Structure Design And Fabrication Of FESE High Temperature Superconducting Nanowire Single Photon Detector

The superconducting nanowire single photon detector(SNSPD)is a quantum limit sensitive detector.Compared with traditional single-photon detectors,it has the advantages of high detection efficiency,low dark count,small time jitter,and short recovery time.So far,the superconducting materials for SNSPD system mainly have ultralow superconducting transition temperatures(Tc),and suffer from the problems including low critical current density,high dynamic inductance,small output signal amplitude,and high cost caused by low-temperature systems.These problems could be solved by developing the SNSPD system based on hightemperature superconducting materials.However,compared with low-temperature superconducting materials,the preparation process of high-temperature superconducting materials is really complicated and uncontrollable.Meanwhile,the detection efficiency of these devices could be suppressed by the high superconducting band gap voltage.Therefore,the development of high performance SNSPD based on high-temperature superconducting materials is a great challenge.In this work,the structure design and integrated preparation of the single photon detector based on FeSe superconducting nanowires were performed.The main research contents include:(1)Design of the enhanced optical absorption structure.The FeSe superconducting material layer in the superconducting nanowire single-photon detector is quite thin and exhibits poor optical absorption performance,leading to low detection efficiency of the detector.In this work,the structure for enhancing the optical absorption of SNSPD based on FeSe/STO materials were designed.Taking into account the process compatibility,the structure modeling of anti-reflective layer,meta-surface,optical resonant cavity,surface plasmon micro-nano structure was proposed.The optical simulations based on FDTD software were conducted and the structure parameters were optimized.As expected,the peak optical absorption efficiency at 1550 nm was enhanced to 78%.(2)Design and optimization of the fabrication process compatibility for FeSe superconducting nanowire device.Because FeSe superconducting material exhibits poor stability in the atmosphere,it is difficult to be compatible with traditional micronano fabrication technology.Therefore,the fabrication of FeSe superconducting nanowire meet a big challenge.In this work,the FeSe superconducting nanowire device process route and process compatibility optimization design were carried out.By reducing the exposure time of FeSe materials,preparing an insulating protective layer,and improving the de-glue process,the superconductivity of FeSe materials after nanowire processing and device integration is guaranteed.It is found that the device remains in the atmosphere for one month and still maintains good superconducting properties.Then,the mask with larger protective layer area was optimized,further improving the stability and working life of the device.In addition,in order to avoid the direct micro-processing of the FeSe film,the nanowire pattern was pre-etched on the STO substrate,on which the FeSe layer could be epitaxially grown.This is an effective strategy to fabricate FeSe nanowire detection structure with high stability.