  We have fabricated an array of subgap kinetic inductance detectors (SKIDs)
made of granular aluminum ($T_c\sim$2~K) sensitive in the 80-90 GHz frequency
band and operating at 300~mK. We measure a noise equivalent power of
$1.3\times10^{-16}$~W/Hz$^{0.5}$ on average and
$2.6\times10^{-17}$~W/Hz$^{0.5}$ at best, for an illuminating power of 50~fW
per pixel. Even though the circuit design of SKIDs is identical to that of the
kinetic inductance detectors (KIDs), the SKIDs operating principle is based on
their sensitivity to subgap excitations. This detection scheme is advantageous
because it avoids having to lower the operating temperature proportionally to
the lowest detectable frequency. The SKIDs presented here are intrinsically
selecting the 80-90 GHz frequency band, well below the superconducting spectral
gap of the film, at approximately 180 GHz.
