A micromachining process for die-scale pattern transfer in ceramics and its application to bulk piezoelectric actuators

This paper reports on a batch mode planar pattern transfer process for bulk ceramics, glass, and other hard, brittle, nonconductive materials suitable for micromachined transducers and packages. The process is named LEEDUS, as it combines lithography, electroplating, batch mode micro electro-discharge machining ([micro]EDM) and batch mode micro ultrasonic machining ([micro]USM). An electroplating mold is first created on a silicon of metal wafer using standard lithography, then using the electroplated pattern as an electrode to [micro]EDM a hard metal (stainless steel or WC/Co) tool, which is finally used in the [micro]USM of the ceramic substrate. A related process (SEDUS) uses serial [micro]EDM and omits lithography for rapid prototyping of simple patterns. Feature sizes of 25 [micro]m within a 4.5 x 4.5 [mm.sup.2] die have been micromachined on glass-mica (Macor) ceramic plates with 34 [micro]m depth. The ultrasonic step achieves 18 [micro]m/min. machining rate, with a tool wear ratio of less than 6% for the staiuless steel microtool. Other process characteristics are also described. As a demonstration, octagonal and circular spiral shaped in-plane actuators were fabricated from bulk lead zirconate titanate (PZT) plate using the LEEDUS/SEDUS process. A device of 20/[micro]m thickness and 450 [micro]m x 420 [micro]m footprint produces a displacement of [approximately equal to] 2[micro]m at 40 V. [1652] Index Terms--Ceramic micromachining, microelectro-discharge machining (EDM), piezoelectric micro actuator, ultrasonic micromachining.