arXiv subjects

Valentin Emberger

Publications and source records attributed to Valentin Emberger.

6 recordsLinked to original sources

arXiv2026

Radiation effects and noise evolution in NewAthena WFI flight-production sensors

The Wide Field Imager (WFI), one of the two instruments on ESA's next large X-ray observatory NewAthena, is designed for imaging spectroscopy in the 0.2-15 keV range, combining a large field of view with high count-rate capability. Its focal plane is equipped with back-illuminated DEPFET (Depleted p-channel field-effect transistor) sensors that offer high radiation tolerance and provide near Fano-limited energy resolution. Achieving this performance requires an exceptionally low readout noise, with about 3 electrons ENC expected at beginning of life. Consequently, the devices are highly sensitive to radiation-induced changes in noise behavior. In this work, we investigate the impact of both total non-ionizing dose (TNID) and total ionizing dose (TID) on the relevant noise components, including their temperature dependence. A detector module containing a 64x64-pixel sensor from a flight-production wafer was irradiated with 62.4 MeV protons at the MedAustron accelerator facility in Wiener Neustadt to a total dose equivalent to 2.6 $\cdot$ 10$^9$ 10-MeV-protons/cm$^2$. The detector was fully biased and operated throughout the irradiation and subsequent measurements, maintaining the nominal operating temperature of 213 K. To study short-term annealing behavior at low temperature, a second, identical module was exposed to a comparable proton dose within a much shorter timescale by exploiting the available high beam flux. TID effects were investigated separately by irradiating another device with 17.4 keV Mo-K_alpha X-rays to a total dose of 15 Gy. We report the resulting changes in readout noise, dark current, and threshold voltage, and compare them with results from an earlier irradiation campaign using pre-flight sensors. Implications for the instrument's required operating temperature and its expected end-of-life performance are discussed.

astro-ph.IM↗

arXiv2026

Characterisation of the NewAthena WFI's DEPFET Flight Production's Operational Parameters

NewAthena's Wide Field Imager (WFI) uses detectors made up from Depleted P-Channel Field Effect Transistor (DEPFET) pixels operated in rolling shutter mode. The Large Detector Array (LDA) contains a 2 $\times$ 2 array of 512 $\times$ 512 pixels Large Detectors (LDs) allowing for a field of view of 40' $\times$ 40' with a frame time of 2 ms while the 64 $\times$ 64 pixels Fast Detector (FD) can observe very bright X-ray sources due to a faster frame time of 0.08 ms. Prototype sensors (64 $\times$ 64 pixels) were used to analyse the sensor's operational range and to optimise the ASIC and DEPFET parameters i.e. current and voltage settings, as well as the DEPFET read-out timing parameters, resulting in an improved energy resolution, reduced noise and otherwise improved sensor characteristics.

astro-ph.IM↗

arXiv2024

Spectroscopic Performance of Detectors for Athena's WFI: Measurements and Simulation

The depleted p-channel field effect transistor is the chosen sensor type for the Wide Field Imager of the Athena mission. It will be used in two types of cameras. One will enable observations of a field of view of 40' x 40' by using an array of four 512 x 512 pixel sensors in a 2 x 2 configuration. A second, small one is designed to investigate bright, point-like sources with a time resolution of up to 40 microseconds. Sensors of final size, layout, and technology were fabricated, assembled and characterised. Also, first results from the flight production are available and confirm the excellent performance. In order to be able to estimate the future performance of degraded detectors, a simulation was developed that takes into account the non-analytical threshold effects on the basis of measurement results. We present the measurement analysis and the comparison of simulated and measured values as well as first attempts to use the Monte Carlo simulation to predict performance results based on noise measurements.

