Abstract
The gas sensor market is growing fast, driven by many socioeconomic and industrial factors. Mid-infrared (MIR) gas sensors offer excellent performance for an increasing number of sensing applications in healthcare, smart homes, and the automotive sector. Having access to low-cost, miniaturized, energy efficient light sources is of critical importance for the monolithic integration of MIR sensors. Here, we present an on-chip broadband thermal MIR source fabricated by combining a complementary metal oxide semiconductor (CMOS) micro-hotplate with a dielectric-encapsulated carbon nanotube (CNT) blackbody layer. The micro-hotplate was used during fabrication as a micro-reactor to facilitate high temperature (>700 ^{circ }C) growth of the CNT layer and also for post-growth thermal annealing. We demonstrate, for the first time, stable extended operation in air of devices with a dielectric-encapsulated CNT layer at heater temperatures above 600 ^{circ }C. The demonstrated devices exhibit almost unitary emissivity across the entire MIR spectrum, offering an ideal solution for low-cost, highly-integrated MIR spectroscopy for the Internet of Things.
Highlights
The gas sensor market is growing fast, driven by many socioeconomic and industrial factors
We show that alumina (Al2O3)-encapsulated carbon nanotube (CNT) grown on a micro-electromechanical system (MEMS) micro-hotplate can withstand temperatures in excess of 800 ◦ C when operated in air
The microhotplate cross-section is shown in Fig. 1a and consists of a multi-ring resistive tungsten (W) heating element (800 μ m diameter) embedded within a ∼ 5 μ m thick silicon dioxide (SiO2 ) membrane (1200 μ m diameter), to ensure low direct current (DC) power c onsumption[19]
Summary
The gas sensor market is growing fast, driven by many socioeconomic and industrial factors. Multi-species spectroscopic detection requires the MIR source to operate at an ensemble of target MIR wavebands, making the overall CNT broadband emission e nhancement[11,12] attractive for spectroscopy[1] Despite their blackbody-like advantages[15,16], far most research has observed such CNT, and in general all graphitic nanocarbon adlayers, burning off in air when operated at temperatures above 400 ◦C17,18. This poses a limit (optical emission and operational stability) to their integration into CMOS MEMS micro-hotplate MIR sources, which are typically operated at these temperatures[19]. The work paves the way for encapsulation techniques to be more widely applied to temperature and air sensitive nanomaterials, allowing them to operate stably in air, well above their normal temperature threshold
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