Appeal No. 1998-0129 Page 9
Application No. 08/438,062
From our review of Koyama, we find that Koyama discloses
(32.1.1, col. 1) that
With the recent increase in the integration
density of DRAMs, a large charge storage density has
been required, so several high dielectric constant
materials, i.e., PZT[1,2], PLZT[3], BaTiO [4],
3
SrTiO [5] and (Ba Sr )TiO [6] have been proposed for3 x 1-x 3
DRAM capacitors. A DRAM capacitor film needs a high
dielectric constant and low leakage current and high
reliability for voltage stress. We chose (Ba Sr
x 1-
)TiO among them due to the following reasons; (1)
x 3
The composition control is easy, so the electrical
characteristics should be stable. (2) The phase is
paraelectric over the device operating temperature
range, so the film should have no fatigue problems.
. . .
This paper describes the fabrication and electrical
properties of the stacked capacitor realized by
utilizing
a high-dielectric-constant material (Ba Sr )TiO for the
05 05 3
first time. ([] original).
We find that Koyama, having considered several high dielectric
materials including, inter alia, PZT, PLZT, and BST, chose BST
for the reasons quoted, supra. From these teachings of
Koyama, we are in agreement with the examiner (answer, page 7)
that Koyama would have suggested replacing the PZT or PLZT
layer of Miller with BST to exhibit stable electrical
characteristics and to avoid the problem of fatigue.
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