astro-ph.IM↗

arXiv2024

Low temperature proton irradiation with DEPFETs for Athena's Wide Field Imager

The Wide Field Imager (WFI), one of two instruments on ESA's next large X-ray mission Athena, is designed for imaging spectroscopy of X-rays in the range of 0.2 to 15 keV with a large field of view and high count rate capability. The focal plane consists of back-illuminated DEPFET (Depleted p-channel field effect transistor) sensors that have a high radiation tolerance and provide a near Fano-limited energy resolution. To achieve this, a very low noise readout is required, about 3 electrons ENC at beginning of life is foreseen. This makes the device very susceptible to any radiation induced worsening of the readout noise. The main mechanism of degradation will be the increase of dark current due to displacement damage caused primarily by high energy protons. To study the expected performance degradation, a prototype detector module with fully representative pixel layout and fabrication technology was irradiated with 62.4 MeV protons at the accelerator facility MedAustron in Wiener Neustadt. A total dose equivalent to 3.3 $\textstyle{10^{9}}$ 10-MeV protons/$\mathrm{cm^{2}}$ was applied in two steps. During, in-between and after the irradiations the detector remained at the operating temperature of 213 K and was fully biased and operated. Data was recorded to analyze the signal of all incident particles. We report on the increase of dark current after the irradiation and present the current related damage rate at 213 K. The effect of low temperature annealing at 213 K , 236 K, 253 K, 273 K, and 289 K is presented.

astro-ph.IM↗

arXiv2022

Spectroscopic performance of flight-like DEPFET sensors for Athena's WFI

The Wide Field Imager for the Athena X-ray telescope is composed of two back side illuminated detectors using DEPFET sensors operated in rolling shutter readout mode: A large detector array featuring four sensors with 512x512 pixels each and a small detector that facilitates the high count rate capability of the WFI for the investigation of bright, point-like sources. Both sensors were fabricated in full size featuring the pixel layout, fabrication technology and readout mode chosen in a preceding prototyping phase. We present the spectroscopic performance of these flight-like detectors for different photon energies in the relevant part of the targeted energy range from 0.2 keV to 15 keV with respect to the timing requirements of the instrument. For 5.9 keV photons generated by an iron-55 source the spectral performance expressed as Full Width at Half Maximum of the emission peak in the spectrum is 126.0 eV for the Large Detector and 129.1 eV for the Fast Detector. A preliminary analysis of the camera's signal chain also allows for a first prediction of the performance in space at the end of the nominal operation phase.

astro-ph.IM↗

arXiv2022

Total ionizing dose test with DEPFET sensors for Athena's WFI

The focal plane of Athena's WFI consists of spectroscopic single photon X-ray detectors that contain arrays of DEPFETs (DEpleted P-channel Field-Effect Transistor) as well as ASICs that are used for steering, readout and analog signal shaping. These components have to be examined regarding the effect of ionizing radiation. A Total Ionizing Dose (TID) test was done with prototype detector modules with 64x64 DEPFETs and one SWITCHER and VERITAS ASIC each. The current design of the WFI detector head features a proton shield equivalent to 4 cm of aluminum in order to prevent a strong increase of leakage current in the fully depleted 450 $\mu$m thick bulk of the sensor. This keeps the expected doses and dose rates during the nominal mission relatively low ($\sim$5 Gy). It is nevertheless important to study the current system in a dedicated TID test in order to exclude unforeseen effects and to study any radiation related changes that can have an effect on the very sensitive readout chain and the detector performance. The combination of low doses, low dose rates, low operating temperature (<-60{\deg}C) but high sensitivity on small changes of the threshold voltages represent somehow unusual boundary conditions in comparison to TID tests for standard radiation hard electronic components. Under these circumstances it was found beneficial to do the test in our own laboratory with an X-ray source in order to realize irradiation during nominal operation conditions. Furthermore, it facilitated to take annealing effects into account. Reasonably accurate dosimetry is achieved by measuring the X-ray spectrum and intensity with the device under test. After irradiation to a total dose of 14 Gy and subsequent annealing the threshold voltage of the DEPFETs were shifted by a mean value of 80 mV, the performance remained unchanged apart from a slight increase in readout noise by 10%.

physics.ins-det↗