film on Si(111) has been studied by in situ observation of reflective high energy electron diffraction combined with ex situ Auger electron spectroscopy depth profile analysis. The direct phase formed at the top surface after iron coverage has been determined to be mixture Fe3Si and Fe5Si3, FeSi, and β‐FeSi2, respectively, according to the results of different deposit temperature. Diffraction patterns as well as the depth profile for the Fe/Si ratio have been discussed.

Preparation of hafnium oxide thin film by electron beam evaporation of hafnium incorporating a post thermal process

Electron beam evaporation was employed to deposit hafnium on silicon (100) substrate, followed by a rapid thermal oxidation process to fabricate hafnium dioxide thin film. Hafnium was transformed to hafnium oxide above a oxidizing temperature of 500 °C. An interfacial layer of hafnium silicate was observed between HfO2 and silicon substrate. Oxidation temperature greatly affects interfacial quality and leakage current of the film.

Preparation of PZT on diamond by pulsed laser deposition with Al2O3 buffer layer

For the purpose of broad-bandwidth high frequency surface acoustic wave devices fabrication, we report on the successful preparation of Pb(Zr0.52Ti0.48)O-3 (PZT) films by pulsed laser deposition (PLD) process on (1 1 1)-oriented polycrystalline diamond substrates with aluminum oxide (Al2O3) as buffer layer. Al2O3 was deposited on diamond substrates by high-vacuum electron-beam evaporation method at 200 degreesC. Then PLD technique was used for PZT deposition. The chemical states of Al and O in Al2O3 were investigated by X-ray photoelectron spectroscopy. The surface morphology of Al2O3 and PZT films was studied by the atom force microscopy image. X-ray diffraction results showed that before annealing, 350 degreesC-prepared PZT was amorphous and 550 degreesC-prepared PZT was (2 2 2)-oriented pyrochlore phase PZT After rapid thermal annealing at 650 degreesC, (1 0 1)-oriented pure perovskite phase PZT could be obtained from the 350 degreesC-prepared PZT film

Characterization of FeSix film by codeposition on β‐FeSi2 template

We report the characterization of FeSix (x∼3) thin film prepared by simultaneous electron beam evaporation of Fe and Si onto a β‐FeSi2 template at 250 °C. The in situ reflective high energy electron diffraction observation and ex situ cross‐section transmission electron microscope characterization of the as‐deposited film imply that the as‐deposited film has the structure similar to that of β‐FeSi2. But the spreading resistance measurement shows that the film is metallic. Auger electron spectroscopy suggests that the chemical environment of Fe atoms in the as‐deposited FeSix film is different from that in the annealed film (β‐FeSi2 film). We explain this paradox by assuming that the as‐deposited film has the crystal lattice similar to β‐FeSi2 but with ingredient disorder due to the low transport viscosity of Fe and Si atoms at this temperature.

Interfacial stability between zirconium oxide thin films and silicon

We studied the interfacial properties of ZrO2 thin films deposited by ultra-high vacuum electron beam evaporation (UHV-EBE). Some samples were annealed in O2 ambient by rapid thermal annealing (RTA) at different temperatures ranging from 300 to 700 °C. X-ray photoelectron spectroscopy (XPS) of all films, whether annealed or not, revealed that the binding energies of Zr3d5/2 and Zr3d3/2 are 183.5 and 185.7 eV, respectively, which are the typical peak values of Zr4+. X-ray diffraction (XRD) results showed that the as-deposited film was amorphous, and it remained stable up to the annealing temperature of 600 °C. But when the temperature increased further attaining 700 °C, it began to crystallize. All the surfaces of the thin films were smooth and uniform. The typical RMS roughness ranged from 0.546 to 0.666 nm across an area of 50 × 50 µm. Steep and clear interfaces between zirconium oxide thin film and Si substrate were obtained both by spreading resistance profile (SRP) and cross-sectional transmission electron microscopy (XTEM). High quality of the interface without interfacial oxide was achieved when the annealing temperatures were kept under 600 °C, but when the temperature was raised to 700 °C, ∼ 1-nm thick oxide product was detected by XTEM. The component of the oxide product is not exactly known yet, but may be SiOx or ZrSixOy.

