A PIN diode has a unique structure with a wide, undoped intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region. The p-type and n-type regions are typically heavily doped and used for ohmic contacts. The high resistive layer of the intrinsic region provides the large electric field between the P and N-region. The electric field induces because of the movement of the holes and the electrons. The direction of the electric field is from n-region to p-region.
pin diode structure
The PIN diode has three main layers.
The intrinsic layer of the PIN diode is responsible for the deviation in properties from a normal PN junction diode. The intrinsic region is a undoped pure semiconductor. In most PIN diodes it is very thin - of the order of between 10 and 200 microns.
Pin diode working
When PIN diode is unbiased, the charge carriers will flow from N-type region to intrinsic region due to the concentration gradient. Thus, the width of the depletion region at NI junction (Intrinsic and N-type material) will be more on N side and less on I-side.
The reason behind this is N-type material is heavily doped while the Intrinsic layer is not doped or doping level is extremely low. Thus, when charge carriers (electrons-majority carriers in N-type) flow from N-type to Intrinsic layer the depletion region will be created, but the width of it on both the sides of N-I junction will be different.
pin diode applications
Pin diode RF switches
Pin diode RF attenuators
Pin diode RF modulators
Pin diode RF phase shifters
Pin diode control circuits for wireless communication systems
Pin diode control circuits for HF band industrial applications
Pin diodes for magnetic resonance
pin diode characterisitcs
The PIN diode is used in various applications exploiting its unique structural design proving some properties which are of particular use. The intrinsic layer between the P-type and N-type regions of the PIN diode is responsible for the PIN diode properties such as a high reverse breakdown voltage , and a low level of capacitance , and there are also other properties such as carrier storage when it is forward biased that enable it to be used for certain microwave applications.
High voltage rectifier :
The PIN diode can be used as a high voltage rectifier. Because of the width of the intrinsic region providing good separation between the P and N regions, higher reverse voltages can be tolerated by the diode, which is helpful in High voltage rectification without the breakdown.
The PIN diode is an ideal RF & microwave switch because it has less capacitance for easy switching action. The diode has the structure of a capacitor with the P & N regions acting as parallel plates and the intrinsic layer as the insulator. The width of the insulator is synonymous with the distance between the parallel plates. The large intrinsic layer width decreases the capacitance between them, thereby increasing he level of isolation. But for this the diode is connected in reverse biase.
As the conversion of light into current takes place within the depletion region of a photodiode. The depletion layer in a PIN diode is its intrinsic layer and increasing the depletion region by accumulation of the intrinsic layer thickness improves the performance by increasing the volume in which light conversion occurs.
Attenuator and RF protection Circuit:
When PIN diode is forward biased, it works as a variable resistor. Thus, it can be used for protection of RF circuit from high current which may damage the circuit. When the forward biased is increased the resistance decreases suddenly, thus, it can be used as an attenuator.
These are three of the main applications for PIN diodes, although they can also be used in some other areas as well.
pin diode equivalent circuit
pin diode advantages
1 Rugged, High Reliability
2 High Voltage Capability > 2000 Volts
3 High Current Capability > 25 Amperes continuous
4 High surge Current Capability > 500 Amperes (1 pulse 8.3 ms ,½ sine)
5 Low Distortion < -60dBc @ 455 KHz
6 High Power Gain > 10,000 : 1
7 Fast Switching speed < 100 ns
8 Small Physical Size
9 Various Thermal Packaging Available
10 RF Relay Replacement - mechanical, mercury, etc.
pin diode disadvantages
High Reverse Recovery Time, power losses are significant.