Topographical Evolution of Lead Zirconate Titanate (PZT) Thin Films Patterned by Micromolding in Capillaries

Abstract

The patterning of sol-gel-derived thin films by micromolding in capillaries can produce unintended topographical deviations from the shape of the original mold that may limit the utility of the technique in potential applications. During drying and heat treatment, nonuniform shrinkage across the film due to the densification of the gel matrix results in "double-peak" film topographies whereby the film thickness is greater at the lateral edges than in the middle. Using the same framework used to understand the imbibition and wetting of the sol-gel in the capillary channels, we developed a mechanism to explain the formation of the double-peak profile. As a model system, patterned Pb(Zr 0.52 Ti 0.48 )O 3 thin films were studied. Atomic force microscopic characterization was used to quantify the effect of the rate of gelation on the topography of the patterned thin films. Modifications to the channel mold design eliminate the peak formation, producing more homogeneous patterns that better replicate the features of the mold.

Microchannel Molding: A Soft Lithography-inspired Approach to Micrometer-scale Patterning

“…The PDMS can be used either as a mold to impart patterns via physical confinement of a fluid precursor that dries to form the final structured thin film or as a stamp to directly transfer the material to the target substrate. The confinementbased techniques include microtransfer molding (TM), [2][3][4] micromolding in capillaries (MIMIC), [5][6][7][8][9][10][11][12][13][14] and embossing, [9][10][11][12][13][14][15][16][17][18] while microcontact printing (CP) [19][20][21][22][23][24][25][26][27][28] is an example of stamping. Schematic drawings of these techniques are provided in Fig.…”

“…A considerable amount of shrinkage occurs during drying and sintering, during which time the contours of the thin film may deviate from the original shape of the mold. 13 For instance, the use of MIMIC to pattern thin films derived from sol-gels results in the formation of a final sintered topography in which the material has a greater thickness at the lateral edges than in the middle, as shown in the scanning electron microscope (SEM) images in Fig. 2.…”

“…2. 13 This defect, referred to as the "double-peak" topographical profile, can cause problems when the patterned thin film is used in the fabrication of hierarchical structures requiring pattern alignment for successive depositions of additional layers. 13 In many microelectromechanical systems (MEMS) applications, such as microcantilever beams and resonators, control over the cross-sectional shape of the patterned thin film is desired to maintain the fidelity of the resonance modes.…”

“…Thus, the drying film has not yet detached from the corner of the mold at gelation, resulting in the shape of the corners to be preserved in the final dried and sintered patterns. 13 One solution to the problem of the double-peak topography is to eliminate the presence of sharp corners in the PDMS mold. Using rounded corners decreases the increased rate of evaporation at the corners and produces patterned thin films that better replicate the shape of the mold.…”

“…Using rounded corners decreases the increased rate of evaporation at the corners and produces patterned thin films that better replicate the shape of the mold. 13 However, this solution does not permit the ability to pattern thin films whose cross-section has sharp corners.…”