Chapter 1-1
Microelectronics Microelectronics Circuit Analysis and Circuit Analysis and DesignDesign
Donald A. NeamenDonald A. Neamen
Chapter 1Chapter 1
Semiconductor Materials and Semiconductor Materials and DevicesDevices
Chapter 1-2
In this chapter, we will:In this chapter, we will: Gain a basic understanding of Gain a basic understanding of
semiconductor material propertiessemiconductor material properties– Two types of charged carriers that exist Two types of charged carriers that exist
in a semiconductorin a semiconductor– Two mechanisms that generate currents Two mechanisms that generate currents
in a semiconductorin a semiconductor
Chapter 1-3
Determine the properties of a pn Determine the properties of a pn junctionjunction
– Ideal current–voltage characteristics Ideal current–voltage characteristics of a pn junction diodeof a pn junction diode
Examine dc analysis techniques Examine dc analysis techniques for diode circuits using various for diode circuits using various models to describe the nonlinear models to describe the nonlinear diode characteristicsdiode characteristics
Chapter 1-4
Develop an equivalent circuit for a diode Develop an equivalent circuit for a diode that is used when a small, time-varying that is used when a small, time-varying signal is applied to a diode circuitsignal is applied to a diode circuit
Gain an understanding of the properties Gain an understanding of the properties and characteristics of a few specialized and characteristics of a few specialized diodesdiodes
Design a simple electronic thermometer Design a simple electronic thermometer using the temperature characteristics of a using the temperature characteristics of a diodediode
Chapter 1-5
Intrinsic Intrinsic SemiconductorsSemiconductors Ideally 100% pure materialIdeally 100% pure material
– Elemental semiconductorsElemental semiconductors Silicon (Si)Silicon (Si)
– Most common semiconductor used todayMost common semiconductor used today
Germanium (Ge)Germanium (Ge)– First semiconductor used in p-n diodesFirst semiconductor used in p-n diodes
– Compound semiconductorsCompound semiconductors Gallium Arsenide (GaAs)Gallium Arsenide (GaAs)
Chapter 1-6
Silicon Silicon (Si)(Si)
Covalent bonding of one Si atom with four other Si atoms to form tetrahedral unit cell.
Chapter 1-7
Effect of TemperatureEffect of Temperature
At 0K, no bonds are broken.
Si is an insulator.
As temperature increases, a bond can break, releasing a valence electron and leaving a broken bond (hole).
Current can flow.
Chapter 1-8
Energy Energy Band Band DiagraDiagramm
EEvv – Maximum energy of a valence electron or hole – Maximum energy of a valence electron or hole
EEcc – Minimum energy of a free electron – Minimum energy of a free electron
EEgg – Energy required to break the covalent bond – Energy required to break the covalent bond
Chapter 1-9
Movement of HolesMovement of Holes
A valence electron in a nearby bond can move to fill the broken bond, making it appear as if the ‘hole’ shifted locations.
Chapter 1-10
Intrinsic Carrier Intrinsic Carrier ConcentrationConcentration
kT
E
i
g
eBTn 223
B – coefficient related to specific semiconductorT – temperature in KelvinEg – semiconductor bandgap energy
k – Boltzmann’s constant(86х10-6eV/K)
310105.1)300,( cmxKSini
Chapter 1-11
Semiconductor Semiconductor constantsconstants
Material Eg(ev) B(cmMaterial Eg(ev) B(cm -3-3KK-3/2-3/2))
------------------------------------------------------------------------------------------------------------
Silicon 1.1 5.23X10Silicon 1.1 5.23X101515
Gallium arsenide(GaAs) 1.4 Gallium arsenide(GaAs) 1.4 2.10X102.10X101414
Germanium 0.66 1.66X10Germanium 0.66 1.66X101515
Chapter 1-12
Exercise Exercise
1.1 Calculate the intrinsic carrier 1.1 Calculate the intrinsic carrier concentration in silicon at concentration in silicon at T=300K.T=300K.
1.2 Calculate the intrinsic carrier 1.2 Calculate the intrinsic carrier concentration in Gallium arsenide concentration in Gallium arsenide and Germanium at T=300K.and Germanium at T=300K.
Chapter 1-13
Extrinsic Extrinsic SemiconductorsSemiconductors Impurity atoms replace some of Impurity atoms replace some of
the atoms in crystalthe atoms in crystal– Column V atoms in Si are called Column V atoms in Si are called
donor impurities.donor impurities.– Column III in Si atoms are called Column III in Si atoms are called
acceptor impurities.acceptor impurities.
