Direct Patterning of Piezoelectric Thin Films by Inkjet Printing

Abstract

Inkjet printing is currently gaining momentum as a low‐cost and eco‐friendly additive manufacturing technique for electronics. Patterning of functional metal oxide thin films on high surface energy substrates via inkjet printing remains a challenge and requires assistance from lithographic processes. This work unveils a novel process for lithography and etching‐free patterning of lead zirconate titanate (PZT) films on pristine platinized silicon through the use of inkjet‐printed alkanethiolate‐based templates. The technique requires neither lithography nor etching, respectively, before and after PZT printing. The described process allows for feature sizes in the sub‐100 µm range with control over the thickness of the final film. Inkjet‐printed PZT displays typical ferroelectric and piezoelectric properties of solution‐derived thin films, with remnant polarization 13 µC cm−2, coercive field 58 kV cm−1, permittivity 900, dielectric losses 0.07, and effective longitudinal piezoelectric coefficient 50 pm V−1.

On the importance of pyrolysis for inkjet-printed oxide piezoelectric thin films

“…We previously reported on inkjet-printed PZT thin films. 15 Although encouraging when compared to similar works on inkjet printing, 13,14,16 the electromechanical properties of our layers were inferior to state-of-the-art CSD-derived films, which could be ascribed to porosity originating from incomplete elimination of the high-boiling-point solvents during pyrolysis. This issue was not thoroughly addressed in previous works.…”

“…The PZT spin coating solution and the PZT ink were prepared based on the procedure described in Godard et al 15 Freezedried lead(II) acetate, zirconium(IV) butoxide and titanium(IV) isopropoxide were used as metal precursors. The stoichiometry of metal cations was such that Pb : Zr : Ti = 1.10 : 0.53 : 0.47 (morphotropic phase boundary composition with 10% Pb excess).…”

“…Following the seminal work of Bathurst et al, 13 CSD-based inkjet printing of PZT thin films was described in a number of publications. [14][15][16] These works shed light upon the challenges related to inkjet printing. Indeed, several requirements need to be fulfilled for successful implementation of CSD in the IJP process.…”

“…The adjunction of highboiling-point co-solvents, such as glycerol and ethylene glycol, increases solution viscosity, which strongly improves jetting stability and helps prevent nozzle clogging. 15 In addition, it was shown that such a ternary solvent system also serves a purpose related to the ink drying behavior. The coffee ring effect refers to capillary flow-driven transport of material to the edge of a drying liquid film as the solvent evaporates.…”

“…Typical solutions to this issue are represented by surface modification with polymeric layers 21 or self-assembled monolayers. 15 Precise control of surface wettability can enable lithography-free printing resolution in the sub-100 nm range. 22 Finally, it follows that modifications in the solution composition may bring about adaptations in the thermal post-printing steps.…”