Preamplifier development for superconducting tunnel junction array X-ray detector electronics

We have developed a very low noise preamplifier that meets the low-cost, high-density requirements for use with superconducting tunnel junction (STJ) arrays. The design allows the STJs' bias points to be digitally set at the μV level. We then trace out noise versus bias curves under computer control and, by showing the correlation between this noise and detector energy resolution, establish the ability to automatically select optimum STJ operating points. Working with a 75 μm × 75 μm STJ with a Ta x-ray absorber, we achieved better than 7 eV FWHM at the 525 eV O-K line with about 2 eV coming from the preamplifier.