A.B. Campbell

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. >

Direct measurement of transient pulses induced by laser and heavy ion irradiation in deca-nanometer devices

This paper investigates the transient response of 50-nm gate length fully and partially depleted SOI and bulk devices to pulsed laser and heavy ion microbeam irradiations. The measured transient signals on 50-nm fully depleted devices are very short, and the collected charge is small compared to older 0.25-/spl mu/m generation SOI and bulk devices. We analyze in detail the influence of the SOI architecture (fully or partially depleted) on the pulse duration and the amount of bipolar amplification. For bulk devices, the doping engineering is shown to have large effects on the duration of the transient signals and on the charge collection efficiency.

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. >

Pulsed laser-induced single event upset and charge collection measurements as a function of optical penetration depth

We use picosecond laser pulses to investigate single event upsets and related fundamental charge collection mechanisms in semiconductor microelectronic devices and circuits. By varying the laser wavelength the incident laser pulses deposit charge tracks of variable length, which form an approximation to the charge tracks resulting from high energy space particle strikes. We show how variation of the charge track length deposited by laser pulses allows the mechanisms of charge collection in semiconductor devices to be probed in a sensitive manner. With the aid of computer simulations, new insight into charge collection mechanisms for metal–semiconductor field effect transistor (MESFET) devices and heterojunction bipolar transistor devices is found. In the case of the MESFET we point out the correlation between charge collection in the device and the ensuing single event upset in the composite circuit. In favorable cases, we show how probing circuits with tunable laser pulses can estimate a charge collectio...

Analysis of multiple bit upsets (MBU) in CMOS SRAM

Multiple Bit Upsets (MBU) have been studied in a 256 k CMOS static RAM irradiated at normal incidence and grazing angle. In normal incidence the sensitive areas have been identified with pulsed laser irradiation. The laser power thresholds have been determined for single to quadruple upsets in adjacent cells. Both experimental data and 3D simulations emphasize the role of delayed charge collection, by diffusion, and charge sharing between sensitive areas. Upset tracks have been recorded at grazing angle and used to determine the charge collection depth. These data revealed the existence of an LET threshold for MBU at grazing angle. As the ion LET increases different types of tracks are observed and correlated to the topological pattern in adjacent memory cells. This phenomenon is due to an unexpected charge collection mechanism, which couples adjacent sensitive areas and results in charge transfer between memory cells. The comparison with previous data on the same device indicates a strong influence of both ion energy and angle of incidence on the cross section, emphasizing the intrinsic limitation of standard characterizations with low energy ions. These results indicate that the basic assumption of a rectangular parallelepipedic volume does not take into account coupling phenomena, such as occurs in MBUs, and is no longer valid at grazing angle.

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.

Laser Simulation of Single Event Upsets

A pulsed picosecond laser was used to produce upsets in both a commercial bipolar logic circuit and a specially designed CMOS SRAM test structure. Comparing the laser energy necessary for producing upsets in transistors that have different upset sensitivities with the single event upset (SEU) level predicted from circuit analysis showed that a picosecond laser could measure circuit sensitivity to SEUs. The technique makes it possible not only to test circuits rapidly for upset sensitivity but also, because the beam can be focussed down to a small spot size, to identify sensitive transistors.

Effect of ion energy upon dielectric breakdown of the capacitor response in vertical power MOSFETs

The effect of ion energy upon the ion-induced dielectric breakdown response of the capacitor response in vertical power metal-oxide semiconductor field effect transistors (MOSFETs) was investigated. The single event gate rupture response was experimentally determined using mono-energetic ion beams of copper, niobium, and gold. Irradiations were conducted using an ion species tuned to different energies, producing a range of linear energy transfer (LET) values for that ion. Numerous MOSFETs were characterized to identify the onset of ion-induced dielectric breakdown. These data along with previously taken data demonstrated that the ion-induced dielectric breakdown cannot be adequately described in terms of LET, but is better described in terms of atomic number (Z). Based upon these observations, a new semi-empirical expression is presented describing the critical ion-induced breakdown response in terms of Z instead of LET. This expression is shown to be a better single event gate rupture model of the capacitor response.

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.