An SRAM SEU Cross Section Curve Physics Model

Abstract

Static random access memories (SRAMs) are prone to a single-event upset (SEU), also known as soft errors, due to transient noise caused by a single strike of radiation. Beam testing has been extensively used to measure the SEU cross section of SRAMs as a function of the linear energy transfer (LET) of charged particle radiation. The evolution of the cross section as a function of LET is called the cross section curve, which plays a vital role in upset rate analysis for hardness assurance. Various analytical models have been developed to describe SRAM SEU cross section curves, and they have proven to be useful in reducing the cost of beam testing as well as revealing the physics behind test results. However, they involve arbitrary parameters, which make it challenging to predict cross section curves without any beam results. Moreover, the current method of analyzing cross section curves or the LET dependence of cross sections relies on a model different from that is used in the analysis of power-supplyvoltage dependence, which is becoming increasingly important because of the demand for low-power operation. To overcome these problems, this article proposes a unified equation that describes both LET and the power-supply-voltage dependence of SRAM SEU cross sections. It comprises only parameters that are physically clear and familiar to SEU researchers. As well as giving possible constraints, comparisons with data from the literature suggest it can be applied to SRAMs fabricated in bulk and silicon-on-insulator (SOI) processes across generations from the early 1000-nm-scale to the current 10-nm-scale technology nodes.

Threshold and Characteristic LETs in SRAM SEU Cross Section Curves

“…Numerical device simulation was used to investigate the validity of the hypothesis. Although the previous study [8] showed the good applicability of the original expression to various SRAMs (without the factor of 5), the study relied on literature data. Some of the model parameters were not available explicitly and hence estimated through fits of data and surveys of information about similar SRAMs.…”

“…1. Cross section curves of an SOI SRAM measured (symbols) and predicted (lines) under two voltage conditions (after [8]). The tested SRAM was fabricated in a 65-nm process, not hardened by design.…”

“…A survey [7] suggests ζ ≈ 2 across technology nodes. * 2 MeV•cm 2 /mg was used in the original article [8].…”

“…This model is similar to others such as the Weibull [9] and the Edmonds [10] models but is unique because all the parameters are physically clear and familiar to SRAM SEU researchers. In [8] this model showed its wide applicability to various SOI SRAMs and-with a…”

“…For silicon-on-insulator (SOI) SRAMs, we recently proposed the following model to describe this curve [8]:…”