Monolithic Silicon Pixel Research Articles

Testbeam results of irradiated SiGe BiCMOS monolithic silicon pixel detector without internal gain layer

Samples of the monolithic silicon pixel ASIC prototype produced in 2022 within the framework of the Horizon 2020 MONOLITH ERC Advanced project were irradiated with 70 MeV protons up to a fluence of 1 × 1016 neq/cm2, and then tested using a beam of 120 GeV/c pions. The ASIC contains a matrix of 100 μm pitch hexagonal pixels, read out by low noise and very fast frontend electronics produced in a 130 nm SiGe BiCMOS technology process. The dependence on the proton fluence of the efficiency and the time resolution of this prototype was measured with the frontend electronics operated at a power density between 0.13 and 0.9 W/cm2. The testbeam data show that the detection efficiency of 99.96% measured at sensor bias voltage of 200 V before irradiation becomes 96.2% after a fluence of 1 × 1016 neq/cm2. An increase of the sensor bias voltage to 300 V provides an efficiency to 99.7% at that proton fluence. The timing resolution of 20 ps measured before irradiation rises for a proton fluence of 1 × 1016 neq/cm2 to 53 and 45 ps at HV = 200 and 300 V, respectively.

Measurement of Si pixel sensor alignment for the ALICE ITS detector

Abstract A Large Ion Collider Experiment (ALICE) experiment is one of the four experiments at the Large Hadron Collider (LHC) designed to investigate the status of matter under very high energy densities produced during heavy-ion collisions. The ALICE inner tracking system (ITS) consists of seven concentric cylindrical layers of monolithic silicon pixel sensors known as ALICE pixel detector (ALPIDE). The sensors are used to reconstruct the paths of charged particles generated in the collisions. The sensor alignment of the detector must be adjusted to a high precision standard. The adjustment objective is to obtain a detector that can undertake high-resolution measurements. This paper introduces a method for measuring the reference markers utilized in sensor alignment determination. Markers engraved at the chip corners have been detected using the Hough transform, Canny edge detection, and template matching techniques. The distances between two markers are measured to determine the accuracy of the pixel sensor alignment before and after assembly. The proposed methods exhibit an accuracy exceeding 99% and demonstrate high speed analysis. The average processing times for detecting the circle and cross markers are 105.9 ms/image and 113.8 ms/image, respectively. The sensor alignment of the detector must be adjusted to a high precision standard. However, recent studies have shown deviations of up to 5 μ m above the desired value in the measured sensor position. Such deviations do not represent a major issue, nevertheless it is important to measure them in order to speed-up and make more accurate the recursive track-based alignment procedure used to reconstruct the position of each pixel sensor in the tracking detector. The proposed method offers a promising solution to deliver precise and rapid measurements for a large number of examined objects.

Time resolution of a SiGe BiCMOS monolithic silicon pixel detector without internal gain layer with a femtosecond laser

The time resolution of the second monolithic silicon pixel prototype produced for the MONOLITH H2020 ERC Advanced project was studied using a femtosecond laser. The ASIC contains a matrix of hexagonal pixels with 100 μm pitch, readout by low-noise and very fast SiGe HBT frontend electronics. Silicon wafers with 50 μm thick epilayer with a resistivity of 350 Ωcm were used to produce a fully depleted sensor. At the highest frontend power density tested of 2.7 W/cm2, the time resolution with the femtosecond laser pulses was found to be 45 ps for signals generated by 1200 electrons, and 3 ps in the case of 11k electrons, which corresponds approximately to 0.4 and 3.5 times the most probable value of the charge generated by a minimum-ionizing particle. The results were compared with testbeam data taken with the same prototype to evaluate the time jitter produced by the fluctuations of the charge collection.

Expected performance of the High Energy Particle Detector (HEPD-02) tracking system on board of the second China Seismo-Electromagnetic Satellite

The China Seismo-Electromagnetic Satellite (CSES) is a scientific space program that aims to deepen the comprehension of the time correlation between the main earthquake shocks and an increase in the electron flux in the inner Van Allen belt. For this purpose, the suite of payloads on board the second CSES satellite (CSES-02) consists of several detectors. The launch of CSES-02 is foreseen in 2024. The present work is focused on the second generation High-Energy Particle Detector (HEPD-02), developed by Limadou Italian collaboration, and in particular on its tracking system (Direction Detector — DD) to reconstruct the incident particle angle. The DD is made of five standalone tracking modules, consisting, as first and unique case, of monolithic silicon pixel sensors (MAPS), namely ALTAI. This chip was developed in the framework of the ALICE (A Large Ion Collider Experiment) ITS sensor studies. The results on the DD performance are discussed based on the demanding requirements of space applications.

