The ATLASPix sensor has been developed as a monolithic High Voltage CMOS sensor candidate for the ATLAS inner tracker upgrade. The ATLASPix3 is the third version, and is the first full reticle-sized sensor developed for multi-module compatibility. The detector is operational, and has been tested as a single chip, and as a 4-layer telescopes in an electron testbeam, with energies up to 6 GeV at DESY. First results of the testbeam data analysis are presented here

Andreazza, A.

Dong, R.

Dopke, J.

Feng, Z.

Fox, H.

Gao, Y.

Hutchinson, E.

Jones, T.

Li, Y.

Martin, J.

Meng, L.

Moss, S.

Muenstermann, D.

Peric, I.

Sabatini, F.

Schimassek, R.

Velthuis, J.

Wilson, F.

Xu, X.

Zanzottera, Riccardo

Zeng, S.

Zhong, Y.

English

KITopen

PoS(Pixel2022)069First Results of ATLASPix3.1 TestbeamR. Zanzottera,𝑎,𝑏,∗ E. Hutchinson,𝑐,1,∗ A. Andreazza,𝑎,𝑏 R. Dong,𝑑,𝑒 J. Dopke, 𝑓Z. Feng,𝑔 H. Fox,𝑐 Y. Gao,ℎ T. Jones,𝑖 Y. Li,𝑒 J. Martin,ℎ L. Meng,𝑐 S. Moss, 𝑓D. Muenstermann,𝑐 I. Perić,𝑑 F. Sabatini,𝑎,𝑏 R. Schimassek,𝑑 J. Velthuis,𝑔F. Wilson, 𝑓 X. Xu,𝑒, 𝑗 S. Zeng𝑒,𝑘 and Y. Zhong𝑐𝑎INFN, Via Celoria 16, 20133, Milan, Italy𝑏University of Milan, Via Celoria 16, 20133, Milan, Italy𝑐Physics Department, Lancaster University, Bailrigg, Lancaster, LA1 4YW, United Kingdom𝑑Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany𝑒Institute of High Energy Physics, 19B Yuquan Road, Shĳingshan District, Beĳing, China𝑓 Rutherford Appleton Laboratory, Rutherford Avenue, Harwell Campus, Didcot, Oxford, OX11 OGD,United Kingdom𝑔University of Bristol, Beacon House, Queens Road, Bristol, BS8 1QU, United KingdomℎUniversity of Edinburgh, Old College, South Bridge, Edinburgh, EH8 9YL, United Kingdom𝑖Department of Physics, University of Liverpool, The Oliver Lodge Laboratory, Liverpool, L69 7ZE,United Kingdom𝑗Tsinghua University, Haidian District, Beĳing, 100084, China𝑘South China University of Technology, 381 Wushan Road, Tianhe District, Guangzhou, GuangdongProvince, ChinaE-mail: riccardo.zanzottera@studenti.unimi.it,e.hutchinson@lancaster.ac.ukAbstract: The ATLASPix sensor has been developed as a monolithic High Voltage CMOSsensor candidate for the ATLAS inner tracker upgrade. The ATLASPix3 is the third version,and is the first full reticle-sized sensor developed for multi-module compatibility. The detector isoperational, and has been tested as a single chip, and as a 4-layer telescopes in an electron testbeam,with energies up to 6 GeV at DESY. First results of the testbeam data analysis are presented here.10th International Workshop on Semiconductor Pixel Detectors for Particles and Imaging (Pixel2022)12-16 December 2022Santa Fe, New Mexico, USA1Poster and proceedings author∗Speaker© Copyright owned by the author(s) under the terms of the Creative CommonsAttribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). https://pos.sissa.it/PoS(Pixel2022)069First Results of ATLASPix3.1 Testbeam R. Zanzottera and E. Hutchinson1. Technical SetupThe ATLASPix sensor has been developed as a monolithic High Voltage CMOS sensor can-didate for the ATLAS inner tracker upgrade [1, 2]. The sensors were produced by AMS/TSI in180 nm technology on 200 Ωcm wafers with the deep n-well as charge collecting diode with largefill factor. The reticle size is 20.2 × 21 mm2, consisting of 132 columns × 372 rows of pixels, witha pixel size of 150 × 50 `m2.The sensor can be configured through a serial bus, an SPI bus or a command line interface.The sensor supports zero suppressed readout. The chip can be configured as both triggered ortrigger-less column-drain readout via two separate structures. Each pixel has its own thresholdoffset, which is set via a 3-bit TDAC. For each signal hit an 8-bit time over threshold (ToT) and a10-bit timestamp of the crossing of the threshold are recorded. The hit information is transmittedwith up to 1.28 Gbit/s through a serial link. Readout of a single sensor and a multi-layer telescopewith up to four layers is achieved using the GECCO (GEneric Configuration and COntrol) system[3].The chip is generally low power (160 mW/cm2, 120 mW/cm2 of which is analog), althoughspecific power requirements will depend on the number of hits and the readout mode. The chip canbe operated with a threshold as low as 400 e, and a material budget as low as 50 `m [4].The version of the chip used in the testbeam was the ATLASPix3.1. Version 3.1 has addedvarious changes. The pixel biasing structure has been improved, and the capacitance has beendecreased to half of the original value in order to reduce time walk. Capcitance has also been addedto the voltage regulators in order to avoid oscillations, at the cost of limiting the