According to data from the British research company Omdia, the world power semiconductor market size was about $14.5 billion in 2020 and is expected to increase to about $17.3 billion by 2024, a year-on-year increase of about 19. 
With the rise of the third generation of semiconductors, power semiconductors have become a new outlet. 
As the most basic unit in the electronic system, power semiconductor devices play a vital role in various industries including automotive electronics, consumer electronics, network communications, electronic equipment, aerospace, equipment, instrumentation, industrial automation, medical electronics, etc., and are known as "behind-the-scenes heroes of energy saving".
How to define a discrete device for power semiconductors
Power electronic devices, also known as power electronic devices and power electronic devices, refer to electronic devices that can be directly used to process electrical energy in the main circuit to realize the conversion or control of electric energy, and its functions are mainly divided into power conversion, power amplification, power switching, line protection and rectification. Power semiconductors can be broadly divided into two categories: power semiconductor discrete devices (including power modules) and power semiconductor integrated circuits (power IC).Figure 1 illustrates the structural relationships in the semiconductor industry. Among them, power semiconductor discrete devices refer to semiconductor devices that are specified to complete a certain basic function and cannot be subdivided in function. 
Fig.1 Relationship between the structure of the semiconductor industry In 1957, General Electric (GE) of the United States developed the world's first industrial ordinary thyristor, marking the birth of power semiconductor discrete devices. The development of power semiconductor discrete devices has gone through the first stage with thyristors as the core, the second stage represented by MOSFETs and IGBTs, and is now entering a new development stage with wide bandgap semiconductor devices as the core. 
Figure 2: The structure of the whole industry chain of semiconductor power devices.
How to classify power semiconductor discrete devices
According to the device structureIt is divided into diodes, power transistors, thyristors, etc., among which power transistors are divided into bipolar junction transistors (BJT), junction field effect transistors (JFETs), metal oxide field effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs). According to the power handling capacityIt is divided into low-voltage and low-power semiconductor discrete devices, medium-power semiconductor discrete devices, high-power semiconductor discrete devices and high-voltage ultra-high-power semiconductor discrete devices. According to the nature of the signal that the drive circuit adds between the control side and the common side of the device, (except for power diodes) can be divided into current-driven and voltage-driven. Current-driven:A power semiconductor discrete device that shuts down by injecting or extracting current from the control terminal.
Voltage-driven:A power semiconductor device that turns on or off by applying a certain voltage signal between the control and the common side.
The degree to which the device is controlled according to the control circuit signalIt can be divided into uncontrollable type, semi-control type and full control type. Uncontrollable Devices:The power semiconductor discrete device that cannot control its on-off through the control signal represents the power diode;
Semi-control device:The power semiconductor discrete devices that can control their conduction but cannot control their turn-off through the control signal represent the thyristor and most of its derivative devices;
Fully controlled devices:The power semiconductor discrete devices that can control both their conduction and shutdown through the control signal, including insulated gate bipolar transistors, power field-effect transistors, gate-off thyristors, etc.;
According to the situation in which the two carriers, electrons and holes, participate in the conductionIt can be divided into unipolar devices, bipolar devices and composite devices. Unipolar devices:A discrete power semiconductor device in which there is a carrier (electron or hole) involved in conducting electricity;
Bipolar devices:A discrete device of power semiconductors with the participation of electron and hole carriers in conducting electricity;
Composite Devices:Power semiconductor discrete devices composed of integrated and hybrid unipolar devices and bipolar devices;
According to the different substrate materials of power semiconductor devicesThe materials of existing power semiconductor discrete devices can be divided into three generations: the first generation of semiconductor materials are mainly represented by germanium (an early product, which is now uncommon) and silicon.
The second-generation semiconductor materials are mainly compound semiconductor materials represented by gallium arsenide (Gaas) and indium phosphide (INP).
The third-generation semiconductor materials are mainly wide bandgap semiconductor materials represented by silicon carbide (SiC) and gallium nitride (GaN). (See previous tweet for details: Wide bandgap semiconductors: Disruptors or disruptors?) ）
Power semiconductor discrete devices are used in
Power semiconductor discrete devices are widely used, covering almost all electronics manufacturing industries, including consumer electronics, network communications, industrial motors, etc. In recent years, new energy vehicles and charging systems, rail transit, smart grids, new energy power generation, aerospace and advanced equipment have gradually become emerging application fields of power semiconductor discrete devices. Consumer Electronics:It is used in power supplies and charging systems for various electronic devices, power semiconductor lighting power supplies, inverters for household appliances, etc. Industrial Motors:In the industry, a large number of AC and DC motors need to be used to supply them with controllable rectifier power supply or DC chopper power supply, and the core device of the motor's variable frequency drive system. Automotive Electronics & Charging Systems:power supply, lighting and other systems of traditional automobiles; Charging piles, converters, inverters and other applications for new energy vehicles. Rail Transit:Rectifier device in DC locomotive, frequency conversion device in AC locomotive, DC chopper in rail transit such as high-speed rail, bullet train, maglev train, power conversion system, drive control system and battery charging system of new energy vehicles, and power supply system in various vehicles, aircraft and ships. Smart Grid:Direct current transmission, flexible current transmission, reactive power compensation technology, harmonic suppression technology and technology to improve power supply quality in smart grid power transmission, such as preventing instantaneous power outages, instantaneous voltage drops, and flicker. New energy power generation:In inverters, converters and other devices in photovoltaic inverters, wind power generation, solar power generation, geothermal power generation, bioenergy and fuel cell power generation systems. Aerospace:The third-generation semiconductor devices have super anti-radiation ability and have absolute application advantages in aerospace. *Equipment:Electromagnetic lighter device, power supply system for long-range missiles, radar, electromagnetic catapult systems.
