Fabrication and characterization of suspended microchannel dispensers with an integrated heater for high resolution patterning

Abstract

Microchannel cantilevers, one of the physical microelectromechanical systems (MEMS) devices that have embedded microchannels thus various fluid samples, have been widely used in gravimetric sensing applications of liquids and particles with various solution samples injected to the microchannel. Recently they also have been used for dispensing and patterning applications of biomolecules and functional ink materials. Mainly due to the absence of integrated active heating elements, micro-channel cantilevers are mostly used at or near room temperature even for nonbiological samples although there are unlimited potential applications at elevated temperatures such as materials synthesis, calorimetric measurements, and phase change mediated manipulation or control.In this thesis, suspended microchannel dispensers with an integrated heater are proposed as a new platform enabling drop-on-demand thermal bubble jet printing with fast and efficient heating and real-time printing process monitoring for the first time. Suspended microchannel dispensers with an integrated heater are batch fabricated via polysilicon sacrificial process. Then, local temperatures of fabricated microcantilever heaters are calibrated with micro Raman thermometry. Temperature calibrated microcantilever heaters are thoroughly characterized under various pulsed heating powers sufficient for bubble generation and bubble jet microdroplet dispensing with a reference printing solution. Upon pulsed heating, heating thermal time constants are extracted from both electrothermal and electrothermomechanical responses, each of which are based on temperature-dependent electrical resistance and resonance frequency, respectively. Heating pulses of several tens of mW and hundreds of μs are turned out to be sufficient to induce bubble generation near the dispensing nozzle within the microchannel. In addition, by simultaneously measuring the first and second resonance frequencies in real time using two phase-locked loops, the basis is prepared for the inertial imaging of bubbles created, expanded, contracted, and disappeared inside the channel.The microchannel cantilever with integrated heating element introduced in this thesis for the first time is expected to have a variety of potential applications such as measurement of thermal properties of liquid and colloidal samples, and hydrothermal synthesis of nanomaterials in the future.