Semiconducting YBCO detectors

Room temperature terahertz 2D thermal imaging arrays

 

Context

Low power terahertz waves are fully harmless electromagnetic waves in the frequency range from 500 to 5000 GHz (= 5 THz). These waves can penetrate dielectric or non-conducting materials like plastics, ceramics, paper, wood, fabric, etc. By contrast, metallic or conducting surfaces are reflecting those waves.

THz imaging is therefore a promising technique in the civil security field to detect suspect objects concealed underneath clothing, for instance. In addition to the popular civil security issues, applications also encompass environment domain, health domain (blood circulation, tumour detection), fusion plasma imaging (renewable energy), industry (temperature control, hostile media), low cost cameras, etc.

We are developing pyroelectric detectors made from semiconducting Y-Ba-Cu-O (hereafter YBCO) oxide materials. These semiconductor oxides can be prepared at room temperature in the form of thin films and can be integrated with already processed CMOS electronic readout technologies. Near infrared (IR) tests (at 0.850 µm wavelength) of detectors made from these films show impressive performance in terms of response time (2-3 µs) as compared to commercial pyroelectric detectors (0.1-100 ms). We are now developping these detectors for longer wavelengths (THz waves).


Materials science aspect

Yttrium-based oxides (originally developed in our team in their superconducting phase), exhibit a high bolometric sensitivity when elaborated in the amorphous state, to achieve pixel arrays operating in the direct detection mode. As these materials can be deposited close to room temperature on silicon substrates, co-integration with readout circuitry is possible, therefore leading to attractiveness from an industrial point of view. Thermal coefficients of resistance achieved so far compare favourably to other commercially used oxides (Fig. 1).

Electromagnetic coupling and thermal budget aspects

These concern first the implementation of micro-antennas associated with the elementary pixels, so to optimize the electromagnetic coupling between the incoming radiation and the sensing element. The specificity here is to accommodate the large pixel impedance (several kW) while maintaining a large bandwidth (1 to 4 THz, typically), which leads to non-standard antenna structures (Fig. 2).

To cope with thermal aspects (bolometer sensitivity, crosstalk between pixels), modelling is performed to design pixel arrays with optimized surface density.

                 

Figure 1. TCR values as a function of deposition temperature of semiconductor YBaCuO.  Two temperature windows are evidenced. After Ref. 11  

Figure 2. “Chicken leg” antenna. After Ref. 9

 

Readout electronics aspect

This deals with the design, realization and test of readout and signal processing circuitry associated with the pixel array, currently in CMOS technologies. In particular, low noise, high gain and large bandwidth amplifiers are required.

Figure 3. ASIC Readout circuits layout realized in 0.35 mm CMOS technology (in collaboration with L2E UPMC Univ Paris 06). After Ref. 10

 

   

 

Optical engineering aspect

As an initial step, it concerns the design of detector optical characterization setups, from the near infrared to the far infrared. In view of a direct detection active imaging system design, the main concerns are the scene illumination with a scanned THz source and the associated focusing optics, to reach a compromise between pixel sensitivity, array size and frame rate.

                                       
 

Figure 4. Near infrared (CW or pulsed) characterization of bolometric pixel response (uncooled or cooled devices)

 

          Figure 5. Optical response in the near infrared of a metal / semiconductor YBaCuO / metal trilayer exhibiting pyroelectric high-pass behavior. After Ref. 2 

Related publications

1. M. Razanoelina, S. Ohashi, I. Kawayama, H. Murakami, A. F. Dégardin, A. J. Kreisler, and M. Tonouchi “Measurable lower limit of thin film conductivity with parallel plate waveguide terahertz time domain spectroscopy,” Optics Letters 42 (15), pp. 3056-3059 (2017).

2. A.J. Kreisler, A.F. Dégardin, X. Galiano & D. Alamargui, “Low noise and fast response of IR sensing structures based on amorphous Y-Ba-Cu-O semiconducting thin films sputtered on silicon,” Thin Solid Films 617, pp. 71-75 (2016).

3. A.F. Dégardin, V.S. Jagtap, X. Galiano & A.J. Kreisler, “Semiconducting Y-Ba-Cu-O thin films sputtered on MgO and SiOx/Si substrates: Morphological, electrical and optical properties for infrared sensing applications,” Thin Solid Films 601, pp. 93-98 (2016). doi: 10.1016/j.tsf.2015.11.016

4. X. Galiano, A.F. Dégardin, V.S. Jagtap, A.J. Kreisler, "Fast pyroelectric response of semiconducting Y-Ba-Cu-O detectors with high IR sensitivity," International Conference on Infrared, Millimeter and THz Waves (IRMMW-THz 2015), Hong-Kong (23-28 August 2015), Oral presentation #H1D-2, IEEE Proceedings. doi: 10.1109/IRMMW-THz.2015.7327488

5. A. F. Dégardin, X. Galiano, A. Gensbittel, O. Dubrunfaut, V. S. Jagtap & A. J. Kreisler, "Amorphous Y–Ba–Cu–O oxide thin films: Structural, electrical and dielectric properties correlated with uncooled infrared pyroelectric detection performances," Thin Solid Films 553, pp. 104-108 (2014).

6. A. J. Kreisler, V. S. Jagtap, A. F. Dégardin, “Infrared response in the 95 to 300 K range of detectors based on oxygen-depleted Y-Ba-Cu-O thin films,” Physics Procedia 36, pp. 223-228 (2012).

7. V. S. Jagtap, A. F. Dégardin & A. J. Kreisler, “Low temperature amorphous growth of semiconducting Y-Ba-Cu-O oxide thin films in view of infrared bolometric detection,” Thin Solid Films 520, pp. 4754-57 (2012).

8. A. Gensbittel, O. Dubrunfaut, V. S. Jagtap, A. J. Kreisler & A. F. Dégardin, “Radiofrequency dielectric properties of amorphous semiconducting YBaCuO oxide thin films for bolometric detection,” Thin Solid Films 520,pp. 4749-4753 (2012).

9. A. J. Kreisler, I. Türer, X. Gaztelu, A. Scheuring & A. F. Dégardin, “Terahertz broadband micro-antennas for continuous wave imaging,” in Non Standard Antennas, F. Le Chevalier et al. Eds, Wiley-ISTE, Chapter 6, pp. 119-145 (2011).

10. V. Michal, G. Klisnick, G. Sou, M. Redon, A.J. Kreisler & A.F. Dégardin, “Fixed-gain CMOS differential amplifiers with no external feedback for a wide temperature range,” Cryogenics 49 (11), pp. 615-619 (2009).

11. M. Longhin, A. J. Kreisler and A. F. Dégardin, “Semiconducting YBCO Thin Films for Uncooled Terahertz Imagers”, Materials Science Forum, 587-588, pp. 273-277 (2008).