M. Redaelli

Effect on charge collection and structure of n-type silicon detectors irradiated with large fluences of fast neutrons

Abstract Float-Zone (FZ) silicon detectors have been irradiated with large fast neutrons fluences (up to 1014 n/cm2). The charge collection efficiency (eff) dependence on the reverse bias voltage (V) and on the fluence (Φ) have been investigated. The charge collection dependence on V indicates that, after large neutron irradiation, the relation between charge carrier concentration and full depletion voltage does not obey any longer the standard equation for an unsymmetrical step junction. The charge collection efficiency is found to have a logarithmic dependence on Φ.

Study of current-voltage characteristics of irradiated silicon detectors

Abstract Current-voltage (I-V) characteristics of non-irradiated and irradiated p+-n-n+ detectors, with neutron fluences (φ) up to 1014 n/cm2 were measured and the obtained data were analyzed. The If-Vf characteristics confirmed the existence of a critic fluence boundary (φb > 5 × 1011 n/cm2), similar to those found by other types of measurement (DLTS, C-V). We found that at φb the rectification ratio is reduced drastically, but a large reverse voltage can, nevertheless, be applied. The series resistivity (ϱ) calculated from the If-Vf characteristics, for both non-irradiated (NI) and irradiated detectors, shows that for NI detectors the resistivity is of the order of that of the silicon bulk (1200 Ωcm). The resistivity (ϱ) for irradiated devices increases (with increasing values of φ, of up to 1014 n/cm2), up to ∼4 × 10 3 Ω cm . As a result of the increase of ϱ with φ, the p+-n-n+ becomes a p+-v-n+ device. This study explains the rather good charge collection efficiency in spite of str affected physical properties.

DLTS measurement of energetic levels, generated in silicon detectors

DLTS (deep level transient spectroscopy) measurements were performed on irradiated Si detectors to record data on the energetic levels traps generated by neutrons. For moderate fluences (φ) of neutrons (φ < 1012 n cm−2) electron and hole trap levels have been detected. Four electron trap levels were found for both FZ (float zone) and MCZ (magnetic Czochralsky) types of Si detectors but only two hole trap levels in FZ and one in MCZ detectors. This indicates that the type of silicon has an influence on the traps generated by irradiation. From the values obtained for the relative concentration of E1 centers in MCZ and FZ detectors, it results that the E1 centers are oxygen and not vacancy limited. Since the concentration of the E2, E3, and E4 levels are larger in FZ than in MCZ detectors, it may be assumed that the “gettering effect” can control the formation of deeper traps. Filling pulses were applied for various voltages and at the flat band filling voltage, maximum ratio of NtN of the E1 center was achieved. This may indicate that the concentration of E1 centers, near the p+-n interface, can be larger than in the rest of the junction.

Radiation damage study of a fast bipolar monolithic charge sensitive preamplifier

A fast bipolar monolithic Charge Sensitive Preamplifier (CSP) implemented in the monolithic 2 μm BiCMOS technology (called HF2CMOS), was studied after neutron irradiation at fluences between 1.26 × 1012 and 1.09 × 1014 n/cm2. Neutron fluence effects on the base spreading resistance, rbb′, and the parallel noise of the bipolar npn input device and on the PMOS transistor in the second stage of the preamplifier, are presented. It is shown that, with the HF2CMOS process, a hardened CSP can be realized.

Systematic investigation of the electromagnetic energy resolution on sampling frequency using silicon calorimeters

The energy resolution, of electromagnetic sampling calorimeters using silicon mosaics as active medium, has been measured for Pb and Fe absorbers at incoming electron energies of 2, 4, and 6 GeV. The energy resolution, found for the Si/Pb and Si/Fe calorimeters, is well represented by σ(E)E = KτE(GeV), where τ is the sampling frequency and E the incoming electron energy. The energy resolution can be rewritten as a function of the dead area energy losses (D): σ(E)/E = (K0(1 + a1D))%τE(GeV) with K0 = (17.6 ± 0.3)%, (22.8 ± 0.8)%, for Si/Pb, Si/Fe, respectively; a1 = 0.07 ± 0.02 for both absorbers.

Systematic study of neutron irradiation effects on the performance of FZ and MCZ silicon detectors

Abstract Charge collection efficiency dependence on reverse bias voltage ( V B ) and on a neutron fluence (φ) was studied for both Float-Zone (FZ) and Magnetic-Czochralski (MCZ) silicon detectors, irradiated with fast neutron fluences, larger than 10 13 n/cm 2 . For both types of irradiated detectors, the charge collection efficiency was found to have a logarithime dependence on φ and its dependence on V B indicated that the relation between charge-carrier concentration and full depletion voltage is not according to the standard equation of a p +  n  n + device.

High-speed monolithic read-out system for high energy physics experiments

Design considerations regarding the monolithic realization of a high-speed read-out system to be used in future high luminosity colliders such as LHC are presented, System and circuit solution are presented for the first two blocks: the preamplifier and the RC-CR noise shaper. The electronics will be exposed to neutron irradiation and so the required radiation-hard performance is obtained with a design which takes into account the characterisation of the employed bipolar devices before and after neutron radiation,.<<ETX>>

Radiation damage investigation for the design of a hardened fast bipolar monolithic charge sensitive preamplifier

In order to implement a high-speed, radiation hardened, Charge Sensitive Preamplifier (CSP) in the monolithic 2 μ m BiCMOS technology (called HF2CMOS), the performance of the available NPN and PNP transistors were measured, before and after neutron irradiation. Furthermore, also monolithic CSPs, realized with the same technology, were irradiated and investigated. Results on the neutron irradiation effect on the base spreading resistance ( r bb′ ) of the CSP input NPN-transistor are presented. Design strategies, to reduce the radiation damage effects in the CSP performance, were studied. Results confirm that the HF2CMOS process is suitable to sustain the radiation environment of the future LHC collider. A design for a new CSP version is proposed. A novel method for measuring the series noise of the CSP, at large input capacitances, was used. The method minimized the errors caused by the CSP rise-time.

Design and implementation of a monolithic bipolar read-out system

Design and implementation issues regarding a bipolar high-speed read-out system to be used at future high luminosity colliders, such as LHC, are presented. The entire system consists of two blocks (the preamplifier and the RC-CR shaper) to be located in separate positions. For this purpose different monolithic solutions were realized for testing. Noise and speed considerations led to use of bipolar technology. Preliminary experimental results in good agreement with simulations, are given for one of the realized electronic chains.

Test system for an optical readout chain of a silicon microstrip detector

Abstract A test system, for an optical readout chain of a double-sided silicon microstrip detector, is presented. The system can be used for a quick but complete test of the working performance of the optical readout chain, and for finding exactly the faulty part of the readout chain, in case that an error is detected. It was designed, developed, and built for a silicon microvertex detector used at the LEP collider. A description, of both the hardwave and software of the system, is given. Finally, experimental results, of laboratory tests, are shown.