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Polycrystallization effects on the nanoscale electrical properties of high-k dielectrics.

Lanza M, Iglesias V, Porti M, Nafria M, Aymerich X - Nanoscale Res Lett (2011)

Bottom Line: In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties.The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept, Eng, Electrònica, Edifici Q, Campus UAB, 08193 Bellaterra, Spain. mario.lanza@uab.cat.

ABSTRACT
In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties. The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

No MeSH data available.


Grain analysis of a current image measured on the sample annealed at 950°C. White areas correspond to currents above the noise level (0.2 pA.)
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Figure 2: Grain analysis of a current image measured on the sample annealed at 950°C. White areas correspond to currents above the noise level (0.2 pA.)

Mentions: The results presented until now demonstrate that the polycrystallization of the Al2O3 layers leads to a larger inhomogeneity of the sample conduction and charge trapped in the stack, which could be attributed to the different electrical properties of nanocrystals and grain boundaries. Taking advantage of the large lateral resolution of the CAFM, a more detailed analysis has been performed to explore this point. Toward this aim, the areas with smaller conductivity have been evaluated from the current images of the sample that has polycrystallized (Figure 2). In Figure 2, the white areas correspond to the regions with a current above 0.2 pA, while the black areas show a current lower than the noise level. The table in Figure 2 includes the results of the statistical analysis of the image, indicating the number, density, and size of the regions with a smaller conductivity (black regions). Note that the average size of these areas is approximately 20 nm, which is compatible with the results obtained from TEM images (Figure 1) for the sizes of the Al2O3 nanocrystals. Therefore, these results suggest that the regions with a smaller conductivity could be related to the grains in the polycrystalline structure: the nanocrystals are more insulating whereas the grain boundaries show a larger conductivity. Note that, in Figure 2, the width of the regions attributed to the grain boundaries is much larger than that estimated in other studies [22], when AFM measurements were performed in ultra high vacuum (UHV). This apparent discrepancy can be explained by considering the impoverishment of the lateral resolution of CAFM experiments when working in air, compared to UHV measurements [22,24]. The differences in electrical behaviors between nanocrystals and grain boundaries could explain the larger inhomogeneity detected in the current and CPD images after polycrystallization. Grain boundaries, probably with an excess of some kind of defects or trapping sites generated during the polycrystallization (which could be related to O-vacancies [25]), could enhance the gate current through them, probably because of trap-assisted-tunneling (TAT) through the defects detected with KPFM [23].


Polycrystallization effects on the nanoscale electrical properties of high-k dielectrics.

Lanza M, Iglesias V, Porti M, Nafria M, Aymerich X - Nanoscale Res Lett (2011)

Grain analysis of a current image measured on the sample annealed at 950°C. White areas correspond to currents above the noise level (0.2 pA.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211152&req=5

Figure 2: Grain analysis of a current image measured on the sample annealed at 950°C. White areas correspond to currents above the noise level (0.2 pA.)
Mentions: The results presented until now demonstrate that the polycrystallization of the Al2O3 layers leads to a larger inhomogeneity of the sample conduction and charge trapped in the stack, which could be attributed to the different electrical properties of nanocrystals and grain boundaries. Taking advantage of the large lateral resolution of the CAFM, a more detailed analysis has been performed to explore this point. Toward this aim, the areas with smaller conductivity have been evaluated from the current images of the sample that has polycrystallized (Figure 2). In Figure 2, the white areas correspond to the regions with a current above 0.2 pA, while the black areas show a current lower than the noise level. The table in Figure 2 includes the results of the statistical analysis of the image, indicating the number, density, and size of the regions with a smaller conductivity (black regions). Note that the average size of these areas is approximately 20 nm, which is compatible with the results obtained from TEM images (Figure 1) for the sizes of the Al2O3 nanocrystals. Therefore, these results suggest that the regions with a smaller conductivity could be related to the grains in the polycrystalline structure: the nanocrystals are more insulating whereas the grain boundaries show a larger conductivity. Note that, in Figure 2, the width of the regions attributed to the grain boundaries is much larger than that estimated in other studies [22], when AFM measurements were performed in ultra high vacuum (UHV). This apparent discrepancy can be explained by considering the impoverishment of the lateral resolution of CAFM experiments when working in air, compared to UHV measurements [22,24]. The differences in electrical behaviors between nanocrystals and grain boundaries could explain the larger inhomogeneity detected in the current and CPD images after polycrystallization. Grain boundaries, probably with an excess of some kind of defects or trapping sites generated during the polycrystallization (which could be related to O-vacancies [25]), could enhance the gate current through them, probably because of trap-assisted-tunneling (TAT) through the defects detected with KPFM [23].

Bottom Line: In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties.The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dept, Eng, Electrònica, Edifici Q, Campus UAB, 08193 Bellaterra, Spain. mario.lanza@uab.cat.

ABSTRACT
In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties. The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

No MeSH data available.