Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1997-02-20
2002-09-24
Ver Steeg, Steven H. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192150, C204S192220, C438S381000, C438S393000
Reexamination Certificate
active
06454914
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ferroelectric capacitor, more specifically, improvement of ferroelectricity and other characteristics of the capacitor.
BACKGROUND ART
FIG. 10
shows a conventional ferroelectric capacitor. A silicon oxidation layer
4
is formed on a silicon substrate
2
. A lower electrode
6
made of platinum is provided thereon. A PZT (PbZr
x
Ti
1−x
O
3
) film
8
as a ferroelectric layer is formed on the lower electrode
6
, and an upper electrode
10
made of platinum is provided thereon. Thus, the ferroelectric capacitor is formed by the lower electrode
6
, the PZT film
8
and the upper electrode
10
.
The reason to use platinum for the lower electrode
6
is as follows. The PZT film
8
must be formed on a layer which can be oriented. The ferroelectricity of PZT is degraded if the PZT film can not be oriented, for example, when the PZT film is formed on an amorphous layer. Meanwhile, the lower electrode
6
must be formed under insulation from the silicon substrate
2
. As such, the silicon oxidation layer
4
is formed on the silicon substrate
2
. The silicon oxidation layer
4
is made of amorphous material. In general, although a layer formed on an amorphous material becomes nonorientable, a layer made of platinum has a characteristic of becoming orientable even when it is formed on the amorphous material. Therefore, platinum is used for forming the lower electrode because of the reason described in the above.
However, the conventional ferroelectric capacitor has following problem to be resolved.
The problems is degradation of ferroelectricity caused by frequent inversion of polarization, aging and leakage of oxygen from the ferroelectric substance (PZT), since platinum has a tendency of allowing oxygen and Pb to pass through it. In other words, there is high probability of leakage of oxygen and Pb contained in the ferroelectric substance through the columnar crystals of platinum shown in FIG.
11
. The problem also arises in a capacitor using dielectric substance having high dielectric constant.
DISCLOSURE OF THE PRESENT INVENTION
It is an object of the present invention to provide a ferroelectric capacitor having less degradation of ferroelectricity caused by frequent inversion of polarization and aging or by a dielectric capacitor maintaining high dielectric constant, both of which resolve the problem described in the above.
The word “capacitor” in the present invention defines structure providing for electrodes on both sides of an insulator, also it is a concept having the structure stated in the above regardless of using the structure for electric storage.
In accordance with characteristic of the present invention, a ferroelectric capacitor comprises:
a lower electrode having an oxidation layer made of any one of following layers, the layers at least including a layer made of WOx, a layer made of TiOx, a layer made of TaOx, a layer made of IrO
2
, a layer made of PtO
2
, a layer made of RuOx, a layer made of ReOx, a layer made of PdOx and a layer made of OsOx,
a dielectric layer composed by either of ferroelectric substance or dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower electrode, and
an upper electrode formed on the dielectric layer.
In other words, the lower electrode has at least one of following oxidation layers such as the Wox layer, the TiOx layer, the TaOx layer, the IrO
2
layer, the PtO
2
layer, the RuOx layer, the ReOx layer, the PdOx layer and the OsOx layer. Therefore, it is possible to prevent leakage of oxygen from the dielectric layer as well as suppressing degradation of ferroelectricity caused by aging.
Also, in accordance with characteristic of the present invention, the lower electrode is composed by forming a conductive layer made of any one of following layers, the layers at least including a layer made of W, a layer made of Ti, a layer made of Ta, a layer made of Ir, a layer made of Pt, a layer made of Ru, a layer made of Re, a layer made of Pd and a layer made of Os on the oxidation layer, and a ferroelectric layer is formed on the conductive layer.
Further, in accordance with characteristic of the present invention, the lower electrode is formed on a silicon oxidation layer located on a substrate, and wherein the lower electrode has a contact layer contacted to the silicon oxidation layer.
That is, one of the following conductive layer such as the W layer, the Ti layer, the Ta layer, the Ir layer, the Pt layer, the Ru layer, the Re layer, the Pd layer and the layer Os layer is provided on the oxidation layer. Then the dielectric layer is formed on the conductive layer. Therefore, leakage current can be decreased.
Still further, in accordance with characteristic of the present invention, a ferroelectric capacitor comprises:
a lower electrode,
a dielectric layer composed by either of ferroelectric substance or dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower electrode, and
an upper electrode formed on the dielectric layer and having an oxidation layer made of any one of following layers, the layers at least including a layer made of WOx, a layer made of TiOx, a layer made of TaOx, a layer made of IrO
2
, a layer made of PtO
2
, a layer made of RuOx, a layer made of ReOx, a layer made of PdOx and a layer made of OsOx.
In other words, the upper electrode has at least one of following conductive layers such as the WOx layer, the TiOx layer, the TaOx layer, the IrO
2
layer, the PtO
2
layer, the RuOx layer, the ReOx layer, the PdOx layer and the OsOx layer. Therefore, it is possible to prevent leakage of oxygen from the dielectric layer as well as suppressing degradation of ferroelectricity caused by aging.
In accordance with characteristic of the present invention, the lower electrode is formed on a silicon oxidation layer located on a substrate, and wherein the lower electrode has a contact layer contacted to the silicon oxidation layer.
Also, in accordance with characteristic of the present invention, a ferroelectric capacitor comprises:
a lower electrode having an oxidation layer made of any one of following layers, the layers at least including a layer made of WOx, a layer made of TiOx, a layer made of TaOx, a layer made of IrO
2
, a layer made of PtO
2
, a layer made of RuOx, a layer made of ReOx, a layer made of PdOx and a layer made of OsOx,
a dielectric layer composed by either of ferroelectric substance or dielectric substance having a high dielectric constant, the dielectric layer being formed on the lower electrode, and
an upper electrode having an oxidation layer made of any one of following layers, the layers at least including a layer made of WOx, a layer made of TiOx, a layer made of TaOx, a layer made of IrO
2
, a layer made of PtO
2
, a layer made of RuOx, a layer made of ReOx, a layer made of PdOx and a layer made of OsOx.
That is, both of the upper electrode and the lower electrode have at least one of following oxidation layers such as the WOx layer, the TiOx layer, the TaOx layer, the IrO
2
layer, the PtO
2
layer, the layer RuOx layer, the ReOx layer, the PdOx layer and the OsOx layer. Therefore, it is possible to prevent leakage of oxygen from the dielectric layer as well as suppressing degradation of ferroelectricity caused by aging.
Further, in accordance with characteristic of the present invention, the lower electrode is composed by forming a conductive layer made of any one of following layers, the layers at least includes a layer made of W, a layer made of Ti, a layer made of Ta, a layer made of Ir, a layer made of Pt, a layer made of Ru, a layer made of Re, a layer made of Pd and a layer made of Os on the oxidation layer, and wherein a ferroelectric layer is formed on the conductive layer.
Still further, in accordance with characteristic of the present invention, the lower electrode is formed on a silicon oxidation layer located on a substrate, and wherein the lower electrode has a contact layer contacted to the silicon oxidation layer.
In other word
Darby & Darby
Rohm & Co., Ltd.
Ver Steeg Steven H.
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