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

Abstract

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 µm 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 µm × 500 µm in lateral dimensions, each consisting of a 10 µm wide metal strip with 10 µm clearance between the strips. The total length of each strip is 12.5 mm. The material used for the meanders is 100 nm thick sputtered gold. The sensor was tested in a temperature chamber in the range from 80 °C to −50 °C. The matching between the sensor's output and the readings obtained by the Pt1000 reference sensor was within ±0.1 °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.