The present invention generally concerns compositions and methods for fabricating semiconducting devices; and more particularly, in various representative and exemplary embodiments, to deposition of BST on low-loss, insulating substrates for frequency agile applications.
An ordered and stable silicon (Si) surface is most desirable for subsequent epitaxial growth of single crystal thin films on silicon for numerous device applications, e.g., ferroelectrics or high dielectric constant oxides for non-volatile high density memory and logic devices. It is pivotal to establish an ordered transition layer on the Si surface, especially for subsequent growth of single crystal oxides, e.g., perovskites.
Some reported growth of these oxides, such as BaO and BaTiO3 on Si(100) was based on a BaSi2 (cubic) template by depositing one fourth monolayer of Ba on Si(100) using reactive epitaxy at temperatures greater than 850xc2x0 C. See, for example: R. McKee et al., Appl. Phys. Lett. 59(7), pp 782-784 (Aug. 12, 1991); R. McKee et al., Appl. Phys. Lett. 63(20), pp. 2818-2820 (Nov. 15, 1993); R. McKee et al., Mat. Res. Soc. Symp. Proc., Vol. 21, pp. 131-135 (1991); U.S. Pat. No. 5,225,031, issued Jul. 6, 1993, entitled xe2x80x9cProcess for Depositing an Oxide Epitaxially onto a Silicon Substrate and Structures Prepared with the Processxe2x80x9d; and U.S. Pat. No. 5,482,003, issued Jan. 9, 1996, entitled xe2x80x9cProcess for Depositing Epitaxial Alkaline Earth Oxide onto a Substrate and Structures Prepared with the Processxe2x80x9d. However, atomic level simulation of this proposed structure indicates that it likely is not stable at elevated temperatures.
Growth of SrTiO3 on silicon (100) using an SrO buffer layer has been accomplished. T. Tambo et al., Jpn. J. Appl. Phys., Vol. 37 (1998), pp. 4454-4459. However, the SrO buffer layer was thick (100 xc3x85), thereby limiting application for transistor films, and crystallinity was not maintained throughout the growth.
Furthermore, SrTiO3 has been grown on silicon using thick metal oxide buffer layers (60-120 xc3x85) of Sr or Ti (B. K. Moon et al., Jpn. J Appl. Phys., Vol. 33 (1994), pp. 1472-1477); however such thick buffer layers would considerably limit applications to transistors. In the case of BST, use of amorphous buffer layers between substrates and crystalline BST films has been investigated (see, for example: Chang et al., JAP vol. 92, 1528); however, these approaches generally do not address thermal expansion problems nor loss problems associated with amorphous BST turning crystalline upon annealing. Accordingly, a composition and method for fabricating relatively thin, stable amorphous interfaces with BST for low-loss, frequency agile applications is desired.
In various representative aspects, the present invention provides a microwave regime frequency-agile device. An exemplary method for fabricating such a device is disclosed as comprising the steps of inter alia: providing an insulating substrate; providing a layer of silicon on the surface of the substrate; providing a layer of alkaline earth metal over the silicon layer; and heating the structure in the presence of oxygen to transform the crystalline silicon layer into amorphous silicon dioxide. Fabrication is relatively simple and straightforward. Additional advantages of the present invention will be set forth in the Detailed Description which follows and may be obvious from the Detailed Description or may be learned by practice of exemplary embodiments of the invention. Still other advantages of the invention may be realized by means of any of the instrumentalities, methods or combinations particularly pointed out in the claims.