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 mm wave passband filter for a mm-wave emission source, fabricated photolithographically on a substrate, comprising:
at least one resonant cavity formed in a plurality of substrates, wherein the cavity is formed by registration of voids formed using photolithographic methods in adjacent ones of the plurality of substrates to form a substrate stack, wherein the resonant cavity in the substrate stack 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 1 mm and 7 mm.
2. The mm wave passband filter of claim 1 , further comprising:
a lid substrate including an input and an output port formed in a lid substrate, wherein the lid substrate is bonded to a top wafer in the substrate stack.
3. The mm wave passband filter of claim 1 , further comprising:
a metallization layer formed on surfaces of the at least one resonant cavity.
4. The 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.
5. The mm wave passband filter of claim 1 , wherein the characteristic dimension is between 1 mm and 7 mm.
6. The mm wave passband filter of claim 1 , wherein the at least one cavity has an aspect ratio (length:width) of at least 5:1.
7. The mm wave passband filter of claim 1 , wherein the photolithographic methods include photoresist deposition, curing, and chemical, plasma or vacuum etching.
8. The mm wave passband filter of claim 1 , wherein the at least one resonant cavity comprises a plurality of resonant cavities, wherein the plurality of resonant cavities are collocated on a semiconductor substrate.
9. The mm wave passband filter of claim 1 , wherein the at least one resonant cavity comprises four cavities, and four resonant cavities define a resonant structure, each resonant structure comprising the four resonant cavities and eight resonant structures defining the mm wave passband filter.
10. The mm wave passband filter of claim 1 , wherein the resonant cavity comprises a top and a bottom surface and with sidewalls formed by the plurality of substrates between the top and the bottom surfaces, wherein the sidewalls are not parallel along any dimension.
11. The mm wave passband filter of claim 10 , further comprising:
a reflective material deposited over the top surface, the bottom surface and sidewalls of the resonant cavity.
12. The 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.
13. The 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 4 GHz and centered at 28 GHz.