Radiation hardened Trench-Isolated Low-Gain Avalanche Diode (TI-LGAD)

The current generation of low gain avalanche diodes (LGAD) suffers from large fractional dead area at the edges of the pixel, resulting in an important loss of fill factor if the pixel size is in the order of 100 micron. For example, the LGADs planned to be used in the timing detectors of both ATLAS and CMS have a pixel pitch of 1.3 mm. Furthermore, current generations of LGADs have only moderate radiation hardness. The main obstacle of LGADs and their successful use at future experiments in high energy physics is the degradation of gain with fluence. LGADs will be exposed at the HL-LHC to equivalent fluences of up to 𝛷𝑒𝑞 = 2x1015 n/cm2. At these fluences the gain due to the p+ layer completely disappears. The challenge is to obtain a gain of ~50 (or at least x10-20) after high fluence, all for a reasonable bias voltage. This can be accomplished by using a few-micron deep and narrow gain layer. The aim of the Phase I proposal is to develop radiation hardened LGADs for faster time and space resolution based on engineering substrate developed at Cactus Materials, Inc. as part of previous Phase I/II project. An alternative solution for LGAD segmentation is the deep trench isolation (DTI) technology, which exploits physical trenches in the silicon substrate to provide electrical isolation among nearby pixels. Such a solution has been extensively used in CMOS image sensors as well as in silicon photomultipliers, where DTI reduces both electrical and optical crosstalk among cells. The application of DTI technology to LGAD design: trench-isolated LGADs (TI-LGADs) are designed to attain fine pixel segmentation and very high FF, preserving the timing capabilities and the radiation hardness when coupled with the deep and narrow gain layer. The present innovation in engineering substrate with industry standard fabrication process will provide a more stable, radiation hard detector with a much higher fill factor for small pixels than any previous device. This design will directly be applicable for the upgrade of CMS or ATLAS experiment in high luminosity large hardon collider (HL-LHC), ATLAS high granularity timing detector (HGTD) and other applications. A radiation hardened engineering substrate for fast time and space resolutions was developed and fabricated We will leverage those substrates in this project. Key application for these LGADs sensors ranges from high energy physics (HEP) to healthcare. 4D sensors for tracking particles in HEP, scintillator coupling for photon detection applicable in healthcare such as medical imaging in positron emission tomography (PET) scanner, soft x-ray cameras with higher frame rate and other applications. Cactus materials, Inc. and Dr. Gabriele of Brookhaven National Lab will collaborate in this project,