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How exactly does a semiconductor chip work?

2024-02-29 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > IT Information >

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Shulou(Shulou.com)12/24 Report--

In the last article (for Xiaobai's chip semiconductor science popularization), Xiao Zaojun introduced some basic knowledge of chip semiconductor.

In today's article, we continue to talk about the birth of chips-from vacuum tubes and transistors to integrated circuits, from BJT, MOSFET to CMOS, how chips develop and work.

█ vacuum tube (electron tube) Edison effect in 1883, the famous inventor Thomas Edison (Thomas Edison) observed a strange phenomenon in an experiment.

At that time, he was testing the life of the filament (carbon filament). Next to the filament, he placed a copper wire, but the copper wire was not connected to any electrode. In other words, the copper wire is not electrified.

After the carbon wire is energized normally, it begins to glow and heat. After a while, Edison turned off the power. He inadvertently discovered that an electric current was also generated on the copper wire.

Edison could not explain the reason for this phenomenon, but as a shrewd "businessman", the first thing he thought of was to patent the discovery. He also named this phenomenon the "Edison effect".

Now we know that the essence of the Edison effect is the emission of hot electrons. In other words, after the filament is heated, the electrons on the surface become active and "escape", resulting in being captured by the copper wire, resulting in an electric current.

After applying for a patent, Edison did not think of the use of this effect, so he put it on the shelf.

In 1884, British physicist John Ambrose Fleming (John Ambrose Fleming) visited the United States to meet with Edison. Edison showed Fleming the Edison effect and left a deep impression on Fleming.

It will be more than a decade before Fleming diodes actually use this effect.

In 1901, Galilmo Marconi (Guglielmo Marconi), the inventor of wireless telegraphy, launched a long-distance radio communication experiment across the Atlantic. Fleming joined the experiment to help study how to enhance the reception of wireless signals.

To put it simply, it is to study how to detect and amplify the signal at the receiving end, so that the signal can be interpreted perfectly.

Everyone knows how to amplify the signal, so what is the detection signal?

The so-called signal detection is actually signal screening. The signals received by the antenna are very messy and there are all kinds of signals. The signal we really need (the signal with a specified frequency) needs to be "filtered" from these messy signals, which is detection.

Unidirectional conductivity (unidirectional conductivity) is the key to realize detection.

Wireless electromagnetic waves are high-frequency oscillations with frequencies as high as hundreds of thousands of times per second. The induced current generated by wireless electromagnetic waves also changes with the "positive, negative, positive and negative". If we use this current to drive headphones, one positive and one negative is zero, the headphones will not be able to accurately identify the signal.

With unidirectional conductivity, the negative half cycle of the sine wave is gone, all are positive, and the current direction is the same. After filtering out the high frequency, the headset can easily sense the change of current.

Without the negative half-cycle, the direction of the current becomes consistent and easy to interpret. In order to detect the signal, Fleming thought of the "Edison effect"-- could a new type of geophone be designed based on the electron flow of the Edison effect?

In this way, in 1904, the world's first vacuum electronic diode was born under Fleming's hands. At that time, the diode was also called "Fleming valve". Vacuum tubes, vacuum tube, or electronic tubes, are sometimes called "bile ducts". )

Fleming's diode, Fleming's diode, has a very simple structure: a vacuum glass bulb stuffed with two poles: a cathode (Cathode) that emits electrons after heating (cathode ray), and an anode (Anode) that can receive electrons.

The reason why there is a vacuum in the glass tube of the side-heating diode is to prevent gas ionization, affect the normal electron flow and destroy the characteristic curve. Vacuum can also effectively reduce the oxidation loss of the filament. )

The emergence of transistor diodes solved the needs of detection and rectification, which was a major breakthrough at that time. However, there is room for improvement.

De Forrest 1906, the American scientist de Forrest (De Forest Lee) in the vacuum diode, skillfully added a grid ("grid"), invented the vacuum Triode tube.

