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How to achieve a homogeneous sensitivity in THz detector arrays. M. Sakhno , J. Gumenjuk-Sichevska , F. Sizov Institute of Semiconductor Physics NASU, Kiev, Ukraine, e-mail: [email protected]. THz CMOS FPA principle. Antenna. Advantages of Si FET THz Detectors - PowerPoint PPT Presentation
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How to achieve a homogeneous sensitivity in
THz detector arrays
M. Sakhno, J. Gumenjuk-Sichevska, F. Sizov
Institute of Semiconductor Physics NASU, Kiev, Ukraine,
e-mail: [email protected]
2
THz CMOS FPA principle
• Advantages of Si FET THz Detectors Based on standard silicon technology with high level of integrationUn-cooled Can be assembled into arrays for real time THz/mm wave imaging;Mechanically robust;Low costs at high volumes
Antenna
FET
3
Detector characterization
'
2
4
meas el
A
SNEP NEPG
1. Uniform NEP for different
elements of the array2. Minimal NEP
Goal
1. Maximal G and ηa
2. Uniform G and ηa
NEP – noise equivalent power. Minimal power which can be detected by detector
• NEPel electrical NEP of detector itself
• G the antenna gain• ηa matching between the
antenna and the detector
4
System photograph (silicon FET array implementation)
Printed antennas on finite electrically thick substrate
Modelled system
5
System parameters
10
75.8
164
20
104
1a ,μm
2a ,μm
r,μm
d ,μm
φ,deg
Modeling using EMSS FEKO
10 mm
1 mm
1mm
The modeled system design: 8 antennas on a substrate of finite size. Antennas are positioned symmetrically relative to the substrate center
6
Cut-off frequency of the first mode fc1 for infinite substrate
1 ,4 1c
r
cfh
h, µm εr=2 εr=7 εr =12
50 1.5THz 0.612 THz 0.452 THz
140 0.536 THz 0.219 THz 0.162 THz650 0.116 THz 0.047 THz 0.035 THz
Pozar, D.: Considerations for millimeter wave printed antennas. IEEE Trans. Antennas Propag. 31, 740–747 (1983)
1cf f 0.25critical dielh
7
2r
7r
12r
1cf f
1cf f
1cf f
0.071diel
h
0.132diel
h
0.173diel
h
Linear gain diagram for substrate thickness h=50 μm, f=300GHz
Each antenna was simulated and the results were combined on one picture to facilitate the comparison of different elements
8
Linear gain diagram for substrate thickness h=140 μm, f=300GHz
2r
7r
12r
1cf f
1cf f
1cf f
0.197diel
h
0.37diel
d
0.484diel
d
9
Linear gain diagram for substrate thickness h=650 μm, f=300GHz
2r
7r
12r
1cf f
1cf f
1cf f
0.920diel
h
1.72diel
h
2.25diel
h
10
Antenna pattern for different substrate relative permittivities
1cf f1cf f
Substrate thickness is h=140 μm
11
Dependence of the calculated total antenna gain G in the normal direction on the substrate permittivity
2 4 6 8 10 12
-25
-20
-15
-10
-5
0
5
10
G, d
Bi
r
G1 G2 G3 G4
1 2 3 4 5 6 7 8
12
Calculated gain for normal direction for 1st and 4th elements
280 290 300 310 320-30
-25
-20
-15
-10
-5
0
5
10
G, d
Bi
f, GHz
1, =2 4, =2 1, =12 4, =12
1 2 3 4 5 6 7 8
13
Antenna – transistor matching
2max
Re Re4 ant tra
tr ant
P Z ZP Z Z
,int1
tr S G GSp
Z R R Zj C
Antenna FET
RG = 150 Ω, RS = 50 Ω, Cp= 4 fFZtr= (200 – j130) Ω at f = 300 GHz
1-μm Si MOSFETW/L = 20/2 (μm)
Sakhno, M., Golenkov, A., & Sizov, F. (2013). Uncooled detector challenges: Millimeter-wave and terahertz long channel field effect transistor and Schottky barrier diode detectors. Journal of Applied Physics, 114(16), 164503. doi:10.1063/1.4826364
14
Antenna-detector matching for different substrate thickness
1 2 3 4 5 6 7 8 • Optimal matching is not for electrically thinnest substrate
• Matching coefficient variation is less than gain variation
15
System with the lens
lh la
123
4
1 2 3 40
5
10
15
20
25 1
2
3
Ang
le fo
r max
imum
gai
n
Element number
Modelled points Linear fit
4
The angle of maximum gain versus the element position for the system with the lens (only the first four elements are shown because of the mirror symmetry). The substrate parameters are h=50 μm, r=2, the incident radiation frequency is 300 GHz
16
Conclusions• The substrate electric thickness in THz FPAs plays a crucial role in the
frequency characteristics of the system• Electrically thick substrate makes NEP of elements non-uniform• Degradation of antenna pattern can be explained by excitation of
substrate modes. • Critical substrate thickness is approximately 0.25 wavelength in
dielectric• Simulation shows that Si CMOS system (substrate thickness h = 50μm
and εr = 2) with the lens can operate as FPA
17
Acknowledgements• This work is partly supported by the SPS:NUKR.SFP 984544 Project
and a joint grant 01-02-2012 from the National Academy of Sciences of Ukraine and Russian Academy of Sciences.
18
Thank You !