M. Sampietro

Silicon drift detectors for high resolution room temperature X-ray spectroscopy

New cylindrical silicon drift detectors have been designed, fabricated and tested. They comprise an integrated on-chip amplifier system with continuous reset, on-chip voltage divider, electron accumulation layer stabilizer, large area, homogeneous radiation entrance window and a drain for surface generated leakage current. The test of the 3.5 mm2 large individual devices, which have also been grouped together to form a sensitive area up to 21 mm2 have shown the following spectroscopic results: at room temperature (300 K) the devices have shown a full width at half maximum at the MnKα line of a radioactive 55 Fe source of 225 eV with shaping times of 250 to 500 ns. At −20°C the resolution improves to 152 eV at 2 μs Gaussian shaping. At temperatures below 200 K the energy resolution is below 140 eV. With the implementation of a digital filtering system the resolution approaches 130 eV. The system was operated with count rates up to 800 000 counts per second and per readout node, still conserving the spectroscopic qualities of the detector system.

Suboptimal filtering of 1/ƒ-noise in detector charge measurements☆

Processing of 1tf-noise by suboptimal filters in detector charge measurements is considered. The achievable values of equivalent noise charge are compared to those provided by the optimum filter. Some aspects of filters processing 1tf-noise, like the degradation in the accuracy of charge measurements due to a bipolar or to a unipolar, flat-topped weighting function are described. Several conclusions are expected to be useful in the design of analog processors for radiation detectors when the front-end 1tf-noise is not negligible.

Low-mass e+e− pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2<m<2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed pt.We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed pt.Abstract We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 ≤ m ≤ 2.0 GeV/c 2 is enhanced by a factor of 3.5 ± 0.4 (stat) ± 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV/c 2 . For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed p ⊥ .

Modeling of organic thin film transistors : Effect of contact resistances

Field effect transistors require an Ohmic source contact and an Ohmic drain contact for ideal operation. In many real situations, however, and specifically in organic devices, the injection of charge carriers from metals into semiconductors can be an inefficient process that is non-Ohmic. This has an adverse impact on the performance of thin film transistors and makes the analysis of electrical measurements a complex task because contact effects need to be disentangled from transistor properties. This paper deals with the effects of non-Ohmic contacts on the modeling of organic transistors and gives specific rules on how to extract the real transistor parameters (mobility, threshold voltage, and contact resistances) using only electrical measurements. The method consists of a differential analysis of the transfer characteristic curves (current versus gate voltage) and exploits the different functional dependences of current on gate voltage which is induced by the presence of contact resistances. This pape...

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>>

Dielectric-constant measurement of thin insulating films at low-frequency by nanoscale capacitance microscopy

We demonstrate a method for quantitatively probing the local low-frequency dielectric constant of thin insulating films by nanoscale capacitance microscopy. The calibrated capacitance-distance curves are measured on the dielectric film and analyzed by using a tip-sample capacitance model here proposed. Applied to SiO2 films as small as 1×1μm2 area and 20–30nm thickness, the method gives a dielectric constant on the submicron scale in agreement with the value determined on the large scale. The observed precision is set by the capacitance noise level of the instrument and the tip radius.

Dynamics of electrons in drift detectors

Abstract The dynamics of electrons generated in silicon drift chambers by ionizing events is studied. Diffusion effects, mutual electrostatic repulsion between the electrons as well as the focusing properties of the depletion field during the electron transport to the anode are considered. The theoretical computations show that the effect of the mutual electrostatic repulsion in the spreading of the charge packet are not negligible even at charge densities produced by a minimum ionizing particle traversing 300 μm of the detector. Experimental results support theoretical expectations.

e + e − -pair production in Pb-Au collisions at 158 GeV per nucleon

Abstract.We present the combined results on electron-pair production in 158 GeV/n Pb-Au (

Optimum filters for detector charge measurements in presence of 1f noise

\sqrt{s}

Spectrum analyzer with noise reduction by cross-correlation technique on two channels

= 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31