When the gate is added to the Triode invented by de Forrest, when the voltage of the gate is positive, it attracts more electrons emitted by the cathode. Most of the electrons pass through the grid and reach the anode, which will greatly increase the current on the anode.

If the voltage of the gate is negative, the electrons on the cathode will have no power to go to the gate, let alone the anode.

A small change in the current on the gate can cause a great change in the current of the anode. Moreover, the variation waveform is completely consistent with the gate current. Therefore, the Triode has the function of signal amplification.

At first, the transistor was a single gate, then it became a double gate sandwiched between two boards, and then it simply became a whole enclosed fence.

The birth of grid vacuum Triode is a milestone in the field of electronic industry.

This small component really realizes the use of electricity to control electricity (in the past, it is controlled by mechanical switches, which has the problems of low frequency, short life, and easy to be damaged), and uses "small current" to control "large current".

It integrates the functions of detection, amplification and oscillation, which lays a foundation for the development of electronic technology.

Based on it, we have more and more powerful radio stations, radios, gramophones, movies, radio stations, radar, radio intercom and so on. The widespread popularity of these products has changed people's daily life and promoted social progress.

Vacuum tube in 1919, Schottky in Germany proposed the idea of adding a curtain grid between the gate and the positive. This idea was realized by England's Lund in 1926. This was later known as the Tetrode. Later, Holst and Tellegen in the Netherlands invented the pentode.

In the 1940s, computer technology research entered the most exciting part. It has been found that the unidirectional conduction characteristics of electron tubes can be used to design some logic circuits (such as and gate circuits, or gate circuits).

So they began to introduce electronic tubes into the field of computers. At that time, almost all electronic computers, including ENIAC (which used more than 18000 tubes), were based on tubes.

Eniak, let's talk briefly about the door circuit here.

When we learn the basics of computers, we must have learned basic logical operations, such as and, OR, no, XOR, XOR, and so on.

The computer only knows 0 and 1. Its calculation is based on these logical operation rules.

For example, 2-1, which is 0010-0001 in binary, does an XOR operation, which is equal to 0011, that is, 3.

The circuit that realizes the functions of these logic gates is the logic gate circuit. The unidirectional conductive electron tube (vacuum tube) can be formed into a variety of logic gate circuits.

For example, "OR gate circuit" and "and gate circuit" below.

With the rapid development and application of A, B as input and F as output █ transistor transistor, people gradually find that this product has some disadvantages:

On the one hand, the electronic tube is easy to be damaged and the failure rate is high; on the other hand, the electronic tube needs to be heated and a lot of energy is wasted on heating, which also brings high power consumption.

So, people begin to wonder if there is a better way to detect, rectify and amplify the circuit.

Of course there are ways. At this time, a great material is about to appear, that is, semiconductors.

The green shoots of semiconductors we continue to move forward to the earlier 18th century.

In 1782, the famous Italian physicist Alessandro Volt (Alessandro Volta), after the summary of experiments, found that solid matter can be roughly divided into three types:

The first, metals such as gold, silver, copper and iron, conduct electricity easily and are called conductors.

Second, materials such as wood, glass, ceramics, mica, etc., are not easy to conduct electricity and are called insulators.

The third, between the conductor and the insulator, will discharge slowly.

Because of the bizarre properties of the third material, Volt named it "Semiconducting Nature", that is, "semiconductor properties". This is the first time in human history that the term "semiconductor" appears.

Alessandro Volt later, a number of scientists, intentionally or inadvertently, discovered some semiconductor properties. For example:

In 1833, Michael Michael Faraday discovered that the resistance of silver sulphide decreases as the temperature increases (the thermosensitive properties of semiconductors).

In 1839, French scientist Alexander Becquerel (Alexandre Edmond Becquerel) discovered that light can cause a potential difference between the two ends of some materials (the photovoltaic effect of semiconductors).

In 1873, Willoughby Smith found that the conductivity of selenium materials increased under the irradiation of light (the photoconductive effect of semiconductors).

At that time, no one could explain these phenomena, nor did they attract much attention.

