The Malta CMOS pixel detector prototype for the ATLAS Pixel ITK

Abstract

The ATLAS experiment is planning a major upgrade of its tracking detectors, both strip and pixel, to take full advantage of the High Luminosity LHC. A novel Monolithic Active Pixel Sensor based on 180 nm TowerJazz CMOS imaging technology, dubbed MALTA, has been designed to meet the radiation hardness requirements (1.5x10 15 1 MeV n eq /cm 2) of the outer barrel layers of the ITk Pixel detector. MALTA combines low noise (ENC<20 e −) and low power operation (1 µW/pixel) with a fast signal response (25 ns bunch crossing) in small pixel size (36.4x36.4 µm 2), with a novel high-speed asynchronous readout architecture to cope with the high hit-rates expected at HL-LHC. Extensive lab testing and characterisation in particle beam tests have been conducted on this design and compared with previous prototypes of the same technology. An overview of the sensor technology and readout architecture are presented along with the preliminary results from laboratory tests, radioactive source tests and beam tests.

Depleted Monolithic Active Pixel Sensors in the LFoundry 150 nm and TowerJazz 180 nm CMOS Technologies

“…The higher efficiency measured for the RDPW region suggests that the shape of deep pwell may modulate the field lines towards the sensing node. Similar effects have also been observed in the MALTA chip sharing a similar sensor configuration as TJ-Monopix1 [7]. By projecting the efficiency into sub-pixel regions, low efficient corners have been observed in the unirradiated chip.…”

“…Hence, during the last decade, there has been a trend to improve the depletion within the sensitive layer of CMOS pixels [4], leading eventually to designs with fast charge collection through drift, namely DMAPS. Recently, significant progress has been made for DMAPS devices with several large-scale demonstrator chips developed in different CMOS technologies [5][6][7][8][9]. These devices combine a fully depleted sensitive layer with on-chip fast readout electronics, and are expected to tolerate particle fluences of at least 10 15 n eq /cm 2 and total ionization doses of at least 80 Mrad, while being able to cope with a particle rate higher than 100 MHz/cm 2 and distinguish hits from different LHC bunch crossings (25 ns).…”

Radiation hard monolithic CMOS sensors with small electrodes for the HL-LHC and beyond

“…It features an asynchronous readout with a clock-less matrix architecture, and 2-3 collection electrode size [2,3]. The first prototypes showed poor lateral field after irradiation [4,5] for which additional process modifications were necessary, namely one with an additional extra deep p-well (EDPW) and the other with a gap in the n-layer blanket (NGAP). These were studied on the Mini-MALTA prototype that is a 5 × 1.7 mm 2 DMAPS demonstrator, with 64 × 16 pixels of the same size of the MALTA, that showed full efficiency in particle beam tests after 1e15 n eq /cm 2 at 200 electrons threshold and 6 V bias on sectors with enlarged transistors [6].…”

“…This value is extracted from the convolution of a Gaussian distribution with a two-sided step function with 36. 4 width corresponding to the pixel pitch of MALTA, as shown on figure 2 (top left). However, when data is fitted to a double Gaussian distribution where the RMS of one of the Gaussians is constrained to 10.5 compatible with the resolution of the epitaxial based MALTA telescope, the second Gaussian yields a width of 9.4,…”