Laboratory 2:
BJT
OBJECTIVES
➢ The purpose of this lab is to learn how to use Atlas – Silvaco TCAD Tool.
➢ We learn how to use the Atlas command language to define a semiconductor device.
➢ We examine BJT Characteristic.
PREPARATION FOR LAB 2
➢ Install Silvaco Tool.
➢ Read User manual.
REFERENCE
1. Atlas User’s Manual
2. TCAD Examples
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 1
Laboratory 2:
BJT
EXPERIMENT 1
Objective: Understand how to describe a BJT and analyze the I-V characteristics of BJT.
Requirement: Write a code to define a theory npn BJT in Figure 1. The BJT has parameters:
- NDE = 6,7.1018 cm-3 , NDC = 1,3.1014 cm-3, NAB = 3,6.1016 cm-3
- LE = 6 μm, LB = 3 μm, LC = 6 μm
- a = 2 μm
- W1 = 5 μm, W2 = 1 μm
The spacing of x-axis and y-axis are 0.2μm and 0.1μm.
Figure 1
Write the code to show the input characteristic: IB = f(VBE) at VCE = 5V and the output
characteristic: IC = f(VCE) at IB = 2.10-5A
Instruction:
- In this experiment, there are some missing regions. Define them by using an oxide region.
- To calculate the input characteristic IB = f(VBE) at VCE = 5V, a 5V voltage source is applied at
the collector. Then, solve the voltage at the base from 0V to end point (for example 1V). The code
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 2
Laboratory 2:
BJT
for this step is shown below:
#Ib vs Vbe at Vce = 5V
solve vcollector=5
save outf=bjtdata1.str master
load inf=bjtdata1.str master
log outf=bjtdata1.log
solve vbase=0.0 vstep=0.05 vfinal=1 name=base
tonyplot bjtdata1.log
- To calculate the output characteristic IC = f(VCE) at IB = 2.10-5A, a current source is applied at
the base. Then, solve the voltage at the base from 0V to end point (for example 12V). The code
for this step is shown below:
#Ic vs Vce at Ib = 2e-5
contact name=base current
solve ibase=2e-5
save outf=bjtdata2.str master
load inf=bjtdata2.str master
log outf=bjtdata2.log
solve vcollector=0.0 vstep=0.25 vfinal=12.0 name=collector
tonyplot bjtdata2.log
The statement “contact name=base current” is used to switch a current source at the base.
Note: in the simulation, the emitter is always connected to the ground (0V).
Check:
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 3
Laboratory 2:
BJT
➢ Show three results in TonyPlot Tool: the input and output characteristics and structure of
BJT in 2D.
➢ From the input characteristic, calculate the VBE(ON) at VCE = 5V.
➢ From the output characteristic, calculate the VCEsat at IB = 2.10-5A.
➢ In TonyPlot Window display structure, right click and choose “Display…”. Then choose
to display: Contours and Electrodes. Capture the result.
➢ On Toolbar menu, choose Tools → Cutline. Draw a horizontal cutline at 2 micron. Show
the concentration allocation with respect to x-coordinate. Capture and explain why we have
this graph.
➢ Right click, choose to Display Electric Field. Capture and explain the graph.
➢ Then, choose to Potential. Capture and explain the graph.
➢ Then, choose to Total Current Density. Capture and explain the graph.
Note: If you want to display potential, electric field, … on the structrure, you must save .str file
after the electrical simulation step.
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 4
Laboratory 2:
BJT
EXPERIMENT 2
Objective: Understand how to describe a BJT and analyze the I-V characteristics of BJT.
Requirement: Use the npn BJT in experiment 1, write the code to show:
- The input characteristic IB = f(VBE) at VCE = 1V, 3V, 5V, 7V, 9V, 12V
- The output characteristic: IC = f(VCE) at IB = 1.10-5A, 2.10-5A, 4.10-5A, 8.10-5A, 10-4A.
Show all the input characteristics in one graph and all the output characteristics in the other graph.
Instruction:
- In this experiment, we need to simulate and show the input characteristic at 6 conditions of VCE.
We show the example for two conditions:
solve vcollector=1
save outf=bjtdata1.str master
solve vcollector=3
save outf=bjtdata2.str master
load inf=bjtdata1.str master
log outf=bjtdata1.log
solve vbase=0.0 vstep=0.05 vfinal=1 name=base
load inf=bjtdata2.str master
log outf=bjtdata2.log
solve vbase=0.0 vstep=0.05 vfinal=1 name=base
tonyplot -overlay bjtdata2.log bjtdata1.log
Use “tonyplot -overlay” to show all the characteristics on a graph.
