Marcel Stanitzki

A novel CMOS monolithic active pixel sensor with analog signal processing and 100% fill factor

We have designed and fabricated a CMOS monolithic active pixel sensor (MAPS) in a novel 0.18 micrometer image-sensor technology (INMAPS) which has a 100% fill factor for charged particle detection and full CMOS electronics in the pixel. The first test sensor using this technology was received from manufacture in July 2007. The key component of the INMAPS process is the implementation of a deep p-well beneath the active circuits. A conventional MAPS design for charged-particle imaging will experience charge sharing between the collection diodes and any PMOS active devices in the pixel which can dramatically reduce the efficiency of the pixel. By implementing a deep p-well, the charge deposited in the epitaxial layer is reflected and conserved for collection at only the exposed collection diode nodes. We have implemented two pixel architectures for charged particle detection. The target application for these pixels is for the sensitive layers of an electromagnetic calorimeter (ECAL) in an international linear collider (ILC) detector. Both pixel architectures contain four n- well diodes for charge-collection; analog front-end circuits for signal pulse shaping; comparator for threshold discrimination; digital logic for threshold trim adjustment and pixel masking. Pixels are served by shared row-logic which stores the location and time-stamp of pixel hits in local SRAM, at the bunch crossing rate of the ILC beam. The sparse hit data are read out from the columns of logic after the bunch train. Here we present design details and preliminary results.

A tera-pixel calorimeter for the ILC

To extract the physics required at the International Linear Collider, the detectors will need a jet energy resolution of 30%/radicE (GeV). The most promising approach to reach that goal is the use of particle flow algorithms. Particle flow algorithms measure jet energies by combining both tracking and calorimeter information. This requires the use of highly granular calorimeter systems. For the electromagnetic calorimeter (ECAL) the choice is to use silicon-tungsten sampling calorimeters with a highly granular readout. We propose to use Monolithic Active Pixel Sensors (MAPS) as both sensor and readout for such a calorimeter. This novel design would have an extremely fine granularity of 50 x 50 mum2 with binary readout. With a total area of 2000 m2 of silicon this leads to a Tera-Pixel ECAL. An overview of the MAPS detector concept will be given along with the potential advantages of this design. For the optimization of the design detailed sensor simulations have been used. A first prototype sensor using MAPS has been produced and we show first results obtained with this sensor. We also address system level issues like the required DAQ bandwidth and the power consumption.

Design and performance of a CMOS study sensor for a binary readout electromagnetic calorimeter

We present a study of a CMOS test sensor which has been designed, fabricated and characterised to investigate the parameters required for a binary readout electromagnetic calorimeter. The sensors were fabricated with several enhancements in addition to standard CMOS processing. Detailed simulations and experimental results of the performance of the sensor are presented. The sensor and pixels are shown to behave in accordance with expectations and the processing enhancements are found to be essential to achieve the performance required.

First radiation hardness results of the TeraPixel Active Calorimeter (TPAC) sensor

The TeraPixel Active Calorimeter (TPAC) sensor is a novel Monolithic Active Pixel Sensors (MAPS) device developed for use as the active layers of a large area, digital electromagnetic calorimeter (DECAL) at a future e+e− collider. Further applications, which include the tracking and vertex systems for future lepton colliders and LHC upgrades have been proposed and it is therefore essential to characterise the behaviour of the sensor for these applications. We present the first studies of radiation hardness testing of the TPAC sensor. The performance of the sensor has been evaluated after exposures up to 5 Mrad of 50 keV x-rays. Under realistic ILC operating conditions a maximum decrease in the signal to noise ratio of 8% (15%) was observed after 200 krad (5 Mrad) which is already sufficient for proposed applications in future e+e− colliders.

Beam test results of FORTIS, a 4T MAPS sensor with a signal-to-noise ratio exceeding 100

We have tested the first 4T Monolithic Active Pixel Sensor (MAPS) for particle physics, FORTIS in a beam test. We have measured a signal-to-noise ratio of more than 100 for MIPs due to the excellent noise performance of the 4T architecture. Two versions of the sensor were tested; with and without deep P-well areas in-pixel. The deep P-well areas allow the incorporation of PMOS transistors inside the pixels without signal charge loss. The measured position resolutions were around 2 μm.

TPAC: A 0.18 micron MAPS for digital electromagnetic calorimetry at the ILC

For the ILC physics program, the detectors will need an unprecedented jet energy resolution. For the electromagnetic calorimeter, the use of a highly granular silicon-tungsten calorimeter has been proposed. We have developed a Monolithic Active Pixel-based readout for such a calorimeter, which will have extremely fine granularity and will make use of a digital readout. The first generation chip (TPAC1) implements a 168x168 array comprising 50x50 μm2 pixels. Each pixel has an integrated charge pre-amplifier and comparator. TPACI has been manufactured in the 0.18 μm INMAPS process which includes a deep p-well. We present results of the performance of the TPACI chip together with comparison to simulations and give an outlook to the second generation chip.

Optimizing the design of the Final-Focus region for the International Linear Collider

The International Linear Collider (ILC) is a proposed linear electron positron collider with a center-ofmass energy of 250 GeV in its rst stage. After the discovery of the Higgs boson at the Large Hadron Collider (LHC) at CERN in 2012, the physics goals of the ILC include the measurements of the Higgs boson properties and its interactions, but also measurements of the top quark and searches beyond the Standard Model are part of the ILC program in the di erent ILC stages. The ILC, however, is not in competition with the LHC, but is a complementary collider experiment, since it is aimed at unprecedented precisions rather than at high collision energies. In order to achieve such precisions, both the accelerator design and the detector designs have to be optimized with respect to limiting the detector background below an acceptable limit. For the evaluation of various background sources, di erent Monte Carlo event generators have been used to generate background events that were then analyzed in a full detector simulation of the SiD detector. SiD is one of the proposed detector concepts for the ILC, for which a speci c critical acceptance limit for background rates has been set. Throughout the chapters of this thesis, the acceptance limit has been used to assess the arising background occupancy in SiD. If the occupancy has been found to be close to or to exceed the limit, possibilities to reduce the background level have been tested and recommendations for design optimizations have been made. The presented background simulation studies contain three major background sources: the e+e− pair background from beam-beam interactions, the machine background created by interactions of the beam with the accelerator components, and the neutron background produced in the ILC main beam dumps. In addition to the background study for the main beam dumps, the beam dump designs that are based on water dumps have also been analyzed with respect to the arising irradiation of the surroundings. The pair background was studied with respect to its dependency on di erent ILC running schemes, such as the proposed changes in the beam parameter sets for the ILC stage at 250 GeV. The results of these studies have been used in 2017 to inform the ILC design decision regarding these beam parameters. Besides the mentioned simulation studies, measurements of the machine background in dependency of certain accelerator conditions have been performed at the Accelerator Test Facility 2 at KEK in Japan. The goal of these measurements was to validate the functionality of a recently installed vertical beam halo collimator that is planned to be used at the ILC as well. For all the presented topics, recommendations for accelerator and detector design optimizations are given, with which the background level in the SiD detector can be reduced in order to reach the aimed-for precision at the ILC.