Electronic Devices and Circuits - Introduction with Real Time Examples

Electronic Devices and Circuits

Introduction Class about EDC Course:

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Definition:

An electron is a negatively charged subatomic particle. It can be either free or bound to the nucleus of an atom as shown in figure 0.0. It is a charged particle, the charge, or quantity, of negative electricity and the mass of the electron have been found to be 1.60 X 10^-19 C (Coulombs) and 9.11 X 10^-31 kg respectively. 

Figure 0.0 

Device Definition: A thing (System) is designed for a particular purpose, especially a piece of Mechanical or Electrical or Electronic Equipment. This is taken input and gives output.

These Devices are generally categorized into various types like Electronic Devices, Electrical Devices and Mechanical Devices shown in following figure 0.1

Figure 0.1

Electronic Devices Definition: a device which is having electronic components for controlling the flow of electrical currents for the purpose of information processing and system control. Electronic devices (Control Systems) are usually small and can be grouped together into packages called integrated circuits. This is taken input and produces desired electronic DC output.

Figure 0.2

Circuit Definition:

A roughly circular line, route, or movement that starts and finishes at the same place, in general way every electronic component having terminals, joining of these terminals can design circuit. It is very necessary for making Electronic Devices.

The motion of electrons through a conductor gives us electric current. This electric current can be produced with the help of batteries and generators. The device which controls the flow of electrons is called electronic device. These devices are the main building blocks of electronic circuits.

What is electronics?

The word electronics is derived from electron mechanics, which means to study the behavior of an electron under different conditions of applied electric field.

Electronics Definition

The branch of engineering in which the flow and control of electrons in vacuum or semiconductor are studied is called electronics. Electronics can also be defined as the branch of engineering in which the electronic devices and their utilization are studied.

Electronics have various branches include, digital electronics, analog electronics, micro electronics, nano-electronics, optoelectronics, integrated circuit and semiconductor device.

History of electronics

Diode vacuum tube was the first electronic component invented by J.A. Fleming. Later, Lee De Forest developed the triode, a three element vacuum tube capable of voltage amplification. Vacuum tubes played a major role in the field of microwave and high power transmission as well as television receivers. 

In 1947, Bell laboratories developed the first transistor based on the research of Shockley, Bardeen and Brattain. However, transistor radios are not developed until the late 1950’s due to the existing huge stock of vacuum tubes.

In 1959, Jack Kilby of Texas Instruments developed the first integrated circuit. Integrated circuits contain large number of semiconductor devices such as diodes and transistors in very small area. 

Advantages of electronics:

Electronic devices are playing a major role in everyday life. The various electronic devices we use in everyday life include 

• Computers 

Today, computers are using everywhere. At home, computers are used for playing games, watching movies, doing research, paying bills and reservation of tickets for railways and airlines. At school, students use computers to complete their assignments.

• Mobile phones

Mobile phones are used for variety of purposes such as for sending text messages, making voice calls, surfing internet, playing games, and listening songs.

• ATM

ATM is an electronic telecommunication device particularly used for withdrawing money at anytime from anywhere. ATM stands for automated teller machine. The customer can withdraw money up to a certain limit during anytime of the day or night.

• Television

Television is an electronic device primarily used for entertainment and knowledge. It is used for watching movies for entertainment, news for knowledge, cartoons for children’s.

• Digital camera

Digital camera is a camera used for taking pictures and videos. This images and videos are stored for later reproduction.

Technologies in Electronics:

SEMICONDUCTOR MATERIALS: Ge, Si, AND GaAs

The construction of every discrete (individual) solid-state (hard crystal structure) electronic device or integrated circuit begins with a semiconductor material of the highest quality.

Introduction about Semiconductor Physics

Semiconductors are a special class of elements having conductivity between that of a good conductor and that of an insulator. 

 In general, semiconductor materials fall into one of two classes:  single-crystal and compound.  Single-crystal semiconductors such as germanium (Ge) and silicon (Si) have a repetitive crystal structure, whereas compound semiconductors such as gallium arsenide (GaAs), cadmium sulfide (CdS), gallium nitride (GaN), and gallium arsenide phosphide (GaAsP) are constructed of two or more semiconductor materials of different atomic structures.

Figure:  Atomic structure of (a) silicon; (b) germanium; and (c) gallium and arsenic.  

As indicated in Fig. 1.3, silicon has 14 orbiting electrons, germanium has 32 electrons, gallium has 31 electrons, and arsenic has 33 orbiting electrons (the same arsenic that is a very poisonous chemical agent). For germanium and silicon there are four electrons in the outermost shell, which are referred to as valence electrons. Gallium has three valence electrons and arsenic has five valence electrons. Atoms that have four valence electrons are called tetravalent, those with three are called trivalent, and those with five are called pentavalent. The term valence is used to indicate that the potential (ionization potential) required to remove any one of these electrons from the atomic structure is significantly lower than that required for any other electron in the structure. 

 In a pure silicon or germanium crystal the four valence electrons of one atom form a bonding arrangement with four adjoining atoms, as shown in Fig.   1.4   .

The three semiconductors used most frequently in the construction of electronic devices are Ge, Si, and GaAs.

