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In this paper, we report on the microstructural and magnetic properties of CrxAl1-xN thin films with Cr concentrations ranging up to x=(8.5 ± 0.5) at. %. The thin films are sputter deposited on silicon substrates and exhibit a wurtzite type microstructure verified by X-ray diffraction measurements. A vibrating sample magnetometer based measurement equipment is used to investigate magnetic properties of the Cr doped thin films in a temperature range of T=10 K-300 K, revealing a paramagnetic behavior. With increasing temperature, the temperature independent diamagnetic contribution of the substrate material dominates the overall response characteristics. No room temperature ferromagnetism is observed for all samples investigated. [ABSTRACT FROM AUTHOR]

This paper presents a novel analogue Q-control circuit. A self-actuated and self-sensing piezoelectric microstructure in combination with a lock-in amplifier is used to provide a feedback signal with a substantially reduced noise level. This DC-value being proportional to the piezoelectric current is multiplied with a carrier sinusoidal signal on a custom-designed analogue printed circuit board applying an analogue amplifier IC. With this generated analogue feedback signal a complete analogue Q-control circuit is realized enabling faster response and as a consequence measurement cycles are less time consuming. Using this proposed Q-control technique, the Q-factor is increased from 397 to about 8,537 in air without pushing the feedback loop circuitry to stability limits. We believe that these promising results will stimulate further activities for a reliable on-line monitoring of even highly viscous liquids in the near future. [ABSTRACT FROM AUTHOR]

This paper presents a robust g-control approach based on an all-electrical feedback loop enhancing the quality factor of a resonant microstructure by using the self-sensing capability of a piezoelectric thin film actuator made of aluminium nitride. A lock-in amplifier is used to extract the feedback signal which is proportional to the piezoelectric current. The measured real part is used to replace the originally low-quality and noisy feedback signal to modulate the driving voltage of the piezoelectric thin-film actuator. Since the lock-in amplifier reduces the noise in the feedback signal substantially, the proposed enhancement loop avoids the disadvantage of a constant signal-to-noise ratio, which an analogue feedback circuit usually suffers from. The quality factor was increased from the intrinsic value of 1766 to a maximum of 34 840 in air. These promising results facilitate precise measurements for self-actuated and self-sensing MEMS cantilevers even when operated in static viscous media. [ABSTRACT FROM AUTHOR]

Abstract: Aluminium nitride (AlN) reactively sputter-deposited from an aluminium target is an interesting piezoelectric thin film material with high CMOS compatibility. A good c-axis orientation is essential for obtaining high piezoelectric coefficients. Therefore, the influence of different sputtering conditions on the microstructure of AlN thin films with a typical thickness of about 500nm was investigated. In this study it is demonstrated that highly c-axis oriented AlN thin films can be deposited on nominally unheated (100) silicon substrates, most preferentially when using a pure nitrogen atmosphere. The degree of c-axis orientation increases with higher nitrogen concentration and with decreasing the sputtering pressure, whereas the influence of plasma power on the microstructure was found to be negligible. A low sputtering pressure is also useful for minimizing the amount of oxygen contaminations in the deposition chamber and hence for reducing the incorporation of impurities into the AlN films. Intrinsic stress values of AlN thin films were determined by wafer bow measurements and were found to be between −3.5 and 750MPa depending on choice of deposition parameters. Finally, the piezoelectric coefficients d 33 and d 31 were determined experimentally by laser scanning vibrometry in conjunction with a theoretical model. Effective values in c-axis oriented 500nm films with FWHM of 0.33° are 3.0 and −1.0pm/V. For a film of 2.4μm thickness, values of 5.0 and −1.8pm/V were measured, which are near the bulk values. [Copyright &y& Elsevier]

Abstract: In this work, the influence of sputter conditions and film thickness on both the morphology and the resistivity of tantalum (Ta) thin films will be investigated. Glass wafers were used as substrates. With increasing back pressure level ranging from 0.3 to 6 Pa at a fixed plasma power of 100 W, the microstructure changes from a dense to an open porous characteristics. At a moderate back pressure level of 0.9 Pa, the stable α-phase is detected when the film thickness exceeds a value of about 1.3 µm. Besides the impact of phase composition, the microstructure influences in addition the electrical performance of the Ta films. Therefore, the room-temperature resistivity can be varied within two orders of magnitude by applying different parameters for film deposition. [Copyright &y& Elsevier]

In micro-/nanomachined devices and systems, aluminum nitride (AlN) thin films are widely used due to their piezoelectric properties. This work evaluates the potential of modifying the interface between the AlN thin film and the silicon (Si) wafer serving as bottom electrode for optimized crystallographic orientation and, hence, improved electrical and piezoelectric properties. The films were analyzed using temperature-dependant leakage current measurements, transmission electron microscopy, and x-ray diffraction. By preconditioning of the Si substrate surface applying sputter etching prior to film deposition, leakage current levels are substantially decreased and an increased (002) orientation of the AlN grains is observed. [ABSTRACT FROM AUTHOR]

In the field of MEMS, aluminum nitride (AlN) in the wurtzite phase is an important functional material due to its piezoelectricity. To further enhance device performance, transition metal alloying of AlN is proposed to achieve a higher piezoelectric response. In this work, the effect of moderate chromium (Cr) doping (up to x = (5.0 ± 0.6) at.%) as well as the influence of changing deposition pressures and gas composition are investigated, focusing on the microstructure, morphology and piezoelectric response of sputter deposited Cr x Al 1 −x N thin films. X-ray diffraction analyses reveal a wurtzite type structure with highest degree in c-axis orientation for lowest deposition pressures and Cr concentrations. With increasing deposition pressure, a deterioration in crystal quality and the formation of other crystal orientations within the films are observed. The presence of crystallite orientations away from the 〈002〉 orientation is linked to the presence of randomly oriented, conical-shaped grains which are embedded in the fine grainy thin film surface topography as indicated by atomic force microscopy. By using piezo force microscopy, these grains are identified to cause a reduction in the effective piezoelectric response. Furthermore, we show that combining both the analysis of orientation distribution and surface morphology, is by far more reliable for estimating the piezoelectric response of thin films than the sole use of one method. [ABSTRACT FROM AUTHOR]

Abstract: In this study film properties of sputter-deposited tantalum nitride (TaN x ) thin layers are investigated focusing on the impact of substrate properties, varying nitrogen content for film synthetization as well as post-deposition annealings in the temperature range up to 500°C. For comparison, these investigations are done on low temperature co-fired ceramics and on silicon based substrates whereas the latter approach ensures defined and well-known surface properties. Furthermore, results on the phase evolution with high temperature annealings are presented showing a transformation of Ta4N to Ta2N in the temperature range between 350°C and 500°C. With increasing nitrogen content (i.e. nitrogen flow during film deposition) in the TaN x layers the topography shows first an increase in surface roughness, next a range where a smoothing of the surface characteristics is observed, and finally buckling and the existence of grain agglomerates. All these analyses are further evaluated with electrical measurements on the film resistivity and on the oxidation behaviour to gain deeper insight into material parameters relevant for micromachined devices which are operated under harsh environmental conditions. [Copyright &y& Elsevier]