Position-sensitive transition edge sensor with sub-micrometer accuracy developed for future x-ray interferometry mission

Abstract

An X-ray interferometer is a promising technology to achieve an unprecedentedly high-spatial resolution, which provides us further understandings of astrophysical objects and the Universe. The most critical key to realize a space telescope of X-ray interferometry is downsizing the optics, and one method for that is to develop an X-ray sensor with high position accuracy that can detect narrow X-ray interference fringes. For this purpose, we are developing a position-sensitive X-ray sensor by applying the Transition-Edge Sensor (TES) technology. We designed a prototype sensor as two Ti/Au (40/90 nm) TES pixels (140 × 140 μm) connected by a single oblong Au absorber (1400 μm × 20 μm × 1 μm) aiming the sub-micrometer position accuracy. Depending on an X-ray incident position, a photon energy is divided into the two TES pixels causing individual pulses. By measuring the difference of rising edges of the two pulses, we can determine the photon-incident position. We fabricated the prototype sensor, and performed an X-ray irradiation experiment by using an 55Fe radioactive source. As a result, we successfully detected pulses with different trigger times which reflect different rising edges up to ∼ 5 μsec, corresponding to the X-ray photon incident positions up to ∼ 0.5 mm from the center of the absorber. Here, the position accuracy depends on the accuracy of determining the rising edges. The response of our sensor is observed as ∼ 0.5 mm/5 μsec, indicating that a sub-micrometer position determination could be achieved by observing rising edges with nsec accuracy as a future prospect. In this paper, we introduce the design, fabrication, and X-ray irradiation experiment of this new position-sensitive X-ray sensor.