In 1874, German scientist Karl Braun (Karl Ferdinand Braun) discovered the unidirectional current conduction characteristics of natural ores (metal sulfides). This is a huge milestone.

Carl Braun 1906, American engineer Greenleaf Whitler Picard (Greenleaf Whittier Pickard), based on brass ore crystals, invented the famous ore geophone (crystal detector), also known as the "cat beard geophone" (the geophone has a probe on it, much like a cat's beard, hence its name).

Ore geophone is the earliest semiconductor device of human beings. Its appearance is a "small test knife" of semiconductor materials.

Although it has some defects (poor quality control, unstable work, because the ore purity is not high), it has strongly promoted the development of electronic technology. At that time, radio receivers based on ore geophones promoted the popularization of broadcasting and wireless telegraphy.

With the advent of theory, people use ore geophones, but they still don't understand how they work. Over the next 30 years, scientists pondered repeatedly why there were semiconductors. Why can semiconductors conduct electricity in one direction?

In the early days, many people even wondered whether semiconductor materials really existed. Famous physicist Pauli once said: "people should not study semiconductors, it is a dirty mess, who knows if there are semiconductors."

Later, with the birth and development of quantum mechanics, the theoretical research of semiconductors finally made a breakthrough.

In 1928, Max Planck (Max Karl Ernst Ludwig Planck), a German physicist and one of the founders of quantum mechanics, put forward the solid energy band theory for the first time in the application of quantum mechanics to the study of metal conductivity.

Planck, the father of quantum theory, believes that under the action of external electric field, semiconductor conduction can be divided into "hole" participating conduction (i.e. P-type conduction) and electron-participating conduction (i.e. N-type conduction). Many of the strange properties of semiconductors are determined by holes and electrons.

Later, the band theory was further improved and formed, systematically explaining the essential differences between conductors, insulators and semiconductors.

Let's take a brief look at the theory of energy.

We have learned in high school physics that objects are made up of molecules and atoms, and the outer layer of atoms is electrons.

When the atoms of a solid object get close together, electrons will mix together. According to quantum mechanics, electrons cannot stay on one track and will "crash". As a result, the orbit split into several thin orbits.

In quantum mechanics, this kind of fine orbit is called energy level. The wide orbits formed by multiple thin orbits squeezed together are called energy bands.

Of the two energy bands, the lower one is the valence band, the upper one is the conduction band, and the middle one is the forbidden band. There is a forbidden band between the valence band and the conduction band. The distance of the band gap is the band gap (band gap).

When electrons move in a wide orbit, they conduct electricity macroscopically. There are too many electrons, so they are too crowded to move. Macroscopically, they do not conduct electricity.

Some full orbits are very close to the empty orbits. electrons can easily run from the full orbits to the empty orbits and move freely. This is the conductor.

The two orbitals are too far apart and the gap is too large for electrons to run through, so there is no way to conduct electricity. However, if you add an energy from the outside, you can change this state.

If the band gap is within 5 electron volts (5ev) and an extra energy is added to the electron, the electron can complete the leapfrog and move freely, that is, conduction occurs. This belongs to semiconductors. The band gap of silicon is about 1.12eV and that of germanium is about 0.67eV. )

If the band gap exceeds 5 electron volts (5ev), under normal circumstances, electrons cannot cross, so they belong to insulators. If the outside world adds a lot of energy, it can also be forcibly helped to cross the past. For example, air is an insulator, but high voltage can also break through air and form an electric current. )

It is worth mentioning that the "wide band gap semiconductors" we often hear about are the third generation semiconductors including silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), diamond, aluminum nitride (AlN) and so on.

They have the advantages of large band gap (> 2.2ev), high breakdown electric field, high thermal conductivity, strong radiation resistance, high luminous efficiency and high frequency, and can be used in high temperature, high frequency, anti-radiation and high power devices.

We mentioned electrons and holes earlier. There are two kinds of carriers in semiconductors: free electrons and holes. Free electrons are familiar to everyone, but what is a hole?

