CMOS Compatible Thermal Conductivity Detector (TCD)


Aim of the project

In this project the “hot-wire” sensing principle is used for measuring the therrmal conductivity of a gas. This assignment should prove that it is possible to fabricate low cost therrmal conductivity detectors (TCD’s) using simple MEMS postprocessing on commercial CMOS wafers.



Project description

TCD’s are popular for measuring gas or liquid compositions in process control and gas chromatography and have a high potential for measuring hydrogen content in gas mixtures. A simple sensor technique is the hot-wire sensor, which is based on a thin metal wire simultaneously operating as a heater and sensing element. For this the sensor will be driven by a sinusoidal signal and the temperature signal will be read using the 3ω method, i.e. and the third harmonic of this signal will be used as the temperature signal.


Main challenges:TCD3

  • Feasability study of the 3ω method for polysilicon wires.
  • Verify by measurements on existing MEMS devices (photo)
  • Analysis and design of a CMOS chip detecting the small third harmonic of the thermal actuation signal in presence of a large fundamental frequency signal.
  • Design of the complete “hot-wire” TCD by simple post processing of CMOS dies.

We offer an interesting, innovative project for a motivated MSc student interested in IC fabrication technology.



Ger de Graaf