Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy carrier and as a chemical reactant. There are an immense number of sensors reported in the literature for hydrogen detection and in this work these sensors are classified into eight different operating principles. Characteristic performance parameters of these sensor types, such as measuring range, sensitivity, selectivity and response time are reviewed and the latest technology developments are reported. Testing and validation of sensor performance are described in relation to standardisation and use in potentially explosive atmospheres so as to identify the requirements on hydrogen sensors for practical applications.

Hydrogen Sensors - A review

Metal oxide semiconductor gas sensors are utilised in a variety of different roles and industries. They are relatively inexpensive compared to other sensing technologies, robust, lightweight, long lasting and benefit from high material sensitivity and quick response times. They have been used extensively to measure and monitor trace amounts of environmentally important gases such as carbon monoxide and nitrogen dioxide. In this review the nature of the gas response and how it is fundamentally linked to surface structure is explored. Synthetic routes to metal oxide semiconductor gas sensors are also discussed and related to their affect on surface structure. An overview of important contributions and recent advances are discussed for the use of metal oxide semiconductor sensors for the detection of a variety of gases—CO, NOx, NH3 and the particularly challenging case of CO2. Finally a description of recent advances in work completed at University College London is presented including the use of selective zeolites layers, new perovskite type materials and an innovative chemical vapour deposition approach to film deposition.

https://www.mdpi.com/1424-8220/10/6/5469/pdf

Metal Oxide Semi-Conductor Gas Sensors in Environmental Monitoring

The theoretical and experimental issues relevant to neutrinoless double beta decay are reviewed. The impact that a direct observation of this exotic process would have on elementary particle physics, nuclear physics, astrophysics, and cosmology is profound. Now that neutrinos are known to have mass and experiments are becoming more sensitive, even the nonobservation of neutrinoless double beta decay will be useful. If the process is actually observed, we will immediately learn much about the neutrino. The status and discovery potential of proposed experiments are reviewed in this context, with significant emphasis on proposals favored by recent panel reviews. The importance of and challenges in the calculation of nuclear matrix elements that govern the decay are considered in detail. The increasing sensitivity of experiments and improvements in nuclear theory make the future exciting for this field at the interface of nuclear and particle physics.

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Double Beta Decay, Majorana Neutrinos, and Neutrino Mass

An apparatus may include a semiconductor chip and a fluidics assembly. The semiconductor chip has an array of wells and an array of sensors and each sensor of the array of sensors is in fluid communication with a well of the array of wells. The fluidics assembly is located on top of the semiconductor chip and is configured to deliver fluids to the semiconductor chip. The fluidics assembly includes a flow expansion chamber configured to introduce the fluids, an outlet portion configured to pipe out the fluids, and a flow chamber portion. The flow chamber portion is configured to allow the fluids to flow from the flow expansion chamber to the outlet portion and to allow the fluids to interact along the way with material in the array of wells. The flow expansion chamber has a curved wall at the top or bottom so that the height of the flow expansion chamber at the center is less than at the walls that restrict the fluids to the left and right.

Methods and apparatus for measuring analytes using large scale fet arrays

Methods and apparatus relating to FET arrays including large FET arrays for monitoring chemical and/or biological reactions such as nucleic acid sequencing-by-synthesis reactions. Some methods provided herein relate to improving signal (and also signal to noise ratio) from released hydrogen ions during nucleic acid sequencing reactions.

Methods and apparatus for measuring analytes

Monolithic silicon bolometers with implanted thermistors, micromachined thermal masses and suspension beams have been developed. These devices are intended for accurate β-decay spectrum measurements in the Milano neutrino mass experiment. By means of a dedicated micromachining fabrication process very small thermal masses (700×430×15 μm3) and links (2150×22×15 μm3) have been directly integrated in the device, thus obtaining reproducible bolometers which are suitable for use in detector arrays. The fabrication process involves a combination of standard IC technologies and bulk micromachining techniques, based on wet etching steps in tetramethylammonium hydroxide (TMAH) water solutions. Protection of aluminum metal lines and surface roughness control are two important features of the developed technique. The proposed micromachining approach eventually aims at fabricating hundreds of highly reproducible bolometers, to be used simultaneously in order to improve the sensitivity of the neutrino mass experiment.

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Fabrication of silicon bolometers with bulk micromachining technology

Wafer-level and chip-level bonding of micro-caps to protect sensitive parts are crucial process steps for MEMS integration and packaging. The use of a photosensitive polymer as a bonding and sealing layer is a cheap and simple solution. Hot roll lamination of dry film guarantees very uniform coating of thick polymer layers over wafers with complex topology and moreover has the capability to bridge over etched cavities. The paper presents the results obtained bonding both quartz and glass caps over MEMS devices, either wafer to wafer or single cap to chip, using two different kinds of permanent dry film.

MEMS packaging by using dry film resist

This paper reports on the first RF MEMS capacitive switch with a capacitance ratio of 130 that is stable almost up to 3 W of RF power. From an RF point of view the device behaves as a shunt capacitive switch, but employs an ohmic contact between the movable membrane and a floating metal deposited on the dielectric-coated stationary electrode, which is used to provide a high and repeatable ON state capacitance. In addition strain-relief anchor springs guarantee almost stable performances at high temperature and high power.

High-power high-contrast RF MEMS capacitive switch

A novel set of microstructures for on-wafer stress measurement is presented, based on a lancet principle, with dedicated design for the amplification of the dimensional variations induced by the internal stress of the structural material. A tilted arm geometry was adopted in order to maximize the strain induced movement, keeping the design relatively simple and robust and the lancet on the wafer plane. A set of simulations, as well as an analytical examination of the structure was performed to establish the optimal geometry: different tilt angles were simulated in a range between −200 and 200 MPa internal stress. Test structures were then realized by means of surface micromachining, adopting photoresist as sacrificial layer and electroplated gold as structural layer: the novel geometry was sided by traditional rotating structures [Sens. Actuators A 37/38 (1993) 756] and wafer curvature measurements to confirm the readout. Plastic regime simulations were adopted to analyze the behavior of the gold structures, based on a stress–strain curve obtained experimentally.

Benno Margesin

Papers

Fabrication of silicon bolometers with bulk micromachining technology

MEMS packaging by using dry film resist

High-power high-contrast RF MEMS capacitive switch

Novel test structures for stress diagnosis in micromechanics

RF-MEMS Based Switch Matrices for Complex Switching Networks