  Tantalum and aluminum on sapphire are widely used platforms for qubits of
long coherent time. As quantum chips scale up, the number of Josephson
junctions on Sapphire increases. Thus, both the uniformity and stability of the
junctions are crucial to quantum devices, such as scalable superconducting
quantum computer circuit, and quantum-limited amplifiers. By optimizing the
fabrication process, especially, the conductive layer during the electron beam
lithography process, Al/AlOx/Al junctions of sizes ranging from 0.0169 to 0.04
{\mu}m2 on sapphire substrates were prepared. The relative standard deviation
of room temperature resistances (RN) of these junctions is better than 1.7% on
15 mmx15 mm chips, and better than 2.66% on 2 inch wafers, which is the highest
uniformity on sapphire substrates has been reported. The junctions are robust
and stable in resistances as temperature changes. The resistances increase by
the ratio of 9.73% relative to RN as the temperature ramp down to 4K, and
restore their initial values in the reverse process as the temperature ramps
back to RT. After being stored in a nitrogen cabinet for 100 days, the
resistance of the junctions changed by1.16% in average. The demonstration of
uniform and stable Josephson junctions in large area paves the way for the
fabrication of superconducting chip of hundreds of qubits on sapphire
substrates.
