Schottky diodes are not made by using the principle that p-type semiconductors and n-type semiconductors contact to form PN junctions, but by using the principle of metal semiconductor junctions formed by metal semiconductor contact. Therefore, Schottky diode is also called metal semiconductor (contact) diode or surface barrier diode, which is a hot carrier diode.
The main advantages of SBD include two aspects:
1) Because the Schottky barrier height is lower than the PN junction barrier height, the forward conduction threshold voltage and forward voltage drop are lower than those of the PN junction diode (about 0.2V lower).
2) Because Schottky diode is a kind of most carrier conductive device, there is no minority carrier lifetime and reverse recovery. The reverse recovery time of Schottky diode is only the charge and discharge time of Schottky barrier capacitor, which is completely different from the reverse recovery time of PN junction diode. Because the reverse recovery charge of Schottky diode is very small, the switching speed is very fast and the switching loss is particularly small, which is especially suitable for high-frequency applications.
However, the reverse breakdown voltage of the Schottky diode is relatively low because the reverse barrier of the Schottky diode is thin and breakdown easily occurs on its surface. Because Schottky diodes are more prone to thermal breakdown than PN junction diodes, the reverse leakage current is larger than that of PN junction diodes.
application
The structure and characteristics of Schottky diode make it suitable for high-frequency rectification in low-voltage and large current output fields, detection and mixing at very high frequencies (such as X-band, C-band, S-band and Ku band), and clamping in high-speed logic circuits. Schottky diodes are often used in ICs. Integrated circuits such as Schottky diodes have become the mainstream of TTL circuits and are widely used in high-speed computers.
In addition to the characteristic parameters of the common PN junction diode, the electrical parameters of the Schottky diode used for detection and mixing also include the intermediate frequency impedance (refers to the impedance of the Schottky diode when the rated local oscillation power is applied to the specified intermediate frequency, generally between 200 Ω and 600 Ω), the voltage standing wave ratio (generally ≤ 2), and the noise figure.
effect
Schottky diode is a kind of semiconductor device with low power consumption and high speed. It is characterized by extremely short reverse recovery time (as small as a few nanoseconds), and the forward conduction voltage drop is only about 0.4V. It is mainly used as high-frequency, low-voltage, large current rectifier diode, free wheeling diode, protection diode, and also used as rectifier diode and small signal detection diode in microwave communication and other circuits. It is common in communication power supply and frequency converter.
A typical application is that in the switching circuit of the bipolar transistor BJT, the Shockley diode is connected to the BJT to clamp, so that the transistor is actually in a very close off state in the on state, thereby improving the switching speed of the transistor. This method is a technique used in TTL internal circuits of typical digital ICs such as 74LS, 74als, and 74As.
Another characteristic of Schottky diode is that the forward voltage drop VF is relatively small. Under the same current, its forward voltage drop is much smaller. In addition, its recovery time is short. It also has some disadvantages: the withstand voltage is relatively low, and the leakage current is slightly larger. Comprehensive consideration shall be taken when selecting.