Humidity Sensing of Ordered Macroporous Silicon With ${\rm HfO} _{2}$ Thin-Film Surface Coating

Porous silicon (PS), as a gas/chemical sensing material, has been widely investigated. In this paper, the humidity sensing characteristics of n-type macroporous silicon with ordered structure and metal oxide thin-film coating is studied. The ordered PS has uniform pore size, pore shape and distribution. All pores are aligned vertically and open to the environment. The PS heterostructure (PS/Si substrate) and self-supporting membrane are fabricated and their resistance responses are measured under room temperature. A resistance variation of 23.5% and 28.3% for each structure are obtained, respectively. Surface modification for sensing enhancement is also investigated. The resistance and capacitance responses of ordered PS heterostructure with HfO₂ thin-film coating are characterized. The HfO₂ modified PS show high sensing variation and near-linear response to a wide range of relative humidity (RH). It is also demonstrated that PS with HfO₂ thin-film coating is able to sense the RH change faster than a commercial humidity sensor. To the best of our knowledge, this is the first time that humidity sensing with ordered porous silicon and HfO₂ thin-film is reported. Possible sensing mechanisms and future work are also discussed.