US 2014/0313264 A1
Method for manufacturing a fluid ejection device and fluid ejection device
STM is one of the largest manufacturers of printheads in the world, making a large proportion of the dies for HP. In 2014 they announced projects to develop piezo MEMS devices, including page wide array ink jet printheads.
The manufacturing processes for a thin film piezo printhead is shown below. Previous designs have used 4 wafers but this design only uses 3, with subsequent cost savings and reduced manufacturing complexity as now only two alignment and bonding steps are required.
Here the printhead is shown with the piezo actuator deflecting into the actuator chamber 232. The components made from the three wafers are designated 100, 200 and 300. The central wafer 200 is made from SOI (silicon on insulator) type. The top layer is process to form the diaphragm,piezo actuator and the bottom part the actuator chamber. Layer 300 can also be made from a SOI wafer, and forms the structure of the printhead with ink feed channels 316. The third wafer forms both the nozzle plate and the sealed chamber for the actuators. The full manufacturing process is shown in the patent.
Compared to previous designs, the saving of a wafer is achieved by processing the nozzle layer and actuator capping structure in one piece. This is then brought into contact with the actuator wafer in the step shown. Bonding occurs due to the adhesive layer 230 coated onto the contact parts of the top structure.