S. Rescia

Implanted silicon JFET on completely depleted high-resistivity devices

To satisfy the increasing interest in the integration of electronics onto optical and ionizing particle fully depleted detectors, a nonconventional JFET (junction field-effect transistor), designed to operate on a completely depleted, 2-k Omega -cm resistivity silicon substrate, has been designed, fabricated, and tested at room temperature. The devices show very low gate leakage current, low output conductance, a transconductance per unit gate width of 3 mS/mm, and a pinch-off voltage of -1.5 V. The integration of the devices onto the detectors makes possible the matching of the input capacitance of the JFET to the detectors output capacitance, which is of the order of few hundreds of femtorads. The measured gate capacitance of 200 fF is shown to correspond to an expected resolution in charge measurements, at room temperature, of less than 40 electrons rms. The fabrication constraints, imposed by the limited number of production steps of the detectors, are reported.<<ETX>>

Speed and noise limits in ionization chamber calorimeters

Abstract Relations among the speed of response, the signal-to-noise ratio and the charge collection time in ionization chamber calorimeters are analyzed. A dominant limiting factor to the speed of response is the charge transfer time from the electrodes to the amplifier determined by the electrode capacitance CD and the inductance of connections Ls. The time parameter L s C D sol1 2 has to be at least an order of magnitude smaller than the required length of the overall calorimeter response. The charge collection time plays a secondary role in determining the speed of response, while together with the charge yield it affects the signal-to-noise ratio.

Small animal simultaneous PET/MRI: initial experiences in a 9.4 T microMRI

We developed a non-magnetic positron-emission tomography (PET) device based on the rat conscious animal PET that operates in a small-animal magnetic resonance imaging (MRI) scanner, thereby enabling us to carry out simultaneous PET/MRI studies. The PET detector comprises 12 detector blocks, each being a 4 × 8 array of lutetium oxyorthosilicate crystals (2.22 × 2.22 × 5 mm(3)) coupled to a matching non-magnetic avalanche photodiode array. The detector blocks, housed in a plastic case, form a 38 mm inner diameter ring with an 18 mm axial extent. Custom-built MRI coils fit inside the positron-emission tomography (PET) device, operating in transceiver mode. The PET insert is integrated with a Bruker 9.4 T 210 mm clear-bore diameter MRI scanner. We acquired simultaneous PET/MR images of phantoms, of in vivo rat brain, and of cardiac-gated mouse heart using [(11)C]raclopride and 2-deoxy-2-[(18)F]fluoro-D-glucose PET radiotracers. There was minor interference between the PET electronics and the MRI during simultaneous operation, and small effects on the signal-to-noise ratio in the MR images in the presence of the PET, but no noticeable visual artifacts. Gradient echo and high-duty-cycle spin echo radio frequency (RF) pulses resulted in a 7% and a 28% loss in PET counts, respectively, due to high PET counts during the RF pulses that had to be gated out. The calibration of the activity concentration of PET data during MR pulsing is reproducible within less than 6%. Our initial results demonstrate the feasibility of performing simultaneous PET and MRI studies in adult rats and mice using the same PET insert in a small-bore 9.4 T MRI.

Energy linearity and resolution of the ATLAS electromagnetic barrel calorimeter in an electron test-beam

A module of the ATLAS electromagnetic barrel liquid argon calorimeter was exposed to the CERN electron test-beam at the H8 beam line upgraded for precision momentum measurement. The available energies of the electron beam ranged from 10 to 245 GeV. The electron beam impinged at one point corresponding to a pseudo-rapidity of eta=0.687 and an azimuthal angle of phi=0.28 in the ATLAS coordinate system. A detailed study of several effects biasing the electron energy measurement allowed an energy reconstruction procedure to be developed that ensures a good linearity and a good resolution. Use is made of detailed Monte Carlo simulations based on Geant which describe the longitudinal and transverse shower profiles as well as the energy distributions. For electron energies between 15 GeV and 180 GeV the deviation of the measured incident electron energy over the beam energy is within 0.1%. The systematic uncertainty of the measurement is about 0.1% at low energies and negligible at high energies. The energy resolution is found to be about 10% sqrt(E) for the sampling term and about 0.2% for the local constant term.

