Vacuum wafer bonding technology provides a number of very effective techniques to produce low-cost, hermetic sealed packages for micromachined sensors and actuators. Beside the protection of the device from outside environmental stresses, the package must also provide a cavity ambient compatible with the device performance and reliability. The paper reviews the shortcomings of existing fine leak tests to assess the stability of the cavity atmosphere over long time. A new ultra-fine leak test based on Q-factor monitoring was developed that has the potential to be used for in-line critical leak rate testing on wafer level before device singulation. With the example of a poly-silicon resonating microsensor, it is shown that the test is sensitive enough to predict the cavity pressure for a demanded device lifetime of 15 years. The role of an integrated thin film getter in stabilizing the cavity vacuum and extending device lifetime is discussed.

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Selectively n-doped Al x Ga 1−x As/GaAs heterostructures with an additional p-type doped GaAs compensation layer on top were prepared by solid-source molecular beam epitaxy. If properly designed, these layer-compensated heterostructures are not conducting with the compensation layer present, whereas a two-dimensional electron gas (2DEG) is formed at the heterointerface if the compensation layer is removed. This makes the material well suited as a base material for nanolithography because lateral patterning of the compensation layer results in a laterally structured 2DEG. We found by simulation as well as experimentally that the n-type delta doping concentration is very critical and has to be correct within ±15% to obtain properly compensated heterostructures. For the non-compensated case, i.e. with the compensation layer removed, electron densities up to 4.3 × 10 11 cm −2 before illumination and 9 × 10 11 cm −2 after illumination have been achieved in structures that are insulating with a compensation layer. The obtained electron mobilities in the 2DEG are high, reaching a maximum value of 1.1 × 10 6 cm 2 V −1 s −1 at 4.2 K after illumination.

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