Key processes for power semiconductor discrete devices
The main process flow of power semiconductor discrete devices includes:The chip is processed on the silicon wafer (the main process is thin film manufacturing, ** and etching), the chip is packaged, and the technical performance index test of the processed chip is carried out, of which the main production processes are epitaxy process, photolithography process, etching process, ion implantation process and diffusion process. Epitaxial process technologyFor Si power semiconductor devices, the epitaxial process is based on different silicon sources (SiH2Cl2, SiHC3, SiCl4), at a temperature of 1100-1180 °C, and then one or more layers of intrinsic (doped), N-type (PH3-doped) or P-type (B2H6-doped) monocrystalline silicon on the surface of the silicon wafer, and the thickness and resistivity of the silicon layer, the uniformity of thickness and resistivity, and the surface defects should be controlled within the allowable range. For SiC power semiconductor devices, it is very difficult to grow a single crystal with low defect density, because the crystal growth of SiC substrate needs to be carried out at a temperature of 2300 °C, and SIH4 and CH4 or C3H8 need to be used as reaction gases in H2 protective atmosphere, and the growth rate is generally only a few microns per hour, and there is still the problem that the crystal defects in the SiC substrate extend to the epitaxial layer, so the cost of SiC wafers, especially high-quality and large-area SiC wafers, is much higher than that of Si wafers. Lithography process technologyThe photolithography process is a process technology that transfers the mask (photolithography) pattern to the photoresist on the surface of the substrate to form the pattern required for the product, and the accuracy of the lithography machine generally refers to the minimum size of the photolithography pattern obtained during photolithography. The higher the resolution, the finer the lines and the higher the level of integration. Etching process technologyEtching is the process of selectively removing unwanted materials from the surface of silicon wafers by physical or chemical methods, and the basic role of etching is to accurately replicate the mask pattern to ensure that various processes in the production line are carried out normally. Other advanced etching technologies include wet etching, dry etching and plasma-enhanced reactive ion etching, electron cyclotron resonance etching (ECR), inductively coupled plasma etching (ICP) and other advanced etching technologies. Ion implantation process technologyIon implantation is the injection of doping elements required by the device into the silicon wafer through high-tech equipment. Diffusion process technologyThe main purpose of the semiconductor doping process is to control the type, concentration, depth, and p-n junction of impurities in a specific region of the semiconductor. Diffusion technology is a simple and convenient way to achieve this.
A family member of power semiconductor discrete devices
Power diodesPIN Diode:Most power diodes operate primarily on the principle of unidirectional conduction of the PN junction and have extremely low on-state resistance, called pin diodes. From an application point of view, PIN diodes can be divided into rectifier diodes and fast recovery diodes.
Schottky diodesSchottky diodes are unipolar devices, which use the metal-semiconductor junction formed by the contact between metal and semiconductor as the Schottky barrier to produce the effect of rectification, and are widely used in medium and high power fields.
ThyristorsThyristor is commonly known as thyristor, which is a semi-controlled rectifier device, small size, no heating filament, long life, high reliability, cheap, and is mostly used in motor drive control, high-voltage direct current transmission (HVDC), dynamic reactive power compensation, ultra-large current electrolysis and other occasions. TransistorsA transistor is a semiconductor device that is capable of providing electrical power amplification and has three or more electrodes. According to the main use, which are divided into two categories: switch tubes and amplification tubes. The switch works in the cut-off area and saturation area, and is mostly used in digital circuits to achieve logic functions; The amplifier tube is generally near the working area, and is used in analog circuits to achieve signal or power amplification. In accordance with the main process, which are divided into bipolar transistors and field-effect transistors. Bipolar transistors are fluidic devices with fast response speed and strong driving ability. MOSFETs are voltage-controlled devices with high input impedance and relatively low power consumption. A bipolar transistor is a transistor that has at least two junctions and relies on a majority and a minority carrier for its function.
A field-effect transistor is a type of transistor in which the current flowing through the conductive channel is controlled by the electric field generated by the voltage applied to the outlet of the gate source. MOSFETs can be divided into JFETs, MESFETs and MISFETs.
Insulated Gate Bipolar Transistor (IGBT)Insulated Gate Bipolar Transistor IGBT is a power semiconductor discrete device composed of MOSFET and bipolar transistor, which controls the pole insulated gate FET and outputs the pole bipolar power transistor, so it has the advantages of both speed and driving ability, and overcomes the shortcomings of both. At present, the withstand voltage is up to 5kV or even higher, and the current is up to 12ka。
Power semiconductor discrete device modulesThe discrete device power module is a module that is connected by two or more semiconductor discrete device chips according to a certain circuit and installed on a ceramic-based copper clad laminate (DCB), sealed in an insulating shell or encapsulated with plastic packaging with protective materials such as elastic silicone gel, to realize the function of semiconductor discrete devices. It is mainly used in high-voltage and high-current occasions, such as smart grids, high-speed rail EMUs, etc. Wide bandgap power semiconductor devicesSiC power semiconductor devices include SiC power diodes, SiC JFETs, SiC MOSFETs, SiC IGBTs, and SiC power modules. GaN power semiconductor devices include GaHemt high electron mobility transistors and GaN diodes based on GaN semiconductor materials.