Chapter 1-14
Phosphorous – Donor Impurity in SiPhosphorous – Donor Impurity in Si
Phosphorous (P) replaces a Si atom and forms four covalent bonds with other Si atoms.
The fifth outer shell electron of P is easily freed to become a conduction band electron, adding to the number of electrons available to conduct current.
Chapter 1-15
Boron – Acceptor Impurity Boron – Acceptor Impurity in Siin Si
Boron (B) replaces a Si atom and forms only three covalent bonds with other Si atoms.
The missing covalent bond is a hole, which can begin to move through the crystal when a valence electron from another Si atom is taken to form the fourth B-Si bond.
Chapter 1-16
Electron and Hole Electron and Hole ConcentrationsConcentrationsn = electron concentrationn = electron concentration
p = hole concentrationp = hole concentrationpnni 2
n-type:n-type:
n = Nn = NDD, the donor concentration, the donor concentration
p-type:p-type:
p = Np = NAA, the acceptor concentration, the acceptor concentration
Ai Nnn /2
Di Nnp /2
Chapter 1-17
Drift Drift CurrentsCurrents
Electrons and hole flow in opposite directions when under the influence of an electric field at different velocities.
The drift currents associated with the electrons and holes are in the same direction.
Chapter 1-18
Diffusion CurrentsDiffusion Currents
Both electrons and holes flow from high concentration to low.
The diffusion current associated with the electrons flows in the opposite direction when compared to that of the holes.
Chapter 1-19
p-n Junctions
A simplified 1-D sketch of a p-n junction (a) has a doping profile (b).
The 3-D representation (c) shows the cross sectional area of the junction.
Chapter 1-20
Built-in PotentialBuilt-in Potential
This movement of carriers creates a space charge or depletion region with an induced electric field near x = 0.
A potential voltage, vbi, is developed across the junction.
Chapter 1-21
Calculate VCalculate Vbibi
2 2ln lna d a d
bi Ti i
N N N NkTV V
e n n
Where VT=kT/e, k=Boltzmann’s constant. T=absolute temperature, e=the magnitude of the electronic charge, and Na and Nd are the net acceptor and donor concentrations in the p- and n- regions, respectively.
Chapter 1-22
Reverse BiasReverse Bias
Increase in space-charge width, W, as VR increases to VR+VR.
Creation of more fixed charges (-Q and +Q) leads to junction capacitance.
Chapter 1-23
Forward Biased p-n Forward Biased p-n JunctionJunction
Applied voltage, vD, induces an electric field, EA, in the opposite direction as the original space-charge electric field, resulting in a smaller net electric field and smaller barrier between n and p regions.
Chapter 1-24
Minority Carrier ConcentrationsMinority Carrier Concentrations
Gradients in minority carrier concentration generates diffusion currents in diode when forward biased.
Chapter 1-25
Ideal Current-Voltage (I-V) Ideal Current-Voltage (I-V) CharacteristicsCharacteristics
The p-n junction only conducts significant current in the forward-bias region.
iD is an exponential function in this region.
Essentially no current flows in reverse bias.
Chapter 1-26
)1( nkT
qv
sD
D
eII
Ideal Diode EquationIdeal Diode EquationA fit to the I-V characteristics of a diode yields the following equation, known as the ideal diode equation:
kT/q is also known as the thermal voltage, VT.
VT = 25.9 mV when T = 300K, room temperature.
Chapter 1-27
)1( T
D
V
v
sD eII
Chapter 1-28
Ideal Diode EquationIdeal Diode Equation
)log(log
)log( sDT
D IvnV
ei
The y intercept is equal to IS.
The slope is proportional to 1/n.
When n = 1, iD increased by ~ one order of magnitude for every 60-mV increase in vD.
Chapter 1-29
Circuit SymbolCircuit Symbol
Conventional current direction and polarity of voltage drop is shown
Chapter 1-30
Breakdown VoltageBreakdown Voltage
Mechanism:
(1) Avalanche breakdown
(2) Zener breakdown
breakdown voltage (BV)
Chapter 1-31
Transient ResponseTransient Response
Chapter 1-32
Transient ResponseTransient Response
It is composed of a storage time, ts, and a fall time, tf.
Chapter 1-33
EX1.3 Determine VEX1.3 Determine Vbi bi for a silicon pn for a silicon pn junction at T=300K forjunction at T=300K for (a) N (a) Naa=10=101515cmcm-3-3, N, Ndd=10=101717cmcm-3-3, ,
and for and for
(b) N(b) Naa=N=Nd d =10=101717cmcm-3-3..
