Method for producing ferroelectric film, ferroelectric film, and usage thereof
Provided is a method for forming a ferroelectric film of a metal oxide having a fluorite-type structure at a low temperature of lower than 300° C., and a ferroelectric film obtained at a low temperature. The present invention provides a production method of a ferroelectric film comprising a crystalline metal oxide having a fluorite-type structure of an orthorhombic crystal phase, which comprises using a film sputtering method comprising sputtering a target at a substrate temperature of lower than 300° C., to deposit on the substrate a film of a metal oxide which is capable of having a fluorite-type structure of an orthorhombic crystal phase, and having a subsequent thermal history of said film of lower than 300° C.; or applying an electric field to said film after said deposition or after said thermal history of lower than 300° C. Also provided are the ferroelectric film, which is formed on an organic substrate, glass, or metal substrate, which can be used only at low temperatures, and a ferroelectric element and a ferroelectric functional element or device using the ferroelectric film.
1. A production process of a ferroelectric film, which comprises
using a sputtering method comprising sputtering a target at a temperature of a substrate of 250° C. or lower, to deposit on the substrate a film of a metal oxide which is capable of having a fluorite-type structure of an orthorhombic crystal phase, and
having a thermal history of said film of 250° C. or lower at the time of said sputtering and after said sputtering, or applying an electric field to said film which has a thermal history of 250° C. or lower at the time of said sputtering and after said sputtering,
whereby a ferroelectric film comprising a crystalline metal oxide having a fluorite-type structure of an orthorhombic crystal phase is produced.
2. The production method of a ferroelectric film according to claim 1 , wherein the metal of said metal oxide comprises hafnium (Hf), zirconium (Zr), cerium (Ce), or two or more of these, or comprises hafnium (Hf), zirconium (Zr), cerium (Ce), or two or more of these and at least one metal element selected from the group consisting of aluminum (Al), silicon (Si), strontium (Sr), barium (Ba) and rare earth elements (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).
3. The production method of a ferroelectric film according to claim 1 , wherein said sputtering is carried out in an inert atmosphere having an oxygen partial pressure of less than 1%.
4. The production method of a ferroelectric film according to claim 1 , wherein said substrate is selected from the group consisting of a substrate comprising a glass having a glass transition point of 250° C. or lower, a substrate comprising a macromolecular organic layer, a substrate comprising a metal layer having a softening temperature of 250° C. or lower, and an inside of a semiconductor device.