F. J. Franco

Evidence of the Robustness of a COTS Soft-Error Free SRAM to Neutron Radiation

Radiation tests with 15-MeV neutrons were performed in a COTS SRAM including a new memory cell design combining SRAM cells and DRAM capacitors to determine if, as claimed, it is soft-error free and to estimate upper bounds for the cross-section. These tests led to cross-section values two orders of magnitude below those of typical CMOS SRAMs in the same technology node. MUSCA SEP3 simulations complement these results predicting that only high-energy neutrons ( > 30 MeV) can provoke bit flips in the studied SRAMs. MUSCA SEP3 is also used to investigate the sensitivity of the studied SRAM to radioactive contamination and to compare it with the one of standard CMOS SRAMs. Results are useful to make predictions about the operation of this memory in environments such as avionics.

Single Event Effects on Digital Integrated Circuits: Origins and Mitigation Techniques

New generation electronic devices have become more and more sensitive to the effects of the natural radiation coming from the surrounding environment. These radiation sources are cosmic rays and radioactive impurities, able to corrupt the content of memory cells or to induce transient pulses in combinational logic. The growing sensitivity seems to be related to two main factors: the lower and lower charge needed to define the logic levels in advanced devices and the increasing number of basic components inside the modern integrated circuits. In this paper, are described state-of-art techniques to mitigate these effects as well as typical tests to verify the radiation-tolerance of the devices and/or systems.

Modification of the LM124 Single Event Transients by Load Resistors

The influence of a load resistor on the shape of the single event transients was investigated in the LM124 operational amplifier by means of laser tests. These experiments indicated that, as a general rule, load resistors modify the size of the transients. SPICE simulations helped to understand the reasons of this behavior and showed that the distortion is related to the necessity of providing or absorbing current from the load resistor, which forces the amplifier to modify its operation point. Finally, load effects were successfully used to explain the distortion of single event transients in typical feed-back networks and the results were used to explain experimental data reported elsewhere.

Degradation of Power Bipolar Operational Amplifiers in a Mixed Neutron and Gamma Environment

Power operational amplifiers were irradiated in a mixed neutron and gamma radiation environment. These experiments showed that the degradation of the power operational amplifiers shares a great deal of characteristics with that of the low signal devices (e.g., shift of the input offset voltage, increase of the input bias currents, and degradation of the frequency behavior). However, other phenomena were observed without equivalence in the family (linear dependence of the inverse of the quiescent current on the neutron fluence, more significant degradation of the negative output current and collapse of the primary operational amplifiers). These phenomena were explained from the special characteristics of the output stage, optimized to provide a current of several amperes. Finally, even though power devices are especially sensitive to radiation damage, some of the tested devices are suitable for radiation levels on the order of 5 ldr 1013 - 1014 n ldr cm-2 in case the whole electronic system, in which the device is integrated, is carefully designed.

SPICE Simulations of Single Event Transients in Bipolar Analog Integrated Circuits Using Public Information and Free Open Source Tools

This paper proposes a technique to build SPICE micromodels of integrated circuits in bipolar technology appropriate to simulate single event transients. First of all, we will show how to obtain SPICE models of the internal transistors from texts in the scientific and academic literature. Next, several strategies to figure out the internal structure of the integrated circuits and bias point will be shown. Finally, simulation results will be compared to data issue from experiments, either performed by the authors or by other researchers. As the simulations do not require expensive software or hardware, this paper can be a start point for research groups with small budget or for academic purposes at universities.

LASER system for space environment emulation

The Sensors and Electronic Instrumentation Group of the University Complutense of Madrid has developed a system to emulate the cosmic radiations effects on electronic devices by LASER irradiations. Of great interest to the nuclear industry and space electronics, this project was carried out partially supported by the company ALTER SPAIN S.A., specialized in engineering, quality management and testing of high reliability electronic components for space applications.

Inactivity Windows in Irradiated CMOS Analog Switches

Radiation tests have shown the existence of inactivity windows in analog switches. It means that the devices lose their ability to switch between ON and OFF states if the total radiation dose is placed between two characteristic values. Once the total radiation dose goes beyond the top value of the window, the switching ability reappears. A physical mechanism based on the evolution of the threshold voltage of irradiated NMOS transistors is proposed in this paper. Finally, consequences of inactivity windows in the conception of radiation tests are discussed

Peak Detector Effect in Low-Dropout Regulators

The peak detector effect is a phenomenon that makes single event transients much longer once an error amplifier switches from linear to saturation zone due to the presence of external capacitors. This is so-called since it was discovered in a simple voltage reference in which a parasitic lossy peak detector was unwillingly built in the output stage. In this paper, peak detector effect is generalized to explain the appearance of long duration pulses in typical low dropout voltage regulator built with discrete devices. This effect has been related to the way in which the negative feedback loop is closed and to the kind of pass device in the output stage. Thus, if the linear voltage regulator consists in an error amplifier the output of which controls a current source, the peak detector effect will occur if the current source is unidirectional, the output load does not drain enough current and is in parallel with an external capacitor.

New Details About the Frequency Behavior of Irradiated Bipolar Operational Amplifiers

The frequency behavior of a bipolar operational amplifier (op amp) is always expected to worsen when the device is irradiated. In other words, parameters like the slew rate and the gain-bandwidth product are to decrease after either neutron or gamma tests. However, some neutron and TID tests performed on a large variety of bipolar op amps have shown that the evolution of the frequency behavior is not as simple as it is usually believed. In fact, there is evidence of an increasing influence of the power supply values on the former parameters, which can be extremely important in some devices. Also, the relationship among different frequency parameters has been investigated and, finally, an interesting and scarcely reported phenomenon is depicted. This phenomenon is the appearance of spontaneous oscillations in fed-back op amps, without doubt related to the modification of the gain and phase margins of the devices

Radiation effects on XFET voltage references

XFET references make up a new kind of voltage references different from the popular band-gap or buried Zener devices. These references are built by means of a reference cell consisting of a couple of p-channel junction field effect transistors with different pinch-off voltage values and an operational amplifier for the purpose of improving the output characteristics of the whole device. An irradiation in a mixed gamma and neutron environment was performed at the Portuguese Research Reactor for a complete characterization of the devices. Some of the parameters were measured during the irradiation while the rest of them were obtained once the samples were removed from the neutron facility. Experimental results show that some references belonging to this class are interesting candidates for a design of radiation-tolerant electronic systems based on COTS devices.