# Patent

## Title
Integrated MMIC modules for millimeter and submillimeter wave system applications

## Abstract

An integrated circuit module comprising integrated coupling transmission structures protruding from the main body of the integrated circuit with extra substrate material removed around and/or under the coupling transmission structures.

## Background
STATEMENT OF GOVERNMENT INTEREST
This invention was made with government support under Contract No. F33615-99-C-1512 funded by the Air Force Research Laboratories and DARPA-MTO.


FIELD OF THE INVENTION
This invention relates to Integrated Circuits with coupling transmission structures that are being used as onboard probes or onboard antennas, which eliminate ribbon/wire bonding as well as the higher order modes in the waveguide.
BACKGROUND AND PRIOR ART
Monolithic Microwave Integrated Circuits (MMIC) are implemented with conventional microstrip or grounded coplanar waveguide (GCPW) circuit elements on thin semiconductor substrates. The thickness of the substrate depends on the frequency of operation. Although at mm-wave frequencies wafer measurements of MMICs have shown satisfactory performance, MMICs actually suffer significantly in performance once removed from the wafer and packaged using either a ribbon bond approach or a flip-chip approach. The ribbon bond and flip-chip packaging approaches have a severe and detrimental effect on the performance of the MMICs at mm-wave frequencies.
At higher-mm-wave and sub-mm-wave frequencies, most of the measurement equipment and MMIC modules have waveguide Inputs/Outputs (I/Os). Researchers have demonstrated MMIC modules by coupling MMIC I/Os to waveguide using, either waveguide transitions or antennas. These transitions can be placed on a semiconductor substrate and ribbon bonded to the MMIC, as shown in FIGS. 1 and 2. However, transitions that have been placed on the MMIC semiconductor substrate degrade the MMIC module performance by introducing higher order parasitic modes because MMICs are developed on semiconductor materials like InP, SiGe, GaAs.
The transitions that have been designed on high performance substrates are ribbon bonded to the MMIC. Unfortunately, the assembly approach is complicated, MMIC module designs with ribbon-bonding suffer from impedance mismatch and produce lower power than expected, and at sub-millimeter frequencies, planar coupling transmission structures need to have narrow width for desired circuit impedances.
Transitions have also been integrated into the MMIC module. See Weinreb, S., Faier, T., Lai, R., Barsky, M., Leong, Y. C., and Samoska, L., “High-Gain 150–215-Ghz MMIC Amplifier with Integral Waveguide Transitions”, IEEE Microwave and Guided Wave Letters, Vol. 9, No. 7, pp 282–284, July 1999 (Weinreb). However; this approach still presents problems by introducing higher order modes. See FIG. 3.
The presently disclosed technology addresses the issues of higher order modes, parasitic modes, impedance mismatches by utilizing an integrated waveguide MMIC module quite unlike Weinreb. The presently disclosed technology eliminates or reduces the higher order modes in the waveguide by etching away extra high resistivity substrate around and/or underneath the coupling transmission structures. This allows the development of high-performance MMIC modules and subsystems at sub-millimeter and higher-millimeter wave frequencies.



BRIEF DESCRIPTION OF THE FIGURES AND THE DRAWINGS
FIGS. 1 and 2 depict transition probes, on a semiconductor substrate, ribbon bonded to the MMIC for waveguide coupling, “Prior Art”;
FIG. 3 depicts a schematic of transition probes on the MMIC semiconductor substrate, “Prior Art”;
FIG. 4A depicts a thinned wafer with streets to define MMIC chip areas;
FIG. 4B–4D depict individual Integrated circuits located within MMIC chip areas;
FIGS. 4E, 4F and 4G depict some of possible shapes and positions of the coupling transmission structures;
FIG. 5A depicts the integrated circuit with the substrate material removed around the coupling transmission structures;
FIG. 5B depicts the integrated circuit with the substrate material removed around the coupling transmission structures placed in the waveguide;
FIGS. 6a–j depict the process of removing the substrate material from around the coupling transmission structures that are extending from the integrated circuit;
FIG. 7 depicts the integrated circuit with the substrate material removed from around and under the transition probes;
FIGS. 8a–l depict the process of removing the substrate material from around and under the coupling transmission structures that are extending from the integrated circuit;
FIG. 9 depicts the integrated circuit including an etch stop layer wherein the substrate material removed from around and under the transition probes;
FIGS. 10a–l depict the process of removing the substrate material from around and under the coupling transmission structures that are extending from the integrated circuit by using an etch stop layer.