The hole is also called Electron hole.

At room temperature, due to thermal motion, a small number of high-energy electrons at the top of the valence band may cross the forbidden band and rise to the conduction band to become "free electrons".

After the electron runs away, it leaves a "hole". The rest of the unpromoted electrons can enter the "hole" and generate electricity. Note that the hole itself is motionless, but the hole "filling" process produces a positive electric flow effect, so it is also regarded as a kind of carrier.

In 1931, British physicist Charles Wilson (Charles Thomson Rees Wilson) put forward the physical model of semiconductors on the basis of energy band theory.

In 1939, the Soviet physicist. Davydov, Neville Mott, a British physicist, and Walter Hermann Schottky, a German physicist, all contributed to the basic theory of semiconductors. Davydov first recognized the role of minority carriers in semiconductors, while Schottky and Mott put forward the famous "diffusion theory".

Based on the contributions of these leaders, the basic theory building of semiconductors has been gradually laid.

After the birth of the transistor ore geophone, scientists found that the performance of this geophone has a great relationship with the purity of the ore. The higher the purity of the ore, the better the performance of the geophone.

Therefore, many scientists have studied the purification of ore materials (such as lead sulfide, copper sulfide, copper oxide, etc.), and the purification process has been continuously improved.

In the 1930s, Russell Shoemaker Ohl, a scientist at Bell Labs, proposed that geophones made of purified crystal materials would completely replace electronic diodes. You know, electronic tubes were absolutely dominant in the market at that time. )

Russell Orr, the father of modern solar cells, has tested more than 100 materials one by one, and he believes that silicon crystals are the ideal material for making geophones. To test his conclusion, he extracted a high-purity silicon crystal fusion with the help of his colleague Jack Skaff.

Because Bell Labs did not have the ability to cut silicon crystals, Orr sent the fusion to a jewelry store and cut it into crystal samples of different sizes.

Unexpectedly, one of the samples showed positive electrode (positive) at one end and negative electrode (negative) at the other end after illumination. Orr named them P region and N region respectively. In this way, Orr invented the world's first semiconductor PN junction (PMI N Junction).

During World War II, Western Electric, a subsidiary of AT&T, made a number of silicon diodes based on purified semiconductor crystals. These diodes are small in size and low in failure rate, which greatly improves the performance and reliability of the allied radar system.

Orr's invention of PN junctions and the excellent performance of silicon diodes have strengthened Bell Labs' determination to develop transistor technology.

In 1945, William Shockley (William Shockley) of Bell Labs, after communicating with Russell Orr, drew the band diagrams of P-type and N-type semiconductors based on the energy band theory, and on this basis, put forward the "field effect hypothesis".

Shockley's field effect assumes that the internal charge of the silicon wafer can move freely. if the wafer is thin enough, electrons or holes in the wafer will emerge on the surface under the influence of applied voltage, greatly improving the electrical conductivity of the wafer. In order to achieve the effect of current amplification.

According to this idea, on December 23, 1947, John Bardeen and Walter Bratton of Bell Labs made the world's first semiconductor transistor amplifier. This is the following thing that looks very strange and crude:

The world's first transistor (based on germanium semiconductors)

The circuit model of the transistor according to the experimental records, this transistor can achieve "voltage gain of 100, power gain of 40, current loss of 1 to 2.5." Oh, the performance was excellent.

At the time of naming, Bardeen and Bratton believe that the device can amplify the signal because of its resistance transformation characteristics, that is, from "low resistance input" to "high resistance output". So they named it trans-resistor (conversion resistor). Later, it was abbreviated to transistor.

Many years later, Qian Xuesen, a famous scientist in China, translated it into Chinese as transistor.

Let me sum up that the semiconductor property is a special conductive ability (subject to external factors). Materials with semiconductor properties are called semiconductor materials. Silicon and germanium are typical semiconductor materials.

Microscopically, substances arranged neatly according to certain rules are called crystals. Silicon crystal has single crystal, polycrystal, amorphous crystal and other forms.

