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Abstract: A bio-inspired dome-shape SiO2/SiN membrane-in-recess is fabricated by two subsequent wet-etching steps, continued with membrane material thin film deposition, and backside deep reactive ion etching for releasing the membrane. White light interferometer (WLI) confirmed the shape of the membrane. The middle apex of the membrane has 12 μm positive indentation from the edge, which is recessed 2-4 μm. The strain-amplifying mechanical characteristics are modeled by finite element. For verification, the structure is attached onto another plate structure being axially pushed and pulled. The membrane is vertically displaced ∼200 nm under 4 μ-strain applied strain, displaying two orders of amplification. [Copyright &y& Elsevier]

Abstract: This work presents a simple evanescent wave-sensing system based on plasma-enhanced chemical vapour deposition (PECVD) silicon carbide (SiC) waveguides. Thin SiC films were deposited on Si substrates with a SiO2 film acting as a cladding layer around the carbide core. In the sensor, the evanescent tale of the light travelling in a waveguide senses an absorbant medium placed above the waveguide. By using a 1×2 power splitter, the sensor is calibrated using one arm as a reference. This shows that the sensitivity of such a sensor is improved by choosing SiC as waveguide material compared to silicon nitride (SiN) films. [Copyright &y& Elsevier]

The initial attraction of polysilicon was the ability to deposit semiconductor layers on a wide range of substrates. This leads to the development of polysilicon gate MOS, polysilicon emitters and a range of passive devices. In the field of sensors and actuators, the strain sensors, based on piezoresistive effect, was one of the first successful applications. However, it was probably the development of surface micromachining, which received the most attention. The ability to deposit polysilicon on oxide meant that free-standing structures could be fabricated and this has lead to a wide range of successful devices. Polysilicon has a structure comprising small single-crystal grains with many orientations separated by thin grain boundaries. The size of these grains is highly dependent upon processing and therefore a wide range of electrical and mechanical properties can be achieved. This yields greater flexibility but this sensitivity to process parameters can lead to problems in obtaining a stable process. This paper will look back at the development of polysilicon, its structure, fabrication and both mechanical and electrical properties. [Copyright &y& Elsevier]

This paper investigates the suitability of porous polysilicon and porous SiC as materials for sensing humidity. The investigation is a continuation of earlier work on porous single-crystalline silicon, where it was shown that this material was appropriate for humidity sensing, and could be easily integrated with standard Si processing. It was also shown that membrane structures enable the integration of a heating device to ‘reset’ the system. The best microstructure for humidity sensing was obtained for low-doped p-type silicon. The advantage of using polysilicon is that it is possible to tune its response (by doping) so that it has only a very small temperature coefficient of resistance. The idea is that a humidity sensor with a very small temperature dependence could be realised. The advantage of using SiC is that it offers the possibility of a humidity sensor that could withstand very harsh chemical environments. [Copyright &y& Elsevier]

Abstract: When used as the dielectric in a capacitive sensing arrangement, porous SiC has been found to be extremely sensitive to the presence of ammonia (NH3) gas. The exact sensing method is still not clear, but NH3 levels as low as ∼0.5ppm could be detected. We report the fabrication and preliminary characterisation of NH3 sensors based on porous SiC and Al electrodes. SiC is a very durable material and should be good for sensors in harsh environments. So far, the only NH3 sensors using SiC have been FET based, and the SiC was not porous. In our devices, SiC was deposited by PECVD on standard p-type single-crystal Si and was then made porous by electrochemical etching in 73% HF using anodisation current densities of 1–50mA/cm2. Preliminary data is given for our devices response to NH3 in the range 0–10ppm NH3 in dry N2 carrier gas. [Copyright &y& Elsevier]