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Alternative Gate Dielectrics

Many materials have been envisaged to replace SiO2 in a FET but the ideal candidate seems still not been found. Hf-based solutions might hold for the 45 nm node of the ITRS-roadmap but other materials are needed for further downscaling. We investigate ternary oxides (Rare Earth-Scandates) which are promising materials for this purpose. These materials are integrated in long channel MOSFETs and tested in other devices (e.g. ChemoFETs, nanowire-FET).

Alternative dielectrics with high dielectric constants (k) are urgently needed for future nanoelectronics. In order to improve the device performance the thickness of the thermally grown gate oxide SiO2 is steadily decreased. However, intolerable leakage currents through ultrathin (≈ 1,2 nm) oxides prohibit further scaling. This problem can be solved by suitable alternative oxides with sufficiently large k (k>20). Many materials have been envisaged, however, the ideal candidate seems still not been found. The new oxide must fulfil numerous prerequisites. Aside a sufficiently large k-value, a large electronic band gap and large band-offsets are needed to prevent leakage. Furthermore the materials must be structurally and chemically stable on silicon as well as compatible with CMOS processing. Particularly critical is the oxide/silicon interface in terms of interface state density and its impact on the carrier mobility. We believe that Rare Earth-Scandates are most promising materials.

Optical Band GapD.G. Schlom et. al.,Gate Oxides Beyond SiO2, MRS Bulletin V. 33, November 2008,1017-1025

The activities are integrated into two main European research projects: NANOSIL and DECISIF (MEDEA+).

Publications:

Durgun Özben, E.; Lopes, J.M.J.; Nichau, A.; Schnee, M.; Lenk, S.; Besmehn, A.; Bourdelle, K.K.*; Zhao, Q.T.; Schubert, J.; and Mantl, S.
Integration of LaLuO3 (к ~30) as High-ĸ Dielectric on Strained and Unstrained SOI MOSFETs with a Replacement Gate Process
IEEE Electronic Device Letters 32 (2011), 15-17

Roeckerath, M.; Lopes, J.M.J.; Durğun-Özben, E.; Sandow, C.; Lenk, S.; Heeg, T.; Schubert, J.; Mantl, S.
Gadolinium scandate as an alternative gate dielectric in field effect transistors on conventional and strained silicon
Appl. Phys. A 94 (2009) 521–524

Durğun-Özben,E.; Lopes, J.M.J.; Roeckerath, M.; Lenk, St.; Holländer, B.; Jia, Y.; Schlom, D.G.; Schubert, J.; Mantl, S.
SmScO3 thin films as an alternative gate dielectric
Appl. Phys. Lett. 93, (2008) 052902 (3 pages)

Lopes, J.M.J.; Roeckerath, M.; Heeg, T.; Littmark, U.; Schubert, J.; Mantl, S.; Jia, Y.; Schlom, D.G.
La-based ternary rare-earth oxides as alternative high-k dielectrics
Microelectronic Engineering 84 (2007) 1890–1893

Wagner, M.; Heeg, T.; Schubert, J.; Lenk, St.; Mantl, S.; Zhao, C.; Caymax, M.
Gadolinium scandate thin films as an alternative gate dielectric prepared by electron beam evaporation
Appl. Phys. Lett. 88, (2006) 172901

Lopes, J.M.J.; Roeckerath, M.; Heeg, T.; Rije, E.; Schubert, J.; Mantl S.; Afanas’ev, V.V.; Shamuilia, S.; Stesmans, A.; Jia, Y.; Schlom, D.G.
Amorphous lanthanum lutetium oxide thin films as an alternative high-k gate dielectric
Appl. Phys. Lett. 89, (2006) 222902 (3 pages)

Zhao, C.; Witters, T.; Brijs, B.; Bender, H.; Richard, O.; Caymax, M.; Heeg, T.; Schubert, J.; Afanas’ev, V.V.; Stesmans, A.; Schlom, D.G.
Ternary rare-earth metal oxide high-k layers on silicon oxide
Appl. Phys. Lett. 86, (2005) 132903

Afanas’ev, V.V.; Stesmans, A.; Zhao, C.; Caymax, M.; Heeg, T.; Schubert, J.; Jia, Y.; Schlom, D.G.; Lucovsky, G.
Band alignment between (100)Si and complex rare earth/transition metal oxides
Appl. Phys. Lett. 85, (2004) 24, 5917-5919


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