Applications of amorphous silicon devices

from which a current density in the on-state of about 10 A cm is estimated. 

There is presently no complete explanation of how the device works. There is evidently a reversible structural change in the filament, which may have as its origin either the high field, high current flow, or local heating. Crystallization of the filament has been ruled out for several reasons - for example this would not give a reversible effect. 

Many applications of a-Si H have been proposed or are under development, and it is impossible to describe them all here. Almost all the applications depend on the ability to deposit a-Si H in a large area. The next few years will tell which of the suggestions prove to be viable and marketable. The following is not intended to be a complete list, but rather an illustration of some different possibilities. 

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Commercialization of amorphous silicon solar cells started in 1980 when Sanyo introduced calculators powered only by small solar-cell panels (total area 5 cm2). Shortly thereafter, Fuji Electric also started producing a-Si H solar cells for calculators. As of 1983, a-Si H photovoltaic devices are produced for several other applications such as photodetectors, power supplies for watches, and NiCd battery chargers. Before the end of 1984 one may see a-Si H solar panels used in larger-scale applications such as irrigation and remote electrification. 

The DC characteristics of the organic transistors were measured in air prior to the application of the rnbber pressnre sensor lihn. The field-effect mobility is 1.4 cmWs in the saturation regime. The on/off ratio is 10 if the off current is defined as the minimum drain current at Vqs = h-40 V, while it is 10 if the off current is measured at Vqs = 0 V. The mobility of the present device is comparable to or slighdy larger than that of amorphous silicon ( 1.0 cmWs). 

While amorphous silicon TFT sulfers from low electronic performance, it is very flexible in application and manufacturing. One important advantage is that amorphous Si can be deposited at temperatures as low as 75°C. This makes it possible for the device to be made not only on glass, but also on plastics. In addition, amorphous silicon can be deposited over very large areas by plasma-enhanced chemical vapor deposition (PECVD) with standard industrial equipments. Both features make mass-scale production of amorphous silicon TFT-based devices relatively easy and economic. The main application for amorphous silicon TFT is on liquid crystal displa (LCDs), in which each pixel is individually driven by a TFT transistor. 

To achieve high performance. Various attempts have been made from a practical point of view to attain good transport and optical performance. In particular, if the mobility of the molecular thin-film devices exceeds that of amorphous silicon (the level of 1 cm /Vs), potential feasibility in industrial applications (especially, the display technology) is very large. 

Methods of Deposition of Hydrogenated Amorphous Silicon for Device Applications... 

Over the past decades the term device quality has come to refer to intrinsic PECVD hydrogenated amorphous silicon that has optimum properties for application in a certain device. Of course, depending on the type of device, different optimum values are required nevertheless the properties as listed in Table I are generally accepted, e.g. [6, 11]. Many of these properties are interrelated, which has to borne in mind when attempting to optimize only one of them. 

Methods of Deposition of Hydrogenated Amorphous Silicon for Device Applications Wilfried G. J. H. M. van Sark, Debye Institute, Utrecht University, NL-3508 TA Utrecht, The Netherlands... 

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