was calculated from the intensity and τ of the peak of the pseudo ICTS spectra. The trap densities
of (a) as-deposited, (c) O
2
annealed (3 min) and (d) O
2
annealed (6 min) were 8.8×10
15
, 6.3×10
15
and 7.6×10
15
cm
-3
, respectively. Thus, the trap density of the Pt/YMnO
3
/Y
2
O
3
/Si capacitor
decreases as decreasing the leakage current at low electric field. From these results, the retention
degradation mechanism of the Pt/YMnO
3
/Y
2
O
3
/Si capacitor can be explained as follows. Traps in
YMnO
3
layer affect the leakage current of the capacitor at low electric field. During the retention,
the remanent polarization of YMnO
3
was neutralized by the leakage current which is induced by
the depolarization field in the YMnO
3
layer. The retention time is prolonged with decreasing the
trap density of the YMnO
3
layer, because the leakage current at low electric field and the amount
of the trapped charge are decreased.
CONCLUSIONS
The relationship between the leakage current and memory retention properties of
Pt/YMnO
3
/Y
2
O
3
/Si capacitors was investigated. It was found that the leakage current of the
capacitors could be decreased by the annealing in nitrogen and that the retention time was
prolonged from 10
3
to 10
4
s. From the analysis of the leakage current, it was revealed that at high
electric field, Poole-Frenkel emission from Y
2
O
3
layer was the dominant leakage mechanism. On
the other hand, the dominant leakage current mechanism at low electric field, which has strong
relationship with the retention time, was ohmic conduction. Although further investigations such
as temperature and time dependences are needed to eliminate the
transient current effects etc., it is
suggested that the reduction of defects is important to improve the retention property.
ACKNOWLEDGMENTS
This work was supported by a Grant-in-Aid for Scientific Research (B), No. 08555078,
from the Ministry of Education, Science, Sports, and Culture of Japan, a Grant-in-Aid for
Scientific Research, No. 13875009, a Grant-in-Aid Exploratory Research, No. 13875009,
Grant-in-Aid for Scientific Research (S), No. 14102021 from the Japan Society for the Promotion
of Science, and THE MURATA SCIENCE FOUNDATION.
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