Ion-beam deposition of NbNxCythin films for microelectronic applications

We have fabricated high quality superconducting NbN
x
C
y
thin films using a low-energy dual ion-beam fabrication method. In this method, one ion beam sputters Nb to the substrate while the second beam bombards the growing film with low energy (∼100 eV) N
2
+CH
4
ions. The use of methane as a source of carbon is essential for this method. NbN
x
C
y
thin films fabricated in this way have T
c
up to 13.2K, resistivity
\sim80-120 \mu\Omega
cm, residual resistance ratio ∼1.0 and calculated magnetic penetration depths <285 nm. These films are deposited on Si wafers which are not intentionally heated or cooled. Electronic tunneling studies indicate that these films are strong coupled superconductors (
2\Delta/kT_{c} \leq 4.0
) with superconducting energy gaps up to 2.43 meV. NbN
x
C
y
/native oxide/Pb-alloy Junctions have properties suitable for SIS mixer applications.