This paper presents an analysis of the sol deposition process on porous silicon in order to produce highly sensitive gas detectors. Sol solutions were deposited within the dendrite structural pore regions of n-type silicon. The parameters for the structures, built of metal oxides (Fe, Ni, Sn), were analyzed. A morphological study of porous silicon, with embedded metal oxide nanocomposites, was carried out using atomic force microscopy. Cross-sections of porous silicon were examined using a scanning electron microscopy. Impedance spectroscopy was used to study the electrical properties of nanomaterials, based on porous silicon, with embedded metal oxide nanocomposites. Gas-sensitivity measurements of the synthesized samples were made. It turned out that, applying variable frequency interference to the sensory structures in a changing environment, changes the impedance response of gas. New perspectives for increasing sensitivity and selectivity are shown.

Porous silicon with embedded metal oxides for gas sensing applications

This study presents a silicon-based pressure sensor with temperature compensation The eight piezoresistors were designed on the polycrystalline silicon membrane and constructed by two concentric Wheatstone-bridge circuits to perform two sets of sensors The sensor in the central circuit measures the membrane deflection caused by the combined effects of pressure and temperature, while the outer one measures only the deflection caused by the working temperature From this arrangement, it is reliable and accurate to measure the pressure by comparing the output signals from the two concentric Wheatstone-bridge circuits The optimal positions of the eight piezoresistors were simulated by simulation software ANSYS The investigated pressure sensor was fabricated by the micro electro-mechanical systems (MEMS) techniques The measuring performance and an indication of the conventional single Wheatstone-bridge pressure sensor is easily affected under variation of different working temperature and causes a maximum absolute error up to 455%, while the double Wheatstone-bridge pressure sensor is able to compensate the error, and reduces it down to 113% The results in this paper demonstrate an effective temperature compensation performance, and have a great performance and stability in the pressure measuring system as well

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Investigation of a Pressure Sensor with Temperature Compensation Using Two Concentric Wheatstone-Bridge Circuits

Fusion of the transduction mechanism in micro and macro nanopores of porous silicon (PS) was employed to fabricate an MEMS-based aliphatic alcohol impedance sensor. The presence of a nanopore network on silicon was confirmed by the SEM image. The morphology of the PS nanopores was roughly distributed in a uniform manner. The performance of the sensor was studied using Impedance spectroscopy at room temperature. Electrochemical impedance spectroscopy and an equivalent circuit analysis of the small amplitude (± 10 mV) AC impedance measurements (frequency range 0.1 Hz–1 kHz) at ambient temperature were carried out. The Sensing layer consists of nanopores (45.30–71.13 nm), micropores (0.95–5 µm), and comb type alumina electrodes with the micro PS layer having a thickness of about 0.2 µm and the macro PS layer having a thickness of about 4 µm. These results were used to assess the effect of the micro PS and macro PS of the particulate layer on the conductivity of the given aliphatic gases. The measured impedance was approximately 2.3e5 for the micro PS, and 3.22e5 macro PS for 8 ppm of gas injected into the gas chamber. The grain boundary resistance increases with an increase in the concentration of butane, benzene, and methane, which ranges from 2 to 16 ppm.

Fast response and recovery of nano-porous silicon based gas sensor

Nowadays, the micro and nanotechnology field integrates a wide range of materials that can be defined as “fragile” because of their shape, dimension or density. In this work, three materials of this kind, at different level of technological and industrial maturity are studied by time of flight secondary ion mass spectrometry (ToF-SIMS). These materials are: mesoporous silicon, thin polymethacrylate films deposited by initiated Chemical Vapour Deposition (i-CVD)and hybrid organosilicate (SiOCH) dielectric materials (low-k). The objective is to verify and validate the ToF-SIMS as a reliable characterisation technique for describing the chemical properties of these materials. Indeed, because of this intrinsic ‘fragility’ the consistency of the chemical information is connected to an appropriate interpretation of the specific ion/matter interactions taking place.For mesoporous silicon, a systematic analysis is carried out considering various sputtering ion sources (Caesium, Xenon and Oxygen); both sputtering and ionisation behaviours are examined relatively to the nonporous silicon, taking into account energy of the sputtering beam and porosity rate of the target material.Concerning nanometric thick polymer films, low damaging analysis conditions are applied by the use of argon cluster primary ion sources in order to obtain a significant molecular secondary ion information. In these conditions, a discrimination of quasi-identical nanometre thick structures is made possible and a quantification method for copolymers is then proposed. In addition, with the supplement of data principal component analysis (PCA) an innovative and significant correlation is obtained between main Principal Component and sample molecular weights.Finally, the effect of several industrial integration processes (such as etching or wet cleaning) applied on low-k materials are studied in order to understand their detrimental impact on low-k insulating properties. To achieve a depth-resolved chemical information, low energy caesium sputterings are shown to be the most adapted and sensitive strategy. In addition, PCA is shown to be almost essential to amplify differences between samples significantly. This approach allowed combining the variation of physical properties (dielectric constant) with the chemical ones.

https://tel.archives-ouvertes.fr/tel-01488629/document

ToF-SIMS characterisation of fragile materials used in microelectronic and microsystem devices : validation and enhancement of the chemical information

This work reports the manufacture of a Nano porous silicon (NPS) gas sensor and its butane detection mechanism. The sensor’s resistance changes with the gas concentration. This transduction mechanism has been tested using a gas injection precalibration method. Nanopores were developed using HF- based wet electrochemical etching on p- type substrates. The presence of nanoporeson silicon has been confirmed and its morphology has been studied by SEM imagery and its uniform distribution has been demonstrated. Impedance spectroscopy was performed at room temperature and increased grain boundary resistance was observed for a range of 2–6 ppm of butane gas.

Fabrication of E Nose Sensor for Detection of Butane Gas by using Nano Porous Silicon

Since porous silicon (PS) has a much lower Young's modulus than single crystalline silicon, Si/PS composite membranes deflect more and can be used to fabricate pressure sensors with improved sensitivity. However, PS has some drawbacks, like weaker structural stability and being more susceptible to humidity due to its large surface-to-volume ratio. We discuss the fabrication and testing of Si/PS composite membrane pressure sensors with MicroPS and MacroPS of varying porosity. For the same porosity, the composite membranes with Si/MicroPS show higher sensitivity than Si/MacroPS. The sensor output is linear and repeatable at pressures less than 1 bar. The deformation of composite membranes measured up to 10 bar showed that it saturates at high pressure and is irreversible. Composite membranes also exhibit higher offset voltage than single crystal silicon membranes, which could be attributed to the stress developed in the membrane during PS formation and subsequent processing. The composite membrane pressure sensors were packaged on TO 39 headers, and the effect of humidity and temperature variation were investigated.

Vishwas S. Kale

Papers

Critical study of high-sensitivity pressure sensors with silicon/porous silicon composite membranes