1. Terahertz Characterization of Electronic
Components
Kiarash Ahi, Navid Asadizanjani, Sina Shahbazmohamadi, Mark
Tehranipoor and Mehdi Anwar
If you want to use these slides, please reference to our work:
K. Ahi, N. Asadizanjani, S. Shahbazmohamadi, M. Tehranipoor, and M. Anwar,
“Terahertz characterization of electronic components and comparison of terahertz
imaging with X-ray imaging techniques,” in . Proc. SPIE 9483, Terahertz Physics,
Devices, and Systems IX: Advanced Applications in Industry and Defense, 94830X
(May 13, 2015).
https://www.researchgate.net/publication/278034592_Terahertz_characterization_of_ele
ctronic_components_and_comparison_of_terahertz_imaging_with_x-
ray_imaging_techniques

2. Overview
 Background and principles of THz pulse generation and detection for
producing THz images
 Experimental Setup in Transmission mode
 Applications of THz radiation in characterization of objects (refractive
indices, absorption coefficients) in Transmission mode
 Producing THz images in transmission mode: Using Attenuation
Coefficient and Time Delay
 Experimental Setup in reflection mode
 Applications of THz radiation in characterization of objects (seeing
the different layers, that floppy disk, blacktopped ICs) in reflection
mode
 THz images in reflection mode: THz tomography
TransmissionmodeReflectionmode

3. Table of content
Classification of counterfeit electronic components; the green ticks
indicates classes which are distinguishable by THz techniques

4. Background and principles of THz pulse generation
and detection for building THz images
The first THz imaging system was introduced less than twenty
years ago, in 1995 by AT&T Bell Laboratories .
Since pulsed femtosecond THz lasers were not commercially
available until just less than two decades ago, THz imaging and
THz spectroscopy have yet to find their roles in wide variety of
applications.
THz techniques can be used for determining the materials in wide
variety of objects from medicines to electronic components.
THz techniques have several advantages over other inspection
and characterization techniques. THz radiation is non-ionizing
and thus not only safer for human in compare to ionizing
techniques like X-ray or gamma inspections but also
nondestructive for electronic components and other objects.

5. Experimental Setup: Transmission mode
Receiver
Transmitter
15 20 25 30 35 40
-1.7
-1.6
-1.5
-1.4
-1.3
-1.2
-1.1
Time Delay[Picoseconds]
DetectedPukse[a.u.] Detected THz pulse after passing an IC
Detected THz pulse where no objects is palced
Time
delay Attenuation

6. Refractive index
The fraction of the speed of light in the vacuum, c, in compare
to its speed in a material, v, is defined as refractive index, n:
(1)
Which gives equation (2) to be used for calculating the
refractive index of the ICs in this experiment setup.
(2)
Where:
c
n
v

1
c t
n
T

 
c: speed of light in
the vacuum
v: speed of light in
the material
Δt: The measured
time delay and
T: The Thickness

7. Attenuation coefficient
By equation (3) the attenuation coefficient in units of dB/cm can be calculated:
Where:
1020(log ) 8.7e
a a  
(3)
1020(log ) 8.7e
a a  
0
1
ln z
a
A
z A
   (4) 0
a z
zA A e 
 (5)
µa: amplitude attenuation
factor
A0: amplitude of the
traveling wave
Az: attenuated amplitude of
the traveling wave
z: transmitter to the
receiver axis
and

8. Characterization Based on Refractive Index and
Attenuation Coefficient
Refractive Index of the Authentic ICs at 1 THz :
1.79
Refractive Index of the Counterfeit ICs at 1 THz :
1.82
Attenuation Coefficient of the Authentic ICs at 1 THz :
2.263×104
Attenuation Coefficient of the Counterfeit ICs at 1 THz :
2.475×104 dB/cm

9. Characterization Based on Refractive Index and
Attenuation Coefficient

10. Broadband terahertz characterization of the
refractive index
Variations of refractive indices of materials in different THz frequencies can give
a signature to characterize them.
In the following Figure refractive indices of two authentic ICs and their
counterfeit one are depicted.
Interestingly, the refractive indices of the authentic ICs are the same in the THz
frequency domain while that of the counterfeit one stands out.
2

11. THz techniques in reflection mode
The transmitted THz pulse
The received
THz pulse
X-ray

12. Distance between the different layers of an object
Having the refractive index (calculating it using the method in
transmission mode) one can calculate the distance between the surface,
the die and the leads using the equation (7).
Where θ is calculated by equation (8).
In this experiment and thus . Substituting the values into equation (7)
gives the thickness of the layer between the surface and the die as 766
μm which is in consistence with results of the thickness measurements
of x-ray tomography.
12
1
1
cos
2
t
d
n



1 1 1
2
sin
sin ( )
n
n

 

(7)
(8)

13. Discrimination of Blacktopped IC
THZ:
Using equation (7) and the refractive
index for organic materials gives the
thickness of the blacktopped layer as
250 μm.
X-ray tomography:
Blacktopping materials are transparent to
x-ray, thus x-ray tomography imaging
cannot be used for distinguishing the
blacktopped components.
Other Techniques:
Fourier Transform Infrared Spectroscopy
(FTIR) and Energy Dispersive X-ray
Spectroscopy (EDS), Scanning electron
microscopy (SEM) and scanning acoustic
microscopy (SAM) can be used but these
are more time consuming than THz,
expensive and mostly destructive.

14. Conclusions
THz pulse lasers have not been commercially available until only two
decades ago and thus THz techniques need to be developed for
different aspects of science and engineering.
One of the highly promising fields for THz techniques is characterization
and inspection via imaging of inside the objects.
It was also showed that, a wide variety of counterfeit electronic
components are also distinguishable with THz techniques.
THz techniques are fast, economically reasonable, reliable, accessible
for wide variety of consumers, nonhazardous and nondestructive.
Other techniques are mostly destructive, time consuming, hazardous to
personnel, human dependent and thus expensive and with higher errors
while THz is nondestructive, fast, safe for personnel and accurate.