ETCHED PIEZOELECTRIC STRUCTURES.

Miniaturized piezoelectric devices can be fabricated from wafers of lead zirconate titanate (PZT) using techniques developed by the semiconductor industry for the production of integrated circuitry. Patterns generated in a polymeric photoresist are transferred to the surface of the substrate by selective chemical etching of the ceramic. In this fashion, complex device geometries can be obtained with relative ease. The behavior of PZT in several acidic solutions was examined in an attempt to derive an etchant suitable for microfabrication. Concentrated HF, HCl, H//2 SO//4 , HNO//3 , H//3 PO//4 , and aqua regia were investigated, and it was found that hydrochloric acid combined a high etching rate and a compatibility with commercially available photoresists. Powdery residues found on the surface of the wafers after etching with HCl were identified by X-ray diffraction as pure PZT, suggesting that the acid dissolves around grain boundaries, freeing grains rather than etching through them. This was confirmed by scanning electron microscopy. Although this limits the minimum feature size, it also eliminates many of the restrictions on device geometry due to the use of isotropic etchants.