Thermal Structure
A miniature heating element integrated onto a thin dielectric membrane enables precise temperature control for gas sensing films. Integration of a micro hotplate allows for rapid heating and cooling cycles with very low power consumption. It typically consists of a resistive heater made from platinum or polysilicon buried within layers of silicon nitride or silicon dioxide.
Heat Transfer
Power dissipation occurs primarily through conduction through the membrane supports and convection to the surrounding air. The design minimizes the thermal mass to achieve millisecond response times.
Mechanical Stress
Thermal expansion mismatch between the heater material and the membrane can lead to structural failure during high temperature operation. Engineers must carefully select the layer thicknesses to balance the internal stresses and prevent cracking or buckling.
Calibration Sequence
Temperature sensors integrated into the heater circuit provide feedback to a control loop that maintains a constant resistance. This resistance to temperature relationship is established during a primary calibration step using an oven or an infrared pyrometer. Over thousands of cycles, the heater resistance may shift due to electromigration or oxidation.
Precision instruments track this drift and adjust the drive voltage to maintain the target operating temperature for the sensing material.
