  The separation and optimization of noise components is critical to
microwave-kinetic inductance detector (MKID) development. We analyze the effect
of several changes to the lumped-element inductor and interdigitated capacitor
geometry on the noise performance of a series of MKIDs intended for
millimeter-wavelength experiments. We extract the contributions from two-level
system noise in the dielectric layer, the generation-recombination noise
intrinsic to the superconducting thin-film, and system white noise from each
detector noise power spectrum and characterize how these noise components
depend on detector geometry, material, and measurement conditions such as
driving power and temperature. We observe a reduction in the amplitude of
two-level system noise with both an elevated sample temperature and an
increased gap between the fingers within the interdigitated capacitors for both
aluminum and niobium detectors. We also verify the expected reduction of the
generation-recombination noise and associated quasiparticle lifetime with
reduced inductor volume. This study also iterates over different materials,
including aluminum, niobium, and aluminum manganese, and compares the results
with an underlying physical model.

Instrumentation and Methods for Astrophysics;Instrumentation and Detectors