M Milovanović

Bio: M Milovanović is an academic researcher from Jožef Stefan Institute. The author has contributed to research in topics: Silicon & Electric field. The author has an hindex of 7, co-authored 10 publications receiving 198 citations.

Investigation of Irradiated Silicon Detectors by Edge-TCT

Abstract: A Transient Current Technique (TCT) utilizing an IR laser with 100 ps pulse width and beam diameter of FWHM = 8 μm was used to evaluate non-irradiated and irradiated p-type silicon micro-strip detectors. The beam was parallel with the surface and perpendicular to the strips (Edge-TCT) so that the electron hole pairs were created at known depth in the detector. Induced current pulses were measured in one of the strips. The pulse shapes were analyzed in a new way, which does not require the knowledge of effective trapping times, to determine drift velocity, charge collection and electric field profiles in heavily irradiated silicon detectors. The profiles were studied at different laser beam positions (depth of carrier generation), voltages and fluences up to 5·1015 neutrons cm-2. A strong evidence for charge multiplication at high voltages was found with the detector irradiated to the highest fluence.

Modeling of electric field in silicon micro-strip detectors irradiated with neutrons and pions

Abstract: Edge-TCT method was used to extract velocity profiles in heavily irradiated silicon micro-strip detectors. Detectors were irradiated up to 1016 c -2 with reactor neutrons, 200 MeV pions and a combination of both. A simple electric field model assuming two space charge regions at each side of the detector and neutral bulk in-between was found to describe the field profile. It was observed that after heavy irradiation a sizeable electric field is present in the entire detector volume. For pion-irradiated detectors strikingly different profiles were obtained and attributed to the large oxygen concentration in the detector bulk. The model parameters were also studied during the long term annealing. The space charge region near the strips was found to shrink which in turn leads to larger electric field and impact ionization. The model parameters extracted from the measurements were fed to the device simulation program which showed reasonable agreement between simulated and measured data at lower fluences.

TCT measurements of irradiated strip detectors with a focused laser beam

Abstract: Electrical signals induced by pulses of a focused IR (λ = 1064 nm) laser beam in strip detectors were measured using a wide bandwidth current amplifier. The laser beam was focused to a spot with a diameter of about 8 μm and directed to the detector surface. The detector was mounted on a high precision moving stage allowing measurements of signals induced by a laser beam directed to different locations on the detector surface. Measurements were performed with miniature micro-strip detectors made by implanting n+ type readout strips on p-type silicon bulk (n+-p). Special type of detectors, with implants not fully covered by metal, allowed TCT measurements with a laser beam directed on the implant. The detectors were irradiated with reactor neutrons up to fluences of 51015 neq/cm2. The signals were measured at reverse bias voltages up to 1000 V. The measurements were repeated after several annealing steps at 60°C. Strong dependence of charge collection on distance of laser beam from the implant was observed in heavily irradiated detectors indicating that charge multiplication is increased at implant edges.

Effects of accelerated long term annealing in highly irradiated n+-p strip detector examined by Edge-TCT

Abstract: Effects of long term annealing on the charge collection properties of a miniature p-type micro-strip detector, irradiated to a fluence of 1016 neq/cm2 with reactor neutrons, were examined with the Transient Current Technique with edge-on laser injection (Edge-TCT). The detector was annealed at 60°C in steps to a cumulated time of 10240 min. A large increase of the measured charge was observed even at low bias voltages at late annealing stages. Long term annealing causes build up of negative space charge at the n+-p junction (strip implants), consequently resulting in very high electric fields, sufficient for initiating the process of impact ionization, leading to charge multiplication. The increase of charge collection is correlated with the increase of leakage current.