Check:
➢ Show two results in TonyPlot Tool: the input and output characteristics.
➢ From the input characteristic, calculate the VBE(ON) at each condition. Fill the table 1.
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 5
Laboratory 2:
BJT
Table 1: VBE(ON) at each condition
VCE (V)
1
3
5
7
9
VBE(ON) (V)
From the table, comment on the trend of the input characteristic.
➢ From the output characteristic, calculate the VCEsat at each condition. Fill the table 2.
Table 2: VCEsat at each condition
IB (A)
1.10-5
2.10-5
4.10-5
8.10-5
10-4
VBE(ON) (V)
From the table, comment on the trend of the output characteristic.
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 6
Laboratory 2:
BJT
EXPERIMENT 3
Objective: Understand how to describe a BJT and analyze the I-V characteristics of BJT.
Requirement: Write a code to define a theory pnp BJT in Figure 2. The BJT has parameters:
- NAE = 8,15.1018 cm-3 , NAC = 2,67.1014 cm-3, NDB = 4,66.1016 cm-3
- LE = 7 μm, LB = 3 μm, LC = 6 μm
- a = 2 μm
- W1 = 5 μm, W2 = 1 μm
The spacing of x-axis and y-axis are 0.2μm and 0.1μm.
Figure 2
Write the code to show the input characteristic: IB = f(VEB) at VEC = 5V and the output
characteristic: IC = f(VEC) at IB = 2.10-5A
Instruction:
- In this experiment, there are some missing regions. Define them by using an oxide region.
- Remember that the emitter is always connected to the ground (0V). In this case, we need to set
the voltage at the base and the collector negative.
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 7
Laboratory 2:
BJT
- The current at collector and base flow from inside BJT to outside, so the value of currents here
is negative.
Check:
➢ Show three results in TonyPlot Tool: the input and output characteristics and structure of
BJT in 2D.
➢ From the input characteristic, calculate the VEB(ON) at VEC = 5V.
➢ From the output characteristic, calculate the VECsat at IB = 2.10-5A.
➢ In TonyPlot Window display structure, right click and choose “Display…”. Then choose
to display: Contours and Electrodes. Capture the result.
➢ On Toolbar menu, choose Tools → Cutline. Draw a horizontal cutline at 2 micron. Show
the concentration allocation with respect to x-coordinate. Capture and explain why we have
this graph.
➢ Right click, choose to Display Electric Field. Capture and explain the graph.
➢ Then, choose to Potential. Capture and explain the graph.
➢ Then, choose to Total Current Density. Capture and explain the graph.
Note: If you want to display potential, electric field, … on the structrure, you must save .str file
after the electrical simulation step.
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 8
Laboratory 2:
BJT
EXPERIMENT 4
Objective: Understand how to describe a BJT and analyze the I-V characteristics of BJT.
Requirement: Write a code to define a practical npn BJT in Figure 3. The BJT has parameters:
- NDE = 8,15.1018 cm-3 , NDC = 2,67.1014 cm-3, NAB = 5,12.1016 cm-3
- LE = 4 μm, LB = 9 μm, LC = 12 μm
- WE = 4 μm, WB = 6 μm, WC = 8 μm
- a = 2 μm
The length of metal contact is 1 μm.
The spacing of x-axis and y-axis are 0.2μm and 0.1μm.
Figure 3
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 9
Laboratory 2:
BJT
Write the code to show the input characteristic: IB = f(VBE) at VCE = 5V and the output
characteristic: IC = f(VCE) at IB = 1.10-5A
Instruction:
- Devide the structure into many regions.
- In this experiment, there are some missing regions. Define them by using an oxide region.
Check:
➢ Show three results in TonyPlot Tool: the input and output characteristics and structure of
BJT in 2D.
➢ From the input characteristic, calculate the VBE(ON) at VEC = 5V.
➢ From the output characteristic, calculate the VCEsat at IB = 1.10-5A.
➢ In TonyPlot Window display structure, right click and choose “Display…”. Then choose
to display: Contours and Electrodes. Capture the result.
➢ On Toolbar menu, choose Tools → Cutline. Draw a horizontal cutline at 2 micron. Show
the concentration allocation with respect to x-coordinate. Capture and explain why we have
this graph.
➢ Right click, choose to Display Electric Field. Capture and explain the graph.
➢ Then, choose to Potential. Capture and explain the graph.
➢ Then, choose to Total Current Density. Capture and explain the graph.
Note: If you want to display potential, electric field, … on the structrure, you must save .str file
after the electrical simulation step.
Department of Electronics
Semiconductor Devices Laboratory (Advanced Program)
Page | 10