Optoelectronic Sensor Design and Fabrication

Optoelectronic Sensor for NIR Biomarker Detection

1. Intro

During my undergraduate capstone project, we identified a gap in the availability of low-cost, high-sensitivity optical sensors capable of detecting near-infrared (NIR) wavelengths, specifically in the 900–1200 nm range—an important region for biological marker detection. This insight laid the groundwork for my graduate research. In my first semester of graduate school, I successfully restored our lab’s plasma-enhanced sputter deposition (PESD) system, which had been offline since 2019. This enabled me to begin fabricating custom thin-film semiconductors and explore new sensor architectures.

2. What I Did

We designed and fabricated a multilayer optoelectronic sensor prototype using thin-film deposition and semiconductor fabrication techniques. The device was constructed on an FTO-coated glass substrate and comprised the following functional layers:

Silicon (Si): Serves as the base absorbing semiconductor

Titanium Dioxide (TiO₂): Acts as an electron transport and anti-reflective layer

P3HT: A conjugated polymer serving as the hole transport layer

MXene (Ti₃C₂): Used as the high-conductivity anode material

FTO Glass: Transparent conductive substrate enabling light transmission and electrical contact

Thin layers of silicon and titanium dioxide were deposited via RF sputtering. The performance of the sensor was evaluated by measuring its photoresponse when illuminated by NIR light through various concentrations of glucose and biological media.

Mounting fixture containing two sensors coated with TiO2 paste.

3. Results / What I Learned

After repairing and calibrating our lab’s sputter system, we successfully fabricated multilayer optical sensors and tested their performance using a calibrated light source spanning from 190 nm to 1200 nm.

Responsivity analysis showed that our sensor outperformed commercial silicon photodiodes in the 900–1200 nm near-infrared range, which is particularly useful for applications involving biological markers and aqueous media.

Impedance analysis revealed that the sensor exhibits behavior consistent with a passive RLC circuit, providing insight into the device’s charge transport and capacitive behavior. This also opens up opportunities for frequency-domain sensing and signal conditioning techniques.

These results validate our hybrid material stack and design approach, showing that a low-cost, lab-fabricated device can exceed the performance of industry-standard detectors in targeted applications.

4. What’s Next?

Advanced modeling: Use the impedance and responsivity data to refine our equivalent circuit model of the device and simulate its behavior under different light intensities and biological fluid concentrations.

Material optimization: Experiment with annealing protocols and plasma treatments to reduce interfacial defects and improve charge carrier mobility, especially at the TiO₂/P3HT and Si/MXene interfaces.

Functional validation: Test sensor performance in dynamic setups, such as flowing aqueous solutions or varying pH, to mimic real-world biosensing conditions.

Integration and packaging: Begin developing a modular sensor package that includes amplification electronics, wireless transmission, and a portable readout interface for potential field or clinical use.