shielding of the testsignal injection, introducing some crosstalk.2. Single Chip CharacterisationThe ATLASPix has been characterised in the lab. Presented here is the single chip characteri-sation for the ATLASPix3 version.Every pixel has a separate offset with respect to the global threshold setting to compensate forpedestal variations. The desired setting for each pixel is obtained by varying the voltage used forthe charge injection and measuring the pixel hit efficiency, resulting in S-curves. Figure 1a showsthe pre-tuned S-curves for a particular row, and Figure 1b shows the same S-curves after tuningeach pixel. Early lab tests were performed with a number of sources, with Strontium-90 shown inFigure 2. The source signal is clearly observed.2PoS(Pixel2022)069First Results of ATLASPix3.1 Testbeam R. Zanzottera and E. Hutchinson(a) Untuned S-curves at TDAC = 5 for row 40, 𝜎 = 47 mV. (b) Tuned S-curves for row 40, 𝜎 = 18 mV.Figure 1: Figure 1a shows the S-curves before each pixel is tuned to its optimal value, and Figure 1b showsthe S-curves for the same row after tuning.Figure 2: Hitmap obtained using a Strontium-90 source. The source profile can be clearly seen.3PoS(Pixel2022)069First Results of ATLASPix3.1 Testbeam R. Zanzottera and E. Hutchinson3. Testbeam ReconstructionFigure 3: This image shows the 2 interleaved telescope arms, the left from the UK, the right from KIT, andthe quad module from INFN. There is a separation distance of 1.27cm between the planes of the interleavedmodules.In April 2022, the ATLASPix3 was tested at DESY using an electron testbeam with a rangeof energies (up to 6 GeV). Various configurations were tested, including a 4-layer telescope andtwo interleaved telescopes. The data were taken over a period of a week. Figure 3 shows theexperimental layout.Currently, the analysis focuses on the 4-plane telescope configuration. The sensors wereoperated in zero-suppressed, triggerless mode. For each hit, a time stamp, location, and ToT wereregistered. Tracks are reconstructed using the Corryvreckan package [5]. Figure 4 shows thecorrelation between the column number on a given plane against that of the reference plane (plane0). As part of analysis process, the Corryvreckan package aligns the planes to ensure that trackingand track reconstruction is accurate. We see strong diagonal lines in Figure 4, showing that boththe Corryvreckan package and the 4-layer telescope are functioning as intended.0 20 40 60 80 100 120Col number020406080100120Col number, layer 0210310Events(a) Layer one against layer zero.0 20 40 60 80 100 120Col number020406080100120Col number, layer 0210310Events(b) Layer two against layer zero.0 20 40 60 80 100 120Col number020406080100120Col number, layer 0210310Events(c) Layer three against layer zero.Figure 4: Correlation in 𝑥 (columns) of layer 𝑛 against layer zero.During the analysis process, a Device Under Test (DUT) layer can be designated after thealignment process. The DUT, layer two here, is not used in track reconstruction. Figure 5 shows4PoS(Pixel2022)069First Results of ATLASPix3.1 Testbeam R. Zanzottera and E. Hutchinsona map of the clusters associated with tracks. Since the pixels are large with respect to the size ofthe charge cloud, there is little charge sharing as can be seen in Figure 6a where the cluster sizedistribution is shown. By far most clusters consist of a single pixel, with a small fraction of largerclusters. The total cluster charge in ToT units is shown in Figure 6b, with the distribution followingthe well-known Landau distribution.0 20 40 60 80 100 120 cluster col050100150200250300350 cluster row012345678Map of associated clustersFigure 5: Map of clusters associated with tracks.0 2 4 6 8 10 12 14 16 18cluster size05101520253035310× # entriesSize distribution of associated clusters(a) Size distribution.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1310×cluster charge [a.u.]0100200300400500600# entriesCharge distribution of associated clusters(b) Charge distribution.Figure 6: Distributions of size and charge of clusters associated with tracks.5PoS(Pixel2022)069First Results of ATLASPix3.1 Testbeam R. Zanzottera and E. Hutchinson400− 300− 200− 100− 0 100 200 300 400m]µ  [hit-xtrackx0100200300400500600# entriesResidual in global X(a) Global residual in 𝑥400− 300− 200− 100− 0 100 200 300 400m]µ  [hit-ytracky020406080100120140160180200220240# entriesResidual in global Y(b) Global residual in 𝑦Figure 7: After alignment procedure, reconstructed global position in 𝑥 (𝑦) minus actual global position in 𝑥(𝑦). Shown here is an unusually distinct multiple peak structure, which is found in both telescopes and DUTresiduals. This