A. Kaminski

Radiation hardness of silicon detectors for high-energy physics applications

Oxygenated and standard (not oxygenated) silicon diodes processed by CNM and IRST have been irradiated by 27 MeV protons and compared with standard devices from ST Microelectronics. As expected, the leakage current density increase rate (/spl alpha/) and its annealing do not show any significant dependence on starting material, oxygenation and/or device processing. On the contrary, oxygenation improves the radiation hardness by decreasing the acceptor introduction rate (/spl beta/) and mitigating the depletion voltage (V/sub dep/) increase, with the /spl beta/ parameter depending also on starting material and/or effects related to device processing for standard diodes. Finally, these results are included in a general review on the state of the art for silicon detector radiation hardening, confirming the good performance of the considered technologies.

Low- and high-energy proton irradiations of standard and oxygenated silicon diodes

Oxygenated and standard (not oxygenated) silicon diodes processed by two different manufacturers (ST Microelectronics and Micron Semiconductor) have been irradiated by low (27 MeV) and high- (24 GeV) energy protons. The leakage current density increase rate (/spl alpha/) and its annealing do not show any significant dependence on oxygenation and are the same for both manufacturers. Oxygenation improves the radiation hardness by decreasing the acceptor introduction rate (/spl beta/) and mitigating the depletion voltage (V/sub dep/) increase. Nevertheless, standard ST diodes present /spl beta/ values lower than Micron standard devices and close to oxygenated devices, whose /spl beta/s are similar for both manufacturers. The amplitude of the V/sub dep/ reverse annealing is reduced by oxygenation, which in addition delays the electrically active defect increase, at least for high-energy protons. Oxygenation is consequently the best approach for silicon substrate radiation hardening.

Neutron irradiation effects on standard and oxygenated silicon diodes

Silicon diodes processed on standard and oxygenated silicon substrates by two different manufacturers have been irradiated by neutrons in a nuclear reactor and by the /sup 9/Be(d,n)/sup 10/B nuclear reaction. The leakage current density (J/sub D/) increase is linear with the neutron fluence. J/sub D/ and its annealing curve at 80/spl deg/C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. On the contrary, standard devices from one manufacturer present the lowest acceptor introduction rate (/spl beta/) for the effective substrate doping concentration (N/sub eff/), showing that the /spl beta/ dependence on the particular process can be important, overtaking the small substrate oxygenation effect. Finally, the average saturation value of the N/sub eff/ reverse annealing is slightly lower for the oxygenated samples, pointing out a positive effect of the substrate oxygenation even for devices irradiated by neutrons.

New evidence of dominant processing effects in standard and oxygenated silicon diodes after neutron irradiation

Abstract Silicon diodes processed on standard and oxygenated silicon substrates by three different manufacturers have been irradiated by neutrons in a nuclear reactor. The leakage current density ( J D ) increase is linear with the neutron fluence. J D and its annealing curve at 80°C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. The acceptor introduction rate ( β ) of the effective substrate doping concentration ( N eff ) is independent from the oxygen concentration when standard and oxygenated devices from the same manufacturer are considered. On the contrary, β significantly varies from one manufacturer to another showing that the β dependence on the particular process can be important, overtaking the small substrate oxygenation effect. Finally, the average saturation value of the N eff reverse annealing is slightly lower for the oxygenated samples, pointing out a positive effect of the substrate oxygenation even for devices irradiated by neutrons.

