Yordan Stefanov

Carbon Nanotube Transistor Fabrication Assisted by Topographical and Conductive Atomic Force Microscopy

In this work, fully functional carbon nanotube field-effect transistors (CNT-FETs) have been fabricated using a simple and inexpensive process including in-situ chemical vapor deposition (CVD) growth of the nanotubes. The temperature used is 900 °C and the catalyst layer is nickel on aluminum. Simultaneously, the catalyst metal areas are used as source/drain electrodes. The CNT-FET fabrication is compatible with conventional complementary metal oxide semiconductor (CMOS) technology. For process optimization, every major process step is controlled by atomic force microscopy (AFM). The nondestructive AFM technique provides both a complete overview of the structures as well as the detailed geometrical properties of the nanotubes. We have also fabricated CNT-FET test structures in which the source/drain electrodes have a direct conductive path to the substrate, in order to perform electrical measurements at the nanoscale by conductive AFM (C-AFM). In this way, we obtain current images of the structures and the electrical characteristics of each individual nanotube can be measured.

Electrical characterisation of crystalline praseodymium oxide high-k gate dielectric MOSFETs

We have successfully completed the process integration of crystalline praseodymium oxide (Pr/sub 2/O/sub 3/) high-k gate dielectric in order to fabricate fully functional Pr/sub 2/O/sub 3/ MOSFETs with gate leakages <10/sup -6/ A/cm/sup 2/. Gate leakage is found to be size dependent and may be related to defects at Pr/sub 2/O/sub 3/ grain boundaries. Although fully functional, Pr/sub 2/O/sub 3/ NMOS transistors showed a lower performance when compared to conventional SiO/sub 2/ MOSFETs with the same EOT. The performance degradation is attributed to mobility reduction due to large amounts of trapped charges. In addition, a reversible Vt-instability is observed, even at operating conditions. These results suggest that charging/discharging of defects via tunneling within Pr/sub 2/O/sub 3/ and near the interfaces is a likely mechanism.