Source: Fresh Date Classroom
Original Author: Xiaozao Jun
This article describes the birth of chips – from vacuum tubes, transistors to integrated circuits, from BJT, MOSFET to CMOS, how chips have developed and how they work.
█ Vacuum Tubes (Electronic Tubes)
In 1883, the famous inventor Thomas Edison observed a strange phenomenon during an experiment.
At that time, he was testing the lifespan of a 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 was not powered.
When the carbon filament was powered, it began to glow and heat up. After a while, Edison disconnected the power. He accidentally discovered that there was also a current in the copper wire.
Edison could not explain the reason for this phenomenon, but he patented this discovery, naming it the “Edison Effect”.
Now we know that the essence of the “Edison Effect” is thermionic emission. In other words, when the filament is heated, the electrons on its surface become active and “escape”, resulting in a current captured by the copper wire.
After applying for the patent, Edison did not think of any use for this effect, so he shelved it.
In 1884, British physicist John Ambrose Fleming visited the United States and met Edison. Edison showed Fleming the Edison Effect, leaving a deep impression on him.
Fleming
It was not until many years later that Fleming truly utilized this effect.
In 1901, the inventor of wireless telegraphy Guglielmo Marconi started a long-distance radio communication experiment across the Atlantic. Fleming joined this experiment to help study how to enhance the reception of wireless signals.
In simple terms, it was about studying how to detect and amplify signals at the receiving end, allowing the signals to be perfectly interpreted.
Everyone understands amplifying signals, but what is signal detection?
Signal detection is essentially signal filtering. The signals received by the antenna are very chaotic, containing all kinds of signals. The signals we actually need (specific frequency signals) need to be “filtered” out from these chaotic signals, which is detection.
To achieve detection, unidirectional conductivity (unidirectional conduction) is key.
Radio electromagnetic waves oscillate at high frequencies, reaching hundreds of thousands of times per second. The induced current generated by radio electromagnetic waves also changes continuously with “positive, negative, positive, negative”. If we use this current to drive headphones, one positive and one negative equals zero, and the headphones cannot accurately identify the signal.
By using unidirectional conductivity, the negative half of the sine wave is eliminated, leaving only the positive half, making the current direction consistent. After filtering out the high frequency, the headphones can easily sense the changes in current.
Removing the negative half makes the current direction consistent, which is easy to interpret
To detect signals, Fleming thought of the “Edison Effect” – could a new type of detector be designed based on the electron flow of the Edison Effect?
Thus, in 1904, the world’s first vacuum diode was born in Fleming’s hands. At that time, this diode was also called the “Fleming Valve”. (Vacuum tube, also known as electronic tube, is sometimes called “valve tube”.)
The diode invented by Fleming
Fleming’s diode is actually very simple in structure, consisting of a vacuum glass bulb with two electrodes: a cathode (Cathode) that emits electrons when heated (cathode rays) and an anode (Anode) that receives electrons.
Indirectly heated diode
The reason for vacuuming the glass tube is to prevent gas ionization, which would affect normal electron flow and destroy the characteristic curve. (Vacuuming also effectively reduces the oxidation loss of the filament.)
The emergence of the diode solved the needs for detection and rectification, which was a major breakthrough at the time. However, there was still room for improvement.
De Forest
In 1906, American scientist De Forest Lee cleverly added a grid (“gate”) to the vacuum diode, inventing the vacuum triode.
The triode invented by De Forest
After adding the grid, when the grid voltage is positive, it attracts more electrons emitted from the cathode. Most electrons pass through the grid to reach the anode, greatly increasing the current at the anode.
If the grid voltage is negative, the electrons on the cathode have no motivation to reach the grid and will not reach the anode.
A small change in current at the grid can cause a large change in current at the anode. Moreover, the waveform of the change is completely consistent with the grid current. Therefore, the triode has a signal amplification function.
Initially, the triode was single-grid, later it became double-grid with two plates sandwiched together, and eventually evolved into a fully encapsulated structure.
Encapsulated grid
The birth of the vacuum triode was a milestone event in the field of electronic industry.
This small component truly realized the control of electricity by electricity (previously mechanical switches controlled electricity, which had issues of low frequency, short lifespan, and fragility), allowing “small current” to control “large current”.
It integrated detection, amplification, and oscillation functions, laying the foundation for the development of electronic technology.
