Page 305 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

BIO(CHEMICAL) SENSORS 285

Table 8.17 Some commercial gas sensors based on semiconducting metal oxide
Manufacturer Model Material Measurand Range (Power Cost a
(PPM) mW) (euro)
Figaro Inc. (Japan) TGS842 Doped SnO 2 Methane 500-10000 835 13
Figaro Inc. (Japan) TGS825 Doped SnO 2 Hydrogen 5-100 660 50
sulfide
Figaro Inc. (Japan) TGS800 Doped SnO 2 Air quality <10 660 13
(smoke)
FiS (Japan) SB5000 Doped SnO 2 Toxic gas - 10-1000 120 13
CO
FiS (Japan) SP1100 Doped SnO 2 Hydrocarbons 10-1000 400 15
b
Capteur (UK) LGS09 Undoped Chlorine 0-5 650 25
oxide
Capteur (UK) LGS21 Undoped Ozone 0-0.3 800 25
oxide
a
Price for 1 to 9 units 1 euro is $1.1 here
part of First Technology plc (UK)

Table 8.17 lists some tin oxide gas sensors that are commercially available together
with their properties.
The requirement to run this type of gas sensor at a high temperature causes the power
consumption of about 0.8 W of a Taguchi-type device to be a problem for handheld
units. Consequently, there has been considerable effort since the late 1980s toward the
use of silicon planar technology to make micropower gas sensors in volume at low cost
(less than €5). Designs of silicon planar microhotplates started to appear around the
late 1980s when Demarne and Grisel (1988) and later Corcoran et al. (1993) reported
on the first silicon-based tin oxide gas microsensors. There are two basic configurations
of a microhotplate; these are illustrated in Figure 8.54. The first comprises a resistive
heater (e.g. platinum) embedded between layers that make up a solid diaphragm (Gardner
et al. 1995) or a resistive heater (e.g. doped polysilicon) embedded between layers in a
suspended microbridge configuration.

Figure 8.54 Two basic designs of silicon gas sensors: (a) a solid diaphragm and (b) a suspended
bridge that contains a meandering resistive heater