transistor - Introduction, Importance, History, Types, Usage, Advantages of transistors over vacuum tubes, Gallery, Transistor manufacturers

A solid-state device, made from a sandwich of semiconductors, usually germanium or silicon, with different electrical characteristics (p- and n-type). A p-type (positive) semiconductor is made by adding impurities such as boron or aluminium. An n-type (negative) semiconductor is made by adding arsenic or phosphorous. Transistors can be used as amplifiers or rectifiers. Small, robust, and safe (since they need low voltage), and needing little power to operate, transistors have replaced thermionic valves in television, radio, and computers, and have revolutionized the construction of electronic circuits.

A transistor is a three-terminal semiconductor device that can be used for amplification, switching, voltage stabilization, signal modulation,oscillator and many other functions. The transistor is the fundamental building block of both digital and analog integrated circuits — the circuitry that governs the operation of computers, cellular phones, and all other modern electronics.

Introduction

Transistors are divided into two main categories: bipolar junction transistors (BJTs) and field effect transistors (FETs). Application of current in BJTs and voltage in FETs between the input and common terminals increases the conductivity between the common and output terminals, thereby controlling current flow between them. For more details on the operation of these two types of transistors, see field effect transistor and bipolar junction transistor.

In analog circuits, transistors are used in amplifiers, (direct current amplifiers, audio amplifiers, radio frequency amplifiers), and linear regulated power supplies. Transistors are also used in digital circuits where they function as electronic switches.

Importance

The transistor is considered by many to be one of the greatest inventions in modern history, ranking in importance with the printing press, automobile and telephone.

Although millions of individual (known as discrete) transistors are still used, the vast majority of transistors are fabricated into integrated circuits (often abbreviated as IC and also called microchips or simply chips) along with diodes, resistors, capacitors and other electronic components to produce complete electronic circuits. A logic gate comprises about twenty transistors whereas an advanced microprocessor, as of 2006, can use as many as 1.7 billion transistors (MOSFETs) .

The transistor's low cost, flexibility and reliability have made it a universal device for non-mechanical tasks, such as digital computing.

Because of the low cost of transistors and hence digital computers, there is a trend to digitize information.

History

The first three patents for the field-effect transistor principle were registered in Germany in 1928 by physicist Julius Edgar Lilienfeld, but Lilienfeld published no research articles about his devices, and they were ignored by industry. In 1934 German physicist Dr. Oskar Heil patented another field-effect transistor. The Other Transistor, R. Arns

On 16 December 1947 William Shockley, John Bardeen and Walter Brattain succeeded in building the first practical point-contact transistor at Bell Labs.

Bell Telephone Laboratories needed a generic name for the new invention: "Semiconductor Triode", "Solid Triode", "Surface States Triode", "Crystal Triode" and "Iotatron" were all considered, but "transistor," coined by John R. The rationale for the name is described in the following extract from the company's Technical Memorandum calling for votes:

Transistor.

—Bell Telephone Laboratories — Technical Memorandum (May 28, 1948)

Pierce recalled the naming somewhat differently:

The way I provided the name, was to think of what the device did. The vacuum tube had transconductance, so the transistor would have 'transresistance.' And the name should fit in with the names of other devices, such as varistor and thermistor. I suggested the name 'transistor.'

—John R.

Bell put the transistor into production at Western Electric in Allentown, Pennsylvania. They also licensed it to a number of other electronics companies, including Texas Instruments, who produced a limited run of transistor radios as a sales tool. Early transistors were "unstable" and only suitable for low-power, low-frequency applications, but as transistor design developed, these problems were slowly overcome. Over the next two decades, transistors gradually replaced the earlier vacuum tubes in most applications and later made possible many new devices such as integrated circuits and personal computers.

Shockley, Bardeen and Brattain were honored with the Nobel Prize in Physics "for their researches on semiconductors and their discovery of the transistor effect". Since Bell Labs did not make a public announcement of the transistor until June 1948, the transistron was considered to be independently developed.

Types

Transistors are categorized by:

Semiconductor material: germanium, silicon, gallium arsenide, silicon carbide Structure: BJT, JFET, IGFET (MOSFET), IGBT, "other types" Polarity: NPN, PNP, N-channel, P-channel Maximum power rating: low, medium, high Maximum operating frequency: low, medium, high, radio frequency (RF), microwave (The maximum effective frequency of a transistor is denoted by the term fT, an abbreviation for "frequency of transition". The frequency of transition is the frequency at which the transistor yields unity gain). Application: switch, general purpose, audio, high voltage, super-beta, matched pair Physical packaging: through hole metal, through hole plastic, surface mount, ball grid array

Thus, a particular transistor may be described as: silicon, surface mount, BJT, NPN, low power, high frequency switch.

