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REVIEW 3 major objections 6 minor 16 references

X-ray Irradiation Studies on the Monopix DMAPS in 150$\,$nm and 180$\,$nm

T0 review · 3 major / 6 minor · reviewed 2026-08-07 · deepseek-v4-flash

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Pith's one-line read Two monolithic pixel detector prototypes survive 100 Mrad of X-ray irradiation with no significant performance loss.

desk verdict Useful 100 Mrad qualification data for the Monopix2 chips, but the dose claim needs a stated uncertainty before it can be taken to the bank. read the letter →

arxiv 2506.04776 v1 pith:C6F7CXEJ submitted 2025-06-05 physics.ins-det

Christian Bespin , Marlon Barbero , Pierre Barrillon , Patrick Breugnon , Ivan Caicedo , Yavuz Degerli , Jochen Dingfelder , Tomasz Hemperek
show 14 more authors
Toko Hirono Hans Krüger Fabian Hügging Konstantinos Moustakas Patrick Pangaud Heinz Pernegger Petra Riedler Piotr Rymaszewski Lars Schall Philippe Schwemling Walter Snoeys Tianyang Wang Norbert Wermes Sinou Zhang
This is my paper
classification physics.ins-det
keywords depletedmonolithicactivepixelsensorDMAPStotalionizingdoseX-rayirradiationradiationhardnessdetectorthresholdtuning
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper reports X-ray irradiation tests of two large monolithic active pixel sensor prototypes, LF-Monopix2 in 150 nm CMOS and TJ-Monopix2 in 180 nm CMOS, up to a total ionizing dose of 100 Mrad. It claims both devices remained fully functional at the highest dose, with no significant degradation of threshold, noise, gain, or hit-detection efficiency. The point of the work is to show that these depleted monolithic pixel sensor designs can tolerate the ionizing radiation expected in the outer pixel layer of the High-Luminosity LHC tracker. If the claim holds, the two chips satisfy the ionizing-dose requirement for that application and can be operated by periodically retuning their in-pixel thresholds.

What carries the argument

The argument is carried by a controlled irradiation-and-characterization loop. Devices are powered and held at 0 °C on a cold plate in front of a tungsten-anode X-ray source, with the dose rate at each position determined by a silicon-diode dose map. Before, during, and after exposure the authors track the current of each power domain, front-end gain, threshold, threshold dispersion, equivalent noise charge, and, for TJ-Monopix2, beam-test hit efficiency. The load-bearing mechanism on the performance side is the in-pixel threshold tuning circuitry, which compensates the radiation-induced threshold shifts and keeps the dispersion from pushing low-threshold pixels below the noise level. The physical explanation offered for the current changes is the standard NMOS total-ionizing-dose picture: trapped positive oxide charge and interface traps shift threshold voltages and alter leakage current.

What would settle it

Take a fresh LF-Monopix2 or TJ-Monopix2, irradiate it with an independently calibrated dosimetry chain (for example, radiochromic film or alanine dosimeters traceable to a standards lab) to an absorbed dose of 100 Mrad, and repeat the threshold, noise, and beam-test efficiency measurements. If the chip loses functionality, or if the threshold dispersion cannot be retuned to an operational value at that independently measured dose, the paper's central claim would be contradicted.

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Extended reading notes

Core claim

On the paper's own terms, the central discovery is that 100 Mrad of X-ray total ionizing dose does not break either chip: both LF-Monopix2 and TJ-Monopix2 remained operational throughout the campaign and at the end point. After irradiation, LF-Monopix2's operational threshold was 1983 e- versus 2055 e- before, TJ-Monopix2's was 254 e- versus 230 e-, and equivalent noise charge rose modestly (92 to 112 e- for LF, 6 to 13 e- for TJ). TJ-Monopix2's hit efficiency in a test beam after 100 Mrad was (99.94 ± 0.05)%, consistent with the pre-irradiation value of 99.96%. The observed changes in power consumption follow the known total-ionizing-dose behavior of NMOS transistors, and in-pixel threshold tuning keeps threshold dispersion within operational limits. The paper concludes that both devices meet the ionizing-radiation tolerance required for the outer pixel layer.

Load-bearing premise

The load-bearing premise is that the silicon-diode dose map correctly gives the X-ray dose actually absorbed by each chip, and that this dose really is 100 Mrad; no uncertainty is quoted, and a systematic calibration error would invalidate the pass claim.

