The sensor element consists of a silicon chip with a thin membrane approximately 1mm2 in size of a material with extremely good electrical and thermal insulating properties. Integrated into the membrane are two thin film resistors which are used both for heating the membrane and for measurement of its temperature Tm. The resistors as well as the conductor tracks are passivated to protect them from the effects of the gas. The membrane is completely covered by a second small silicon chip with a rectangular cavity etched in. The hollow space thus formed above the membrane is the thermal conductivity section. The gas passes to the measuring section through a small lateral opening in the membrane cover by diffusion only, and not by flow.
The sensor chip and its cover are attached to a silicon support which also permits gas exchange to the lower side of the membrane. The sensor is electrically connected to an eight pin base (similar to TO8) by gold wire bonding.
- Thermal conductivity sensor for gases in silicon micromechanics
- Minimal power consumption, low temperatures
- Very small dimensions, short time constants
- Measurement of very small gas volumes
- Gas exchange by diffusion, independent of flow
- Integrated temperature compensation resistors
- TO8-style base, shock proof