Bipolar junction transistor

The bipolar junction transistor (BJT) was the first type of transistor to be mass-produced. Bipolar transistors are so named because they conduct by using both majority and minority carriers.

Bipolar transistors can be made to conduct by light, since absorption of photons in the base region generates a photocurrent that acts as a base current;

Field-effect transistor

The field-effect transistor (FET), sometimes called a unipolar transistor, uses either electrons (N-channel FET) or holes (P-channel FET) for conduction.

A voltage applied between the gate and source (body) controls the current flowing between the drain and source.

FETs are divided into two families: junction FET (JFET) and insulated gate FET (IGFET).

MESFETs are JFETs, in which the reverse biased PN junction is replaced by a semiconductor-metal Schottky-junction.

Unlike bipolar transistors, FETs do not inherently amplify a photocurrent.

FETs are further divided into depletion-mode and enhancement-mode types, depending on whether the channel is turned on or off with zero gate-to-source voltage.

Other transistor types

Heterojunction Bipolar Transistor Unijunction transistors can be used as simple pulse generators. They include two or more transistors on a common substrate to ensure close parameter matching and thermal tracking, characteristics that are especially important for long tailed pair amplifiers. Darlington transistors comprise a medium power BJT connected to a power BJT. This provides a high current gain equal to the product of the current gains of the two transistors. Insulated gate bipolar transistors (IGBTs) use a medium power IGFET, similarly connected to a power BJT, to give a high input impedance. Single-electron transistors (SET) consist of a gate island between two tunnelling junctions. Nanofluidic Transistor Control the movement of ions through sub-microscopic, water-filled channels. Nanofluidic transistor, the basis of future chemical processors Trigate transistors (Prototype by Intel) Avalanche transistor Ballistic transistor Electron bounce their way through maze. Spin transistor Magnetically-sensitive Thin film transistor Used in LCD display. Floating gate transistor Used for non-volatile storage. Photo transistor React to light Inverted-T field effect transistor Ion sensitive field effect transistor To measure ion concentrations in solution. FREDFET Fast-Reverse Epitaxal Diode Field-Effect Transistor EOSFET Electrolyte-Oxide-Semiconductor Field Effect Transistor (Neurochip) Quantum transistor Extensive list of transistor types at T-Transistor.com

Semiconductor material

The first BJTs were made from germanium (Ge) and some high power types still are.

Characteristics of the most common semiconductor materials used to make transistors are given in the table below:

Semiconductor material characteristics

Semiconductor material	Junction forward voltage V @ 25 °C	Electron mobility m²/Vs @ 25 °C	Hole mobility m²/Vs @ 25 °C	Max. junction temp. °C
Ge	0.27	0.39	0.19	70 to 100
Si	0.71	0.14	0.05	150 to 200
GaAs	1.03	0.85	0.05	150 to 200
Al-Si junction	0.3	—	—	150 to 200

The junction forward voltage is the voltage applied to the emitter-base junction of a BJT in order to make the base conduct a specified current. The lower the junction forward voltage the better, as this means that less power is required to "drive" the transistor.

The electron mobility and hole mobility columns show the average speed that electrons and holes diffuse through the semiconductor material with an electric field of 1 volt per meter applied across the material. In general, the higher the electron mobility the faster the transistor. However, Ge has four major shortcomings compared to silicon and gallium arsenide:

its maximum temperature is limited it has relatively high leakage current it cannot withstand high voltages it is less suitable for fabricating integrated circuits

Because the electron mobility is higher than the hole mobility for all semiconductor materials, a given bipolar NPN transistor tends to be faster than an equivalent PNP transistor type. This temperature should not be exceeded or the transistor may be damaged.

Al-Si junction refers to the high-speed (aluminum-silicon) semiconductor-metal barrier diode, commonly known as a Schottky diode.

Packaging

Transistors come in many different packages (chip carriers) (see images).

