Forward Pixel Research Articles

Development of a timing chip prototype in 110 nm CMOS technology

We present a readout chip prototype for future pixel detectors with timing capabilities. The prototype is intended for characterizing 4D pixel arrays with a pixel size of 100x100 μm2, where the sensors are Low Gain Avalanche Diodes (LGADs). The long term focus is towards a possible replacement of disks in the extended forward pixel system (TEPX) of the CMS experiment during the High Luminosity LHC (HL-LHC). The requirements for this ASIC are the incorporation of a Time to Digital Converter (TDC) in the small pixel area, low power consumption, and radiation tolerance up to 5 × 1015 n eq cm−2 to withstand the radiation levels in the innermost detector modules for 3000 fb−1 of the HL-LHC (in the TEPX). A prototype has been designed and produced in 110 nm CMOS technology at LFoundry and UMC with different versions of TDC structures, together with a front end circuitry to interface with the sensors. The design of the TDC will be discussed, with the test set-up for the measurements, and the first results comparing the performance of the different structures.

CMS Phase-1 pixel detector refurbishment during LS2 and readiness towards the LHC Run 3

The CMS Phase-1 pixel detector was extracted from the underground cavern after the end of the LHC Run 2 in 2019 and has been kept cold to protect the silicon sensors during the long shutdown period (LS2) in 2019–2021. The LHC is now preparing for the next period of data taking, Run 3, which is scheduled to start in spring 2022. The Phase-1 pixel detector was going through a series of refurbishment and repairs this year to improve the quality of the collected data and enhance the detector performance. The innermost barrel pixel layer has been replaced with new modules and features improved front-end readout chips (PROC600v4), token bit manager chips (TBM10d), and circuit boards to rectify the issues discovered in Run 2. The forward pixel detector has been equipped with new cooling inlets for safe handling and features a revised high-voltage power distribution scheme to better match the low-voltage granularity. All the DC-DC converter modules have been replaced with new modules featuring an improved FEAST2.3 ASIC, which is considerably more robust against the total ionizing dose effect and thus prevents them from breaking during operation. Overall, this article will summarize the refurbishment work of the pixel detector during LS2, and highlight the readiness towards the LHC Run 3 after installation and commissioning.

Quality control of silicon pixel wafers for the CMS Phase-1 pixel upgrade

The CMS detector at the CERN Large Hadron Collider features as its innermost component a silicon pixel detector. The original pixel detector was completely replaced during the 2016-2017 winter technical stop. One of the goals of this Phase-1 Upgrade of the pixel detector was to replace the sensors in the original CMS forward pixel detector with new, unirradiated sensors. The new CMS forward pixel detector must survive an integrated luminosity of 300 fb$^{-1}$ before being replaced again prior to the High-Luminosity LHC era. Just as in the original construction, the Phase-1 forward pixel sensors were made of n$^{+}$-in-n Diffusion Oxygenated Float Zone silicon. This note documents the quality spot-checking of the new sensors, comparing our results with those provided by the vendor. In general there was good agreement between the results.

Intellectual Property-Based Lossless Image Compression for Camera Systems [Hardware Matters

This article presents a novel framework for intellectual property (IP)- based lossless image compression used for camera systems. The proposed approach presents two subframeworks: a) two-dimensional (2-D) Haar wavelet transformation (HWT)- based forward pixel calculator IP for image compression and b) 2-D HWTbased inverse pixel calculator IP for image decompression. Each framework is capable of fully compressing and decompressing images through onestage computation during forward and inverse transformations. The proposed approach has been tested on images of critical data sets of medical applications [e.g., computed tomography (CT) images and satellite applications, including NASA images]. Results of compressed and decompressed images along with compression efficiency through the proposed framework for IP-based lossless image compression are also reported in this article.

CMS Pixel Detector design for HL-LHC

The LHC machine is planning an upgrade program which will smoothly bring the luminosity to about 7.5×1034cm−2s−1 in 2028, to possibly reach an integrated luminosity of 3000 fb−1 by the end of 2037. This High Luminosity scenario, HL-LHC, will present new challenges in higher data rates and increased radiation. In order to maintain its physics reach the CMS collaboration has undertaken a preparation program of the detector known as Phase-2 upgrade. The CMS Phase-2 Pixel upgrade will require a high bandwidth readout system and high radiation tolerance for sensors and on-detector ASICs. Several technologies for the upgrade sensors are being studied. Serial powering schemes are under consideration to accommodate significant constraints on the system. These prospective designs, as well as new layout geometries that include very forward pixel discs, will be presented together with performance estimation.

