Final Report Summary - ASCEND (Advanced SuperConducting devices for ENhanced infrared Detection (ASCEND))
The objectives and milestones of the proposed research plan for the project ASCEND 327846 (Annex I part B of the Grant Agreement) are:
Objectives:
1. To develop next generation single pixel superconducting nanowires single photon detecrors (SNSPDs) with large active area and high quantum efficiency via optical cavity and parallel nanowire designs.
2. To integrate, for the first time, multiple detectors into a practical arrayed infrared receiver system with large active area for use in advanced imaging, communication, and remote sensing applications.
Milestones:
M1 Source of high quality superconducting thin films established.
M2 Testing of first batch of single pixel SNSPDs completed.
M3 Realization of optimized single pixel SNSPDs with areas up to 50 μm x 50 μm.
M4 Realization of first generation 2x2 array with area up to 100 μm x 100 μm.
M5 Implementation of a robust readout scheme for SNSPD arrays
M6 Realization of second generation optimized 4 x 4 SNSPD arrays with imaging capability and areas up to 200 μm x 200 μm.
M7 Demonstration of SNSPDs arrays with imaging capability in advanced photon counting applications.
The main work performed to accomplish the objectives of the project was focused on:
Optimization of the Electron Beam Lithography (EBL) process:
Since the beginning of the project, I worked on the development and optimization of the process to realize SNSPDs using superconducting thin Nb, NbN, NbTiN and MoSi films. This involves a double step of EBL, a metal sputtering deposition and a reacting ion etching (RIE). At the end of the optimization I was able to routinely fabricate SNSPDs using nanowires having width of 60 - 70 nm, spaced each other by 90 nm, with a very good uniformity.
Optimization of high quality superconducting thin films:
Since the delivery of a sputter depoisition tool for superconducting thin films to the University of Glasgow in May 2014, I worked in tandem with the PhD student Archan Banerjee to optimize the process for the fabrication of high quality thin NbN, NbTiN and MoSi films. In parallel, I also started to design the optical cavity stack to be fabricated on Si substrate to enhancing the absorption of the single mid IR photons in the superconducting 6 nm thick nanowires. The structure of choice is made by 5 bilayers of Si (270 nm)/SiO (270 nm) acting as a distributed dielectric Bragg refractor and a final layer of SiO (270 nm) behaving as a quarter wavelength cavity at 1550 nm. According to the performed simulation the absorptance of the light in the 5 nm thick NbTiN nanowires should increased from the 18% (no optical cavity) up to 90 % (with optical cavity) in the wavelength range between 1.25-1.58 μm. I commissioned the fabrication of this optical cavity structure on Si wafer to the HELIA Photonics Company (Edinburgh, UK).
Design, fabrication and characterization of SNSPD arrays:
I designed, fabricated and characterized 2x2 pixels array of SNSPDs having a coverage area of 30x30 μm2 (single pixel having area of 15x15 μm2) and 60x60 μm2 (single pixel having area of 30x30 μm2). For the first generation of 30x30 μm2 SNSPDs array, I used the 7 nm NbTiN films purchased from STAR Cryoelectronic (US) with no optical cavity. For the 60x60 μm2 area 2x2 pixels SNSPDs array I used NbTiN 5 nm thick film deposited in Glasgow on the optical cavity stack substrate. Each pixel was biased and read out individually for a “per pixel” read out scheme. From electrical/optical characterization at cryogenic temperature, the devices looked to be very uniform in fabrication and properties. These arrays are suitable for all the applications where a multimode optical or Mid Infrared fibre (50 - 60 μm core diameter) coupling is needed for high collection efficiency of the incoming light.
Development of electronic read out scheme for multipixel SNSPD arrays:
I also worked on the development of two innovative strategies for the readout of NxN SNSPDs arrays (N>2 and no per pixel bias/readout) for imaging applications.
The first approach is based on my original idea to bias/read out the single pixel SNSPDs in the array though an RF coupling of a coplanar waveguide (CPW) with the single SNSPDs pixels. This configuration would allow operation in frequency domain multiplexing of 20 or more SNSPDs pixels simultaneously using only two co-axial cables for a strong reduction of the thermal load in the cryostat. Preliminary simulation (performed in tandem with the PhD student Andrea Pizzone) and fabrication of prototype devices were accomplished. RF cryogenic characterization/measurements are expected shortly. This readout scheme is compatible with the lumped-element superconducting parametric amplifier (SC paramp) for a wideband, low noise and high dynamic range pre-amplification stage integrated on-chip. I am currently working in collaboration with the group of Prof Kent Irwin at Stanford University on the development of such SC paramp thanks to the SU2P Science Bridges Exchange scheme. The SC paramp prototype has been successfully fabricated and the RF testing in cryostat present in Stanford is expected in short time.
