We have developed a novel and highly radiation-tolerant n-in-p silicon microstrip sensor for very high radiation environments such as in the Super Large Hadron Collider. The sensors are designed for a fluence of 1×1015 neq/cm2 and are fabricated from p-type, FZ, 6 in. (150 mm) wafers onto which we lay out a single 9.75 cm×9.75 cm large-area sensor and several 1 cm×1 cm miniature sensors with various n-strip isolation structures. By evaluating the sensors both pre- and post-irradiation by protons and neutrons, we find that the full depletion voltage evolves to approximately 800 V and that the n-strip isolation depends on the p+ concentration. In addition, we characterize the interstrip resistance, interstrip capacitance and the punch-through-protection (PTP) voltage. The first fabrication batch allowed us to identify the weak spots in the PTP and the stereo strip layouts. By understanding the source of the weakness, the mask was modified accordingly. After modification, the follow-up fabrication batches and the latest fabrication of about 30 main sensors and associated miniature sensors have shown good performance, with no sign of microdischarge up to 1000 V.

Development of n-on-p silicon sensors for very high radiation environments

We are developing n+-in-p, p-bulk and n-readout, microstrip sensors, fabricated by Hamamatsu Photonics, as a non-inverting radiation hard silicon detector for the ATLAS tracker upgrade at the super-LHC (sLHC) proposed facility. The bulk radiation damage after neutron and proton irradiations is characterized with the leakage current, charge collection and full depletion voltage. The detectors should provide acceptable signal, signal-to-noise ratio exceeding 15, after the integrated luminosity of 6000 fb−1, which is twice the sLHC integrated luminosity goal.

/pdf/testing-of-bulk-radiation-damage-of-n-in-p-silicon-sensors-15vcakysbt.pdf

Testing of bulk radiation damage of n-in-p silicon sensors for very high radiation environments

We are developing n+-in-p, p-bulk and n-readout, microstrip sensors as a non-inverting radiation hard silicon detector for the ATLAS Tracker Upgrade at the super LHC experiment. The surface radiation damages of the sensors fabricated by Hamamatsu Photonics are characterized on the interstrip capacitance, interstrip resistance and punch-through protection evolution. The detector should provide acceptable strip isolation, exceeding the input impedance of the signal readout chip ∼1 kΩ, after the integrated luminosity of 6 ab−1, which is twice the luminosity goal.

/pdf/testing-of-surface-properties-pre-rad-and-post-rad-of-n-in-p-36kukcarfd.pdf

Testing of surface properties pre-rad and post-rad of n-in-p silicon sensors for very high radiation environment

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.

https://iopscience.iop.org/article/10.1088/1748-0221/8/04/P04016/pdf

TCT measurements of irradiated strip detectors with a focused laser beam

Charge collection measurements with silicon detectors with implanted n-type readout strips in p-type silicon bulk (n+-p) are presented. Detectors were irradiated with 191 MeV pions at the Paul Scherrer Institute (PSI) in Villigen in Switzerland. Signals induced by electrons from 90Sr source were measured with SCT128 chip. Collected charge and detector current were measured after several annealing steps summing up to over 10000 minutes at 60?C. It was observed that irradiation of these detectors with pions results in only ~ 30% of the increase of Vfd seen after irradiation with neutrons to the same NIEL equivalent fluence. Charge multiplication effects in pion irradiated detectors were seen only after long accelerated annealing time. Both effects are consistent with smaller space-charge introduction rates after irradiation with charged hadrons, characteristic for oxygenated detector material. It was confirmed that, at sufficient bias voltage, reverse annealing after pion irradiation does not represent a problem for application of these detectors in trackers at upgraded LHC.

Accelerated annealing of n + -p strip detectors irradiated with pions

Radiation tolerance up to 1015 1-MeV neq/cm2 is required for the silicon microstrip sensors to be operated at the Super LHC experiment. As a candidate for such sensors, we are investigating non-inverting n+-on-p sensors. We manufactured sample sensors of 1 times 1 cm in 4" and 6" processes with implementing different interstrip electrical isolation structures. Industrial high resistive p-type wafers from FZ and MCZ growth are tested. They are different in crystal orientations lang100rang and lang111rang with different wafer resistivities. The sensors were irradiated with 70-MeV protons and characterized in views of the leakage current increase, noise figures, electrical strip isolation, full depletion voltage evolution, and charge collection efficiency.

/pdf/development-of-radiation-hard-rm-n-on-p-silicon-microstrip-2hj0thm3dl.pdf

T. Meguro

Papers

Development of Radiation Hard ${\rm N}^{+}$ -on-P Silicon Microstrip Sensors for Super LHC