Hydrogen Gas Sensor with Enhanced Detection Limit Using Cracked Template Lithography and Palladium Nanogaps

Hydrogen gas sensors are crucial in environmental monitoring, energy, and biomedical fields. As hydrogen is a clean energy source, accurate detection is essential to prevent fires or explosions caused by leaks. Additionally, hydrogen can serve as a biomarker for inflammatory diseases and oxidative stress, making hydrogen detection important in healthcare. Hence, developing precise hydrogen gas sensor technologies remains a key focus.

Compared to oxide semiconductor-based hydrogen gas sensors, palladium (Pd)-based sensors exhibit superior hydrogen selectivity and have the ability to react with hydrogen at relatively lower temperatures, altering the metal’s electrical properties. This allows Pd-based sensors to function efficiently even at room temperature.

Palladium nanogap gas sensors utilize the hydrogen-induced lattice expansion property, where Pd absorbs hydrogen gas, causing the atomic lattice to expand. These sensors have drawn attention for overcoming the high detection limits of traditional Pd films and the scalability limitations of Pd nanowires. In Pd nanogap sensors, the width and density of the gaps are critical in determining hydrogen sensitivity. However, traditional Pd nanogap sensor fabrication, often utilizing laser lithography or nanoimprinting, is effective at controlling the nanogap width but is costly and labor-intensive when it comes to increasing gap density.

This study presents a palladium nanogap-based hydrogen gas sensor using Cracked Template Lithography. A polyvinyl alcohol (PVA) layer was spin-coated with a SiO₂ solution to form the nanogap structure, which was then replicated onto the PVA layer using O₂ plasma etching. Following this, an RF sputtering process was used to deposit a palladium thin film on top of the PVA layer, creating the hydrogen sensor. During this process, it was observed that adjusting the thickness of the PVA layer allowed for the control of the nanogap width and density, providing the conditions necessary to enhance the sensor’s sensitivity.

Results showed that the distribution of nanogap width and density varied with PVA layer thickness, which significantly influenced hydrogen detection performance. When the nanogap width was controlled within the range of 50 nm to 300 nm, the sensor demonstrated stable detection of hydrogen gas at concentrations as low as 2 ppm, up to 20 ppm. This represents a significantly lower detection limit compared to conventional Pd sensors, making it highly promising for applications requiring precise detection of low hydrogen concentrations.

The Cracked Template Lithography method, by enabling precise control of nanogap width and density through adjustments in PVA layer thickness, not only simplifies the fabrication process but also enhances performance. This research presents a highly effective hydrogen sensing solution for various industrial and biomedical applications, offering a practical approach to achieving high sensitivity and low detection limits in hydrogen gas sensors.