  Kinetic inductance detectors (KIDs) show promise as a competitive technology
for astronomical observations over a wide range of wavelengths. We are
interested in comparing the fundamental limitations to the sensitivity of KIDs
with that of transition edge sensors (TESs) at millimeter wavelengths,
specifically over the wavelengths required for studies of the Cosmic Microwave
Background (CMB). We calculate the total fundamental noise arising from optical
and thermal excitations in TESs and KIDs for a variety of bath temperatures and
optical loading scenarios for applications at millimeter wavelengths. Special
consideration is given to the case of ground-based observations of 100 GHz
radiation with a 100 mK bath temperature, conditions consistent with the
planned second module of the QUBIC telescope, a CMB instrument. Under these
conditions, a titanium nitride KID with optimized critical temperature pays a
few percent noise penalty compared to a typical optimized TES.
