Planar sensors

Planar constructions of gas sensors are generally considered today to be better than ceramics for the development of gas-sensing devices. These structures can be fabricated by a number of microelectronic protocols as single-sided or double-sided designs. The choice depends mostly on how to 

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FIGURE 4.15 Two pH and two K+ planar sensors in the in-situ porcine heart preparation at midmyocar-dial depth (a) and the recorded fall in the pH and increase in K+ activity, respectively, during the course of coronary artery occlusion (b). (From [18].)... 

We have shown that antiresonant dielectric layers can be used to design low-loss liquid-core waveguides that are suitable for implementing planar sensor device geometries. The following sections will describe in more detail how the design principles laid out here were implemented in silicon-based LC-ARROW chips and used for optical sensing and detection of a wide variety of substances. 

Compatibility between sensors and automatic and automated analytical systems is crucial as it allows two Analytical Chemistry trends to be combined (see Fig. 1.1). Probe-type and planar sensors can be used in automated batch systems including robot stations, as well as in continuous (mixed in-line/on-line) systems. On the other hand, flow-through sensors are only compatible with continuous configurations. 

The most salient feature of flow-through sensors is the way in which the sample is brought into contact with the sensitive microzone (see Fig. 1.14), which distinguishes them from probe and drop-planar sensors. In fact, the liquid (or gaseous) sample is passed over the microzone rather than dropped onto it or used to immerse the probe [1]. 

Fig. 8.11 Two versions of a SnC>2 sensor with incorporated heating element (a) a ceramic tube sensor and (b) planar sensor (adapted from Heiland, 1982)...

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.

Figure 4.3 Schematic drawings illustrate two mated window chamber plates, one containing a planar sensor and its connector (a), while the companion plate has an open ring for the placement of a glass coverslip (b).

The configuration of the dorsal tissue window chamber plates used as described here allows the installation of a circular, planar sensor array 1.2 cm in diameter (Figure 4.5). 

Fig. 4.38 Planar sensor format (adapted from the Automotive Electronics Handbook, 1994).

For a voltammetric sensor, the current or potential peak shift that may relate to the concentration of the sensing species is an important measurement. In a dynamic situation in which polarization characteristics are obtained, it is essential that the mass transfer characteristics are reproducible for both calibration and actual measurements. In the case of a stationary planar sensor, stagnant solution or steady flow conditions in a flow cell provides good reproducibility. Or in another case, a sufficiently high concentration of an electrolyte is used to maintain a constant ohmic drop in the cell, regardless of the concentration of the pertinent sensing component. Under these conditions, the mass transfer can be purely diffusional and adequately described by Pick s law of diffusion. 

E. and Traversa, E. (2006) Non-Nernstian planar sensors based on YSZ with Ta (10 at %)-doped nanosized titania as a sensing electrode for high-temperature applications. Int. J. Appl. Ceram. Technol., 3 (5), 393-400. 

FIG. 1 Schematic cross sections of selected microelectrode configurations, (a) Nomenclature for parts of microelectrode, (b) Na+-sensitive microelectrode (22), (c) recessed-tip Na+-sensitive microelectrode (27), (d) liquid ion-exchanger micropipette electrode (38), (e) coated wire electrode (16), (f) flow-through ISE (e.g., NOVA 6, Boehringer ISE 2020), (g) micro-capillary glass electrode of tubular shape (e.g., Radelkis OP-266), (h) planar sensor fabricated by microelectronic technology (93), (i) ISFET sensor (94). 

For planar sensors manufactured by multilayer technology, the recently developed ceramic tape casting process was improved further [17, 18]. ZrOz powder is mixed into an organic matrix of binders, plasticizers, and solvents and is tape cast onto a Mylar supporting tape or a steel belt After drying, the ceramic tape is separated from the support tape and the flexible green tape can be punched to form individual substrates. 

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