Non-Ideal MOS Capacitor

In Chapter 18, you saw the operation of ideal MOS capacitors where the substrate was grounded, the gate metal and semiconductor had the same workfunctions (flat-band condition) and there were no charges inside the gate insulator. Let’s see what happens when we relax each of these assumptions.

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Body Voltage

P-Type MOS Capacitor

Let’s assume you can control the gate and body voltages independently. What combination of the voltages will take the device in accumulation? What about Inversion? What happens if the two voltages are non-zero but equal?

Doping Density (per cm3):

Gate Voltage (V): 0.0

0

0.4

0.8

1.2

1.6

2.0

Body Voltage (V): 0.0

0

0.4

0.8

1.2

1.6

2.0

Total Voltage: 0.0 V

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Body Voltage

N-Type MOS Capacitor

You can do the same experiments with this N-Type MOS capacitor.

Doping Density (per cm3):

Gate Voltage (V): 0.0

0

0.4

0.8

1.2

1.6

2.0

Body Voltage (V): 0.0

0

0.4

0.8

1.2

1.6

2.0

Total Voltage: 0.0 V

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Gate Metal Work Function

P-Type Capacitor

Change the workfunction of the gate metal and find the workfunction that results in flat-band condition. What is the workfunction of the semiconductor? Change the gate metal workfunction to and see how you should change the gate voltage to have a flat band-diagram inside the semiconductor and compare it to the difference between the workfunctions of the metal and semiconductor.

Doping Density (per cm3): 1017

Metal Work Function:

4.2

4.6

5.0

Applied Voltage (V)

-1.2

-0.8

-0.4

0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

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Gate Metal Work Function

N-Type MOS Capacitor

What happens if we change the doping type? Repeat the experiments and see what changes.

Doping Density (per cm3): 1017

Metal Work Function:

4.2

4.6

5.0

Applied Voltage (V)

-1.2

-0.8

-0.4

0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

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Charge Inside Gate Insulator

P-Type MOS Capacitor

In most cases, there is some charge trapped inside the gate insulator. Change the position, sign, and amount of charge and see how the voltage that results in a flat band-diagram inside the semiconductor changes

Doping Density (per cm3):

Charge in Insulator: 0 μC/cm²

-0.56

-0.28

0

0.28

0.56



Charge Position: -10nm

Applied Voltage (V)

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

z

1.6

2.0

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Charge Inside Gate Insulator

N-Type MOS Capacitor

In most cases, there is some charge trapped inside the gate insulator. Change the position, sign, and amount of charge and see how the voltage that results in a flat band-diagram inside the semiconductor changes

Doping Density (per cm3):

Charge in Insulator: 0 μC/cm²

-0.56

-0.28

0

0.28

0.56



Charge Position: -10nm

Applied Voltage (V)

-2.0

-1.6

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

1.6

2.0

To know how scroll.js works, this div provides whitespace to the last scene.