Periodic silicon nanostructures for spectroscopic microsensors (original) (raw)
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Macroporous silicon photonic crystals for gas sensing
2013 Spanish Conference on Electron Devices, 2013
a) b) Figure 1. 3-D macroporous silicon samples fabricated in our laboratory. Pores are modulated with a sine-like profile. B) image shows a plane defect in the structure: missing "bump".
IEEE Transactions on Nanotechnology, 2000
The 9/11 events have led to an increase in the request for sensors and sensor systems that can detect rapidly, efficiently, and at moderate cost trace explosives and a whole range of toxic substances at diverse control points, e.g., at airports and inside air conditioning systems in aircraft and public buildings. To date, the security screening instruments of choice are ion mobility spectrometers (IMS), which are basically time-of-flight mass spectrometers (Sielemann, 1999 and Stach, 1997). Such instruments allow for the detection of explosives, chemical warfare agents, and illicit drugs. Widespread adoption of the IMS technology in civilian security screening applications, for instance, at airports, has been hindered due to the fact that state-of-the-art spectrometers employ radioactive ion sources. We report on fabrication and measurements of large-scale-ordered silicon nanotip arrays, used to replace the radioactive source for IMS gas ionization. Surface ionization mechanisms on the platinum-coated silicon surface can be significantly increased compared to flat structures due to the strong field enhancement at the tips. We will show measurements of the ion current of planar surfaces compared to microstructured surfaces as well as a photoelectrochemical etching process that allows to etch flat tips with a low aspect ratio as well as long tips with high aspect ratios with exact control about the tip profile.
Design of an Optical Gas Sensor Based on Silicon
The sensitivity of optical gas sensors depends on the length of interaction between detected radiation and the gas under investigation. A reduction in cell size of the sensor generally results in reduced sensitivity. Photonic crystals possess certain regions of their photonic band structure which offer low group velocities. Making use of these effects, smallervery compact -gas sensors should be possible. Problems to solve with numerical calculations are the identification of the operating point in relation to the photonic bandstructure and selection of an appropriate photonic crystal, the calculation of transmission through the photonic structure with and without the gas inside the sensor cell and the determination of an optimized anti-reflection-layer to improve the air-sensorinterface, since the low group velocity results in a high reflectivity.
Porous Silicon Structures as Optical Gas Sensors
Sensors, 2015
We present a short review of recent progress in the field of optical gas sensors based on porous silicon (PSi) and PSi composites, which are separate from PSi optochemical and biological sensors for a liquid medium. Different periodical and nonperiodical PSi photonic structures (bares, modified by functional groups or infiltrated with sensory polymers) are described for gas sensing with an emphasis on the device specificity, sensitivity and stability to the environment. Special attention is paid to multiparametric sensing and sensor array platforms as effective trends for the improvement of analyte classification and quantification. Mechanisms of gas physical and chemical sorption inside PSi mesopores and pores of PSi functional composites are discussed.
Miniature infrared gas sensors using photonic crystals
Journal of Applied Physics, 2011
We present an optical gas sensor based on the classical nondispersive infrared technique using ultracompact photonic crystal gas cells. The ultracompact device is conceptually based on low group velocities inside a photonic crystal gas cell and low-reflectivity antireflection layers coupling light into the device. Experimentally, an enhancement of the CO 2 infrared absorption by a factor of 2.6 to 3.5 as compared to an empty cell, due to slow light inside a 2D silicon photonic crystal gas cell, was observed; this is in excellent agreement with numerical simulations. We show that, theoretically, for an optimal design enhancement factors of up to 60 are possible in the region of slow light. However, the overall transmission of bulk photonic crystals, and thus the performance of the device, is limited by fluctuations of the pore diameter. Numerical estimates suggest that the positional variations and pore diameter fluctuations have to be well below 0.5% to allow for a reasonable transmission of a 1 mm device.
Silicon Multi-Pass Gas Cell for Chip-Scale Gas Analysis by Absorption Spectroscopy
Micromachines
Semiconductor and micro-electromechanical system (MEMS) technologies have been already proved as strong solutions for producing miniaturized optical spectrometers, light sources and photodetectors. However, the implementation of optical absorption spectroscopy for in-situ gas analysis requires further integration of a gas cell using the same technologies towards full integration of a complete gas analysis system-on-chip. Here, we propose design guidelines and experimental validation of a gas cell fabricated using MEMS technology. The architecture is based on a circular multi-pass gas cell in a miniaturized form. Simulation results based on the proposed modeling scheme helps in determining the optimum dimensions of the gas cell, given the constraints of micro-fabrication. The carbon dioxide spectral signature is successfully measured using the proposed integrated multi-pass gas cell coupled with a MEMS-based spectrometer.
Design of a silicon microsensor array device for gas analysis
Microelectronics Journal, 1996
This paper describes the design of a silicon-based microsensor array for application in gas or odour monitoring. Individual sensor cells consist of both lateral and vertical electrode pairs to measure film conductance and/or capacitance. The fabrication process involves standard silicon technologies to integrate a platinum or nickel-iron heater below the sensor cells. A simulation of the device gives a thermal response time of only 60ms and an ultra low power loss of about 50roW at 400°C per sensor. This compares well with experimental values observed on a similar device. The process technology is suitable for both the deposition of organic: materials (e.g. conducting polymers) and inorganic materials (e.g. semiconducting oxides). A scheme of the transducer interface circuitry is also provided, and could be used in a portable battery-powered instrument.
Silicon Nanowires for Gas Sensing: A Review
Nanomaterials
The unique electronic properties of semiconductor nanowires, in particular silicon nanowires (SiNWs), are attractive for the label-free, real-time, and sensitive detection of various gases. Therefore, over the past two decades, extensive efforts have been made to study the gas sensing function of NWs. This review article presents the recent developments related to the applications of SiNWs for gas sensing. The content begins with the two basic synthesis approaches (top-down and bottom-up) whereby the advantages and disadvantages of each approach have been discussed. Afterwards, the basic sensing mechanism of SiNWs for both resistor and field effect transistor designs have been briefly described whereby the sensitivity and selectivity to gases after different functionalization methods have been further presented. In the final words, the challenges and future opportunities of SiNWs for gas sensing have been discussed.