Transmission media in integrated circuits (ICs and MICs) Which transmission structure is commonly implemented on or within integrated circuits and microwave integrated circuits for routing RF signals?

Introduction:
On-chip and substrate-based RF routing requires planar transmission structures that can be fabricated with lithography. Microwave integrated circuits (MICs) and monolithic microwave ICs (MMICs) therefore use planar lines that are compatible with thin-film processes, semiconductor PDKs, and packaging constraints in compact modules and boards.

Given Data / Assumptions:

• Silicon, GaAs, or other RF substrates using metallization layers over a ground plane.
• Need for compact, manufacturable, and well-modeled interconnects across GHz bands.
• Standard foundry support for passive structures.

Concept / Approach:

Microstrip (a conductor over a ground plane with dielectric in between) is the most common planar line for MICs and PCBs due to ease of fabrication and design. Coplanar waveguide is also common, but among the listed choices, microstrip is the canonical answer. Coaxial and twin-wire lines are not practical for planar IC fabrication; shielded cables and open-wire lines are used for off-chip interconnects, not on-substrate routing.

Step-by-Step Solution:

Verification / Alternative check:

Foundry PDKs provide microstrip (or microstrip-like) and CPW models; reference designs for MMICs routinely route RF in these structures, supporting filters, couplers, and matching networks on the same die or substrate.

Why Other Options Are Wrong:

Coax and cables are off-chip media; twin-wire and ladder lines are not IC-friendly nor adequately shielded for dense integration and crosstalk control at microwave frequencies.

Common Pitfalls:

Assuming coax is universally the best due to superior shielding in cables; in integrated processes, planar realizations dominate for manufacturability and integration with active devices.

Final Answer:

Microstrip line.