The crystal morphology determines the energy band structure, and the energy band structure determines the electrical properties. Therefore, as a semiconductor material, silicon (germanium) crystal has such great application value.

Diodes, transistors and transistors are named functionally. Electron tubes (vacuum tubes), transistors (silicon transistors, germanium transistors) are named in principle.

The transistor invented by Bardeen and Bratton should actually be called a point contact transistor. As can be seen from the picture below, this design is too crude. Although it achieves the amplification function, it has a fragile structure, is sensitive to external vibration, is not easy to manufacture, and does not have the ability of commercial application.

Shockley saw this defect and began to work on a new transistor design. On January 23, 1948, after more than a month of efforts, Shockley proposed a new transistor model with a three-layer structure, which is called junction transistor (Junction Transistor).

Shockley's Junction Transistor Design

It was Morgan Spark and Gordon Kidd Teal who helped Shockley complete the final product.

I need to talk about this Gordon Thiel in particular.

He found that replacing polycrystals with single crystal semiconductors can lead to significant performance improvements. Moreover, he also found that the Czochralski method can be used to purify metal single crystals. This method has been used since then, and it is the most important single crystal fabrication method in the semiconductor industry.

The birth of transistors is of great significance to the development of human science and technology.

It has the ability of electronic tube, but it overcomes all the shortcomings of large volume, high energy consumption, low magnification, short life and high cost. From the moment it was born, it was decided that it would fully replace the electron tube.

In the field of wireless communication, transistors, like electronic tubes, can emit, detect and amplify electromagnetic waves. In the field of digital circuits, transistors can also realize logic circuits more easily. It lays a solid foundation for the take-off of the electronics industry.

Later, the emergence of █ integrated circuit transistors, a growing family of transistors, makes it possible for circuits to be miniaturized.

In 1952, Jeff Geoffrey Dummer, a famous scientist at the Royal Radar Research Institute, pointed out at a conference:

"with the advent of transistors and the comprehensive study of semiconductors, it seems conceivable that electronic devices in the future will be solid components without connecting wires."

In August 1958, Kilby, a new employee of Texas Instruments, discovered that tiny microcircuits made up of many devices could be made on a single chip. In other words, different electronic devices (such as resistors, capacitors, diodes and transistors) can be made on silicon wafers and connected by thin wires.

Soon after, on September 12, based on his own idea, Kilby successfully produced a germanium chip circuit that is 16 inches long and 16 inches wide, which is also the first integrated circuit (Integrated Circuit) in the world.

The circuit is a single transistor oscillator with RC feedback, which is glued to the glass carrier and looks very simple. The devices of the circuit are connected by messy thin wires.

While Kilby invented the integrated circuit, another person also made a breakthrough in this field. This man is Robert Norton Noyce of Fairchild Semiconductor (Fairchild), who later founded Intel Intel.

Xiantong is a company co-founded by the "eight traitors" in Silicon Valley (see Legend of Fairy Child for details), which has a strong strength in semiconductor technology.

One of the eight traitors, Jean-Ahmed Horney (Jean Hoerni), invented the very important graphic process (Planner Process).

In this process, a layer of silicon oxide is added to the silicon wafer as an insulating layer. Then, a hole is made in this layer of insulating silicon oxide and an aluminum film is used to connect the devices that have been made by silicon diffusion technology.

The birth of planar technology enables Xiantong to produce very small size high-performance silicon transistors and makes it possible to connect devices in integrated circuits.

On January 23, 1959, Noyce wrote in his work notes:

"by making all kinds of devices on the same silicon wafer and connecting them with a planar process, you can create a multi-functional electronic circuit. this technology can reduce the size, weight and cost of the circuit."

When Noyce learned that Kilby had submitted the integrated circuit patent, Noyce was very remorseful and thought he was too late. However, he soon discovered that Kilby's invention was flawed.

Kilby's integrated circuits are connected by flying wires, which simply cannot be produced on a large scale and lack of practical value.

