Solid State Components The term solidstate refers to the ability to control electron flow in solid substances rather than electromagnetic relay mechanical.

Solid State ComponentsSolid State Components

The term The term solidstatesolidstate refers to the ability to control refers to the ability to control electron flow in solid substances rather than electron flow in solid substances rather than electromagnetic relay mechanical movements. At the electromagnetic relay mechanical movements. At the early stages in the development of electricity the early stages in the development of electricity the opening and closing of switches was done by opening and closing of switches was done by electromagnets. A electromagnets. A relayrelay is a component that allows a is a component that allows a current to pass through a coil of wire wrapped current to pass through a coil of wire wrapped around an iron core. This causes the core to become around an iron core. This causes the core to become

magnetized and pulls the switch closes.magnetized and pulls the switch closes.

When the current is stopped the spring-loaded When the current is stopped the spring-loaded switch in the relay snaps back to open setting. switch in the relay snaps back to open setting. These relays were used to run computers built These relays were used to run computers built as early as the 1920s and large governmental as early as the 1920s and large governmental agencies were running these computers to agencies were running these computers to solve mathematical equations and scientific solve mathematical equations and scientific problems (too bulky and expensive for the problems (too bulky and expensive for the common person to own). common person to own).

These computers were so large that they filled These computers were so large that they filled rooms the size of your classroom. Each time a rooms the size of your classroom. Each time a “query” was run the computer would make “query” was run the computer would make thousands of loud clicking noises due to the thousands of loud clicking noises due to the electromagnetic relays snapping open and electromagnetic relays snapping open and closed. closed.

In 1883 while Thomas In 1883 while Thomas EdisonEdison was was investigating light bulbs and filaments, he investigating light bulbs and filaments, he noticed that noticed that electronselectrons could be driven off a hot could be driven off a hot filament of a lamp and collect them on a filament of a lamp and collect them on a receivingreceiving plate. He called this the “Edison plate. He called this the “Edison Effect”. In 1904 J.A. Fleming built a circuit Effect”. In 1904 J.A. Fleming built a circuit (in a vacuum tube) that changed AC to DC (in a vacuum tube) that changed AC to DC (this is known as rectifier). (this is known as rectifier).

Dr. Lee Deforest went on to produced a Dr. Lee Deforest went on to produced a vacuum tube diode, that used concepts vacuum tube diode, that used concepts developed by Thomas Edison, that allow developed by Thomas Edison, that allow current to flow in only one direction through a current to flow in only one direction through a circuit. circuit.

This was the earliest form of current control This was the earliest form of current control that was not done by relays. Soon after that was not done by relays. Soon after Transistors (or triodes) were developed by Transistors (or triodes) were developed by placing a control grid in the path of the placing a control grid in the path of the flowing electrons. Now they had a variable flowing electrons. Now they had a variable way to control current instead of a switch from way to control current instead of a switch from on to off.on to off.

It wasn’t until It wasn’t until 19481948 at at BellBell Laboratories Laboratories where three scientists Shockley, Brattian, and where three scientists Shockley, Brattian, and Bardeen came up with a way to build Bardeen came up with a way to build diodesdiodes, , triodes, and rectifiers without the need for triodes, and rectifiers without the need for vacuums tubes. These scientists used silicon-vacuums tubes. These scientists used silicon-based materials to produce components that based materials to produce components that control electron flow within solid substances control electron flow within solid substances A.K.A Solid-State. A.K.A Solid-State.

Silicon can be modified to act like a conductor Silicon can be modified to act like a conductor or an insulator depending on the application or an insulator depending on the application and therefore is referred to as a and therefore is referred to as a semiconductorsemiconductor. .

Several materials can be use to produce Several materials can be use to produce semiconductors, but silicon, the main semiconductors, but silicon, the main ingredient of sand, is the most widely used in ingredient of sand, is the most widely used in solid state circuits. Silicon forms 27.7 % of solid state circuits. Silicon forms 27.7 % of the earth’s crust so there is an endless the earth’s crust so there is an endless resource, and the only other material that is resource, and the only other material that is more common is oxygen. Silicon is rarely more common is oxygen. Silicon is rarely found in its pure state, but when purified it is found in its pure state, but when purified it is dark gray in color.dark gray in color.

   Because of silicon ‘s crystal structure in pure Because of silicon ‘s crystal structure in pure

form silicon is a good form silicon is a good insulatorinsulator..

There are two reasons silicon atoms are so There are two reasons silicon atoms are so useful as a semiconductive material: useful as a semiconductive material:

Silicon, like diamonds, form crystal structures Silicon, like diamonds, form crystal structures that hold a very tight bond that act as a good that hold a very tight bond that act as a good insulator. A silicon atom has insulator. A silicon atom has 1414 protons and protons and 1414 electrons but only electrons but only 44 electrons are in the electrons are in the valence (outer most) shell. A valence shell can valence (outer most) shell. A valence shell can actually hold 8 electrons and so silicon finds actually hold 8 electrons and so silicon finds other silicon atoms to share electrons in its other silicon atoms to share electrons in its outer shell. This is know as a covalent bond. outer shell. This is know as a covalent bond.

and in its outer valance shells, as seen in the and in its outer valance shells, as seen in the periodic table box shown below, but it would periodic table box shown below, but it would prefer to have 8 to become Isoelectrically prefer to have 8 to become Isoelectrically neutral neutral (acting like Argon which is a neutral (acting like Argon which is a neutral Ions), see fig 8 - 1a. So naturally each silicon Ions), see fig 8 - 1a. So naturally each silicon atom easily finds four other atoms to share atom easily finds four other atoms to share four other electrons. four other electrons.

