In nowadays deeply scaled CMOS technologies, time-dependent variability effects have become important concerns for analog and digital circuit design. Transistor parameter shifts caused by Bias Temperature Instability and Random Telegraph Noise phenomena can lead to deviations of the circuit performance or even to its fatal failure. In this scenario extensive and accurate device characterization under several test conditions has become an unavoidable step towards trustworthy implementing the stochastic reliability models. In this paper, the statistical distributions of threshold voltage shifts in nanometric CMOS transistors will be studied at near threshold, nominal and accelerated aging conditions. Statistical modelling of RTN and BTI combined effects covering the full voltage range is presented. The results of this work suppose a complete modelling approach of BTI and RTN that can be applied in a wide range of voltages for reliability predictions.

Journal Paper - Solid-State Electronics, vol. 185, article 108112, 2021 ELSEVIER
DOI: 10.1016/j.sse.2021.108112    ISSN: 0038-1101    » doi

Quail eggs have been widely used in field experiments, mainly to study factors associated with the risk of nest predation. Some shortcomings of using quail eggs in this type of study have been previously addressed (e.g., these eggs might be too big for some predators of eggs of small birds). Here, we show experimental evidence of another shortcoming of the use of these eggs in field experiments. Quail eggs exposed to sunlight rapidly faded in colour after three days, both in the visible and UV spectra, and this change was related to the amount of solar radiation received. This caused changes in the camouflage of the eggs, which may be perceived by predators with different visual systems (dichromatic, trichromatic, and tetrachromatic (for both violet- and UV-sensitive species)). Therefore, the results of field studies of nest predation using quail eggs might be questioned in those cases in which the camouflage has been altered due to the rapid changes in coloration, as this can affect the resulting predation rates. We recommend that researchers planning to use quail eggs should perform a prospective assessment of changes in coloration of eggs exposed to environmental conditions in the nest sites used by the target species.

Journal Paper - PeerJ 9:e11725, 2021 PEERJ
DOI: 10.7717/peerj.11725    ISSN: 2167-8359    » doi

This article presents a new methodology to extract, at a given operation condition, the statistical distribution of the number of active defects that contribute to the observed device time-dependent variability, as well as their amplitude distribution. Unlike traditional approaches based on complex and time-consuming individual analysis of thousands of current traces, the proposed approach uses a simpler trace processing, since only the maximum and minimum values of the drain current during a given time interval are needed. Moreover, this extraction method can also estimate defects causing small current shifts, which can be very complex to identify by traditional means. Experimental data in a wide range of gate voltages, from near-threshold up to nominal operation conditions, are analyzed with the proposed methodology.

Journal Paper - IEEE Transactions on Electron Devices, first online, 2021 IEEE
DOI: 10.1109/TED.2021.3086448    ISSN: 0018-9383    » doi

The collective behavior of many coupled oscillator systems is currently being explored for the implementation of different non-conventional computing paradigms. In particular, VO2 based nano-oscillators have been proposed to implement oscillatory neural networks that can serve as associative memories, useful in pattern recognition applications. Although the dynamics of a pair of coupled oscillators have already been extensively analyzed, in this paper, the topic is addressed more practically. Firstly, for the application mentioned above, each oscillator needs to be initialized in a given phase to represent the input pattern. We demonstrate the impact of this initialization mechanism on the final phase relationship of the oscillators. Secondly, such oscillatory networks are based on frequency synchronization, in which the impact of variability is critical. We carried out a comprehensive mathematical analysis of a pair of coupled oscillators taking into account both issues, which is a first step towards the design of the oscillatory neural networks for associative memory applications.

Journal Paper - IEEE Transactions on Circuits and Systems II: Express Briefs, first online, 2021 IEEE
DOI: 10.1109/TCSII.2021.3085133    ISSN: 1549-7747    » doi

In nowadays deeply scaled CMOS technologies, time-zero and time-dependent variability effects have become important concerns for analog and digital circuit design. For instance, transistor parameter shifts caused by Bias Temperature Instability and Hot-Carrier Injection phenomena can lead to progressive deviations of the circuit performance or even to its catastrophic failure. In this scenario, and to understand the effects of these variability sources, an extensive and accurate device characterization under several test conditions has become an unavoidable step towards trustworthy implementing the stochastic reliability models and simulation tools needed to achieve reliable integrated circuits. In this paper, the statistical distributions of threshold voltage shifts in nanometric CMOS transistors will be studied at nominal and accelerated aging conditions. To this end, a versatile transistor array chip and a flexible measurement setup have been used to reduce the required testing time to attainable values.

Journal Paper - Solid-State Electronics, vol. 185, article 108037, 2021 ELSEVIER
DOI: 10.1016/j.sse.2021.108037    ISSN: 0038-1101    » doi