How Transistors Work

Transistors are devices that control the movement of electrons, and consequently, electricity. They work something like a water faucet -- not only do they start and stop the flow of a current, but they also control the amount of the current. With electricity, transistors can both switch or amplify electronic signals, letting you control current moving through a circuit board with precision.

The transistors made at Bell Labs were initially made from the element germanium. Scientists there knew pure germanium was a good insulator. But adding impurities (a process called doping) changed the germanium into a weak conductor, or semiconductor. Semiconductors are materials that have properties in-between insulators and conductors, allowing electrical conductivity in varying degrees.

The timing of the invention of transistors was no accident. To work properly, transistors require pure semiconductor materials. It just so happened that right after World War II, improvements in germanium refinement, as well as advances in doping, made germanium suitable for semiconductor applications.

Depending on the element used for doping, the resulting germanium layer was either negative type (N-type), or positive type (P-type). In an N-type layer, the doping element added electrons to the germanium, making it easier for electrons to surge out. Conversely, in a P-type layer, specific doping elements caused the germanium to lose electrons, thus, electrons from adjacent materials flowed towards it.

Place the N-type and P-type adjacent to each other and you create a P-N diode. This diode allows an electrical current to flow, but in only one direction, a useful property in the construction of electronic circuits.

Full-fledged transistors were the next step. To create transistors, engineers layered doped germanium to make two layers back to back, in a configuration of either P-N-P or N-P-N. The point of contact was called a junction, thus the name junction transistor.

With an electrical current applied to the center layer (called the base), electrons will move from the N-type side to the P-type side. The initial small trickle acts as a switch that allows much larger current to flow. In an electric circuit, this means that transistors are acting as both a switch and an amplifier.

These days, in place of germanium, commercial electronics use silicon-based semiconductors, which are more reliable and more affordable than germanium-based transistors. But once the technology caught on, germanium transistors were in widespread use for more than 20 years.

Transistors work primarily as switches and amplifiers. Given those functions, it's no surprise that sound-related devices were the first commercial products to use transistors. In 1952, transistorized hearing aids hit the market. These were niche products, though, compared to transistor radios that emerged in 1954. Radios exposed manufacturers and consumers alike to the revolutionizing potential of transistors.

The function of transistors in radios is straightforward. Sounds are recorded through a microphone and turned into electrical signals. Those signals travel through a circuit, and the transistor amplifies the signal, which is subsequently much louder when it reaches a speaker.

Convincing manufacturers that this basic concept would work on mass-produced products, however, wasn't such a simple task. In 1954, transistors were proven but novel electronic components. Device manufacturers had been using vacuum tubes profitably for many years, so they were understandably leery about switching to transistors.

But Pat Haggerty, vice president at a company called Texas Instruments, was convinced that transistors were going to revolutionize the electronics industry. Texas Instruments used Bell Labs' breakthroughs in germanium transistors to develop a small, pocket-sized transistor radio, with the help of a small Indiana company named IDEA. Together, the two companies created a radio called the Regency TR-1, which was announced on Oct. 18, 1954.

From start to finish, the race to create the TR-1 required innovative new parts that would fit inside a pocket-sized case, which would be small enough to really capture the world's attention. The speaker, capacitors, and other components were created just for this project. The transistors, though, were what really made the project possible.

Texas Instruments devised processes for mass-producing transistors for their radios, and in the process, proved that transistors and their subsequent products could be affordable, more portable and more effective than vacuum tubes. Within a year, other companies, such as Emerson, General Electric and Raytheon, all began selling transistor-based products. The modern electronics boom had begun.

Once mass-produced transistorized hearing aids and radios became realities, engineers realized that transistors would replace vacuum tubes in computers, too. One of the first pre-transistor computers, the famous ENIAC (Electronic Numerical Integrator and Computer) weighed 30 tons, thanks in part to its more than 17,000 vacuum tubes. It was obvious that transistors would completely change computer engineering and result in smaller machines.

Germanium transistors certainly helped start the computer age, but silicon transistors revolutionized computer design and spawned an entire industry in California's aptly-named Silicon Valley.

In 1954, George Teal, a scientist at Texas Instruments, created the first silicon transistor. Soon after, manufacturers developed methods for mass-producing silicon transistors, which were cheaper and more reliable than germanium-based transistors.

Silicon transistors worked wonderfully for computer production. With smart engineering, transistors helped computers power through huge numbers of calculations in a short time. The simple switch operation of transistors is what enables your computer to complete massively complex tasks. In a computer chip, transistors switch between two binary states -- 0 and 1. This is the language of computers. One computer chip can have millions of transistors continually switching, helping complete complex calculations.

In a computer chip, the transistors aren't isolated, individual components. They're part of what's called an integrated circuit (also known as a microchip), in which many transistors work in concert to help the computer complete calculations. An integrated circuit is one piece of semiconductor material loaded with transistors and other electronic components.

Computers use those currents in tandem with Boolean algebra to make simple decisions. With many transistors, a computer can make many simple decisions very quickly, and thus perform complex calculations very quickly, too.

Computers need millions or even billions of transistors to complete tasks. Thanks to the reliability and incredibly small size of individual transistors, which are much smaller than the diameter of a single human hair, engineers can pack an unfathomable number of transistors into a wide array of computer and computer-related products.

In the 1960s and 1970s, transistorized products mostly used the fundamental junction transistor design developed by Bell Labs. Advances in silicon development in the 1970s led to metal oxide semiconductor field effect transistors (MOSFET). MOSFETs utilize the same principles as other transistors, but the N- and P-types of silicon are less expensive, are arranged differently and are doped with other types of metals and oxides, depending on the intended use.

There are many other transistor types, too. Engineers categorize transistors by their semiconductor material, application, structure, power ratings, operating frequencies and other variables. As technology advanced, engineers learned that they could manufacture many transistors simultaneously, on the same piece of semiconductor material, along with other components like capacitors and resistors.

The result is what's called an integrated circuit. These circuits, usually called just "chips," contain billions of infinitesimal transistors. Since the 1960s, the number of transistors per unit area has been doubling every 1.5 years, meaning engineers can cram more of them into smaller and smaller products.

Modern silicon commercial transistors may be smaller than 45 nanometers in size. They're so small that NVDIA's new graphics card (codenamed GF100) has more than 3 billion transistors, the most ever jammed into one chip. And these transistors are behemoths compared to what's coming in the future.

Scientists from Yale and South Korea recently created the world's first molecular transistor, which is made from a single benzene molecule. Although the tiny size is amazing, engineers stress that they're not concerned so much with bulk as they are efficiency. Contemporary chips create a lot of wasted heat because their transistors don't pass along energy as efficiently as product makers would like; molecular transistors may hold the key to improving efficiency in big ways.

Transistor materials are changing, too, thanks to recent advances in a material called graphene. Graphene transfers electrons much faster than silicon, and could lead to computer processors that are 1,000 times faster than silicon-based products.

No matter where development goes, it's certain that transistors will continue to drive product research and technological advances we can't yet even begin to imagine. Computers will become faster, cheaper and more reliable. Cell phones and music players will shrink to super-tiny dimensions, and still cost less than previous models.

That's the power of transistors in altering the landscape of technology, and ultimately, of our society as a whole. Not a bad run for a simple device invented more than 60 years ago.