  We have recently found in insulating granular Al thin film a new experimental
feature (Delahaye et al., Phys. Rev. Lett. 106, 186602, 2011), namely the
existence of a conductance relaxation that is not sensitive to gate voltage
changes. This conductance relaxation is related to the existence of a
metallic-like screening in the film and can be used to estimate its
characteristic length scale. In the present paper, we give some experimental
details on how this feature was measured and present our first results on the
screening length temperature dependence.
