Lead-free piezoelectric ceramic films and a method for making thereof
This invention relates to a method of making lead-free piezoelectric ceramic films. Specifically, the invention is directed to a method for fabricating lead-free piezoelectric free standing films having enhanced piezoelectric properties. The films may be used for a number of applications including incorporation in microelectronic devices such as energy harvesting devices and sensor technologies.
1. A method for making a lead-free piezoelectric material comprising the steps of:
formulating a precursor suspension from lead-free compounds and a dopant material;
producing a precursor-coated lead-free powder mixture; and
sintering said powder mixture to produce the lead-free piezoelectric material.
2. The method of claim 1 , wherein said precursor suspension is further formulated from niobium oxide, titanium oxide particles or a combination thereof.
3. The method of claim 1 , further comprising the step of tape-casting said powder mixture.
4. The method of claim 3 , further comprising the step of separating the lead-free piezoelectric material from tape used in said tape-casting step to provide a free standing film.
5. The method of claim 1 , further comprising the step of milling said powder mixture.
6. The method of claim 1 , further comprising the step of doping said precursor with at least one additional piezoelectric property-enhancing dopant.
7. The method of claim 1 , wherein in said dopant material is selected from a compound, precursor or particle containing an element selected from the group consisting of: Sb, Sr, Ba, V and Bi.
8. The method of claim 1 , further comprising the step of mixing said powder mixture with compounds selected from the group consisting of: dispersing resins, plasticizers and mixtures thereof.
9. The method of claim 1 , wherein said sintering step involves the step of packing said powder to seal a crucible.
10. The method of claim 1 , wherein said lead-free piezoelectric material is formed as a free standing film.
11. The method as claimed in claim 4 wherein said free standing film has a piezoelectric coefficient −d 31 of about 200 pm/V to about 2000 pm/V.
12. The method as claimed in claim 11 , wherein said piezoelectric coefficient −d 31 is about 1500 pm/V to about 1800 pm/V.
13. The method as claimed in claim 11 , wherein said piezoelectric coefficient −d 31 is about 1600 pm/V to about 1700 pm/V.
14. The method as claimed in claim 4 , wherein said free standing film has a thickness of about 4 μm to about 100 μm.
15. The method as claimed in claim 11 further comprising the step of incorporating the free standing film into a microelectronic device.
16. The method of claim 15 , wherein said device is selected from the group consisting of: an energy harvesting device and a cantilever sensor.
17. The method of claim 15 , wherein said microelectronic device is a cantilever sensor.
18. The method of claim 7 , wherein said dopant contains Sb and the lead-free piezoelectric material comprises from about 3% to about 6% Sb.
19. The method of claim 1 , wherein said lead-free piezoelectric material comprises a material selected from the group consisting of: Sb—NKNLN; Sb—NKNLT; Sr—NKNLN; Sr—NKNLT; SrSb—NKNLN; SbSr—NKNLT; BKT; BNT; BZT; BiZT; NKN; BKBT; BNKT; BNBT; BNBZT and BNBK.
20. The method of claim 1 , wherein said precursor suspension contains at least one material having a cation selected from the group consisting of Li, Na and K.