TiN nanobridge Josephson junctions and nanoSQUIDs on SiN-buffered Si

We report the fabrication and properties of titanium nitride (TiN) nanobridge Josephson junctions (nJJs) and nanoscale superconducting quantum interference devices (nanoSQUIDs) on SiN-buffered Si substrates. The superior corrosion resistance, large coherence length, suitable superconducting transition temperature and highly selective reactive ion etching (RIE) of TiN compared to e-beam resists and the SiN buffer layer allow for reproducible preparation and result in long-term stability of the TiN nJJs. High-resolution transmission electron microscopy reveals a columnar structure of the TiN film on an amorphous SiN buffer layer. High-resolution scanning electron microscopy reveals the variable thickness shape of the nJJs. A combination of wet etching in 20% potassium hydroxide and RIE is used for bulk nanomachining of nanoSQUID cantilevers. More than 20 oscillations of the V(B) dependence of the nanoSQUIDs with a period of similar to 6 mT and hysteresis-free I(V) characteristics (CVCs) of the all-TiN nJJs are observed at 4.2 K. CVCs of the low-I (c) all-TiN nJJs follow theoretical predictions for dirty superconductors down to similar to 10 mK, with the critical current saturated below similar to 0.6 K. These results pave the way for superconducting electronics based on nJJs operating non-hysteretically at 4.2 K, as well as for all-TiN qubits operating at sub-100 mK temperatures.