Photoacoustic cell on silicon for mid-infrared QCL-based spectroscopic analysis Jean-Guillaume Coutard* a , Alain Glière a , Jean-Marc Fedeli a , Olivier Lartigue a , Jules Skubich a , Guillaume Aoust b , Alexandre Teulle a , Thomas Strahl c , Sergio Nicoletti a , Mathieu Carras b , Laurent Duraffourg a . a Univ. Grenoble Alpes, CEA, LETI, MINATEC Campus, 38054 Grenoble, FRANCE; b mirSense, 91120 Palaiseau, FRANCE; c Fraunhofer-Institut für Physikalische Messtechnik (IPM), 79110 Freiburg, GERMANY ABSTRACT 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. Keywords: Miniaturized gas sensor, QCL, MIR, Silicon, CMOS pilot line 1. INTRODUCTION Since the use of canaries in mines at the beginning of the 20th century, gas measurement techniques have been widely developed in a large number of activity sectors such as transport, industry, safety, etc. Among the most widespread applications, in line with current concerns, we can cite indoor air monitoring, greenhouse gas monitoring and industrial process monitoring. Many detection methods have been used to meet the application requirements. They can be classified into two main families: based on variations in electrical property or on other types of variations 1 . In the first category, we can mention solid state sensors, like MOS (metal oxide semiconductor), or polymers based sensors. In the second the optical, acoustic and chromatographic methods. Among the optical methods, the subcategories multiply with the use of schemes such as OFCEAS, TDLAS, NDIR 2 . In this paper, the focus is placed on the technique of photoacoustic spectroscopy. Long after the discovery of the photocacoustic effect by Graham Bell in 1880, this technique was revived in the 1970s with the availability of laser sources and has since spread widely. When applied to gas detection, it achieves performance levels that allow to reach gas trace detection, i.e. much lower than the part per million (ppm) 3 . *jean-guillaume.coutard@cea.fr; phone 33 4 38 78 55 53; www.leti.fr