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Biography
Tibor Grasser was born in Vienna, Austria, in 1970. He received the Diplomingenieur degree in communications engineering, the PhD degree in technical sciences, and the venia docendi in microelectronics from the Technische Universität Wien, in 1995, 1999, and 2002, respectively. He is currently employed as an Associate Professor at the Institute for Microelectronics. Since 1997 he has headed the Minimos-NT development group, working on the successor to the highly successful MiniMOS program. He was a visiting research engineer for Hitachi Ltd., Tokyo, Japan, and for the Alpha Development Group, Compaq Computer Corporation, Shrewsbury, USA. In 2003 he was appointed head of the Christian Doppler Laboratory for TCAD in Microelectronics, an industry-funded research group embedded in the Institute for Microelectronics. His current scientific interests include circuit and device simulation, device modeling, and reliability issues.
Hydrogen-Related Volatile Defects as the Possible Cause for the Recoverable Component of NBTI and RTN
The recently suggested Time-Dependent Defect Spectroscopy (TDDS) has allowed us to study the Bias Temperature Instability (BTI) at the single-defect level. The most intriguing recent observation is the various degrees of volatility, as previously active defects can disappear without a trace and become spontaneously active at a later point in time. Since an active defect always has the same impact on the threshold voltage, we conclude that the defect must be at a fixed geometrical position along the channel, ruling out mobile species as defect candidates. However, since the defects can transform into a neutral and nonchargeable form, the defect is unlikely to consist only of silicon, oxygen, and nitrogen atoms, which are supposedly rather immobile under typical NBTI conditions. Also, if an oxygen vacancy — a typical defect candidate previously considered — moved by hopping of a neighboring oxygen atom, an oxygen vacancy would be created at the neighboring site, which should be observable as a defect with different properties. This, however, we have never seen. Rather, our results are consistent with the idea that hydrogen can bind to a suitable defect host site, thereby transforming it into an electrically active defect. The defect-hydrogen complex could be charged and discharged until the hydrogen atom escapes, a mechanism previously suggested at KU Leuven. If the defect recaptures a H atom, the cycle starts afresh. Recent observations have revealed similar features in detailed Random Telegraph Noise (RTN) signals, lending strong support to the idea that both BTI and RTN are due to the same defects. In summary, our observations strongly support the idea that the recoverable component of negative BTI is due to hydrogen-related defects, which are active when a hydrogen atom is at the defect site and inactive when not.
Fig. 1: The activity of defects A7 and A8 monitored over a long period. If inactive, the defects show no response whatsoever to changes in the gate voltage. After a 1 month-long bake step at 300C, the previously inactive defects are reactivated.
