A transistor is a 3-terminal semiconductor/solid state device (Balkanski & Wallis, 2000). In a 3-terminal device, the electric voltage or electric current between two terminals can be controlled by applying an electric voltage or current on the third terminal. The capability of having three terminals is what makes a transistor ideal for making voltage or current amplifiers that are common in most of the electronic devices of the modern age. Another area where the transistor has found application is in the making of electronic switches which in turn can be controlled by other switches. These switches can then be cascaded to form complex logic circuits used in the modern day digital electronics. Such logic circuits have the ability to be built compact on a silicon chip that has more than one million transistors per square centimeter (Theraja, 2004). By switching these transistors on and off every 0.000000001 seconds, complex calculations and instructions can be performed.
The semiconductor transistor is not the first electronic device that was invented. It was preceded first by an era of vacuum tubes. It was not the first device to have three terminals. The semiconductor device was preceded by the vacuum tube triode by almost fifty years (Michael, 2001). This vacuum had a vital role in the manufacture of home electronics as well as important role in the areas of scientific discoveries and technical inventions and innovations which formed the firm foundation of modern day electrical and electronic technology. Thomas Edison incorporated vacuum tubes into his light bulbs. He placed a third electrode in the vacuum tube and observed that there were cathode rays on the filament of the bulb. This formed the grounds for cathode ray tube by Joseph J. Thompson in the late 1890s and was rewarded with the Nobel Prize in Physics for his discovery of electrons in 1906. With physicists unraveling the mysteries behind the cathode rays, engineers were employing these technologies to come up with functional electronic devices. Lee De Forest, an American physicist and inventor, came up with a vacuum triode and named it audion that enabled him to develop an amplifier for audio signals which paved way for the development of amplitude modified (AM) radio possible, which revolutionized the field of information and entertainment.
The vacuum tubes also formed basis for the early computers. Various computer designs incorporated vacuum tubes and the best remembered is the ENIAC, which meant Electrical Numerical Integrator And Calculator. This mammoth machine was developed in the year 1946 by John Mauchy partnering with John Eckert (Mccartney, 2001). It was sponsored by the American military since they army needed a computer for ballistic calculations. To make this computer, 17,468 vacuum tubes, around 70,000 resistors and about 10,000 capacitors, 6,000 manual switches all connected logically using over five million soldiered joints. The entire computer covered an area of 167m2 with a gross weight of thirty tons and was powered with 130 kilowatts of electrical power. However, due to the increased demands for computational speed as well as need to produce computers that had economic space, the vacuum tubes limit was reached. Designing of electrical circuits became extremely complex and there was the need for engineers to come up with compact designs. Another disadvantage of vacuum tubes is that they were susceptible to electrical leaks and there was frequent burnout of the tubes and the same time they consumed excessive electrical power.
In 1947, scientists found out that by making two contacts to be close to each other in a semiconductor, they could make a three terminal device, which was the first “point contact” transistor. These transistors were quickly incorporated into audio amplifiers, and these devices did not heat up and neither did they require warming up like the vacuum tubes. This type of transistor was invented by Bardeen and Brattain, and together with William Shockley, they were awarded with the Nobel Prize in Physics in the year 1956 for their research work on semiconductors and the discovery of the transistor effect (Klooster, 2009). The junction transistor was born which was built on thin slices of semiconductor device and was easier to theoretically understand, design and develop with high degree of reliability. In earlier applications, the junction transistors were incorporated as individual components to the circuit board in addition to capacitors, resistors, diodes inductors and other electrical components. Their advantage was that they were smaller than the vacuum tubes and their power consumption was minimal. Complex, faster switching devices were now possible to come up with. However, the limits of this circuit construction technique became evident. Circuits became extremely large and extremely difficult to construct as there were very many components to be dealt with. The solution was to pack as many transistors into a single pack, which was to be known as the integrated circuit (IC). The designers achieved this by making several transistors from the same semiconductor wafer and the packaged to either dual inline packages (DIP) (Tummala & Rymaszewski, 1997), for instance. This revolutionized electronics which faced an exponential growth with development of micro chips and micro-controllers used in personal computers and in robotics. As result of the IC, Gordon Moore, an early pioneer and co-founder of Intel Corporation was awarded the 2000 Nobel Prize in Physics.
An integrated device on dual inline package
Working/Use of the Transistor
The transistor device enables it to function as a switch or amplifier, which is accomplished by using small amount of electrical current or voltage to control a gate that has a larger supply of electrical current or voltage (Balkanski & Wallis, 2000). The figure below shows a simplified transistor.
A transistor is made up of three major parts, the base, collector and the emitter. The base is usually the device that controls the gate for the large voltage or current supply. The collector receives the large supply while the emitter acts as the outlet for the regulated supply. The base terminal is used to send varying control voltage or current which in turn regulates the amount of voltage or current flowing through the gate from the collector to the emitter. Therefore, small amount of electricity can be used to control/regulate large amounts of electricity thus enable the transistor to function as an amplifier. Using the same technique, binary codes can be derived from the transistor, but only this time there the gate is either opened or shut-off. The transistor that acts as a digital switch is made way that the gate is opened by a predetermined voltage, which is usually at +5V and allow voltage to pass through the gate from collector to the emitter. A transistor at this state is said to be ON, and as long as the base current remains +5V, the state remains. When the base current falls to zero, the gate is closed (Shut-off) and no voltage flows through the gate from the collector to the emitter. The transistor at this state is said to be OFF. Using clock cycles, the ON-OFF property for the transistor develops the unique binary codes that are foundation of the modern digital electronics.
Advantages and Disadvantages of Transistor
The transistor represents a huge milestone in the area of electronics. Resulting from a man’s desire to conquer the world through technology during the WWII, the transistor completely replaced the vacuum tubes. This is because the transistor semiconductor transistor had many advantages compared to their predecessors. The size of the transistor is small and compact. This means that the many transistors can fit into a single chip which allows ease in placement into printed circuit boards (PCBs). The reduction in size has also enabled production of devices that are small and very powerful in comparison to mammoths like the ENIAC. With reduction in size came also reduction in weight. Transistors weigh less making even devices made of them much lighter compared to the vacuum tube devices. Transistors did not require warming out heat therefore their function is instant unlike vacuum tubes that had to wait until heated so that they could function. This has saved precious processing time. Another thing about heat is that transistors do not dissipate a lot of heat in comparison to vacuum tubes and therefore do not require complex cooling systems (Singh & Agnohotri, 2009). A transistor attached to a small fin heat sink can be mounted onto a densely populated circuit board and remains functional for a long time. Transistors also consume less power as most of their operations are regulated within +5V or -5V levels. They are also durable and hardy unlike the vacuum tubes that are susceptible to blow out or even break when accidently dropped. Programming transistor devices such as microcontrollers are very easy in comparison to vacuum tubes. However, these advantages may come with a high cost for higher processing power integrated circuits. Another disadvantage is that if a transistor blows inside an integrated circuit, the whole IC has to be plucked off, of which is a difficult task to achieve in densely populated circuit boards (Singh & Agnohotri, 2009).
It can be seen that transistors brought an enormous change into the way of building electronic devices. Transistors are found almost in each electronic component ranging from simple toys, to voltmeters, to cell phones and even to super computers, all which take pride in the advantages of the transistor.