High breakdown strength ferroelectric SrHfO
Methods for making metastable lead-free piezoelectric materials are presented herein.
1. A ferroelectric induced piezoelectric material having a piezoelectric response (d 33 ) of greater than about 5.2 pm V −1 wherein the piezoelectric material comprises a metastable SrHfO 3 polymorph with a P4 mm structure and wherein the polymorph is grown on a substrate suitable for epitaxial growth of the polymorph; and wherein the substrate is SrTiO 3 .
2. The material of claim 1 wherein the polymorph has a breakdown strength of greater than about 25 MV/cm.
3. The material of claim 1 wherein the polymorph is capable of a piezoelectric response (e 33 ) of at least 8.8 C m −2 .
4. The material of claim 1 having an average coercive field of about 83 kVcm −1 and a remnant polarization of about 1.2 μCcm −2 .
5. The material of claim 1 wherein the polymorph is epitaxially stabilized by a substrate upon which the polymorph is grown.
6. A method for making a lead-free piezoelectric material comprising the steps of using pulsed laser deposition to grow epitaxial films from a SrHfO 3 target on a SrTiO 3 substrate wherein the lead-free piezoelectric material has a response of 5.2 pm V −1 for a 35 nm film, wherein the film comprises a metastable SrHfO 3 polymorph with a P4 mm structure and identifying the lead-free piezoelectric material comprising a piezoelectric tensor (e ij max ) of greater than 3 C m −2 by using density functional theory (DFT); and identifying a substrate that is capable of epitaxially stabilizing the piezoelectric material.
7. The method of claim 6 wherein the growth takes place at a temperature of greater than about 450° C.
8. The method of claim 6 wherein the growth takes place at a total pressure of about 100 mTorr oxygen.
9. The method of claim 6 wherein the growth takes place by using a pulse rate of the laser of between about 10 and about 40 Hz.
10. The method of claim 6 wherein the lead-free piezoelectric material has a breakdown strength of greater than about 25 MV/cm.
11. The method of claim 6 wherein the lead-free piezoelectric material is a film that is capable of a ferroelectric-induced large signal effective converse piezoelectric response of 5.2 pm V −1 .
12. The method of claim 6 wherein the lead-free piezoelectric material has an average coercive field of about 83 kVcm −1 and a remnant polarization of about 1.2 μCcm −2 .