  We report first results of laboratory tests of Si:As blocked-impurity-band
(BIB) mid-infrared (4 to 28 um) detectors developed by IMEC. These prototypes
feature 88 pixels hybridized on an integrated cryogenic readout electronics
(CRE). They were developed as part of a technology demonstration program for
the future DARWIN mission. In order to be able to separate detector and readout
effects, a custom build TIA circuitry was used to characterize additional
single pixel detectors. We used a newly designed test setup at the MPIA to
determine the relative spectral response, the quantum efficiency, and the dark
current. All these properties were measured as a function of operating
temperature and detector bias. In addition the effects of ionizing radiation on
the detector were studied. For determining the relative spectral response we
used a dual-grating monochromator and a bolometer with known response that was
operated in parallel to the Si:As detectors. The quantum efficiency was
measured by using a custom-build high-precision vacuum black body together with
cold (T ~ 4 K) filters of known (measured) transmission.