Figure 1.0 Electronic Panel boards using Semiconductor Materials

GaAs was more difficult to manufacture at high levels of purity, was more expensive, and had little design support in the early years of development. However, in time the demand for increased speed resulted in more funding for GaAs research, to the point that today it is often used as the base material for new high-speed, very large scale integrated (VLSI) circuit designs.

Insulators, Semi Conductors, and Metals

Types of Materials:

1.      Insulators

2.      Semi Conductors

3.      Metals

Definition: A Very poor Conductor of electricity is called an Insulator: an excellent conductor is a Metal and a substance whose conductivity lies between these extremes is a Semiconductor.

Table 1. Comparison table between Conductor Semiconductor and Insulator

#	Characteristics	Conductor or Metal	Semi-Conductor	Insulator
1	Conductivity	High	Moderate	Low
2	Resistivity	Low	Moderate	Very High
3	Forbidden gap	No forbidden gap	Small forbidden gap	Large forbidden gap
4	Conduction	Large number of Electrons for Conduction	Very small number of Electrons for Conduction	Moderate number of Electrons for Conduction
5	Conductivity value	Very high 10-7mho/m	Between those of conductors and insulators i.e. 10-7 mho/m to 10-13mho/m	Negligible like 10-13mho/m
6	Resistivity value	Negligible; less than 10-5 Ω-m	Between those of conductors and insulators i.e. 10-5 Ω-m to 105 Ω-m	Very high; more than 105 Ω-m
7	Current flow	Due to free electrons	Due to holes and free electrons	Due to negligible free electrons
8	Number of current carriers at normal temperature	Very high	Low	Negligible
9	Band Overlap (Energy Gap)	Both Conduction and Valence bands are Overlapped.	Both bands are separated by an energy gap of 1.1eV	Both bands are separated by an energy gap of  6eV to 10eV
10	0 Kelvin Behavior	Acts like a superconductor	Acts like an insulator	Acts like an insulator
11	Formation	Formed by metallic bonding	Formed by covalent bonding	Formed by ionic bonding
12	Valence Electrons	One valence electron in outermost shell	Four valence electron in outermost shell	Eight valence electron in outermost shell
13	Examples	Copper, Mercury, Aluminum, Silver	Germanium, Silicon	Wood, Rubber, Mica, Paper

Insulators:

 Figure 1.1 Insulator Materials Using Plastic Rubber Material

 Figure 1.2 Insulator Materials Using Ceramic Materials

 Figure 1.3 Different types of Insulating Materials 

Beyond the Syllabus: Topics are covered in Lower Sections. 

Energy levels:

Within the atomic structure of each and every isolated atom there are specific energy levels associated with each shell and orbiting electron, as shown in Fig. 1.1. The energy levels associated with each shell will be different for every element.

However, in general,

The farther an electron is from the nucleus, the higher is the energy state, and any electron that has left its parent atom has a higher energy state than any electron in the atomic structure. 

            Note in Fig. 1.4 that only specific energy levels can exist for the electrons in the atomic structure of an isolated atom. The result is a series of gaps between allowed energy levels.

Figure 1.4 Energy Band Diagrams of Insulator, Semiconductor and Metal

A material may be placed in one of these three classes, depending upon its Energy-Band Structure as shown in above figure.

Insulator:

The energy band structure is indicated schematically shown in figure 1.4a (Energy Gap is E_g = 6eV). The large forbidden band separates the filled valence region from the vacant conduction band. Hence the electron cannot acquire sufficient applied energy so that conduction is not possible i.e insulator. The number of free electrons in an insulator is very small, roughly around 10⁷ electrons /m³

Semiconductor:

A substance for which the width of the forbidden energy region is relatively small (Energy Gap is  1 eV) is called Semiconductor. The number of free electrons in semiconductor lies between 10⁷ electrons /m³ to 10²⁸ electrons /m³.

Review of semi conductor physics:

 

Mobility and Conductivity:

Mobility: In some materials, ability to movement of electrons freely and easily with a drift velocity due to the electric field is applied.

v_d is the drift velocity for electrons so that  V_d α E

V_d=µE

 µ is the mobility constant unit is m²/V-sec 

 

#	Si	Ge	GaAs	InAs
mn (cm2/Vžs)	1400	3900	8500	30,000
mp (cm2/Vžs)	470	1900	400	500

 Conductivity: The degree to which a specified material conducts electricity, calculated as the ratio of the current density in the material to the electric field which causes the flow of current and it is property of a material

i= neAv_d

J =  = nev_d

J = neµE

J = σE (where σ = neµ)

Conductivity property in Materials

 Metal: The conduction in metals is only due to the electrons. When an electric field is applied, few electrons may acquire enough additional energy and move to higher energy within the conduction band. Thus the electrons become mobile. Since the additional energy required for transfer of electrons from valence band to conduction band is extremely small, the conductivity of metal is excellent.

σ = neµ

For a good conductor n is very large, approximately, 10²⁸ electrons/m³

 Semiconductor: The conductivity of a material is proportional to the concentration of free electrons in a semiconductor lies between 10⁷ electrons /m³ to 10²⁸ electrons /m³. Thus, a semiconductor has conductivity much greater than that of an insulator but much smaller than that of a metal.

 Insulator: In this material no electrical conduction is possible due to the number of free electrons in insulator is very small, roughly about 10⁷ electrons/m³.