Transistors What Are They and How Do They Work

A transistor is an electronic component used in a circuit to control a large amount of current or voltage with a small amount of voltage or current. This means that it can be used to amplify or switch (rectify) electrical signals or power, allowing it to be used in a wide array of electronic devices. It does so by sandwiching one semiconductor between two other semiconductors. Because the current is transferred across a material that normally has high resistance (i.e. a resistor), it is a transfer-resistor or transistor. The first practical point-contact transistor was built in 1948 by William Bradford Shockley, John Bardeen, and Walter House Brattain. Patents for the concept of a transistor date as far back as 1928 in Germany, though they seem to have never been built, or at least no one ever claimed to have built them. The three physicists received the 1956 Nobel Prize in Physics for this work. Basic Point-Contact Transistor Structure There are essentially two basic types of point-contact transistors, the npn transistor and the pnp transistor, where the n and p stand for negative and positive, respectively. The only difference between the two is the arrangement of bias voltages. To understand how a transistor works, you have to understand how semiconductors react to an electric potential. Some semiconductors will be n-type, or negative, which means that free electrons in the material drift from a negative electrode (of, say, a battery its connected to) toward the positive. Other semiconductors will be p-type, in which case the electrons fill holes in the atomic electron shells, meaning that it behaves as if a positive particle is moving from the positive electrode to the negative electrode. The type is determined by the atomic structure of the specific semiconductor material. Now, consider an npn transistor. Each end of the transistor is an n-type semiconductor material and between them is a p-type semiconductor material. If you picture such a device plugged into a battery, youll see how the transistor works: the n-type region attached to the negative end of the battery helps propel electrons into the middle p-type region.the n-type region attached to the positive end of the battery helps slow electrons coming out of the p-type region.the p-type region in the center does both. By varying the potential in each region, then, you can drastically affect the rate of electron flow across the transistor. Benefits of Transistors Compared to the vacuum tubes that were used previously, the transistor was an amazing advance. Smaller in size, the transistor could easily be manufactured cheaply in large quantities. They had various operational advantages, as well, which are too numerous to mention here. Some consider the transistor to be the greatest single invention of the 20th century since it opened so much in the way of other electronic advancements. Virtually every modern electronic device has a transistor as one of its primary active components. Because they are the building blocks of microchips, computer, phones, and other devices couldnt exist without transistors. Other Types of Transistors There are a wide variety of transistor types that have been developed since 1948. Heres a list (not necessarily exhaustive) of various types of transistors: Bipolar junction transistor (BJT)Field-effect transistor (FET)Heterojunction bipolar transistorUnijunction transistorDual-gate FETAvalanche transistorThin-film transistorDarlington transistorBallistic transistorFinFETFloating gate transistorInverted-T effect transistorSpin transistorPhoto transistorInsulated gate bipolar transistorSingle-electron transistorNanofluidic transistorTrigate transistor (Intel prototype)Ion-sensitive FETFast-reverse epitaxal diode FET (FREDFET)Electrolyte-Oxide-Semiconductor FET (EOSFET) Edited by Anne Marie Helmenstine, Ph.D.