Radiation tolerance of SiGe BiCMOS monolithic silicon pixel detectors without internal gain layer

A monolithic silicon pixel prototype produced for the MONOLITH ERC Advanced project was irradiated with 70 MeV protons up to a fluence of 1 × 1016 1 MeV n eq/cm2. The ASIC contains a matrix of hexagonal pixels with 100 μm pitch, readout by low-noise and very fast SiGe HBT frontend electronics. Wafers with 50 μm thick epilayer with a resistivity of 350 Ωcm were used to produce a fully depleted sensor. Laboratory tests conducted with a 90Sr source show that the detector works satisfactorily after irradiation. The signal-to-noise ratio is not seen to change up to fluence of 6 × 1014 n eq/cm2. The signal time jitter was estimated as the ratio between the voltage noise and the signal slope at threshold. At -35°C, sensor bias voltage of 200 V and frontend power consumption of 0.9 W/cm2, the time jitter of the most-probable signal amplitude was estimated to be σ t 90Sr = 21 ps for proton fluence up to 6 × 1014 n eq/cm2 and 57 ps at 1 × 1016 n eq/cm2. Increasing the sensor bias to 250 V and the analog voltage of the preamplifier from 1.8 to 2.0 V provides a time jitter of 40 ps at 1 × 1016 n eq/cm2.

The first test of a monolithic silicon pixel detector ASIC for the detection of electromagnetic showers of TeV energy in the FASER experiment at the LHC

The FASER experiment at the LHC is designed to look for new, long-lived fundamental particles. A W-Si preshower detector is currently under construction, with the objective of enabling the discrimination of photon pairs with O(TeV) energies and separation down to 200 μm, extending the discovery potential of the experiment. The detector will be based on a new monolithic silicon pixel sensor in 130 nm SiGe BiCMOS. The first test of the ASIC from a pre-production run shows that the building blocks of the monolithic silicon pixel detector are functional.

Development of novel low-mass module concepts based on MALTA monolithic pixel sensors

The MALTA CMOS monolithic silicon pixel sensors has been developed in the Tower 180 nm CMOS imaging process. It includes an asynchronous readout scheme and complies with the ATLAS inner tracker requirements for the HL-LHC. Several 4-chip MALTA modules have been built using Al wedge wire bonding to demonstrate the direct transfer of data from chip-to-chip and to read out the data of the entire module via one chip only. Novel technologies such as Anisotropic Conductive Films (ACF) and nanowires have been investigated to build a compact module. A lightweight flex with 17 μm trace spacing has been designed, allowing compact packaging with a direct attachment of the chip connection pads to the flex using these interconnection technologies. This contribution shows the current state of our work towards a flexible, low material, dense and reliable packaging and modularization of pixel detectors.

20 ps time resolution with a fully-efficient monolithic silicon pixel detector without internal gain layer

A second monolithic silicon pixel prototype was produced for the MONOLITH project. The ASIC contains a matrix of hexagonal pixels with 100 μm pitch, readout by a low-noise and very fast SiGe HBT frontend electronics. Wafers with 50 μm thick epilayer of 350 Ωcm resistivity were used to produce a fully depleted sensor. Laboratory and testbeam measurements of the analog channels present in the pixel matrix show that the sensor has a 130 V wide bias-voltage operation plateau at which the efficiency is 99.8%. Although this prototype does not include an internal gain layer, the design optimised for timing of the sensor and the front-end electronics provides a time resolutions of 20 ps.

The 100[formula omitted]PET project: A small-animal PET scanner for ultra-high resolution molecular imaging with monolithic silicon pixel detectors

Recent developments in semiconductor pixel detectors allow a new generation of positron-emission tomography (PET) scanners that, combined with advanced image reconstruction algorithms, will allow for a few hundred microns spatial resolutions. Such novel scanners will pioneer ultra-high resolution molecular imaging, a field that is expected to have an enormous impact in several medical domains, neurology among others.The University of Geneva, the École Polytechnique Fédérale de Lausanne, and the University of Lucerne, have launched the 100μPET project that aims to produce a small-animal PET scanner with ultra-high resolution. The scanner will be composed of 4 ”towers”, each containing a stack of 60 monolithic silicon pixel sensors for the direct measurement of the annihilation photons. The sensors are 270 μm thick, providing unprecedented depth-of-interaction measurement. Monte Carlo simulations were done simulating different scanner conditions, resulting in a spatial resolution down to 0.2 mm FWHM and a sensitivity of 3.2%.

