Sensors and Actuators B 106 (2005) 489–497 Detection of hydrocarbon species using silicon MOS capacitors operated in a non-stationary temperature pulse mode P. Kreisl a , A. Helwig a , A. Friedberger a , G. M ¨ uller a,∗ , E. Obermeier b , S. Sotier c a Corporate Research Centre, EADS Deutschland GmbH, D-81663 Munich, Germany b Technical University of Berlin, Gustav-Meyer-Allee 25, D-13355 Berlin, Germany c Munich University of Applied Sciences, Lothstr. 34, D-80335 Munich, Germany Received 3 May 2004; received in revised form 18 July 2004; accepted 22 July 2004 Available online 22 September 2004 Abstract The paper reports on the detection of hydrocarbon species using silicon metal-oxide-semiconductor (Si-MOS) capacitors operated in a non-stationary temperature pulse mode. In this mode of operation, high-temperature chemical interaction of analyte gases with a catalytically active electrode and low-temperature electrical read-out of the CV characteristic is performed in a time-sequential way. Due to this kind of sequencing, hydrocarbon species could be detected with narrow-bandgap Si devices, which previously has only been possible using MOS devices fabricated on wide-bandgap materials such as silicon carbide (SiC) or gallium nitride (GaN). In order to successfully implement a time- sequential sensor operation, the Si-MOS capacitors were integrated into a micromachined hotplate-array fabricated from silicon-on-insulator (SOI) wafers. © 2004 Elsevier B.V. All rights reserved. Keywords: Metal–insulator–semiconductor; Hydrocarbon gas sensor; Low power consumption; Micromachining; Silicon-on-insulator; Non-stationary mode of operation; Micro-hotplate 1. Introduction In 1975, Lundstr ¨ om et al. [1–3] discovered that MOS de- vices with a dense, catalytically active noble metal electrode could be used to detect hydrogen gas. Lundstr ¨ om also related the gas-sensing effect to a hydrogen-induced dipole layer at the metal–insulator interface. This dipole layer causes a shift in the CV characteristics of the MOS device thus enabling an electrical measurement of the gas concentration. Since their invention, silicon MOS gas sensors (Si-MOS sensors) have undergone considerable development. A more recent version, featuring a hybrid suspended gate electrode and a passive reference transistor has been described by Eisele and co-workers [4]. For more details about Si-MOS sensors, the interested reader is also referred to the extensive review by Crocker [5]. ∗ Corresponding author. Tel.: +49 89 607 27847; fax: +49 89 607 24001. E-mail address: gerhard.mueller@eads.net (G. M ¨ uller). Staying within the narrow temperature limits set by the silicon semiconductor material, H 2 was the only gas that could be detected by room-temperature operation. In order to overcome the temperature limitations of silicon devices, the Lundstr¨ om group later introduced wide-bandgap SiC MOS devices (MOSiC: metal-oxide-silicon carbide), which retain their semiconducting properties up to about 800 ◦ C [6–8]. Under such high-temperature conditions not only hydrogen but also much more stable hydrocarbon species could be de- tected. Later similar kinds of devices were also realised on the basis of wide-bandgap III-nitride materials such as GaN and Ga x Al 1-x N heterostructures [9–11]. In the meantime, such wide-bandgap sensors have found a variety of applications, most of them relating to applications in hot and corrosive en- vironments such as exhaust and flue gas monitoring [12–22]. In the present paper, we should like to describe a novel method of MOS sensor operation that extends the gas-sensing capabilities of Si-MOS devices to relatively stable hydro- carbon species, which previously could only be detected 0925-4005/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2004.07.030