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Electrodes comprising conductive perovskite-seed layers for perovskite dielectrics
| Details |
Inventors: Summerfelt, Scott R.; Beratan, Howard R.;
Assignee: Texas Instruments Incorporated (Dallas, TX)
Primary Examiner: Robinson; Ellis
Assistant Examiner: Jones, III; Leonidas J.
Attorney, Agent or Firm: Carlson; Brian A., Kesterson; James C., Donaldson; Richard L.
A preferred embodiment of this invention comprises a perovskite-seed layer (e.g. calcium ruthenate 40) between a conductive oxide layer (e.g. ruthenium oxide 36) and a perovskite dielectric material (e.g. barium strontium titanate 42), wherein the perovskite-seed layer and the conductive oxide layer each comprise the same metal. The metal should be conductive in its metallic state and should remain conductive when partially or fully oxidized. Generally, the perovskite-seed layer has a perovskite or perovskite-like crystal structure and lattice parameters which are similar to the perovskite dielectric layer formed thereon. At a given deposition temperature, the crystal quality and other properties of the perovskite dielectric will generally be enhanced by depositing it on a surface having a similar crystal structure. Undesirable crystal structure formation will generally be minimized and lower processing temperatures may be used to deposit the perovskite dielectric layer. Another benefit of this electrode system is that the perovskite-seed layer should do little or no reduction of the perovskite dielectric layer. |
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DETAILED DESCRIPTION As used herein, the term "high-dielectric-constant" means a dielectric constant greater than about 50 at device operating temperature.
As used herein the term "perovskite" means a material with a perovskite or perovskite-like crystal structure.
As used herein the term "dielectric", when used in reference to a perovskite, means a non-conductive perovskite, pyroelectric, ferroelectric, or high-dielectric-constant oxide material.
The deposition of a perovskite dielectric usually occurs at high temperature (generally greater than about 500.
degree.
C.
) in an oxygen containing atmosphere.
The lower electrode structure should be stable during this deposition, and both the lower and upper electrode structures should be stable after this deposition.
It is herein recognized that there are several problems with the materials thus far chosen for the lower electrode in thin-film (generally less than 5 um) applications; many of these problems are related to semiconductor process integration.
For example, Pt has several problems as a lower electrode which hinder it being used alone.
Pt generally allows oxygen to diffuse through it and hence typically allows neighboring materials to oxidize.
Pt also does not normally stick very well to traditional dielectrics such as SiO.
sub.
2 or SiN.
sub.
4, and Pt can rapidly form a silicide at low temperatures.
A Ta layer has been used as a sticking or buffer layer under the Pt electrode, however during BST deposition, oxygen can diffuse through the Pt and oxidize the Ta and make the Ta less conductive.
This may possibly be acceptable for structures in which contact is made directly to the Pt layer instead of to the Ta layer, but there are other associated problems as described hereinbelow.
For example, Pt has a radioactive isotope, Pt-190, that, even though it has a relatively long half-life and makes up a small percentage of the total number of Pt atoms, could create a substantial number of detrimental alpha-particles when used in a standard thin-film structure
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Active Solid-state 