TID and SEE characterization and damaging analysis of 256 Mbit COTS SDRAM for IEEM application

To map out device sensitivity with submicrometric resolutions it is traditional to use a microbeam. In recent years ion electron emission microscopy (IEEM) is emerging as an innovative method for device characterization. An advanced implementation of this instrument is under development at the SIRAD irradiation facility at the Legnaro national laboratory (LNL). The aim of this work is the final test and the characterization of the SIRAD IEEM in a realistic environment by using synchronus dynamic RAM (SDRAM) commercial off the shelf (COTS) devices to confirm the capability of the SIRAD IEEM to map out the single event effect (SEE) sensitivity of a typical microelectronic device and to measure its resolution. A potential problem during IEEM operations is the large number of ions that have to be collected on the device under test (DUT) that will induce a degradation of the device characteristics similar to that generated by total ionizing dose (TID). This paper investigates this issue and proposes an online method to monitor the degradation of the devices under test based on the measurement of the bit retention time (BRT), that is the time the information is retained in a memory cell without refresh in SDRAM devices. This paper presents the experimental setup and the results of TID and SEE tests performed to validate the method. The results of TID tests with 60Co gamma ray, initially performed to investigate the method, show that BRT measurements could be used to online monitor the level of TID the device accumulates. The same tests performed during heavy ion irradiation show that ions produce similar effects on the SDRAM so that BRT could be used during IEEM operation to monitor the degradation of the DUT. TID and single event upset (SEU) effects have been investigated on Micron 256 Mb MT48LC64M4A2Y96A SDRAM devices at the 60Co gamma facility of the Istituto per la Sintesi Organica e la Fotoreattivita and at the SIRAD irradiation facility at the XTU Tandem of the INFN - CNR Legnaro National Laboratories (LNL).

Radiation damage studies of XAA1.2 ASIC chip for the SuperAGILE experiment onboard AGILE

SuperAGILE is the X-ray instrument of the AGILE Mission. It is a set of silicon micro-strip detectors tiles coupled with a tungsten coded mask. The front end electronics of SuperAGILE is based on 48 ASIC XAA1.2 chips, each one collecting and conditioning the signals from 128 strips of the detector. Since this chip was not developed as a radiation resistant component for space applications and in order to predict and prevent the potential problems deriving from the space radiation environment, we irradiated two of such chips with ions of different chemical specie, ranging from 16O to 127I. At the 15 MV Tandem accelerator of the Laboratori Nazionali INFN di Legnaro we measured the occurrence of latch-up and Single Event Upset and the effects due to the absorbed total dose on the supply currents and on the bias currents which control the performances of the chip. In this paper we discuss how the results can be scaled to the AGILE environment and the impact of these data on the experiment design and on the observing strategy.

Charge collection efficiency of standard and oxygenated silicon microstrip detectors

Abstract Two silicon microstrip detectors, one fabricated from a standard and the second from a highly oxygenated substrate, were non-uniformly irradiated by 24 GeV protons to fluences ranging between 2.3 and 6.3×10 14 cm −2 . Charge collection efficiency measurements, performed by pulsing the detectors with a 1060 μ m wavelength laser, show that the beneficial effect of the oxygenation remains, although reduced with respect to that observed by C – V measurements on diodes fabricated with the detectors.

Lithium ion irradiation effects on diodes manufactured on epitaxial silicon

Diodes manufactured on a thin and highly doped epitaxial silicon layer grown on a Czochralski silicon substrate have been irradiated by high-energy Lithium ions in order to investigate the effects of high bulk damage levels in such devices. This information is useful for possible developments of pixel detectors in future very high luminosity colliders because these new devices present superior radiation hardness than nowadays silicon detectors. The leakage current density increase, the variation of the depletion voltage and their annealing characteristics, as well as the charge collection properties of these new devices are presented and discussed in this study.

Radiation hardness of silicon diodes for high energy physics applications

Oxygenated and standard (not oxygenated) silicon diodes processed by CNM and IRST have been irradiated by 27 MeV protons and compared with standard devices from ST Microelectronics. As expected the leakage current density increase rate (/spl alpha/) and its annealing do not show any significant dependence on the starting material, oxygenation and/or processing of the considered devices. On the contrary, oxygenation improves the radiation hardness by decreasing the acceptor introduction rate (/spl beta/) and mitigating the depletion voltage (V/sub dep/) increase, with the /spl beta/ parameter depending also on starting material and/or effects related to device processing for standard diodes. Finally these results are included in a general review on the state of the art for silicon detector radiation hardening, confirming the good performance of the considered technologies.