Transcript PowerPoint
Basic electronic components A review Made by Yulia I. Isakova As a template for students’ presentations Tomsk 2015 Aim of presentation The aim for today’s presentation is to review basic electronic components which are used to build semiconductor devices. Outline • Different types of materials – Conductors – Insulators – Semiconductors • Silicon as the most common material for semiconductors • Basic electronic component: – Diode – Transistor – Optoelectronics • Examples of application • Conclusion Terminology • • • • • • • • • • • • • • • • Conductivity Conductors Insulators Semiconductors flow of electrons pure silicon wafer crystalline lattice Device Diodes P-n junction Silicon Transistor Lead Optoelectronics Liggh emmiting diode (LED) Infrared detector • • • • To permit To contain To join together biased Electrical conductivity of materials • Materials that permit flow of electrons are called conductors (e.g., gold, silver, copper, etc.). • Materials that block flow of electrons are called insulators (e.g., rubber, glass, Teflon, mica, etc.). • Materials whose conductivity falls between those of conductors and insulators are called semiconductors. • Semiconductors are “part-time” conductors whose conductivity can be controlled. Fig. 1 - Electrical conductivity Silicon • • • Atoms in a pure silicon wafer contains four electrons in outer orbit (called valence electrons). In the crystalline lattice structure of Si, the valence electrons of every Si atom are locked up in covalent bonds with the valence electrons of four neighboring Si atoms. – In pure form, Si wafer does not contain any free charge carriers. – An applied voltage across pure Si wafer does not yield electron flow through the wafer. – A pure Si wafer is said to act as an insulator. In order to make useful semiconductor devices, materials such as phosphorus (P) and boron (B) are added to Si to change Si’s conductivity. Fig. 2 – Atomic configuration and structure of Si Basic electronic components 1. Diodes • A diode is a 2 lead semiconductor that acts as a one way gate to electron flow. – Diode allows current to pass in only one direction. •A pn-junction diode is formed by joining together n-type and p-type silicon. Fig.3 – Schematic symbols of a diode Diode: How it Works —I When a diode is connected to a battery as shown, electrons from the n-side and holes from the p-side are forced toward the center by the electrical field supplied by the battery. The electrons and holes combine causing the current to pass through the diode. When a diode is arranged in this way, it is said to be forward biased. Fig. 5 – Schematic illustration of a p-n junction Basic electronic components 2. Transistor • A three lead semiconductor device that acts as: – an electrically controlled switch, or – a current amplifier. • Transistor is analogous to a faucet. – Turning faucet’s control knob alters the flow rate of water coming out from the faucet. – A small voltage/current applied at transistor’s control lead controls a larger current flow through its other two leads. Fig. 6 – Explanation of a transistor operation Transistor Types: BJT, JFET, and MOSFET • Bipolar Junction Transistor (BJT) – NPN and PNP • Junction Field Effect Transistor (JFET) – N-channel and Pchannel • Metal Oxide Semiconductor FET (MOSFET) – Depletion type (n- and p-channel) and enhancement type (n- and p-channel) Fig. 7 - Different types of transistors Optoelectronics Light emitting diodes Infrared detector In optoelectronics we deal with 2 types of electronic devices. • Light emitting electronic devices: ones that generate electromagnetic energy under the action of electrical field. Example: light emitting diodes (visible and infrared light). • Light detecting devices: ones that transform electromagnetic energy input into electrical current/voltage. Examples: photoresistors, photodiodes, phototransistors, etc. Fig. 8 - Examples of optoelectronics devices: LEDs and IR detector How LED Works • The light-emitting section of an LED is made by joining n-type and p-type semiconductors together to form a pn junction. • When a voltage is applied to the P-N junction, electrons in the n side are excited and move across the pn junction into the p side, where they combine with holes. • As the electrons combine with the holes, photons are emitted. • The pn-junction section of an LED is encased in an epoxy shell that is doped with light scattering particles to diffuse light and make the LED appear brighter. • Often a reflector placed beneath the semiconductor is used to direct the light upward. Fig.9 – Schematic illustration of LED Fig.10 – Principle of light generation in p-n junction Application of LEDs • LED uses fall into four major categories: • Visual signals where light goes more or less directly from the source to the human eye, to convey a message or meaning. • Illumination where light is reflected from objects to give visual response of these objects. • Measuring and interacting with processes involving no human vision.[141] • Narrow band light sensors where LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light Traffic light using LED LED daytime running lights ofAudi A4 Fig.11 – Examples of LEDs application LED digital display that can display four digits and points Conclusion • Depending on electrical conductivity all materials can be divided into three main groups: conductors; insulators and semiconductors • Silicon is the most common material used to build semiconductor devices. • We have reviewed three main components that are used to build electronic devices, namely: diodes, transistors, LEDs.