Noyce's vision is:

All the circuits and components of an electronic device are made into a negative plate and then engraved on a silicon wafer. Once this silicon wafer is engraved, it is all the circuits and can be directly used to assemble the product. In addition, the way of evaporating and depositing metal can replace the hot welding wire and completely eliminate the flying wire.

Xiantong's silicon crystal integrated circuit on July 30, 1959, based on his own idea, Noyce applied for a patent: "Semiconductor device-wire structure".

Strictly speaking, Noyce's invention is closer to the integrated circuit in the modern sense. Noyce's design is based on the silicon substrate plane process, while Kilby's design is based on the germanium substrate diffusion process. Relying on the advantages of Xiantong's silicon technology, Noyce's circuit is indeed more advanced than Kilby.

In 1966, the court finally ruled that the invention of the integrated circuit idea (hybrid integrated circuit) was granted to Kilby, the integrated circuit packaged into a chip (the real integrated circuit) used today. And the invention of the manufacturing process was awarded to Noyce.

Kilby is known as "the inventor of the first integrated circuit", while Noyce is the one who "put forward the theory of integrated circuit suitable for industrial production".

In March 1960, Texas Instruments based on Jack. Kilby's design, officially launched the world's first commercial integrated circuit product-type 502 silicon bistable multi-resonant binary flip-flop, the sales price is 450USD.

After the birth of integrated circuits, the military field was the first to be used (at that time, the most sensitive period of the Cold War).

In 1961, the United States Air Force launched the first computer driven by integrated circuits. In 1962, the Americans used integrated circuits in the guidance system of militia ballistic missiles (Minuteman).

Later, the famous Apollo moon landing program purchased millions of integrated circuits, which made Texas Instruments and Fairchild a lot of money.

The success of the military market has driven the expansion of the civilian market. In 1964, Zenith used integrated circuits in hearing aids, which was the first landing of integrated circuits in the civilian field.

Everyone should be familiar with the story after that. With the joint efforts of materials, processes and processes, the number of transistors in integrated circuits is increasing, the performance continues to improve, and the cost is gradually decreasing. We have entered the era of Moore's Law.

Moore's Law: the number of transistors that can be held on an integrated circuit doubles about every 18 months, and its performance doubles. Large-scale and ultra-large-scale integrated circuits based on integrated circuits pave the way for the emergence of semiconductor storage and microprocessors.

In 1970, Intel released the world's first DRAM (dynamic random access memory) integrated circuit 1103. The following year, they launched the world's first programmable computing chip, Intel 4004, including an arithmetic unit and a controller.

The golden age of IT technology has officially begun.

The evolution of █ transistors let's go back and talk about transistors.

Since the advent of transistors, the shape has undergone many major changes. Generally speaking, it is mainly from bipolar type to unipolar type. Unipolar type, from FET to MOSFET. From a structural point of view, it goes from PlanarFET to FinFET, and then to GAAFET.

Acronyms are a little too much, and they are relatively close, so it is easy to get dizzy. Everybody be patient and look at it one by one.

The junction transistor invented by bipolar and unipolar Shockley in 1948 is called bipolar junction transistor (Bipolar Junction Transistor,BJT) because it uses both hole and electron carriers to conduct electricity.

BJT transistors have two structures: NPN and PNP:

We can see that the BJT transistor is on a semiconductor substrate, making two PN junctions very close to each other. Two PN junctions divide the whole semiconductor into three parts, with the base (Base) in the middle and the emitter (Emitter) and collector (Collector) on both sides.

The working principle of BJT transistor is more complicated, and it is seldom used now, so I won't introduce it much because of the limited space. In essence, the main function of this transistor is to make the collector produce a large current change through a small current change in the base, which has an amplifying effect.

Xiao Zaojun mentioned the logic circuit earlier. The combination of diode and BJT transistor is called DTL (Diode-Transistor Logic) circuit. Later, there were TTL (Transistor-Transistor Logic) circuits built entirely by transistors.

