arXiv subjects

Norbert Wermes

Publications and source records attributed to Norbert Wermes.

28 records · Page 2Linked to original sources

arXiv2014

DMAPS: a fully depleted monolithic active pixel sensor - analog performance characterization

Monolithic Active Pixel Sensors (MAPS) have been developed since the late 1990s based on silicon substrates with a thin epitaxial layer (thickness of 10-15 $μ$m) in which charge is collected on an electrode, albeit by disordered and slow diffusion rather than by drift in a directed electric field. As a consequence, the signal is small ($\approx$ 1000 e$^-$) and the radiation tolerance is much below the LHC requirements by factors of 100 to 1000. In this paper we present the development of a fully Depleted Monolithic Active Pixel Sensors (DMAPS) based on a high resistivity substrate allowing the creation of a fully depleted detection volume. This concept overcomes the inherent limitations of charge collection by diffusion in the standard MAPS designs. We present results from a test chip EPCB01 designed in a commercial 150 nm CMOS technology. The technology provides a thin (50 $μ$m) high resistivity n-type silicon substrate as well as an additional deep p-well which allows to integrate full CMOS circuitry inside the pixel. Different matrix types with several variants of collection electrodes have been implemented. Measurements of the analog performance of this first implementation of DMAPS pixels will be presented.

physics.ins-det↗

arXiv2012

Signal and noise of Diamond Pixel Detectors at High Radiation Fluences

CVD diamond is an attractive material option for LHC vertex detectors because of its strong radiation-hardness causal to its large band gap and strong lattice. In particular, pixel detectors operating close to the interaction point profit from tiny leakage currents and small pixel capacitances of diamond resulting in low noise figures when compared to silicon. On the other hand, the charge signal from traversing high energy particles is smaller in diamond than in silicon by a factor of about 2.2. Therefore, a quantitative determination of the signal-to-noise ratio (S/N) of diamond in comparison with silicon at fluences in excess of 10$^{15}$ n$_{eq}$ cm$^{-2}$, which are expected for the LHC upgrade, is important. Based on measurements of irradiated diamond sensors and the FE-I4 pixel readout chip design, we determine the signal and the noise of diamond pixel detectors irradiated with high particle fluences. To characterize the effect of the radiation damage on the materials and the signal decrease, the change of the mean free path $λ_{e/h}$ of the charge carriers is determined as a function of irradiation fluence. We make use of the FE-I4 pixel chip developed for ATLAS upgrades to realistically estimate the expected noise figures: the expected leakage current at a given fluence is taken from calibrated calculations and the pixel capacitance is measured using a purposely developed chip (PixCap). We compare the resulting S/N figures with those for planar silicon pixel detectors using published charge loss measurements and the same extrapolation methods as for diamond. It is shown that the expected S/N of a diamond pixel detector with pixel pitches typical for LHC, exceeds that of planar silicon pixels at fluences beyond 10$^{15}$ particles cm$^{-2}$, the exact value only depending on the maximum operation voltage assumed for irradiated silicon pixel detectors.

physics.ins-det↗

arXiv2010

PIXEL 2010 - a Resume

The Pixel 2010 conference focused on semiconductor pixel detectors for particle tracking/vertexing as well as for imaging, in particular for synchrotron light sources and XFELs. The big LHC hybrid pixel detectors have impressively started showing their capabilities. X-ray imaging detectors, also using the hybrid pixel technology, have greatly advanced the experimental possibilities for diiffraction experiments. Monolithic or semi-monolithic devices like CMOS active pixels and DEPFET pixels have now reached a state such that complete vertex detectors for RHIC and superKEKB are being built with these technologies. Finally, new advances towards fully monolithic active pixel detectors, featuring full CMOS electronics merged with efficient signal charge collection, exploiting standard CMOS technologies, SOI and/or 3D integration, show the path for the future. This résumé attempts to extract the main statements of the results and developments presented at this conference.

physics.ins-det↗

arXiv2008

Pixel Detectors for Charged Particles

Pixel Detectors, as the current technology of choice for the innermost vertex detection, have reached a stage at which large detectors have been built for the LHC experiments and a new era of developments, both for hybrid and for monolithic or semi-monolithic pixel detectors is in full swing. This is largely driven by the requirements of the upgrade programme for the superLHC and by other collider experiments which plan to use monolithic pixel detectors for the first time. A review on current pixel detector developments for particle tracking and vertexing is given, comprising hybrid pixel detectors for superLHC with its own challenges in radiation and rate, as well as on monolithic, so-called active pixel detectors, including MAPS and DEPFET pixels for RHIC and superBelle.

