Verification of 100 nm resolution in a superconducting nanostrip single-photon detector for hard x-ray image reconstruction

We propose a method using a superconducting nanostrip single-photon detector (SNSPD) that can significantly reduce resolution compared with conventional imaging detectors. An SNSPD is advantageous for miniaturization because it consists of a single superconducting strip and allows the direct detection of hard x rays when a thick superconductor with a high atomic number is utilized. A two-dimensional image can be obtained by arranging superconducting strips in a one-dimensional array, rotating the detector or sample, and reconstructing the image using computed tomography technology. One-dimensional SNSPD arrays made of tantalum nitride with a pitch of 100 nm, corresponding to the resolution, were fabricated. A prototype detector was assembled using a counter located at room temperature, incorporating flexible printed circuits with 100 signal cables connected the SNSPD array to the counter via a relay connector to dissipate heat at room temperature. It was demonstrated that the heat flow to the SNSPD array and the signal loss during x-ray detection could be effectively suppressed. By simultaneously obtaining x-ray detection signals from two adjacent strips, it was observed that crosstalk occurred; however, increasing the film thickness helped reduce the occurrence of crosstalk. For strips with a thickness of 270 nm, the crosstalk occurrence rate was approximately 35%, which was deemed acceptable. We conclude that a resolution of 100 nm for hard x rays can be achieved using the SNSPD array.