LGAD Sensors on 12-Inch Wafers Enable Wafer-Scale Hybrid Bonding to 28nm CMOS ROICs

The arXiv submission details design, TCAD simulation, and first electrical tests of reach-through, AC-coupled, and deep-junction LGAD variants plus test structures. Fabrication occurred at a commercial 12-inch foundry, targeting full wafer-to-wafer bonding with 28 nm ROICs to reduce interconnect parasitics and enable larger active areas. This approach directly addresses yield and cost barriers that have limited LGAD deployment in timing-critical systems.

Standard LGADs already provide 30-50 ps timing in beam tests at facilities such as Fermilab and CERN. Scaling to 12-inch wafers increases die count per wafer by roughly 2.25 times over 8-inch lines while maintaining the thin gain layer required for low excess noise. Hybrid bonding compatibility with 28 nm CMOS opens paths to on-sensor digitization, lowering power and material budget in trackers.

Medical imaging and environmental dosimetry stand to benefit from the same timing precision and radiation tolerance once production volumes rise. The current submission remains an early engineering run; statistics on breakdown voltage uniformity and gain variation across the full wafer are still limited.

Next steps include completing the hybrid bonding demonstration and beam tests to quantify timing resolution after bonding. Successful results would accelerate adoption in HL-LHC upgrades and compact PET prototypes.