  The demand for the three-dimensional (3D) integration of electronic
components is on a steady rise. The through-silicon-via (TSV) technique emerges
as the only viable method for integrating single-crystalline device components
in a 3D format, despite encountering significant processing challenges. While
monolithic 3D (M3D) integration schemes show promise, the seamless connection
of single-crystalline semiconductors without intervening wafers has yet to be
demonstrated. This challenge arises from the inherent difficulty of growing
single crystals on amorphous or polycrystalline surfaces post the
back-end-of-the-line process at low temperatures to preserve the underlying
circuitry. Consequently, a practical growth-based solution for M3D of single
crystals remains elusive. Here, we present a method for growing
single-crystalline channel materials, specifically composed of transition metal
dichalcogenides, on amorphous and polycrystalline surfaces at temperatures
lower than 400 {\deg}C. Building on this developed technique, we demonstrate
the seamless monolithic integration of vertical single-crystalline logic
transistor arrays. This accomplishment leads to the development of
unprecedented vertical CMOS arrays, thereby constructing vertical inverters.
Ultimately, this achievement sets the stage to pave the way for M3D integration
of various electronic and optoelectronic hardware in the form of single
crystals.
