Abstract
Recently demands for thermal IR sensors are increasing for industrial or automotive uses. This is due to their simple structure and operation without cooling. An advance in micromachining techniques has enabled the realization of thermally isolated structures and the miniaturization of IR detection cells for an array sensor. Various types of silicon micromachined IR sensors with cantilevers or diaphragms have been developed, mainly using pyroelectric or thermopile detecting techniques. Among them are the thermopile IR sensors utilizing the Seebeck effect of silicon. This type of sensors has the potential of being used in an array for imaging applications, due to considerable integration from their compatibility with the IC fabrication process, although someapplications require larger responsivities.
This paper describes the fabrication, testing and modeling of the thermal resistance of an IR sensor using p-type/n-type polysilicon thermocouples on a dielectric diaphragm and incorporating a heater resistor on the center of the diaphragm. This structure increases the thermal resistance by eliminating metal interconnections on the diaphragm and doubles the output of each thermocouple compared to the Si/metal type. The measured responsivity of the sensor with a 1mm square diapharagm using thermal excitation was 83.5V/W, which was in reasonable agreement with the calculated value, although the one, measured using optical excitation by a laser diode, was a little smaller. A larger responsivity will be obtained through the design optimization of this sensor.
