Total Ionizing Dose Effects on CMOS Image Sensor for the ULTRASAT Space Mission

ULTRASAT (ULtraviolet TRansient Astronomy SATellite) is a wide-angle space telescope that will perform deep time-resolved surveys in the near-ultraviolet spectrum. ULTRASAT is a space mission led by the Weizmann Institute of Science and the Israel Space Agency and is planned for launch in 2025. The camera implements backside-illuminated, stitched pixel sensors. The pixel has a dual-conversion-gain 4T architecture, with a pitch of $9.5$ $\mu m$ and is produced in a $180$ $nm$ process by Tower Semiconductor. Before the final sensor was available for testing, test sensors provided by Tower were used to gain first insights into the pixel's radiation tolerance. One of the main contributions to sensor degradation due to radiation for the ULTRASAT mission is Total Ionizing Dose (TID). TID measurements on the test sensors have been performed with a Co-60 gamma source at Helmholz Zentrum Berlin and CC-60 facility at CERN and preliminary results are presented.Comment: Part of the conference: Frontier Detectors for Frontier Physics: 15th Pisa Meeting on Advanced Detectors, La Biodola - Isola d'Elba Published in: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Available online 15 June 2023, 168463. In Press, Journal Pre-proo

The scientific payload of the Ultraviolet Transient Astronomy Satellite (ULTRASAT)

The Ultraviolet Transient Astronomy Satellite (ULTRASAT) is a space-borne near UV telescope with an unprecedented large field of view (200 sq. deg.). The mission, led by the Weizmann Institute of Science and the Israel Space Agency in collaboration with DESY (Helmholtz association, Germany) and NASA (USA), is fully funded and expected to be launched to a geostationary transfer orbit in Q2/3 of 2025. With a grasp 300 times larger than GALEX, the most sensitive UV satellite to date, ULTRASAT will revolutionize our understanding of the hot transient universe, as well as of flaring galactic sources. We describe the mission payload, the optical design and the choice of materials allowing us to achieve a point spread function of ~10arcsec across the FoV, and the detector assembly. We detail the mitigation techniques implemented to suppress out-of-band flux and reduce stray light, detector properties including measured quantum efficiency of scout (prototype) detectors, and expected performance (limiting magnitude) for various objects.Comment: Presented in the SPIE Astronomical Telescopes + Instrumentation 202

Total Ionizing Dose effects on CMOS image sensor for the ULTRASAT space mission

ULTRASAT (ULtraviolet TRansient Astronomy SATellite) is a wide-angle space telescope that will perform deep time-resolved surveys in the near-ultraviolet spectrum. ULTRASAT is a space mission led by the Weizmann Institute of Science and the Israel Space Agency and is planned for launch in 2025. The camera implements backside-illuminated, stitched pixel sensors. The pixel has a dual-conversion-gain 4T architecture, with a pitch of 9.5 μm and is produced in a 180nm process by Tower Semiconductor. Before the final sensor was available for testing, test sensors provided by Tower were used to gain first insights into the pixel’s radiation tolerance. One of the main contributions to sensor degradation due to radiation for the ULTRASAT mission is Total Ionizing Dose (TID). TID measurements on the test sensors have been performed with a Co-60 gamma source at Helmholz Zentrum Berlin and CC-60 facility at CERN and preliminary results are presented

Sensor characterization for the ULTRASAT space telescope

The Ultraviolet Transient Astronomical Satellite (ULTRASAT) is a scientific space mission carrying an astronomical telescope. The mission is led by the Weizmann Institute of Science (WIS) in Israel and the Israel Space Agency (ISA), while the camera in the focal plane is designed and built by Deutsches Elektronen Synchrotron (DESY) in Germany. Two key science goals of the mission are the detection of counterparts to gravitational wave sources and supernovae.$^1$ The launch to geostationary orbit is planned for 2024. The telescope with a field-of-view of ≈ 200 deg$^2$, is optimized to work in the near-ultraviolet (NUV) band between 220 and 280 nm. The focal plane array is composed of four 22:4-megapixel, backside-illuminated (BSI) CMOS sensors with a total active area of 90 x 90mm$^2$.$^2$ Prior to sensor production, smaller test sensors have been tested to support critical design decisions for the final flight sensor. These test sensors share the design of epitaxial layer and antireflective coatings with the flight sensors. Here, we present a characterization of these test sensors. Dark current and read noise are characterized as a function of the device temperature. A temperature-independent noise level is attributed to on-die infrared emission and the read-out electronics' self-heating. We utilize a high-precision photometric calibration setup$^3$ to obtain the test sensors' quantum efficiency relative to PTB/NIST-calibrated transfer standards (220-1100 nm), the quantum yield for $λ$ >300 nm, the non-linearity of the system, and the conversion gain. The uncertainties are discussed in the context of the newest results on the setup's performance parameters. From the three ARC options Tstd, T1 and T2, the last assists the out-of-band rejection and peaks in the mid of the ULTRASAT operational waveband. We recommend ARC option T2 for the final ULTRASAT UV sensor

Design of the ULTRASAT UV camera

The Ultraviolet Transient Astronomical Satellite (ULTRASAT) is a scientific UV space telescope that will operate in geostationary orbit. The mission, targeted to launch in 2024, is led by the Weizmann Institute of Science (WIS) in Israel and the Israel Space Agency (ISA). Deutsches Elektronen Synchrotron (DESY) in Germany is tasked with the development of the UV-sensitive camera at the heart of the telescope. The camera's total sensitive area of ≈90mm x 90mm is built up by four back-side illuminated CMOS sensors, which image a field of view of ≈200 deg2. Each sensor has 22:4 megapixels. The Schmidt design of the telescope locates the detector inside the optical path, limiting the overall size of the assembly. As a result, the readout electronics is located in a remote unit outside the telescope. The short focal length of the telescope requires an accurate positioning of the sensors within ±50 μm along the optical axis, with a flatness of ±10 μm. While the telescope will be at around 295K during operations, the sensors are required to be cooled to 200K for dark current reduction. At the same time, the ability to heat the sensors to 343K is required for decontamination. In this paper, we present the preliminary design of the UV sensitive ULTRASAT camera