Wafer (electronics)

In electronics, a wafer is a thin slice of semiconductor, such as a crystalline silicon, used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The wafer serves as the substrate for microelectronic devices built upon the wafer, it undergoes many microfabrication processes, such as doping, ion implantation, thin-film deposition of various materials, photolithographic patterning. The individual microcircuits are separated by wafer dicing and packaged as an integrated circuit. In the 1950s, Mohamed Atalla investigated the surface properties of silicon semiconductors at Bell Labs, where he adopted a new method of semiconductor device fabrication, coating a silicon wafer with an insulating layer of silicon oxide, so that electricity could reliably penetrate to the conducting silicon below, overcoming the surface states that prevented electricity from reaching the semiconducting layer; this is known as surface passivation, a method that became critical to the semiconductor industry as it made possible the mass-production of silicon integrated circuits.

The surface passivation method was presented by Atalla in 1957, was the basis for the metal-oxide-semiconductor process invented by Atalla and Dawon Kahng in 1959. By 1960, silicon wafers were being manufactured in the U. S. by companies such as MEMC/SunEdison. In 1965, American engineers Eric O. Ernst, Donald J. Hurd, Gerard Seeley, while working under IBM, filed Patent US3423629A for the first high-capacity epitaxial apparatus. Wafers are formed of pure, nearly defect-free single crystalline material, with a purity of 99.9999999% or higher. One process for forming crystalline wafers is known as Czochralski growth invented by the Polish chemist Jan Czochralski. In this process, a cylindrical ingot of high purity monocrystalline semiconductor, such as silicon or germanium, called a boule, is formed by pulling a seed crystal from a melt. Donor impurity atoms, such as boron or phosphorus in the case of silicon, can be added to the molten intrinsic material in precise amounts in order to dope the crystal, thus changing it into extrinsic semiconductor of n-type or p-type.

The boule is sliced with a wafer saw and polished to form wafers. The size of wafers for photovoltaics is 100–200 mm square and the thickness is 100–500 μm. Electronics use wafer sizes from 100–450 mm diameter; the largest wafers made are not yet in general use. Wafers are cleaned with weak acids to remove unwanted particles, or repair damage caused during the sawing process; when used for solar cells, the wafers are textured to create a rough surface to increase their efficiency. The generated PSG is removed from the edge of the wafer in the etching. Silicon wafers are available in a variety of diameters from 25.4 mm to 300 mm. Semiconductor fabrication plants, colloquially known as fabs, are defined by the diameter of wafers that they are tooled to produce; the diameter has increased to improve throughput and reduce cost with the current state-of-the-art fab using 300 mm, with a proposal to adopt 450 mm. Intel, TSMC and Samsung are separately conducting research to the advent of 450 mm "prototype" fabs, though serious hurdles remain.

Wafers grown using materials other than silicon will have different thicknesses than a silicon wafer of the same diameter. Wafer thickness is determined by the mechanical strength of the material used; the weight of the wafer goes up along with its diameter. A unit wafer fabrication step, such as an etch step, can produce more chips proportional to the increase in wafer area, while the cost of the unit fabrication step goes up more than the wafer area; this was the cost basis for increasing wafer size. Conversion to 300 mm wafers from 200 mm wafers began in earnest in 2000, reduced the price per die about 30-40%. Larger diameter wafers allow for more die per wafer: There is considerable resistance to the 450 mm transition despite the possible productivity improvement, because of concern about insufficient return on investment. There are issues related to increased inter-die / edge-to-edge wafer variation and additional edge defects. 450mm wafers are expected to cost 4 times as much as 300mm wafers, equipment costs are expected to rise by 20 to 50%.

Higher cost semiconductor fabrication equipment for larger wafers increases the cost of 450 mm fabs. Lithographer Chris Mack claimed in 2012 that the overall price per die for 450 mm wafers would be reduced by only 10–20% compared to 300 mm wafers, because over 50% of total wafer processing costs are lithography-related. Converting to larger 450 mm wafers would reduce price per die only for process operations such as etch where cost is related to wafer count, not wafer area. Cost for processes such as lithography is proportional to wafer area, larger wafers would not reduce the lithography contribution to die cost. Nikon planned to deliver 450-mm lithography equipment in 2015, with volume production in 2017. In November 2013 ASML paused development of 450-mm lithography equipment, citing uncertain timing of chipmaker demand; the timeline for 450 mm has not been fixed. In 2012, it was expected. Mark Durcan CEO of Micron Technology, said in February 2014 that he expects 450 mm adoption to be delayed indefinitely or discontinued.

