Thin-film gas sensors based on high-temperature-operated metal oxides

Abstract

Research into the characteristics of semiconducting metal-oxide films that are stable at high temperatures intensified with the aim of providing reproducible and reliable gas detection in various ambients. First, there is a discussion of the specifics relating to these materials, for example, the effect of grain-boundary barriers on the sensing mechanism, the influence of humidity, and the temperature dependence of the sensing mechanism. Then, the technology for the preparation of the gas sensors will be described. Examples that have already been implemented like λ detection, oxygen and NOx measurements in exhaust gases, detection of explosive and toxic gases in air, as well as hydrogen leakage detection are discussed.

Wet Thermal Oxidation of GaAs and GaN

“…Responses on oxygen, NO, CO, CH 4 , H 2 , ethanol and acetone are most often investigated. Ga 2 O 3 sensors exhibit faster response and recovery time, and lower cross-sensitivity to humidity than SnO 2 based sensors, see Fig. 14 (Fleischer & Meixner, 1999). Additional advantages are long-term stability and no necessity of pre-ageing.…”

“…(Fleischer & Meixner, 1999) However, sensitivities of three different morphologies of -Ga 2 O 3 as single crystals, bulk ceramics with closed pore structure and polycrystalline thin film were also investigated (see Fig. 16) (Fleischer & Meixner, 1999). Baban et al proposed sandwich structure with double Ga 2 O 3 layer and mesh double Pt electrode layer (Fig.…”

“…Type A) (usually platinum) deposited on the sensing layer composed of polycrystalline Ga 2 O 3 with grain sizes of 10 and 50 nm or 50-100 nm (Schwebel et al, 2000;Fleischer & Meixner et al, 1995). (Fleischer & Meixner, 1999) However, sensitivities of three different morphologies of -Ga 2 O 3 as single crystals, bulk ceramics with closed pore structure and polycrystalline thin film were also investigated (see Fig. 16) (Fleischer & Meixner, 1999).…”

“…14. Temperature dependence of the effect of humidity on the conductivity of Ga 2 O 3 thin films, measured in synthetic air (Fleischer & Meixner, 1999) Typical structure of a gas sensor consists of interdigital electrode ( Fig. 16.…”

Growth of gallium oxide thin films on silicon by the metal organic chemical vapor deposition method

“…For the production of Ga 2 O 3 films, various synthetic methods such as oxidation of Ga-containing surfaces [11][12][13], evaporation [14], sol-gel process [15], sputtering [16][17][18], pulsed laser deposition [19], molecular beam epitaxy [20], and chemical vapor deposition (CVD) have been studied. In order to use the metal organic CVD method, which has an advantage of more flexibility, good step coverage, producing uniform, pure, reproducible, and adherent films, the precursors of Ga(hfac) 3 [22] have been developed.…”