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Transistors: Building Blocks to A Space Age and Beyond

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History: From Trans-resistance to Transistors

The vacuum tube-based thermionic triode in the early 1900s allowing amplified radio and telephone technology was impractical due to its fragility; in the absence of discovery of semiconductors at the time, a transistor was academically conceptualized by Lilienfeld, but not reduced to practice. The 1947 discovery at AT&T’s Bell Labs by Bardeen and Brattain, noting that two gold point contacts applied to a germanium crystal resulted in amplification of the input power. Thereafter, William Shockley used semiconductors and the John Pierce-transformation of “transresistance” to derive “transistor.” Rather than the field effect transistor conceptualized by Lilienfeld, this point-contact transistor invented by Shockley, Bardeen, and Brattain was awarded the 1956 Nobel Prize in physics.

These times heralded a series of firsts in transistors – (1) Philco’s high-frequency transistor using Indium sulfate to etch depressions into N-type germanium base leading to the first all-transistor car radio in 1955 (Philco/Chrysler), (2) silicon transistor (Bell Labs, 1954 by Tanenbaum), and (3) the first commercial silicon transistor by Texas Instruments (Teal, 1954).

Modern-day history continues, as we know, with many of our modern-day gadgets incorporating millions if not billions of such transistors.

Present-day Transistor Use

Present-day use of transistors is widespread, with about 20 transistors used in a typical logic gate function, and as many as 3 billion transistors used in a microprocessor (with upto 4 billion envisioned by some on a processor). The transistor can be used as either an amplifier or a “switch” based upon other circuit elements. Two types of transistors – a bipolar (with base, collector, and emitter) and field-effect (with gate, source, and drain) exist, with each considered separately: (1) as a switch, the voltage between collector and emitter reaches zero upon saturation such that current flows preferentially to the load (e.g. light bulb) switching it on – alternatively, with loss of current the switch may be turned off in an amplified manner, hence acting as a switch with either on or off settings; (2) as an amplifier, using a similar principle, small changes in input voltage result in large changes in output voltage – used in sound, radio, and other signal processing amplification.

The B-C-E structure (base, collector, emitter) allows for different theoretical models for transistors (covered to some extent under our article on semiconductors, also under www.RavishOnTechnology.com) — these allow P-channel or N-channel designs, with compounds such as germanium, silicon, gallium, silicon carbide, and other materials used (with a doping discussion also included under our previously noted semiconductor article).

Significant advances in transistors include benefits such as smaller size (typically as part of integrated circuits), low operating voltages requiring smaller batteries, near-instant function, long life (>50 years in many cases), and this should be weighed against disadvantages such as sensitivity to radiation (e.g. when used on spacecrafts).

Different types of transistors serve different functions, and these have included bipolar junction transistors (BJTs), low-input-impedance devices – with higher transconductance, and hence able to be made to conduct by light exposure. Absorption by photons in the base region results in photocurrent (acting as base current), with collector current a multiple (beta, the common-emitter current gain) of the photocurrent (with such phototransistor devices using a transparent window for light). Field Effect Transistors (FETs) connect the source region to the drain region; metal oxide semiconductor FETs (or MOSFETs) have become popular in integrated circuit use – as voltage regulators, amplifiers, and drivers for motors.

Transistor Future

The June, 2014 news of 2-dimensional field effect transistors using silicon “suffered no performance drop-off under high voltages and provided high electron mobility… even when scaled to a monolayer thickness” per the Berkeley Lab Researchers quoted in the University of California article. At other universities (e.g. University of Texas at Austin and Northwestern University), an alternative proposed to silicon, named PVDF-TrFE on a single-walled carbon nanotube, transistors and ring oscillator circuits were shown to have superior results to impurities-attributed slowing. These use graphene, which has also been explored by Rice University among others, as previously detailed.

Perhaps the greatest realizations of transistors as one of the leading inventions of the 20th century can be found in both their widespread use in all from computers to spaceships, and constant miniaturization which continues to occur. True to Moore’s law that has held through the decades, transistors keep being able to be reduced in size with more powerful functionality being incorporated into smaller spaces (and hence smaller computers). More recently, research on purification adds to the efficiency, and some of these realizations to our practical everyday life may include ability to use iPhones or Android phones with greater battery life, having even thinner/lightweight microcomputers, and other conveniences. Transistors represent yet another example of how an advance in the highly specialized field of electronics and electrical engineering has resulted in everyday use by many of us who don’t have a clue how transistors work, but are glad they do.

(Information above has been acquired from numerous sources, including www.pbs.org, www.newscenter.lbl.gov(Berkeley Lab), www.wikipedia.org, www.phys.org, and others)