M. Ullan

Bulk damage in DMILL npn bipolar transistors caused by thermal neutrons versus protons and fast neutrons

DMILL bipolar transistors (npn) were exposed to 24 GeV protons and fast and thermal neutrons to fluences up to 6/spl middot/10/sup 14/ n/cm/sup 2/. Transistor common emitter current gain (/spl beta/=I/sub collector//I/sub base/) was measured after irradiations. It was found that /spl beta/ degradation scales as /spl Delta/(1//spl beta/)=k/sub T//spl middot//spl Phi//sub T/ where /spl Phi//sub T/ is the fluence of thermal neutrons and as /spl Delta/(1//spl beta/)=k/sub eq//spl middot//spl Phi//sub eq/, with /spl Phi//sub eq/ 1-MeV equivalent fluence, if transistors are irradiated with protons or fast neutrons. Large damage factor k/sub T//spl sim/3/spl middot/k/sub eq/ was measured. Thermal neutrons do not have sufficient energy to displace a Si atom. Their damage mechanism is, therefore, identified with /sup 10/B(n,/spl alpha/)/sup 7/Li reaction from which energetic /spl alpha/ and Li particles produce bulk damage in the base of the device. Boron is used as the base dopant in these transistors having also highly doped regions below base contacts. Irradiations with neutrons with energies distributed from thermal to fast show that gain degradation adds up as /spl Delta/(1//spl beta/)=k/sub T//spl middot//spl Phi//sub T/+k/sub eq//spl middot//spl Phi//sub eq/.

Proton Radiation Damage on SiGe:C HBTs and Additivity of Ionization and Displacement Effects

Proton irradiation results are shown here for three different SiGe:C HBT technologies from IHP Microelectronics. High damages are observed although the transistors remain usable for their application on the Super-LHC. Considerations on the ionization and displacement effects additivity are also presented in order to validate parameterized experiments. This study shows a reasonable agreement between proton irradiations and previous gamma and neutron irradiations.

Comparison of radiation hardness of P-in-N, N-in-N, and N-in-P silicon pad detectors

The very high radiation fluence expected at LHC (Large Hadron Collider) at CERN will induce serious changes in the electrical properties of the silicon detectors that will be used in the internal layers of the experiments (ATLAS, CMS, LHCb). To understand the influence of the fabrication technology in the radiation-induced degradation, silicon detectors were fabricated simultaneously with the three different possible technologies, P-in-N, N-in-N, and N-in-P, on standard and oxygenated float-zone silicon wafers. The diodes were irradiated with protons to fluences up to 10/sup 15/ cm/sup -2/. The measurements of the electrical characteristics, current-voltage and capacitance-voltage, are presented for the detectors manufactured with the three technologies. In terms of alpha factor (leakage current) the three technologies behave similarly. In terms of beta factor (effective doping concentration) N-in-P devices show the best performances.

Performance limits of a 55-/spl mu/m pixel CdTe detector

In this work, the results from simulation of a CdTe pixel detector with a pixel size of 45 mum and a pitch of 55 mum are presented. Simulation of charge sharing between neighboring pixels has been compared with experimental results obtained by the use of the Medipix2 photon counting chip by means of a unique read-out system developed for the Dear-Mama project. Electrical simulations have been performed using the commercial software package DESSIS (ISETCAD) and combined with the Monte Carlo code GEANT4 to simulate the process of interaction and subsequent charge transport of charges induced by radiation. This allowed the analysis of charge sharing between pixel elements, an important limiting factor in imaging applications. Simulation was compared with experimental results obtained by means of a 1 mm thick CdTe detector. Each of these pixel electrodes was connected to the corresponding readout pixel on the Medipix2 chip, via an indium bump-bond. The backside contact was biased at -100 V, so that the pixel electrodes were collecting electrons. The results obtained imply that using a detector 1 mm thick with a pixel size smaller than 55 mum in single photon counting mode is unrealistic, because such fine spatial resolution cannot be attained in the corresponding image due to charge sharing

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.

Bump bonding of pixel systems

Abstract A pixel detector consists of an array of radiation sensing elements which is connected to an electronic read-out unit. Many different ways of making this connection between these two different devices are currently being used or considered to be used in the next future. Bonding techniques such as flip chip technology can present real advantages because they allow very fine pitch and a high number of I / O s. This paper presents a review of the different flip chip technologies available and their suitability for manufacturing pixel detectors. The particular problems concerning testing of pixel detectors and thermal issues related to them are pointed out.

Lithium ion irradiation of standard and oxygenated silicon diodes

The next generation silicon detectors for future very high luminosity colliders or a possible LHC upgrade scenario will require radiation-hard detectors for fluences up to 10/sup 16/ 1-MeV equivalent neutrons/cm/sup 2/. These high fluences present strong constraints because long irradiation times are required at the currently available proton irradiation facilities. Energetic (58 MeV) Lithium ions present a nonionizing energy loss higher than protons and neutrons, and could consequently be a new promising radiation source for investigating the radiation hardness of silicon detectors up to very high particle fluences. Starting from this premise, we have investigated the degradation, as measured by the leakage current density increase and depletion voltage variations in the short- and long-term characteristics, induced by 58 MeV Li ions in state-of-the-art silicon diodes processed by two different manufacturers on standard and oxygenated silicon substrates. Finally, the correlation between the radiation damage induced by 58 MeV Li ions and 27 MeV protons is discussed.

Gamma Radiation Effects on Different Varieties of SiGe:C HBT Technologies

We have studied the ionization damage produced by gamma irradiation on transistors from three different varieties of SiGe:C HBT technologies from Innovation for High Performance Microelectronics (IHP), Germany. The results show strong gain degradations at the highest doses, with an indication of damage saturation. We did not observe strong differences in radiation tolerance among the three different technologies. These studies are in the framework of the radiation assurance tests of SiGe BiCMOS technologies for their possible application in the front-end readout electronics of the detector modules of the future ATLAS upgrade for the Super-LHC, but space-oriented applications are also considered. A comparison is presented with previous gamma irradiations of different SiGe technologies in the literature.

Trapping of Electrons and Holes in p-type Silicon Irradiated with Neutrons

Trapping times of drifting electrons and holes were measured in high resistivity standard, oxygenated and magnetic Czochralski p-type materials with charge correction method. Diodes were irradiated with neutrons up to equivalent fluence Phi = 3 times 10¹⁴ cm^-2. Trapping times were parameterized as 1/tau = betaPhi. Average beta was measured to be beta_e = 4.2 times 10^-16 cm² ns^-1 for electrons and beta_h = 4.3 times 10^-16 cm² ns^-1 for holes.

Double Sided 3D Detector Technologies at CNM-IMB

A new architecture for 3D silicon radiation detectors is proposed which simplifies the fabrication process and avoids the limitations of 3D detectors technology. The detector consists in a three-dimensional array of electrodes that penetrate into the detector bulk. The geometry of the detector is such that a central anode is surrounded by four cathode contacts. This geometry gives a uniform electric field with the maximum drift and depletion distance set by the electrode spacing rather than detector thickness. This structure is similar to a conventional 3D detector, but has a simpler fabrication process. The technological and the electrical simulations together with the fabrication steps of this new detector configuration are reported in this paper.