Fine-pitch semiconductor detector for the FOXSI mission

TL;DR

The paper presents the design, fabrication, and testing of a fine-pitch double-sided silicon strip detector with a custom ASIC for the FOXSI solar X-ray mission, achieving high spatial and energy resolution in laboratory conditions.

Contribution

It introduces a novel 128-strip silicon detector with 75 μm pitch and a dedicated low-noise ASIC, optimized for high-resolution solar X-ray observations in space.

Findings

Energy resolution of 430 eV at 14 keV achieved

Successful laboratory operation at -20°C with 300 V bias

Fine-pitch imaging demonstrated through shadow imaging

Abstract

The Focusing Optics X-ray Solar Imager (FOXSI) is a NASA sounding rocket mission which will study particle acceleration and coronal heating on the Sun through high sensitivity observations in the hard X-ray energy band (5-15 keV). Combining high-resolution focusing X-ray optics and fine-pitch imaging sensors, FOXSI will achieve superior sensitivity; two orders of magnitude better than that of the RHESSI satellite. As the focal plane detector, a Double-sided Si Strip Detector (DSSD) with a front-end ASIC (Application Specific Integrated Circuit) will fulfill the scientific requirements of spatial and energy resolution, low energy threshold and time resolution. We have designed and fabricated a DSSD with a thickness of 500 {\mu}m and a dimension of 9.6 mm x 9.6 mm, containing 128 strips with a pitch of 75 {\mu}m, which corresponds to 8 arcsec at the focal length of 2 m. We also developed a low-noise ASIC specified to FOXSI. The detector was successfully operated in the laboratory at a temperature of -20 C and with an applied bias voltage of 300 V, and the energy resolution of 430 eV at a 14 keV line was achieved. We also demonstrated fine-pitch imaging successfully by obtaining a shadow image, hence the implementation of scientific requirements was confirmed.