  We recently demonstrated a 1$^{\textrm{st}}$-order axial gradiometer SQUID
system, which is operated in a liquid He dewar with negligible noise
contribution. The achieved close to SQUID-limited measured coupled energy
sensitivity $\varepsilon_{c}$ of $\sim 30\,h$ corresponds to a white field
noise below 180~aT~Hz${^{-1/2}}$. In order to further improve the SQUID noise
performance, the junction capacitance was reduced by decreasing its lateral
size from $2.5~\mu$m to below $1~\mu$m. This was realized by extending the
fabrication process for submicrometer-sized Josephson Junctions based on the
HfTi self-shunted junction technology to an SIS process with AlO$_{\textrm{x}}$
as the insulating layer. We achieved energy sensitivities of 4.7$\,h$ and
20$\,h$ at 4.2~K for uncoupled and coupled SQUIDs, respectively. We also
investigated the temperature dependence of the noise of the uncoupled SQUIDs
and reached an energy sensitivity of 0.65$\,h$ in the white noise regime at
400~mK.
