S. Buchner

Comparison of error rates in combinational and sequential logic

A pulsed laser was used to demonstrate that, for transients much shorter than the clock period, error rates in sequential logic were independent of frequency, whereas error rates in combinational logic were linearly dependent on frequency. In addition, by measuring the error rate as a function of laser pulse energy for fixed clock frequency, the logarithmic dependence of the SEU vulnerable time period prior to the clock edge in combinational logic was established. A mixed mode circuit simulator program was used to successfully model the dynamic response of the logic circuit to pulses of laser light.

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. >

A digital CMOS design technique for SEU hardening

A new cell design technique is described which may be used to create SEU hardened circuits. The technique uses actively biased, isolated well transistors to prevent transients in combinational logic from reaching the output node.

Heavy ion and proton-induced single event multiple upset

Individual ionizing heavy ion events are shown to cause two or more adjacent memory cells to change logic states in a high density CMOS SRAM. A majority of the upsets produced by normally incident heavy ions are due to single-particle events that causes a single cell to upset. However, for grazing angles a majority of the upsets produced by heavy-ion irradiation are due to single-particle events that cause two or more cells to change logic states. Experimental evidence of a single proton-induced spallation reaction that causes two adjacent memory cells to change logic states is presented. Results from a dual volume Monte-Carlo simulation code for proton-induced single-event multiple upsets are within a factor of three of experimental data for protons at normal incidence and 70 degrees.

Laboratory tests for single-event effects

Integrated circuits are currently tested at accelerators for their susceptibility to single-event effects (SEEs). However, because of the cost and limited accessibility associated with accelerator testing, there is considerable interest in developing alternate testing methods. Two laboratory techniques for measuring SEE, one involving a pulsed laser and the other /sup 252/Cf, are described in detail in this paper. The pulsed laser provides information on the spatial and temporal dependence of SEE, information that has proven invaluable in understanding and mitigating SEE in spite of the differences in the physical mechanisms responsible for SEE induced by light and by ions. Considerable effort has been expended on developing /sup 252/Cf as a laboratory test for SEE, but the technique has not found wide use because it is severely limited by the low energy and short range of the emitted ions that are unable to reach junctions either covered with dielectric layers or deep below the surface. In fact, there are documented cases where single-event latchup (SEL) testing with /sup 252/Cf gave significantly different results from accelerator testing. A detailed comparison of laboratory and accelerator SEE data is presented in this review in order to establish the limits of each technique.

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 probing of bipolar amplification in 0.25-/spl mu/m MOS/SOI transistors

The parasitic bipolar amplification in MOS/SOI transistors determines the SEU sensitivity of actual devices. This response is experimentally measured in a set of single transistors using a focused picosecond laser with submicrometer spatial resolution. This technique, validated by comparing the SEU behavior of registers irradiated with both laser and heavy ions, is relevant for both device physics and hardness assurance applications.

Effect of amplifier parameters on single-event transients in an inverting operational amplifier

Laser data and simulation tools are combined to investigate the single-event transient response of the LM124 operational amplifier. The effect of the bandwidth and gain on transients originating in different stages in the operational amplifier is studied. We found that the single-event transient response of the LM124 operational amplifier in an inverting configuration was dependent on the bandwidth of the amplifier, the gain, and on the values of the resistors used to program the gain of the amplifier. We show the results of simulations which illustrate how these changes impact the single-event transient response of the amplifier. An analysis of the results suggests which properties of an operational amplifier will provide a better single-event transient response.

Laser confirmation of SEU experiments in GaAs MESFET combinational logic (for space application)

Majority vote and self-scrubbing circuitry were utilized to harden the registers of a GaAs logic circuit to single event upsets (SEUs). Ion beam testing of the hardened part at low scrub frequencies showed fewer system upsets than that of an unhardened part. At high frequencies, the upset rate increased with frequency, indicating a clock-dependent SEU sensitive node. A pulsed laser was used to identify an input node in the self-scrubbing circuitry as being the source of the upsets at high frequencies. Because the node was only sensitive for a short duration prior to the rising clock edge, more clock-edge-dependent SEUs could occur at higher frequencies. The relative SEU thresholds of the registers and the input node measured with the laser showed excellent agreement with ion data. All single-point SEU failure nodes were identified and their upset thresholds measured. With this information it was possible to redesign the circuit to reduce its sensitivity to SEU at high scrub frequencies. >