  Dielectrics featuring a high relative permittivity, i.e., high-k dielectrics,
have become the standard insulators in gate architectures, enhancing the
electrical performance of both room temperature and cryogenic electronics. This
study delves into the cryogenic (3 K) performance of high-k dielectrics
commonly used as gate insulators. We fabricated Al2O3 and HfO2 layers via
Atomic Layer Deposition (ALD) and we extrapolated relative permittivity (k) and
dielectric strength (EBD) from AC (100 Hz to 100 kHz) and DC measurements on
metal-insulator-metal capacitors. Our findings reveal a strong dependence of
HfO2 cryogenic performance on the ALD growth temperature, while the latter
shows a negligible impact on Al2O3. We estimated a ~9 % and ~14 % reduction of
the relative permittivity of HfO2 and Al2O3, respectively, from 300 K to 3 K.
Additionally, we designed and fabricated Al2O3/HfO2 bilayers and we checked
their properties at cryogenic temperatures. The study also investigates the
impact of the patterning method, namely, UV or electron-beam lithography
(acceleration voltage of 10, 20, or 30 kV), on the high-k dielectric
properties.