BJT transistor has the advantages of high working frequency and strong driving ability. However, it also has some disadvantages, such as high power consumption and low integration. Its manufacturing process is also complicated, and there are some disadvantages in using plane technology.

So, with the passage of time, a new kind of transistor began to appear, that is, field effect transistor (Field Effect Transistor,FET).

In 1953, Ian Ross of Bell Laboratories collaborated with George George Dacey to produce the world's first prototype of junction field effect transistors (Junction Field Effect Transistor,JFET).

JFET (junction field effect transistor), this is N-channel JFET is a three-pole (three-terminal) structure of semiconductor devices, including the source (Source), drain (Drain), gate (Gate).

JFET is divided into N-channel (N-Channel) JFET and P-channel (P-Channel) JFET. The former consists of two P-type semiconductors made on both sides of an N-shaped semiconductor (pictured above). The latter is a P-shaped semiconductor that makes two N-type semiconductors on both sides.

The working principle of JFET, simply put, is to control the PN junction between gate and channel by controlling the voltage between gate G and source S (VGS in figure) and the voltage between drain D and source S (VDS in figure), thus controlling the depletion layer.

The wider the depletion layer, the narrower the channel, and the higher the channel resistance, the smaller the drain current (ID) that can pass through. The state in which the channel is completely covered by the depletion layer is called the pinch-off state.

When a JFET transistor works, it needs only one kind of carrier, so it is called a monopole transistor.

In 1959, a new kind of transistor was born, which is the famous MOSFET (metal oxide semiconductor field effect transistor).

It was invented by Egyptian scientist Mohamed Atala (renamed Martin Atala) and Korean scientist Dawon Kahng (also translated as Jiang Dayuan).

MOSFET also consists of source, drain and gate. "M" in "MOS" refers to the gate originally realized by metal (metal). "O" means that the gate is isolated from the substrate by oxide (Oxide). "S" means that the whole MOSFET is realized by semiconductor.

MOSFET transistor, also known as IGFET (In-sulated Gate FET, insulated gate field effect transistor).

MOSFET (N type), this kind of MOSFET transistor, is also divided into "N type" and "P type", namely NMOS and PMOS. According to the type of operation, it is also divided into enhanced type and depletion type.

The N-type MOS (more commonly used) in the above figure is taken as an example. Using P-type silicon semiconductor as substrate, two N-type regions were diffused on its surface, and then covered with a layer of silicon dioxide (SiO2) insulating layer. Finally, above the N zone, two holes are made by etching. Three electrodes are made on the insulating layer and in two holes by metallization: G (gate), S (source) and D (drain).

The P-type silicon substrate has a terminal (B) connected to the source S by a lead.

How MOSFET works is relatively simple:

Normally, a neutral depletion region is formed between the N region and the substrate P because of the natural recombination of carriers.

After supplying the positive voltage to the gate, the electrons in the P region will gather under the gate silicon oxide under the action of the electric field, forming a region with electrons as many carriers, that is, a channel.

Now, if a voltage is applied between the drain and the source, the current will flow freely between the source and the drain to achieve the conduction state.

The gate G is similar to a gate that controls the voltage. If a voltage is applied to the gate G, the gate opens and the current can lead from the source S to the drain D. Remove the voltage from the gate, the gate is closed, and the current cannot pass through.

In particular, it should be pointed out that in 1967, Jiang Dayuan co-invented the "floating gate" FGMOS (Floating Gate MOSFET) structure with Chinese scientist Shi Min, which laid the foundation for semiconductor storage technology. Later, all flash memory, FLASH, EEPROM, etc., are based on this technology.

Just now I introduced BJT, JFET and MOSFET. Let me draw a picture first, so don't be confused:

In 1963, Frank of Fairchild Semiconductor. Frank Wanlass and C.T. Sah (Chih-Tang Sah, Chinese) proposed CMOS transistor for the first time.

They combine PMOS and NMOS transistors to form a complementary structure with almost no static current. This is also the origin of "C (Complementary, complementary)" of CMOS transistors.