Based on it, we have increasingly powerful broadcasting stations, radios, phonographs, movies, radio stations, radar, and walkie-talkies. The widespread popularity of these products has changed people’s daily lives and promoted social progress.
Vacuum tubes
In 1919, Germany’s Schottky proposed the idea of adding a screen grid between the gate and the anode. This idea was realized by England’s Lang in 1926. This led to the later development of tetrodes. Later, Dutch scientists Holst and Telegen invented pentodes.
In the 1940s, computer technology research reached its peak. People discovered that the unidirectional conduction characteristics of electronic tubes could be used to design some logic circuits (such as AND gate circuits, OR gate circuits).
Thus, they began to introduce electronic tubes into the field of computing. At that time, almost all electronic computers, including ENIAC (which used more than 18,000 electronic tubes), were manufactured based on electronic tubes.
Here, let’s briefly talk about gate circuits.
When we study the basics of computing, we definitely learn about basic logical operations, such as AND, OR, NOT, XOR, NOR, NAND, etc.
Computers only recognize 0 and 1. Their calculations are based on these logical operation rules.
For example, 2 + 1 is the binary representation of 0010 + 0001, and doing an “XOR operation” equals 0011, which is 3.
The circuits that implement these logical gate functions are called logic gate circuits. The unidirectional conduction electronic tubes (vacuum tubes) can be assembled into various logic gate circuits.
For example, the following “OR gate circuit” and “AND gate circuit”.
A, B are inputs, F is output
While electronic tubes rapidly developed and were applied, people gradually discovered that this product had some drawbacks:
On one hand, electronic tubes are prone to damage and have a high failure rate; on the other hand, they need to be heated to operate, wasting a lot of energy on heat, resulting in high power consumption.
Therefore, people began to think – is there a better way to achieve the detection, rectification, and signal amplification of circuits?
Of course, there is a method. At this time, a great material was about to emerge, which is – semiconductor.
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Emergence of Semiconductors
We continue to move back in time to the earlier 18th century.
In 1782, the renowned Italian physicist Alessandro Volta summarized through experiments that solid materials can roughly be divided into three types:
The first type, like metals such as gold, silver, copper, and iron, conducts electricity easily and is called a conductor;
The second type, like wood, glass, ceramics, and mica, does not conduct electricity easily and is called an insulator;
The third type, which lies between conductors and insulators, discharges slowly.
Volta named the characteristics of this third type of material as “Semiconducting Nature.” This was the first time in human history that the term “semiconductor” appeared.
Later, several scientists, intentionally or unintentionally, discovered some semiconductor characteristic phenomena. For example:
In 1833, Michael Faraday discovered that the resistance of silver sulfide decreases when the temperature rises (thermal sensitivity of semiconductors).
In 1839, French scientist Alexandre Edmond Becquerel discovered that light could generate a potential difference across certain materials (photovoltaic effect of semiconductors).
In 1873, Willoughby Smith discovered that the conductivity of selenium increases when exposed to light (photoelectric effect of semiconductors).
At that time, no one could explain these phenomena, and they did not attract much attention.
In 1874, German scientist Karl Ferdinand Braun discovered the unidirectional conduction characteristics of natural minerals (metal sulfides). This was a significant milestone.
In 1906, American engineer Greenleaf Whittier Pickard invented the famous crystal detector based on the crystal of chalcopyrite, also known as the “cat whisker detector” (the detector has a probe that looks like a cat’s whisker, hence the name).
The crystal detector is the earliest semiconductor device created by humanity. Its emergence was a “small trial” of semiconductor materials.
Although it had some defects (poor quality control, unstable operation due to low purity of minerals), it strongly promoted the development of electronic technology. At that time, radio receivers based on crystal detectors facilitated the popularization of broadcasting and telegraphy.
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Emergence of Energy Band Theory
People used crystal detectors but could never understand their working principle. Over the next 30 years, scientists repeatedly pondered – why do semiconductor materials exist? Why can semiconductor materials achieve unidirectional conduction?
In the early days, many people even doubted whether semiconductor materials really existed. The famous physicist Pauli once stated: “People should not study semiconductors; it is a dirty mess, and who knows if semiconductors exist.”
Later, with the birth and development of quantum mechanics, theoretical research on semiconductors finally made breakthroughs.