Chapter 1-34
dc Model of Ideal Diodedc Model of Ideal Diode
Equivalent Circuits
Chapter 1-35
Half-Wave Half-Wave Diode RectifierDiode Rectifier
Diode only allows current to flow through the resistor when vI ≥ 0V. Forward-bias equivalent circuit is used to determine vO under this condition.
Chapter 1-36
Graphical Analysis Graphical Analysis TechniqueTechnique
Simple diode circuit where ID and VD are not known.
PS D D
PS DD
PS D
V I R V
V VI
RV V
R R
Chapter 1-37
Load Line AnalysisLoad Line Analysis
PS D D
PS DD
PS D
V I R V
V VI
RV V
R R
Chapter 1-38
Piecewise Linear ModelPiecewise Linear Model
Two linear approximations are used to form piecewise linear model of diode.
Chapter 1-39
Diode Piecewise Equivalent CircuitDiode Piecewise Equivalent Circuit
The diode is replaced by a battery with voltage, V, with a resistor, rf, in series when in the ‘on’ condition (a) and is replaced by an open when in the ‘off’ condition, VD < V.
Chapter 1-40
Q-pointQ-point
The x intercept of the load line is the open circuit voltage and the y intercept is the short circuit current.
The Q-point is dependent on the power supply voltage and the resistance of the rest of the circuit as well as on the diode I-V characteristics.
Chapter 1-41
Load Line: Reverse Biased DiodeLoad Line: Reverse Biased Diode
The Q-point is always ID = 0 and VD = the open circuit voltage when using the piecewise linear equivalent circuit.
Chapter 1-42
PSpice AnalysisPSpice Analysis
V1 sweep from 0 to 5V.
Chapter 1-43
1.4 Diode Circuits: AC 1.4 Diode Circuits: AC Equivalent CircuitEquivalent Circuit
Objective: Develop an equivalent Objective: Develop an equivalent circuit for a diode that used when circuit for a diode that used when a small, time-varying signal is a small, time-varying signal is applied to a diode circuit.applied to a diode circuit.
Chapter 1-44
ac Circuit Analysisac Circuit AnalysisCombination of dc and sinusoidal input voltages modulate the operation of the diode about the Q-point.
Chapter 1-45
Sinusoidal AnalysisSinusoidal Analysis
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Chapter 1-46
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Chapter 1-47
ExampleExample Objective: Analyze the circuit Objective: Analyze the circuit
shown in figure below.shown in figure below.
Assume circuit and diode parameters of VPS=5V, R=5KΩ, Vγ=0.6V, and vi=0.1sinwt(V).
Chapter 1-48
Solution: DC+AC Solution: DC+AC methodmethod
For the DC analysis: set vFor the DC analysis: set v ii=0,=0,
mAR
VVI PS
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The DC value of the output voltage is
Chapter 1-49
For the ac analysis, set VFor the ac analysis, set VPSPS=0. =0. The ac kirchhoff voltage law The ac kirchhoff voltage law (KVL) equation becomes(KVL) equation becomes
Chapter 1-50
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Chapter 1-51
EX1.4 Assume the circuit EX1.4 Assume the circuit and diode parameters for and diode parameters for the circuit in figure the circuit in figure 1.34(a) are 1.34(a) are VVPSPS=10V,R=20K=10V,R=20KΩΩ,V,Vγγ=0.7V,=0.7V,and vand vII=0.2sinwtV. =0.2sinwtV. Determine the quiescent Determine the quiescent diode current and the diode current and the time-varying diode time-varying diode current.current.
Chapter 1-52
!! !! Comment: Throughout the text, we Comment: Throughout the text, we will divide the circuit analysis into a will divide the circuit analysis into a dc analysis and an ac analysis. To do dc analysis and an ac analysis. To do so, we will use separate equivalent so, we will use separate equivalent circuit models for each analysis.circuit models for each analysis.
Chapter 1-53
Minority Carrier ConcentrationMinority Carrier Concentration
Time-varying excess charge leads to diffusion capacitance.
Frequency response
Chapter 1-54
Equivalent CircuitsEquivalent Circuits
When ac signal is small, the dc operation can be decoupled from the ac operation.
First perform dc analysis using the dc equivalent circuit (a).
Then perform the ac analysis using the ac equivalent circuit (b).
