High resolution multi-temperature sensors for biomedical application

A temperature sensor array was designed in order to study local temperature variations and temperature gradients in biological samples. The sensor probe was inserted in the optical cortex of rabbits in order to study temperature changes during normal brain activity as well as under artificial ventilation conditions. Temperature sensitive areas of 0.14 mm x 0.1 mm are arranged in a row with interdistances of 0.4 mm yielding high spatial resolution. A temperature resolution of 0.1 mK and a 90% response time of maximum 3 milliseconds was obtained utilizing the high temperature dependence of 2%/K of the conductivity of vacuum evaporated germanium films. The sensor is passivated by a 1 micron thick PECVD-silicon nitride layer and can be placed on glass-, alumina- and polymer substrates. For brain tissue studies, in order to minimize tissue damage the temperature sensors were placed on a 0.1 mm thick needle-shaped glass substrate. A sensor element mounted on a glass substrate and immersed in water showed a self heating of less than 5 mK due to the applied measurement current of 2.1 microA.