Microwave kinetic inductance detectors for visible to near infrared astronomy (Conference Presentation)

Abstract

Mazin Lab at UCSB is developing MKID instrument for astronomy at near infrared, optical and ultraviolet wavelength. We use MIKDs as single photon detectors by measuring the arrival time of incoming photons with an accuracy of a few microseconds and with a relatively high energy resolution (R~10 at 1um). We fabricate kilopixels array of MKIDs and we incorporate them in our own instruments for UVOIR astronomy with the main application being exoplanets direct imaging. We present the work being made in our lab in the development and fabrication of 10 to 20k pixels arrays for the DARKNESS (Dark-speckle Near-IR Energy-resolved Superconducting Spectrophotometer) and MEC (MKID Exoplanet Camera) instruments, respectively. The 6-step fabrication process has been upgraded over the last months in order to improve the sensitivity of the arrays. The detectors are made of platinum silicide (PtSi) since MKIDs with very high internal quality factor have been successfully fabricated from this material. Furthermore, PtSi with very uniform superconducting properties over 4inch substrate are much more easier to deposit than the regular TiN used in most existing MKIDs technology. Among various upgrades, we coated the PtSi sensitive area with a SiO2/Ta2O5 bi-layer in order to reduce the reflection of optical photons hitting the detectors. The light absorption is increased by a factor of 2 in the instruments bandwidth. The DARKNESS instrument has been successfully commissioned last summer and MEC, the world largest superconducting camera, is installed at the Subaru telescope since the beginning of the year. Our effort leads to the fabrication of arrays of detectors with a median internal quality factor of 100 000 with an energy resolution of 10 at 1um and a pixel yield approaching 95%. In addition, we will present new MKID design in which the conventional meander inductor and interdigitated capacitor are replaced by a square inductor and a large parallel plate capacitor made of two metal plates separated by a ~10-nm thick dielectric layer. This parallel plate design allows us to drive the MKIDs at a higher power, which in turns should increase the sensitivity of the detectors. Following promising results from our first design, second generation of parallel plate MKID devices have been made from Hf/HfO2/Nb tri-layers deposited in-sit. We obtained high quality factor from the parallel plate MKIDs and we were able to detect photons with this new MKIDs design. Another way to improve the sensitivity of MKIDs is to use a low Tc material, compared to Tc ~ 1K usually used. We fabricated MKIDs arrays with superconducting Hafnium, Tc = 450mK, and we demonstrated that resonators with very high internal quality factors Qi~300 000 and an energy resolution of 9 at 808nm can be achieved.