A silicon thermal astable multivibrator for flow and temperature sensing

Here we report for the first time on a thermal astable multivibrator modality made possible with a silicon bulk micromachined flow sensor. The sensor shows an oscillatory response for constant current input. Further, the frequency of oscillation is modulated with the temperature of the sensing element, realizing the performance of a thermal multivibrator. The temperature variation is induced via air flow and a change in frequency of 5 Hz is observed for air flow velocities in the range of 0-21 m/s. The low output frequencies (20-25 Hz) observed clearly suggest that the oscillations are purely thermal in origin. In contrast, others have reported many electronic switching effects obtained by the various physical mechanisms via negative differential resistance regimes, which typically give rise to much higher frequencies of oscillations in the range of kHz-GHz.