Characterization of AC coupled SOI pixel sensor with pinned depleted diode structure

The experiment of the future electron–positron​ colliders has unprecedented requirements on the vertex resolution, such as around 3μm single point resolution for the inner most detector layer, with fast readout, and very low power-consumption density and material budget. Significant efforts have been put into the development of monolithic silicon pixel sensors, but there have been some challenges to combine all those stringent specifications in a small pixel area. This paper presents a compact prototype pixel sensor fabricated in LAPIS 200 nm SOI process and focuses on the characterization of capacitance of the sensing node with a pinned depleted diode (PDD) structure adopting a novel method of forward bias voltage and AC-coupling on the diode. Three PDD structures with 16 × 20μm2 pixel size were designed and compared using radioactive sources and injected charge. The measurements shows that the designed PDD structure has very low leakage current and around 3.7fF of equivalent input capacitance.

Heavy-ion beam test of a monolithic silicon pixel sensor with a new 130 nm High-Resistivity CMOS process

The Topmetal-M is a newly designed monolithic silicon pixel sensor for charged particle tracking based on a novel detector structure and implemented in a new 130 nm High-Resistivity (>1 kΩ cm) CMOS process. This sensor integrates the functionality of the Monolithic Active Pixel Sensor (MAPS) and the Topmetal sensor. It has a matrix of 512 × 400 pixels with the pitch of 40μm×40μm. Heavy-ion campaigns with a 181Ta35+ beam have been performed to study the performance of this Topmetal-M sensor. The test results demonstrate it has an excellent response to particle energy deposition. Furthermore,this sensor is still fully functional after exposure to ∼14.1 krad, and no Single Event Latch-up (SEL) occurred. In addition, the baseline, the Equivalent Noise Charge (ENC), and the number of bad pixels show relatively good performance.

Efficiency and time resolution of monolithic silicon pixel detectors in SiGe BiCMOS technology

A monolithic silicon pixel detector prototype has been produced in the SiGe BiCMOS SG13G2 130 nm node technology by IHP. The ASIC contains a matrix of hexagonal pixels with pitch of approximately 100 μm. Three analog pixels were calibrated in laboratory with radioactive sources and tested in a 180 GeV/c pion beamline at the CERN SPS. A detection efficiency of (99.9-0.2 +0.1)% was measured together with a time resolution of (36.4 ± 0.8) ps at the highest preamplifier bias current working point of 150 μA and at a sensor bias voltage of 160 V. The ASIC was also characterized at lower bias voltage and preamplifier current.

Studies for low mass, large area monolithic silicon pixel detector modules using the MALTA CMOS pixel chip

The MALTA monolithic silicon pixel sensors have been used to study dicing and thinning of monolithic silicon pixel detectors for large area and low mass modules. Dicing as close as possible to the active circuitry will allow to build modules with very narrow inactive regions between the sensors. Inactive edge regions of less than 5μ m to the electronic circuitry could be achieved for 100μm thick sensors. The MALTA chip (Cardella et al., 2019) also offers the possibility to transfer data and power directly from chip to chip. Tests have been carried out connecting two MALTA chips directly using ultrasonic wedge wire bonding. Results from lab tests show that the data accumulated in one chip can be transferred via the second chip to the readout system, without the need of a flexible circuit to route the signals. The concept of chip to chip data and power transfer to achieve low mass modules has also been studied on prototype wafers using Cu-stud interconnection bridges. First results are presented, outlining technical challenges and possible future steps to achieve a low mass large area monolithic pixel sensor module.

Time resolution and power consumption of a monolithic silicon pixel prototype in SiGe BiCMOS technology

SiGe BiCMOS technology can be used to produce ultra-fast, low-power silicon pixel sensors that provide state-of-the-art time resolution even without internal gain. The development of such sensors requires the identification and control of the main factors that may degrade the timing performance as well as the characterisation of the dependance of the sensor time resolution on the amplifier power consumption. Measurements with a 90Sr source of a prototype sensor produced in SG13G2 technology from IHP Microelectronics shows a time resolution of 140 ps at an amplifier current of 7 μA and 45 ps at a power consumption of 150 μA. The resolution on the measurement of the signal time-over-threshold, which is used to correct for time walk, is the main factor affecting the timing performance of this prototype.

