SEMICONDUCTORS & TRANSISTORS
Foundations
What's a Semiconductor?
Insulator
SemiConductors
Conductors
Conductivity
Does not conduct electricity at all
Nonmetals (Ex: O , F, Cl)
Conducts a small amount of electricity
Metalloids (Ex: Si, Ge)
Conducts electricity really well
Metals (Ex: Au, Cu)
Can be increased in semiconductors by increasing TEMPERATURE
Can be increased in semiconductors by adding IMPURITIES
2
Pure Silicon is considered an insulator
Adding Impurities N-Type
When replacing a Si within a crystalline structure of them, with a 5 valence electron nonmetal (for ex: Phosphorous), you create an N-type semiconductor. This now has free valence electron that now can move around
Called a N-Type or negative type because before junction it is slightly negative due to extra valence electrons
Adding Impurities P-Type
When replacing a Si within a crystalline structure of them, with a 3 valence electron metal or metalloid (for ex: Boron), you create an P-type semiconductor. This now has Hole where an electron is not bonded.
Called the P-types for the positive type, because of the lack of electrons before the junction
Combing a P-type & N-Type
Take a P-Type Si crystal and N-Type Si crystal and combine them to form a PN junction. The extra valence electron in the N-type fills in the hole in the P-type to create that final covalent bond in the PN junction
PN Junction Formtion
The PN Junction forms when the free valence electron moves from the N to the P side across the electric field, which causes a buildup of negative charge on the P-type and a build up of positive charge on the N-type
This PN Junction has a build up of positive and negative charges in the middle creating a depletion region. This depletion region is harder to move more electrons across now. This PN Junction is the basis for diodes, transistors, and solar cells.
PN Junction
PN Circuits
Reverse bias circuit is set up when the P-Type and negative end of the battery are connected and the N-Type and positive end of the battery. It increases the gap or depletion region and no current can flow
PN Circuits
Forward bias circuit is set up when the P-Type and positive end of the battery are connected and the N-Type and negative end of the battery. It collapses or removes the gap or depletion region and current can flow
Circuits to Diodes
Forward bias circuit pushes the electrons to fill the holes and have a free moving circuit. This creates a one way current which can be used as a one way Diode
NPN & PNP Diodes
NPN Diode set up with a circuit in this pattern has a large Depletion region and does not allow anything across it. Currently this circuit does not conduct a current
NPN & PNP Diodes
NPN Diode set up with a circuit in this pattern has a small Depletion region and does allows current across it. It is the addition of the second battery and smaller circuit to reduce the gap. Currently this circuit does conduct a current
The second circuit creates an electrical switch, which then matkes this overall circuit a transistor
Transistors
Types of Transistors
CMOS
BJTs
A bipolar junction transistor using valence electron movement to create N-Type or P-type semiconductors. This will be explained in depth
Complementary Metal oxide semiconductor using P-type and N-type MOSFETs used in many applications, including OpenROAD
Transistors are switches with small currents and bipolar junctions. The E is the emitter, the C is the collector, the B is the Base, and the P and N are the semiconductors.
Transistors
Two Main Types: NPN & PNP
NPN
Current goes into the base
The current through E is the sum of C and B
PNP
Current flows out of the base
Base should go to a low voltage (to prevent overheating)
Current moves high to low
Electrons go low to high
NPN & PNP are completely opposite
NPTransistors Equations
I = I + I
E
C
B
Example 1
Ic = (200)(50) = 10,000 uA = 10 mA
Ie = Ic = I b
= 10,000 + 50= 10,050 uA = 10.05 mA
If the hFE is large, then the Ic approx. equal to the Ie
Example 2
V= potential voltage
R= resistor
Vce = Vc - Ve
Vbe = Vb- Ve = 0.6 ->0.7V
Vcb = Vc - Vb
Vcc = +9v (given)
Vee = 0V (ground)
Example 2
Vce = Vc - Ve
use a multimeter to find this one
Vbe = Vb- Ve = 0.6 ->0.7V
this is a constant for the transistor
Vcb = Vc - Vb
use a multimeter to find this one
Example 3
S = switch
D= diode
R= resistor
Q = transistor
The switch uses a small current to control a large amount of current, close the switch to have current flow through Ib to E & C and turn them ON
Example 3
To solve with the given:
Rb 100 K Ohm
Rc 220 Ohm
Beta 100
Ic (max) = Vcc/ Rc = Sat current
Vbe = 0.6 V Ib Vbe
Ib = Va- Vb / Rb
= 12V- 0.6V/100k Ohms = .114 mA
Ohm's Law says that if you divide
volts by Ohms = Amps
volts by k Ohms = m Amps
Example 3
Use the equation above
= (100)(.114 mA)
Ic = 11.4 mA
V = Ir
Va - Vd = Ic(Rc)
Vd= Va- Ic(Rc)
=12V-(.0114A)(220 Ohms)
= 9.492 V
Green LEDs are typically 2V
Vce = 7.49 V
Vce = 1/2 Vcc, so Vcc = 12V
Vce = 6V (midpoint bias)
3 Types of Operating Regions
Type 1: Cutoff
3 Types of Operating Regions
Type 2: Active
Vcc - Vd
Rc
Ib Ic (sat)
Vcc
3 Types of Operating Regions
Type 3: Saturation
C(sat)
Rc + Re
Moore's Law
Intel celebrated 75 years of the transistor and Moore's Law with a pledge to hit 1 trillion transistors by 2030. They are actively researching and working towards this goal, but is it attainable?
The future demands a low power, more sustainable chip--will it be Intel or someone else? Or will Moore's Law end?
The End