The MPI/AIT X-ray imager (MAXI) — High speed pn CCDs for X-ray detection

MAXI (MPI/AIT X-ray Imager) is part of a proposal submitted to the European Space Agency (ESA) as focal plane instrumentation of the X-ray Multi Mirror Mission (XMM). Within a collaboration of 13 European institutes we have proposed a fully depleted (sensitive) pn CCD of 280 μm thickness with a homogeneous sensitive area of 36 cm2 and a pixel size of 150×150 μm2 which is well matched with the telescopes angular resolution of 30 arcsec translating to a position resolution of approximately 1 mm in the focal plane. The X-ray sensitivity will be higher than 90% from 250 eV up to 10 keV, the readout time in the full frame mode of the complete focal plane will be 2 ms with a readout noise of better than 5 e− (rms). Prototypes of all individual components of the camera system have been fabricated and tested. The camera concept will be presented. The measured transfer properties of the CCD and the on-chip electronics will be treated. Taking into account the coupling of the on-chip amplifier to the following front-end electronics the expected performance will be derived.

Design of a charge sensitive preamplifier on high resistivity silicon

A low-noise, fast, charge-sensitive preamplifier was designed on high-resistivity, detector-grade silicon. It is built at the surface of a fully depleted region of n-type silicon, allowing it to be placed very close to a detector anode. The preamplifier uses the classical input-cascode configuration with a capacitor and a high-value resistor in the feedback loop. The output stage of the preamplifier can drive a load up to 20 pF. The power dissipation of the preamplifier is 13 mW. The amplifying elements are single-sided gate JFETs developed for this application. Preamplifiers connected to a low-capacitance anode of a drift-type detector should achieve a rise time of 20 ns and have an equivalent noise charge, after suitable shaping, of less than 50 electrons. This performance translates to a position resolution better than 3 mu m for silicon drift detectors. >

Radiation effects at cryogenic temperatures in Si-JFET, GaAs MESFET, and MOSFET devices

Front-end electronics for liquid ionization chamber calorimetry at hadron collider experiments may be exposed to substantial levels of ionizing radiation and neutron fluences in a cryogenic environment. Measurements of devices built with rad-hard technologies have shown that devices able to operate in these conditions exist. Several families of devices (Si-JFETs, rad-hard MOSFETs, and GaAs MESFETs) have been irradiated and tested at a stable cryogenic temperature up to doses of 55 Mrad of ionizing radiation and up to neutron fluences of 4/spl times/10/sup 14/ n/cm/sup 2/. Radiation effects on DC characteristics and on noise will be presented.

Sampling and optimum data processing of detector signals

Abstract The optimum processing of data, obtained by sampling detector signals, is developed for signals known a priori in shape, their time of occurrence and amplitude being unknown. The processing is based on the maximum-likelihood method. The resolutions in the time and amplitude estimations of the pulse are compared with those obtained from an optimum analog filter. Results are presented for a fixed number of samples points at different sampling rates. It is shown that undersampling does not introduce systematic errors because of the pulse shape known a priori but only decreases the resolution and makes it somewhat sensitive to the position of the pulse in relation to the sampling comb. The paper gives the criteria needed for reconstructing the weighting function for digital processors, stressing the links between conventional analog processing and sampled data processing. This makes it possible to choose the best compromise between achievable resolution and computational requirements.

Transmission line connections between detector and front end electronics in liquid argon calorimetry

Abstract With the long electronic shaping times traditionally used for liquid argon calorimetry, a transmission line connecting the detector to the preamplifier will be responsible for an unacceptable noise increase. Here we show that this is not necessarily the case when the shaping times are of the order of, or less than, the transmission line delay, which is a condition imposed by high luminosity colliders (LHC, SSC). We also describe a non-integrating preamplifier which, while presenting a “cold” termination to the line, has a dynamic range compatible with the new high energy machines.

Feedback charge amplifier integrated on the detector wafer

Abstract A charge sensitive preamplifier was realized on high resistivity detector grade silicon. The amplifier operates on a fully depleted bulk of a silicon wafer. As the anode region of any radiation detector operates at the full depletion as well, the possibility of direct integration of the preamplifier close to the detector anode was demonstrated. All production steps are compatible with production steps for radiation detectors. The implementation of the preamplifier is based on a new type of single sided field effect transistor which is the only type of active element in the design. The performance of single components and of the whole preamplifier is reported.