  The most developed integrated receivers for THz radiation nowadays are based
on Josephson junction SIS devices. In this kind of devices, the highest
receivable frequency is determined by the energy gap of the superconducting
electrodes and limited to approximately 700 GHz in case of Nb/AlOx/Nb
multilayers. We have developed a technology for NbN/AlN/NbN Josephson junctions
on sapphire substrates which allow operation at frequencies above 1 THz. The
trilayers are deposited in-situ in a 3-chamber DC-magnetron sputtering system
at temperatures as high as 775 {\deg}C. Each layer is reactively sputtered in
an argon and nitrogen atmosphere. By variation of the partial gas pressures and
discharge current of the plasma, optimum deposition conditions for the
tri-layers were found. So far, gap voltages as high as 5.1 mV at 4.2 K have
been achieved which allows the operation frequency of the JJ devices to exceed
1 THz.
