Commercially available water quality monitoring systems for Total Phosphorus (TP), Total Nitrogen (TN), and Total Organic Carbon (TOC) analysis offer high sensitivity and accuracy. However, they are limited by large size, complex pretreatment processes, and high cost. Traditional systems require a pretreatment process in which fluid samples are heated to over 120 °C for more than 30 minutes to break down chemically bound phosphorus, nitrogen, and organic carbon in various forms. These pretreatment conditions, which involve high pressures and temperatures, pose significant challenges to system miniaturization.

To overcome these limitations, our laboratory employs ambient-temperature photocatalytic reactions in the pretreatment process instead of relying on high-temperature and high-pressure conditions. Pretreatment is carried out using a microfluidic channel based on MEMS technology, featuring a titanium dioxide (TiO2) photocatalytic surface illuminated by ultraviolet (UV) light. This innovative approach eliminates the need for high temperatures and pressures, simplifying the pretreatment process and enabling greater flexibility in the design and fabrication of lab-on-a-chip (LOC) devices. Furthermore, this method significantly reduces the amount of sample required for both pretreatment and measurement, drastically shortening the overall pretreatment time.

The conventional biosensors have challenges such as low throughput and signal-to-noise ratio. we propose a microfluidic chip with multiple detection gates to enhance the throughput while maintaining a simple operational system. A hydrodynamic sheathless particle focusing on a detection gate by modulation of the channel structure and measurement circuit with a reference gate to minimize the noise during detection is used for detecting resistive pulses. The proposed microfluidic chip can analyze the physical properties of 200 nm polystyrene particles and exosomes from MDA-MB-231 with high sensitivity with an error of less than 10 % and high-throughput screening of more than 200,000 exosomes per second. The proposed microfluidic chip can analyze the physical properties with high sensitivity so that it can be potentially used for exosome detection in biological and in vitro clinical applications. 

Flip-chip microbump bonding technology between InP and SiC substrates for a millimeter-wave wireless communication application is demonstrated. The proposed process of flip-chip μ-bump bonding to achieve high-yield performance utilizes a SiO2-based dielectric passivation process, a sputtering-based pad metallization process, an electroplating bump process enabling a flat-top μ-bump shape, a dicing process without the peeling of the dielectric layer, and a SnAg-to-Au solder bonding process. By using the bonding process, 10 mm long InP-to-SiC coplanar waveguide lines with 10 daisy chains interconnected with a hundred μ-bumps are fabricated. All twelve CPW lines show uniform performance with insertion loss deviation within ±10% along with an average insertion loss of 0.25 dB/mm, while achieving return losses of more than 15 dB at a frequency of 30 GHz, which are comparable to insertion loss values of previously reported conventional CPW lines. In addition, an InP-to-SiC resonant tunneling diode device is fabricated for the first time and its DC and RF characteristics are investigated.