5. Main metal oxide sensors and their applications

To date, most of the semiconductor sensors marketed and used industrially are based on tin oxide (SnO ₂ ). These are highly sensitive to combustible gases (methane, propane, CO, etc.), but, equally, to many other gases such as ammonia, nitrogen oxides as well as volatile organic compounds (VOCs) and consequently have been widely exploited despite their lack of selectivity. Over the last twenty years or so, other materials have also been used.