Fabrication sensor arrays

The combination of pin printing and sol-gel processing techniques provides a simple method to rapidly fabricate reusable chemical sensor element into arrays that exhibit good analytical figures of merit. This methodology also provides a straightforward means to fabricate reusable sensor arrays for simultaneous multianalyte quantification. 

In some applications, silver/silver chloride or calomel electrodes are considered cumbersome to use and maintain. More importantly, they are extremely difficult to miniaturize particularly with regard to their combined use with potentiometric membrane electrodes (see Section 18a.4.5.4) that have been fabricated into highly miniaturized and compact screen-printed sensor arrays for clinical use. Thus, several reference electrodes are manufactured with the same polymeric materials that are needed to design the responsive ion-selective membranes [7]. Incorporation of suitable active agents into such membranes leads to potentiometric responses that are ideally independent of the sample... 

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. 

The thermal resistance of the circular hotplate was measured to be 5.8 °C/mW for the coated and uncoated transducer. An increased thermal resistance is desirable for sensor arrays with one approach being the reduction of the heated membrane area. At the moment the smallest possible diameter of drop-deposited tin-oxide is 100 pm. A microhotplate with a heated area of 100 pm in diameter was fabricated and featured an increased thermal resistance of approximately 10 °C/mW. 

U. Milnch, D. Jaeggi, N. Schneeberger, A. Schaufelbuhl, O. Paid, H. Baltes, and J. Jasper. Industrial fabrication technology for CMOS infrared sensor arrays , Dig. Tech. Papers Transducers 97, Vol. 1, Chicago, IL, USA, (1997), 205-208. 

Individual microelectrodes offer very small responses and one approach for overcoming this problem is to use many microelectrodes together in the form of an array to allow a cumulative and so larger response to be measured. Microelectrode arrays may be fabricated by a number of approaches although techniques such as photolithography or laser ablation have to date proved cost prohibitive for the mass production of disposable sensor strips. We have previously described a novel sonochemical fabrication approach [38,39] for the production of microelectrodes, that lends itself to the mass production of sensor arrays. 

These luminescent sensor films can easily be inserted into microarray formats. Two general ways for the fabrication of ready-made sensor arrays are feasible ... 

GENERAL DESIGN AND FABRICATION OF THE PLANAR SENSOR ARRAY... 

Figure 4.2 Graphical recording of oxygen levels measured from several different oxygen electrodes of an implanted planar sensor array. The oxygen levels inhaled by the subject were varied, and despite the fact that the sensors were fabricated to precise specifications and the output current calibration was adjusted, the oxygen levels measured across tissue distances of 1-2 mm varied considerably.

Fabrication of Base Sensors For fabrication of redundant sensor arrays on metal or flexible insulating substrates, processes used in the semiconductor industry can be utilized as shown in Figure 8.2.44,45 Photolithography, wet etch, dry etch, sputtering, and evaporation are a few processes that have been used.46,47 The techniques described in this section can be used many times on the same sample to lead to numerous metals (or different electrodes) being fabricated on the same substrate, which can then be implanted in vivo. 

BronkKS, Walt DR. Fabrication of patterned sensor arrays with aryl azides on a polymer-coated imaging optical fiber bundle. Analytical Chemistry 1994, 66, 3519-3520. 

Screen printing is an excellent method for fabrication of ISEs on an industrial scale. Ag/AgCI electrodes can be screen printed onto a suitable support such as Kapton polyimide. The selective membrane is then printed onto the ISE, often with an intervening layer of a hydrogel such as poly(vinyl alcohol) soaked with NaCl solution to act as the internal reference solution. The reductions of cost associated with the mass-production of these electrodes allow them to be sold as single-use disposable devices. Also their small size relative to conventional ISEs allows them to be assembled into sensor arrays. 

Figures 1IC-E show SEM images of test patterns of silver that were fabricated using pCP with hexadecanethiol, followed by selective chemical etching [102], The SAMs protect the underlying substrates from dissolving by blocking the dilSisional access of etchants. The ability to generate arrays of microstructures of coinage metals with controlled shapes and dimensions is directly useful in fabricating sensors and arrays of microelectrodes.

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