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What is Transistor and How Does IT Work

This paper will mainly introduce the exact meaning of transistors and their detailed history and working principle. Transistor is a kind of solid semiconductor device, which has many functions, such as detection, rectification, amplification, switching, voltage stabilization, signal modulation and so on. As a variable current switch, the transistor can control the output current according to the input voltage. Unlike conventional mechanical switches, such as relays and relays, transistors use telecommunication signals to control their switching on and off, and the switching speed can be very fast, reaching over 100 GHz in the laboratory. In 2016, Lawrence Berkeley National Laboratory broke through. Physical limit, which reduces the most complex transistor process from 14nm to 1nm, has made a breakthrough in computing technology.

What is Transistor

Transistors are semiconductor devices, usually used in amplifiers or electronic switches. Transistors are the basic components that regulate the operation of computers, mobile phones and all other modern electronic circuits.

Because of its high response and high precision, transistors can be used for a variety of digital and analog functions, including amplifiers, switches, regulators, signal modulation and oscillators. Transistors can be packaged independently or in a small area to accommodate parts of 100 million or more transistor integrated circuits. Strictly speaking, transistors refer to all single elements based on semiconductor materials, including diodes, transistors, field effect transistors, thyristors and so on, which are made of various semiconductor materials. Transistors mainly refer to crystal triodes. Transistors fall into two main categories: bipolar transistors (BJT) and field effect transistors (FET).

Transistors have three poles: bipolar transistors have three poles: N-type and P-type: emitter, base and collector; field effect transistors have three poles: source, gate and drain. Because of the three polarities of transistors, there are also three ways to use them: grounded emitter (also known as common emitter amplifier/CE configuration), grounded base (also known as common base amplifier/CB configuration) and grounded collector (also known as common collector) to set amplifier/CC configuration/emitter coupler.

The History of Transistor

Where did the emergence of transistors begin? It’s a long story. I’ll start with the invention of the telephone. Many people have different opinions as to who actually invented the first usable electrical prototype; however, there is no dispute that Alexander Graham Bell obtained his first patent 3 on March 7, 1876, and subsequently founded the American Telephone and Telegraph Corporation (aka AT&T). Around 1894, Bell’s patent expired. Although AT&T dominated the telephone market from the beginning to the early 20th century, AT&T customers were constantly snatched away by other newly established companies. Therefore, AT&T is aware of the need to continue to control and expand the telephone market. In 1909, Theodore Vail 1, president of AT&T, wanted to make telephone transmissions across the mainland (New York to California). But to do this, they need high-quality amplifiers or repeaters to enhance long-distance transmission of signals. As early as 1906, Lee De Forest borrowed from John A. Fleming’s work (Fleming invented a vacuum tube device called “oscillator” based on Thomas Edison’s work to detect radio waves) and improved it to produce a triode, an inefficient three-terminal amplifier. Subvacuum tube. In 1912, Harold Arnold of Western Electric Company (AT&T manufacturer) invited Forest to show off his invention. Although Forest’s transistor can work at low voltage, Arnold needs a transistor to work at higher voltage in order to make a repeater that can transmit sound over long distances effectively. Arnold thought he could make better transistors, so he hired scientists to study how the device works and how it could be improved. In October 1913, he succeeded. Soon afterwards, telephone lines began to be installed on a large scale. AT&T has hired top scientists for many years to do various kinds of research. Investments in this area have made it realize that in-depth research can give them competitive advantages. So in 1925, Bell Telephone Laboratory was established.

Tens of thousands of vacuum tubes and relays are needed to keep the telephone line running properly. However, the vacuum tube has high power consumption, large volume and often burns out. Mervin Kelly, research director at Bell Laboratories, drew inspiration from the technological development of crystal rectifiers (for radar enablement) during World War II. He felt that the answer to creating a component to replace expensive and unreliable vacuum tubes might lie in semiconductors (a solid-state device). Kelly found William Shockley, one of the best physicists in the lab, and explained to him his ideas on improving the components that transmit sound over the wire. Kelly said it would be a great pleasure to have a noisy mechanical relay and a high-power vacuum tube replaced by a solid-state electronic device. This idea has always been in Sockley’s mind and has become his main goal. Kelly put Shockley in charge of finding ways to implement the idea.

Although he is an outstanding theorist, he is not good at turning his ideas into reality. Shockley has tried many times to prove his theory, that is, to stimulate the plates above the semiconductor through the field effect electron transfer theory, so as to connect the two sides of the semiconductor. He failed. In frustration, he sought help from two other physicists at Bell Laboratory, John Bardeen (proficient in semiconductor electronics) and Walter Brattain (good at prototyping and using laboratory equipment). Then they joined his team. Shockley agreed that the two men would form a team to conduct their own research. Over the years, they have tried many times to realize the field effect theory, but all failed. They examined the results carefully and found that they should be feasible in theory. Later, Bardeen and Brattain broke the stereotype and experimented with silicon and germanium sheets in an attempt to make the field effect work. In the autumn of 1947, when Brattain encountered the difficulty of condensation water on the surface of semiconductors, the experiment took a turn for the better. Instead of drying the water, he dripped water on the top of the silicon and stimulated the upper plate, finally observing the amplification effect. Water droplets help to solve the problem of surface barriers and thus help to form electron streams, but the effect is too small to clearly amplify the sound signal to the extent needed to transmit sound.

