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that will be used in the later fabrication steps. During processing, the features
on the mask will be reduced by a factor of 5 when they are transferred to the
wafer. Since the smallest features in our design are on the length scales of 1 µm,
the “printing” of the masks is somewhat involved and requires a specialized maskwriter.
It uses a laser or shuttered light source to create the pattern rather than
a simple ink-jet or thermo-transfer printer, which is sufficient for feature sizes of
10’s to 100’s of µms.
5.2 Fabrication Overview
The basic qubit design consists of five layers that are defined in seven lithography
steps. The bottom layer, the “Base Wiring” layer, contains aluminum traces
that define most of the electrical connections in the circuit. This layer is covered
by an “Insulator” layer followed by another wiring layer, the “Top Wiring” layer.
Vias (holes) in the insulator layer allow for electrical connections between the base
and the top wiring layers. Up to here, the qubit design very closely resembles a
miniaturized two-layer printed circuit board. The fourth layer, called the “Junction
Dielectric” layer, is a very thin oxide layer on top of the top wiring layer.
This layer is capped with the “Junction Wiring” layer, another aluminum layer
that provides the electrical counter-contact to the junctions. Overall, these five
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