Iue Annual Review 2013

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.

On the Microscopic Origin of Frequency Dependence of Hole Capture

A detailed understanding of the physical mechanisms behind hole capture in pMOSFETs is essential for a number of reliability issues, including the Negative Bias Temperature Instability (NBTI), hot carrier degradation, random telegraph and 1/f noise. Conventionally, hole capture is explained by a first-order process using effective capture and emission time constants. Our experimental data clearly reveals, however, that this assumption is incorrect under higher frequencies where modern digital applications typically operate.
In order to better understand this frequency dependence, we study the hole capture events on individual defects by extending the recently suggested Time-Dependent Defect Spectroscopy (TDDS) to the AC case. The TDDS is a variant of Deep-Level Transient Spectroscopy (DLTS) and has already allowed us to study charge capture and emission times of individual defects in much greater detail than possible using conventional Random Telegraph Noise (RTN) analysis. These TDDS studies have revealed that the hole capture time constants in pMOSFETs are very sensitive to the gate bias but tend to saturate for very large biases. Furthermore, hole capture is thermally activated, consistent with a Nonradiative Multi-Phonon (NMP) process. However, the observed hole emission times are much larger than one could expect for a conventional NMP process, requiring the introduction of an intermediary metastable state (2'). Also, in some defects (switching traps) hole emission is considerably accelerated once the transistor is switched towards accumulation. Finally, by studying various defects in an AC-TDDS setting, we observe a ubiquitous frequency dependence of the capture times. This frequency dependence clearly confirms that hole capture must occur via the intermediate metastable state 2'. Interestingly, this metastable state was previously introduced to explain the DC-TDDS data and is now found to also fully explain the AC-TDDS case.

The four state oxide defect model extracted from DC TDDS experiments: Each defect has two stable states, 1 and 2, and possibly two metastable states 1' and 2'. The metastable state 2' seems to be always present, while the existence of the metastable state 1' decides on whether the trap behaves like a fixed positive or a switching trap.

Comparison of model (lines) and data (syms) for the frequency dependence of the effective capture time of defect #4 under AC conditions as a function of the gate bias. With increasing f, the time constant becomes larger.