X3D: Heterogeneous Monolithic 3D Integration of “X” (Arbitrary) Nanowires: Silicon, III–V, and Carbon Nanotubes

We experimentally demonstrate a new paradigm for monolithic three-dimensional (3D) integration: X3D, which enables a wide range of semiconductors - including silicon (Si), III-V, and nanotechnologies such as carbon nanotubes (CNTs) - to be heterogeneously integrated together in monolithic 3D integrated systems. Such flexible heterogeneous integration has potential for a wide range of applications, as each layer of monolithic X3D integrated circuits (ICs) can be customized for specific functionality (e.g., wide-bandgap III-V-based circuits for power management, CNT field-effect transistors (CNFETs) for energy-efficient computing, and tailored materials for custom sensors or imagers). As a case study, we experimentally demonstrate monolithic X3D ICs with five vertical circuit layers heterogeneously integrating three different semiconductors: Si junctionless nanowire field-effect transistors (JNFETs), III-V JNFETs, and CNFETs (also junctionless). The layers of monolithic X3D IC are, from bottom-to-top: Si p-JNFETs, n-CNFETs, Si n-JNFETs, p-CNFETs, and III-V n-JNFETs. Each layer is fabricated using an identical process flow for ease of integration. Importantly, we show that circuits fabricated on each vertical layer are agnostic to subsequent monolithic X3D processing, experimentally demonstrating ability to interleave these “X” (arbitrary) semiconductors in arbitrary vertical ordering. As a final demonstration, we fabricate complementary digital logic circuits comprising different technologies that span multiple vertical circuit layers. This work demonstrates a new paradigm for ICs, allowing for flexible and customizable electronic systems.