Electroplated helical slow-wave structures for high-frequency signals
Traveling-wave tube amplifiers and methods for making slow-wave structures for the amplifiers are provided. The SWSs include helical conductors that are self-assembled via the release of stressed electrically conductive strips from a sacrificial material. The helical conductors can be electroplated post-self-assembly to fortify the helix, reduce losses, and tailor the dimensions and operating parameters of the helix.
1. A traveling-wave tube amplifier comprising:
a dielectric support;
a slow-wave structure on the dielectric support, the slow-wave structure comprising an electrically conductive helix comprising a continuous helical strip of electrically conductive material and having an inner diameter of no greater than 30 μm;
an electron gun positioned to direct one or more beams of electrons axially through the electrically conductive helix or around the periphery of the electrically conductive helix; and
an electron collector positioned opposite the electron beam source.
2. The amplifier of claim 1 , wherein the helical strip comprises a seed layer and a plating layer on a surface of the seed layer.
3. The amplifier of claim 1 , wherein the helical strip of electrically conductive material consists of a single layer of a metal.
4. The amplifier of claim 3 , wherein the metal is gold.
5. The amplifier of claim 3 , wherein the metal is copper, nickel, or silver.
6. The amplifier of claim 1 , wherein the helical strip comprises a central seed layer of a metal and a plating layer of the metal disposed around the central seed layer.
7. The amplifier of claim 1 , wherein the helical strip of electrically conducting material is a bilayer strip comprising a first metal layer and a second metal layer, wherein the second metal is disposed on the top of the first metal along the length of the helical strip.
8. The amplifier of claim 7 , wherein one of the first and second metal layers is a chromium layer and the other of the first and second metal layers is a gold layer.
9. The amplifier of claim 7 , wherein the helical strip further comprises a plating layer of the first metal on a surface of the first metal layer.
10. The amplifier of claim 1 , wherein the helical strip comprises a right-handed helical segment, a left-handed helical segment, and a connection segment connecting the right-handed helical segment to the left-handed helical segment.
11. The amplifier of claim 1 , further comprising one or more contact pads on the dielectric support, wherein one or more turns along the length of the electrically conductive helix are connected to the one or more contact pads.
12. The amplifier of claim 1 , wherein the dielectric support comprises diamond, aluminum nitride, aluminum oxide, or silicon nitride.
13. The amplifier of claim 1 , wherein the electrically conductive helix has an inner diameter in the range from 1 μm to 30 μm.
14. The amplifier of claim 1 , wherein the electrically conductive helix has a length in the range from 100 μm to 2 cm.
15. A method of making a slow-wave structure, the method comprising:
forming a layer of sacrificial material on a portion of a surface of a dielectric support;
forming a continuous stressed electrically conductive strip on the layer of sacrificial material, the electrically conductive strip having a leading end and a trailing end, wherein the trailing end of the electrically conductive strip is attached to the dielectric support, and further wherein the electrically conductive strip comprises an electrically conductive material in contact with the layer of sacrificial material;
selectively removing the layer of sacrificial material, wherein the continuous stressed electrically conductive strip relaxes into the form of a helix;
connecting the leading end of the electrically conductive strip to a first electrical contact;
connecting the trailing end of the electrically conductive strip to a second electrical contact; and
electroplating the surface of the helix with an electrically conductive material.
16. The method of claim 15 , further comprising connecting one or more turns in the helix with one or more contact pads positioned on the dielectric support between the first electrical contact and the second electrical contact.
17. The method of claim 16 , further comprising electroplating the first electrical contact, the second electrical contact, and the contact pads.
18. The method of claim 15 , wherein the continuous stressed electrically conductive strip is a linear strip.
19. The method of claim 15 , wherein the continuous stressed electrically conductive strip comprises a first linear segment and a second linear segment, wherein the first and second angles are joined at an angle of less than 180°.
20. The method of claim 15 , wherein the sacrificial material is an oxide and the continuous stressed electrically conductive strip comprises only a single layer of metal or comprises two or more vertically stacked layers of different metals.