W.J. Stapor

Critical evaluation of the pulsed laser method for single event effects testing and fundamental studies

In this paper we present an evaluation of the pulsed laser as a technique for single events effects (SEE) testing. We explore in detail the important optical effects, such as laser beam propagation, surface reflection, and linear and nonlinear absorption, which determine the nature of laser-generated charge tracks in semiconductor materials. While there are differences in the structure of laser- and ion-generated charge tracks, we show that in many cases the pulsed laser remains an invaluable tool for SEE testing. Indeed, for several SEE applications, we show that the pulsed laser method represents a more practical approach than conventional accelerator-based methods. >

Charge collection in silicon for ions of different energy but same linear energy transfer (LET)

Charge collection measurements in thin silicon structures have indicated that more charge is collected for higher energy ions than for the lower energy ions for incident ions with the same LET. The observed differences are larger than can be explained by uncertainties in energy-loss calculations. A possible explanation is in differences in initial track structure. The higher energy track is more diffuse and might yield more charge to be collected because there is less initial electron-hole pair recombination. >

Two parameter Bendel model calculations for predicting proton induced upset (ICs)

The two-parameter model of W.L. Bendel and E.L. Petersen (1984) represents an improvement over the existing single-parameter model in terms of the goodness of fit to actual proton upset data. It especially gives a better fit to the data from devices with small feature dimensions, which ultimately leads to a more accurate proton error rate prediction. Small feature sized devices have a proton upset energy dependence that cannot be accurately described with the one-parameter model and only one data point. There are no substantial differences in proton error rate predictions from one- and two-parameter approaches for older devices with larger feature sizes. >

Low temperature proton induced upsets in NMOS resistive load static RAM

Proton-induced upset measurements were performed on some NMOS resistive-load static RAMs for temperatures down to -125 degrees C. Results show that the upset cross section strongly depends on temperature as well as the incident beam flux. SPICE modeling for the critical charge versus temperature is not sufficient to explain the data. An explanation is provided that describes multiple subcritical linear-energy-transfer particle strikes within RAM cell integration times that cause upsets. >

The effects of radiation on MEMS accelerometers

Exposing just the mechanical part (sensor) of MEMS accelerometers to protons and heavy ions caused large changes in outputs representing the measured acceleration for the ADXL50 and very small changes for the ADXL04. The large voltage shift measured for the ADXL50 is attributed to charge generated by the ions and trapped in dielectric layers below the moveable mass. The trapped charge alters the electric field distribution which, in turn, changes the output voltage. The construction of the ADXL04 differs from that of the ADXL50 in that the dielectric layers are covered with a conducting polycrystalline silicon layer that effectively screens out the trapped charge, leaving the output voltage unchanged.

Ion Track Shunt Effects in Multi-Junction Structures

Charge collection processes are discussed for heavy ion hits across multiple p-n junctions in bipolar transistor or CMOS structures. The concept of a resistive-like ion track shunt bridging two like conductivity regions is introduced and a first-order-model developed for the charge transported along the ion track shunt. This model is shown to be consistent with charge collection measurements on multi-junction CMOS-like structures. It is found that the charge collection at a given p-n junction is influenced and can even be changed in sign by voltages present at a second p-n junction when the ion track penetrates both junctions. This has important consequences for the design of radiation hard integrated circuits and such ion track shunt effects become more important as device dimensions are scaled to smaller values.

Energy Dependence of Proton-Induced Displacement Damage in Gallium Arsenide

Nonionizing energy deposition in gallium arsenide has been calculated for protons with energies ranging from 1 to 1000 MeV. The calculations are compared with new experimental results for ion implanted gallium arsenide resistors and Hall samples irradiated with protons in the energy range 1 to 60 MeV. Results are also compared with recent studies of proton induced displacement damage in silicon.

Numerical simulation of heavy ion charge generation and collection dynamics

Describes a complete simulation approach to investigating the physics of heavy-ion charge generation and collection during a single event transient in a p-n diode. The simulations explore the effects of different ion track models, applied biases, background dopings and LET (linear energy transfer) on the transient responses of a p-n diode. The simulation results show that ion track structure and charge collection via diffusion-dominated processes play important roles in determining device transient responses. The simulations show no evidence of rapid charge collection in excess of that deposited in the device depletion region in typical funneling time frames. Further, the simulations clearly show that the device transient responses are not simple functions of the ions incident LET. The simulation results imply that future studies should consider the effects of ion track structure and extend transient charge collection times to insure that reported charge collection efficiencies include diffusion-dominated collection processes. >

Charge Transport by the Ion Shunt Effect

Information on the quantity of charge transported between two junctions by the ion shunt effect is presented as a function of bias voltages and ionization densities.

Pulsed laser-induced SEU in integrated circuits: a practical method for hardness assurance testing

A pulsed picosecond laser was used to measure the threshold for single event upset (SEU) and single event latchup (SEL) for a detailed study of a CMOS SRAM and a bipolar flip-flop. Comparing the ion and laser upset data for two such vastly different technologies gives a good measure of how versatile the technique is. The technique provided both consistent and repeatable results that agreed with published ion upset data for both types of circuits. However, measurements of the absolute threshold linear energy transfer (LET) using infrared laser light do not agree with those of the ions, being about 50% too high for the SRAMs, and about 20% too high for the bipolar flip-flops. The consistency of the results, together with the advantages of using a laser system, suggests that the pulsed laser can be used for SEU/SEL hardness assurance of integrated circuits. >