The second readout approach I am working on is based on the use of alternative RSFQ technology that will allow for the integration on chip with the SNSPDs array. I’m collaborating with Dr. Jane Ireland on the development of the Nanobridge SFQ-based readout technology supported by a TSB/Innovate UK Quantum Technology Feasibility Study Grant. In this approach the SFQ logic can be fabricated by using single layer of Nb or NbTiN (the same materials used for SNSPDs fabrication) and single EBL step for on-chip integration with the arrays. This grant will allow me to work for further four months, after the end of the fellowship, on the development of this technology for the time domain multiplexing of NxN SNSPDs array to be applied in imaging applications.
To summarize, during the fellowship I progressed in research activity to obtain the following achievements in line with the objectives (milestones and deliverable) of the proposed plan:
1) Deposition of high quality Superconducting thin NbN (5 nm with Tc = 12K), NbTiN (5 nm with Tc = 10.4 K) and MoSi (10 nm with Tc = 5.5 K) film (M1).
2) Patterning of superconducting thin film in high uniformity superconducting nanowires having width down to 60 nm and spacing of 90 nm for SNSPD fabrication (M2).
3) Realization and characterization of 2x2 SNSPD arrays having covering area of 30x30 μm2 and 60x60 μm2 with high performances (detection efficiency up to ~35%, timing jitter down to ~70 ps and recovery time of few ns) for multimode optical fibre coupling (M3 and M4).
4) Performed simulation and device fabricated to be tested for the development of two different electronic readout scheme for multi pixel NxN (N>2) SNSPDs array to be applied for single photon imaging applications (collaboration with Stanford University, US, and NPL, UK) (M5).
The expected final result of this project is to deliver the underpinning technology of SNSPDs arrays with imaging capability for a range of frontier research fields including secure communication, metrology, remote sensing and advanced imaging. This work holds the key to a wealth of high tech applications in industry and it is of strategic importance to future European scientific and economic competitiveness. This technology will boost not only scientific research across a wide range of disciplines but will also allow for the delivery of next generation devices to be used in real world applications with wide socio-economic impact.
Contact details:
Scientist in Charge:
Professor Robert H Hadfield FInstP
Head of Division of ENE
School of Engineering
University of Glasgow
Rankine Building, Oakfield Avenue,
Glasgow G12 8LT, UK
Tel: +44 141 330 4929
Email: Robert.hadfield@glasgow.ac.uk
Prinicipal Investigator:
Dr Alessandro Casaburi MInstP
Research Fellow
School of Engineering
University of Glasgow
Rankine Building, Oakfield Avenue
Glasgow G12 8LT (UK)
Tel: +44 141 330 3159
Email: Alessandro.Casaburi@glasgow.ac.uk
Objectives:
1. To develop next generation single pixel superconducting nanowires single photon detecrors (SNSPDs) with large active area and high quantum efficiency via optical cavity and parallel nanowire designs.
2. To integrate, for the first time, multiple detectors into a practical arrayed infrared receiver system with large active area for use in advanced imaging, communication, and remote sensing applications.
Milestones:
M1 Source of high quality superconducting thin films established.
M2 Testing of first batch of single pixel SNSPDs completed.
M3 Realization of optimized single pixel SNSPDs with areas up to 50 μm x 50 μm.
M4 Realization of first generation 2x2 array with area up to 100 μm x 100 μm.
M5 Implementation of a robust readout scheme for SNSPD arrays
M6 Realization of second generation optimized 4 x 4 SNSPD arrays with imaging capability and areas up to 200 μm x 200 μm.
M7 Demonstration of SNSPDs arrays with imaging capability in advanced photon counting applications.
The main work performed to accomplish the objectives of the project was focused on:
Optimization of the Electron Beam Lithography (EBL) process:
Since the beginning of the project, I worked on the development and optimization of the process to realize SNSPDs using superconducting thin Nb, NbN, NbTiN and MoSi films. This involves a double step of EBL, a metal sputtering deposition and a reacting ion etching (RIE). At the end of the optimization I was able to routinely fabricate SNSPDs using nanowires having width of 60 - 70 nm, spaced each other by 90 nm, with a very good uniformity.
Optimization of high quality superconducting thin films:
Since the delivery of a sputter depoisition tool for superconducting thin films to the University of Glasgow in May 2014, I worked in tandem with the PhD student Archan Banerjee to optimize the process for the fabrication of high quality thin NbN, NbTiN and MoSi films. In parallel, I also started to design the optical cavity stack to be fabricated on Si substrate to enhancing the absorption of the single mid IR photons in the superconducting 6 nm thick nanowires. The structure of choice is made by 5 bilayers of Si (270 nm)/SiO (270 nm) acting as a distributed dielectric Bragg refractor and a final layer of SiO (270 nm) behaving as a quarter wavelength cavity at 1550 nm. According to the performed simulation the absorptance of the light in the 5 nm thick NbTiN nanowires should increased from the 18% (no optical cavity) up to 90 % (with optical cavity) in the wavelength range between 1.25-1.58 μm. I commissioned the fabrication of this optical cavity structure on Si wafer to the HELIA Photonics Company (Edinburgh, UK).