The pixel tracking telescope at the Fermilab Test Beam Facility

An all silicon pixel telescope has been assembled and used at the Fermilab Test Beam Facility (FTBF) since 2009 to provide precise tracking information for different test beam experiments with a wide range of Detectors Under Test (DUTs) requiring high resolution measurement of the track impact point. The telescope is based on CMS pixel modules left over from the CMS forward pixel production. Eight planes are arranged to achieve a resolution of less than 8μm on the 120GeV proton beam transverse coordinate at the DUT position. In order to achieve such resolution with 100×150μm2 pixel cells, the planes were tilted to 25 degrees to maximize charge sharing between pixels. Crucial for obtaining this performance is the alignment software, called Monicelli, specifically designed and optimized for this system. This paper will describe the telescope hardware, the data acquisition system and the alignment software constituting this particle tracking system for test beam users.

Reliability and performance studies of DC-DC conversion powering scheme for the CMS pixel tracker at SLHC

The upgrades of the Large Hadron Collider (LHC) introduce a significant challenge to the power distribution of the detectors. DC-DC conversion is the preferred powering scheme proposed to be integrated for the CMS tracker to deliver high input voltage levels and performing a step-down conversion nearby the detector modules. In this work, we propose a step-up/step-down powering scheme by performing voltage step up at the CAEN supply unit and voltage step down near the detector. We designed step-up converters and investigate the pixel performance and power loss on the FPIX power distribution system. Tests are performed using the PSI46 pixel readout chips on a forward pixel panel module and the DC-DC converters developed at CERN and Fermilab. Reliability studies include the voltage drop measurements on the readout chips and the power supply noise generated from the converter. Performance studies include pixel noise and threshold dispersion results. Comparison between step-down only and step-up/step-down conversion powering schemes are provided.

Commissioning of the Forward Pixel system before the final installation in CMS

I will present the results of the commissioning of the CMS Forward Pixel system, that has been carried out at CERN before the final installation in CMS. The commissioning was meant to check every mechanical and electrical aspect of the system and to verify that the actual performance of the detector, once assembled and with the same power and readout systems that will be used in the final experiment, was still of the same high quality as during the production phase. The Forward Pixel system presents a negligible number of dead channels, lower than 0.04%, and an average noise lower than 120 electrons.

Commissioning of the CMS Forward Pixel Detector

The Compact Muon Solenoid (CMS) experiment is scheduled for physics data taking in summer 2009 after the commissioning of high energy proton-proton collisions at the Large Hadron Collider (LHC). At the core of the CMS all-silicon tracker is the silicon pixel detector, comprising three barrel layers and two pixel disks in the forward and backward regions, accounting for a total of 66 million channels. The pixel detector will provide high-resolution, 3D tracking points, essential for pattern recognition and precise vertexing, while being embedded in a hostile radiation environment. The end disks of the pixel detector, known as the Forward Pixel detector, has been assembled and tested at Fermilab, USA. It has 18 million pixel cells with dimension 100 × 150 μm2. The complete forward pixel detector was shipped to CERN in December 2007, where it underwent extensive system tests for commissioning prior to the installation. The pixel system was put in its final place inside the CMS following the installation and bake out of the LHC beam pipe in July 2008. It has been integrated with other sub-detectors in the readout since September 2008 and participated in the cosmic data taking. This report covers the strategy and results from commissioning of CMS forward pixel detector at CERN.

Radiation tolerance of the CMS forward pixel detector

In this paper we present some results on the radiation tolerance of the CMS forward pixel detector. They were obtained from a beam test at Fermilab of a pixel-detector module, which was previously irradiated up to a maximum dose of 45 Mrad of protons at 200 MeV. It is shown that CMS forward pixel detector can tolerate this radiation dose without any major deterioration of its performance.

Geometry simulation and physics with the CMS forward pixel detector

The Forward Pixel Detector of CMS is an integral part of the Tracking system, which will play a key role in addressing the full physics potential of the collected data. It has a very complex geometry that encompasses multilayer structure of its detector modules. This presentation describes the development of geometry simulation for the Forward Pixel Detector. A new geometry package has been developed, which uses the detector description database (DDD) interface for the XML (eXtensive Markup Language) to GEANT simulation. This is necessary for digitization and GEANT4 reconstruction software for tracking. The expected physics performance is also discussed.

