Microfabrication of PZT force sensors for minimally invasive surgical tools

Minimally invasive surgery (MIS) is the most exciting and rapidly developing area where force sensing is actually of central importance. Micromachined piezoelectric sensors can be integrated onto MIS tools for improved diagnosis and treatment monitoring. A micro-machined freestanding lead zirconate titanate (PZT) force sensor is fabricated using five masks process incorporating deep reactive ion, ion beam and wet-chemical etching techniques. The PZT sensor is designed as a parallel plate capacitor structure in which the sol-gel prepared 1-νm thick PZT film is sandwiched between top (Au/Cr) and bottom (Pt/Ti) metal electrodes mounted on a thin Si membrane. This paper also describes a new wet chemical approach for patterning PbZr_0.52Ti _0.48O₃ films. The etch recipe provided excellent etch control, minimized undercut, preserved the photoresist mask, and effectively removed the residues on the etched surfaces. A high etch rate (200 nm/min), high selectivity with respect to photoresist, and limited under-cutting (1.5:1, lateral : thickness) were obtained. The fabricated force sensor exhibited good ferroelectric properties. The current fabrication procedure and electrical analysis can be considered as a breakthrough for fabricating freestanding PZT force sensor in any desired shape and dimensions, as well as a good example of ferroelectric microdevices.