Giant magnetoresistance and structural properties in Co/Cu/Co sandwiches with Si and Cr buffer layers

Abstract Cobalt 5.5 nm/Cu 3 nm/Co 5.5 nm sandwiches with Si and Cr buffer layers were prepared by ultra-high vacuum electron beam evaporation. A large in-plane anisotropy of the giant magnetoresistance (GMR) effect was found in Si buffered sandwiches when the buffer layer thickness was equal to or larger than 0.9 nm. In the easy axis, the GMR effect reached a value of 5.5% with a high field sensitivity of approximately 0.7%/Oe, while in Cr-buffered Co/Cu/Co sandwiches, the GMR effect showed only in-plane isotropic properties with a maximum GMR value of 6%. The XRD spectrum and HRTEM image revealed that there exists a Co2Si compound between the Si buffer and the lower Co magnetic layer. All these results indicate that the anisotropic GMR effect in Si-buffered sandwiches results from the cobalt silicide between the Si buffer and the lower Co magnetic layer.

Deposition of high k ZrO/sub 2/ thin films by high vacuum electron beam evaporation at room temperature

Amorphous zirconium oxide (ZrO/sub 2/) films have been deposited on P type Si [100] substrates using High Vacuum Electron Beam Evaporation (HVEBE) at room temperature. The chemical composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). The experimental results reveal that the dominating chemical state of zirconia thin films is fully oxidized state, Zr/sup 4+/, no matter whether annealed in oxygen. The structure information from X-ray Diffraction (XRD) shows that zirconia thin film deposited at room temperature by HVEBE was completely amorphous. Spreading Resistance Profile (SRP) indicates that ZrO/sub 2/ thin films annealed or not have excellent insulating property (with resistance of more than 10/sup 8/ /spl Omega/) and the thickness is 800 A. After thermal treatment at 600/spl deg/C in O/sub 2/ ambient, the RMS roughness changed a little to 13.8 A across an area of 1 /spl times/ 1 /spl mu/m/sup 2/, and that of the as-deposited film is 8.09 A.

Preparation of high quality amorphous Al/sub 2/O/sub 3/ thin film on silicon and its applications

Al/sub 2/O/sub 3/ thin films were deposited on silicon substrates by high-vacuum electron-beam evaporation method at 650/spl deg/C. Ferroelectric oxide (Pb(Zr/sub 0.52/Ti/sub 0.48/)O/sub 3/) (PZT) films were prepared on the Al/sub 2/O/sub 3/ buffer layer by pulsed laser deposition (PLD) method at 350/spl deg/C and rapid thermal annealing (RTA) at 650/spl deg/C. X-ray diffraction (XRD), X-ray photoelectron spectroscopes (XPS) and atomic force microscopy (AFM) results show that high quality amorphous Al/sub 2/O/sub 3/ could be obtained even at temperature as high as 650/spl deg/C. XRD result also indicates that highly [101]-oriented perovskite PZT can be obtained on the above mentioned Al/sub 2/O/sub 3/ buffer layer.

New ceramic coating technique using laser spraying process

A new ceramic coating technique using a CO2 laser has been developed. A high power density laser beam passes near the substrate. Coating materials are supplied by an extra-high accuracy powder supply device and pass across the laser beam. The coating materials are melted in the laser beam and deposited on the substrate surface. A YSZ (Yttria Stabilized Zirconia) layer and a LaCoO3 layer are made for high temperature solid oxide fuel cells. The crystal structures of the coated layers are the same as that of the original coating materials. Superconducting BPSCCO ceramic films are also made with this process. The films show super-conductivity with Tc at 81 K. The Jc of the specimen is 440 A/cm2 at 77 K. We can easily handle and arrange not only metal but also refractory materials. By adopting a multi-axis robot and a surface treatment laser technique, the laser spraying method described here makes it possible to produce highly functional and three dimensional parts of devices directly from raw powder materials. Thus the proposed method will open the path to an unexplored field of key production technology.