Monade

Mo.Na.De. (Modulated Nanostructured Devices): YBCO response to FIR

The aim of the project is twofold: characterizing the response to far infrared (FIR) radiation of nanostructured YBa₂Cu₃O_7-x (YBCO) films, and showing the advantages of the adopted nanostructuring technique for THz applications. Nanostructuring is obtained by locally modulating the critical current of patterned YBCO film by means of high energy heavy ions (HEHI) irradiation (http://www.polito.it/ricerca/superconductivity/Irradiations). The spatial modulation of the superconductive properties along a single sensor unit is aimed at the FIR signal detection in optimally controlled and thermalized environment.

The product of this research will be a nanostructured demonstrator fitting the project requirements. The data base will allow the development in the next future of a detector in direct or in mixer configuration, especially for medical and space applications.

In fact, studies of electromagnetic radiation in the terahertz frequency range (0.3–3 THz) are important in a number of scientific research fields, such as radioastronomy, atmospheric physics, climatology, military and security applications, biomedical and genetic diagnostic etc. Many device concepts, developed in the past decades, are now obsolete and new solutions must be explored, especially for novel materials, in order to overcome the performance limits of present devices.

This project is intended as an innovative contribution to the improvement of superconducting devices for THz photon detection. Superconductors, used as detectors, offer several advantages with respect to technology based on standard semiconducting materials: fast response time, very low power consumption, broad band in the THz region, ultra low noise. In particular, YBCO-based devices can operate at temperatures accessible by cryocoolers, with the sensitivity and noise level suitable for applications. Moreover, YBCO is robust and chemically stable, compared to other superconducting materials.

Thus, in summary, this project is aimed at characterizing and optimizing the bolometric response to FIR of YBCO thin-film-based sensors; within such sensors, arrays of micrometric-sized active regions will be obtained by HEHI irradiation local nanostructuring [A. Rovelli, E. Mezzetti et al., Nucl. Instr. Meth. B, 240 (2005) 842]. This nanostructuring technique gives localized modulation of critical current by means of columnar defects in YBCO and local strain induced by the substrate, where ions implant. Main advantages of this technique, are: (i) increase of sensitivity to FIR of irradiated regions, in terms of responsivity; (ii) possibility to select the device working temperature between 68-77K; (iii) reduction of the Johnson noise by the pristine non-dissipative banks surronding the irradiated area; (iv) optimal hot-spot diffusion in the active areas through tailoring of the micrometric irradiation confinement; (v) enhancement of speed of future device’s response.