Showing papers by "Peter Fischer published in 2001"

The ATLAS silicon pixel sensors

Abstract: Prototype sensors for the ATLAS silicon pixel detector have been developed. The design of the sensors is guided by the need to operate them in the severe LHC radiation environment at up to several hundred volts while maintaining a good signal-to-noise ratio, small cell size, and minimal multiple scattering. The ability to be operated under full bias for electrical characterization prior to attachment of the readout integrated circuit electronics is also desired.

Medical X-ray Imaging with Energy Windowing

Abstract: A photon counting pixel read-out chip for medical X-ray imaging with energy windowing is presented. It consists of 32×32 pixels of 200 μm×200 μm size, each of them contains two discriminators and two 18-bit counters. Both discriminator thresholds can be adjusted individually for good image homogeneity and a circuit has been designed to avoid threshold drift. Measurements on the noise behaviour, threshold variation and threshold drift are shown.

Spectroscopic and imaging performance of DEPFET pixel sensors

Abstract: DEPFET pixel sensors consist of a p-channel JFET directly integrated into a high-ohmic n-silicon substrate. They offer a very low-noise performance at room temperature and are therefore of interest for applications in biomedicine, X-ray astronomy and particle physics. Measurements on single pixel devices demonstrating the low-noise potential of DEPFET sensors are shown. The DEPFET pixel bioscope system is based on a 64×64 matrix of DEPFET pixels. Measurements of the homogeneity of the charge collection efficiency and of the spatial resolution of the system as well as on the capability of DEPFET sensors to detect tritium with a good efficiency are presented.

A counting CdTe pixel detector for hard X-ray and /spl gamma/-ray imaging

Abstract: A 0.5-mm-thick cadmium telluride (CdTe) semiconductor pixel sensor with 1024 pixels has been bump-bonded onto a two-dimensional (2-D) single photon counting pixel read out chip (MPEC 2.1) using a special gold-stud technique. The pixel size is 200 /spl times/ 200 /spl mu/m/sup 2/, the active area is 6.4 /spl times/ 6.4 mm/sup 2/. The successful operation of this high-Z imaging pixel device is demonstrated. Noise and threshold dispersion as well as the imaging performance are reported.

First implementation of the MEPHISTO binary readout architecture for strip detectors

Abstract: Today's front-end readout chips for multi-channel silicon strip detectors use pipeline-like structures for temporary storage of hit information until arrival of a trigger signal. This approach leads to large-area chips when long trigger latencies are necessary. The MEPHISTO architecture uses a different concept. Hit strips are identified in real time and only the relevant binary hit information is stored in FIFOs. For the typical occupancies in LHC detectors of ≈1 hit per clock cycle this architecture requires less than half the chip area of a typical binary pipeline. This reduces the system cost considerably. At a lower data rate, operation with very long trigger latencies or even without any trigger is possible due to the real-time data sparsification. The Mephisto II architecture is presented and the expected performance is discussed.

Digital column readout architecture for the ATLAS pixel 0.25 /spl mu/m front end IC

Abstract: A fast low noise, limited power, radiation-hard front-end chip was developed for reading out the Atlas Pixel Silicon Detector. As in the past prototypes, every chip is used to digitize and read out charge and time information from hits on each one of its 2880 inputs. The basic column readout architecture idea was adopted and modified to allow a safe transition to quarter micron technology. Each pixel cell, organized in a 160/spl times/18 matrix, can be independently enabled and configured in order to optimize the analog signal response and to prevent defective pixels from saturating the readout. The digital readout organizes hit data coming from each column, with respect to time, and output them on a low-level serial interface. A considerable effort was made to design state machines free of undefined states, where single-point defects and charge deposited by heavy ions in the silicon could have led to unpredicted forbidden states.

Comparison of hybrid pixel detectors with Si and GaAs sensors

Abstract: Hybrid pixel detectors for medical X-ray imaging applications with Si and GaAs sensors are compared. Both sensor types are bump-bonded onto the MPEC single photon counting pixel read out chip. The image homogeneity and count rate of the two assemblies are compared. For the GaAs assembly the active layer thickness and charge collection efficiency have been measured.

Pixel electronics for the ATLAS experiment

Abstract: The ATLAS experiment at LHC will use 3 barrel layers and 2×5 disks of silicon pixel detectors as the innermost elements of the semiconductor tracker. The basic building blocks are pixel modules with an active area of 16.4 mm ×60.8 mm which include an n+ on n-type silicon sensor and 16 VLSI front-end (FE) chips. Every FE chip contains a low power, high speed charge sensitive preamplifier, a fast discriminator, and a readout system which operates at the 40 MHz rate of LHC. The addresses of hit pixels (as well as a low resolution pulse height information) are stored on the FE chips until arrival of a level 1 trigger signal. Hits are then transferred to a module controller chip (MCC) which collects the data of all 16 FE chips, builds complete events and sends the data through two optical links to the data acquisition system. The MCC receives clock and data through an additional optical link and provides timing and configuration information for the FE chips. Two additional chips are used to amplify and decode the pin diode signal and to drive the VCSEL laser diodes of the optical links.

Active pixel sensor for X-ray imaging spectroscopy

Abstract: A promising candidate for the wide field imaging spectrometer of the European Space Agency's X-ray Evolving Universe Spectroscopy (XEUS) mission is the Active Pixel Sensor (APS) based on the Depleted P-channel Field Effect Transistor (DEPFET). This concept combines low electronic noise with low power consumption, random accessibility of the pixels, high speed readout by parallel multi-channel processing, a fill factor of 100% by backside illumination and high quantum efficiency by an optimized entrance window and a fully depleted bulk. The DEPFET is a monolithic combination of detector and preamplifier with minimized capacitance and the possibility of repetitive non-destructive readout of the same signal thus reducing read noise. In this paper the DEPFET principle and the concepts of the APS and repetitive non-destructive readout are explained, measurements of single DEPFET structures and small APS prototypes are presented.

A CVD diamond beam telescope for charged particle tracking

Abstract: Chemical vapor deposition (CVD) diamond is a radiation-hard sensor material that may be used for charged particle tracking near the interaction region in experiments at high-luminosity colliders. The goal of the work described in this paper is to investigate the use of several detector planes made of CVD diamond strip sensors for charged particle tracking. Toward this end, a tracking telescope composed entirely of CVD diamond planes has been constructed. The telescope was tested in muon beams, and its tracking capability has been investigated.