Nanogap Formation Using a Chromium Oxide Film and Its Application as a Palladium Hydrogen Switch

Developing high response hydrogen sensors manufacturable in a large scale is desirable in hydrogen industry. In this study, a chromium oxidation-based nanogap formation process was developed to fabricate a hydrogen switch with suspended palladium and gold films having a tens of nanometer-sized gap. The nanogap was formed by using oxidized chromium as a self-alignment shadow mask. The hydrogen switch operates by the principle of volume expansion of palladium upon exposure to the hydrogen gas and the current reading by closing of a nanogap formed between suspended palladium and gold films. Further improvement of the sensor performance was achieved by optimizing the design parameters such as suspended film lengths and thicknesses. The fabricated palladium nanogap hydrogen sensor showed an ultrahigh sensitivity of ΔI/I₀ > 10⁸ with a fast response time (22 s) to 4% hydrogen. The complementary metal-oxide-semiconductor-compatible fabrication of the hydrogen switch is easily scalable with low manufacturing cost.