DETAILED DESCRIPTION
The present disclosure addresses the issues of higher order modes, parasitic modes, and impedance mismatches in the waveguide by disclosing an integrated waveguide MMIC. Based on the presently disclosed technology, monolithic modular components can be developed to eliminate the need for wirebonding planar coupling transmission structure-to-waveguide transition probes. The transition probe or antenna, depending on the desired function, is an integral part of the MMIC chip. The higher order modes in the waveguide can be eliminated or reduced by etching away extra high resistivity substrate around the coupling transmission structure (coupling probe or antenna). The reduction of higher order modes allows MMICs to operate at sub-millimeter and higher-millimeter wave frequencies.
FIG. 4A shows a wafer 10 with streets 11 defining MMIC chip areas 12 before the chips are released from the wafer. MMIC chips 13, 14 and 15, as shown in FIGS. 4B, 4C and 4D, respectively, depict individual Integrated Circuits (ICs) located with in MMIC chip areas 12 of the wafer 10.
Integrated Circuits 18 are developed on the substrate material 19 of a wafer 10 with coupling transmission structures 20 extending from the Integrated Circuits 18, as shown by FIGS. 4B, 4C and 4D.
This disclosure is not limited to shape and positions of the coupling transmission structures 20 as depicted in FIGS. 4B to 4D. Coupling transmission structures 20 can vary in shape and can extend at different locations from the Integrated Circuit 18, for example, see FIGS. 4E, 4F and 4G.
In one embodiment, the presently disclosed technology improves the performance and reduces higher order modes of the Integrated Circuit module by removing excess semiconductor substrate material 19 around the coupling transmission structures 20, as shown by FIG. 5A. In this embodiment, the peripheral edge of the semiconductor substrate material 19 closely follows the peripheral edges of the Integrated Circuit 18 and coupling transmission structures 20. The distance between the peripheral edges of the semiconductor substrate material 19 and the peripheral edges of the Integrated Circuit 18 and coupling transmission structures 20 in FIG. 5A is exaggerated for illustration purposes.
FIG. 5B shows the placement of the Integrated Circuit 18 module as depicted in FIG. 5A inside the waveguide block 21. The removal of the extra substrate material decreases higher order modes.
The extra parasitic substrate material can be removed using a backside processing shown and described with reference to FIGS. 6a–j. FIGS. 6a–j represent the cross section of a wafer, containing multiple ICs, for each of the backside process steps.
In FIG. 6a, a wafer comprises a substrate 30 and a circuitry layer 25. The wafer is mounted with the circuitry layer 25 down on to a support substrate 40 and held in place with a wax or other suitable material 35. The substrate 30 can be a semi-insulating semiconductor InP wafer, for example. The circuitry layer 25 contains multiple ICs.
In FIG. 6b, a thinning process is performed on the substrate 30. The thinning process can be performed, for example, either by lapping the substrate 30; by etching the substrate 30 (wet or dry); grinding the substrate 30; or a combination of any of these processes can be used to obtain a desired thickness depending on design requirements.
In FIGS. 6c–h, a via process is performed on the substrate 30. The via process can be performed by: applying and imaging a via mask 45 to the substrate 30, as shown by FIG. 6c; creating a via pattern 50 in the via mask 45, as shown by FIG. 6d; etching via holes 55 through the substrate 30 and removing the via mask 45, as shown by FIG. 6e; depositing a metallization layer 65 to the backside of the substrate 30 thereby covering via holes 55 with metal, as shown by FIG. 6f; applying and imaging a metal mask 70 as shown by FIG. 6g; etching the metallization layer 65; and removing the metal mask 70, as shown by FIG. 6h. 
The via mask 45 and metal mask 70 can be but are not limited to a photoresist material. The metallization layer 65 can consist of but is not limited to first depositing Ti followed by Au metals. The metallization layer 65 can be developed by either evaporating or sputtering metal onto substrate 30 and then plating metal to desired thickness. Etching of the metallization layer 65 can be done through wet etch technique. Wet etching can consist of applying potassium iodide, to etch Au followed by hydrofluoric acid to etch Ti.
