The suitability of reactive ion etching for the fabrication of microelectro mechanical systems (MEMS) has been evaluated by characterizing the change of lateral dimensions versus depth in etching deep structures in silicon. Fluorine, chlorine, and bromine containing gases have provided the basis for this investigation. A conventional planar RIE (reactive ion etching) reactor has been used, in some cases with magnetic field enhancement or an inductive coupled plasma source and low substrate temperature. For RIE based on Cl2 or Cl2/HBr plasma a slightly ‘‘positive’’ (top wider than bottom) slope is achieved when etching structures with a depth of several 10 μm, whereas a ‘‘negative’’ slope is obtained when etching with an SF6 /CCl2F2-based plasma. A pattern transfer with vertical walls is obtained for RIE based on SF6 (with O2 added) when maintaining the substrate at low temperature (≊−70 °C). Further optimization of plasma chemistries and RIE procedures should result in runouts on the order of 0.1/100 μm depth in Si as well as in organic materials.

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Electronic noses based on polymer‐like carbon nitride (CNx) are investigated by these authors. The gas‐sensing properties of CNx are examined, focusing on the detection of humidity and ammonia. Two basic types of gas sensor—capacitance and microelectromechanical (see Figure)—are discussed. It is found that the sensors are highly sensitive, stable, and have short response and recovery times.

An energy-resolving quadrupole mass spectrometer (E-QMS) was assembled underneath the powered electrode of a diode reactive ion etcher. The plasma ions reach the E-QMS through an orifice in the powered electrode with a diameter of 100 μm. The ion energy distributions (IEDs) of ionic species from SF6 plasmas in the pressure range of 0.1–1.5 Pa for dc bias potentials between 50 and 300 V and a rf of 13.56 MHz were investigated. The IEDs always show a saddle shaped peak at an energy corresponding to a total potential drop across the sheath given by USh=Udc+UP, where Udc is the dc bias potential and UP is the time averaged plasma potential. In the energy range from 0 eV to eUdc there are multiple peaks in the IEDs of SF+x (x=1..5), whereas the F+, F+2, and S+ IEDs show only a single peak in this range. These peaks are the result of ion generating collisions in the sheath. On pressure variation the IEDs do not change significantly. We also measure IEDs of negative ions. The IEDs of these ions show a broad distribution with an intensity maximum appearing at the half of UP and a width corresponding to max[UP(t)], where UP(t) is the time varying plasma potential. These correlations suggest that these ions originate from the plasma bulk.

We report on the performance of a measurement system for the recognition of individual analytes and their binary mixtures which is based on a multiarray of four micromachined silicon cantivelers actuated at their resonance frequency. The cantilevers have been functionalized by organic polymers [polydimethylsiloxane (PDMS) and polyvinylpyridine (PVP)] and amorphous nitrogen-rich carbon nitride films. We found that the sensitivity and selectivity of the cantilevers coated with CNx films change according to the layer thickness. Our results show that the selected combination of sensitive layers ensures a wide range of specific, reversible and reproducible sensor responses upon exposure to methanol, 2-propanol, water and their binary mixtures. Further, it was found that the differences in recovery times of PDMS and CNx films after exposure to the two alcohols and their mixtures could be used especially for low analyte concentrations as a second characteristic in addition to the resonance frequency shift for the identification of individual components in the mixtures.