← Back to Path
1 / 6
SHADOW EVAPORATION
Make a junction with a shadow
The bridge
Suspended resist casts a shadow.
Two angles
Evaporate, oxidise, evaporate again.
One pump-down
The barrier never sees air.
A clever geometry makes a nanometre barrier without patterning it.
GEOMETRY
Aim the overlap
Shift
h · tan θ for each evaporation.
Overlap
2h · tan θ minus the bridge width.
Target
About 0.2 µm.
Resist thickness and angle matter as much as the mask.
OXIDATION
Grow the tunnel barrier
Exposure
Oxygen pressure × time.
Self-limiting
Thickness grows only slowly with exposure.
Resistance
Rn = (resistance × area) ÷ area.
Two knobs, area and oxidation, set every junction.
ALTERNATIVE
The Manhattan junction
Two crossing lines
No suspended bridge needed.
Rotate 90°
Each evaporation fills one line.
Bandage
A final layer connects the junction to the circuit.
Simpler resist, more reproducible junctions.
VARIATION
No two junctions are identical
Edge roughness
A few nanometres changes the area.
Frequency
A 2% spread in resistance gives about 1% in frequency.
State of the art
About 1 to 2% spread in resistance.
Spread is why frequency targeting needs its own step.
UNIT 24 STUDY COMPLETE
🌗
Ready for the Fab Challenge?
You've made a junction by shadow evaporation, aimed its overlap, oxidised its barrier, built a Manhattan junction and measured the spread.