Hard Materials Seminar - "Monolithic 3D Integration of Silicon Transistors"

Monolithic, three-dimensional (3D) integrated circuits promise advantages in packing density, energy consumption and interconnectivity bandwidth but require forming high-performance semiconductors and transistors on top tiers under the constraint of a limited thermal budget compatible with back-end-of-line integration1,2. Back-end-of-line compatible transistors have been built on laser-annealed polycrystalline silicon, metal-oxide semiconductors, carbon nanotubes and two-dimensional chalcogenides3–5. However, their performance and reliability are much inferior to bottom-tier silicon metal-oxide-semiconductor field-effect transistors, which mask most of the improvements offered by monolithic 3D integrated circuits. Here we show that uniformly doped, ultrathin (≤10 nm) single-crystalline silicon nanomembranes can be vertically stacked using a roll-transfer-printing process that is scalable to wafer-scale and tolerant to substrate topology and surface roughness, enabling multi-tiers of complementary junctionless transistors to be sequentially fabricated on the same starting substrate under a processing temperature ≤400 °C. These devices achieve performance approaching that of silicon metal-oxide-semiconductor field-effect transistors with current density above 650 µA µm−1 and sub-10 nm inter-tier registration for high-density vertical integration. We vertically constructed logic gates, including inverters, NAND, NOR gates and static random-access memory cells, based on up to three-tier integration at transistor-level granularity. Our demonstrations provide a promising route towards silicon-based monolithic 3D circuits, especially for research and low-volume prototyping.