Design, fabrication and characterization of SNSPD arrays:
I designed, fabricated and characterized 2x2 pixels array of SNSPDs having a coverage area of 30x30 μm2 (single pixel having area of 15x15 μm2) and 60x60 μm2 (single pixel having area of 30x30 μm2). For the first generation of 30x30 μm2 SNSPDs array, I used the 7 nm NbTiN films purchased from STAR Cryoelectronic (US) with no optical cavity. For the 60x60 μm2 area 2x2 pixels SNSPDs array I used NbTiN 5 nm thick film deposited in Glasgow on the optical cavity stack substrate. Each pixel was biased and read out individually for a “per pixel” read out scheme. From electrical/optical characterization at cryogenic temperature, the devices looked to be very uniform in fabrication and properties. These arrays are suitable for all the applications where a multimode optical or Mid Infrared fibre (50 - 60 μm core diameter) coupling is needed for high collection efficiency of the incoming light.
Development of electronic read out scheme for multipixel SNSPD arrays:
I also worked on the development of two innovative strategies for the readout of NxN SNSPDs arrays (N>2 and no per pixel bias/readout) for imaging applications.
The first approach is based on my original idea to bias/read out the single pixel SNSPDs in the array though an RF coupling of a coplanar waveguide (CPW) with the single SNSPDs pixels. This configuration would allow operation in frequency domain multiplexing of 20 or more SNSPDs pixels simultaneously using only two co-axial cables for a strong reduction of the thermal load in the cryostat. Preliminary simulation (performed in tandem with the PhD student Andrea Pizzone) and fabrication of prototype devices were accomplished. RF cryogenic characterization/measurements are expected shortly. This readout scheme is compatible with the lumped-element superconducting parametric amplifier (SC paramp) for a wideband, low noise and high dynamic range pre-amplification stage integrated on-chip. I am currently working in collaboration with the group of Prof Kent Irwin at Stanford University on the development of such SC paramp thanks to the SU2P Science Bridges Exchange scheme. The SC paramp prototype has been successfully fabricated and the RF testing in cryostat present in Stanford is expected in short time.
The second readout approach I am working on is based on the use of alternative RSFQ technology that will allow for the integration on chip with the SNSPDs array. I’m collaborating with Dr. Jane Ireland on the development of the Nanobridge SFQ-based readout technology supported by a TSB/Innovate UK Quantum Technology Feasibility Study Grant. In this approach the SFQ logic can be fabricated by using single layer of Nb or NbTiN (the same materials used for SNSPDs fabrication) and single EBL step for on-chip integration with the arrays. This grant will allow me to work for further four months, after the end of the fellowship, on the development of this technology for the time domain multiplexing of NxN SNSPDs array to be applied in imaging applications.
To summarize, during the fellowship I progressed in research activity to obtain the following achievements in line with the objectives (milestones and deliverable) of the proposed plan:
1) Deposition of high quality Superconducting thin NbN (5 nm with Tc = 12K), NbTiN (5 nm with Tc = 10.4 K) and MoSi (10 nm with Tc = 5.5 K) film (M1).
2) Patterning of superconducting thin film in high uniformity superconducting nanowires having width down to 60 nm and spacing of 90 nm for SNSPD fabrication (M2).
3) Realization and characterization of 2x2 SNSPD arrays having covering area of 30x30 μm2 and 60x60 μm2 with high performances (detection efficiency up to ~35%, timing jitter down to ~70 ps and recovery time of few ns) for multimode optical fibre coupling (M3 and M4).
4) Performed simulation and device fabricated to be tested for the development of two different electronic readout scheme for multi pixel NxN (N>2) SNSPDs array to be applied for single photon imaging applications (collaboration with Stanford University, US, and NPL, UK) (M5).
The expected final result of this project is to deliver the underpinning technology of SNSPDs arrays with imaging capability for a range of frontier research fields including secure communication, metrology, remote sensing and advanced imaging. This work holds the key to a wealth of high tech applications in industry and it is of strategic importance to future European scientific and economic competitiveness. This technology will boost not only scientific research across a wide range of disciplines but will also allow for the delivery of next generation devices to be used in real world applications with wide socio-economic impact.
Contact details:
Scientist in Charge:
Professor Robert H Hadfield FInstP
Head of Division of ENE
School of Engineering
University of Glasgow
Rankine Building, Oakfield Avenue,
Glasgow G12 8LT, UK
Tel: +44 141 330 4929
Email: Robert.hadfield@glasgow.ac.uk
Prinicipal Investigator:
Dr Alessandro Casaburi MInstP
Research Fellow
School of Engineering
University of Glasgow
Rankine Building, Oakfield Avenue
Glasgow G12 8LT (UK)
Tel: +44 141 330 3159
Email: Alessandro.Casaburi@glasgow.ac.uk