Real-Time and In-Flow Sensing Using a High Sensitivity Porous Silicon Microcavity-Based Sensor

Abstract

Porous silicon seems to be an appropriate material platform for the development of high-sensitivity and low-cost optical sensors, as their porous nature increases the interaction with the target substances, and their fabrication process is very simple and inexpensive. In this paper, we present the experimental development of a porous silicon microcavity sensor and its use for real-time in-flow sensing application. A high-sensitivity configuration was designed and then fabricated, by electrochemically etching a silicon wafer. Refractive index sensing experiments were realized by flowing several dilutions with decreasing refractive indices, and measuring the spectral shift in real-time. The porous silicon microcavity sensor showed a very linear response over a wide refractive index range, with a sensitivity around 1000 nm/refractive index unit (RIU), which allowed us to directly detect refractive index variations in the 10−7 RIU range.

How to Improve the Performance of Porous Silicon‐Based Gas and Vapor Sensors? Approaches and Achievements

“…From analysis of the principles of gas sensor operations, it follows that to increase the sensitivity of both PSi‐based capacitance and refractometric optical sensors, high porosity of the PSi layer is required, because high porosity increases total volume, where the target substance can be infiltrated . In combination with a small pore diameter, high porosity allows a higher surface‐to‐volume ratio to be reached, which makes it possible to immobilize more surface centers that can interact with the analyte.…”

“…However, the extremely high porosity of the layers makes the structure of these layers more fragile and easily destructible. Therefore, in most studies, developers are limited to using PSi with porosity not exceeding 85% . In this case, the highest sensitivity can be achieved while maintaining the strength of the structure.…”

“…This is confirmed by the data in Table obtained for an optical sensor based on a PSi MC (PSMC). The sensing structure consisted of an optical MC built between two BRs . The PSMC sensor developed by Caroselli et al showed a very linear response in a wide range of RIs.…”

“…The sensing structure consisted of an optical MC built between two BRs . The PSMC sensor developed by Caroselli et al showed a very linear response in a wide range of RIs. In addition, the sensor had a sensitivity of about 1000 nm/RI unit (RIU) which provided the direct detection of RI changes in the range of 10 −7 RIU.…”

“…This allowed detecting ethanol vapor with a concentration of ≈ 10 −3 %. Caroselli et al believe that such high sensitivity was achieved because sensing took place directly inside the photonic structure, which contributed to a higher interaction of light with matter compared with conventional photon‐sensitive structures with a vanishing wave. In the latter case, only a small part of the optical field interacted with the target substance.…”