Resonant filter using mm wave cavity
Systems and methods for forming a mm wave resonant filter include a lithographically fabricated high Q resonant structure. The resonant structure may include a plurality of cavities, each cavity having a characteristic frequency that defines its passband. A filter may include a plurality of resonant structures, and each resonant structure may include a plurality of cavities. These cavities and filters may be fabricated lithographically.
1. A method for manufacturing a mm wave passband on a substrate filter for a mm-wave emission source, comprising:
forming a plurality of through substrate features, each on one of a plurality of adjacent substrates using photolithographic methods, wherein the feature has a characteristic dimension;
aligning the substrates such that the through substrate feature on each adjacent substrate is registered with the through substrate feature on each other adjacent substrate; and
forming at least one resonant cavity by aligning the through substrate features in each substrate and bonding the substrates togethers to form a substrate stack with the resonant cavity therein, wherein the resonant cavity has a characteristic dimension of about one half of a wavelength in the frequency spectrum of the mm-wave emission source, wherein the at least one cavity is dimensioned to define a resonant structure for at least some frequencies in the frequency spectrum of the mm wave source, and the characteristic dimension is between about 1 mm and 7 mm.
2. The method for manufacturing a mm wave passband filter of claim 1 , wherein the resonant cavity comprises a top surface and a bottom surface and with sidewalls formed by the plurality of substrate between the top and the bottom surfaces, wherein the sidewalls are not parallel along any dimension.
3. The method for manufacturing a mm wave passband filter of claim 2 , further comprising:
depositing a reflective material covering the top surface, the bottom surface and the sidewalls of the resonant cavity.
4. The method for manufacturing a mm wave passband filter of claim 1 , further comprising:
forming a lid substrate including an input and an output port; and
bonding the lid substrate to a top wafer in the substrate stack.
5. The method for manufacturing a mm wave passband filter of claim 1 , further comprising:
depositing a layer of metallization on surfaces of the cavity.
6. The method for manufacturing a mm wave passband filter of claim 1 , wherein the characteristic dimension determines at least one of a width of the passband, a sharpness of the cut off, and an amount of out of band rejection.
7. The method for manufacturing a mm wave passband filter of claim 1 , wherein the at least one cavity has an aspect ratio (length:width) of at least about 5:1.
8. The method for manufacturing a mm wave passband filter of claim 1 , wherein the photolithographic methods include photoresist deposition, curing, and chemical, plasma or vacuum etching.
9. The method for manufacturing a mm wave passband filter of claim 1 , wherein forming the cavity includes forming a plurality of cavities, wherein the plurality of cavities are collocated on a semiconductor substrate.
10. The method for manufacturing a mm wave passband filter of claim 1 , wherein the at least one resonant cavity comprises four resonant cavities, and four resonant cavities define a resonant structures, each resonant structure comprising the four resonant cavities and eight resonant structures defining the mm wave passband filter.
11. The method for manufacturing a mm wave passband filter of claim 1 , wherein forming at least one resonant cavity comprises forming four resonant cavities, wherein all the resonant cavities lie in substantially the same plane.
12. The method for manufacturing a mm wave passband filter of claim 1 , wherein the at least one resonant cavity comprises four resonant cavities configured to have a passband with a width of about 4 GHz and centered at about 28 GHz.