P.J. McNulty

A comparison of Monte Carlo and analytic treatments of displacement damage in Si microvolumes

In this paper, we compare Monte Carlo and analytic calculations of displacement damage resulting from inelastic proton reactions in Si. These comparisons include the nonionizing energy loss rate, the mean recoil damage energy spectra, and their associated variance. In the limit of bulk material, both approaches are in good agreement. Sensitive volumes shrink and incident proton energies increase, the ranges of the spallation recoil fragments approach the smallest dimension of the microvolume, and the pixel-to-pixel damage variance increases rapidly. In this regime, a Monte Carlo approach is used to describe the damage energy distribution. Indeed, we show that such simulations predict the 63 MeV proton-induced dark current histograms more accurately than present analytic methods. The Monte Carlo code is also used to explore ground test fidelity issues for devices with small sensitive volumes. >

Determination of SEU parameters of NMOS and CMOS SRAMs

Procedures for determining the SEU parameters for advanced memory devices are demonstrated for CMOS and resistor-loaded NMOS SRAMs. The dimensions of the sensitive volume are either obtained from charge collection measurements on test structures or estimated from similar measurements on the SRAMs themselves. Values of the critical charge determined from simple proton measurements agree with the values obtained for three SRAMs from extensive heavy-ion data. >

Dosimetry based on the erasure of floating gates in the natural radiation environments in space

A new method is described for measuring ionizing radiation on spacecraft using an array of floating gate avalanche injected metal oxide silicon (FAMOS) transistors. A commercial ultraviolet erasable programmable read only memory (UVPROM) is used to demonstrate the technique for both ground and space dosimetry applications. An indirect measurement of the charge remaining on the floating gate is used to determine the absorbed dose. This method of determining dose leaves the data and the detector intact and capable of further measurements. The device requires power only during readout. Measurements of different ionizing radiation types are presented. Results from an experiment using this technique aboard the Microelectronics and Photonics Test Bed (MPTB) satellite are discussed.

A simple algorithm for predicting proton SEU rates in space compared to the rates measured on the CRRES satellite

A new simulation code, the Clemson Omnidirectional Spallation Model for Interaction in Circuits (COSMIC), is described and its predictions agree with SEU data from four devices flown as part of the microelectronics package experiment on the CRRES satellite. The code uses CUPID for determining the energy depositions in the sensitive volumes. It allows proton exposures with arbitrary angles of incidence including random omnidirectional exposure; and the user specifies the thickness of shielding on six sides of the sensitive volume. COSMIC is used as part of an algorithm developed to predict the rate proton induced single event upsets occur in the space radiation environment given by AP-8. In testing the algorithm, the position coordinates are taken from the satellites ephemeris data, but calculations based on position coordinates from orbital codes were also in agreement with the measured values. >

Proton induced spallation reactions

Abstract Proton-induced upsets are becoming an important problem for modern digital electronics used on satellites that traverse the inner radiation belts. The mechanism for this single event phenomenon is the proton-induced spallation reaction. Computer simulations are used to illustrate the kinematics of the spallation reaction and the resulting energy deposition in microvolumes which have dimensions typical of the elements comprising modern devices.

Implications of angle of incidence in SEU testing of modern circuits

Simulations show that ignoring the angular dependence of proton SEU cross sections produces errors in predictions of SEU rates in space. Moreover, they suggest that devices with thin sensitive volumes may upset to protons at grazing incidence despite high threshold LET values (>80 MeV cm/sup 2/) at normal incidence. Incorporating angular effects in space predictions requires accurate knowledge of the dimensions of the sensitive volume associated with the SEU-sensitive junction, especially the thickness. A method is proposed for using proton SEU measurements at different angles and energies combined with simulations to determine the thickness of the sensitive volume and to test the reliability of the predictions. >

Proton and heavy ion upsets in GaAs MESFET devices

Proton and heavy SEU data has been obtained for devices made by several GaAs MESFET manufacturers. Proton energy dependence and proton and heavy ion upset cross sections are reported. Measurements of charge collection from latches designed with various gate widths show that charge collection depths appear deeper than the 1 mu m depth expected. Critical charge does not scale linearly with area. Proton upset cross sections are reduced with increased device width. >

Charge collection spectroscopy

Monitoring pulses measured between the power pins of a microelectronic device exposed to high LET (linear energy transfer) ions yields important information on the SEU (single event upset) response of the circuit. Analysis of p-well CMOS devices is complicated by the possibility of competition between junctions, but the results suggest that charge collection measurements are still sufficient to determine SEU parameters accurately. It is shown that the charge collection obtained off the power lines of a p-well CMOS device can be explained if one takes into account the fact that the well-substrate and source-well junctions compete for the diffusion charge. To produce a pulse that lies within the peak, the ion must cross the top and bottom junctions of the sensitive volume. The first-order model remains a valid approximation of the complicated charge collection mechanisms that occur when an ion strikes each of the junctions. A comparison of experimental data with the new theories is given. >

Modeling charge collection and single event upsets in microelectronics

Abstract Single event upsets (SEU) result when modem microelectronic circuits are exposed to energetic charged particles in space, around accelerators and in the various natural or manmade radiation environments encountered by computers on earth. Estimating a circuits SEU sensitivity at an early stage of system design requires detailed understanding of the physical phenomena through which upsets are induced, the localized generation of charge, its collection at the SEU-sensitive junction and the circuits response. The amount of charge collected depends on the contribution from drift, field tunneling and diffusion as well the removal of charge through recombination. Decreasing the area of the junction through improvements in lithography increases the complexity of the charge collection in a way which significantly complicates modeling.

Test of SEU algorithms against preliminary CRRES satellite data

The CRRES satellites highly elliptical orbit exposes the SEU-sensitive devices within the microelectronics package to both the trapped protons of the inner radiation belts and the cosmic rays of deep space. Preliminary data from sensitive devices show more upsets due to protons than due to cosmic rays on this type orbit. This is consistent with pulse-height spectra measured from a photodiode within the package. Preliminary data obtained with the ratemeter experiment in the inner radiation belts are in reasonable agreement with predictions based on the trapped proton spectra given by the NASA AP8 model for solar maximum combined with CUPID simulations of the spallation reactions near the sensitive volumes of the memory elements. The more limited data from deep space are in agreement with the CREME calculations for cosmic ray traversals. CUPID is also in relatively good agreement with the pulse-height spectra measured in the inner belts as part of the PHA experiment. >