Depleted fully monolithic active CMOS pixel sensors (DMAPS) in high resistivity 150 nm technology for LHC

Abstract

Depleted monolithic CMOS active pixel sensors (DMAPS) have been developed in order to demonstrate their suitability as pixel detectors in the outer layers of a toroidal LHC apparatus inner tracker (ATLAS ITk) pixel detector in the high-luminosity large hadron collider (HL-LHC). Two prototypes have been fabricated using 150 nm CMOS technology on high resistivity (≥ 2 kΩ·cm 2 ) wafers. The chip size is equivalent to that of the current ATLAS pixel detector readout chip. One of the prototypes is used for detailed characterization of the sensor and the analog readout of the DMAPS. The other is a fully monolithic DMAPS including fast readout digital logic that handles the required hit rate. In order to yield a strong homogeneous electric field within the sensor volume, thinning of the wafer was tested. The prototypes were irradiated with X-ray up to a total ionization dose (TID) of 50 Mrad and with neutrons up to non-ionizing energy loss (NIEL) of 10 15 n eq /cm 2 . The analog readout circuitry maintained its performance after TID irradiation, and the hit-efficiency at > 10 −7 noise occupancy was as high as 98.9 % after NIEL irradiation.

CMOS monolithic pixel sensors based on the column-drain architecture for the HL-LHC upgrade

“…By applying a sophisticated threshold tuning algorithm based on the pixel noise occupancy, the threshold was tuned to 1500 e − with a dispersion of ≈ 100 e − . The achieved threshold value is low compared to the MPV, which is higher than 12 keV for an unirradiated sample and 4.5 keV after irradiation [6]. While the threshold value is not significantly affected after irradiation, the ENC did increase from 200 e − to 350 e − due to the background TID, with a dispersion equal to 30 − 70 e − depending on the CSA flavor.…”

“…Its depth can vary from 750 µm to 100 µm after backside processing. The generated strong and uniform electric field ensures high radiation tolerance to Non Ionizing Energy Loss (NIEL) damage and high charge collection efficiency [4,6]. The disadvantage of this implementation is the large sensor capacitance (≈ 300 − 400 f F) that degrades the analog performance in terms of noise and signal rise time, and has to be compensated with increased power consumption.…”

“…The LF-Monopix chip [6,7,10] is the successor to CCPD LF and LF-CPIX [4,6] development line in 150 nm LFoundry technology and the first to incorporate a full standalone fast readout. It consists of a 129x36 matrix of pixels with 50x250 µm 2 size, while its total size is 10x9.5 mm 2 .…”

“…Moreover they must be able to comply with the 25ns timing requirement of the ATLAS experiment. DMAPS prototypes manufactured in different technologies have been reported with encouraging results regarding the sensor radiation tolerance [4,5,6,7]. Additionally, multiple nested wells offered by modern CMOS processes allow for complex readout circuitry to be implemented inside the pixel, enabling the use of fast readout architectures.…”

Progress on the radiation tolerance of CMOS Monolithic Active Pixel Sensors

“…Hereafter, it was found to withstand depleting voltages above 260 V. A full depletion is reported to occur at a voltage of 60 V for the 200 µm thick, non-irradiated sensor. Radiation test results from LF-Monopix and its precurser LF-CPIX are reported in [131]. The LF-CPIX, which hosts similar analog pixel structures but misses the complex readout structure, was exposed to up to 50 Mrad soft X-rays.…”