Geometry simulation and physics with the CMS forward pixel detector

Geometry simulation and physics with the CMS forward pixel detector

Construction of the forward pixel detector

The Compact Muon Solenoid (CMS) Experiment is scheduled for data taking in 2008 at the Large Hadron Collider (LHC). It has an all-silicon tracking system with a Pixel Detector as the innermost component. The silicon Pixel Detector is made of two disks on each side of the interaction point with three barrel layers in between. It will play a crucial role in realizing the physics potential at LHC by providing a 3D space resolution on the order of ten microns for pattern recognition and track reconstruction. The disks are collectively called the Forward Pixel Detector and are being assembled at Fermilab, USA The detector modules for the disks alone consist of eighteen million pixels. The design and present status of the Forward Pixel Detector is presented here.

Experience with mass production bump bonding with outside vendors in the CMS FPIX project

The experience with mass production bump bonding with outside vendors gained in the CMS Forward Pixel project is discussed. Results from two different vendors are presented. After an initial R&D and pre-production phase, 20% of the production parts have been completed. The main results are shown here.

The Renaissance: A test-stand for the Forward CMS Pixel Tracker assembly

The CMS Forward Pixel Tracker will consist of two end-cap blocks, each made of two disks lodging sensors and Read-Out Chips (ROCs) (grouped into plaquettes of different sizes) for a total of about 18 million read-out channels. During the assembly phase, prior to the physical mounting of the plaquettes on the disks a thorough electronic test is necessary to check each channel for functionality, noise level, required threshold trimming and bump-bond quality. To this extent a complete test-stand system, based on custom PCI cards and specialized software, has been developed. Different methods have been evaluated and implemented to electronically assess the amount of malfunctioning bump-bonds. Determination of the correct parameters for initialization of the ROCs has also been implemented as an automatic procedure; data are finally fed into a centralized database for subsequent retrieval during detector initialization or for off-line analysis. In this paper we describe requirements, design and implementation of such a system, which is currently in use at the Silicon Detector Facility (SiDet) Laboratory of FNAL for the final assembly of the Forward Tracker system.

CMS forward pixels geometry simulation

The large hadron collider (LHC) is being built at the European Center for Nuclear Research (CERN) to produce collisions between protons and protons at an unprecedented energy of 14 TeV. Compact muon solenoid (CMS) is one the five detectors that will be placed on the 17-mile-long ring of the LHC to record data for physics analysis from these collisions. The forward pixel detector of CMS is an integral part of the tracking system, which would play a key role in addressing the full physics potential of the collected data. This note describes the development of geometry simulation for the forward pixel detector.

The CMS Forward Pixel Detector

At the core of CMS all-silicon tracker is the pixel detector. It provides fine granularity for charged track reconstruction in three-dimensional space with resolutions on the order of 10 μm. It consists of two parts—barrels and disks. The disks are called the Forward Pixel Detector and are being assembled at Fermilab, USA. There are eighteen million readout channels for the four disks. Production for this detector begins in summer of 2006. The design and the present status of the detector are reviewed here.

Module testing for the CMS Forward Pixel detector

The Forward Pixel detector for the CMS Experiment consists of four disks. In total, 672 modules are needed to assemble the disks. This translates into 18 million readout channels that need to be tested for their correct functionality making this task extremely challenging. This paper will present the procedure for testing these modules.

Hit efficiency study of CMS prototype forward pixel detectors

In this paper I describe the measurement of the hit efficiency of a prototype pixel device for the CMS forward pixel detector. The data were taken with the 120 GeV proton beam at Fermilab during the period of December 2004–February 2005. The detectors proved to be highly efficient ( 99.27 ± 0.02 % ) . The inefficiency was primarily located near the corners of the individual pixels.

Study of Radiation Hardness of Silicon Pixel Deieciors after Neuiron and Proton Irradiations

A new design of silicon pixel detectors with n+/n/p+ (pixel array/bulk/pad) configuration has been developed for more radiation-tolerant CMS forward pixel sensors. In this design, a single (640 jim wide) n+ implant is placed on the n+ side, and guard rings on the p+ side are always kept active before and after type inversion. The whole n+ side is grounded and connected to readout chips. All tested devices were fabricated from both standard (normal) and oxygen-enriched silicon wafers, and radiation-hardness effects after neutron (1 MeV equivalent) and proton (24 GeV) irradiations of these devices were investigated. Other electrical characteristics such as the leakage current and the potential distribution over guard rings were tested using standard measurement techniques.