Channel stops

Fig. 11. Cutaway view of a CCD shift register where the ( ) represent gate electrodes. Voltage pulses appHed to the phase gates move photogenerated charge in the charge-transfer direction. The channel stops confine the charge during integration and transfer. See text.

Figure 16. Simplified schematic of the architecture of a single CCD pixel. The channel stops permanently define the pixel boundaries in the column direction. The pixel rows are defined by the electric fields applied to the three pixel phases. For a 15 /urn pixel CCD, channel stops are 2-3 /um wide and the phases are each 5 /um wide.

Figure 10. Top, three-dimensional view of an oxide-isolated bipolar transistor. (Reproduced with permission from reference 13. Copyright 1988 McGraw-Hill.) Bottom, schematic of a common base n-p-n transistor circuit. Abbreviations are defined as follows n-epi, n-type-doped epitaxial-grown silicon and p-CHAN-STOPy p-type channel stop.

An alternative way of creating channel stops is disclosed in JP-A-60140869. The isolation regions are formed by exposing the substrate to Hg vapour and heating the regions using a laser beam. 

An imager in which CCD registers are separated by regions having high impurity concentration (channel stops) and a method of manufacturing the imager is shown in JP-A-58171848 (Fujitsu KK, Japan, 08.10.83). 

A p-type HgCdTe substrate 1 is exposed to Hg vapour at a high temperature. This treatment removes Hg atoms from the substrate and high carrier concentration layers 9 are formed. Then, windows W are formed in a mask 10. The device is subjected to Hg vapour at a low temperature to diffuse Hg atoms into the surface areas of the windows These areas return to the same carrier concentration as the one of the substrate while the areas covered by the mask will keep the high carrier concentration and consequently form the channel stops of the device. 

In a second embodiment the strip detectors A to H are mounted on an intrinsic p-type silicon substrate 3A covered by a silicon oxide layer 3B. A patterned arrangement of conductor tracks 21 is formed in the semiconductor base 3B. Each track is formed by diffusion or ion-implantation of an n-type dopant material, and isolated from adjacent tracks by means of a channel stop network 23. Bridging links of nichrome-gold are formed to define and connect the read-out regions to the tracks 21. The links 25 are paired and thus provide voltage detection contacts. The tracks 21 are connected to connection pads 29. Signal processing circuitry is incorporated in the semiconductor base layer 3B. 

Using an alternative geometry Evans et al. [16] developed the channel stopped flow method (CSFM). This technique, to date, has been used to measure solution diffusion coefficients (independent of knowledge of the concentration of the electroactive species) and crystal dissolution kinetics. The channel flow cell consisted of a rectangular electrode, typical dimensions 2.5 mm long and 6.25 mm wide, situated in a rectangular duct, 10 mm wide and 0.25-1.0 mm high. The electrode was placed a suitable distance... 

Fig. 10.15. Experimental (—) and theoretical (—) chronoamperometric response for the diffusion-limited oxidation of 2 x 10-3 mol dm-3 Fe(CN)S in 0.1 mol dm-3 KC1 at a rectangular electrode, 2.5 mm long and 6.25 mm wide, in a 0.5 mm high channel flow cell under channel stopped flow conditions. The initial volume flow rate of the solution was 0.197 cm3 s-1, which gave a limiting current at the channel electrode, defined as / . At time, f.top, solution flow was retarded (Evans et al., in preparation). The theoretical data has been simulated assuming Df (cn)2 = 6.5 x 10-6 cm2 s l.

In their analysis Holmes et al. demonstrated that the spiral length is limited by heat transfer (see Fig. 24.5). The fluid entering the cavity solidifies upon contact with the wall, resulting in a reduced cross section for flow. This freezing on the wall continues until the solid layers meet in the centre of the channel, stopping the flow. In the tip of the spiral a core of liquid is left which freezes after the flow has stopped. This core solidifies stress-free and is optically isotropic, whereas the rest of the spiral solidifies under stress and is birefringent. 

E = p-type "channel stop for p-well intra-well (E and inlet-well P) field isolation. 

I n-well ( tub Jetructuro contains PMOS transistors. J - n-type channel stop for n-wel I i nira-weti J) and inter-well (J ) field insolation. 

Figure 8. Fast, sensitive ac resistance bridge (a) single-channel stopped-flow, I msec at 0.1 m°C sensitive (b) differential bridge.

In Figure 5-la is shown a schematic representation of a silicon MOSFET (metal-oxide-semiconductor field effect transistor). The MOSFET is the basic component of silicon-CMOS (complimentary metal-oxide-semiconductor) circuits which, in turn, form the basis for logic circuits, such as those used in the CPU (central processing unit) of a modern personal computer [5]. It can be seen that the MOSFET is isolated from adjacent devices by a reverse-biased junction (p -channel stop) and a thick oxide layer. The gate, source and drain contact are electrically isolated from each other by a thin insulating oxide. A similar scheme is used for the isolation of the collector from both the base and the emitter in bipolar transistor devices [6],... 

Figure 15. Ion implantation used for channel stopping. (Adapted with permission from Reference 27, copyright 1983, John Wiley and Sons).

A very low power condition might appear trivial in a normal machine if the power decreases too much, it is made to rise again by the dedicated controls but in a nuclear reactor and especially in a RBMK, this is not so. Besides the reluctance of any reactor to increase power after a reduction, due to some isotopes which slow the chain reaction down and which are produced precisely in these transients, in an RBMK at low power the steam production in the channels stops and they fill up with water. As described earlier, the nuclear power level tends to decrease even more (the typical instabUity of RBMKs). 

Cq thus increases as the well fills up and W decreases. Before the well fills up, if (2ee5N ) /Co <(KG), then the oxide capacitance will be much larger than the depletion layer capacitance and (f) will track Vq. For this reason lightly doped material and thin gate oxide layers ( 1000 A) are needed. Examination of (6.1) also shows that barriers can be permanently built into the device by varying and/or by changing the oxide thickness (which changes C ). These techniques are used to form channel stops to define the CCD channel and can also be used to provide the built-in barriers necessary for two-phase CCD operation. 

FIGURE 7.25 A high performance n channel MOSFET. The device is isolated from its neighbors by a surrounding thick field oxide under which is a heavily doped channel stop implant intended to suppress accidental channel formation that could couple the device to its neighbors. The drain contacts are placed over the field oxide to reduce the capacitance to the body, a parasitic that slows response times. These structural details are described later. Source After Brews, J.R. 1990. The submicron MOSFET. In High-Speed Semiconductor Devices, ed. S.M. Sze, pp. 139 210. Wiley, New York.)... 

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