Thin-film four-resistor temperature sensor for measurements in air

A temperature sensor based on four thin-film resistors is presented. Four resistors are made in the form of thin metal layer meanders on the surface of a silicon chip. Two resistors are covered with a layer of 2.3 mu m thick hard baked photoresist. Two other resistors are exposed to ambient air. The photoresist cover on two of the resistors makes a mismatch in the temperature coefficient of resistance between the covered and exposed resistors, thus enabling functionality of the system as a temperature sensor. The resistors are connected in the Wheatstone bridge configuration in order to enhance the sensitivity of the structure. Resistor meanders are 500 mu m x 500 mu m in lateral dimensions, each consisting of a 10 mu m wide metal strip with 10 mu m clearance between the strips. The total length of each strip is 12.5 mm. The material used for the meanders is 100nm thick sputtered gold. The sensor was tested in a temperature chamber in the range from 80 degrees C to -50 degrees C. The matching between the sensor's output and the readings obtained by the Pt1000 reference sensor was within +/- 0.1 degrees C (static), but the influence of water vapor adsorption at the exposed resistors surface on temperature measurements was visible. The sensor has potential applications in temperature measurements in air.