E. Spencer

Type inversion in silicon detectors

Abstract Silicon strip detectors and photodiodes were irradiated in an 800 MeV proton beam. The change of the effective doping concentration was monitored by measuring diode C - V curves. Type inversion is observed at a fluence Φ = 1.5 × 10 13 cm −2 . Further evidence for type inversion is obtained from a study of pulses generated by an infrared LED in silicon strip detectors. A two-level parametrization is used to describe donor removal and acceptor state creation during proton irradiation: N eff = N 0 exp(− cφ )− βφ . We measure values of c = (5.5 ± 1.1) × 10 14 cm 2 and β = (0.031 ± 0.006) cm −1 . After type inversion the depletion voltage increases with proton fluence. This may set the limit for the lifetime of silicon detectors at future colliders. However, the occurence of type inversion does not degrade the performance of silicon strip detectors. The effective doping concentration showed a complex post irradiation behaviour. After a short term annealing period the doping concentration increased beyond the value that had been reached immediately after the exposure.

Temperature dependence of the radiation induced change of depletion voltage in silicon PIN detectors

Abstract We present a study of how temperature affects the change in the depletion voltage of silicon PIN detectors damaged by radiation. We study the initial radiation damage and the short-term and long-term annealing of that damage as a function of temperature in the range from −10°C to +50°C, and as a function of 800 MeV proton fluence up to 1.5×10 14 p/cm 2 . We express the pronounced temperature dependences in a simple model in terms of two annealing time constants which depend exponentially on the temperature.

Design, testing and performance of the frontend electronics for the LPS silicon microstrip detectors

Abstract We present our experience in design, construction, testing and operation of the frontend electronics (FEE) for the LPS silicon strip detectors for HERA. A total of about 22 000 channels has been operated as close as the 10σ envelope of the 820 GeV proton beam. This FEE system is binary, controlled by one threshold set at about 0.8 fC, and has been optimized by combining a fast low-noise bipolar amplifier/comparator VLSI with a low-power digital pipeline manufactured in radiation-hard CMOS.

Radiation hardness measurements on components of a full custom bipolar process

Abstract We present the characterization of various components of the full custom bipolar process SHPi by Tektronix with respect to radiation hardness. The motivation of this work is to design a low-power, low-noise frontend with fast shaping for silicon microstrip detectors. We have tested BJTs ( npn of various size and a lateral pnp ), JFETs, Schottky diodes, implanted resistors and NiChrome resistors. The devices were irradiated to 60 Co dose of up to 5 Mrad in few steps, to fluence of 5.5∗10 13 n cm −2 of neutrons from a spallation source in few steps and to fluence of up to 1.1∗10 14 cm −2 of 650 MeV protons. It allows us to characterize the sensitivity of the devices on both ionization effects and displacement damage. We have measured the radiation effects on the dc parameters and characteristics of all components as well as on noise in npn BJTs of various size considered as candidates for the preamplifier input transistor. The most significant effect which we observe is the decrease of the current gain β in bipolar transistors for low emitter current densities. Both important noise sources, i.e. the shot noise of the collector current and the thermal noise of the base spread resistance are unaffected by irradiation.

Study of the effects of neutron irradiation on silicon strip detectors

Abstract Silicon strip detectors and test structures were exposed to neutron fluences up to Φ = 6.1 × 1014 n/cm2, using the ISIS neutron source at the Rutherford Appleton Laboratory (UK). In this paper we report some of our results concerning the effects of displacement damage, with a comparison of devices made of silicon of different resistivity. The various samples exposed showed a very similar dependence of the leakage current on the fluence received. We studied the change of effective doping concentration, and observed a behaviour suggesting the onset of type inversion at a fluence of ∼ 2.0 × 1013 n/cm2, a value which depends on the initial doping concentration. The linear increase of the depletion voltage for fluences higher than the inversion point could eventually determine the maximum fluence tolerable by silicon detectors.

Study of radiation effects on AC-coupled silicon strip detectors

Abstract AC-coupled silicon strip detectors were exposed to neutron fluences of 5·10 13 n/cm 2 and to Co 60 photon doses of 2.8 Mrad. No change in the value of the coupling capacitors was observed. Polysilicon resistor values increased by 15% and saturated after 200 krad photon dose. They were stable under neutron irradiation. Thee interstrip punchthrough threshold voltage increased from 4 to 13 V under photon irradiation. The accumulation of fixed charges in SiO 2 was measured using MOS capacitors and the photon-induced surface current generation velocity was determined with gated diodes.

Test results on silicon micro-strip detectors for ATLAS

We report results from beam tests on silicon microstrip detectors using a binary readout system for ATLAS. The data were collected during the H8 beam test at CERN in August/September 1995 and the KEK test in February 1996. The binary modules tested had been assembled from silicon microstrip detectors of different layout and from front-end electronics chips of different architecture. The efficiency, noise occupancy and position resolution were determined as a function of the threshold setting for various bias voltages and angles of incidence for both irradiated and non-irradiated detectors. In particular, the high spatial resolution of the beam telescope allowed the evaluation of the performance as a function of the track location in between detector strips.

Test of radiation hardness of CMOS transistors under neutron irradiation

Abstract We have tested 2 μm CMOS test structures from various foundries in the LAMPF beam stop for radiation damage under prolonged neutron irradiation. The fluxes employed were higher than the ones expected to be encountered at the SSC and led to fluences of up to 10 15 neutrons/cm 2 in about 500 h of running. We show that test structures which have been measured to survive ionizing radiation of the order of Mrad also survive these high neutron fluences.

Radiation hardness evaluation of a 130 nm SiGe BiCMOS technology for the ATLAS electronics upgrade

Final results for a comprehensive radiation hardness evaluation of a high performance, low cost, 130nm SiGe BiCMOS technology are presented. After a survey of several available SiGe technologies, one was chosen in terms of performance, power consumption, radiation hardness, and cost and it is presented as a suitable technology for the front-end electronics of the Inner Detector and the Liquid Argon calorimeter. Gamma, neutron and proton irradiations have been performed up to target dose and fluence values, together with ELDRS assessment.

A Bipolar front end integrated circuit for the BaBar helium drift chamber

Abstract A Bipolar chip consisting of 4 channels, each with a digital, and an analog output has been developed for use with the BaBar drift chamber. The full design is described and results from the prototype are presented.