Yury Illarionov was born in Leningrad (now Saint-Petersburg) in 1988. He studied solid state physics at the Physical Science and Technology Faculty of St. Petersburg State Polytechnical University where he received the B.Sc. and M.Sc. degrees in 2009 and 2011, respectively. From 2010 to 2012 he studied advanced material science in Grenoble Institute of Technology (France) and University of Augsburg (Germany) in frameworks of Functionalized Advanced Materials and Engineering (FAME) Erasmus Mundus program and in September 2012 received a double European M.Sc. degree. His scientific carrier has started in October 2007 in Ioffe Physical-Technical Institute (Russia) and in November 2011 he joined the PhD program there. He also visited IRCELYON (France, May-July 2011) and Singapore Institute of Manufacturing Technology (Singapore, February-July 2012) as a young guest researcher. He joined the Institute for Microelectronics in February 2013. In January 2015 he received the PhD degree in semiconductor physics from Ioffe Physical-Technical Institute and in December 2015 the Dr.techn. degree from Technische Universität Wien. Since January 2016 Dr. Yury Illarionov is a postdoc researcher working on reliability of the next-generation 2D FETs with graphene, MoS2 and phosphorene.
Long-Term Stability and Positive Aging of Black Phosphorus Field-Effect Transistors
Black phosphorus (BP), also known as phosphorene in the single-layer limit, is an almost unexplored "beyond graphene" material now considered a promising candidate for next-generation two-dimensional FETs. Several successful attempts at fabricating BP field-effect transistors (BPFETs) have already been reported. However, detailed analysis of the main properties of these devices was not possible due to their poor air-stability. More specifically, BP devices have been known to completely dissolve after several hours or days due to their reaction with water molecules present in the ambient air.
In order to solve this problem, conformal encapsulation schemes have been recently introduced (Fig. 1a). In the course of this study, we have performed a detailed analysis of the long-term stability of back-gated BPFETs with 80 nm thick SiO2 as a gate insulator and conformal Al2O3 (25 nm) encapsulation (Fig. 1b). Seventeen months following the fabrication of our devices (provided by the University of Texas at Austin), we measured their gate transfer (Id-Vg) characteristics using a constant sweep rate S = 0.02 V/s, both in a vacuum and in the ambient. In between the Id-Vg sweeps, the devices have been either stored in the ambient or intensively stressed in a vacuum at various temperatures (Fig. 1c).
Our results show that the Id-Vg characteristics measured at different stages of our long-term study are similar (Fig. 1d). In particular, some drifts in the charge neutrality point have been observed only after several months of intensive stressing, while long storage in ambient conditions does not have any considerable impact on device performance. At the same time, the Id-Vg characteristics consecutively measured in a vacuum and in the ambient are similar.
Finally, the most recent curves exhibit the highest on/off current ratio, the steepest subthreshold slope and the smallest hysteresis of all measurements. We can therefore conclude that our BPFETs have not only exhibited unexpectedly high stability over a period of seventeen months but have also improved over time. The latter can be referred to as positive aging. As such, conformal encapsulation offers a considerable technological advance in the fabrication of BPFETs.
Fig. 1: (a) Stability scenarios of BPFETs. While bare devices are unstable in air, conformal encapsulation guarantees long-term stability. (b) Schematic layout of our BPFETs (provided by the University of Texas at Austin) with Al2O3 encapsulation. (c) Measurement activity versus time since fabrication of the devices. "0" means that the devices have been stored in ambient conditions, while "1" expresses intensive measurements in a vacuum (mostly electrical stressing, 0.5-2.5 MV/cm) at various temperatures (27 to 165℃). (d) The Id-Vg characteristics of a BPFET measured at different stages of our long-term study (as marked in (c)).