Study of Radiation-Tolerant SRAM Design

Static Random Access Memories (SRAMs) are important storage components and widely used in digital systems. Meanwhile, with the continuous development and progress of aerospace technologies, SRAMs are increasingly used in electronic systems for spacecraft and satellites. Energetic particles in space environments can cause single event upsets normally referred as soft errors in the memories, which can lead to the failure of systems. Nowadays electronics at the ground level also experience this kind of upset mainly due to cosmic neutrons and alpha particles from packaging materials, and the failure rate can be 10 to 100 times higher than the errors from hardware failures. Therefore, it is important to study the single event effects in SRAMs and develop cost-effective techniques to mitigate these errors. The objectives of this thesis are to evaluate the current mitigation techniques of single event effects in SRAMs and develop a radiation-tolerant SRAM based on the developed techniques. Various radiation sources and the mechanism of their respective effects in Complementary Metal-Oxide Semiconductors(CMOS) devices are reviewed first in the thesis. The radiation effects in the SRAMs, specifically single event effects are studied, and various mitigation techniques are evaluated. Error-correcting codes (ECC) are studied in the thesis since they can detect and correct single bit errors in the cell array, and it is a effective method with low overhead in terms of area, speed, and power. Hamming codes are selected and implemented in the design of the SRAM, to protect the cells from single event upsets in the SRAM. The simulation results show they can prevent the single bit errors in the cell arrays with low area and speed overhead. Another important and vulnerable part of SRAMs in radiation environments is the sense amplifier. It may not generate the correct output during the reading operation if it is hit by an energetic particle. A novel fault-tolerant sense amplifier is introduced and validated with simulations. The results showed that the performance of the new design can be more than ten times better than that of the reference design. When combining the SRAM cell arrays protected with ECC and the radiation-tolerant hardened sense amplifiers, the SRAM can achieve high reliability with low speed and area overhead