The Mu3e scintillating fiber timing detector

A new experiment, Mu3e, to search for charged Lepton Flavor Violation in the rare neutrinoless μ+→e+e+e− decay is in preparation at the Paul Scherrer Institute using the most intense continuous surface muon beam in the world. The Mu3e detector is based on thin monolithic active silicon pixel sensors (HV-MAPS) for very precise tracking in conjunction with scintillating fibers and scintillating tiles coupled to silicon photomultipliers (SiPMs) for accurate timing measurements and is designed to operate at very high intensities.In order to reach a sensitivity of 10−16, all backgrounds must be rejected below this level. To suppress all forms of combinatorial background, a very thin (thickness ∼0.2% of a radiation length X0) Scintillating Fiber detector with few 100 ps time resolution, efficiency in excess of 96%, and spatial resolution of ∼100μm has been developed. In this paper we report on the development and performance of the fiber detector, from the scintillating fiber ribbons through the SiPM array photo-sensors up to the front end electronics.

Development of the Thin TOF-PET scanner based on fast monolithic silicon pixel sensors

The Thin-TOF PET (TT-PET) project aims at the construction of a small-animal PET scanner based on silicon monolithic pixel sensors with 30ps time resolution for 511keV photons, equivalent to 100ps time resolution for minimum ionizing particles. Iterative image reconstruction on Monte-Carlo simulation shows that the scanner can produce high signal-to-noise ratio images with good spatial resolution throughout the whole field of view. The demonstrator chip, comprising a 3 × 10 pixel matrix and a 50ps binning TDC, was tested at the CERN SPS beam test facility. The demonstrator shows an efficiency greater than 99.9% and a time resolution for minimum ionizing particles of approximately 110ps.

The Mu3e experiment at PSI

Mu3e will search for charged Lepton Flavor Violation in the neutrinoless muon decay \mu^+ \rightarrow e^+ e^- e^+μ+→e+e−e+ with a sensitivity down to 10^{-16}10−16 (90% C.L.) using the world most intense continuous muon beam at PSI. This search requires a large acceptance detector capable of coping with rates of up to 2 \times 10^92×109 stopped muons per second with excellent momentum, spatial, and time resolution. The Mu3e detector is based on thin monolithic active silicon pixel sensors for tracking in conjunction with scintillating fibers and tiles for timing measurements. The Mu3e apparatus is under constructions and first data is expected in 2020.

Characterization of the demonstrator of the fast silicon monolithic ASIC for the TT-PET project

The TT-PET collaboration is developing a small animal TOF-PET scanner based on monolithic silicon pixel sensors in SiGe BiCMOS technology. The demonstrator chip, a small-scale version of the final detector ASIC, consists of a 03 × 1 pixel matrix integrated with the front-end, a 50 ps binning TDC and read out logic. The chip, thinned down to 100 μm and backside metallized, was operated at a voltage of 180 V. The tests on a beam line of minimum ionizing particles show a detection efficiency greater than 99.9% and a time resolution down to 110 ps.

Experimental investigation of new ultra-lightweight support and cooling structures for the new Inner Tracking System of the ALICE Detector

Thermal cooling performances of extremely lightweight mechanical carbon fiber support structures with an integrated liquid cooling system for monolithic silicon pixel detectors have been investigated. The high heat removal efficiency using single-phase liquid flow is shown for a power density up to 0.5 W/cm2. These solutions provide therefore possibility to build a detector with a record radiation length of 0.3% per layer, ensuring considerable extensions of the physical program of investigations of the quark-gluon plasma in ultra-relativistic heavy-ion collisions at the Large Hadron Collider.

Test beam measurement of the first prototype of the fast silicon pixel monolithic detector for the TT-PET project

The TT-PET collaboration is developing a PET scanner for small animals with 30 ps time-of-flight resolution and sub-millimetre 3D detection granularity. The sensitive element of the scanner is a monolithic silicon pixel detector based on state-of-the-art SiGe BiCMOS technology. The first ASIC prototype for the TT-PET was produced and tested in the laboratory and with minimum ionizing particles. The electronics exhibit an equivalent noise charge below 600 e− RMS and a pulse rise time of less than 2 ns , in accordance with the simulations. The pixels with a capacitance of 0.8 pF were measured to have a detection efficiency greater than 99% and, although in the absence of the post-processing, a time resolution of approximately 200 ps .