Page 239 - MEMS Mechanical Sensors

228 Flow Sensors

Thermopile 1 Thermopile 2

Membrane Heater

Figure 9.18 Photograph of the flow sensor developed by Ashauer et al. [41]. The picture shows
the 5-µm-wide polysilicon heating element and 20 polysilicon temperature sensing elements (ther-
2
mopiles) in series on either side. The 100-nm-thick silicon-nitride membrane is 600 × 600 µm .

and silicon nitride to render them inert to various gases and liquids. There are sev-
eral ways to package the sensor to be used for measurements in a nanoliter dosing
system, in small tubes (Figure 9.19), for flow in large diameter pipes and in open
flow. It is stated that the sensor has been tested with high viscous fluids like glue,
paste, and oil [41, 61]. This flow sensor is used in air-conditioning systems. The sen-
sor production started in 2003 with a quantity of 30,000 sensors.
An interesting application developed by HSG-IMIT is the thermodynamic incli-
nation and acceleration sensor [76]. The sensor is built similar to a calorimetric flow
sensor having a heater and temperature sensors, but the elements are inside a gas-
filled, closed chamber. The heating element produces convection along the gravity
field. Any movement of the sensor due to inclination or acceleration causes an
imbalance between the temperature sensors, which is detected. The sensor is distrib-
uted by Vogt Electronic AG, Germany.

Figure 9.19 Photograph of a packaged sensor chip. (Courtesy HSG-IMIT.)