Dr. S K Chaudhuri
Former Director, RCI, DRDO, Hyderabad
Fundamental of semiconductors should give directions to young minds for seeds of mini silicon valley of Kolkata. ‘Semiconductor’ The name itself speaks all about it. It is neither conductor like metal nor insulator like wool. This is the reason for which semiconducting material has opened a vast domain called semiconductor electronics. In the modern electronics almost all the components and devices starting from computing chip, mobile phone chip, television chip and so on, are made of semiconductors The major feature of semiconductor material is the scalability of conductivity of the material as per our need.
That means the conductivity of material can be varied by adding additional conducting element like electrons is called doping. And this is the starting point of the electronic component. Materials like Silicon (Si), Germanium (Ge) are such kind of semiconductor material. Well known electronic components which are now basic part of almost of the electronic chip are such as transistors, diodes, capacitances etc. are made of the materials like Si and Ge. Transistor consists of two words ‘transfer’ and ‘resistor’, together ‘transfer-resistor’ and with final abbreviation with ‘transistor’. Transistor, which is considered to be the heart of the semiconductor chip, is basically works in the principle of transfer of electrons and resistance being shown on it on its travelling path. Conducting material only transfers the electrons from one end to the another end with a constant low resistance. Insulating material never transfer electrons rather it always create huge resistance in the current conducting path. But transistor is developed keeping both the properties of conductor and insulator. When voltage is being applied to transistor it acts as a simple conductor with decent resistance but after a certain voltage the conducing behaviour no more exists rather it starts showing resistive behaviour where current does not increase. It remains constant with applied voltage Figure 1 shows the typical behaviour of transistor.
Transistor is a 3-terminal device as shown in Figure 2. It has a special property to amplify the input signal given to it. Among the 3 legs shown in the Figure 2, one leg is being grounded during the amplifier application and between the other two legs, one is considered signal input and the other is considered signal output. This amplifier configuration of transistor is used basically in all kind of communication chips like in mobile phone, television, radio, radar, satellite etc. Similarly transistor can be used as switches by applying certain amount of voltages to the input terminal to switch it ‘on’ and certain amount of voltage to switch it ‘off’. This switching behaviour of transistor which has opened another new dimension.
in the field of electronics is called VLSI. Millions of transistors control the digital signal by switching on and off in VLSI chip. Computer processor is an ideal example of this kind of chips which basically depends on the switching behaviour of transistor. Apart from the transistor device only, semiconductor offers varieties of devices like diode which has only two electrodes, capacitor, inductor, resistor etc. Any electronic circuit which consists of the above mentioned devices along with transistor is shown in the Figure 3. Figure 3 shows the basic circuit of an amplifier circuit where input signal is given in between two electrodes and output voltage is taken from the 3rd terminal as Vout. Corresponding circuit is implemented in printed circuit board (PCB) is shown in the figure 4. The dimension of the PCB board is not less than 3 cm by 3 cm. one can observe that implementation of the circuit with only 7 components the minimum numbers are required is almost about 9 cm2. Can you imagine the area required to implement a VLSI circuit like a computer processors which contains millions of transistors? But now we can find a computer processor intel i7 consisting of 731 millions transistor in 100 cm2 area. So this is the advantage of usage of semiconductor devices. It gives scalability and provides best performances in all the field of electronics. Semiconductor devices are generally smaller in size, it consumes very less space and less power. Now a days, semiconductor technology has become so advanced that it has become less expensive due to its large volume production. It has also longer shelf life. Apart from the large application in VLSI it has equally excelled in the domain of wireless communication.
Modules of communication systems are set up using many components like transmitter, receiver and antennas. Each sub-systems of the communication system consists of lots of electronics circuits and components. Presently, we are using mobile phones which has a complete communication system built in a small handset. This has become only due the growth and development in the field semiconductor. Figure 5 shows the block diagram of a communication module which is integrated in the mobile phone. Similarly, in the space research everything is dependent on the signal which are being sent from Earth station or the signal which are coming from the space. Satellite communication is the only means to get connected to it which is placed in the hundreds of kilometers from the ground. During satellite design every extra pound pays to calculate the accurate
placement of the satellite in the space. Only semiconductor chips due to its light weight and smaller dimension has enabled us thing positive about the space missions. Figure 5 shows the block diagram of a communication system.
Figure 6 shows the communication module in the form of chip and corresponding die. The die is the basic block on semiconductor on which entire circuit has been fabricated. It contains a complete circuit of a commucation sub-system which is having max 9 mm2. If that module would not have been implemented in semiconductor its are would have been 200 cm2 or more than that. The die is properly cut from the wafer and put in a package to make a final product. The following figure shows picture of a die and the die in the chip of a communication chip. A bare semiconductor wafer before fabrication is shown in the figure 7.
The final applications of the semiconductors in the field of communication is visible in the form of towers, antennas, radars, mobile phones etc. as shows in the figure 8. Now in the modern era mainly in every field of application starting from the agriculture, automation, computer science, media, medical field, education electronics has become unavoidable just because of the all the advantages discussed in the field of semiconductor. So, This is how it has shown its power. Future semiconductor is in the hand of next
generation. This is an attempt to make our future generations aware of the semiconductor mission of India.
