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Register a new userCharacterization of Thin Pixel Sensor Modules Interconnected with SLID Technology Irradiated to a Fluence of 2$cdot 10^{15}$,n$_{mathrm{eq}}$/cm$^2$
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P. Weigell
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A new module concept for future ATLAS pixel detector upgrades is presented, where thin n-in-p silicon sensors are connected to the front-end chip exploiting the novel Solid Liquid Interdiffusion technique (SLID) and the signals are read out via Inter Chip Vias (ICV) etched through the front-end. This should serve as a proof of principle for future four-side buttable pixel assemblies for the ATLAS upgrades, without the cantilever presently needed in the chip for the wire bonding. The SLID interconnection, developed by the Fraunhofer EMFT, is a possible alternative to the standard bump-bonding. It is characterized by a very thin eutectic Cu-Sn alloy and allows for stacking of different layers of chips on top of the first one, without destroying the pre-existing bonds. This paves the way for vertical integration technologies. Results of the characterization of the first pixel modules interconnected through SLID as well as of one sample irradiated to $2cdot10^{15}$, eqcm{} are discussed. Additionally, the etching of ICV into the front-end wafers was started. ICVs will be used to route the signals vertically through the front-end chip, to newly created pads on the backside. In the EMFT approach the chip wafer is thinned to (50--60),$mu$m.
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Small-pitch 3D silicon pixel detectors have been investigated as radiation-hard candidates for the innermost layers of the HL-LHC pixel detector upgrades. Prototype 3D sensors with pixel sizes of 50$times$50 and 25$times$100 $mu$m$^{2}$ connected to the existing ATLAS FE-I4 readout chip have been produced by CNM Barcelona. Irradiations up to particle fluences of $3times10^{16}$ n$_{mathrm{eq}}$/cm$^2$, beyond the full expected HL-LHC fluences at the end of lifetime, have been carried out at Karlsruhe and CERN. The performance of the 50$times$50 $mu$m$^{2}$ devices has been measured in the laboratory and beam tests at CERN SPS. A high charge collected and a high hit efficiency of 98% were found up to the highest fluence. The bias voltage to reach the target efficiency of 97% at perpendicular beam incidence was found to be about 100 V at $1.4times10^{16}$ n$_{mathrm{eq}}$/cm$^2$ and 150 V at $2.8times10^{16}$ n$_{mathrm{eq}}$/cm$^2$, significantly lower than for the previous IBL 3D generation with larger inter-electrode distance and than for planar sensors. The power dissipation at -25$^{circ}$C and $1.4times10^{16}$ n$_{mathrm{eq}}$/cm$^2$ was found to be 13 mW/cm$^2$. Hence, 3D pixel detectors demonstrated superior radiation hardness and were chosen as the baseline for the inner layer of the ATLAS HL-LHC pixel detector upgrade.
Low Gain Avalanche Detectors (LGADs) are silicon sensors with a built-in charge multiplication layer providing a gain of typically 10 to 50. Due to the combination of high signal-to-noise ratio and short rise time, thin LGADs provide good time resolutions. LGADs with an active thickness of about 45 $mu$m were produced at CNM Barcelona. Their gains and time resolutions were studied in beam tests for two different multiplication layer implantation doses, as well as before and after irradiation with neutrons up to $10^{15}$ n$_{eq}$/cm$^2$. The gain showed the expected decrease at a fixed voltage for a lower initial implantation dose, as well as for a higher fluence due to effective acceptor removal in the multiplication layer. Time resolutions below 30 ps were obtained at the highest applied voltages for both implantation doses before irradiation. Also after an intermediate fluence of $3times10^{14}$ n$_{eq}$/cm$^2$, similar values were measured since a higher applicable reverse bias voltage could recover most of the pre-irradiation gain. At $10^{15}$ n$_{eq}$/cm$^2$, the time resolution at the maximum applicable voltage of 620 V during the beam test was measured to be 57 ps since the voltage stability was not good enough to compensate for the gain layer loss. The time resolutions were found to follow approximately a universal function of gain for all implantation doses and fluences.
This paper presents the possibility of using very thin Low Gain Avalanche Diodes (LGAD) ($25 - 50mu$m thick) as tracking detector at future hadron colliders, where particle fluence will be above $10^{16}; n_{eq}/cm^2$. In the present design, silicon sensors at the High-Luminosity LHC will be 100- 200 $mu$m thick, generating, before irradiation, signals of 1-2 fC. This contribution shows how very thin LGAD can provide signals of the same magnitude via the interplay of gain in the gain layer and gain in the bulk up to fluences above $10^{16}; n_{eq}/cm^2$: up to fluences of 0.1-0.3$cdot 10^{16}; n_{eq}/cm^2$, thin LGADs maintain a gain of $sim$ 5-10 while at higher fluences the increased bias voltage will trigger the onset of multiplication in the bulk, providing the same gain as previously obtained in the gain layer. Key to this idea is the possibility of a reliable, high-density LGAD design able to hold large bias voltages ($sim$ 500V).
Silicon photomultipliers (SiPM) are solid state light detectors with sensitivity to single photons. Their use in high energy physics experiments, and in particular in ring imaging Cherenkov (RICH) detectors, is hindered by their poor tolerance to radiation. At room temperature the large increase in dark count rate makes single photon detection practically impossible already at 10$^{11}$ cm$^{-2}$ 1-MeV-equivalent neutron fluence. The neutron fluences foreseen by many subdetectors to be operated at the high luminosity LHC range up to 10$^{14}$ cm$^{-2}$ 1-MeV-equivalent. In this paper we present the effects of such high neutron fluences on Hamamatsu and SensL SiPMs of different cell size. The advantage of annealing at high temperature (up to 175 $^{circ}$C) is discussed. We demonstrate that, after annealing, operation at the single photon level with a SiPM irradiated up to 10$^{14}$ cm$^{-2}$ 1-MeV-equivalent neutron fluence is possible at cryogenic temperature (77 K) with a dark count rate below 1~kHz.
We present the results of the characterization of novel n-in-p planar pixel detectors, designed for the future upgrades of the ATLAS pixel system. N-in-p silicon devices are a promising candidate to replace the n-in-n sensors thanks to their radiation hardness and cost effectiveness, that allow for enlarging the area instrumented with pixel detectors. The n-in-p modules presented here are composed of pixel sensors produced by CiS connected by bump-bonding to the ATLAS readout chip FE-I3. The characterization of these devices has been performed with the ATLAS pixel read-out systems, TurboDAQ and USBPIX, before and after irradiation with 25 MeV protons and neutrons up to a fluence of 5x10**15 neq /cm2. The charge collection measurements carried out with radioactive sources have proven the feasibility of employing this kind of detectors up to these particle fluences. The collected charge has been measured to be for any fluence in excess of twice the value of the FE-I3 threshold, tuned to 3200 e. The first results from beam test data with 120 GeV pions at the CERN-SPS are also presented, demonstrating a high tracking efficiency before irradiation and a high collected charge for a device irradiated at 10**15 neq /cm2. This work has been performed within the framework of the RD50 Collaboration.
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