RESUMEN
We assessed the accuracy of a prototype radiation detector with a built in CMOS amplifier for use in dosimetry for high dose rate brachytherapy. The detectors were fabricated on two substrates of epitaxial high resistivity silicon. The radiation detection performance of prototypes has been tested by ion beam induced charge (IBIC) microscopy using a 5.5 MeV alpha particle microbeam. We also carried out the HDR Ir-192 radiation source tracking at different depths and angular dose dependence in a water equivalent phantom. The detectors show sensitivities spanning from (5.8 ± 0.021) × 10-8 to (3.6 ± 0.14) × 10-8 nC Gy-1 mCi-1 mm-2. The depth variation of the dose is within 5% with that calculated by TG-43. Higher discrepancies are recorded for 2 mm and 7 mm depths due to the scattering of secondary particles and the perturbation of the radiation field induced in the ceramic/golden package. Dwell positions and dwell time are reconstructed within ±1 mm and 20 ms, respectively. The prototype detectors provide an unprecedented sensitivity thanks to its monolithic amplification stage. Future investigation of this technology will include the optimisation of the packaging technique.
RESUMEN
The paper presents the simulation studies of 10 µµm pitch microstrips on a fully depleted monolithic active CMOS technology and describes their potential to provide a new and cost-effective solution for particle tracking and timing applications. The Fully Depleted Monolithic Active Microstrip Sensors (FD-MAMS) described in this work, which are developed within the framework of the ARCADIA project, are compliant with commercial CMOS fabrication processes. A set of Technology Computer-Aided Design (TCAD) parametric simulations was performed in the perspective of an upcoming engineering production run with the aim of designing FD-MAMS, studying their electrical characteristics, and optimizing the sensor layout for enhanced performance in terms of low capacitance, fast charge collection, and low-power operation. A fine pitch of 10 µµm was chosen to provide high spatial resolution. This small pitch still allows readout electronics to be monolithically integrated in the inter-strip regions, enabling the segmentation of long strips and the implementation of distributed readout architectures. The effects of surface radiation damage expected for total ionizing doses of the order of 10 to 105 krad were also modeled in the simulations. The results of the simulations exhibit promising performance in terms of timing and low power consumption and motivate R&D efforts to further develop FD-MAMS; the results will be experimentally verified through measurements on the test structures that will be available from mid-2021.
RESUMEN
Fully Depleted Monolithic Active Pixel Sensors (FD-MAPS) represent an appealing alternative to hybrid detectors for radiation imaging applications. We have recently demonstrated the feasibility of FD-MAPS based on a commercial 110 nm CMOS technology, adapted using high-resistivity substrates and backside post-processing. A p/n junction diode, fabricated on the detector backside using low-temperature processing steps after the completion of the front-side Back End of Line (BEOL), is reverse-biased to achieve the full depletion of the substrate and thus fast charge collection by drift. Test diodes including termination structures with different numbers of floating guard rings and different pitches were fabricated together with other Process Control Monitor structures. In this paper, we present the design of the backside diodes, together with results from the electrical characterization of the test devices, aiming to improve understanding of the strengths and limitations of the proposed approach. Characterization results obtained on several wafers demonstrate the effectiveness of the termination rings in increasing the breakdown voltage of the backside diodes and in coping with the variability of the passivation layer characteristics. A breakdown voltage exceeding 400 V in the worst case was demonstrated in devices with 30 guard rings with 6 µm pitch, thus enabling the full depletion of high-resistivity substrates with a thickness larger than or equal to 300 µm. Additionally, we show the first direct comparison for this technology of measured pixel characteristics with 3D TCAD simulations, proving a good agreement in the extracted operating voltages.