Editorial extensions

If this is right

  • Both chip lines can be operated through the full 100 Mrad ionizing dose expected for the outer pixel layer, provided thresholds are retuned in-pixel at intervals.
  • LF-Monopix2's front-end gain stays essentially flat over the whole dose range for both feedback-capacitance variants.
  • TJ-Monopix2 retains a hit efficiency consistent with its pre-irradiation value after 100 Mrad, so charge collection and readout remain intact at the full dose.
  • Threshold dispersion, which grows by about a factor of four without correction, can be brought back to an increase of at most 25% using in-pixel tuning, keeping operational thresholds at roughly their pre-irradiation values.
  • The current-consumption changes match known NMOS radiation behavior and do not prevent continuous operation of either chip.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • Our inference: the pass at 100 Mrad is established only for X-ray (ionizing) dose; a full qualification for the High-Luminosity LHC tracker also requires displacement damage from protons or neutrons, which these measurements do not address.
  • Our inference: because dosimetry rests on a single silicon-diode calibration with no stated uncertainty, the '100 Mrad' endpoint could be off by tens of percent; a cross-calibrated dosimeter would turn the pass claim into a quantitative margin.
  • Our inference: the results suggest a testable extension—irradiate fresh samples beyond 100 Mrad, or with bias voltage cycling, to find the actual failure boundary and check whether periodic annealing changes the power-consumption curves.
  • Our inference: since the chips were powered and cold during irradiation, the outcome may not transfer to room-temperature or unbiased operation; a comparison would indicate whether the observed tolerance is condition-dependent.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 6 minor

Summary. The paper reports X-ray total ionizing dose (TID) irradiation studies of two large-scale depleted monolithic active pixel sensor (DMAPS) prototypes, LF-Monopix2 (150 nm CMOS) and TJ-Monopix2 (180 nm CMOS), which are candidates for the ATLAS ITk outer pixel layer. The chips were exposed to 100 Mrad using a tungsten-anode X-ray source and monitored during irradiation: power consumption, gain, threshold dispersion, and ENC were measured as a function of dose. The authors report no significant degradation of gain or threshold after tuning, a factor-of-four increase in raw threshold dispersion for LF-Monopix2 that is compensated by in-pixel tuning, and a post-irradiation hit efficiency of (99.94±0.05)% for TJ-Monopix2 in a DESY beam test, consistent with the pre-irradiation value. The conclusion is that both chips remain fully functional at 100 Mrad and meet the ITk outer layer TID requirement.

Significance. If the 100 Mrad survival claim is correct, this result is significant for the ATLAS ITk upgrade because it demonstrates that both Monopix2 variants can tolerate the expected outer-layer ionizing dose with periodic in-pixel threshold tuning, potentially avoiding the need for a less mature but more radiation-hard technology. The paper provides useful TID response data for deep-submicron CMOS processes in HEP, with direct electrical monitoring during irradiation and a post-irradiation beam test for TJ-Monopix2. The observed current and leakage behavior is consistent with known NMOS TID effects, which lends credibility to the measurements. However, the quantitative central claim rests on a dosimetry assessment that is not fully characterized, and the absence of error bars and the use of single chips limit the precision of the 'no significant degradation' statement.

major comments (3)
  1. [Section 3, Fig. 3] The central claim that both chips survived 100 Mrad depends entirely on the dose-rate map shown in Fig. 3, but the paper provides no uncertainty on the dose rate, no calibration chain or traceability for the silicon diode, no explicit statement of whether 100 Mrad refers to dose in silicon, SiO2, or air, and no discussion of how the map was transferred to the exact chip locations or how the cold plate and device stack perturb the diode calibration. A systematic error of 20–30% in delivered dose would place the actual dose below the ATLAS ITk requirement, so the authors should add an explicit dose definition, an uncertainty estimate (even a conservative one), and a description of the calibration transfer.
  2. [Section 4, Figs. 4–6] The claim that gain and power consumption show 'no significant change' is not statistically supported because the figures plot single measurements without error bars, and the measurements appear to come from one chip per variant (or two front-end configurations on one LF-Monopix2 chip). Without point-to-point uncertainties or repeated measurements, the reader cannot distinguish a real dose effect from chip-to-chip variation or measurement reproducibility. Please add uncertainty estimates to the data points and state explicitly the number of chips and measurements per dose step.
  3. [Section 5.1, efficiency comparison] The post-irradiation efficiency of TJ-Monopix2 is compared to a pre-irradiation value of 99.96% taken from Ref. [13], a separate thesis. The paper should state whether the pre- and post-irradiation measurements were made under the same operating conditions (threshold, bias voltage, temperature, telescope setup) and, if not, discuss how differences in these conditions affect the comparison. This is needed to support the statement that the efficiency is 'consistent' and hence that there is no significant degradation in hit detection efficiency.
minor comments (6)
  1. [Section 4, paragraph 2] The phrase 'the threshold dispersion thatshowsanincreaseofaboutafactoroffour' has missing spaces; it should read 'that shows an increase of about a factor of four'.
  2. [Figure 3 caption] The dose-rate map lacks a color bar and units; please add a color bar with the dose-rate unit (e.g., krad/s) and state the normalization used.
  3. [Section 5.1, first sentence] The sentence 'The device has been cooled to 0 ◦C as during the irradiation and presented measurements' is awkward; clarify that the beam test was performed at 0 °C, matching the irradiation conditions.
  4. [Table 1] The word 'Summarytable' should be 'Summary table', and the entries would benefit from uncertainties, especially for ENC and threshold, to support the comparisons between 0 Mrad and 100 Mrad.
  5. [Section 3, dosimetry description] The paper does not report the X-ray tube operating parameters (e.g., energy, current, dose rate in rad/s) or the irradiation duration; these should be given to enable comparison with other TID studies and to assess dose-rate and annealing effects.
  6. [Section 4, reference [9]] The sentence 'The same study finds that the feedback current in this amplifier design is also unaffected' should explicitly state that Ref. [9] is the study being cited, since the preceding sentence refers to it only as 'earlier measurements'.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the 100 Mrad irradiation result is an empirical measurement with independent baselines, not a derivation from fitted inputs or self-citations.