Transistor packages are made of glass, metal, ceramic or plastic. Power transistors have large packages that can be clamped to heat sinks for enhanced cooling. Additionally, most power transistors have the collector or drain physically connected to the metal can/metal plate. At the other extreme, some surface-mount microwave transistors are as small as grains of sand.

Often a given transistor type is available in different packages. Transistor packages are mainly standardized, but the assignment of a transistor's functions to the terminals is not: different transistor types can assign different functions to the package's terminals. Even for the same transistor type the terminal assignment can vary (normally indicated by a suffix letter to the part number- i.e.

Usage

In the early days of transistor circuit design, the bipolar junction transistor, or BJT, was the most commonly used transistor. Even after MOSFETs became available, the BJT remained the transistor of choice for digital and analog circuits because of their ease of manufacture and speed.

Switches

Transistors are commonly used as electronic switches, for both high power applications including switched-mode power supplies and low power applications such as logic gates.

Amplifiers

From mobile phones to televisions, vast numbers of products include amplifiers for sound reproduction, radio transmission, and signal processing. The first discrete transistor audio amplifiers barely supplied a few hundred milliwatts, but power and audio fidelity gradually increased as better transistors became available and amplifier architecture evolved.

Transistors are commonly used in modern musical instrument amplifiers, where circuits up to a few hundred watts are common and relatively cheap. Transistors have largely replaced valves in instrument amplifiers. Some musical instrument amplifier manufacturers mix transistors and vacuum tubes in the same circuit, to utilize the inherent benefits of both devices.

Computers

The "first generation" of electronic computers used vacuum tubes, which generated large amounts of heat and were bulky, and unreliable. The development of the transistor was key to computer miniaturization and reliability. The "second generation" of computers, through the late 1950s and 1960s featured boards filled with individual transistors and magnetic memory cores. Subsequently, transistors, other components, and their necessary wiring were integrated into a single, mass-manufactured component: the integrated circuit. Transistors incorporated into integrated circuits have replaced most discrete transistors in modern digital computers.

Advantages of transistors over vacuum tubes

Before the development of transistors, vacuum tubes (or in the UK thermionic valves or just valves) were the main active components in electronic equipment. The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are:

Smaller size (despite continuing miniaturization of vacuum tubes) Highly automated manufacture Lower cost (in volume production) Lower possible operating voltages (but vacuum tubes can operate at higher voltages) No warm-up period (most vacuum tubes need 10 to 60 seconds to function correctly) Lower power dissipation (no heater power, very low saturation voltage) Higher reliability and greater physical ruggedness (although vacuum tubes are electrically more rugged. Also the vacuum tube is much more resistant to nuclear electromagnetic pulses (NEMP) and electrostatic discharge (ESD)) Much longer life (vacuum tube cathodes are eventually exhausted and the vacuum can become contaminated) Complementary devices available (allowing circuits with complementary-symmetry: vacuum tubes with a polarity equivalent to PNP BJTs or P type FETs are not available) Ability to control large currents (power transistors are available to control hundreds of amperes, vacuum tubes to control even one ampere are large and costly) Much less microphonic (vibration can modulate vacuum tube characteristics, though this may contribute to the sound of guitar amplifiers)

" Nature abhors a vacuum tube " Myron Glass (see John R.

Gallery

A wide range of transistors has been available since the 1960s and manufacturers continually introduce improved types. (On some datasheets the accuracy of the stated transistor category is a matter of debate.)

2N3904/2N3906, BC182/BC212 and BC546/BC556: Ubiquitous, BJT, general-purpose, low-power, complementary pairs. 2N3055/MJ2955: For years, the venerable NPN 2N3055 has been the "standard" power transistor. These 1 MHz, 15 A, 60 V, 115 W BJTs are used in audio power amplifiers, power supplies, and control. Used for logic level conversion and driving power transistors in amplifiers.

Transistor manufacturers

APT Fairchild Semiconductor Infineon Technologies IRF IXYS Corporation ON Semiconductor Panasonic Semiconductors Powerex Rohm Sanyo Transistors Semikron STMicroelectronics Toshiba Semiconductor Zetex Semiconductors

Patents

U.S. Patent 1745175 — Julius Edgar Lilienfeld 1930 U.S. Patent 2524035 — J. Principles of Transistor Circuits. The invention of the transistor & "The other transistor: early history of the metal-oxide semiconducor fielld-effect transistor". Mataré, An Inventor of the Transistor has his moment", The New York Times, 24 February 2003. "How Europe Missed the Transistor".