Chapter 1-55
Small Signal Equivalent Small Signal Equivalent ModelModel
Simplified model, which can only be used when the diode is forward biased.
Complete model
Chapter 1-56
1.5 Other Diode Types1.5 Other Diode Types
1.5.1 Solar cell1.5.1 Solar cell
1.5.2 Photodiode1.5.2 Photodiode
1.5.3 Light-Emitting Diode1.5.3 Light-Emitting Diode
1.5.4 Schottky Barrier Diode 1.5.4 Schottky Barrier Diode
1.5.5 Zener Diode1.5.5 Zener Diode
Chapter 1-57
1.5.1 Solar cell1.5.1 Solar cell
A solar cell is a pn junction device A solar cell is a pn junction device with no voltage directly applied with no voltage directly applied across the junction, which converts across the junction, which converts solar energy into electrical energy, solar energy into electrical energy, is connected to a load.is connected to a load.
Chapter 1-58
Chapter 1-59
1.5.2 Photodiode1.5.2 Photodiode
Attention: Reverse biasedAttention: Reverse biased
Chapter 1-60
1.5.3 Light-Emitting 1.5.3 Light-Emitting DiodeDiode
Chapter 1-61
Optical Transmission Optical Transmission SystemSystem
LED (Light Emitting Diode) and photodiode are p-n junctions.
Chapter 1-62
1.5.4 Schottky Barrier 1.5.4 Schottky Barrier DiodeDiode
A metal layer replaces the p region of the diode.
Circuit symbol showing conventional current direction of current and polarity of voltage drop.
Chapter 1-63
Comparison of I-V Characteristics: Comparison of I-V Characteristics:
Forward BiasForward Bias
The built-in voltage of the Schottky barrier diode, V(SB), is about ½ as large as the built-in voltage of the p-n junction diode, V(pn),.
Chapter 1-64
1.5.5 Zener Diode 1.5.5 Zener Diode
Usually operated in reverse bias region near the breakdown or Zener voltage, VZ.
Note the convention for current and polarity of voltage drop.
Circuit Symbol
Chapter 1-65
Example 1.13Example 1.13Given VZ = 5.6V
rZ = 0
Find a value for R such that the current through the diode is limited to 3mA
Chapter 1-66
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ZPS
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Chapter 1-67
Design example :Digital Design example :Digital ThermometerThermometer
Use the temperature dependence of the forward-bias characteristics to design a simple electronic thermometer.
Chapter 1-68
SolutioSolutionn
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Given: IS = 10-13 A at T = 300K
Assume: Ideal diode equation can be simplified.
VeEg 12.1
Chapter 1-69
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Chapter 1-70
Chapter 1-71
Note:,Note:,
to complete this design, two to complete this design, two additional components must be additional components must be added to the circuit shown hereadded to the circuit shown here
Chapter 1-72
Two additional Two additional components:components:
An op-amp circuit to measure the An op-amp circuit to measure the diode voltage;diode voltage;
An ADC to convert the voltage to An ADC to convert the voltage to a temperature reading.a temperature reading.
Chapter 1-73
Problem 1.42Problem 1.42
First, determine if the diode is on or off. Is the open circuit voltage for the diode greater or less than V?
Chapter 1-74
The voltage at the node connected to the p side of the diode is
2kW 5V/(4kW) = 2.5V
The voltage at the node connected to n side of the diode is
2kW 5V/(5kW) = 2V
The open circuit voltage is equal to the voltage at the p side minus the voltage at the n side of the diode:
Voc = 2.5V – 2V = 0.5V.
To turn on the diode, Voc must be ≥ V.
Chapter 1-75
EX1.5 (Solution can refer to next EX1.5 (Solution can refer to next page)page)
Design a circuit that has a voltage transfer function shown to the left.
(pp 60)
Chapter 1-76
SolutionSolution
For 0V ≤ vI < 8.2V, the voltage transfer function is linear.
When vI = 0V, vO = 0V so there is no need to include a battery in the piecewise linear model for this voltage range.
Since there is a 1:1 correspondence between vI and vO, this section of the transfer function can be modeled as a 1 resistor.
Chapter 1-77
solution con’tsolution con’t
When vI ≥ 8.2V, the output voltage is pinned at 8.2V, just as if the device suddenly became a battery.
Hence, the model for this section is a battery, where V = 8.2V.
Chapter 1-78
Circuit for 1.63Circuit for 1.63
Chapter 1-79
Or, if you assumed a more common V, say of 0.7V, then the circuit would be:
solution con’tsolution con’t