An Introduction to mems (Micro-electromechanical Systems)

i) Thermo-mechanical 

Thermo-mechanical sensing (and actuation) utilize the fact that all materials have a 

coefficient of thermal expansion.  Consequently, if two different materials are sandwiched 

together and undergo a temperature change, movement in the sandwich assembly would 

occur.  This is the basis for the common bimetallic (or thermal bimorph) sensing and 

actuation. 

ii) Thermoresistive sensors 

ρ

, of most materials changes with 

)

1

2

bT

=

+

ρ

where R is the resistivity of the 

being used.  The rate of change of resistance with temperature is known as the temperature 

coefficient of resistance.  Most common materials exhibit an increase in resistance with 

temperature (e.g. platinum is particularly linear with temperature).  Certain materials – for 

example, carbon, some ceramics and most semiconductors used in thermoresistors or 

‘thermistors’ – exhibit a decrease in resistance with increasing temperature.  They are not as 

linear as platinum, but often cheaper to fabricate and easier to integrate with circuitry in 

MEMS devices. 

iii) Thermocouples 

junction between two different materials and measures the temperature-dependent voltage that 

arises across the junction.  Semiconductor materials often exhibit a better thermoelectric 

effect than metals.  Thermocouples have been used in a wide variety of MEMS sensors in an  

array arrangement  referred to as a thermopile.