 Welcome to the session. Today's topic of the discussion is the Microwave Solid-State Devices. My name is Ajit Subhash Srinishi from the Electronics and Telecommunication Department in the Washington Institute of Technology. So what is the learning outcome of this today's session? At the end of the session, students will be able to describe the construction and working of the solid-state devices, such as the vector diode, pin diode and tunnel diode. So prerequisite, so what should knowledge you have before proceed further into this session is that you should have a basic knowledge of the semiconductors and you should have a knowledge of the p-n junction working and construction and the working of the p-n junction diode. So let's start with the vector diode. So the vector diode name itself suggests it is a variable reactance diode. So it is also called as a vericap. So vericap means variable capacitors. So in the vector diode is a p-n junction diode in which the capacitance is varied by the varying the changing the reverse bias voltage across it. So these are the different symbols for the vector diode. This is one of the symbols. This is one more symbol and most common symbol used is this one. So this arrow is showing the that means this this arrow is itself indicating the capacitance is varied by changing the voltage across it. So coming to the construction of the vector diode is that so it is a p-n junction diode and in the p-n junction diode if the material used for the semiconductor is the silicon it is used it is limited for the lower frequency but for the microbial frequency gallium arsenide is used. So as the gallium arsenide the mobility of the hole and electron is more as compared to the silicon. So for high frequency application gallium arsenide is used. So this is forming the p-n junction at this center and this is the molybdenum structure. So molybdenum is the metal. So this metal is connected to the p-type molybdenum stud. This is molybdenum stud at the anode side and this is molybdenum stud at the cathode side. So this is a positive side and this is a negative side. So p-side should be the upper and n-side should be the lower. So reason for using the molybdenum study is that it can have a better conductivity as compared to other and there is a better charge separation. So there is one more important fact you have to note in this vector diode is that the doping of the in the p-type and n-type semiconductor is a linear. So it is a less in the at the junction side. So it is a it is a less at this junction side and it is increases linearly at the end. So there will be more concentration at the end of the this vector diode. So this is about the structures of the vector diode. So vector diode is working in the reverse bias as you can see here. So the reverse bias is applied it will create the space charge region or the depletion region at the center and these are the mobile charges at the end of this too. So this mobile charges are separated by the depletion region and it is forming the capacitance which can be explained in the next slide as you can see here. So these are the mobile charges and we as we are changing the reverse bias across it. So this is the p side and this is the whole is the majority carriers and this is the n side is the electron is the majority carriers here. So when reverse bias increased it also changes the capacitance. So it is modeled as a capacitance as you can see this is the junction capacitance or you can call it as a transition capacitance. So this is the characteristics of the vector diode. So this in this characteristics capacitance is plotted versus the reverse bias voltage. So as you can see this capacitance is inversely proportional to the reverse bias voltage. So this is a junction capacitance or transition capacitance and this is a reverse voltage and this is a breakdown voltage as you can see it is inversely proportional and this n value is dependent upon the how much the grading also how much you are doping the p-type n side if it is a linear doping if it is a strip a graded doping so that n value depend upon that. So this is obviously it is inversely proportional to it and C0 is the capacitance when there is a no bias is applied to it. So one more important aspect so you can note down here the capacitors is not linearly proportional it is somewhat exponential decrease in the capacitance as there is an increase in the reverse bias voltage. So this is about the vector diode characteristics. Now coming into the equivalent circuit of the vector diode so this is a junction capacitance during the reverse bias and this is a resistance reverse resistance and this is the resistance is called as a bulk itself it is a material resistance and this resistance is due to the reverse bias as reverse bias increases the resistance of the diode is also increases. So this is a reverse resistance and this is the inductance forward inductance so which you can place in the series with this reverse resistance. So this is the model of model of the vector diode. So very interesting facts as the vector diode can be used for the high frequency. So what do you think what is the limitation because of this inductor here think about it write down the paper what is the limitation of this series inductance as you can see this inductance and if there is a limitation write down that limitation and also justify that. So a vector diode application it is used as a automatic frequency controller it is used in the high frequency receiver also as the as the as the capacitors changes as it can be used as a variable tuner also in the tank circuits and it is used in the high frequency radios as a used as a frequency multiplier and it is also used at the band pass filters and it is also used at the harmonic generators that means by changing the frequency you can change the double frequency you can multiply the frequency three times you can multiply the frequency four times that is mean by the harmonic generator by using vector diode. So this is about the vector diode let us come into the pin diode so here pin diode here p p stand for the p type and n stand for the n type and i stands for the intrinsic layer. So this intrinsic layer is very high resistance so intrinsic layer is a sandwich between this two p type and n type material semiconductor material. So again this intrinsic material have a high electric field intensity because it has a resistance because it has a high resistance in between these two regions p type and n type region and symbol is just like a similar to the normal pin junction diode as you can see here. So this is about the pin junction and now come a pin diode so in the pin diode as you can see this is intrinsic layer is a sandwiched between this p type and n type and these are the metal contacts these are the ends of the metal contacts here and this is intrinsic layer in between the p plus and n p plus and n plus which is highly doped of p type and highly doped n type semiconductors and a material used for this is the gallium arsenide for the high frequency. Now working with the pin diode is that as you can see this series resistors is directly proportional to the frequency. So as the frequency is variable also the it is depend upon the voltage so as voltage changes positive voltage changes it act as a variable resistors. So this same can be reflected in the model also. So this is a model of the pin diode so this is act as a variable resistors. So as I told you virector diode act as a variable capacitors and pin diode is act as a variable resistor for the high frequency application. Now application of the pin diode is pin diode can be used as a detector also light detector also and it is used as a high voltage rectifier and in the high frequency it is used as a phase shifter and it is also used as the amplitude modulator. Now this now about the tunnel diode so tunnel diode name itself suggests the current is tunneling between these p sites and n side and this tunnel diode is a highly doped p n junction diode and the current flowing in this tunnel diode is is called as a tunnel current and symbol for the tunnel diode is this as you can see here it is somewhat different than normal conventional p n junction diode. Now coming into the construction of the tunnel diode is this so this is a p type and n type semiconductors which are separated which are connected to this so these are the metal leads this is the metal lead and these are the leads so these are the highly doped p type and n type and this is a substrate so again the material used here is gallium arsenide because for the high frequency application if it is a silicon it is not for the it is not for the high frequency application only the gallium arsenide is used here for the construction of the tunnel diode and this is the encapsulation as you can see here so this is the characteristics of the tunnel diode as you can see this this current is initially increases because this current is a tunneling current and this characteristic is a normal p n junction diode so all this current is due to the tunneling phenomena so tunneling cloud as you can see the small tunneling current flows because of the overlap of this conduction this valence band and this conduction band in n type so small current flows tunnel current flows through the tunnel diode due to the small bias and as the bias increases it reaches to the saturation point and maximum point as you can see here and further increase in the bias as you can see there is a decrease in the tunnel current as as you can see so this already explained in the characteristics of the tunnel out and coming to the application of the tunnel out these are the application it is used as a logical memory devices it is used as a relaxation oscillator it is used in the amplifier also and so and in the microwave application it is used as the oscillator because it's as a retarded oscillator because it has a negative resistance property these are the references thank you