Integrated polysilicon thermistors for microfluidic sensing

This thesis documents results related to the design, fabrication, and testing of integrated polysilicon thermistors for microfluidic sensing in experimental investigations of micro impinging jet cooling and microchannel flow. Such experimental study has yielded fundamental understanding and practical design guidelines of these two microfluidic applications. Novel MEMS devices fabricated include temperature imagers, MEMS nozzles and nozzle arrays, and micro fluidic couplers. A technology for suspended microchannels with integrated polysilicon thermistors has been developed and used for microchannel flow study and flow-rate sensing. Theoretical models have been developed to analyze such micro thermal and fluidic phenomena. In the micro impinging jet cooling study, a MEMS-based heat transfer measurement paradigm has been successfully developed for the first time. This includes technology for MEMS device fabrication, an experimental setup well suited for microscale thermal study, and accurate and efficient data processing techniques. Sensing and heating are integrated into a single thermal imager chip, which allows temperature measurement over a large area at very high spatial resolution. The heat transfer data demonstrate the excellent promise of micro-impinging-jet heat transfer, and provide useful rules for designing impinging-jet-based micro heat exchangers for IC packages. In the investigation of micro channel flow, suspended microchannels with integrated thermistors have successfully been designed and fabricated to study the basic science of micro-scale channel flow. Considerable discrepancies between existing theory and experimental data have been observed, and an improved flow model that accounts for the effects of compressibility, boundary slip, fluid acceleration, non-parabolic fluid velocity profile and channel-wall bulging has been proposed to address such discrepancies. In addition, micro fluidic couplers have been designed and fabricated as the fluidic interface connection between micro fluidic systems and the external macro environment. The experiments show that MEMS couplers are capable of handling pressures as high as 1200 psig. Finally, this thesis presents the development of liquid flow sensors. Resolution of 0.4 nL/min and a capability of bubble detecting have been demonstrated. A numerical model is developed to understand device operation and to guide the design process. Excellent agreement has been found between numerical and experimental results