Via transitions for use as micromachined circuit interconnects

Details Via transitions for use as micromachined circuit interconnects Via transitions for use as micromachined circuit interconnects

1998-12-10

2001-03-27

Sough, Hyung-Sub (Department: 2841)

Electricity: conductors and insulators

Conduits, cables or conductors

Preformed panel circuit arrangement

C174S264000, C216S039000

Reexamination Certificate

active

06207903

ABSTRACT:

BACKGROUND
The present invention relates generally to via interconnects or transitions, and more particularly, to via transitions for use as micromachined circuit interconnects and methods for making such via transitions.
Pyramid-shaped vias have heretofore been used to provide for vertical interconnection between coplanar waveguides on opposite surfaces of a micromachined substrate. Such conventional pyramid-shaped vias are etched from the same surface of a substrate. The span of the ground planes of the coplanar waveguide is dictated by the thickness of the substrate and its anisotropic etching property. The ground plane span frequently approaches one-half wavelength at millimeter-wave frequencies, causing excessive RF signal loss due to radiation. The vertical transition or interconnection is generally inductive in nature, aggravating impedance mismatch at elevated frequencies.
Accordingly, it is an objective of the present invention to provide for improved via interconnects or transitions that may be used as micromachined circuit interconnects or transitions and methods for making such via transitions.
SUMMARY OF THE INVENTION
To accomplish the above and other objectives, in accordance with the principles of the present invention, adjacent via transitions that provide ground-signal-ground interconnection between coplanar waveguides on opposite sides of a high resistivity silicon micro-machined substrate are etched from the opposite surface of the substrate. The resulting metalized vias are physically closer to one another, increasing the capacitance between the signal carrying center via and the two ground vias. This improved ground-signal-ground configuration provides improved RF impedance matching at the via transition. In addition, a smaller distance between the outer edge of the coplanar waveguide ground planes is required to accommodate the new ground-signal-ground vertical interconnect. Reduction of the ground plane span provides for lower radiation loss, and signal attenuation, especially when the total span approaches one-half wavelength (with the dielectric constant of the substrate material taken into account). Furthermore, the use of an integrated stub at the pad area of the three vias drastically confines the field and reduces parasitic radiation.
The present invention minimizes signal attenuation at the vertical interconnect between coplanar waveguides on opposite sides of a micromachined substrate. Etched via hole ground-signal-ground configuration are commonly used. The vias are normally etched from one side of a silicon substrate. The present invention makes use of the anisotropic etching capability of silicon to etch closely spaced, adjacent vies from opposite sides of the substrate, leading to lower signal attenuation at the transition because of reduced radiation loss and improved RF impedance matching.
The present invention is well-adapted for use in airborne millimeter-wave phased array, radars for missile system and weapon systems as well as micromachined technology-based low cost automotive and industrial radar sensors.
The present invention also provides for a method of fabricating a via transition for use as a micromachined circuit interconnect. In the method, a silicon micromachined substrate
1
has a plurality of via holes anisotropically etched through the substrate, wherein alternate via holes are etched from the opposite sides of the substrate. Conductive metallization is then disposed in the vias. In addition, the method may further comprise the steps of forming coplanar waveguides on opposite sides of the substrate, and conductively connecting the coplanar waveguides to the via holes.


REFERENCES:
patent: 5056216 (1991-10-01), Madou et al.
patent: 5614742 (1997-03-01), Gessner et al.
patent: 5765279 (1998-06-01), Moresco et al.
patent: 5841075 (1998-11-01), Hanson
patent: 5962921 (1999-10-01), Farnworth et al.
patent: 6013948 (2000-01-01), Akram et al.

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