  The concept of dielectric-laser acceleration (DLA) provides the highest
gradients among breakdown-limited (nonplasma) particle accelerators and thus
the potential of miniaturization. The implementation of a fully scalable
electron accelerator on a microchip by twodimensional alternating phase
focusing (APF), which relies on homogeneous laser fields and external magnetic
focusing in the third direction, was recently proposed. In this Letter, we
generalize the APF for DLA scheme to 3D, such that stable beam transport and
acceleration is attained without any external equipment, while the structures
can still be fabricated by entirely twodimensional lithographic techniques. In
the new scheme, we obtain signifcantly higher accelerating gradients at given
incident laser field by additionally exploiting the new horizontal edge. This
enables ultra-low injection energies of about 2.5 keV (beta = 0.1) and bulky
high voltage equipment as used in previous DLA experiments can be omitted. DLAs
have applications in ultrafast time-resolved electron microscopy and
-diffraction. Our fndings are crucial for the miniaturization of the entire
setup and pave the way towards integration of DLAs in optical fiber driven
endoscopes, e.g., for medical purposes.
