Process Variation Aware Analysis of SRAM SEU Cross Sections Using Data Retention Voltage

Static random access memory (SRAM) is one the most sensitive devices to radiation. It may often exhibit undesired reversals of memory bits, called single-event upsets or soft errors. Sensitivity to such undesired events is widely quantified with the parameter of cross sections, which varies from cell to cell due to process variations. Many efforts have been made to quantify such variations, most commonly using simulations that often become a hurdle especially for commercial-off-the-shelf SRAMs. In this regard, an analysis method is proposed to extract such variations easily from radiation test data. It relies on the data retention voltage, which is an electrical parameter associated with the static noise margin. This voltage can be measured on a desk without special circuits. The validity of the proposed method is experimentally demonstrated using SRAM fabricated in a 65-nm silicon-on-insulator technology, which was exposed to various high-energy heavy ions simulating the effects of galactic and terrestrial cosmic rays. Theoretical discussion provides further evidence, while revealing an interesting relationship between the data retention voltage and power supply voltage. This relationship suggests power-supply voltage tuning to deal with chip-to-chip variations in cross sections and also with similar variations caused by total-dose effects and aging effects such as negative bias temperature instability.