Trap Rich Layer Physics for RF Silicon Substrates
Trap-rich polysilicon layers beneath buried oxide pin interface carriers to eliminate parasitic conduction and lower sub-6 GHz harmonic generation.
Coplanar Waveguide Attenuation
Meaning
Energy loss per unit length experienced by an electromagnetic wave traveling along a planar transmission line. Total energy decay from coplanar waveguide attenuation results from the combination of conductor resistance and dielectric absorption in the supporting substrate. This metric determines the maximum practical distance a high-frequency signal can travel before requiring amplification.
It governs the design of interconnects in millimeter-wave circuits and high-speed digital systems.
Dissipation Mechanism
Thermal dissipation occurs when currents flow through the non-ideal metal tracks of the waveguide. For coplanar waveguide attenuation, the skin effect concentrates current at the edges of the conductors as the frequency rises. This concentration increases effective resistance and leads to higher signal decay.
Dielectric loss also contributes to the total energy reduction when the alternating electric field polarizes the substrate material.
Substrate Impact
Material selection heavily influences the dielectric component of the total loss. Wafers with high resistivity help minimize coplanar waveguide attenuation by reducing the leakage current through the bulk silicon.
Design Constraint
Layout optimization provides a method for controlling the rate of signal degradation in complex layouts. Engineers adjust the gap between the center signal trace and the ground planes to tune the impedance and minimize coplanar waveguide attenuation. Wider gaps reduce the conductor loss and increase the sensitivity to external interference.
Precise control of metal thickness is a fundamental requirement for meeting the performance targets specified in the link budget.