Phthalocyanine-based ®eld-effect transistor as ozone sensor Marcel Bouvet a,* , Ge Ârard Guillaud b , Arnaud Leroy a,c , Andre  Maillard c , Serge Spirkovitch c , Franc Ëois-Gene Ás Tournilhac a a ESPCI, CNRS, Laboratoire de Chimie Inorganique et Mate Âriaux Mole Âculaires, 10, rue Vauquelin 75231, Paris Cedex 05, France b UCB, Laboratoire d'Electronique 43, bd du 11 nov. 1918, 69622 Villeurbanne, France c ESIEE, Laboratoire de Microe Âlectronique, Cite  Descartes, BP 99 2, bd Blaise Pascal, 93162 Noisy le Grand, France Received 10 August 2000; received in revised form 29 October 2000; accepted 6 November 2000 Abstract In this paper, we present a new sensor, which exhibits a sensitivity to ozone to less than 10 ppb. The device is a phthalocyanine-based ®eld-effect transistor which is capable of working at room temperature. We describe a dynamic procedure, working out of the equilibrium state, to get rid of drift phenomena. A process where 2 min exposure alternates with 8 min static rest period leads, after a conditioning period, to a stable and reproducible signal. The response of the device (55 pA ppb 1 min 1 ) is linearly correlated to the ozone concentration in air, in the range 0±150 ppb. The use of a dynamic rest (¯ow of ozone free air) instead of a static rest reduces the duration of the recovery period, but is not necessary to achieve a good reproducibility. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Gas sensor; Ozone; Phthalocyanine; Field-effect transistor (FET) 1. Introduction Many big cities and their suburbs are exposed to pollution peaks during prolonged sunny periods. The smog, a con- sequence of the industrialization and road traf®c, is con- stituted of different noxious gases, such as ozone. In the absence of atmospheric pollution the concentration of O 3 in air can vary between 5 and 50 ppb, depending on atmo- spheric conditions. Ozone in the upper atmosphere is bene®cial, but in the lower atmosphere is harmful and causes respiratory illness. French legislation established the ®rst threshold of alert in urban atmosphere at 65 ppb (130 mgm 3 ), the second at 90 ppb and the third at 180 ppb. Speci®c safety measures correspond to each level. O 3 pro- duced by laser-printers and photocopiers must also be taken into consideration. High local concentrations up to 100 ppb can be reached in of®ces [1,2], even though recent machines are ®tted with ef®cient ®lters. O 3 is involved in many chemical reactions. In the mixing layer (altitude situated between the ground and 100 to 2000 m) the main mechanism of ozone production is the NO 2 photolysis illustrated by the following reac- tions [3]: NO 2  hn?O  NO 280 nm < l < 430 nm O  O 2 ?O 3 But, the ozone concentration also depends on its reaction with NO NO  O 3 ?NO 2  O 2 These equilibria are not only affected by emissions of NO x and solar radiations, but also by emissions of volatile organic compounds (VOC) since VOC transform a part of NO into NO 2 . It is interesting to note that, a diminution of the NO concentration by a reduction of the traffic can induce an increase of the O 3 concentration, NO being absent for the destruction of O 3 (an example is given in [4]). Ozone is usually monitored by ultraviolet absorption spectroscopy. Concentrations are obtained by differential measurement between sample air and the same air ®ltered through MnO 2 . This method is selective and very sensitive, but the apparatus is quite expensive. Portable devices based on electrochemical detection also exist, but are less sensitive (precision 90 ppb in an example). In the ®eld of gas sensors most of the studies are devoted to the detection of Sensors and Actuators B 73 (2001) 63±70 * Corresponding author. Tel.: 33-1-4079-4631; fax: 33-1-4079-4425. E-mail address: marcel.bouvet@espci.fr (M. Bouvet). 0925-4005/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0925-4005(00)00682-1