We present several integrated technologies on Silicon, from visible to mid-infrared, for particulate matter and gas detection. We present new concepts to detect in the visible particulate matter with a high sensitivity and a discrimination of both particle sizes and refractive indices. For gas detection, mid-infrared technologies developments include on one hand, microhotplate thermal emitters, as a cheap solution for gas sensing, eventually enhanced by plasmonics, and on the other hand quantum cascade lasers-based photoacoustic sensors, for high precision measurement, and for which the integration on Silicon is pushed forward for a reduction of costs.
Photoacoustic (PA) spectroscopy is among the most sensitive techniques used to monitor chemical emission or detect gas traces. In the mid-infrared, where most of gases of interest have their strongest absorption lines, this technique takes advantage of the high optical power and room temperature operation of quantum cascade lasers (QCL). We have recently demonstrated that centimeter-size PA cells can compete, with bulky commercial systems for gas sensing without any compromises on performances. We demonstrate a new step towards cost reduction, extreme integration, and mass deployment of such PA sensors with a miniaturized silicon PA-cell fabricated on standard CMOS tools. The design, fabrication and characterizations of this new sub-centimeter PA cell built on a silicon platform are presented. First, the component has been designed using a detailed physical model, accounting for viscous and thermal losses, and metamodel-based optimization techniques. Second, it has been fabricated on our 200 mm CMOS pilot line. Several wafers have been released and diced. Single chips have then been assembled with commercial capacitive microphones and finally characterized on our reference gas bench. The photoacoustic simulations and the acoustics experiments are in a good agreement. The tiny PA cell exhibits a sensitivity down to the ppm level for CO2 at 2300 cm-1, as well as for CH4 at 3057 cm-1 even in a gas flow. Taking advantage of the integration of QCLs on Si and photonic circuitry, the silicon PA cell concept is currently being extended towards a fully integrated multigas detector.