In general, a device having a PNPN four-layer triple junction structure is a thyristor. Strictly speaking, according to the definition of the International Electrotechnical Commission (IEC), there are 3 or more PN junctions, whose volt-ampere characteristics have conduction and blocking two stable states in at least one quadrant, and can be in two The Power Semiconductor Device switching between states is a thyristor. Thyristors can be divided into many types, such as reverse-conducting thyristors (RC-Thyristor) with antiparallel diodes, TRI-AC (TRI-AC) with bidirectional controlled current, gate-off thyristors (GTO), and gates. Converter thyristor (GCT) and so on. In practical applications, an ordinary half-controlled thyristor with bidirectional blocking capability and only positive conduction can be called directly as a thyristor or SCR (Silicon Controlled Rectifier). Other types of thyristors are named according to their functions and characteristics. .
Thyristors can withstand very large inrush currents in the on-state, and very high voltages in the resistive state. The limit of these two points is the highest among all current devices, if there is no failure to turn off this seriously The flaw, then the thyristor is the perfect power semiconductor device. This is closely related to the structure of the thyristor.
The thyristor is also a three-terminal device. According to the existing application habits, its three terminals are defined as an anode (Aode), a cathode (K, a cathode), and a gate (G, gate). Thyristor symbol and the corresponding definition of the three terminals shown in Figure 1.
In fact, the structure of a typical thyristor is shown in Fig. 2. Generally, the impurity semiconductor from the anode to the cathode is PNPN. Therefore, there are three PN junctions, which are J1, J2, and J3 from the anode to the cathode. At this point, these three junctions no longer have specific names like transistors. The three PN junctions may be formed by an alloy-diffusion method or a full diffusion method. The anode, cathode, and gate electrodes are respectively connected to the corresponding semiconductor layers through metal connections.
For the convenience of analysis, the transistor shown in FIG. 2 is simplified to a simplified structure diagram as shown in FIG. 3, and the doping concentration of each impurity semiconductor is considered to be uniform according to the use of the thyristor in the actual circuit. Also given the peripheral circuit for thyristor operation principle analysis, the current flowing into the thyristor anode is IA, the current flowing out of the cathode of the thyristor is IK, the current flowing into the gate of the thyristor is IG, and the voltage between anode and cathode of the thyristor is UAK. .
The doping concentration of each part of the thyristor is shown in FIG. The heavily doped P+ and N+ layers, which are connected to the anode and the cathode, respectively, are heavily doped P+ layers connected to the gates. The thicknesses of the three layers (which are shown in the figure as widths) are small, and the remaining one The layer is a relatively lightly doped layer N-layer, which has a large thickness, and a lighter doping with a large thickness has a significant effect on the breakdown voltage and on-state characteristics of the device.
