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WHY BRIDGES
Tying the ground together
Split grounds
Lines cut the ground plane into pieces.
Unwanted modes
Slotline modes and floating islands steal energy.
Airbridges
Small arches tie the ground pieces together.
Bridges keep the ground plane one piece.
FABRICATION
Building an airbridge
Scaffold
A resist block, reflowed into a hump.
Metal
Aluminium deposited over it and patterned.
Release
Dissolving the resist leaves a free arch.
A temporary scaffold makes a permanent bridge.
CROSSTALK
Keep signals in their own lines
Leakage
A pulse for one qubit nudges another.
Distance
Helps, but chip area is precious.
Shielding
A grounded strip stitched with bridges.
Good layout keeps every pulse where it belongs.
MECHANICS
How long can a bridge be?
Sag
Grows steeply with span.
Thickness
Thicker metal is stiffer.
Collapse
A sagging bridge can short the line below.
Even a quantum chip has to obey mechanics.
PLACEMENT
Bridge or no bridge?
Stitching
Along long lines that split the ground.
Crossovers
Where one line must cross another.
Islands
Wherever a ground patch would float.
Bridges are small, but a large chip needs thousands.
UNIT 26 STUDY COMPLETE
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Ready for the Fab Challenge?
You've seen why grounds need stitching, built an airbridge, isolated two lines, designed a sturdy bridge and placed bridges on a chip.