 Hello everyone, this is Dr. Rupali Sherke working as an associate professor at electronics department in Wolchen Institute of Technology, Sholapur. In this video lecture, we are going to discuss with the one of the solid state device a microwave transistor. Learning outcomes at the end of this session students are able to describe the micro transistors types of the micro transistors and their construction and parameters related to the microwave transistors. And they can also know few application areas of this micro transistor. These are the contents which are going to covered in this video. Now before starting with the microwave transistor discussion, let us see what is the need of the solid state devices. Why we go for the designing the devices in a using the solid state? Because the solid state devices has reduced the size of the device, there is a deduction of the size of the devices compared to the vacuum tube devices because it is not consist of any liquid or a gases in while constructing as well as it reduces the packet plastic reactants which gives the react limitations for the at a high frequencies. Also it reduces the transit time effect due to is at a high frequency also there will be no phase change in the signal. The commonly used devices to construct the micro solid state devices are the silicon and the gallium arsenide. These devices are been constructed using a molecular beam epitaxial technology for the construction and they are designed the devices which are been designed because has a high mobility compared to the normal mobility of the electrons. So they are called as a high electron mobility transistor and these devices can work up to 100 gigahertz frequencies. Now micro integrated circuits, there are two types of micro integrated circuits. One is the microwave which is called as a MIC's. In this it is a hybrid of the slowed lumped element. Solid lumped element means it consist of the inductance and the resistors and the transit lines of the for the signal transmission and matching part. All these components are integrated in the micro integrated circuit and another is a monolithic micro integrated circuit MMIC's in this all active and passive components are fabricated on a single crystal. Now based on this construction micro integrated circuit they are been classified the first micro components which we are discussing is the micro transistor. There are two types of the micro transistor unipolar and the bipolar. As from the name itself you will understand that bipolar means there are two junctions two junctions while in the unipolar there is a single crystal is been used in construction. Now comparing the two devices bipolar and unipolar, a bipolar there are three semiconductor doping regions are there, three regions are doped that is NP, PNP or NPN while in a unipolar one or two semiconductor doping regions are there which is just of the PNP type of and N type of material. A P type of in the P type of material a majority carriers are the hole and in a N type of material majority carriers are the electrons. Here both electrons and holes are the carriers in a bipolar here either electron or hole is a carrier. Here silicon BJT works at a very high frequency ultra high frequency to the S band and here silicon BJT or gallium fed works in a S to C band which are the range of the microwave frequencies. Here this devices has a higher gain while this devices is better has a better noise performance as well as it can have a higher frequency of operation. Now a micro let us see one by one these devices, micro bipolar transistor this bipolar transistors are constructed with the planar inform that we will see in the next slides and mostly these devices are made by using the silicon. Now for designing of this transistors we use a geometry that that geometries are the inter digitalized geometry, overlay geometry or matrix form geometry. The cutoff frequency that is a passing of the signals through this devices the cutoff frequency is near about 22 gigahertz frequency. Now let us this is a structural diagram of the microwave bipolar transistor we can see here it is consist of a NPM silicon double diffuse epitaxial transistor. In this highly doped N type of substrate is been used across this N type of substrate the P type of material is been layered it is been layered and there are the different terminals are been taken which are acting as a base metals and the emitter metal. Now let us see with the different geometry you can see a this first diagram the A diagram is called as a inter digitalized construction surface geometry of the NPN micro transistor. Here in this layer the alternating fingers how we are holding the two fingers the alternating two layers are been connected the one layer is of the emitter one layer is of the emitter part and one layer acts as a base part you can see here the this region is like a emitter and this is a base metallization. Now in the second part that is a in a over layer layer across the base layer the emitters are been layered out over layered of the emitter is been done I mean some N type of material is over layered on the P type of material while in the matrix form here the P type of P type of material or a P type of is over layered with the N type of material. This are the base and metallizations and these are the emitter metallizations. A descriptive in a short inter digitalized large numbers of emitter strips alternated with the base strips in a over layer large numbers of segmented emitter over layered through the number of the wide metal strip while in a matrix emitter that forms a grid and base filling with the mesh of the grid with the P plus contacts. Now when we consider the parameters we are seeing the cutoff we are measuring the cutoff frequency which is of the 22 gigahertz frequency. This cutoff frequency is given by 1 upon 2 pi T where what is T? T is nothing but a transit time a transit time which is given by T is a sum of the T j e b plus T b plus T b c plus T j c b the suffix here the suffix are the T is the emitter based junction j e c b is the emitter based junction capacitor charging time, T b is a base transit time, b c is the base collector region depletion layer transit time and j b is a junction capacitor charging time. Now the next is microwave unipolar transistor the microwave unipolar transistor as there is a single gate this as it is made of the gallium arsenide why the gallium arsenide is used because the gallium arsenide has a high mobility compared to the other semiconductor devices. Due to this high mobility characteristics they are being used in the construction of the unipolar transistor for at a microwave frequency these devices are called as a metal semiconductor field effect transistor and due to this high mobility they are called as a high electron mobility transistor HEMT. The cutoff frequency is also 22 gigahertz frequency and it is given by the same equation that is F T is equal to 1 upon T which we have seen in the previous slides. The gain of such transistor is in the range of 10 to 15 dB at 2 gigahertz and the noise figure is less than 1 dB. This is a construction diagram of the mesh field structural diagram of the mesh field mesh field here a whole region is designed by the semi insulated gallium arsenide in which a P type of active layers are been used and the three terminals are been drained by the omic contacts which are called as a source drain and gate. In this a gallium arsenide n type of fetexyl layer is been grown on the gallium arsenide fabricated by the gallium arsenide. Now the last part that is applications of micro transistor this micro transistors are used in as a low noise transistors they are being used for as a low noise transistors amplifiers as well as at the low level they can be used as a low level transistors they are used in a RF stage at the receiver side in the RF stage we can use such type of the transistors as well as for the they can be used as a power transistors for driving the power amplifier. These are the few applications area where we are using the micro transistors these are the references thank you.