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 (μEDM) and batch mode micro ultrasonic machining (μUSM). An electroplating mold is first created on a silicon or metal wafer using standard lithography, then using the electroplated pattern as an electrode to μEDM a hard metal (stainless steel or WC/Co) tool, which is finally used in the μUSM of the ceramic substrate. A related process (SEDUS) uses serial μEDM and omits lithography for rapid prototyping of simple patterns. Feature sizes of 25 μm within a 4.5×4.5 mm² die have been micromachined on glass-mica (Macor) ceramic plates with 34 μm depth. The ultrasonic step achieves 18 μm/min. machining rate, with a tool wear ratio of less than 6% for the stainless 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 μm thickness and 450 μm×420 μm footprint produces a displacement of ≈2μm at 40 V.