Silicon-based micromachined sensor

Cutting-edge Silicon-based Micromachined Sensors for Next Generation Household Appliances... 

Mass-produced cantilever sensors, however, have the potential to satisfy the conditions of selectivity, sensitivity, miniature size, low power consumption, and real-time operation [5, 6], Microcantilevers are micromachined from silicon or other materials and can easily be fabricated in multiple-element arrays. They resemble miniature diving boards measuring 100 to 200 pm long by about 20 to 40 pm wide by 0.3 to 1 pm thick and having a mass of a few nanograms. Their primary advantage originates from their sensitivity, which is based on the ability to detect their motion with subnanometer precision. 

U. Schnakenberg, W. Benecke, and B. Lochel, NH OH-based etchants for silicon micromachining. Sensors Actuators A 2 - 1031, 1990. 

R.M. Langdon, Micromachining of silicon for sensors, Proc. NATO ASI on Novel Si-Based Technologies 1989, 143-172. 

Most silicon accelerometers are based on a micromachined variable capacitance element (g-cell) that is converted to a voltage using a C-V converter and then amplified, filtered, and buffered to provide an analog output as shown in Fig. 7.1.4. To date, open-loop implementations for capacitive read-out circuits are more widely employed than closed-loop systems, primarily as a result of the stability of such systems [16]. Interface electronics for micromachined sensors depend not only upon the transduction technique (input specification) and the product requirements (output specification) but also on the packaging approach, as parasit-ics are introduced when a multiple-die packaging technique is used. 

Microfabrication and micromachining techniques have also been used in the manufacture of electrochemical sensors. This includes po and pco sensors. Zhou et al [9] describe an amperometric CO2 sensor using microfabricated microelectrodes. In this development, silicon-based microfabrication techniques are used, including photolithographic reduction, chemical etching, and thin-film metallization. In Zhou s study, the working electrodes are in the shape of a microdisk, 10 pm in diameter, and are connected in parallel. In recent years, silicon-based microfabrication techniques have been applied to the development of microelectrochemical sensors for blood gases, i.e. P02. Pcoj and pH measurements. 

Recently Micro Electro-Mechanical Systems (MEMS) have been emerging as sensor platform for the development of sensors with extreme high sensitivity [8-14]. Micromachined silicon cantilevers are the simplest MEMS sensors that can be micromachined and mass-produced. Microcantilever sensor technology is an upcoming sensing technique with broad applications in chemical, physical, and biological detection. With their compactness and potential low cost, detection techniques based on silicon-based cantilevers provide a path for the development of miniaturized sensors. 

Lorenzelli, L., Benvenuto, A., Adami, A. et al. (2005) Development of a gas chromatography silicon-based microsystem in clinical diagnostics. Biosens Bioelectron, 20 (10), 1968-1976. Zampolli, S., Ehni, I., Stiirmann J. et al. (2005) Selectivity enhancement of metal oxide gas sensors using a micromachined gas chromatographic column. Sens Actual B, 105 (2), 400-406. Bessoth, F.G., Naji, O.P., Eijkel, J.C.T. and Manz, A. (2002) Towards an on-chip gas chromatograph the development of a gas injector and a dc plasma emission detector. J Anal Atom Spectrom, 17 (8), 794-799. 

Electrochemical polymerization tirray of chemiresistive sensors Carbon-polymer composites silicon-based micromachined array of chemiresistive gas sensors Polymer films array of QCM-based sensors ... 

They operate as drive, amplitude control of the drive, detectors for the oscillation nodes, and as actuators to keep the nodes in place. The principle enables a complete self-test by simulating a yaw rate via the piezoactuators of the closed loop. A yaw-rate sensor based on the principle of a vibrating cylinder is used in VDC systems (Fig. 7.2.18). This principle has been used in a similar way in silicon micromachining and is used in a yaw-rate sensor for VDC [9]. 

Zampolli and coworkers have developed a selective hybrid microsystem based on GC to enhance indoor air quality monitoring applications such as CO and NO2 [41]. In the miniaturized GC, a solid-state sensor acts as the detector along with a silicon micromachined packed GC column, a zero grade air unit, a minipump, and a minivalve. It was possible to detect benzene, toluene, and m-xylene in both synthetic and real indoor air down to 5 ppb. 

It then addresses the micro-hotplates concept that has led to the development of different types of micromachined gas sensor devices. The different reahzations of micromachined semiconductor gas sensors are presented thin- and thick-film metal-oxide, field effect, and those using complementary metal-oxide semiconductors (CMOSs) and silicon-on-insulator (SOI) technologies. Finally, recent developments based on gas sensitive nanostructures, polymers, printing and foil-based technologies are highlighted. 

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