Neutron Shielding Effect of Stacked Servers and Its Impact on Reduction of Soft Error Rate

The shielding effect of stacked servers on terrestrial neutrons and its impact on soft error rate of the device in the server are studied. Shielding simulation using the PHITS code is performed with the model of stacked servers and demonstrates its strong effect on neutron attenuation. The measurement of terrestrial neutrons by a Bonner sphere neutron spectrometer is carried out in open air and in a building in order to compare the shielding contributions from stacked servers and from the building. This comparison shows that the neutron attenuation is mainly due to stacked servers depending on its location in the building. Finally, the soft error rate of a 28 nm SRAM cell implemented in CPUs of stacked servers is simulated through PHYSERD with circuit simulation. Our study reveals that the soft error rate is significantly suppressed by the neutron flux attenuation and the distortion of the energy spectrum, both of which are caused by the shielding effect of stacked servers.