  We have incorporated a single crystal silicon shunt capacitor into a
Josephson phase qubit. The capacitor is derived from a commercial
silicon-on-insulator wafer. Bosch reactive ion etching is used to create a
suspended silicon membrane; subsequent metallization on both sides is used to
form the capacitor. The superior dielectric loss of the crystalline silicon
leads to a significant increase in qubit energy relaxation times. T1 times up
to 1.6 micro-second were measured, more than a factor of two greater than those
seen in amorphous phase qubits. The design is readily scalable to larger
integrated circuits incorporating multiple qubits and resonators.
