Low Inductance RFIC Interconnect via Stacked Metal Layers
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Solution Overview
Problem
RF integrated circuits (RFICs) face issues with large inductance in interconnect paths due to path lengths and line widths, leading to non-uniform signal distribution and harmonic tuning variations across transistor cell arrays, resulting in degraded power efficiency, gain, and linearity.
Innovation Solution
The use of a low inductance interconnect formed by a pair of metal layers separated by a thin dielectric medium, such as BCB, over a semiconductor substrate, significantly reduces inductance and provides uniform current delivery to RFIC cells, improving harmonic tuning accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single metal layer over a dielectric stack is used to interconnect input to input terminals of each cell, then the interconnect structure is simple, but the inductance is large leading to non-uniform signal distribution
Solution Approach 1:
The patent transitions from a single-plane metal interconnect to a three-dimensional stacked metal configuration. Multiple metal layers are positioned at different heights (z-dimension) with vertical vias connecting them, creating a volumetric interconnect structure that reduces current path length and inductance while maintaining signal uniformity across the device area
Solution Approach 2:
The patent combines multiple metal layers and vertical vias into an integrated interconnect system. The stacked metal layers are merged through conductive vias to form a unified low-inductance pathway, effectively combining spatial separation with electrical connectivity to reduce overall inductance
2Adaptability or versatility
If path length between cells and harmonic tuning resonator is increased, then more cells can be accommodated, but inductance difference accumulates making harmonic tuning difficult
Solution Approach 1:
The stacked metal layer configuration provides additional spatial dimensions for routing interconnects. This vertical stacking allows interconnect paths to reach more cells across the device area while maintaining controlled and matched inductance values, enabling scalability without sacrificing tuning precision
Solution Approach 2:
The patent changes the physical configuration parameters of the interconnect by using multiple metal layers with specific thicknesses and spacing. This transforms the interconnect from a simple planar trace to a controlled-impedance transmission line structure with optimized inductance characteristics that remain consistent across varying path lengths
Data Source
AI summary
An interconnect path configured for use in RFICs and configured to reduce inductance at the input of an array of cells, and also at the output of the array of cells. According to one preferred embodiment of the present invention, a multi-layered interconnect formed by at least two metal layers separated by dielectric medium is provided. The metal layers are closely spaced and separated by a desirable dielectric to achieve an interconnect having a characteristic inductance (Zo) that is much lower than typical microstrip transmission lines formed by a metal trace over the semiconductor substrate or a dielectric stack that includes the semiconductor substrate. The low Zo line provides much less inductance per unit length.