Oxides gas sensors

K. Ihokura and J. Watson, The Stannic Oxide Gas Sensor, CRC Press, Ann Arbor, Mich., 1994. 

The lifetime of metal oxide gas sensors in general is several years. Nevertheless poisoning effects can occur when exposed to silicones. An example of commercial Ga203-semiconductor gas sensors is shown in Fig. 5.32. 

During the last years, so-called microhotplates (pHP) have been developed in order to shrink the overall dimensions and to reduce the thermal mass of metal-oxide gas sensors [7,9,15]. Microhotplates consist of a thermally isolated stage with a heater structure, a temperature sensor and a set of contact electrodes for the sensitive layer. By using such microstructures, high operation temperatures can be reached at comparably low power consumption (< 100 mW). Moreover, small time constants on the order of 10 ms enable applying temperature modulation techniques with the aim to improve sensor selectivity and sensitivity. 

Most microhotplate-based chemical sensors have been realized as multi-chip solutions with separate transducer and electronics chips. One example includes a gas sensor based on a thin metal film [16]. Another example is a hybrid sensor system comprising a tin-oxide-coated microhotplate, an alcohol sensor, a humidity sensor and a corresponding ASIC chip (Application Specific Integrated Circuit) [17]. More recent developments include an interface-circuit chip for metal oxide gas sensors and the conccept for an on-chip driving circuitry architecture of a gas sensor array [18,19]. 

The central topic of the book was the integration of microhotplate-based metal-oxide gas sensors with the associated circuitry to arrive at single-chip systems. Innovative microhotplate designs, dedicated post-CMOS micromachining steps, and novel system architectures have been developed to reach this goal. The book includes a multitude of building blocks for an application-specific sensor system design based on a modular approach. 

G. Sberveglieri, W. Hellmich, and G. Muller. Silicon hotplates for metal oxide gas sensor elements . Microsystem Technologies 3 (1997), 183-190. 

I. Simon, N. Barsan, M. Bauer, and U. Weimar. Micromachined metal oxide gas sensors opportunities to improve sensor performance . Sensors and Actuators B73 (2001), 1-26. 

P.F. Ruedi, P. Heim, A. Mortara, E. Franzi, H. Oguey, and X. Arreguit. Interface circuit for metal-oxide gas sensor Digest IEEE Custom Integrated Circuits Conference (2001), 109-112. 

J.S. Suehle, R.E. Cavicchi, M. Gaitan, and S. Semancik. Tin oxide gas sensor fabricated using CMOS micro-hotplates and in-situ processing , IEEE Electron Device Letters 14 (1993), 118-120. 

A. Friedberger, R. Kreisl, E. Rose, G. Muller, G. Kuhner, J. Wdllenstein, and H. Bottner. Micromechanical fabrication of robust low-power metal oxide gas sensors . Sensors and Actuators B 93 (2003), 345-349. 

N. Barsan and U. Weimar. Conduction model of metal oxide gas sensors , Journal of Electroceramics 7 (2001), 143-167. 

S. Muller. CMOS-Micro-Hotplate with MOS Transistor Heater for Integrated Metal Oxide Gas Sensors, Diploma thesis, ETH Zurich, Switzerland (2002). 

D. Barrettino, M. Graf, S. Taschini, S. Hafizovic, C. Hagleitner, and A. Hierlemann. CMOS monohthic metal-oxide gas sensor Microsystems , IEEE Sensors Journal 6 (2006), 276-286. 

Oxygen Desorption and Conductivity Change of Palladium-Doped Tin(IV) Oxide Gas Sensor... 

When working with sensors, one of the most important issues is cross-sensitivity. Due to the sensing principle, this notably affects metal oxide gas sensors, especially in the case of measurements performed in real life conditions. To prove real life feasibility, it is necessary to keep as close as possible to the real life conditions of the application. In the present case, the real life conditions are mainly represented by the use of ambient air as a carrier gas, but also by the chosen experimental set up. 

Although the ISEs based on cobyrinates have good selectivity for nitrite over several anions, they also respond to salicylate and thiocyanate. To eliminate this interference, the nitrite-selective electrode based on ionophore 2 was placed behind a microporous gas-permeable membrane (GPM) in a nitrogen oxide gas-sensor mode (75). NOx was generated from nitrite in the sample at pH 1.7 and, after crossing the GPM, was trapped as nitrite by an internal solution that was buffered at pH 5.5 (0.100 M MES-NaOH, pH 5.5, containing 0.100 M NaCl). The internal solution was "sandwiched" between the nitrite-selective electrode and the GPM. 

Gas sensors — (c) Metal oxide gas sensors — Figure 7. Gas sensor based on SnC>2 thick-film... 

Gong, H. Wang, Y. J. Teo, S. C. Huang, L., Interaction between thin-film tin oxide gas sensor and five organic vapors, Sens. Actuators B 1999, 54, 232-235... 

Several commercial instruments are available. Some comprise conducting polymers, others tin oxide gas sensors (thick or film devices) or metal oxide semiconductors, and combinations. However, none of them can evaluate lAQ as the nose does. 

Imanaka, N., Oda, A., Tamura, S. and Adachi, G.-Y. (2004) Total nitrogen oxides gas sensor based on solid electrolytes with refractory oxide-based auxiliary electrode. J. Electrochem. Soc., 151 (5), H113-16. 

Tamura, S. and Imanaka, N. (2007) Nitrogen oxide gas sensor based on multivalent ion-conducting solids. Sens. Mater., 19 (6), 347-63. 

Rothschild, A. and Komem, Y., The effect of grain size on the sensitivity of nanoc-rystaUine metal-oxide gas sensors, J. Appl. Phys. 95 (2004) 6374—6380. 

---