Proton-sensitive custom SRAM detector

Because of the recently discovered importance of protons to the upset of spaceborne electronics, a custom 4-kB SRAM (static random-access memory) chip was tested with protons. The SRAM was developed to determine the single-event-upset hardness of CMOS latches using alpha particle measurements, by adjusting an offset voltage that reduces the charge required to upset a cell. The authors describe a calibration procedure for the SRAM detector. Source spectra were acquired with this chip by measuring the number of upset cells versus offset voltage. The SPICE assisted calibration utilizing 56 fC/V and the proton data identified a 4.32-pm silicon equivalent overlayer and a 6.64+or-0.31 mu m effective charge collection depth for protons and a 6.33- mu m collection depth for alpha particles. These collection depths can be used to predict the SRAM detector response to proton-produced ionization in space. The SRAM collects all of the charge from silicon recoils produced by Rutherford scattering; this charge is collected from very deep in the SRAM substrate.<>