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The Transistor
The transistor is perhaps the most important component in modern electronics and enables the logic of our computers. Based on an electric signal it allows or disallows the passage of a second electric signal, acting like a switch that can be open or closed based on a signal.

The transistor replaced vacuum tubes in mainstream technology in the late 1950s [1] and has been the primary (and pretty much only) method of electrical control in technology since.

Origins and Creation
Vacuum Tubes were originally devised as a way to precisely detect small electrical signals [2]. When provided with power, they will allow current through just like a transistor does, but are comparatively bulky and error-prone. They were used in computation technology well before transistors became mainstream, but limited the minimum size of the computers due to their bulk. They were also notoriously unreliable, and needed regular maintenance. Though they have been for the most part supplanted by their cheaper, smaller, faster replacement the transistor, vacuum tubes are still used for large voltages and currents, where the transistor's size works against it.

The first working transistor was created in Bell labs by a group consisting of William Shockley, John Bardeen, and Walter Brattain [1]. The first "point-contact" transistor they created was based on the signal detectors present in the radios of the time, where a fine wire was placed in contact with a galena crystal [1]. This was error-prone and imprecise due to poor points of contact, as was the transistor based on it, though they used germanium instead of galena [1]. That issue was solved in the next iteration, the "bipolar" transistor where instead of wires, small plates were connected to the semiconductor [1]. This solved the contact problem and made the result reliable enough to put into production [1].

Germanium, however, had problems with temperature that prevented it's use in many situations [3]. This was fixed in the early 1950s, when doped silicon became the material of choice for semiconductor manufacturers [3].

How it Works
The transistor allows or disallows current to flow through it using semiconductors. As stated in their name, semiconductors can insulate or conduct electricity based on the presence or absence of carrier particles, usually electrons [5]. These particles are usually injected during fabrication through doping, but that is not for dynamic transmission or denial. Instead, the semiconductor is doped to add lots of electrons which are then moved around by an electric field [5]. When the electrons form a linear region connecting two electrodes, the current may flow, but when that line is broken, the electricity cannot travel. The electric field is created by building up charge on a metal plate using power supplied by the control signal. if the control signal is on, the plate is charged, the field is present and electrons can flow, and vice versa [5].

The digital logic applications are a product of manipulating both the input and control signals. When both signals are on, the current is present and can flow, creating a signal at the other end [5]. If the input is on, but the control is not, the current is present but cannot flow, and if input is off and control is on (or off), there is no current to flow. The ouput signal is only on when both the input and control signals are on, forming the logical "&" operation [5].

Significance
Vacuum tubes and transistors in a very real way allowed the birth of digital logic, the basis for nearly all modern technology. They allowed electronics, to a certain extent, to make decisions instead of relying on a manual switch or dial for every little thing. The first (room-sized) computers were built with vacuum tubes and performed simple arithmetic, which is quite a leap from modern day smartphones with orders of magnitude more processing power. This drastic miniaturization was permitted only by the invention of the transistor [4].

The vacuum tube may have birthed digital logic, but the transistor was the first solid state logic element, meaning that it was a single part rather than a collection of pieces. Solid state devices, both in general and here specifically, are much less subject to manufacturing and assembly precision due to not having any pieces smaller than the whole, and not needing assembly at all [4]. This meant that the could be made smaller more easily, and while the first transistor might have been the size of a finger, modern versions are ten atoms wide [4].

Citations Go Here
[1] Watkins, Thayer. "History of the Transistor." History of the Transistor. N.p., n.d. Web. 22 Jan. 2017. .

[2] Barbour, Eric. "We carry over 7,800 different vacuum tubes, in Stock!" How Vacuum Tubes Work. N.p., n.d. Web. 22 Jan. 2017. .

[3] Riordan, Michael. "The Lost History of the Transistor." IEEE Spectrum: Technology, Engineering, and Science News. !EEE Spectrum, 30 Apr. 2004. Web. 22 Jan. 2017. .

[4] "100 Years of Innovation: The Transistor." The Huffington Post. The Huffington Post, 16 May 2012. Web. 22 Jan. 2017. .

[5] "SparkFun Inventor's Kit - V3.2." Learn at SparkFun Electronics. SparkFun, n.d. Web. 22 Jan. 2017. .