Radiation Hardened Engineered Substrates for Time and Space Resolution

The current generation of low gain avalanche detector (LGAD) suffers from large fractional dead area at the edges of the pixels, 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 ??? 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. The aim of the Phase II proposal is to develop radiation hardened high fill factor LGADs for faster time and space resolution based on engineering substrate developed in Phase I. 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 devices. This design will directly be applicable for the upgrade of CMS and ATLAS experiment in high luminosity large hardon collider (HL-LHC), ATLAS high granularity timing detector (HGTD). It will also be applicable for tracking at future colliders, where timing and space requirements will be more severe, and other application. At Phase I of the project, radiation hardened engineering substrates were developed and fabricated for fast timing and space resolutions. On these substrates, a full diode structure was built and characterized, resulting in low leakage current, and showing no degradation due to the interface between bonded wafers. TCAD simulations proved that this is a viable way to develop radiation hardened high fill factor LGADs. The work completed on Phase I built a sound foundation for the development a complete radiation hardened LGAD sensor. 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 are foreseen.