Film transfer and bonding techniques for covering single-chip ejector array with microchannels and reservoirs

This paper describes a novel covering technique for an MEMS ejector array that is integrated with liquid reservoirs and microchannels on a single chip. The covering technique is based on wicking of a low viscous epoxy through the gap between the ejector wafer and a plate containing a parylene film, and allows the integrated ejector array to be fully covered by the parylene film with excellent uniformity, repeatability and yield. The technique is batch-processible and is suitable to cover many microfluidic systems with a thin film. The parylene film is tightly attached to the ejector array chip (with excellent bonding strength owing to the epoxy), so that liquid is automatically brought into the ejectors from the reservoirs through the microchannels: (due to capillary force), as the ejectors shoot out liquid droplets. This automatic liquid supply makes the liquid level (in the ejector) be maintained constant throughout the entire ejection process until more than 90% of the liquid stored in the reservoir is delivered to the ejector through the microchannel. This paper describes also a number of other covering methods that we have experimentally tried, and compares those with the new covering technique.