The most important feature of CMOS is that its power consumption is much lower than that of other types of transistors. With the continuous development of Moore's Law, the number of transistors in integrated circuits is increasing, so the demand for power consumption is also increasing. Based on the characteristics of low power consumption, CMOS began to become the mainstream.

Today, more than 95% of integrated circuit chips are manufactured based on CMOS technology.

In other words, the core architecture of transistors has been basically shaped since the 1960s. The integrated circuit ecology represented by CMOS, silicon (the natural stock of silicon is much more than germanium, and its heat resistance is better than germanium, so it has become the mainstream) and planar technology has supported the rapid development of the whole industry for decades.

Although the core architecture principles of PlanarFET, FinFET and GAAFET have not changed, the shape has changed.

Integrated circuits continue to upgrade, and processes and processes continue to evolve. When the number of transistors reaches a certain scale, the process will force the transistors to "deform" in order to meet the needs of development.

In the early days, transistors were mainly planar transistors (PlanarFET).

As the size of the transistor becomes smaller, the length of the gate becomes shorter and shorter, and the distance between the source and the drain is getting closer.

When the manufacturing process (that is, 7nm, 3nm, generally refers to the width of the grid) is less than 20nm, the trouble arises: the gate of MOSFET is difficult to close the current channel, restless electrons can not be blocked, leakage occurs frequently, and the power consumption becomes higher.

In order to solve this problem, Professor Hu Zhengming, a Chinese-American scientist, formally invented the fin field effect transistor (FinFET) in 1999.

Compared with the graphic design of PlanarFET, FinFET has directly become 3D design and three-dimensional structure.

Its current channel becomes a thin vertical piece like a fin, and all three sides are wrapped in a grid. In this way, there is a relatively strong electric field, which improves the efficiency of the control channel and can better control whether the electrons can pass through.

The technology continues to evolve, and when it comes to 5nm, FinFET is dead. At this time, there is a GAAFET (encircling gate technology transistor).

The English full name of GAAFET is Gate-All-Around FET. In contrast, FinFET,GAAFET turns the gate and drain from fins into "sticks" that pass vertically through the gate.

In this way, from the three contact surfaces to the four contact surfaces, and is also divided into several four contact surfaces, the grid control over the current is further improved.

Samsung of South Korea has also designed another form of GAA, ── MBCFET (multi-bridge-channel field effect transistor).

MBCFET uses multi-layer nanowires to replace the nanowires in GAA, and the wider flake structure increases the contact surface, which not only retains all the original advantages, but also minimizes the complexity.

At present, the major chip companies in the industry are still deeply studying the morphological upgrading of transistors in order to find better innovation and support the development of chip technology in the future.

█ conclusion is good, finally finished, tired to death. All that can be seen here is true love.

Generally speaking, both electronic tubes (vacuum tubes) and transistors are small components that use electricity to control electricity. Transistors are based on semiconductor materials, so they can be made small enough. This is the reason why the chip (integrated circuit) can achieve "very small body, great ability".

The properties of semiconductor materials, as well as the role of transistors, look very simple. It is hundreds of millions of these simple "gadgets" that support the development of the entire digital technology of mankind and propel us into the age of digital intelligence.

In the next issue, Mr. Xiaozao will talk to you again:

How on earth is the chip made?

What do you mean by the IDM mode and Fabless mode that the industry often says?

How on earth are so many transistors in the chip connected?

Please look forward to it!

References:

1. A brief History of Semiconductors, Wang Qi and Fan Shuqin, Machinery Industry Press

2. "what on earth is a chip? "Klaus, Zhihu

3. What is a chip? What is IC? What is a semiconductor? ", in the next Zhang Da Meow, Zhihu

4. "Little chips change our lives", Wei Shaojun

5. "learn about the semiconductor process FinFET together". Brother Shu talks about the core and Zhihu.

6. Baidu encyclopedia, Wikipedia

This article comes from the official account of Wechat: fresh Jujube classroom (ID:xzclasscom), author: Xiaozaojun

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