 Hello, this is Dr. Rupali Sherke working as an Associate Professor at Wolchen Institute of Technology in Electronics Department. In today's video, we are going to discuss with the Microsolid state device that is a PIN diode. Learning outcomes at the end of this session, students are able to understand or describe the construction, working and characteristics of the PIN diode and also able to know the applications area of the PIN diode. These are the contents which are going to cover in this video. Now, before starting with the description of the PIN diode, first let us see that what is the symbol we are used for representing the PIN diode. Usually, we know that for the PIN diode, we have the symbol which is being used as a normal PN junction diode we are representing by this symbol. Now, the PIN diode, there are two terminals anode and cathode. Similarly, like a PIN diode, similar like a PN junction diode, the PIN diode is represented. The only difference is there is a center line between this symbol and here also the two terminals cathode and anode. Now, the physical structure or physical appearance of the PIN diode is shown in this figure 3. This is a PIN diode image. Now, let us see the internal structure of the PIN diode. As it is denoted, it is a PIN diode means there are N type of material and P type of material are BIN junctions. Between these two N type and P type of material, there is a incentric layer, here two terminal anode and cathode and the incentric layer is sandwiched between the P type of and N type of material. Now, the diode consists of a P type of regions and N type of region which are being separated by the incentric semiconducting material. Now, what is the P type of regions here? These are the holes which are acting as a majority carriers while in a N type of region, electrons are acting as a majority carrier. The incentric layer has no free charges, so it acts as an insulator between the N and P region. The I region has a high resistance as it is acting like an insulator, it has a high resistance, so it abstracts the flow of the electron flowing from the between these two regions, P type and N type. Now, this P type of as PN junction consists of the three layers, P layer, incentric layer and N layer, so and to separate them there is a high layer which is a highly resistive, so this PIN diode offers a high resistance. Due to the incentric layer between the P layer and N region, it can act as a low capacitance also because as you know this relation C is a capacitance is given by epsilon 0, epsilon r A by D. A is a area between the two capacitance and the effective area and D is nothing but the distance between these two plates. Now, this P region and N regions, the regions between them that acts like a capacitors over there. As this distance goes on increasing, the capacitance value goes on decreasing because they are inversely proportional for that the we can call that the PIN diode offers a low capacitance. So, as there is a the capacitance where there is a highly resistance between these two there is an incentric layer between them, it has a high breakdown voltage to move the electrons from the general from from move the N regions to the P regions, you require a high value of applied voltage which so it is called as a peak inverse voltage is also high. Now, let us see the conditions for the biasing. The first biasing condition if there is a no external voltage is applied across this old across this diode under 0 biasing or no biasing you can call then a electron holds from the P regions and the electrons from the N regions are attracted towards that they are combined in a incentric layer and the depletion regions the depletion regions goes on increasing over here what and the number then again there this depletion regions cause a diffusion of this diffusion of the electrons. Now, when the diode is unbiased that the charges will get diffused there since there is no external voltage there will be that the the motion of the electrons are diffused over here or a motion of the charges are diffuser. Notice diffusion means a diffusion is nothing but a means that a charge carriers of the depletion regions try to move in the region this process of diffusion occur continuously and until the charge becomes a equilibrium in the depletion region the charge carrier which are been moving in the depletion regions are been diffused or become equilibrium in the depletion regions. Now, first forward bias next is a forward bias what is forward bias condition means in a forward bias a P type region is connected to the positive terminal of the battery and N type region is connected to the negative terminal of the battery that is anode is connected to the positive terminal of the battery cathode is connected to the negative terminal of the battery. Now, in a forward bias condition when the diode is forward by the charges are continuously injected in a i regions from the P type and N type region and this will reduce the number of electrons from the N type and holes from P type they start moving towards the opposite direction and there is a flow of charge flow of current into the diode due to this flow of current the resistance at of the depletion region goes on reducing the resistance of the depletion region goes on reducing. So, we can call that as resistance is reduced this becomes this regions this diode can be acts as a variable resistance. Next in a reverse bias condition in a reverse bias condition here is the reverse bias in a reverse bias the condition is opposite P type is connected to the negative terminal of the battery that is anode is connected to the negative terminal of the battery and N is connected N type of region is connected to the positive terminal of the battery. In a reverse bias condition the voltage increases because they are electrons are moving away from the towards the battery and here holes are moving towards the battery. So, this regions goes on the depletion regions start expanding as it goes on expanding the de regions goes on increasing this which is called as a swift voltage as de increases so automatically as the distance between the these two plates or these two layers increases then this C decreases. So, we can call that it can acts the pin diode can act as a variable capacitance also. Now, let us see the different models of the pin diode is the low frequency and high frequency this is the equivalent circuit of the pin diode for the low frequency model. Now, we have seen that the pin diode itself as a capacitor it is acting like a capacitance and resistance. So, these are the junction capacitance we can call and this is a resistance of the at the junctions this R D represents the junction and dynamic resistance and this is called this is called the junction capacitance. Now, this plates or this diode is connected across the plate that is a lead plate and the capacitance plate. Now, package induction plates or you can call as a packet capacitance and this is a series resistance the induct resistance this inductance is in the series and this capacitor is a shunt capacitor. Now, as the at low frequency under the forward bias condition under the forward bias condition the resistance behaves like a variable resistance as the forward bias increases this resistance there is a flow of current this resistance goes on increasing and as the under the reverse bias condition this junction diodes behaves like a variable capacitance. Now, as the as you go on increasing the reverse bias the capacitance value decreases. Now, the working of this are measured by its reactance reactance equation which is given by x c is equal to 1 upon 2 pi f c that is omega c. Now, as the capacitance decreases this junction capacitance start decreasing as it decreases its reactance increases under the reverse bias condition at the reverse bias condition this c decreases and x c increases as the x c increases we neglect the value of the resistance. The pin diode at the high frequency models in at the high frequency models this diode it is similar it seems like a equivalent circuit is same the same here is a resistance and the junction capacitance at the higher frequency the R and D this is a resistance and capacitors behaves like a RF components. Now, this values are becoming changing the value of I D varies from 0.1 to 100 kilo ohms and the capacitance value varies from 0.02 to 2 pico farad. The applications of the pin diodes pin diodes can be used as a high voltage regulator rectifiers they can be used as a RF switch pin diode can be used as a photo detector circuits as well as the variable attenuator. These are the applications of the pin diode these are the references. Thank