Lead-free piezoelectric ceramic films and a method for making thereof
This invention relates to lead-free piezoelectric ceramic films and a method of making thereof. 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 free standing film that is substantially lead-free, wherein the free standing film comprises a lead-free piezoelectric 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 and wherein said film has a piezoelectric coefficient −d 31 of about 200 pm/V to about 2000 pm/V.
2. The film of claim 1 , wherein said piezoelectric coefficient −d 31 is about 1500 pm/V to about 1800 pm/V.
3. The film of claim 1 , wherein said piezoelectric coefficient −d 31 is about 1600 pm/V to about 1700 pm/V.
4. The film of claim 1 , wherein said film has a thickness of about 4 μm to about 100 μm.
5. The film of claim 1 , wherein said film forms a piezoelectric layer of a microelectronic device.
6. The film of claim 5 , wherein said microelectronic device is selected from the group consisting of: an energy harvesting device and a piezoelectric cantilever sensor.
7. A piezoelectric microcantilever sensor comprising:
a non-piezoelectric layer,
a lead-free piezoelectric layer comprising 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,
at least one conducting element operatively associated with the lead-free piezoelectric layer and
a receptor capable of binding a molecule or compound whereby, upon binding, said molecule or compound exerts a force on the piezoelectric layer,
wherein the said lead-free piezoelectric layer has a piezoelectric coefficient −d 31 of about 200 pm/V to about 2000 pm/V.
8. The sensor of claim 7 , wherein said piezoelectric coefficient −d 31 is about 1500 pm/V to about 1800 pm/V.
9. The sensor of claim 7 , wherein said piezoelectric coefficient −d 31 is about 1600 pm/V to about 1700 pm/V.
10. The sensor of claim 7 , further comprising an electrical insulation layer which insulates the conducting elements.
11. The sensor of claim 7 , wherein the electrical insulation layer comprises a material selected from the group consisting of poly-para-xylylene, methyltrimethoxysilane, Al 2 O 3 , SiO 2 and functionalized hydrophobic silanes and mixtures thereof.
12. The sensor of claim 8 , wherein said receptor is bound to the conducting element by an immobilization layer.
13. The film of claim 1 , wherein the free standing film comprises a compound containing at least one element selected from the group consisting of: Sb, Sr, Ba, V and Bi.
14. The film of claim 13 , wherein the free standing film contains an antimony compound.
15. The film of claim 1 , wherein the free standing film contains a cation selected from the group consisting of: Li, Na and K.
16. The film of claim 1 , wherein the free standing film exhibits asymmetrical non-180° domain switching.
17. The film of claim 1 , wherein the free standing film is made by the process of:
formulating a precursor suspension containing lead-free compounds;
doping said precursor suspension;
producing a precursor-coated lead-free powder mixture; and
sintering said powder mixture to produce the lead-free piezoelectric material.
18. The film of claim 17 , wherein said precursor suspension is doped with at least one compound containing an element selected from the group consisting of: Sb, Sr, Ba, V and Bi.
19. The film of claim 18 , wherein said precursor suspension comprises niobium oxide, titanium oxide particles or a combination thereof.
20. The film of claim 19 , further comprising the step of tape-casting said powder mixture.