Uncooled pyroelectric a-YBCO detectors in the NIR to the MIR range: performance enhancement induced by calcium doping

YBa₂Cu₃O_6+<i>x</i> (YBCO) films exhibit semiconducting properties when oxygen-depleted (<i>x</i> &lt; 0.5). Moreover, their low-temperature deposition on silicon substrates leads to an amorphous phase (<i>a</i>-YBCO) with interesting pyroelectric properties, which can be exploited in uncooled infrared detectors. However, <i>a</i>-YBCO films exhibit low direct current electrical conductivity, with strong nonlinearity of the current-voltage curves. Calcium doping is well known to improve the transport properties of oxygen-rich YBCO films (<i>x</i> &gt; 0.7). In this paper, the influence of calcium doping of <i>a</i>-YBCO (with a 10% replacement of Y by Ca) was investigated on the performance of two types of detector structures: planar devices, where the <i>a</i>-YBCO sensing film is deposited on two metal contacts, and small-sized trilayer devices where the <i>a</i>-YBCO sensing film is sandwiched between two metal contacts. The first geometry allows for easy fabrication, while the second geometry allows for a lower access resistance of the detector, a clear advantage for preamplifier impedance matching. The current response of doped and undoped film-based devices as a function of the modulation frequency was explored at different wavelengths using a coherent source (850 nm laser diode) or an incoherent source (blackbody radiation at 1073 K). The best competitive performance was observed for small-sized trilayer calcium-doped <i>a</i>-YBCO detectors tested at a wavelength of 850 nm: noise level as low as 17 pW/Hz^1/2, detectivity higher than 2&times;10⁸ cm&#183;Hz^1/2&#183;W^-1 and time constant as short as 11 ns at a modulation frequency of 10 MHz, which is highly promising for fast and low-cost scanning imaging. First promising results were also obtained with the blackbody source heated to 1073 K.