We report on the current status of device fabrication of a monolithic, micro-machined device able to generate sub-micron diameter (femtoliter) fluidic droplets. Such droplet-on-demand (DoD) devices are important for a wide range of maskless lithography and rapid prototyping technologies, including direct-write patterning on non-standard, highly topographical, or extremely temperature sensitive substrates. Printable circuitry from DoD devices can be generated in non-clean room, extreme, or dynamic conditions. The basic design of these DoD devices places a pressure source at the bottom of a macroscopic fluid reservoir. Upon actuation, the pressure source squeezes the fluid through a microscopic nozzle at the opposite end of the reservoir, thereby forming the droplets. Actuation behavior of the pressure source is critical to the operation of the device as it will define the size, speed, and ejection rate of the droplets. We have chosen a MEMS-based flexure plate actuator, rather than a thermal-bubble method, as it can achieve the requisite pressures for droplets on the scale of sub-micron diameter without introducing any thermal damage to the fluid. Advances in sol-gel-derived lead zirconate titanate (PZT) thin film deposition techniques allow for wafer scale integration of PZT as the active layer of the flexure plate. LPCVD dielectrics serve as structural underlayers for the PZT and a suspended membrane will be formed by a backside through-etch of the Si handle. Fast (~10 MHz) and uniform actuation is crucial in order to produce sufficient pressures for droplet generation, which then requires the fundamental-mode acoustic resonant frequency of these flexure plates be as high as possible. Acoustic resonance is tunable through choice of flexure plate diameter, thickness, and layering composition.
Project end date: 01/29/08