Optical spectrometers enable contactless chemical analysis. However, decreasing both their size and cost appears to be a prerequisite to their widespread deployment. Chip-scale implementation of optical spectrometers still requires tackling two main challenges. First, operation over a broad spectral range extending to the infrared is required to enable covering the molecular absorption spectrum of a broad variety of materials. This is addressed in our work with an Micro-Electro Mechanical Systems (MEMS)-based Fourier transform infrared spectrometer with an embedded movable micro-mirror on a silicon chip. Second, fine spectral resolution Δλ is also required to facilitate screening over several chemicals. A fundamental limit states that Δλ is inversely proportional to the mirror motion range, which cannot exceed the chip size. To boost the spectral resolution beyond this limit, we propose the concept of parallel (or multi-core) FTIR, where multiple interferometers provide complementary optical paths using the same actuator and within the same chip. The concept scalability is validated with 4 interferometers, leading to approximately 3 times better spectral resolution. After the atmospheric contents of a greenhouse gas are monitored, the methane absorption bands are successfully measured and discriminated using the presented device.

This paper deals with the fabrication of carbon nanotube field effect transistors (CNTFETs) for gas sensing applications. Such devices exploit the extremely sensitive change of the Schottky barrier heights between carbon nanotubes (CNTs) and drain/source metal electrodes: the gas adsorption creates an interfacial dipole that modifies the metal work function and so the band bending and the height of the Schottky barrier at the contacts. Our aim is to achieve the fingerprinting of a specific gas using a CNTFET based sensor array. This fingerprinting concept is based on the fact that the change of the metal electrode work function strictly depends on the metal/gas interaction. Consequently the CNTFET transfer characteristics will change specifically as a function of this interaction. To demonstrate this new concept, we have fabricated arrays of CNTFETs with different metal contacts: Au, Pd, Ti and Pt. Using these transistors, we have shown that a particular gas, in our case DiMethylMethyl-Phosphonate (DMMP, a sarin simulant), interacts specifically with each metal: 1 ppm of DMMP (15 min of exposure) reduces the transistor ON current by about 20% for Pt contacted CNTFETs and by nearly one order of magnitude for Pd contacted CNTFETs. We believe that this new approach can be applied for highly selective sensing of various gases, using ultra-compact, room temperature and very low power devices.

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