Noise and sensitivity of aluminum kinetic inductance detectors for sub-mm astronomy

Kinetic inductance detectors are based upon high Q superconducting resonators. We have measured the electrical Noise Equivalent Power (NEP) of 100 nm thick 1/4 lambda coplanar waveguide Aluminum resonators at 100 mK using phase readout and radius readout. We find that the phase NEP is independent of the Q factor of the resonator, limited by excess noise in the KID and given by NEP = 9 x 10(-18) W/root Hz at 100 Hz. It increases with roughly f(-0.5) at lower frequencies. The amplitude NEP is strongly Q factor dependent, limited by the setup noise, nearly frequency independent and as low as NEP = 3 x 10(-18) W/root Hz for a high Q resonator (Q = 454.000). For lower Q resonators the amplitude NEP increases to values equal to or even larger than the phase readout.