Speaker
Description
Understanding radiation effects on detectors and electronics is essential for the success of word-class experiments in fundamental physics at particle accelerators. This is of paramount importance in view of the High Luminosity Large Hadron Collider (HL-LHC) program, which aims at discovering new physics beyond Standard Model by increasing the LHC luminosity by up to a factor of 7.5. This scientific goal poses significant challenges for the reliability of detectors and electronics, as they must operate in high radiation environments. In this context, we are performing radiation qualification of key elements of the new readout system of Resistive Plate Chambers (RPC) of the ATLAS muon trigger for HL-LHC.
Conventional analysis of radiation effects on electronics is mainly based on I-V curves, signal integrity, and noise measurements. In addition, we deploy an approach based on impedance spectroscopy. Impedance spectroscopy is a non-invasive technique commonly used in electrochemistry with applications to the characterization of solar cells, fuel cells, batteries, biosensors, and corrosion studies. In impedance spectroscopy, a small sinusoidal perturbation is applied to the Device Under Test (DUT) over a broad frequency range (typically from a fraction of Hz up to a few MHz) superimposed to a constant bias level [1]. The impedance response is analyzed using Nyquist plots, which graphically represent the imaginary part of the impedance vs. its real part. Fitting Nyquist plots with equivalent circuit models provides insights into charge transfer mechanisms. We recently applied impedance spectroscopy to assess Total Ionizing Dose (TID) effects on different device sections of Low Voltage Differential Signaling (LVDS) receivers, including power rail, input and output networks [2]. This approach complements conventional analysis of radiation effects by revealing aspects that are difficult (or even impossible) to observe by traditional methods.
In the present work, we extend this analysis to LSF0102 level translators and Si photodiodes for which impedance spectroscopy is particularly effective in assessing radiation-induced degradation. Level translators of the LSF family rely on MOSFET switches, which conduct during the low input pulses and switch off during high pulses [3]. Translation between voltage levels is achieved through external pullup resistors. Si photodiodes, on the other hand, are solid-state devices based on pn or p-i-n junctions. TID irradiations, up to 15 kGy, are performed at the CERN CC60 facility equipped with a ~10 TBq 60Co gamma source, while displacement damage effects are evaluated with 18 MeV proton beams from the Beam Transfer Line (BTL) at the Bern medical cyclotron. We developed a specific test bench that allows the DUTs to be powered, exposed to the radiation and remotely controlled by a Raspberry Pi 3 Model B+. During the test of level translators, we monitor the DUT current consumption, variations in amplitude, rise/fall time, jitter, signal-to-noise ratio, and infer bit error rate from oscilloscope eye diagrams. During the test of Si photodiodes, we monitor their output current.
Characterization with impedance spectroscopy is performed before and after irradiation for all DUTs using a Solartron ModuLab XM ECS-Photoechem-MTS system. It includes a potentiostat/galvanostat for controlling DC levels (up to ±100 V and ±100 mA), a frequency response analyzer from 10 µHz to 1 MHz, a light source, a monochromator and a reference photodetector operating in the range 350 nm - 1100 nm. It enables impedance measurements both in dark and under controlled light exposure, as well as measurements of Intensity-Modulated Photocurrent Spectroscopy (IMPS) and Intensity-Modulated photoVoltage Spectroscopy (IMVS). In IMPS and IMVS, the light source intensity is modulated and the DUT response, either in current or voltage, is recorded as a function of modulation frequency.
Using this setup, key properties of a DUT can be studied including charge carrier transport, recombination, lifetime, accumulation, and interface mechanisms. By combining impedance spectroscopy with Mott-Schottky analysis and capacitance-frequency measurements, we can also determine the built-in voltage, doping density, depletion width, trap density distribution and surface uniformity. This characterization is relevant for LSF level translators, which are based on simple MOSFETs and resistors. TID damage on MOSFET, extensively addressed in the literature [4], leads to charge buildup in the SiO2 gate and at the Si-SiO2 interface, primarily causing shift of the threshold voltage. Proper modeling of level translators with impedance spectroscopy provides insights into radiation-induced changes in the charge carrier transport of the MOSFET, and the value of the pullup resistor, which is crucial for the proper functioning of these devices.
We recently applied impedance spectroscopy to study the impedance response of a narrow-base Si diode [5]. Here, the pn junction has been modeled with equivalent circuits that take into account depletion and diffusion processes, as well as interfacial effects, potential and capacitance distributions. We are extending this approach to model the impedance of Si photodiodes under both dark and illumination. This characterization is completed with Photon Detection Efficiency (PDE) measurements pre- and post-irradiation, which are relevant for Si photodiodes.
References
[1] A. C. Lazanas, , & M. I. Prodromidis (2023). ACS Measurement Science Au, 3(3), 162-193. doi: 10.1021/acsmeasuresciau.2c00070
[2] P. Casolaro, V. Izzo, M. D’Angelantonio, C. Principe, A. Vanzanella, and A. Aloisio, 2024 IEEE NSS-MIC-RTSD, Tampa, FL, USA, 2024, pp. 1-1, doi: 10.1109/NSS/MIC/RTSD57108.2024.10656982.
[3] Voltage-Level Translation With the LSF Family, Application Report SLVA675B, available: https://www.ti.com/lit/an/slva675b/slva675b.pdf
[4] J. R. Schwank et al. (2008). IEEE Transactions on Nuclear Science, 55(4), 1833-1853. doi: 10.1109/TNS.2008.2001040
[5] P. Casolaro, V. Izzo, M. D’Angelantonio, C. Principe, A. Vanzanella, and A. Aloisio, J. Appl. Phys. 136, 115702 (2024). doi: 10.1063/5.0230008
