Geometric shape control of thin film ferroelectrics and resulting structures

United States Patent [w]

McKee et al.

[54] GEOMETRIC SHAPE CONTROL OF THIN FILM FERROELECTRICS AND RESULTING STRUCTURES

[75] Inventors: Rodney A. McKee, Kingston;

Frederick J. Walker, Oak Ridge, both of Tenn.

[73] Assignee: UT-Battelle, LLC, Oak Ridge, Tenn.

[ * ] Notice: This patent is subject to a terminal disclaimer.

[21] Appl. No.: 08/868,076

[22] Filed: Jun. 3, 1997

[51] Int. CI.7 C30B 33/04

[52] U.S. CI 117/2; 117/3; 117/4; 423/593

[58] Field of Search 117/2, 3, 4; 423/593

[56] References Cited

U.S. PATENT DOCUMENTS

5,058,250 10/1991 Turnbull 29/25.35

5,225,031 7/1993 McKee et al. .

5,295,218 3/1994 Agostinelli et al 385/122

5,450,812 9/1995 McKee et al. .

5,576,879 11/1996 Nashimoto 359/248

5,654,229 8/1997 Leplingard et al 117/56

5,666,305 9/1997 Mihara et al 365/145

5,830,270 11/1998 McKee et al 117/106

OTHER PUBLICATIONS

Wu et al., "Domain Structure and Polarization reversal in films of ferroelectric bismuth titanate", ferroelectrics, vol. 3, pp. 217-224, 1972.

Primary Examiner—Robert Kunemund

Attorney, Agent, or Firm—Michael E. McKee; George L.

Craig; Joseph A. Marasco

[57] ABSTRACT

A monolithic crystalline structure and a method of making involves a semiconductor substrate, such as silicon, and a ferroelectric film, such as BaTi03, overlying the surface of the substrate wherein the atomic layers of the ferroelectric film directly overlie the surface of the substrate. By controlling the geometry of the ferroelectric thin film, either during build-up of the thin film or through appropriate treatment of the thin film adjacent the boundary thereof, the in-plane tensile strain within the ferroelectric film is relieved to the extent necessary to permit the ferroelectric film to be poled out-of-plane, thereby effecting in-plane switching of the polarization of the underlying substrate material. The method of the invention includes the steps involved in effecting a discontinuity of the mechanical restraint at the boundary of the ferroelectric film atop the semiconductor substrate by, for example, either removing material from a ferroelectric film which has already been built upon the substrate, building up a ferroelectric film upon the substrate in a mesa-shaped geometry or inducing the discontinuity at the boundary by ion beam deposition techniques.

21 Claims, 5 Drawing Sheets