In 1928, German physicist Max Karl Ernst Ludwig Planck, one of the founders of quantum mechanics, first proposed the solid energy band theory while applying quantum mechanics to study the electrical conductivity of metals.
Father of Quantum Theory, Planck
He believed that under the influence of an external electric field, semiconductor conductivity is divided into conduction involving “holes” (P-type conduction) and conduction involving electrons (N-type conduction). Many strange properties of semiconductors are jointly determined by “holes” and electrons.
Later, the energy band theory was further improved and systematically explained the essential differences between conductors, insulators, and semiconductors.
Let’s briefly understand the energy band theory.
As we learned in high school physics, objects are composed of molecules and atoms, with electrons in the outer layer of atoms.
In solid objects, atoms are closely packed together, causing electrons to mix together. Quantum mechanics posits that electrons cannot stay in one orbit and will “collide”. Thus, the orbit splits into several finer tracks.
In quantum mechanics, these fine tracks are called energy levels, and multiple fine tracks packed together form a wide energy band.
Among 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. The distance between the valence band and the conduction band is the bandgap (energy band gap).
When electrons move in the wide energy band, it macroscopically manifests as conductivity. When there are too many electrons, they fill the band and cannot move, which macroscopically manifests as non-conductivity.
Some filled and empty bands are very close, allowing electrons to easily jump from filled bands to empty bands, resulting in free movement, which is conduction.
When two bands are too far apart, with a large gap, electrons cannot cross, resulting in non-conductivity. However, if external energy is applied, this state can be changed.
If the bandgap is within 5 electron volts (5eV), providing additional energy to electrons allows them to jump across and move freely, which characterizes semiconductors. (The bandgap of silicon is about 1.12eV, and germanium is about 0.67eV.)
If the bandgap exceeds 5 electron volts (5eV), electrons cannot jump under normal circumstances, characterizing insulators. (If a very high energy is applied externally, it can forcibly help them jump across. For example, air is an insulator, but high voltage can break through the air, forming a current.)
It is worth mentioning that the “wide bandgap semiconductor” we often hear about includes third-generation semiconductor materials such as silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), diamond, and aluminum nitride (AlN).
They have the advantages of wide bandgap (>2.2eV), high breakdown electric field, high thermal conductivity, strong radiation resistance, high luminous efficiency, and high frequency, making them suitable for high-temperature, high-frequency, radiation-resistant, and high-power devices, which is the direction of strong development in the industry.
Earlier, we mentioned electrons and holes. There are two types of carriers in semiconductors: free electrons and holes. Free electrons are familiar to everyone, but what are holes?
Holes are also known as electron holes.
At room temperature, due to thermal motion, a small number of electrons with high energy at the top of the valence band may jump across the bandgap to the conduction band, becoming “free electrons”.
When electrons leave, they leave behind a “hole”. The remaining electrons that have not jumped can enter this “hole”, thus generating current. Note that holes themselves do not move, but the process of electrons filling holes creates the effect of positive charge flow, so they are also considered a type of carrier.
In 1931, British physicist Charles Thomson Rees Wilson proposed a physical model of semiconductors based on energy band theory.
In 1939, Soviet physicist A.S. Davydov, British physicist Nevill Francis Mott, and German physicist Walter Hermann Schottky all contributed to the foundational theory of semiconductors. Davydov was the first to recognize the role of minority carriers in semiconductors, while Schottky and Mott proposed the famous “diffusion theory”.
Based on the contributions of these pioneers, the foundational theory of semiconductors was gradually established.
After the crystal detector was born, scientists found that the performance of this detector was greatly related to the purity of the minerals. The higher the purity of the minerals, the better the performance of the detector.
Therefore, many scientists conducted research on the purification of mineral materials (such as lead sulfide, copper sulfide, copper oxide, etc.), and the purification process was continuously refined.
In the 1930s, scientists at Bell Labs, led by Russell Shoemaker Ohl, proposed that detectors made from purified crystal materials would completely replace electronic diodes. (At that time, electronic tubes were in absolute market dominance.)
Russell Ohl, also known as the father of modern solar cells
After testing over 100 materials, he concluded that silicon crystals were the most ideal material for making detectors. To validate his conclusion, he, with the help of his colleague Jack Scaff, extracted high-purity silicon crystal melt.
Since Bell Labs did not have the capability to cut silicon crystals, Ohl sent this melt to a jeweler to be cut into different sizes of crystal samples.
