High-speed feedthrough having a stair-like shape transmission line formed through a multi-layer substrate
View Patent ↗A high-speed feedthrough (HSFT) is disclosed for transmitting a signal having a highest frequency of at least 10 GHz between first and second locations separated by a vertical distance of at least approximately half of the shortest transmitted wavelength, and separated by a horizontal distance. A substrate structure includes multiple stacked layers. An RF transmission line is connected through the structure between the first and second locations for transmitting the signal. The RF transmission line comprises a series of sequentially connected horizontal conductors having lengths less than half of the effective wavelength and vertical conductors having heights less than one quarter of the effective wavelength, thereby spanning the horizontal and vertical distance between the two locations in a stairs-like shape through the structure's layers. Each conductor's geometry may deviate from standard 50 ohm buried strip lines and is optimized for complete 3-dimensional structure.
1. A high-speed feedthrough (HSFT) operative to transmit a signal, having a highest frequency of at least 10 GHz corresponding to a shortest free space wavelength, between a first interface location and a second interface location that are separated by a vertical distance of at least a millimeter, and separated by a horizontal distance, the HSFT comprising:
a substrate structure comprising multiple stacked layers; and
an RF transmission line connected through the substrate structure between the first and second interface locations operative to transmit the signal between the first and second interface locations, the RF transmission line comprising a series of sequentially connected horizontal and vertical conductors; the horizontal conductors having lengths less than half of an effective wavelength that corresponds to the shortest free space wavelength of the signal when transmitted through the HSFT, and the vertical conductors having heights less than one quarter of the effective wavelength; thereby spanning the horizontal and vertical distances between the first and second interface locations in a stairs-like shape through the layers of the substrate structure.
2. The HSFT of claim 1 wherein the stairs-like shape through the layers of the substrate structure comprises:
the horizontal conductors being progressively horizontally and vertically shifted for different layers of the substrate structure from a location proximate the first interface location to a location proximate the second interface location; and
the vertical conductors connecting vertically overlapping ends of adjacent horizontal conductors through one or more layers of the substrate structure.
3. The HSFT of claim 1 wherein the horizontal and vertical conductors have geometries deviating from 50 ohm transmission lines in the material of the substrate and have impedances in the range from about 40 ohms to about 60 ohms.
4. The HSFT of claim 1 wherein the horizontal distance between the first interface location and the second interface location is at least a millimeter.
5. The HSFT of claim 1 wherein at least one of the horizontal conductors has a width that varies from that of an ideal 50 ohm transmission line in the material of the substrate by more than 10 percent.
6. The HSFT of claim 1 wherein the substrate structure comprises 10 or less ceramic layers.
7. The HSFT of claim 1 wherein the signal comprises a spectral range from about 10 kHz to about 30 GHz corresponding to a shortest free space wavelength of about 10 millimeters.
8. The HSFT of claim 7 wherein the substrate structure comprises 7 ceramic layers.
9. The HSFT of claim 8 wherein the vertical distance between the first interface location and the second interface location is at least 3 millimeters.
10. The HSFT of claim 9 wherein the horizontal distance between the first interface location and the second interface location is at least 3 millimeters.
11. The HSFT of claim 1 further comprising grounded coplanar lines at the top and bottom layers of the substrate structure.
12. The HSFT of claim 1 wherein the horizontal conductors are coplanar strip lines.
13. The HSFT of claim 1 further comprising at least one of a first terminal electrically connected to the first interface location; and a second terminal electrically connected to the second interface location.
14. The HSFT of claim 1 further comprising another seven RF transmission lines within the HSFT.
15. A package comprising:
a hermetic seal defining an interior and an exterior of the package;
a HSFT according to claim 1 embedded within the hermetic seal;
a chip within the interior of the package connected to the first interface location of the HSFT;
outer terminals connected to the second interface location of the HSFT and exposed to the exterior of the package.
16. A high-speed feedthrough (HSFT) operative to transmit a signal having a highest frequency of at least 10 GHz corresponding to a shortest free space wavelength, the HSFT comprising:
a multilayered substrate structure;
a first terminal connected to the structure;
a second terminal connected to the structure and separated from the first terminal by a vertical distance and a horizontal distance, both distances approximate to or greater than half of an effective wavelength that corresponds to the shortest free space wavelength of the signal when transmitted through the HSFT;
an RF transmission line connecting the first and second terminals through the multilayered substrate structure, the RF transmission line comprising a series of horizontal conductors having lengths less than half of the effective wavelength, the series of horizontal conductors connected to a series of vertical conductors having heights less than one quarter of the effective wavelength;
wherein adjacent horizontal and vertical conductors are progressively horizontally and vertically shifted from the first terminal towards the second terminal.
17. A package comprising:
a hermetic seal defining an interior and an exterior of the package;
a HSFT according to claim 16 embedded within the hermetic seal exposing the second terminal to the exterior of the package; and
a chip within the interior of the package connected to the first terminal of the HSFT.