On-chip sensor solution for hydrogen gas detection with the anodic niobium-oxide nanorod arrays

• Published in: Sensors and actuators. B, Chemical Vol. 284; pp. 723 - 735
• Main Authors: Pytlicek, Zdenek, Bendova, Maria, Prasek, Jan, Mozalev, Alexander
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-04-2019; Elsevier Science Ltd
• Subjects: Aluminum; Ammonia; Anodic alumina; Anodizing; Bilayers; Chemical etching; Density; Detection; Electric wire; Gas sensors; High temperature; Hydrogen; Interlayers; Metal oxides; Multilayers; Nanomaterials; Nanorods; Niobium oxide nanorods; Niobium oxides; On-chip sensor; Organic chemistry; Photolithography; Schottky barrier; Sensor arrays; Silicon dioxide; PAA; Anodic alumina; Anodizing; Hydrogen; Niobium oxide nanorods; On-chip sensor; Schottky barrier
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2019.01.009

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•Novel niobium oxide nanorod arrays are synthesized via anodizing.•Nanorods are integrated as active layer in on-chip microsensors.•Advanced sensor-on-chip design is realized through technological innovations.•New sensors provide fast, sensitive and selective H2 detection.
Two types of anodic niobium-oxide nanofilms were synthesized via anodization of an Al/Nb bilayer sputter-deposited onto a SiO2-coated Si wafer. Type I nanofilm was composed of a 200 nm thick NbO2 layer holding the upright-standing 650 nm long, 50 nm wide, and 70 nm spaced Nb2O5 nanorods, of 7·109 cm−2 density, whereas the Type II nanofilm had similarly long but bigger Nb2O5 nanorods, 100 nm wide, 220 nm spaced, and of 8·108 cm−2 density, aligned directly on a niobium metal without any buffering oxide layer, which was achieved for the first time. Each film was then incorporated in an advanced 3-D architecture and multilayer layout on a silicon chip comprising 33 microsensors, with variable sizes and tuned electrical characteristics, by combining the high-temperature vacuum or air annealing, sputter-deposition and lift-off photolithography to form Pt/NiCr top electrodes and a multifunctional SiO2 interlayer, chemical etching, laser dicing, and ultrasonic wire-bonding. The proposed on-chip sensor solution allowed for a sensitive, fast, and highly selective (toward NH3 and CH4) detection of hydrogen gas. Comprehensive gas sensing tests performed for Type II nanofilm ultimately confirmed the presence of a Schottky-type sensing mechanism, the contribution, however, being substantially weaker than that due to reactions over the surface of the oxide nanorods, especially when the rods show a transition from fully to partially depleted states when interacting with H2 gas. The film formation and chip fabrication technologies may be transferable to other PAA-assisted 1-dimensional metal-oxide nanomaterials suitable for on-chip gas sensing.