Unexpectedly, one of the samples, when exposed to light, showed one end as positive and the other as negative. Ohl named them the P region and N region, respectively. Thus, Ohl invented the world’s first semiconductor PN junction (P-N Junction).
During World War II, AT&T’s Western Electric Company manufactured a batch of silicon crystal diodes based on purified semiconductor crystals. These diodes were small, had low failure rates, and greatly improved the performance and reliability of the Allies’ radar systems.
Ohl’s invention of the PN junction, along with the excellent performance of silicon crystal diodes, solidified Bell Labs’ determination to develop transistor technology.
In 1945, William Shockley of Bell Labs, after communicating with Russell Ohl, drew the energy band diagrams of P-type and N-type semiconductors based on energy band theory and proposed the “field effect hypothesis” based on this.
Shockley’s field effect hypothesis
He hypothesized that the internal charges of silicon chips could move freely. If the chip is thin enough, under the influence of applied voltage, electrons or holes within the silicon chip would emerge at the surface, significantly enhancing the conductivity of the silicon chip, thus achieving current amplification.
Based on this hypothesis, on December 23, 1947, John Bardeen and Walter Brattain of Bell Labs created the world’s first semiconductor transistor amplifier. This is the seemingly strange and simple device below:
The world’s first transistor (based on germanium semiconductor)
According to experimental records, this transistor could achieve “voltage gain of 100, power gain of 40, and current loss of 1/2.5…”, performing exceptionally well.
When naming it, Bardeen and Brattain believed that this device could amplify signals due to its resistance transformation characteristics, where the signal goes from “low resistance input” to “high resistance output”. Thus, they named it trans-resistor (transistor). Later, it was abbreviated to transistor.
Years later, renowned Chinese scientist Qian Xuesen established its Chinese name as: 晶体管.
To summarize, semiconductor characteristics represent a special conductive ability (affected by external factors). Materials with semiconductor characteristics are called semiconductor materials. Silicon and germanium are typical semiconductor materials.
At the microscopic level, substances arranged according to certain rules are called crystals. Silicon crystals can have single crystal, polycrystalline, and amorphous forms.
The crystal form determines the energy band structure, and the energy band structure determines the electrical properties. Therefore, silicon (germanium) crystals as semiconductor materials have significant application value.
Diodes, transistors, and tetrodes are named based on their functions. Electronic tubes (vacuum tubes) and transistors (silicon transistors, germanium transistors) are named based on their principles.
The transistor invented by Bardeen and Brattain should actually be called point contact transistor. As seen in the image below, this design is overly simplistic. While it achieved amplification, its structure is fragile and sensitive to external vibrations, making it difficult to manufacture and unsuitable for commercial application.
Shockley recognized this defect and began to research new transistor designs.
On January 23, 1948, after more than a month of effort, Shockley proposed a new transistor model with a three-layer structure, naming it junction transistor.
Shockley’s junction transistor design
Helping Shockley complete the final product was Morgan Sparks and Gordon Kidd Teal.
It is particularly important to mention Gordon Teal.
He discovered that replacing polycrystalline with single crystal could bring significant performance improvements. Moreover, he was the one who discovered that the Czochralski method could be used to purify metal single crystals. This method has been continuously used and is the main method for producing single crystals in the semiconductor industry.
The birth of the transistor has extremely important significance for the development of human technology.
It possesses the capabilities of electronic tubes while overcoming all the disadvantages of electronic tubes, such as large size, high energy consumption, low amplification factor, short lifespan, and high cost. From the moment it was born, it was destined to completely replace electronic tubes.
Workers producing transistors
In the field of wireless communication, transistors, like electronic tubes, can achieve the transmission, detection, and amplification of electromagnetic waves. In the field of digital circuits, transistors can also more conveniently implement logic circuits. They laid a solid foundation for the rapid development of the electronic industry.
The ever-expanding family of transistors
The emergence of transistors made circuit miniaturization possible.
In 1952, renowned scientist Geoffrey Dummer from the British Royal Radar Research established in a meeting:
“With the emergence of transistors and comprehensive research on semiconductors, it now seems conceivable that future electronic devices could be solid components without connecting wires.”
