Iue Annual Review 2004

Biography:
Siddhartha Dhar was born in New Delhi, India, in 1979. He received his B.E. degree in Electrical Engineering from the Delhi College of Engineering, India in 2001. He then studied Microelectronics and Microsystems at the Technical University of Hamburg-Harburg, Germany, from where he graduated with a M.Sc. degree in 2003. In April 2004, he joined the Institute for Microelectronics where he is currently pursuing his doctoral degree. His research interests include device modeling and simulation of strained Si CMOS transistors and circuit level simulation in general.

Modeling and Simulation of Strained Si CMOS Transistors

In recent years, the performance improvement of VLSI circuits has been attributed to the continuous shrinking of feature size or alternatively to the introduction of new device structures or materials. In this regard, strained Si, due to its different material properties and excellent compatibility with conventional Si technology, has emerged as a promising material. The introduction of strain into the Si layer leads to a splitting of the valence and conduction bands, resulting in enhancement of both the electron and hole mobility. Enhancement ratios as high as 70% and 100% as compared to unstrained Si have been both theoretically verified and experimentally measured for electrons and holes, respectively.

In order to study the performance of strained devices, a reliable set of models for parameters such as mobility, energy bandgap and relaxation times is required for strained Si. The Monte Carlo method serves as an important tool for studying the effect of strain on device characteristics. Based on the Monte Carlo simulations, the required models for the strained Si/SiGe material system can be obtained. These models are to be implemented in Minimos-NT and then used to investigate and design different strained Si device structures.

The bulk mobility enhancement ratio for electrons has been fit to the experimental data by adjusting the inter- and intra-valley coupling constants. An analytical expression for the bulk mobility has been suggested which fits the MC data. This analytical expression for the bulk mobility along with another model for the material composition dependence of the mobility for relaxed SiGe has been implemented in Minimos-NT. Also, it has been possible to fit the experimental data for effective electron mobility versus effective field for strained Si, which shows a large variation, using the well known Lombardi mobility model. Future work will concentrate on modeling of the various parameters based on Monte Carlo results, with special focus on the surface mobility and obtaining device characteristics.