In December 1947 (known as Miracle Month), they came up with the idea of eliminating field effect gaps, removing water, and making gold contacts to contact semiconductors. They switched to germanium, which was easier to handle at the time, and insulated it with a naturally formed thin oxide film. However, many subsequent experiments were unsuccessful. By mid-December, Walter Brattain accidentally washed off the oxygen coating, making the gold contacts directly exposed to germanium! Succeed!!! He observed a good amplification effect, and the transistor worked. Instead of pulling electrons onto the surface of semiconductors as Shockley’s field effect theory assumes, Brattain/Bardeen found that by contacting semiconductors with gold contacts, they injected holes into semiconductors to achieve current flow. Around mid-December 1947, they began working prototypes without Shockley’s knowledge. Brattain finds a triangular plastic sheet, wraps gold foil around the bevel edge of the plastic sheet, and opens a slit in its triangular vertex. This is a very original prototype design. They made springs from paper clips to press triangular plastic sheets into thin germanium semiconductors above thin copper sheets, each with a lead at each end. If desired, the copper plate under the germanium sheet can be used as the third lead (Fig. 7). Finally, a prototype called a point contact transistor is made.

Brattain and Bardeen call Shockley and tell him the good news. My research shows that Shockley was in a complicated mood. On the one hand, he was happy with the success of the experiment, but disappointed that he did not create it directly. On December 23, 1947, a week after the breakthrough was discovered, they presented it to Shockley’s supervisor (publicly announced on June 30, 1948). Later, photographs were taken to commemorate this historic moment (Figure 8). Shockley knows that point contact transistors are fragile and difficult to go into industrial production, so he (alone) does his best to improve them. Shockley worked hard and tried to solve the problem in his own way… By layering semiconductor materials, he makes transistors more integrated and records ideas in the process. He did a lot of more research, and eventually completed the theory, and applied for a patent for junction transistors (June 25, 1948). Functional NPN junction transistors were introduced on April 20, 1950 (with the help of Gordon Teal and Morgan Sparks). Details of this history go far beyond your imagination.

On December 10, 1956, William Shockley, John Bardeen and Walter Brattain won the Nobel Prize for the invention of transistors.

How Does a Transistor Work

We will take the NPN transistor as an example to illustrate the working principle of the transistor. To understand how such components operate as switches, it is simple to imagine water flowing through a valve-controlled pipe. The water pressure represents “voltage” and the flow through the pipe represents “current” (fig. 3). The large water pipe represents the collector/launcher junction, separated by valves in the middle. The valves in the figure are represented by gray ellipse, like a moving baffle, which is actuated by the water flow in the small water pipe representing the base pole. The valve maintains the water pressure from the collector to the emitter. When water flows through smaller pipes (base poles), the valves between collector and emitter junctions will be opened to allow water to flow through emitter poles to the ground (the ground represents all water or voltage/current loops).

npn transistor operation
npn transistor operation

The diagram illustrates the working principle of transistors in a graphical way. When the water flows through the small water pipe (base), the valve between the collector and emitter junction will be opened to let the water flow through the emitter to the ground.

Examples of transistor circuits

The circuit example shown in Figure below is to bias the transistor by exciting the base to open the assembly or applying a 5 V voltage to the base through a sliding switch to turn it on. This example will light up the LED used as a load. When biasing the base, the resistor should be used correctly to prevent overcurrent. I used lead parts in the test board to test my example circuit. Most engineers use surface mounted components (much smaller than the TO-92 package size) when they use transistors in new product designs to be marketed. The links here will show the various package sizes of 3904 transistors.

Since 2N3904 is a NPN transistor, the base needs a positive bias (appropriate voltage level and resistance) to turn on the assembly to obtain the appropriate current. In addition, the use of load resistors (R1) is also important, so that there will be no excessive current passing through the LED and transistor. For more information on this transistor, see the 2N3904 specification.

transistor circuit
transistor circuit

Examples of 2N3904 circuit using EG1218 sliding switch to light up LED include C (collector), E (emitter) and B (base) pins (graphics drawn with Scheme-it).

Select transistors for your applications

If you just want to turn on the circuit or load, you should consider the following points. Determine whether you want to bias or excite transistor switches through positive or negative currents (i.e., NPN or PNP types, respectively). NPN transistors are driven (or turned on) by a positive current biased at the base to control the current from the collector to the emitter. The PNP transistor is driven by a negative current biased at the base to control the current from the emitter to the collector. (Note that the polarity of PNP is opposite to that of NPN.) After determining the bias voltage, the next variable required is the voltage and current required for the load to work. These variables will be the minimum rated voltage and current of the transistor. Table 1 and 2 below provide some common transistors and their main specifications, including their voltage and current limitations.

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