US Patent 11335704 Low parasitic capacitance RF transistors

Structures and fabrication methods for transistors having low parasitic capacitance, the transistors including an insulating low dielectric constant first or second handle wafer. In one embodiment, a Single Layer Transfer technique is used to position an insulating LDC handle wafer proximate the metal interconnect layers of an SOI transistor/metal layer stack in lieu of the silicon substrate of conventional designs. In another embodiment, a Double Layer Transfer technique is used to replace the silicon substrate of prior art structures with an insulating LDC substrate. In some embodiments, the insulating LDC handle wafer includes at least one air cavity, which reduces the effective dielectric constant of material surrounding an RF FET. An insulating LDC handle wafer reduces insertion loss and non-linearity, increases isolation, provides for more ideal voltage division of stacked transistors, enables a higher Q factor due to lower coupling losses, and otherwise mitigates various parasitic effects.