Angular dependency of neutron-induced multiple cell upsets in 65-nm 10T subthreshold SRAM

This paper reports neutron-induced MCU (Multiple Cell Upset) measured in 0.4-V 65-nm 10T SRAM at two incident angles of 0° and 60°. The measurement results show that the ratio of the number of measured MCUs at the angles of 60° to that at 0° is 1.13 in 0.4-V operation, while the ratio of neutrons radiated to the test chip was 50% at 60°. The spatial MCU patterns measured at 60° indicate that forward emission of secondary ions plays an important role to cause the angular dependency in 0.4-V operation. Furthermore, a Monte-Carlo simulation using PHITS (Particle and Heavy Ion Transport code System) was performed to confirm the measured angular dependency of neutron-induced MCUs. The simulation results show that the ratio of the number of MCUs at the angles of 60° to that at 0° is 1.20 and the same tendency of MCU patterns is observed. The measured angular dependency of neutron-induced MCUs is mostly reproduced by the simulated generation and transport of secondary ions.