  High precision calorimetry using superconducting transition edge sensors
requires the use of superconducting films with a suitable $T_c$, depending on
the application. To advance high-precision macrocalorimetry, we require
low-$T_c$ films that are easy to fabricate. A simple and effective way to
suppress $T_c$ of superconducting Iridium through the proximity effect is
demonstrated by using Ir/Pt bilayers as well as Au/Ir/Au trilayers. While Ir/Au
films fabricated by applying heat to the substrate during Ir deposition have
been used in the past for superconducting sensors, we present results of $T_c$
suppression on Iridium by deposition at room temperature in Au/Ir/Au trilayers
and Ir/Pt bilayers in the range of $\sim$20-100~mK. Measurements of the
relative impedance between the Ir/Pt bilayers and Au/Ir/Au trilayers fabricated
show factor of $\sim$10 higher values in the Ir/Pt case. These new films could
play a key role in the development of scalable superconducting transition edge
sensors that require low-$T_c$ films to minimize heat capacity and maximize
energy resolution, while keeping high-yield fabrication methods.
