ā Back to Path
1 / 6
STACKING
A flip-chip processor
Qubit chip
Turned face-down, kept clean.
Wiring chip
Carries the control and readout lines.
Bumps
Superconducting indium joins the two.
Going vertical separates qubits from wiring.
THE PROBLEM
Running out of edge
Area
Qubits grow as nĀ².
Edge
Bond pads grow only as n.
The answer
Bring signals in vertically.
Two-dimensional wiring can't keep up with qubit counts.
BUMP BONDS
Bonding two chips together
Indium
Soft, and superconducting below 3.4 K.
Alignment
About a micrometre.
Gap
Set by the bump height.
Soft metal makes a superconducting joint.
VIAS
Through-silicon vias
Deep etch
The Bosch process drills straight holes.
Coating
Superconducting walls, top to bottom.
Two jobs
Carry signals and tie grounds together.
Vias turn a chip into a three-dimensional circuit.
BOX MODES
When the chip itself rings
Big chips
Ring at lower frequencies.
Danger
A mode in the 4 to 8 GHz band steals qubit energy.
The fix
Via fences split the chip into small cells.
Big processors need vias and bumps everywhere.
UNIT 27 STUDY COMPLETE
š§±
Ready for the Fab Challenge?
You've explored a flip-chip stack, run out of chip edge, bump-bonded two chips, drilled through-silicon vias and tamed box modes.