Mini-MALTA is a Monolithic Active Pixel Sensor prototype developed in the TowerJazz 180 nm CMOS imaging process, with a small collection electrode design (3um), and a small pixel size (36.4 um), on high resistivity substrates and large voltage bias. It targets the outermost layer of the ATLAS ITK Pixel detector for the HL-LHC. This design addresses the pixel in-efficiencies observed in MALTA and TJ-Monopix to meet the radiation hardness requirements. This contribution will present the results from characterisation in particle beam tests that show full efficiency up to 1E15 neq/cm2 and 70 Mrad.

1. ATLAS Phase-II Upgrade Scoping Document, Rep. CERN-LHCC-2015-020; LHCC-G-166, CERN, Geneva, Switzerland, 2015.
   Retrieved from: https://cds.cern.ch/record/2055248
   Retrieved on: Feb. 25, 2019
2. Technical Design Report for the ATLAS Inner Tracker Pixel Detector, Rep. CERN-LHCC-2017-021; ATLAS-TDR-030, CERN, Geneva, Switzerland, 2017.
   Retrieved from: https://cds.cern.ch/record/2285585
   Retrieved on: Feb. 25, 2019
3. P. S. Miyagawa, I. Dawson, Radiation background studies for the Phase II inner tracker upgrade, Rep. ATL-UPGRADE-PUB-2013-012, CERN, Geneva, Switzerland, 2013.
   Retrieved from: https://cds.cern.ch/record/1516824
   Retrieved on: Feb. 25, 2019
4. H. Pernegger et al., “First tests of a novel radiation hard CMOS sensor process for Depleted Monolithic Active Pixel Sensors,” J. Instrum., vol. 12, no. 6, Jun. 2017.
   DOI: 10.1088/1748-0221/12/06/P06008
5. I. Caicedo et al., “The Monopix chips: depleted monolithic active pixel sensors with a column-drain read-out architecture for the ATLAS Inner Tracker upgrade,”in Proc. 9th Int. Workshop Semicond. Pixel Detect. Part. Imaging (PIXEL 2018), Taipei, Taiwan, 2018.
   DOI: 10.1088/1748-0221/14/06/C06006
6. R. Cardella et al., “MALTA: an asynchronous readout CMOS monolithic pixel detector for the ATLAS High-Luminosity upgrade,” in Proc. 9th Int. Workshop Semicond. Pixel Detect. Part. Imaging(PIXEL 2018), Taipei, Taiwan, 2018.
   DOI : 10.1088/1748-0221/14/06/C06019
7. M. Munker et al., “Simulations of CMOS pixel sensors with a small collection electrode, improved for a faster charge collection and increased radiation tolerance,” J. Instrum., vol. 14, no. 5, May 2019.
   DOI: 10.1088/1748-0221/14/05/C05013
8. I. A. Tortajada, “MiniMALTA: Radiation hard pixel designs for small-electrode monolithic CMOS sensors for the High Luminosity LHC,” J. Instrum., Unpublished.
9. M. Kiehn et al., Proteus beam telescope reconstruction version 1.4.0, Zenodo, Geneva, Switzerland, 2019.
   DOI: 10.5281/zenodo.2586736
10. C. Kleinwort, “General broken lines as advanced track fitting method,” Nucl. Instrum. Methods Phys. Res. vol. 673, pp. 107 – 110, May 2012.
    DOI: 10.1016/j.nima.2012.01.024