full rationale

This paper is an experimental irradiation study, not a derivation. The central claim—that TJ-Monopix2 and LF-Monopix2 remain functional after 100 Mrad of X-ray dose—is supported by direct measurements of gain, current consumption, threshold, noise, and beam-test efficiency before and after irradiation. The dose is determined from a silicon-diode dose-rate map (Section 3), which is an external calibration input, not a quantity derived from the chips' behavior. The paper compares post-irradiation performance to pre-irradiation values reported in earlier work by the same collaboration (e.g., Refs. [3], [13], [14]); these are independent baseline measurements, not assumptions that encode the 100 Mrad conclusion. No equation in the paper reduces the headline result to its own inputs, no fitted parameter is renamed as a prediction, and no uniqueness or ansatz is imported via self-citation. The absence of dosimetry uncertainty is a legitimate experimental limitation, but it is not circularity. The result stands as self-contained empirical evidence.

Assumptions & free parameters 0 free parameters · 3 assumptions · 0 invented entities

The paper is an empirical qualification measurement. It introduces no free parameters or invented entities. The central claim relies on dosimetry accuracy and on representative pre-irradiation baselines from prior work.

assumptions (3)
  • domain assumption TID effects in NMOS transistors follow the known mechanisms of hole accumulation in oxide and interface trap formation.
    Invoked in Section 4 to explain the power consumption and threshold changes, citing [10,11].
  • domain assumption The dose rate measured by the silicon diode map (Fig. 3) is representative of the dose absorbed by the chips.
    Section 3 uses this map to position the devices and extract the delivered dose; no calibration uncertainty is reported.
  • domain assumption Pre-irradiation performance values from earlier characterizations (efficiency [13], timing [14]) apply to the specific chips irradiated in this campaign.
    Section 5.1 compares post-irradiation efficiency and timing to these referenced values rather than measuring the same devices before irradiation.

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Cite this review

Pith. "Pith review of X-ray Irradiation Studies on the Monopix DMAPS in 150$\,$nm and 180$\,$nm." pith.science (2026). https://pith.science/paper/C6F7CXEJ

@misc{pith2026250604776,
  author       = {Pith},
  title        = {Pith review of: X-ray Irradiation Studies on the Monopix DMAPS in 150$\,$nm and 180$\,$nm},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/C6F7CXEJ}},
  note         = {Machine review of arXiv:2506.04776}
}
abstract

Monolithic active pixel sensors with depleted substrates present a promising option for pixel detectors in high-radiation environments. High-resistivity silicon substrates and high bias voltage capabilities in commercial CMOS technologies facilitate depletion of the charge sensitive volume. TJ-Monopix2 and LF-Monopix2 are the most recent large-scale chips in their respective development line, aiming for the ATLAS Inner Tracker outer layer requirements. Those include a tolerance to ionizing radiation of up to 100$\,$Mrad. It was evaluated by irradiating both devices with X-rays to the corresponding ionization dose, showing no significant degradation of the performance at 100$\,$Mrad and continuous operability throughout the irradiation campaign.

Figures

Figures reproduced from arXiv: 2506.04776 by the authors.

Figure 1
Figure 1. Schematic cross-section of a pixel in the large collection electrode design of LF [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Schematic cross-section of a pixel in the small collection electrode design of TJ [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Dose rate map of the irradiation setup, measured with a silicon diode. The positions [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figures from the paper (4 more)
Figure 4
Figure 4. Figure 4: Evolution of the gain of LF-Monopix2 versus total ionization dose for two front-ends [PITH_FULL_IMAGE:figures/full_fig_p005_4.png]
Figure 5
Figure 5. Figure 5: Normalized current consumption (at 1.8 V) of the different power domains of LF￾Monopix2 versus the ionization dose. mented as an NMOS device, a significant degradation of the gain has been observed in the expected dose range between 1 Mrad and 10 Mrad. This conclu￾sion…
Figure 6
Figure 6. Figure 6: Normalized current consumption (at 1.8 V) of the different power domains of TJ￾Monopix2 versus the ionization dose. 6. Conclusion Both DMAPS were successfully X-ray irradiated to 100 Mrad and remained fully functional at the highest dose level. The power consumption fo…
Figure 7
Figure 7. Figure 7: In-pixel efficiency map of TJ-Monopix2 after X-ray irradiation to [PITH_FULL_IMAGE:figures/full_fig_p008_7.png]

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Works this paper leans on

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