Khomenkova et al. Nanoscale Research Letters 2011, 6:172 http://www.nanoscalereslett.com/content/6/1/172 N A N O E X P R E S S Open Access Hf-based high-k materials for Si nanocrystal floating gate memories Larysa Khomenkova1*, Bhabani S Sahu2, Abdelilah Slaoui2, Fabrice Gourbilleau1 Abstract Pure and Si-rich HfO2 layers fabricated by radio frequency sputtering were utilized as alternative tunnel oxide layers for high-k/Si-nanocrystals-SiO2/SiO2 memory structures. The effect of Si incorporation on the properties of Hf-based tunnel layer was investigated. The Si-rich SiO2 active layers were used as charge storage layers, and their properties were studied versus deposition conditions and annealing treatment. The capacitance-voltage measurements were performed to study the charge trapping characteristics of these structures. It was shown that with specific deposition conditions and annealing treatment, a large memory window of about 6.8 V is achievable at a sweeping voltage of ± 6 V, indicating the utility of these stack structures for low-operating-voltage nonvolatile memory devices. Introduction In recent years, nanocrystal-based memory devices have attracted considerable attention as a possible solution to overcome the scaling issue of electronic nonvolatile memories (NVMs) http://public.itrs.net/. By using discrete nanocrystals instead of the conventional contin- uous floating gate as charge storage nodes, local-defect- related leakage can be reduced efficiently to improve data retention [1]. In this regard, discrete-trap type semiconductor storage materials such as Si and Ge nanocrystals (Si- and Ge-ncs) embedded in a dielectric matrix have been demonstrated as potential candidates for the fabrication of high-speed, high-density, low- power-consuming, and nonvolatile memories [2-6]. Sev- eral approaches have been reported for nanocrystal formation in a dielectric matrix, such as chemical vapor deposition, molecular beam epitaxy, or sputtering. The main attention was devoted to two major ones, namely deposition in vacuum and ion beam synthesis, since they are also used in the semiconductor industry for other purposes other than nanocrystal fabrication. Another approach for the fabrication of Si-ncs is the radio frequency (RF) magnetron sputtering, as discussed previously [7-11]. The excess Si content in the layers can be obtained by several ways. One of them is the * Correspondence: larysa.khomenkova@ensicaen.fr 1CIMAP, UMR CNRS/CEA/ENSICAEN/UCBN 6252, Ensicaen, 6 Bd Mal Juin, 14050 Caen Cedex 4, France Full list of author information is available at the end of the article sputtering of two separated (pure Si and SiO2) targets [7,8,12] or one composed (SiO2 target topped by Si chips) target in pure argon plasma [7,13,14]. The other one is the reactive approach, which deals with the sput- tering of pure SiO2 target in mixed argon-hydrogen plasma [9-11] or pure Si target in argon-oxygen mixture [15]. The Si excess is controlled by varying the hydrogen [9-11] or oxygen flow rate [15] in the plasma. After sub- sequent high-temperature annealing, Si-ncs can be easily formed in these Si-rich SiO2 (SRSO) composite layers [7-15]. One of the major problems associated with the down- scaling of device dimensions is the quantum tunneling limit of SiO2, conventionally used as a gate dielectric material in metal-oxide-semiconductor field-effect tran- sistors. In recent studies, high-k gate dielectrics replaced the conventional SiO2 dielectric to be used as tunnel and control oxides in NVM devices, which allows for a thinner equivalent oxide thickness without sacrificing the nonvolatility [16-20]. Furthermore, the thicker physi- cal thickness of the high-k dielectrics ensures good retention characteristics, while due to unique band asymmetry with Si, their lower electron barrier height allows for a larger tunneling current at low control gate voltage when the device operates in the programming regime [18,20]. In this regard, Hf-based dielectrics can be of immense interest. In this work, different high-k/SRSO/SiO2 memory structures were fabricated by RF magnetron sputtering. © 2011 Khomenkova et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.