Engineering 1/f noise in porous silicon thin films for thermal sensing applications

The sensitivity of present-day thermal sensors operating in the long-wave infrared region, a critical range for night vision and other reconnaissance applications, is limited by the 1/f noise in the thermistor material, while their widespread applicability is restricted due to microfabrication incompatibilities with the standard processing for silicon-based microelectronics. Porous silicon films have a high temperature coefficient of resistance (TCR similar to 2-10%K-1) and are compatible with microfabrication processes, making them suitable candidates for use in thermal sensors. In this work, the 1/f noise in porous silicon films in conjunction with TCR, both key parameters for high sensitivity thermal sensors are characterized. The inherent 1/f noise in these as-fabricated films is very high and increases significantly after exposure to atmosphere (oxidation). However, surface passivation at 600 degrees C, stabilises the film against atmospheric oxidation and reduces the 1/f noise level by orders of magnitude. Further, decreasing the porosity of passivated films from 90 to 40% decreased the 1/f noise by an order of magnitude. High TCR similar to 6-7%K-1 along with low 1/f noise constant, K similar to 10(-12) are obtainable with an optimised porosity similar to 60-75% for films surface passivated at 600 degrees C. These results confirm great promise of porous silicon for low manufacturing cost, and higher sensitivity of the thermal sensors.

Automated summary

Porous silicon films with high temperature coefficient of resistance and microfabrication compatibility are suitable candidates for thermal sensors. Surface passivation at 600 degrees Celsius can significantly reduce the 1/f noise in the films, leading to higher sensitivity in thermal sensors.