Package-free infrared micro sensor using polysilicon thermopile

In this paper, a new IR thermal micro sensor using an original design and silicon micro technology is presented. The operating principle of the sensor is based on the Seebeck effect. A high thermoelectric power thermopile has been developed using thermoelectric properties of phosphorus and boron doped LPCVD polysilicon. Moreover, low stress membranes have been recessed under each hot and cold junction. The temperature gradient is maintained by increasing the thermal resistance under the thermocouples. A former study allows us to determine the Seebeck coefficients and relative resistance changes of phosphorus and boron LPCVD polysilicon layers within the temperature range of 293-373 K. The sensitivity values reached 72 μV/(W/m2) for 5 mm × 5 mm sensor with low influence to convection. This planar and symmetrical configuration requires no specific packaging, thus minimizing the manufacturing cost compared with existing realizations. The micro sensor is manufactured within the framework of a national project (CNRS-INTERLAB).