  We present a superconducting qubit design that is fabricated in a 2D geometry
over a superconducting ground plane to enhance the lifetime. The qubit is
coupled to a microstrip resonator for readout. The circuit is fabricated on a
silicon substrate using low loss, stoichiometric titanium nitride for capacitor
pads and small, shadow-evaporated aluminum/aluminum-oxide junctions. We observe
qubit relaxation and coherence times ($T_1$ and $T_2$) of 11.7 $\pm$ 0.2 $\mu$s
and 8.7 $\pm$ 0.3 $\mu$s, respectively. Calculations show that the proximity of
the superconducting plane suppresses the otherwise high radiation loss of the
qubit. A significant increase in $T_1$ is projected for a reduced
qubit-to-superconducting plane separation.
