The photon detection technique has several applications. Fractal superconducting nanowire single-photon detectors (SNSPDs) have demonstrated high system detection efficiency for incident photons in all polarization states.
SNSPDs use very thin superconducting wires that switch from a superconducting state to a resistive state when a photon hits, allowing for high-speed detection. These wires are arranged in a Peano arced-fractal pattern that stays the same at different scales. This design helps the detector detect photons regardless of their direction or polarization.
However, challenges arise when it comes to fabrication and performance. A recent IEEE Study offers a comprehensive guide on how to make these detectors. It includes tips for improving the fabrication process to help create reliable and scalable fractal SNSPDs.
Researchers, including Professor Xiaolong Hu and Dr. Kai Zou from Tianjin University, China, have created a technique to address design and performance challenges in scalable single-photon detectors. Their study details the materials and techniques needed to build these detectors and tackles the challenges their intricate fractal design poses.
AF SNSPDs have three main parts: nanowires to detect photons, optical microcavities to catch photons, and keyhole-shaped chips to hold and align the detector with the optical fiber.
Here’s a simplified breakdown of the fabrication process:
Creating the Optical Microcavity:
A silicon wafer is coated with six or eight alternating layers of silicon dioxide (SiO2) and tantalum oxide (Ta2O5) using ion-beam-assisted deposition (IBD). This forms a bottom-distributed Bragg reflector.
A SiO2 defect layer is then added.
Making the Photon-Sensitive Surface:
A 9-nm niobium-titanium nitride (NbTiN) superconducting film is deposited on the defect layer using reactive magnetron sputtering.
Adding Electrodes:
Titanium-gold electrodes are fabricated on this surface using optical lithography and lift-off processes.
The nanowires are crafted into a fractal design through scanning-electron-beam lithography, then etched onto the NbTiN layer using reactive-ion etching.
To complete the microcavity, a top SiO2 defect layer and additional alternating layers of Ta2O5/SiO2 are added using aligned optical lithography and ion-beam-assisted deposition (IBD). The chip is then shaped into a keyhole form using optical lithography, inductively coupled plasma etching, and the Bosch etching process, and finally packaged for optical fiber connections.
The authors offered tips for improving the fabrication of nanowires, optical microcavities, and keyhole-shaped chips. Their suggestions include:
- A 5-nm silicon or 3-nm SiO2 layer is used to improve bonding.
- Employing auxiliary AF nanowire patterns to maintain consistent widths.
- Designing the layout and spacing of optical microcavities carefully to reduce deformation.
- Using precise alignment markers for keyhole-shaped chips.
- Gradually applying heat during curing to enhance stability and reduce defects.
By following the guide, the researchers created SNSPDs that are highly sensitive and efficient at detecting photons.
Prof. Hu said, “These advancements will help simplify the fabrication of fractal SNSPDs, enabling the development of more advanced devices with additional functionalities.”
Journal Reference:
- Kai Zou and Xiaolong Hu. Fabrication Development of High-Performance Fractal Superconducting Nanowire Single-Photon Detectors. IEEE Journal of Selected Topics in Quantum Electronics. DOI: 10.1109/JSTQE.2024.3522176
Source: Tech Explorist
