Optical layout for the measurement of a porous silicon sensor array

Porous materials are ideally suited for gas sensing, characterized by large effective surface area and allowing for adsorption and capillary condensation of volatile organic chemicals. Porous silicon (PSi) fabrication is easily controlled, leading to highly definable parameters such as porosity and refractive index. In practical cases however, PSi sensors suffer from a lack of selectivity problem and one way to overcome it is the use of arrays that provide information and referencing for complementary compensation of other environmental conditions like temperature, humidity and the presence of additional analytes [1]. Pacholski et al. were the first to report two-sensor array based on pSi, where two pSi sensors are stacked on top of the other [2]. The reflected spectrum from those porous Si layers contained three superimposed interference patterns which were resolved by means of the Fourier Transform. Their technique was subsequently used for a variety of sensing schemes [3,4]. In a previous publication we reported a multi-sensing method and demonstrated it for two functionalized pSi sections for simultaneous detection of ammonia and humidity [5]. In the method proposed by us, the device consists of sectioned porous silicon (pSi) sensors placed next to each other, as opposed to stacked on top of the other. The immediate advantage of the side-by-side method is structural and chemical independence of the sections and scalability. The motivation of this paper is to demonstrate this scalability property. The simultaneous readout of four sensors in a planar array by a single white-light beam is reported here for the first time.