Periodic interleaved star with vias electromagnetic bandgap structure for microstrip and flip chip on board applications

Abstract

A hybrid assembly having improved cross talk characteristics includes an electromagnetic band gap (EBG) layer on a substrate having an upper surface and a lower surface and a semiconductor structure (MMIC) mounted above the EBG layer. A plurality of stars made of an EBG material are preferably printed, or deposited, on the upper surface. The EBG material has slow wave characteristics. The plurality of stars tessellates the upper surface between conductive paths. Each of the stars has a center section formed from a regular polygon, the center section having projections extending from the center section. The projections and the center section form a periphery. The periphery engages adjacent stars along the periphery. Stars are separated from adjacent stars by an interspace. Each of the stars is connected to a conductive via, in turn connected to ground potential. A conductive layer at ground potential is electrically continuous with vias used to interconnect all stars forming the EBG layer.

Description

[0001] This application is a continuation in part of parent application titled “Improved Flip Chip MMIC on Board Performance Using Periodic Electromagnetic Bandgap Structures” filed ______ 2004, Ser. No. ______.BACKGROUND OF THE INVENTION [0002] 1. Field of Invention [0003] This invention is in the field of cross-talk suppression in a hybrid assembly at microwave frequencies. [0004] 2. Description of the Related Art [0005] Monolithic Integrated Circuits (MMIC), an example of a semiconductor structure, support many of the present generation of military and commercial radio frequency sensors and communication applications. MMICs include active devices, such as field effect transistors and bipolar transistors, passive elements such as capacitors, thin film / bulk resistors, and inductors integrated on a single semi-insulating substrate, such as Gallium Arsenide. [0006] Hybrid technology relates to methods used for interconnecting a plurality of separate semiconductor structures, such as ...

AI Technical Summary

Benefits of technology

[0015] Above limitations are improved by a hybrid assembly comprising a single electromagnetic band gap (EBG) layer on a substrate having an upper surface and a lower surface and a semiconductor structure (MMIC) mount

Problems solved by technology

While bumps are advantageous as compared to wire inter-connections, their presence between a semiconductor structure and a host substrate presents unique electromagnetic resonance and emission packaging problems.

A particular difficulty introduced by the semiconductor structure mounted on the host substrate is the potential formation of electromagnetic boundaries which support unwanted, parallel plate, waveguide like (surface modes) of energy propagation.

Such unwanted modes can propagate near the surface of the host substrate causing degradation in semiconductor performance because of signal interference.

The degradation in semiconductor performance are caused by unwanted signal transfer among semiconductor structure inputs and outputs, affecting gain and phase response, loss of isolation between adjacent paths in multiple path / multiple channel circuit applications, and circuit instability.

These negative effects are due to the introduction of unwanted coupling or feedback paths.

Maximum frequency operation of the semiconductor in the presence of these unwanted feedback paths are undesirably dependent on the dimensions of the semiconductor structure.

Thus, semiconductor structures with large dimensions with respect to wavelength operating frequency present a potential difficulty.

This difficulty is prevalent with fast Gallium Arsenide (GaAs) semiconductor structures mounted on a host substrate.

Near cutoff, the semiconductor structure may be functional, but unable to operate because the incoming signals are interfering with each other.

Unfortunately, because of semiconductor structure limitations and assembly requirements, this practice of using redundant ground bumps as obstacles to surface propagated electromagnetic waves results in a further increase in both semiconductor structure and substrate size, increasing weight, power consumption and reducing reliability of the resulting hybrid.

The limitation here is that a plurality of of EBG layers may have to be used to achieve the level of attenuation desired.

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