Parasitic Resistance

Parasitic resistance checks identify unwanted ohmic paths, contacts, vias, and interconnect losses before superconducting operation.

#	Parameter	Symbol / Unit	Extraction Method	Typical Q3D Value	Ideal / Optimal	Good Range	Worst Case	Why It Matters	Key Design Note
21	Series JJ Parasitic Resistance	R_ser / Ω	RF impedance spectroscopy; Q3D lead model	< 0.01 Ω	< 0.01 Ω (clean superconducting)	0.01 – 0.1 Ω	> 1 Ω	Quasiparticle conductance in JJ leads causes T₁ decay via Ohmic dissipation in qubit circuit	Quasiparticle poisoning (stray radiation) transiently raises R_ser; shielding critical at mK
22	Shunt Parasitic Resistance (R_p)	R_p / kΩ	Q3D G matrix → R_p = 1/G_ii	> 1 MΩ	> 1 MΩ (effectively open)	100 kΩ – 1 MΩ	< 10 kΩ	Parallel leakage path across qubit capacitor reduces effective Q = R_p·√(C/L)	Substrate residues from lithography are the most common cause; requires thorough O₂ plasma clean
23	Wirebond / Bump Resistance	R_wb / mΩ	4-probe TDR; Q3D bond-wire cylinder model	< 5 mΩ per bond	< 5 mΩ	2 – 20 mΩ	> 100 mΩ	Parasitic series resistance contributes to insertion loss and thermal noise at 4K	Au–Au thermo-compression bonds have lower and more repeatable R_wb than Al wedge bonds
24	Metal Interface Contact Resistance	R_c / mΩ	TLM structure measurement; Q3D metal stack	< 1 mΩ (clean Al–Al)	< 1 mΩ	1 – 10 mΩ	> 50 mΩ	Interface resistance at Al–Au and Al–Nb transitions is critical in 3D integration	Native Al₂O₃ (2–4 nm) must be removed by Ar ion milling before deposition for low R_c