Supply Voltage Dependence of Heavy Ion Induced SEEs on 65 nm CMOS Bulk SRAMs

Soft Error Rates (SER) of hardened and unhardened SRAM cells need to be experimentally characterized to determine their appropriate applications in radiation environments. This characterization is especially important when low supply voltage is preferred. In this paper, we developed an SRAM test chip with four cell arrays including two types of unhardened cells (standard 6T and subthreshold 10T) and two types of hardened cells (Quatro and DICE). This test chip was fabricated in a 65 nm bulk technology and irradiated by heavy ions at different supply voltages. Experimental results show that the SERs of 6T and 10T cells present significant sensitivities to supply voltages when the particle linear energy transfers (LETs) are relatively low. For Quatro and DICE cells, one does not consistently show superior hardening performance over the other. It is also noted that Quatro cells show significant advantage in single event resilience over 10T cells although they consume similar areas. TCAD simulations were carried out to validate the experimental data. In addition, the error amount distributions follow a Poisson distribution very well for each type of cell array.

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