Determination of the electric field in highly-irradiated silicon sensors using edge-TCT measurements

Abstract: A method is presented which allows to obtain the position-dependent electric field and charge density by fits to velocity profiles from edge-TCT data from silicon strip detectors. The validity and the limitations of the method are investigated by simulations of non-irradiated n + p pad sensors and by the analysis of edge-TCT data from non-irradiated n + p strip detectors. The method is then used to determine the position dependent electric field and charge density in n + p strip detectors irradiated by reactor neutrons to fluences between 1 and 10 × 1 0 15 cm−2 for forward-bias voltages between 25 V and up to 550 V and for reverse-bias voltages between 50 V and 800 V. In all cases the velocity profiles are well described. The electric fields and charge densities determined provide quantitative insights into the effects of radiation damage for silicon sensors by reactor neutrons.

Investigation of Irradiated Silicon Detectors by Edge-TCT

Abstract: A Transient Current Technique (TCT) utilizing an IR laser with 100 ps pulse width and beam diameter of FWHM = 8 μm was used to evaluate non-irradiated and irradiated p-type silicon micro-strip detectors. The beam was parallel with the surface and perpendicular to the strips (Edge-TCT) so that the electron hole pairs were created at known depth in the detector. Induced current pulses were measured in one of the strips. The pulse shapes were analyzed in a new way, which does not require the knowledge of effective trapping times, to determine drift velocity, charge collection and electric field profiles in heavily irradiated silicon detectors. The profiles were studied at different laser beam positions (depth of carrier generation), voltages and fluences up to 5·1015 neutrons cm-2. A strong evidence for charge multiplication at high voltages was found with the detector irradiated to the highest fluence.

Displacement Damage in Silicon Detectors for High Energy Physics

Abstract: In this paper, we review the radiation damage issues caused by displacement damage in silicon sensors operating in the harsh radiation environments of high energy physics experiments. The origin and parameterization of the changes in the macroscopic electrical sensor properties such as depletion voltage, leakage current, and charge collection efficiency as a function of fluence of different particles, annealing time, and annealing temperature are reviewed. The impact of impurities in the silicon base crystal on these changes is discussed, revealing their effects on the degradation of the sensor properties. Differences on how segmented and nonsegmented devices are affected and how device engineering can improve radiation hardness are explained and characterization techniques used to study sensor performance and the electric field distribution inside the irradiated devices are outlined. Finally, recent developments in radiation hardening and simulation techniques using technology computer-aided design modeling are given. This paper concludes with radiation damage issues in presently operating experiments and gives an outlook of radiation-hardened technologies to be used in the future upgrades of the Large Hadron Collider and beyond.

3D silicon sensors: Design, large area production and quality assurance for the ATLAS IBL pixel detector upgrade

Abstract: 3D silicon sensors, where electrodes penetrate the silicon substrate fully or partially, have successfully been fabricated in different processing facilities in Europe and USA. The key to 3D fabrication is the use of plasma micro-machining to etch narrow deep vertical openings allowing dopants to be diffused in and form electrodes of pin junctions. Similar openings can be used at the sensor's edge to reduce the perimeter's dead volume to as low as ∼4 μm. Since 2009 four industrial partners of the 3D ATLAS R&D Collaboration started a joint effort aimed at one common design and compatible processing strategy for the production of 3D sensors for the LHC Upgrade and in particular for the ATLAS pixel Insertable B-Layer (IBL). In this project, aimed for installation in 2013, a new layer will be inserted as close as 3.4 cm from the proton beams inside the existing pixel layers of the ATLAS experiment. The detector proximity to the interaction point will therefore require new radiation hard technologies for both sensors and front end electronics. The latter, called FE-I4, is processed at IBM and is the biggest front end of this kind ever designed with a surface of ∼4 cm 2 . The performance of 3D devices from several wafers was evaluated before and after bump-bonding. Key design aspects, device fabrication plans and quality assurance tests during the 3D sensors prototyping phase are discussed in this paper.

Temperature dependence of the current generated in Si bulk

Abstract: The dependence of the current generated in silicon bulk is investigated both theoretically and experimentally. It is demonstrated to be compatible with I∝T2e−1.21 eV/2kT expected for the generation via a level near the middle of the band gap.