Alan P. Constant

Superhard self-lubricating AlMgB14 films for microelectromechanical devices

Performance and reliability of microelectromechanical system (MEMS) components can be enhanced dramatically through the incorporation of protective thin-film coatings. Current-generation MEMS devices prepared by the lithographie-galvanoformung-abformung (LIGA) technique employ transition metals such as Ni, Cu, Fe, or alloys thereof, and hence lack stability in oxidizing, corrosive, and/or high-temperature environments. Fabrication of a superhard self-lubricating coating based on a ternary boride compound AlMgB14 described in this letter has great potential in protective coating technology for LIGA microdevices. Nanoindentation tests show that the hardness of AlMgB14 films prepared by pulsed laser deposition ranges from 45 GPa to 51 GPa, when deposited at room temperature and 573 K, respectively. Extremely low friction coefficients of 0.04–0.05, which are thought to result from a self-lubricating effect, have also been confirmed by nanoscratch tests on the AlMgB14 films. Transmission electron microscopy st...

Microstructure evolution of Al–Mg–B thin films by thermal annealing

The growth of Al–Mg–B thin films on SiO2/Si(100) substrates was performed by nanosecond pulsed laser deposition at three different substrate temperatures (300 K, 573 K, and 873 K). The as-deposited films were then annealed at 1173 K or 1273 K for 2 h. X-ray photoelectron spectroscopy, x-ray diffraction (XRD), and atomic force microscope were employed to investigate the effects of processing conditions on the composition, microstructure evolution, and surface morphology of the Al–Mg–B films. The substrate temperatures were found to affect the composition of as-deposited films in that the Mg content decreases and C content increases at higher substrate temperatures, in particular for the 873 K-deposited film. XRD results show that the as-deposited films were amorphous, and this structure may be stable up to 1173 K. Annealing at 1273 K was found to fully crystallize the room temperature and 573 K-deposited Al–Mg–B films with the formation of the polycrystalline orthorhombic AlMgB14 phase, accompanied by the ...

Electrical transport in amorphous semiconducting AlMgB14 films

The electrical transport properties of semiconducting AlMgB14 films deposited at room temperature and 573K are reported in this letter. The as-deposited films are amorphous, and they exhibit high n-type electrical conductivity, which is believed to stem from the conduction electrons donated by Al, Mg, and/or Fe impurities in these films. The film deposited at 573K is less conductive than the room-temperature-deposited film. This is attributed to the nature of donor or trap states in the band gap related to the different deposition temperatures.

Observation of the phase formation in Fe–N films deposited by reactive pulsed laser deposition

Fe–N films have been grown on SiO2/Si(100) substrates by reactive pulsed laser deposition (PLD). A series of films was deposited at 20 °C and at 250 °C, with a wide range of nitrogen pressures. Both nitrogen pressure and deposition temperature were found to affect the film average compositions, structures, phase percentages, and magnetic properties of the films. The saturation magnetization of the films is shown to depend not only on their average nitrogen content but also on the phases and their relative amounts that make up the films. In particular, the iron nitrides γ′-Fe4N, and e-Fe3N (which has a wide range of composition) play a major role in determining the magnetization. Results can be understood in terms of the relative contributions of the deposition rate and atomic surface diffusion in producing thin-film structure. To date, no giant moments larger than Ms of pure Fe have been observed in this investigation.Fe–N films have been grown on SiO2/Si(100) substrates by reactive pulsed laser deposition (PLD). A series of films was deposited at 20 °C and at 250 °C, with a wide range of nitrogen pressures. Both nitrogen pressure and deposition temperature were found to affect the film average compositions, structures, phase percentages, and magnetic properties of the films. The saturation magnetization of the films is shown to depend not only on their average nitrogen content but also on the phases and their relative amounts that make up the films. In particular, the iron nitrides γ′-Fe4N, and e-Fe3N (which has a wide range of composition) play a major role in determining the magnetization. Results can be understood in terms of the relative contributions of the deposition rate and atomic surface diffusion in producing thin-film structure. To date, no giant moments larger than Ms of pure Fe have been observed in this investigation.

Thin film transistors on polyimide substrates

Abstract The properties of individual inverted gate, thin film transistors (TFT) with a range of channel width to length from 2/2 to 4780/4 fabricated on 5 μm thick polyimide substrates have been investigated. In addition to the room temperature properties, the effects of illumination, bias stress and temperature have been measured. The current as a function of voltage of the TFTs scale linearly with transistor size and the threshold voltages are independent of size. Illumination of the transistors increases the off current and decreases the threshold voltage. Gate characteristics were determined for transistors before and after a bias stress of V GS =20 V for t =10, 10 2 , 10 3 and 10 4 s. The threshold voltage shifted to larger voltages and the on/off ratio decreased with application time. Gate and transfer characteristics of the TFTs were measured every 25°C from 25°C to 125°C. The threshold voltages decreased with increasing temperature while field effect mobilities increased.

Thin Film Transistors based on Microcrystalline Silicon on Polyimiide Substrates

This study reports on the fabrication of inverted gate TFT devices and circuits using a low temperature microcrystalline silicon deposition process compatible with polyimide substrates. Results from the electrical and material characterization of μ-Si:H based TFTs are presented. Device performance is compared with that of α-Si:H based TFTs constructed on polyimide. Results indicate that the anticipated improvement in device performance due to an increase in the α-Si:H Hall mobility (~10 cm 2 /V-sec) over that of α-Si:H (~1 cm 2 /V-sec) is not realized. Properties of μ-Si:H films are related to deposition parameters.