Y-Ba-Cu-O semiconducting pyroelectric thermal sensors: design and test of near infrared amorphous thin film detectors and extension to antenna-coupled THz devices

Since the observation of pyroelectric properties in oxygen depleted semiconducting Y-Ba-Cu-O, the interest of its amorphous phase (a-YBCO) obtained at low deposition temperature (150 degrees C) has been demonstrated for near-infrared (NIR) detection. In the first part of this paper, we investigate material aspects of a-YBCO thin films (surface morphology, electrical transport and optical properties) for a better understanding of the microstructure vs. conductivity relationship. In the second part, we report on the NIR characterization of planar and trilayer detector devices fabricated on silicon substrates. These detectors exhibit a very fast response (time constant tau = 1.9 mu s for planar device; tau = 0.12 mu s for trilayer device) as compared to commercially available pyroelectric sensors. The best noise equivalent power (NEP) and detectivity D*, which are at the state of art, were observed at 10 kHz modulation frequency: NEP = 2.0 pW/Hz(1/2) and D* = 6.6x109 cm.Hz(1/2)/W for planar device; NEP = 2.6 pW/Hz(1/2) and D* = 5.7x10(9) cm.Hz(1/2)/W for trilayer device. We have interpreted this fast response by means of an analytical model without adjustable parameters. In the third part, the potential of THz detection is examined, in the case of a-YBCO coupling to a planar antenna. The general coupling conditions of the THz incident radiation to a-YBCO are examined first, with relation to the film THz absorption coefficient and conductivity measured by time-resolved spectroscopy. The coupling conditions of the film to the readout circuitry are then examined, with relation to the Schottky nature of the metal/a-YBCO contacts.