In August 1958, new employee Jack Kilby at Texas Instruments discovered that very small microcircuits composed of many components could be made on a single chip. In other words, different electronic devices (such as resistors, capacitors, diodes, and transistors) could be made on silicon wafers and then connected with thin wires.
Shortly after, on September 12, Kilby successfully created a germanium circuit measuring 7/16 inches by 1/16 inches, which was the world’s first integrated circuit (Integrated Circuit).
This circuit was a single transistor oscillator with RC feedback, all glued onto a glass substrate, looking very rudimentary. The components of the circuit were connected using scattered thin wires.
While Kilby invented the integrated circuit, another person also made breakthroughs in this field. This person was Robert Norton Noyce of Fairchild Semiconductor (who later founded Intel).
Jean Hoerni invented the very important planar process.
This process involves adding a layer of silicon oxide as an insulating layer on the silicon wafer. Then, holes are made in this insulating silicon oxide layer, and the devices made using silicon diffusion technology are connected with aluminum thin films.
The birth of the planar process allowed Fairchild to manufacture extremely small, high-performance silicon crystal transistors and made the connection between devices in integrated circuits possible.
On January 23, 1959, Noyce wrote in his work notes:
“By making various devices on the same silicon wafer and connecting them with planar processes, multifunctional electronic circuits can be created. This technology can reduce the size of circuits, lighten weight, and lower costs.”
Upon learning that Kilby had submitted a patent for the integrated circuit, Noyce felt very regretful, believing he was a step behind. However, he soon discovered that Kilby’s invention actually had defects.
Kilby’s integrated circuit used flying wire connections, which could not be mass-produced and lacked practical value.
To manufacture all the circuits and components on a base plate, and then etch them onto a silicon wafer. Once this silicon wafer is etched, it contains all the circuits that can be directly used for product assembly.In addition, using evaporative deposition of metals can replace thermal welding of wires, completely eliminating flying wires.
Fairchild’s silicon crystal integrated circuit
On July 30, 1959, based on his idea, Noyce applied for a patent for “semiconductor devices – wire structures”.
Strictly speaking, Noyce’s invention is closer to the modern definition of integrated circuits. Noyce’s design is based on silicon substrate planar processes, while Kilby’s design is based on germanium substrate diffusion processes. Noyce’s circuits, made using Fairchild’s silicon process advantages, were indeed more advanced than Kilby’s.
In 1966, the court ultimately ruled that the invention rights of the idea of integrated circuits (hybrid integrated circuits) were granted to Kilby, while the invention rights of the integrated circuits (in the true sense) that are packaged into a chip and the manufacturing process were granted to Noyce.
Kilby is hailed as the “inventor of the first integrated circuit”, while Noyce is recognized as the one who “proposed the theory of integrated circuits suitable for industrial production”.
In March 1960, Texas Instruments officially launched the world’s first commercial integrated circuit product – the 502 silicon bistable multivibrator, selling for $450.
After the birth of integrated circuits, they were first applied in the military field (at that time, it was the most sensitive period of the Cold War).
In 1961, the U.S. Air Force launched the first computer powered by integrated circuits. In 1962, Americans also used integrated circuits in the guidance system of the Minuteman ballistic missile.
Later, the famous Apollo moon landing program purchased over a million integrated circuits, allowing Texas Instruments and Fairchild to reap substantial profits.
The success in the military market spurred the expansion of the civilian market.In 1964, Zenith Company applied integrated circuits to hearing aids, marking the first implementation of integrated circuits in the civilian field.
The subsequent story is familiar to everyone. With the joint efforts of materials, processes, and manufacturing, the number of transistors in integrated circuits continued to increase, performance continued to improve, and costs gradually decreased, leading us into the era of Moore’s Law.
Moore’s Law: The number of transistors that can be accommodated on an integrated circuit doubles approximately every 18 months, and performance also doubles.
The large-scale and ultra-large-scale integrated circuits developed based on integrated circuits paved the way for the emergence of semiconductor storage and microprocessors.
In 1970, Intel launched the world’s first DRAM (Dynamic Random Access Memory) integrated circuit 1103. The following year, they introduced the world’s first programmable logic chip, which included an arithmetic unit and a controller – the Intel 4004.
The golden age of IT technology officially began.
█ Evolution of Transistors
Looking back, transistors have undergone several significant changes since their invention. In summary, they have shifted from bipolar to unipolar. In terms of unipolar types, they have evolved from FET to MOSFET. From a structural perspective, they have transitioned from Planar FET to FinFET, and then to GAAFET.
