Semiconductors and Displays

Components used in the etch environment have to withstand plasma processing with a nnmber of gas chemistries. PAEK can result in cost savings versus materials such as quartz, ceramics, PBI and polyimides. Ultra high-purity polyaryletheretherketone (PEEK) can be used to reduce contamination by metal ions. 

Fabrication facility downtimes can be reduced because there is less need to replace the rings and this leads to substantial cost savings. 

Finally test and burn in sockets must be able to survive the test conditions with a high degree of tolerance and dimensional stahility. ESD grades of PAEK are use together with precision injection moulding for fine connector arrays. Blends of PAEK with amorphous polymers, or less crystalline polymers such as PEKK, can offer a lower tendency to warp and higher dimensional tolerance. 

Examples of semiconductor process applications are given in Table 

Valves and compressors were amongst the earliest applications areas for PAEK. In static applications the temperature and chemical resistance, coupled with excellent mechanical performance make PAEK suitable for a wide range of metal replacement applications such as housings, linings, thrust washers and seals. However, there are also many moving parts which benefit from excellent dynamic fatigue resistance and wear resistance, with or without lubrication, together with dimensional stability and low-cost fabrication. 

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The most commonly used method for resistance measurements, instead, is the four-point probe technique (Valdes, 1954 Uhlir, 1955 Schroeder, 1998), which is a standard characterization method in semiconductor and display industry (metals ASTM, 1996a TCO ASTM, 2(X)2b) both for bulk materials and thin films. This universal and absolute technique uses four separate electrodes to allow an almost current-less voltage... 

The experimental setup for the four-point probe techniques only requires an adequate probe head that satisfies the desired accuracy, which is mainly limited by the mechanical tolerances of the probe spacings, and a digital multimeter with a high input impedance of at least 10 Q. Today, several measurement systems are available on the market, due to their use in the semiconductor and display industries, ranging from a basically manual device to a fully automated system for substrate mapping. 

The highly conductive class of soHds based on TTF—TCNQ have less than complete charge transfer (- 0.6 electrons/unit for TTF—TCNQ) and display metallic behavior above a certain temperature. However, these soHds undergo a metal-to-insulator transition and behave as organic semiconductors at lower temperatures. The change from a metallic to semiconducting state in these chain-like one-dimensional (ID) systems is a result of a Peieds instabihty. Although for tme one-dimensional systems this transition should take place at 0 Kelvin, interchain interactions lead to effective non-ID behavior and inhibit the onset of the transition (6). 

Sihcon is a Group 14 (IV) element of the Periodic Table. This column iacludes C, Si, Ge, Sn, and Pb and displays a remarkable transition from iasulatiag to metallic behavior with increasing atomic weight. Carbon, ia the form of diamond, is a transparent iasulator, whereas tin and lead are metals ia fact, they are superconductors. SiUcon and germanium are semiconductors, ie, they look metaUic, so that a poHshed siUcon wafer is a reasonable gray-toned mirror, but they conduct poorly. Traditionally, semiconductors have been defined as materials whose resistance rises with decreasiag temperature, unlike metals whose resistance falls. 

The apphcation of a high electric field across a thin conjugated polymer film has shown the materials to be electroluminescent (216—218). Until recentiy the development of electroluminescent displays has been confined to the use of inorganic semiconductors and a limited number of small molecule dyes as the emitter materials. Expansion to the broad array of conjugated polymers available gives advantages in control of emission frequency (color) and facihty in device fabrication as a result of the ease of processibiUty of soluble polymers (see Chromogenic materials,electrochromic). 

Figure 1.1. Growth of semiconductor and flat panel display industries. [Data Source Semiconductor industry sales data from Semiconductor Industry Association (SIA) and flat panel display data from Displaysearch Corp, San Jose, CA.]...

The industrial interest in this area is driven for two reasons The first one is the steady miniaturization of semiconductor devices down to sizes for which the bulk properties of inorganic semiconductors reach their limit and molecular approaches become important. The second is the need for materials for the increasing low-cost consumer market that is dominated by identifier tags, plastic chip cards, and displays for cellular phones that are all driven by small electronic or optoelectronic circuits. The materials for these applications should be cheap, easy to make, and, last but not least, be environment-friendly, combustible, or better yet biodegradable. 

Hematite, wiistite, maghemite and magnetite are semiconductors magnetite displays almost metallic properties. For a compound to be a semiconductor, the essential characteristic is that the separation between the valence band of orbitals and the conduction band is less than 5 eV this condition is met for the above oxides. In a semiconductor the Fermi level (i. e. the level below which all electron energy levels are filled) lies somewhere between the valence band and the conduction band. 

Advances in the synthesis and processing of organic molecules and polymers have led to the development of organic semiconductor-based devices that exhibit a multitude of functionalities, e.g., photovoltaics, memory/logic, and displays ... 

Electronic properties semiconductor and metal conductivity, magneto-resistance, emission of electrons, electronic devices of the molecular size, information recording, diodes, field transistors, cold cathodes, materials for displays, quantum wires and dots, cathodes for X-ray radiation, electric probes, etc. 

Electronic materials have already been encountered under imaging (e g., in OPCs) and displays (e.g., in OLEDs). Two areas worthy of further consideration are organic semiconductors and solar cells. 

Fig. 14.1. The first reported active-matrix display with an organic semiconductor. The display contains 64 by 64 pixels and is driven by 4096 polymer TFT, with solution processed PTV as the semiconductor. An image containing 256 gray levels is shown. The display is refreshed at 50 Hz.

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