We present measurements of specific heat in Mn-doped compounds REBa 2 (Cu 1−x Mn x) 3 O y (RE = Y and Gd) with 0 x 2%. It is found that the transition temperature of Mn-doped YBa 2 (Cu 1−x Mn x) 3 O y (YBaCuMnO) compounds does not change appreciably. On the other hand, in the case of GdBa 2 (Cu 1−x Mn x) 3 O y (GdBaCuMnO) samples, the transition temperature decreases noticeably with the increase in Mn concentration. In REBaCuMnO, a jump in specific heat at the superconducting transition was observed for a low concentration of Mn; however, only a small change in slope was noticed for Mn concentrations above 1%. Replacing 0.5% Cu by Mn has only a marginal effect on the transition temperature, but a threefold suppression of the specific heat jump is observed with such a substitution. This finding clearly demonstrates that these constituents are being incorporated into the superconductors as a whole and not in the form of a local cluster.
Thermal conductivity κ(T)
and thermoelectric power S(T)
studies on (Y,Gd)Ba2(Cu1−xMnx)3O7−δ
(x≤0.02) superconductors are presented here. Thermal conductivity for all the
samples exhibits a hump below the superconducting transition temperature
Tc. The
peak height of the hump decreases with the Mn content in both the Y- and Gd-based systems, barring
GdBa2(Cu0.99Mn0.01)3O7−δ. The peak height reduction in the Gd-based cuprates is much faster
(∼one fourth) compared to the Y-based samples. The thermoelectric power (TEP) of the Y-based samples for
x≤0.0075 is electron-like (up to
∼140 K) whereas it turns
to hole-like even at x = 0.005
for the Gd-based system. On the basis of the structure of the thermal conductivity hump, and of the
electron- or hole-like nature of the thermopower, it has been argued that, in the Y-based system up
to x = 0.0075, Mn produces qualitatively the same effect as Gd in the Gd-based system. An analysis
of the thermal conductivity data in terms of lattice theory, and the TEP data
in terms of a narrow-band picture, has been made to invoke the role of Mn in
these systems. Boundary scattering, point defects and sheet-like faults (from
κ(T) data analysis) and
chemical potential (from S(T)
data analysis) support different roles of Mn for
x≤0.0075
and x>0.0075.
This paper demonstrates a shrinkable triple self-aligned split-gate Flash cell fabricated using a standard 0.13-mcopper interconnect process. The approach used here to create a self-aligned structure is to form a spacer against the prior layer. Due to a higher aspect ratio when the cell pitch decreases, the profile of the spacer structure becomes sharper. This improves process control of the spacer profile and length. All the processes used here are compatible with standard logic process. The word line channel length of the cell is 0.11 m. It is comparable in area with a stacked-gate cell and can be less than 13F 2 . The cell is erased by using poly-poly Fowler-Nordheim tunneling with a sharp floating-gate edge to increase the electric field, and is programmed by source-side injection. As a result, this cell is highly suitable for low power applications and embedded products. Characterization shows considerable program and erase speed, up to 300 K times cycling endurance, and excellent disturb margins.
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