is explained in the text, and confirmed in simulation.Figures 7a and 7b show the spatial resolution in 𝑥 and 𝑦 for the DUT. The spiky nature of thedistribution is well understood. Since the beam is almost perpendicular to the detector planes and amajority of the clusters consist of a single pixel, tracks are reconstructed using the centre locationsof pixels. The result of this is that track angles and thus extrapolated track positions are quantized,resulting in the spikes. This pattern was reproduced using the AllPix2 simulation software [6], inFigure 8.The results show that the sensor is performing well in the lab and in testbeam. Further studiesare underway.400− 300− 200− 100− 0 100 200 300 400m]µ  [hit-xtrackx0246810121416182022310×# entriesResidual in global X(a) Residual in global 𝑥400− 300− 200− 100− 0 100 200 300 400m]µ  [hit-ytracky024681012141618310×# entriesResidual in global Y(b) Residual in global 𝑦Figure 8: Simulation of global residuals in 𝑥 and 𝑦 done in AllPix2 to confirm the quantised peak structure.4. ConclusionThe ATLASPix3 was successfully operated in the testbeam at DESY. The reconstruction andanalysis are still ongoing, but first results show that the sensor functions well. The single chiphas been characterised in the lab, and a multi-chip setup has been shown to be working well.The ATLASPix3 is a working, matured full reticle-size chip. More measurements are planned forunderstanding and further characterisation of the chip. The ATLASPix chip has been shown to be6PoS(Pixel2022)069First Results of ATLASPix3.1 Testbeam R. Zanzottera and E. Hutchinsona good candidate for a large area tracker for Higgs factories and other future experiments. Designand tests of multi-chip modules built out of ATLASPix3 sensors and designs for a light-weightsupport and cooling structure for multi-module chains are discussed in a separate contribution tothis conference [7].AcknowledgementsThe measurements leading to these results have been performed at the Test Beam Facility atDESY Hamburg (Germany), a member of the Helmholtz Association (HGF).References[1] I. Perić, “A novel monolithic pixelated particle detector implemented in high-voltage CMOStechnology,” Nuclear Instruments and Methods in Physics Research Section A: Accelerators,Spectrometers, Detectors and Associated Equipment, vol. 582, no. 3, pp. 876–885, 2007.VERTEX 2006.[2] I. Perić, M. Prathapan, H. Augustin, M. Benoit, R. C. Mohr, D. Dannheim, F. Ehrler, F. G.Messaoud, M. Kiehn, A. Nürnberg, R. Schimassek, M. V. Barreto, E. V. Figueras, A. Weber,W. Wong, and H. Zhang, “A high-voltage pixel sensor for the ATLAS upgrade,” Nuclear Instru-ments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors andAssociated Equipment, vol. 924, pp. 99–103, 2019. 11th International Hiroshima Symposiumon Development and Application of Semiconductor Tracking Detectors.[3] R. Schimassek, “Description of the GECCO Test System.” Published online, 16 February 2022.Accessible at https://git.scc.kit.edu/adl_documents/gecco_documentation/-/raw/main/gecco_description.pdf.[4] R. Schimassek, A. Andreazza, H. Augustin, M. Barbero, M. Benoit, F. Ehrler, G. Iacobucci,A. Meneses, P. Pangaud, M. Prathapan, A. Schöning, E. Vilella, A. Weber, M. Weber, W. Wong,H. Zhang, and I. Perić, “Test results of ATLASPIX3 — A reticle size HVCMOS pixel sensor de-signed for construction of multi chip modules,” Nuclear Instruments and Methods in Physics Re-search Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol. 986,p. 164812, 2021.[5] D. Dannheim, K. Dort, L. Huth, D. Hynds, I. Kremastiotis, J. Kröger, M. Munker, F. Pitters,P. Schütze, S. Spannagel, T. Vanat, and M. Williams, “Corryvreckan: a modular 4D trackreconstruction and analysis software for test beam data,” Journal of Instrumentation, vol. 16,p. P03008, March 2021.[6] S. Spannagel, K. Wolters, D. Hynds, N. Alipour Tehrani, M. Benoit, D. Dannheim, N. Gauvin,A. Nürnberg, P. Schütze, and M. Vicente, “Allpix2: A modular simulation framework for silicondetectors,” Nuclear Instruments and Methods in Physics Research Section A: Accelerators,Spectrometers, Detectors and Associated Equipment, vol. 901, pp. 164–172, 2018.7PoS(Pixel2022)069First Results of ATLASPix3.1 Testbeam R. Zanzottera and E. Hutchinson[7] R. Zanzottera, “ATLASPIX3 modules for experiments at e+e− colliders,” in 10th InternationalWorkshop on Semiconductor Pixel Detectors for Particles and Imaging (Pixel2022), (Santa Fe,New Mexico, USA), 12-16 December 2022.8

First Results of ATLASPix 3.1 Testbeam

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First Results of ATLASPix 3.1 Testbeam

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