Performance optimization of temperature compensated surface acoustic wave biosensors

Temperature has great influences on the surface acoustic wave (SAW) biosensors. Different substrates were tested and the methods for improving the temperature performance of the SAW biosensors were discussed here. The effects of temperature on the SAW sensors mainly result from the temperature coefficient of the SAW device and the oscillating circuit. To eliminate the impact of environment, a twin delay lines SAW biosensor operating at 198 MHz, with a sensor channel and a reference channel, was fabricated on 36°Y-X LiTaO₃ piezoelectric crystals. The signals of the two channels were multiplied by a mixer to compensate the influences of temperature. Since the temperature may affect the quiescent point of amplifier, the open loop phase would change, resulting in a frequency shift of the SAW oscillator. Therefore, a simple and effective circuit structure with a comparator limiting the oscillation amplitude was applied to the design of the SAW oscillator. At last, the temperature performance of our design was tested. Our design was demonstrated having a great performance with a temperature coefficient about 2 ppm/°C.