In FIGS. 6i and 6j, a disjoin process is performed on the substrate 30 and circuitry layer 25. Upon completion of the disjoin process the individual ICs 1 and 2 on the wafer will be disjoined from each other. The disjoin process can be performed by: applying and imaging an integrated circuit mask 80 to the substrate 30 exposing only the portions of the substrate 30 that are between the individual ICs, as shown by FIG. 6i; etching through the substrate 30 and circuitry layer 25; and removing the integrated circuit mask 80, as shown by FIG. 6j. 
Alternatively, the process of disjoining the individual ICs from the wafer can be accomplished by a laser die cutting process instead of masking and etching. The laser cutter is guided where the cutting is to be performed. Upon completion of the laser die cutting process, the individual ICs 1 and 2 will be disjoined from each other, as shown by FIG. 6j. 
Finally, removing the wax or other suitable material 35 enables removal of the individual ICs 1 and 2 from the support substrate 40, as shown by FIG. 6j. The wax 35 can be removed with Tetra-chloro-ethylene (TCE).
In another embodiment, the presently disclosed technology improves the performance and reduces higher order modes of the IC by removing excess semiconductor substrate material 5 around and under the coupling transmission structures 20, as shown by FIG. 7. In this embodiment, the peripheral edge of the semiconductor substrate material 19 closely follows the peripheral edges of the Integrated Circuit 18 and coupling transmission structures 20. The distance between the peripheral edges of the semiconductor substrate material 19 and the peripheral edges of the Integrated Circuit 18 and coupling transmission structures 20 in the FIG. 7 is exaggerated for illustration purposes.
The extra parasitic substrate material can be removed using a backside processing shown and described with reference to FIGS. 8a–l. FIGS. 8a–l represent the cross section of a wafer, containing multiple ICs, for each of the backside process steps.
In FIG. 8a, a wafer comprises a substrate 130 and a circuitry layer 125. The wafer is mounted with the circuitry layer 125 down on to a support substrate 140 and held in place with a wax or other suitable material 135. The substrate 130 can be a semi-insulating InP wafer. The circuitry layer 125 contains multiple ICs.
In FIG. 8b, a thinning process is performed on the substrate 130. The thinning process can be performed, for example, either by lapping the substrate 130; by etching the substrate 130 (wet or dry); grinding the substrate 130; or a combination of any of these processes can be used to obtain a desired thickness depending on design requirements.
In FIGS. 8c–h, a via process is performed on the substrate 130. The via process can be performed by: applying and imaging a via mask 145 to the substrate 130, as shown by FIG. 8c; creating a via pattern 150 in the via mask 145, as shown by FIG. 8d; etching via holes 155 through the substrate 130 and removing the via mask 145, as shown by FIG. 8e; depositing a metallization layer 165 to the backside of the substrate 130 thereby covering via holes 155 with metal, as shown by FIG. 8f; applying and imaging a metal mask 170 as shown by FIG. 8g; etching the metallization layer 165; and removing the metal mask 170, as shown by FIG. 8h. 
The via mask 145 and metal mask 170 can be, but are not limited to, a photoresist material. The metallization layer 165 can consist of but is not limited to first depositing Ti followed by Au metals. The metallization layer 165 can be developed by either evaporating or sputtering metal onto substrate 130 and then plating metal to desired thickness. Etching of the metallization layer 165 can be done through wet etch technique. Wet etching can consist of applying potassium iodide, to etch Au followed by hydrofluoric acid to etch Ti.
In FIGS. 8i and 8j, a coupling transmission structure thinning process is performed on the substrate 130. Upon completion of the coupling transmission structure thinning process there is less substrate 130 material covering the coupling transmission structures extending from the individual ICs than there is substrate 130 material covering the circuitry of individual ICs. The coupling transmission structure thinning process can be performed by applying and imaging a coupling transmission structure mask 175 to the substrate 130, which mask exposes only the portions of the substrate 130 that cover the coupling transmission structures extending from the individual ICs, as shown in FIG. 8i, followed by etching the substrate 130 to remove a portion of the substrate 130 material covering the coupling transmission structures and removing the coupling transmission structure mask 175 covering the substrate 130, as shown by FIG. 8j. 
Alternatively, the coupling transmission structure thinning process can be accomplished with a laser ablation process instead of masking and etching. The laser cutter is guided to where the thinning is to be performed. Upon completion of the laser ablation process a portion of the substrate 130 will be removed, as shown by FIG. 8j. 