There are many abbreviations, and they are quite similar, which can easily confuse people. Please be patient and let’s take a look one by one.
The junction transistor invented by Shockley in 1948 is called a bipolar junction transistor (Bipolar Junction Transistor, BJT) because it uses both holes and electrons as carriers.
BJT transistors come in two structural forms: NPN and PNP:
We can see that the BJT transistor is made on a semiconductor substrate, creating two closely spaced PN junctions. The two PN junctions divide the entire semiconductor into three parts: the middle part is the base (Base), and the two side parts are the emitter (Emitter) and collector (Collector).
The working principle of BJT transistors is relatively complex and is rarely used today. Due to space limitations, I will not elaborate further. Essentially, the main function of this transistor is to allow a small current change at the base to result in a larger current change at the collector, achieving amplification.
Previously, Xiaozao Jun mentioned logic circuits. The circuits formed by combinations of diodes and BJT transistors are called DTL (Diode-Transistor Logic) circuits. Later, circuits entirely built from transistors appeared, known as TTL (Transistor-Transistor Logic) circuits.
BJT transistors have the advantages of high operating frequency and strong driving capability. However, they also have disadvantages, such as high power consumption and low integration. Their manufacturing process is also relatively complex, and using planar processes has some drawbacks.
As time has passed, a new type of transistor has emerged, known as Field Effect Transistor (FET).
In 1953, Ian Ross and George Dacey from Bell Labs collaborated to create the world’s first Junction Field Effect Transistor (JFET) prototype.
JFET (Junction Field Effect Transistor), this is an N-channel
JFET is a three-terminal semiconductor device, consisting of a source (Source), drain (Drain), and gate (Gate).
JFET can be classified into N-channel (N-Channel) JFET and P-channel (P-Channel) JFET. The former consists of an N-type semiconductor with two P-type semiconductors on both sides (as shown above). The latter consists of a P-type semiconductor with two N-type semiconductors on both sides.
The working principle of JFET is simple: by controlling the voltage between the gate G and source S (VGS in the figure), and the voltage between the drain D and source S (VDS in the figure), the PN junction between the gate and channel can be controlled, thus controlling the depletion layer.
The wider the depletion layer, the narrower the channel, the greater the channel resistance, and the smaller the drain current (ID in the figure) that can pass through. The state where the channel is completely covered by the depletion layer is called the cutoff state.
JFET transistors require only one type of carrier to operate, hence they are classified as unipolar transistors.
In 1959, another new type of transistor emerged, namely the famous MOSFET (Metal-Oxide-Semiconductor FET).
Its inventors were Egyptian scientist Mohamed Atala (later renamed Martin Atala) and Korean scientist Dawon Kahng.
MOSFET also consists of a source, drain, and gate. The “M” in “MOS” refers to the initial use of metal to construct the gate. The “O” indicates that the gate is isolated from the substrate by an oxide layer. The “S” signifies that the entire MOSFET is implemented using semiconductor materials.
MOSFET transistors are also known as IGFET (Insulated Gate FET).
This type of MOSFET transistor can also be categorized into “N-type” and “P-type”, namely NMOS and PMOS. Depending on the operational type, they can be classified into enhancement mode and depletion mode.
Taking the N-type MOS (more commonly used) as an example, a P-type silicon semiconductor material is used as the substrate, and two N-type regions are diffused on its surface, followed by a layer of silicon dioxide (SiO2) insulation layer. Finally, two holes are made above the N regions using etching methods. Three electrodes are formed through metallization on the insulation layer and within the two holes: G (gate), S (source), D (drain).
The P-type silicon substrate has one terminal (B), which is connected to the source S through a lead.
The working principle of MOSFET is relatively simple:
Under normal circumstances, a neutral depletion region forms due to the natural recombination of carriers between the N region and the substrate P.
When positive voltage is applied to the gate, electrons from the P region will gather under the electric field at the silicon oxide layer, forming a region with excess electrons, known as a channel.
Now, if voltage is applied between the drain and source, current will flow freely between the source and drain, achieving the conduction state.
The gate G acts like a voltage-controlled gate; when voltage is applied to the gate G, the gate opens, allowing current to flow from the source S to the drain D. When the voltage on the gate is removed, the gate closes, and current cannot pass through.
