The inductor of a microwave kinetic inductance (MKID) directly absorb the incoming photon, a microlens is used to focuses the light onto the inductor. Such an absorber suffers from a low absorption coefficient since most of the light is reflected on the superconductor metal. An anti-reflection layer can be used to lower the reflectance of the surface by creating destructive interference for the reflected light and constructive interferences for the transmitted one. Materials such as SiO2 and Ta2O5 have optical parameters almost constant over a large range of wavelength which allows an almost perfect impedance matching to be achieved. The performance of optical coatings are thickness sensitive and we present simulations results to tune the thickness of the different layers to optimize the absorption into the detectors. We show that a bi-layer of SiO2/Ta2O5 (thickness 98nm/49nm) deposited on top of the PtSi inductor increases the absorption by 30 percent points between 400-1400 nm. We present data of the absorption of PtSi films coated with SiO2/Ta2O5 measured with a spectrometer and finally we give details on the anti-reflection coating deposition and on the integration of this layer into the fabrication process of our 20,000 pixels MEC arrays.
|Less than 5 years of experience since completion of Ph.D||Y|
|Student (Ph.D., M.Sc. or B.Sc.)||N|