1. How to achieve a homogeneous sensitivity in THz detector arrays
M. Sakhno, J. Gumenjuk-Sichevska, F. Sizov
Institute of Semiconductor Physics NASU,
Kiev, Ukraine,

2. THz CMOS FPA principle Advantages of Si FET THz Detectors
Antenna
FET
Advantages of Si FET THz Detectors 
Based on standard silicon technology with high level of integration
Un-cooled
Can be assembled into arrays for real time THz/mm wave imaging;
Mechanically robust;
Low costs at high volumes

3. Detector characterization
NEP – noise equivalent power. Minimal power which can be detected by detector
Goal
Uniform NEP for different elements of the array
Minimal NEP
NEPel electrical NEP of detector itself
G the antenna gain
ηa matching between the antenna and the detector
1. Maximal G and ηa
2. Uniform G and ηa

4. System photograph (silicon FET array implementation)
Printed antennas on finite electrically thick substrate
Modelled system

5. System parameters 10 1 mm 75.8 164 1mm 20 104 10 mm
The modeled system design: 8 antennas on a substrate of finite size. Antennas are positioned symmetrically relative to the substrate center
Modeling using EMSS FEKO

6. Cut-off frequency of the first mode fc1 for infinite substrate
Pozar, D.: Considerations for millimeter wave printed antennas. IEEE Trans. Antennas Propag. 31, 740–747 (1983)
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 THz
650
0.116 THz
0.047 THz
0.035 THz

7. 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

9. Linear gain diagram for substrate thickness h=650 μm, f=300GHz

10. Antenna pattern for different substrate relative permittivities
Substrate thickness is h=140 μm

11. Dependence of the calculated total antenna gain G in the normal direction on the substrate permittivity 1 2 3 4 5 6 7 8

12. Calculated gain for normal direction for 1st and 4th elements2 3 4 5 6 7 8

13. Antenna – transistor matching
FET
1-μm Si MOSFET
W/L = 20/2 (μm)
RG = 150 Ω, RS = 50 Ω, Cp= 4 fF
Ztr= (200 – j130) Ω at f = 300 GHz
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), doi: /

14. Antenna-detector matching for different substrate thickness1 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
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 Project and a joint grant from the National Academy of Sciences of Ukraine and Russian Academy of Sciences.

18. Thank You !