It is particularly noteworthy that in 1967, Dawon Kahng, together with Chinese scientist Min Shi, co-invented the “floating gate” FGMOS (Floating Gate MOSFET) structure, laying the foundation for semiconductor storage technology. Later, all flash memory, FLASH, EEPROM, etc., are based on this technology.
We just introduced BJT, JFET, and MOSFET; let me draw a diagram to keep your thoughts organized:
In 1963, Frank Wanlass and Chih-Tang Sah from Fairchild Semiconductor first proposed the CMOS transistor.
They combined PMOS and NMOS transistors into a complementary structure, which almost has no static current. This is also the origin of the “C (Complementary)” in CMOS.
The biggest 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 has been increasing, thus increasing the demand for low power consumption. Based on its low power consumption characteristics, CMOS has become mainstream.
Today, over 95% of integrated circuit chips are manufactured using CMOS technology.
In other words, since the 1960s, the core architectural principles of transistors have basically been established. The integrated circuit ecosystem represented by CMOS, silicon, (the natural abundance of silicon far exceeds that of germanium, and it has better heat resistance than germanium, making it mainstream) and planar processes has supported the rapid development of the entire industry for decades.
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Planar FET, FinFET, GAAFET
Although the core architectural principles have not changed, the forms have evolved.
As integrated circuits continue to upgrade, processes and manufacturing are constantly evolving. When the number of transistors reaches a certain scale, the process will force transistors to undergo “deformation” to adapt to developmental needs.
In the early days, transistors were mainly planar transistors (Planar FET).
As transistors became smaller, the gate length became shorter, and the distance between the source and drain gradually decreased.
When the process (commonly referred to as 7nm, 3nm, usually referring to the width of the gate) falls below 20nm, problems arise: it becomes difficult for the MOSFET gate to close the current channel, and the restless electrons cannot be stopped, leading to frequent leakage and increased power consumption.
To solve this problem, in 1999, Chinese-American scientist Professor Hu Zhengming formally invented the FinFET (Fin Field Effect Transistor).
Compared to the planar design of Planar FET, FinFET has transformed into a 3D design with a three-dimensional structure.
Its current channel resembles thin vertical fins, with three sides wrapped in gates. This creates a strong electric field, enhancing the efficiency of channel control and better controlling whether electrons can pass through.
As technology continues to evolve, when it reaches 5nm, FinFET also becomes inadequate. At this point, the GAAFET (Gate-All-Around FET) emerged.
GAAFET stands for Gate-All-Around FET. Compared to FinFET, GAAFET transforms the gate and drain from fins into thin rods that vertically penetrate the gate.
This allows for an increase in contact surfaces from three to four and further divides them into several contact surfaces, significantly enhancing the gate’s control over the current.
Samsung has also designed another form of GAA called MBCFET (Multi-Bridge Channel FET).
MBCFET employs multi-layer nanosheets to replace the nanowires in GAA, increasing the contact area, while retaining all original advantages and minimizing complexity.
Currently, major chip companies in the industry are still conducting in-depth research on the evolution of transistor forms, aiming to find better innovations to support the future development of chip technology.
In summary, both electronic tubes (vacuum tubes) and transistors are small components that use electricity to control electricity. Transistors are based on semiconductor materials, allowing them to be made small enough. This is the fundamental reason why chips (integrated circuits) can achieve “extremely small size and extremely large capacity”.
The characteristics of semiconductor materials and the functions of transistors seem very simple. It is precisely the billions of these simple “little things” that support the entire development of human digital technology, propelling us into the era of digital intelligence.
1. “A Brief History of Semiconductors”, Wang Qi, Fan Shuqin, Machinery Industry Press;
2. “What Exactly is a Chip?”, Klaus, Zhihu;
3. “What is a Chip? What is IC? What is a Semiconductor?”, Zhang Da Miao, Zhihu;
4. “A Small Chip Changes Our Lives”, Wei Shaojun;
5. “Understanding Semiconductor Process FinFET”, Shu Ge Tan Xin, Zhihu
6. Baidu Encyclopedia, Wikipedia.
END
Reprinted content only represents the author’s views
It does not represent the position of the Semiconductor Institute of the Chinese Academy of Sciences
Editor: Qian Niao
Chief Editor: Jiang Yu
Submission Email: [email protected]
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