This creates the very stable bond called a This creates the very stable bond called a covalentcovalent bond that forms a crystal structure. Fig 8 - 1b shows bond that forms a crystal structure. Fig 8 - 1b shows a cluster of silicon atoms sharing valance shell a cluster of silicon atoms sharing valance shell electrons. Notice that each atom has a total of 8 electrons. Notice that each atom has a total of 8 electrons in their valance shell once they have electrons in their valance shell once they have combine with other atoms.combine with other atoms.

Fig. 8 - 1aFig. 8 - 1a Fig 8 - 1bFig 8 - 1b

Silicon crystal in pure form is an insulating Silicon crystal in pure form is an insulating material unable to allow current to flow material unable to allow current to flow because of the tight bond the atoms make with because of the tight bond the atoms make with each other. In the Periodic Table, Silicon is each other. In the Periodic Table, Silicon is shown as Si with an atomic number of 14 and shown as Si with an atomic number of 14 and a shell structure of (Ne)3sa shell structure of (Ne)3s22pp2 2 (Ne has a (Ne has a structure of 1sstructure of 1s222s2s22pp66). ).

When bonded to other silicon atoms it shares When bonded to other silicon atoms it shares another 4 electrons to act Isoelectrically and another 4 electrons to act Isoelectrically and become neutral. This bond is so tight that it become neutral. This bond is so tight that it does not allow electrons to travel from one does not allow electrons to travel from one atom to the next. atom to the next.

2) Scientist found out that certain foreign 2) Scientist found out that certain foreign atoms mixed in with the silicon could produce atoms mixed in with the silicon could produce materials that can become good conductors. materials that can become good conductors. These foreign atoms can introduce too many These foreign atoms can introduce too many or too few electrons creating an imbalance in or too few electrons creating an imbalance in the crystalline structure. Fig 8-2 shows how the crystalline structure. Fig 8-2 shows how silicon crystals can be grown in the silicon crystals can be grown in the laboratory. laboratory.

A seed string is inserted into a molten silicon liquid A seed string is inserted into a molten silicon liquid and the atoms begin to attract one another to for a and the atoms begin to attract one another to for a pure silicon mass. If trace amounts of impurities pure silicon mass. If trace amounts of impurities such as Boron or Phosphorous are such as Boron or Phosphorous are saltedsalted into the into the molten silicon an insulative material can become a molten silicon an insulative material can become a useful useful ionion capable of conducting electronics. capable of conducting electronics.

Boron is very similar to silicon except it only has 3 Boron is very similar to silicon except it only has 3 electrons in its outer shell compared to silicon’s 4 electrons in its outer shell compared to silicon’s 4 electrons. If a silicon crystal is salted with a few electrons. If a silicon crystal is salted with a few Boron atoms a slight Boron atoms a slight lackinglacking of electrons is produced of electrons is produced and provide places that need to be filled by free and provide places that need to be filled by free electrons. Known as P-type materials this mixture electrons. Known as P-type materials this mixture allows current to flow by the movement of allows current to flow by the movement of holesholes. .

The picture on the right shows a silicon crystal salted The picture on the right shows a silicon crystal salted

with a few phosphorus atoms.with a few phosphorus atoms. Phosphorus is similar to silicon except it has 5 Phosphorus is similar to silicon except it has 5

electrons in the valance shell, one more than is electrons in the valance shell, one more than is needed. This creates a negatively charged needed. This creates a negatively charged crystal that has an crystal that has an surplussurplus of electrons. Known of electrons. Known as N-Type materials Crystals salted with as N-Type materials Crystals salted with Phosphorous allow current to flow by Phosphorous allow current to flow by electronselectrons..

If an N-Type and a P-Type material are joined If an N-Type and a P-Type material are joined together a solid-state together a solid-state junctionjunction is established is established and depending on the polarity of the power and depending on the polarity of the power source allows or stops current.source allows or stops current.

The significance of this ability to create The significance of this ability to create Semiconductors is that these materials can Semiconductors is that these materials can conduct and respond just as the old vacuum conduct and respond just as the old vacuum tube diodes and transistors or even older relay tube diodes and transistors or even older relay switches, yet these are cheaper to build, more switches, yet these are cheaper to build, more durable, and much durable, and much smallersmaller. The rest of this . The rest of this lesson is introducing a few very common solid-lesson is introducing a few very common solid-state components that will most likely be state components that will most likely be involved in every circuit you will ever build. involved in every circuit you will ever build.