physics.ins-det↗

arXiv2006

Pixel Vertex Detectors

Pixel vertex detectors are THE instrument of choice for the tracking of charged particles close to the interaction point at the LHC. Hybrid pixel detectors, in which sensor and read-out IC are separate entities, constitute the present state of the art in detector technology. Three of the LHC detectors use vertex detectors based on this technology. A development period of almost 10 years has resulted in pixel detector modules which can stand the extreme rate and timing requirements as well as the very harsh radiation environment at the LHC for its full life time and without severe compromises in performance. This lecture reviews the physics and technology of pixel detectors for tracking and vertexing at the LHC.

physics.ins-det↗

arXiv2005

Pixel Detectors

Pixel detectors for precise particle tracking in high energy physics have been developed to a level of maturity during the past decade. Three of the LHC detectors will use vertex detectors close to the interaction point based on the hybrid pixel technology which can be considered the state of the art in this field of instrumentation. A development period of almost 10 years has resulted in pixel detector modules which can stand the extreme rate and timing requirements as well as the very harsh radiation environment at the LHC without severe compromises in performance. From these developments a number of different applications have spun off, most notably for biomedical imaging. Beyond hybrid pixels, a number of monolithic or semi-monolithic developments, which do not require complicated hybridization but come as single sensor/IC entities, have appeared and are currently developed to greater maturity. Most advanced in terms of maturity are so called CMOS active pixels and DEPFET pixels. The present state in the construction of the hybrid pixel detectors for the LHC experiments together with some hybrid pixel detector spin-off is reviewed. In addition, new developments in monolithic or semi-monolithic pixel devices are summarized.

physics.ins-det↗

arXiv2005

Characterization of charge collection in CdTe and CZT using the transient current technique

The charge collection properties in different particle sensor materials with respect to the shape of the generated signals, the electric field within the detector, the charge carrier mobility and the carrier lifetime are studied with the transient current technique (TCT). Using the well-known properties of Si as a reference, the focus is laid on Cadmium-Telluride (CdTe) and Cadmium-Zinc-Telluride (CZT), which are currently considered as promising candidates for the efficient detection of X-rays. All measurements are based on a transient-current technique (TCT) setup, which allows the recording of current pulses generated by an 241Am alpha-source. These signals will be interpreted with respect to the build-up of space-charges inside the detector material and the subsequent deformation of the electric field. Additionally the influence of different electrode materials (i.e. ohmic or Schottky contacts) on the current pulse shapes will be treated in the case of CdTe. Finally, the effects of polarization, i.e. the time-dependent degradation of the detector signals due to the accumulation of fixed charges within the sensor, are presented.

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arXiv2004

Trends in Pixel Detectors: Tracking and Imaging

For large scale applications, hybrid pixel detectors, in which sensor and read-out IC are separate entities, constitute the state of the art in pixel detector technology to date. They have been developed and start to be used as tracking detectors and also imaging devices in radiography, autoradiography, protein crystallography and in X-ray astronomy. A number of trends and possibilities for future applications in these fields with improved performance, less material, high read-out speed, large radiation tolerance, and potential off-the-shelf availability have appeared and are momentarily matured. Among them are monolithic or semi-monolithic approaches which do not require complicated hybridization but come as single sensor/IC entities. Most of these are presently still in the development phase waiting to be used as detectors in experiments. The present state in pixel detector development including hybrid and (semi-)monolithic pixel techniques and their suitability for particle detection and for imaging, is reviewed.

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arXiv2003

Single Photon Counting X-ray Imaging with Si and CdTe Single Chip Pixel Detectors and Multichip Pixel Modules

Multichip modules (MCM) with 4 single photon counting MPEC 2.3 chips bump bonded to 1.3 cm x 1.3 cm large CdTe and Si semiconductor sensors as well as to single chip pixel detectors have been successfully built and operated. The MPEC 2.3 chip provides a pixel count rate up to 1 MHz with a large dynamic range of 18 bit, 2 counters and energy windowing with continuously adjustable thresholds. Each MPEC has 32 x 32 pixels of 200 um x 200 um pixel size. For a MCM the 4 chips are arranged in a 2 x 2 array which leads to a 64 x 64 sensor pixel geometry. The MCM construction is described, and the imaging performance of the different detectors is shown. As readout system a newly developed USB system has been used.

physics.ins-det↗

arXiv2002

Pixel Detectors for Particle Detection and Imaging Applications

Semiconductor pixel detectors offer features for the detection of radiation which are interesting for particle physics detectors as well as for imaging e.g. in biomedical applications (radiography, autoradiography, protein crystallography) or in Xray astronomy. At the present time hybrid pixel detectors are technologically mastered to a large extent and large scale particle detectors are being built. Although the physical requirements are often quite different, imaging applications are emerging and interesting prototype results are available. Monolithic detectors, however, offer interesting features for both fields in future applications. The state of development of hybrid and monolithic pixel detectors, excluding CCDs, and their different suitability for particle detection and imaging, is reviewed.

hep-ex↗