"I am not convinced that 450mm will happen but, to the extent that it does, it’s a long way out in the future. There is not a lot of necessity for Micr

The Avengers (TV series)

The Avengers is a British espionage television series created in 1961. It focused on Dr. David Keel, aided by John Steed. Hendry left after the first series, his most famous assistants were intelligent and assertive women: Cathy Gale, Emma Peel and Tara King. The series ran from 1961 until 1969; the pilot episode, "Hot Snow", aired on 7 January 1961. The final episode, "Bizarre", aired on 21 April 1969 in the United States, on 21 May 1969 in the United Kingdom; the Avengers was produced by a contractor within the ITV network. After a merger with Rediffusion London in July 1968, ABC Television became Thames Television, which continued production of the series, though it was still broadcast under the ABC name. By 1969, The Avengers was shown in more than 90 countries. ITV produced a sequel series, The New Avengers, with Patrick Macnee returning as John Steed, two new partners. In 2004 and 2007, The Avengers was ranked # 20 on TV Guide's Top Cult Shows Ever; the Avengers was marked by different eras as co-stars went.

The only constant was John Steed, played by Patrick Macnee. Associated British Corporation produced a single series of Police Surgeon, in which Ian Hendry played police surgeon Geoffrey Brent, from September through December of 1960. While Police Surgeon did not last long, viewers praised Hendry, ABC Television cast him in its new series The Avengers, which replaced Police Surgeon in January 1961; the Avengers began with the episode "Hot Snow", in which medical doctor David Keel investigates the murder of his fiancée and office receptionist Peggy by a drug ring. A stranger named John Steed, investigating the ring and together they set out to avenge her death in the first two episodes. Steed asked Keel to partner with him. Hendry was considered the star of the new series, receiving top billing over Macnee, Steed did not appear in two episodes; as the first series of The Avengers progressed, Steed's importance increased, he carried the final episode solo. While Steed and Keel used wit while discussing crimes and dangers, the series depicted the interplay—and tension—between Keel's idealism and Steed's professionalism.

As seen in one of the three surviving episodes from the first series, "The Frighteners", Steed had helpers among the population who provided information, similar to the "Baker Street Irregulars" of Sherlock Holmes. The other regular in the first series was Carol Wilson, the nurse and receptionist who replaced the slain Peggy. Carol assisted Keel and Steed in cases, in at least one episode was much in the thick of the action, but without being part of Steed's inner circle. Hafner had played opposite Hendry as a nurse in one episode of Police Surgeon; the series was shot on 405-line videotape using a multicamera setup. There was little provision for editing and no location footage was shot; as was standard practice at the time, videotapes of early episodes of The Avengers were reused. At present, only three complete Series 1 episodes are known to exist and are held in archives as 16-mm film telerecordings: "Girl on the Trapeze", "The Frighteners" and "Tunnel of Fear". Additionally, the first 15 minutes of the first episode, "Hot Snow" exist as a telerecording.

The missing television episodes are being recreated for audio by Big Finish Productions under the title of The Avengers - The Lost Episodes and star Julian Wadham as Steed, Anthony Howell as Dr. Keel and Lucy Briggs-Owen as Carol Wilson. Production of the first series was cut short by a strike. By the time production could begin on the second series, Hendry had quit to pursue a film career. Macnee was promoted to star and Steed became the focus of the series working with a rotation of three different partners. Dr Martin King, a thinly disguised rewriting of the Keel character, saw action in only three episodes, which were produced from scripts written for the first series. King was intended to be a transitional character between Keel and Steed's two new female partners, but while the Dr. King episodes were shot first, they were shown out of production order in the middle of the season; the character was thereafter and dropped. Nightclub singer Venus Smith appeared in six episodes, she was a complete "amateur", meaning that she did not have any professional crime-fighting skills as did the two doctors.

She was excited to be participating in a spy adventure alongside secret agent Steed. Nonetheless, she appears to be attracted to him, their relationship is somewhat similar to that portrayed between Steed and Tara King, her episodes featured musical interludes showcasing her singing performances. The character of Venus underwent some revision during her run, adopting more youthful demeanor and dress; the first episode broadcast in the second series had introduced the partner who would change the show into the format for which it is most remembered. Honor Blackman played Dr. Cathy Gale, a self-assured, quick-witted anthropologist, skilled in judo and had a passion for leather clothes. Widowed during the Mau Mau years in Kenya, she was the "talented amateur" who saw her aid to Steed's case

Otroeda nerina

Otroeda nerina is a species of moth in the tussock-moth subfamily Lymantriinae. It was first described by Dru Drury in 1782 from Sierra Leone, is found in Cameroon, DR Congo, Gabon and Nigeria. Upper Side. Antennae pectinated and brown. Head brown, the front being white. Thorax brown, with two white streaks along it. Abdomen brown. Wings black, streaked with light brown from the shoulders along the tendons, two light yellowish patches crossing the wings from the anterior edges, with a row of white coloured spots placed along the external edges. Posterior wings dark yellow, with a deep black border running along the external edges from the upper to the abdominal corners. Under Side. Palpi black. Mouth white. Neck and breast yellow. Legs brown, yellow at top, white beneath. Abdomen white, streaked longitudinally with brown. Anus yellow. Wings coloured as brighter. Margins of all the wings entire. Wing-span 3½ inches