Abstract-Due to continuous technology scaling, the reduction of nodal capacitances and the lowering of power supply voltages result in an ever decreasing minimal charge capable of upsetting the logic state of memory circuits. In this paper we investigate the critical charge (Q crit ) required to upset a 6T SRAM cell designed in a commercial 90nm process. We characterize Q crit using different current models and show that there are significant differences in Q crit values depending on which models are used. Discrepancies in critical charge characterization are shown to result in under-predictions of the SRAM's associated soft error rate as large as two orders of magnitude. For accurate Q crit calculation, it is critical that 3D device simulation is used to calibrate the current pulse modeling heavy ion strikes on the circuit, since the stimuli characteristics are technology feature size dependant. Current models with very fast characteristic timing parameters are shown to result in conservative soft error rate predictions; and can assertively be used to model ion strikes when 3D simulation data is not available.

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Carrier generation based on sub-bandgap two-photon absorption is used to perform three-dimensional mapping of the single-event transient response of the LM124 operational amplifier. Three classes of single-event-induced transients are observed for the input transistor Q20. A combination of experiment and transistor level modeling is used to assign the different classes of measured transients to charge collection across specific junctions. The largeamplitude, positive-going transients can not be assigned to a single junction, and are identified with a collector-substrate photocurrent. I. INTRODUCTION The picosecond laser has become an important tool for the investigation and understanding of single-event effects (SEEs) in microelectronic circuitry. The most common implementation of the pulsed laser technique is based upon the excitation of carriers in a semiconductor material using tightly focused, above-bandgap optical excitation [1]-[8]. Carrier generation is governed primarily by Beer's law absorption and, for a given material, the optical penetration depth is determined by the wavelength of the laser pulse. In recent years the pulsed laser has been used successfully in a range of investigations of SEE phenomena, including interrogation of the spatial and temporal aspects of singleevent upset (SEU) and single-event latch up (SEL) in a variety of digital circuits [1]-[3], investigation of the basic charge-collection mechanisms of individual transistors [4], and most recently as an essential tool for unraveling the complex SEE response of bipolar linear circuits [5]-[9]. Recently, a new method of laser-induced carrier generation for SEE applications based upon two-photon absorption using femtosecond (TPA) high peak power pulses sub-bandgap optical wavelengths was introduced at and demonstrated [10]. In two-photon absorption, the laser wavelength is chosen to be less than the bandgap of the semiconductor material such that no carriers are generated Manuscript received

Abstract--Generally good agreement was obtained between the single-event output voltage transient waveforms obtained by exposing individual circuit elements of a bipolar comparator and operational amplifier to an ion microbeam, a pulsed laser beam, and circuit simulations using SPICE. The agreement was achieved by adjusting the amounts of charge deposited by the laser or injected in the SPICE simulations. The implications for radiation hardness assurance are discussed.

A comparison of single-event transients (SETs) from heavy-ion and pulsed-laser irradiation of the LM124 operational amplifier shows good agreement for different voltage configurations. The agreement is illustrated by comparing both individual transient shapes and plots of transient amplitude versus width.