Thanks to its unique features at the nanoscale, nanofluidics, the study and application of fluid flow in nanochannels/nanopores with at least one characteristic size smaller than 100 nm, has enabled the occurrence of many interesting transport phenomena and has shown great potential in both bio- and energy-related fields. The unprecedented growth of this research field is apparently attributed to the rapid development of micro/nanofabrication techniques. In this review, we summarize recent activities and achievements of nanofabrication for nanofluidic devices, especially those reported in the past four years. Three major nanofabrication strategies, including nanolithography, microelectromechanical system based techniques, and methods using various nanomaterials, are introduced with specific fabrication approaches. Other unconventional fabrication attempts which utilize special polymer properties, various microfabrication failure mechanisms, and macro/microscale machining techniques are also presented. Based on these fabrication techniques, an inclusive guideline for materials and processes selection in the preparation of nanofluidic devices is provided. Finally, technical challenges along with possible opportunities in the present nanofabrication for nanofluidic study are discussed.

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Review article: Fabrication of nanofluidic devices

Silicon carbide (SiC) is one of the most promising materials for applications in harsh environments thanks to its excellent electrical, mechanical, and chemical properties. The piezoresistive effect of SiC has recently attracted a great deal of interest for sensing devices in hostile conditions. This paper reviews the piezoresistive effect of SiC for mechanical sensors used at elevated temperatures. We present experimental results of the gauge factors obtained for various poly-types of SiC films and SiC nanowires, the related theoretical analysis, and an overview on the development of SiC piezoresistive transducers. The review also discusses the current issues and the potential applications of the piezoresistive effect in SiC. [2015-0092]

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The Piezoresistive Effect of SiC for MEMS Sensors at High Temperatures: A Review

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Beyond gel electrophoresis: Microfluidic separations, fluorescence burst analysis, and DNA stretching

In this Letter we present the electrical and electro-optical characterization of single crystalline germanium nanowires (NWs) under tensile strain conditions. The measurements were performed on vapor–liquid–solid (VLS) grown germanium (Ge) NWs, monolithically integrated into a micromechanical 3-point strain module. Uniaxial stress is applied along the ⟨111⟩ growth direction of individual, 100 nm thick Ge NWs while at the same time performing electrical and optical characterization at room temperature. Compared to bulk germanium, an anomalously high and negative-signed piezoresistive coefficient has been found. Spectrally resolved photocurrent characterization on strained NWs gives experimental evidence on the strain-induced modifications of the band structure. Particularly we are revealing a rapid decrease in resistivity and a red-shift in photocurrent spectra under high strain conditions. For a tensile strain of 1.8%, resistivity decreased by a factor of 30, and the photocurrent spectra shifted by 88 meV...

Tuning the Electro-optical Properties of Germanium Nanowires by Tensile Strain

Miniature Microelectromechanical Systems (MEMS) pressure sensors possess various merits, such as low power consumption, being lightweight, having a small volume, accurate measurement in a space-limited region, low cost, little influence on the objects being detected. Accurate blood pressure has been frequently required for medical diagnosis. Miniature pressure sensors could directly measure the blood pressure and fluctuation in blood vessels with an inner diameter from 200 to 1000 m. Glaucoma is a group of eye diseases usually resulting from abnormal intraocular pressure. The implantable pressure sensor for real-time inspection would keep the disease from worsening; meanwhile, these small devices could alleviate the discomfort of patients. In addition to medical applications, miniature pressure sensors have also been used in the aerospace, industrial, and consumer electronics fields. To clearly illustrate the "miniature size", this paper focuses on miniature pressure sensors with an overall size of less than 2 mm × 2 mm or a pressure sensitive diaphragm area of less than 1 mm × 1 mm. In this paper, firstly, the working principles of several types of pressure sensors are briefly introduced. Secondly, the miniaturization with the development of the semiconductor processing technology is discussed. Thirdly, the sizes, performances, manufacturing processes, structures, and materials of small pressure sensors used in the different fields are explained in detail, especially in the medical field. Fourthly, problems encountered in the miniaturization of miniature pressure sensors are analyzed and possible solutions proposed. Finally, the probable development directions of miniature pressure sensors in the future are discussed.

https://www.mdpi.com/2072-666X/11/1/56/pdf

Recent Progress of Miniature MEMS Pressure Sensors.

