Epitaxial high-T c superconducting bolometers on silicon for IR detection

Abstract

Silicon wafers have shown promise for the fabrication of photothermal IR detectors (i.e., bolometers) from epitaxial HTS thin films of YBa2Cu3O(7-(delta )) (YBCO). Conventional IC-grade wafers, ultrathin wafers, and micromachined-silicon membrane windows in conventional wafers, are all suitable, but the latter provides considerable advantage for bolometer performance. The high thermal conductivity and strength of silicon make it ideal for submicron-thick window designs. Epitaxy in the HTS film is advantageous, since it reduces granular disorder, the primary cause of dark noise (resistance-fluctuations) in the detector. Mid-to-far IR transparency of Si at 90 K is unique among those substrates that support high-quality epitaxial YBCO films. This Si transparency to IR can be used for various improvements in the optical design of these devices. We review the thermal and optical advantages of silicon substrates, device fabrication issues, and bolometer modeling. Thermal modeling of membrane bolometers indicates that the steady- state temperature-rise profile is nonuniform, but that this does not degrade the response linearity of the bolometer. Certain size limits and trade-offs in the design, will be important in the final device performance. We also discuss applications to FTIR instruments, and extensions of this technology to arrays including a novel on-chip transform spectrometer design.