Sensing array, fabrication

Vacuum deposition techniques, such as sputtering, electron beam evaporation, and plasma deposition are common. Photopolymerization and laser-assisted depositions are used for preparation of specialized layers, particularly in the fabrication of sensing arrays. Most commercial instruments have thickness monitors (Chapter 4) that allow precise control of the deposition process. 

To automate the process of SAM synthesis in the microchannels for the generation of sensing arrays, a multichannel chip suitable for continuous flow of reagents was designed. A microchannel chip (4 x 2.2 cm2) with five parallel channels confined in an area of 200 pm was fabricated. Each channel can be individually addressed and... 

Several challenges remain for the ultimate practical use of these sensors. The response time of the solid state sensors are short (seconds) for initial sensing, but recovery times range from minutes to hours at room temperature. The stability of the sensor to drift associated with accumulation of fixed charge at interfaces, as well as the high sensitivity to ubiquitous urban pollutants ozone and N02 are problematic. All MPc OTFTs show some response to moisture, and conductivity is also temperature sensitive so that humidity and temperature compensation are essential. On a basic research level, the detailed characterization of charge trapping states, electronic structure, and the interactions with analytes is not yet fully understood on a quantitative theoretical basis. The time response of sensor initiation and recovery is also not understood in a detailed manner. In spite of these limitations, the intrinsic chemical stability of MPc compounds and their compatibility with microsensor array fabrication make these candidate OTFTs for further research and development. 

In addition to producing the sensing array using OFETs, this team also fabricated much of the peripheral drive circuitry using OFET-based logic elements and introduced a creative architecture in which the unit dimensions can be customized by cutting several elements with scissors and attaching them with a pressure sensitive adhesive [138]. 

Figure 10.49 (a) Resistance response of 80-nm-wide PPY and PEDOT nanowires to analytes at 1000 ppm concentration, (b) Sensing responses from the two nanowires presented on a 2-D scatter plot. Moisture corresponds to 8% relative humidity at 23 °C. IPA stands for isopropyl alcohol. (Reprinted with permission from Advanced Materials, Precisely Defined Heterogeneous Conducting Polymer Nanowire Arrays - Fabrication and Chemical Sensing Applications by Y. Chen and Y. Luo, 21, 20, 2040-2044. Copyright (2009) Wiley-VCH)... 

Y. Chen and Y. Luo, Precisely defined heterogeneous conducting polymer nanowite arrays -fabrication and chemical sensing applications, Adv. Mater., 21, 2040-2044 (2009). 

Shu, L., Hua, T., Want, Y., Li, Q., Feng, D.D., Tao, X., 2010. In-shoe plantar pressure measurement and analysis system based on fabric pressure sensing array. IEEE Trans. Inf. Technol. Biomed. 14 (3), 767-775. 

Fahrication of sensors and sensor arrays is in a state of rapid development. The groups led by Kuhr [225, 226] and Heineman [227, 228] have made significant advances in microfabrication of sensor arrays for simultaneous multianalyte amperometric assays and sensors both have applied their arrays to immunoassays [226, 227]. Further research efforts toward controlled-release microchip fabrication [229] and nanoscale chemical sensors [230] have also shown promise and will aid in the development of sensors and sensing arrays for in vitro and in vivo measurements. 

The formation of nanostructures such as nanodot arrays has drawn a great attention due to the feasible applications in a variety of functional structures and nanodevices containing optoelectronic device, information storage, and sensing media [1-3]. The various methods such as self-assembled nanodots from solution onto substrate, strain-induced growth, and template-based methods have been proposed for the fabrication of nanodot arrays on a large area, [4-6]. However, most of these works can be applied to the small scale systems due to the limited material systems. 

This chapter includes two different sensor system architectures for monolithic gas sensing systems. Section 5.1 describes a mixed-signal architecture. This is an improved version of the first analog implementation [81,91], which was used to develop a first sensor array (see Sect. 6.1). Based on the experience with these analog devices, a complete sensor system with advanced control, readout and interface circuit was devised. This system includes the circular microhotplate that has been described and characterized in Sect. 4.1. Additionally to the fabrication process, a prototype packaging concept was developed that will be presented in Sect. 5.1.6. A microhotplate with a Pt-temperature sensor requires a different system architecture as will be described in Sect. 5.2. A fully differential analog architecture will be presented, which enables operating temperatures up to 500 °C. 

Applications of titania nanotube arrays have been focused up to now on (i) photoelectrochemical and water photolysis properties, (ii) dye-sensitized solar cells, (iii) photocatalysis, (iv) hydrogen sensing, self-cleaning sensors, and biosensors, (v) materials for photo- and/or electro-chromic effects, and (vi) materials for fabrication of Li-batteries and advanced membranes and/or electrodes for fuel cells. A large part of recent developments in these areas have been discussed in recent reviews.We focus here on the use of these materials as catalysts, even though results are still limited, apart from the use as photocatalysts for which more results are available. 

We further addressed the use of the nucleic acids as biopolymers for the formation of supramolecular structures that enable the electronic or electrochemical detection of DNA. Specifically, we discussed the use of aptamer/low-molecular-weight molecules or aptamer/protein supramolecular complexes for the electrical analysis of the guest substrates in these complexes. Also, nucleic acid-NPs hybrid systems hold a great promise as sensing matrices for the electrical detection of DNA in composite three-dimensional assemblies. While sensitive and selective electrochemical sensors for DNA were fabricated, the integration of these sensor configurations in array formats (DNA chips) for the multiplexed analysis of many DNAs can also be envisaged. 

Variations of semiconductor PL and EL intensities resulting from analyte adsorption are promising techniques for chemical sensing. When coupled with films such as MIPS, the selectivity of such structures may be improved. Integrated devices in which forward- and reverse-biased diodes are juxtaposed using microelectronics fabrication methods provide an opportunity to create completely integrated sensor structures on a single chip and to prepare arrays of such structures. 

In order to improve volume efficiency and reduce payload weight for earth-orbital remote-sensing applications, low-mass membrane-based synthetic aperture radar array concepts are being developed. One such system is an inflatable deployable SAR consisting of thin fabrics or membranes that are deployed for L-band operation with dual polarisation. The entire assembly is flexible before employment and is rolled up onto the spacecraft bus. The antenna comprises three membranes positioned vertically over one another the ground plane, the radiation patch, and the microstrip transmission line membranes74. 

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