Fabarication process and noise properties of antenna- coupled microbolometers based on superconducting YBCO films

摘要

An analysis of how the detectivity and lifetimedepend on the fabrication process of Superconducting antenna-coupled microbolometers has been carried out. The temperaturedependences of responsivity and noise equivalent power (NEP)have been estimated in terms of the thermal model. To reveal themain degradation mechanism, 1/f-noise characterization has beenused. Monte-Carlo simulation of the annealing procedure ofYBa_2Cu_3O_7 (YBCO) films for the operating ranges offrequency and temperature has shown that prevailing sources offlicker noise in superconducting microstrips are associated withtransitions of oxygen atoms situated close to low-angleboundaries of the film blocks. The magnetron sputteringtechnique has been optimized to reduce the Hooge parameter forflicker noise to a record-breaking low value for YBCO films ofabout 10~(-4) at 93 K. Comparative analysis of chemical, ionand laser etching techniques by low-temperature scanningelectron microscopy and magneto-optics allowed the fabricationof microstrips with uniform current distribution characterized bycritical current density higher than 10~6 A cm~(-2) at 77 K andlong-time stability. The process of low-energy ion milling ofYBCO films with an Ar~+ beam generated in a duopigatron ionsource was used to reach a width resolution at the topology edgebetter than 0.2 #mu#m. The antenna-coupled bolometersfabricated from the superconducting microstrips were used toregister microwave radiation at a frequency of 70.3 GHz andtemperature of 93 K. It is demonstrated that the developedtechnology makes possible the fabrication of long-lived YBCO-based antenna microbolometers with electrical NEP_e = 1.5 X10~(-12) W Hz~(-1/2). The calculated response time of theantenna is about 3-l50 ns. Further development is associated withfabrication of coupling microbolometers with immersed lens,with predicted optical detectivityD*= (4 X 10~9-4 X 10~(10)) cm Hz~(1/2) W~(-1) in thewavelength range 100-1000 #mu#m.