Min-gu Kim

Bio-inspired fluidic thermal angular accelerometer

This paper reports on a bio-inspired angular accelerometer based on a two-mask microfluidic process using a PDMS mold. The sensor is inspired by the semicircular canals in mammalian vestibular systems and pairs a fluid-filled microtorus with a thermal detection principle based on thermal convection. With inherent linear acceleration insensitivity, the sensor features a sensitivity of 29.8μV/deg/s2=1.7mV/rad/s2, a dynamic range of 14,000deg/s2 and a detection limit of ~20deg/s2.

Surface tension-driven assembly of metallic nanosheets at the liquid-air interface: Application to highly laminated magnetic cores

This paper presents a fabrication technique to develop highly laminated structures comprising stacked thin films, in which the structures are based on surface tension-driven assembly at the liquid-air interface. When multiple metallic films are removed from a liquid solution, there is a surface tension-driven coalescence and self-alignment of the wetted films, resulting in thick metallic microstuctures comprised of many layers of metallic nanosheets after evaporation of the liquid. If the liquid contains a dissolved material, each sheet can further be coated with the material prior to assembly. Based on this technique, we developed laminated structures comprising hundreds of nanoscale layers of alternating metallic film and non-conducting polymer. Electroplated Co44Ni37Fe19 (Cobalt-Nickel-Iron alloy) and a commercial Novec 1700 solution (3M, Minnesota) were utilized for the metallic film and the liquid solution, respectively. However, the assembly process inherently allows a variety of materials to be exploited. Theoretical analysis and experimental results were compared, demonstrating a critical gap between the metallic films, below which capillary force is sufficient for driving self-assembly of the films. As an exemplary application of this technique, highly laminated magnetic cores comprising 600 layers of 500 nm thick CoNiFe that are insulated by 100 nm thick polymer were prepared. A 15-turn toroidal inductor with the fabricated magnetic core exhibited a constant inductance of 2.5 μH up to 30 MHz with a quality factor over 70 at 1 MHz.

Room temperature CO 2 detection using interdigitated capacitors with heteropolysiloxane sensing films

This paper investigates the detection of carbon dioxide at room temperature using microfabricated, interdigitated capacitive (IDC) sensors coated with an amino-functionalized sensing film. Sensing experiments performed at temperatures ranging from room temperature to 100°C indicate two different temperature-dependent sensing mechanisms. Around room temperature, physisorption dominates the sensor response, resulting in fast signal transients and negative capacitance changes. Above 80°C, chemisorption appears to dominate, resulting in larger, positive capacitance changes with longer signal transients.

All-soft sensing platform based on liquid metal for liquid- and gas-phase VOC detection

This paper introduces an all-soft microfluidic sensing platform based on liquid metal (eutectic gallium-indium alloy, EGaIn) and poly(dimethylsiloxane) (PDMS) for volatile organic compound (VOC) detection in the liquid and gas phase. For device fabrication, an advanced liquid metal patterning method based on soft lithography is used to form interdigitated capacitors and integrate them with microfluidics. To highlight flexibility and stretchability, the electrical characteristics of the interdigitated capacitor are investigated subject to mechanical loading. Finally, VOC detection is demonstrated using the all-soft microfluidic sensing platform in both the liquid and gas phase.

Parylene-on-oil encapsulation process for bio-inspired angular accelerometer

This paper reports on a wafer-level parylene-on-oil encapsulation process for a bio-inspired angular accelerometer with thermal transduction. The angular accelerometers microtorus geometry, which is inspired by the semicircular canals, provides inherent linear acceleration insensitivity, while promoting in-plane angular acceleration. Compared to more traditional post-fabrication fluid filling of microchannels, the in-process fluid encapsulation allows for batch-fabricated, bubble-free, fluid-filled microchannels. To show the feasibility of this process, thermal angular accelerometers were fabricated and tested, showing a sensitivity of 24.7μV/deg/s2, which compares well with state-of-the-art capacitive angular accelerometers.

Room-tempearutre CO 2 sensing based on interdigitated capacitors and resonant cantilevers

This paper compares a MEMS-based resonant cantilever and an interdigitated capacitor, both coated with an amino-functionalized sensing film, as room temperature carbon dioxide (CO2) detectors. The sensor sensitivities at room temperature to CO2 are assessed as well as their cross-sensitivities to temperature and humidity. The effectiveness of an uncoated reference cantilever for temperature compensation is demonstrated, reducing the temperature sensitivity of the system by a factor of 300.