  The majority of microfabricated ion traps in use for quantum information
processing are of the 2D 'surface-electrode' type or of the 3D 'wafer' type.
Surface-electrode traps greatly simplify fabrication and hold the promise of
allowing trapped-ion quantum computers to scale via standard semiconductor
industry fabrication techniques. However, their geometry constrains them to
having much lower trapping efficiency, depth, and harmonicity compared to 3D
geometries. Conversely 3D geometries offer superior trap performance but
fabrication is more complex, limiting potential to scale. We describe new
'trench' geometries that exist in the design space between these two paradigms.
They still allow for a simple, planar electrode layer but with much more
favourable trapping properties. We propose such traps could be 3D-printed over
a 2D wafer with microfabricated components already integrated into it, thus
retaining all the integration techniques and scaling advantages of
surface-electrode traps. As a proof of principle we use 2-photon direct laser
writing lithography to print the required electrode structures with the
proposed geometry.