The present invention is directed at a system for carrying out a thermal melt analysis of an organic compound, wherein the system comprises: a microchannel having a first opening and a second opening at opposite ends of the microchannel, wherein the temperature at the opposite ends of the microchannel is different thereby creating a temperature gradient between the opposite ends of the microchannel; a light source emitting light which is coupled into the microchannel through the first opening; a light detector arranged to detect a light signal exiting the microchannel through the second opening; and wherein the first opening of the microchannel is in fluid communication with at least one fluid source providing at least one organic compound. The present invention is also directed to a method of using this device.

Method and system for thermal melt analysis

The recent reports on giant piezoresistance effect in highly resistive silicon nanowires (SiNWs) have offer greater sensitivity in stress measurements. Despite enhanced sensitivity, the piezoresistance of highly conductive silicon are preferred as they are less prone to thermal noises and hence better accuracy. Here we report a thermal induced buckle micro-bridge technique to accurately characterize the temperature dependent piezoresistivity effect in SiNWs. Phosphorus doped SiNWs with 50 nm wide, 60 nm thick and 100 μm in length were encapsulated within SiO2 micro-bridges. The electrical measurement of both reference SiNWs and SiNWs at micro-bridges was carried out, followed by the optical profiling of the micro-bridges with embedded SiNWs. N-type SiNWs with doping of 1×1020 ion/cm3 exhibit a strong dependence on temperature with a piezoresistive coefficient that decreases by 22.5 % between 25 °C to 60 °C; whereas its bulk counterpart is independent of temperature across this range. The results demonstrated that thermal noises may be more detrimental to nano-scale electromechanical sensors than its bulk counterparts.

Extracting Piezoresistance in SiNWs using Thermal Induced Buckling of Micro-Bridges

Here we show how the electromechanical properties of silicon nanowires (NWs) are modified when they are subjected to extreme mechanical deformations (buckling and buckling mode transitions), such as those appearing in flexible devices. Flexible devices are prone to frequent dynamic stress variations, especially buckling, while the small size of NWs could give them an advantage as ultra-sensitive electromechanical stress sensors embedded in such devices. We evaluated the NWs post-buckling behavior and the effects of buckling mode transition on their piezoresistive gauge factor (GF). Polycrystalline silicon NWs were embedded in SiO2 microbridges to facilitate concurrent monitoring of their electrical resistance without problematic interference, while an external stylus performed controlled deformations of the microbridges. At points of instability, the abrupt change in the buckling configuration of the microbridge corresponded to a sharp resistance change in the embedded NWs, without altering the NWs' GF. These results also highlight the importance of strategically positioning the NW in the devices, since electrical monitoring of buckling mode transitions is feasible when the deformations impact a region where the NW is placed. The highly flexible NWs also exhibited unusually large fracture strength, sustaining tensile strains up to 5.6%; this will prove valuable in demanding flexible sensors.

https://iopscience.iop.org/article/10.1088/0957-4484/21/40/405505/pdf

The electromechanical response of silicon nanowires to buckling mode transitions

In an embodiment, a method of controlling giant piezoresistive coefficient of at least one piezoresistive element may be provided. The method may include providing an electric field to the at least one piezoresistive element to thereby create a depletion region in the at least one piezoresistive element; applying a stress onto the at least one piezoresistive element to modulate concentration and mobility of charge carriers along the at least one piezoresistive element; and varying the electric field applied onto the at least one piezoresistive element to control the giant piezoresistive coefficient of the at least one piezoresistive element. The application of stress alone may not change the giant piezoresistive coefficient, it may only change the resistance by changing the concentration and mobility of charge carriers. A piezoresistive sensor may also be provided.

Chee Chung Wong

Papers

Method and system for thermal melt analysis

Extracting Piezoresistance in SiNWs using Thermal Induced Buckling of Micro-Bridges

The electromechanical response of silicon nanowires to buckling mode transitions

A piezoresistive sensor and a method of controlling giant piezoresistive coefficient of at least one piezoresistive element