Superconducting YBCO HEBs

High sensitivity cooled 1D hot electron bolometer mixer arrays

 

Context

Terahertz (THz) electromagnetic waves, the frequency range of which spans from 300 GHz to 10,000 GHz (= 10 THz), currently provide many fields of practical applications (biomedical, industrial control, homeland security, etc.). Besides, they offer a great interest in fundamental research (astrophysics, condensed matter physics, spectro-chemistry), because of the many entities (atoms, ions, radicals, molecules) that exhibit characteristic frequencies in the THz domain.

In this context, we develop specific thermal detectors (i.e., sensitive to the intensity of incident radiation), called Hot Electron nano-Bolometers (HEB). An HEB is a nanoconstriction elaborated in an ultra-thin film (≈ 40 nm) of the high critical temperature superconducting oxide Y-Ba-Cu-O (YBCO, Tc ≈ 92 K) and coupled to a metal planar micro-antenna. The advantage of YBCO is to exhibit the unique feature of an intrinsic electron-phonon interaction time close to the picosecond, which reflects the ultra-fast response exploitable in the nanodetector.

Materials science aspect

This activity concerns the fabrication of nanodevices (sub-micrometre size constrictions) from ultrathin superconducting PrBaCuO / YBaCuO / PrBaCuO trilayers to form hot electron bolometer devices. The technological challenge resides in maintaining good superconducting properties through the whole fabrication process, including the integration of metal micro-antenna structures. We perform technology steps at Paris South CTU-MINERVE clean rooms.

                  

Figure 1. Nanobridge (0.5 × 0.5 µm2) elaborated on a PrBaCuO (4 nm) / YBaCuO (40 nm) / PrBaCuO (4 nm) trilayer (right) coupled to a0.5 mm overall diameter gold log-periodic THz antenna (left).

Electromagnetic coupling and crosstalk aspects

This concerns the implementation of micro-antennas (of the log-periodic type, typically) associated with the elementary pixels, so to optimize the electromagnetic coupling between the incoming radiation and the sensing element. The specificity here is to minimize the electromagnetic crosstalk between antennas while maintaining a high pixel density for optimized spatial resolution of the imaging array. Another challenge resides in intermediate frequency (IF) routing circuitry design to minimize crosstalk at this level, as well, and avoid spurious coupling with both THz signal and local oscillator radiation.

Optical and microwave engineering aspects

In the case of this heterodyne detection passive imaging system, the main tasks reside on i) designing the THz local oscillator distribution system among the pixels, while respecting stringent specifications in terms of amplitude and phase and ii) rendering this system compatible with image formation path, with adequate quasi optical techniques. Concerning the IF frequency chains, the engineering activity consists in defining the whole signal paths, consisting of microwave low noise amplifiers (LNAs) and additional circuitry to optimize matching between the HEB output and the LNA input.

Characterization aspects

These concern first the electrical characterization of the devices (resistance vs. temperature, voltage vs. current), which are rendered particularly delicate due to the extreme fragility (both mechanical and electrical) of the HEB nanostructures. They also concern the THz response measurements (in both direct detection and mixing modes) with solid-state laser sources.

                             

 

Figure 2.   Electrical characterization of the nanobridge shown in figure 1, exhibiting good superconducting transition after the final antenna fabrication step.

 

 

Figure 3.   HEB device installed to check THz antenna response for co-polarisation and cross-polarization orientations (collaboration with L2E / UPMC Univ Paris 06).

Related publications

1.  R. Ladret, A. Dégardin, V. Jagtap, and A. Kreisler, "THz Mixing with High-TC Hot Electron Bolometers: a Performance Modeling Assessment for Y-Ba-Cu-O Devices," Photonics 6(7), 26 pages (2019). doi:10.3390/photonics6010007

2. R.G. Ladret, A.J. Kreisler & A.F. Dégardin, “YBCO-Constriction Hot Spot Modeling: DC and RF Descriptions for HEB THz Mixer Noise Temperature and Conversion Gain,” IEEE Trans. Appl. Supercond. 25 (3), p. 2300505 (2015).

3. V.S. Jagtap, A.J. Kreisler, M. Redon, G. Klisnick & A.F. Dégardin, “Fourier Gratings Used as THz Multiplexers: Design, Simulation, Test,” International Conference on Infrared, Millimeter and THz Waves (IRMMW-THz 2014), Tucson, USA (14-19 September 2014), Oral presentation #W2D19-12, IEEE Proceedings. DOI 10.1109/IRMMW-THz.2014.6956422.

4. A. J. Kreisler, I. Türer, X. Gaztelu & A. F. Dégardin, “UWB Antennas for CW Terahertz Imaging: Cross Talk Issues,” Ultra-Wideband, Short-Pulse Electromagnetics 10, F. Sabath and E.L. Mokole Eds., Springer, Chap. 43, pp. 473-482 (2014).

5. I. Türer, A. F. Dégardin & A. J. Kreisler, “UWB Antennas for CW Terahertz Imaging: Geometry Choice Criteria,” Ultra-Wideband, Short-Pulse Electromagnetics 10, F. Sabath and E.L. Mokole Eds., Springer, Chap. 42, pp. 463-472 (2014).

6. R. G. Ladret, A. F. Dégardin & A. J. Kreisler, "Nano-patterning and hot spot modeling of YBCO ultrathin film constrictions for THz mixers," IEEE Trans. Appl. Supercond. 23(3), p. 23003305 (2013).

7.   V. S. Jagtap, A. F. Dégardin, G. Klisnick, M. Redon & A. J. Kreisler, “First Experiment on THz Beam Multiplexers Based on Reflection Phase Gratings”, Frontiers in Optics (FIO 2010), Rochester, NY, USA (October 2010), Oral presentation. Frontiers in Optics 2010, OSA Technical Digest (CD) (Optical Society of America, 2010), paper FThP7. 

8.   M. Aurino, A. Martinez, I. Türer, V. S. Jagtap, A. Gensbittel, A. F. Dégardin & A. J. Kreisler, “Ageing and embedding issues for high-Tc superconducting hot-electron bolometers for THz imaging,” SPIE Conf. Defense, Security + Sensing, Orlando, Fl, USA, (April 2010), Oral presentation. SPIE Proc. 7671, pp. 767103-1/10 (2010).

9.  Ch. Péroz, A. F. Dégardin, J-C. Villégier and A. J. Kreisler, “Fabrication and Characterization of Ultrathin PBCO/YBCO/PBCO Constrictions for Hot Electron Bolometer THz Mixing Applications”, IEEE Trans. Appl. Supercond. 17-2(2), pp. 637-640 (2007).