Ahi terahertz 1
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Transcript of Ahi terahertz 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_electronic_components_and_comparison_o
f_terahertz_imaging_with_x-ray_imaging_techniques
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
Tra
nsm
issi
on m
ode
Ref
lect
ion
mod
e
Table of content
Classification of counterfeit electronic components; the green ticks indicates classes which are distinguishable by THz techniques
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.
Experimental Setup: Transmission mode
Receiver
Transmitter
The Sample
15 20 25 30 35 40
-1.7
-1.6
-1.5
-1.4
-1.3
-1.2
-1.1
Time Delay[Picoseconds]
De
tec
ted
Pu
ks
e [
a.u
.]
Detected THz pulse after passing an IC
Detected THz pulse where no objects is palced Time delay Attenuation
The Sample
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:
cn
v
1c t
nT
c: speed of light in the vacuum
v: speed of light in the material
Δt: The measured time delay and
T: The Thickness
Attenuation coefficient
By equation (3) the attenuation coefficient in units of dB/cm can be calculated:
Where:
1020(log ) 8.7ea a
(3)1020(log ) 8.7e
a a
0
1ln z
a
A
z A (4) 0
a zzA 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
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
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
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.
121
1
cos2
td
n
1 1 1
2
sinsin ( )
n
n
(7)
(8)
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.
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.