Nanoscale silicon devices and nano-electro-mechanical systems

Prof Cheng


According to the 2001 International Technology Roadmap for Semiconductors (ITRS), the printed gate length of silicon MOSFETs for digital and mixed-signal processing will reach 35nm by 2007. Scaling silicon devices to and below 65nm node exacerbates several well-known challenges, such as leakage current, short channel effects, drive current and control of threshold voltage for digital applications, and linearity, noise, transistor matching for analog/RF applications.[i] New materials and new transistor structures are needed to address these challenges. Several non-classical COMS devices have shown promise, including ultra-thin body silicon-on-insulator (SOI) MOSFET for its improved sub-threshold slope and threshold voltage controllability,30 band-engineered transistor (SiGe or strained Si) for its high drive current and compatibility with the silicon process,[ii] and double-gate MOS for its high drive current and improved sub-threshold and short-channel effect.[iii]











 Figure 1. Ion-selective field effect transistor used to probe protons in polymer materials. The diffusion of protons as catalysts in the activation process of the photoresist is critical to determining the photolithographic resolution. This nano-scale probe can in-situ detect the flux of protons so as to monitor the deactivation process.

Among the most critical challenges for implementing these emerging devices are scaling issues and the need for device characterization and modeling. An electron-beam lithography (EBL) system is essential to efficient fabrication and characterization of these sub-30nm silicon devices. In addition to silicon MOSFETs, the area of Nano Electro-Mechanical Systems (NEMS) is rapidly developing and has attracted a lot of attentions for their very high fundamental frequencies and mechanical responsibility.[iv] We propose the development of nano-arrays of NEMS (dense lines with less than 100nm width) integrated with antibody and MOS circuits used as probes of chemical signals and ion-selective field effect transistor used to probe diffusion-reaction processes in photopolymer materials (Figure 1). These NEMS devices will be fabricated with EBL and could generate great impact on characterizing materials and processes of semiconductors and more general chemical and biological systems.[v]




[i] International SEMATECH, International Technology Roadmap for Semiconductors Process Integration, Devices and Structures and Emerging Research Devices, 2001 Edition.

[ii] R. Hartmann et al, Si/SiGeC Heterostructures: a path high mobility channels, in:S. Luryi et al (Eds.), Future Trends in Microelectronics (1999 John Wiley & Sons, Inc), pp133-141.

[iii] F. Allibert et al, From SOI materials to innovative devices, Solid State Electron, 45 (2001) pp559-566.

[iv] M. Roukes, Nanomechanical systems: progress, challenges, and ultimate limits, Device Research Conference, 2000, pp99 100.

[v] A. Campitelli and E. Parton, BioMEMS: Marrying ICs and biotech, Solid State Technology, July 2002.