Parasitic Resistance
====================

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

.. list-table::
   :header-rows: 1

   * - #
     - 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