In FIGS. 8k and 8l, a disjoin process is performed on the substrate 130 and circuitry layer 125. Upon completion of the disjoin process, the individual ICs 101 and 102 on the wafer will be disjoined from each other. The disjoin process can be performed by: applying and imaging an integrated circuit mask 180 to the substrate 130 exposing only the portions of the substrate 130 that are between the individual ICs, as shown by FIG. 8k; and etching through the substrate 130 and circuitry layer 125 and removing the integrated circuit mask 180, as shown by FIG. 8l. 
Alternatively, the process of disjoining the individual ICs from the wafer can be accomplished by a laser die cutting process instead of masking and etching. The laser cutter is guided to where the cutting is to be performed. Upon completion of the laser die cutting process the individual ICs 101 and 102 will be disjoined from each other, as shown by FIG. 8l. 
Finally, removing the wax or other suitable material 135 enables removal of the individual ICs 101 and 102 from the support substrate 140, as shown by FIG. 8l. The wax 135 can be removed with Tetra-chloro-ethylene (TCE).
In another embodiment, the presently disclosed technology improves the performance and reduces higher order modes of the IC by including an etch stop layer 204 under the circuitry layer 201 and removing all the excess semiconductor substrate material 203 that is under the portion of the etch stop layer that is under the coupling transmission structures 202, as shown by FIG. 9. The presently disclosed technology is not limited to the etch stop layer being disposed between the circuitry layer 201 and the substrate material 203. In this embodiment, the peripheral edges of the semiconductor substrate material 203 and etch stop layer 204 closely follow the peripheral edges of the circuitry layer 201 and coupling transmission structures 202. The distances between the peripheral edges of the semiconductor substrate material 203 and etch stop layer 204 and the peripheral edges of the circuitry layer 201 and coupling transmission structures 202 in the FIG. 9 are exaggerated for illustration purposes.
The extra parasitic substrate material can be removed using a backside processing shown in FIGS. 10a–l. FIGS. 10a–l represent the cross section of a wafer, containing multiple ICs, for each of the backside process steps.
In FIG. 10a, a wafer comprises a substrate 230, an etch stop layer 210 and a circuitry layer 225. The wafer is mounted with the circuitry layer 225 down on to a support substrate 240 and held in place with a wax or other suitable material 235. The substrate 230 can be a semi-insulating InP wafer. The circuitry layer 225 contains multiple ICs.
In FIG. 10b, a thinning process is performed on the substrate 230. The thinning process can be performed, for example, either by lapping the substrate 230; by etching the substrate 230 (wet or dry); grinding the substrate 230; or a combination of any of these processes can be used to obtain a desired thickness depending on design requirements.
In FIGS. 10c–h, a via process is performed on the substrate 230. The via process can be performed by: applying and imaging a via mask 245 to the substrate 230, as shown by FIG. 10c; creating a via pattern 250 in the via mask 245, as shown by FIG. 10d; etching via holes 255 through the substrate 230 and the etch stop layer 210 and removing the via mask 245, as shown by FIG. 10e; depositing a metallization layer 265 to the backside of the substrate 230 thereby covering via holes 255 with metal, as shown by FIG. 10f; applying and imaging a metal mask 270 as shown by FIG. 10g; etching the metallization layer 265; and removing the metal mask 270, as shown by FIG. 10h. 
The via mask 245 and metal mask 270 can be, but are not limited to, a photoresist material. The metallization layer 265 can be formed by, but is not limited to, first depositing Ti followed by Au metals. The metallization layer 265 can be developed by either evaporating or sputtering metal onto substrate 230 and then plating metal to a desired thickness. Etching of the metallization layer 265 can be done through wet etch technique. Wet etching can consist of applying potassium iodide to etch Au followed by hydrofluoric acid to etch Ti.
In FIGS. 10i–j, a coupling transmission structure thinning process is performed on the substrate 230. Upon completion of the coupling transmission structure thinning process there is less substrate 230 material covering a portion of the etch stop layer 210 that is covering the coupling transmission structures extending from the individual ICs than there is substrate 230 material covering the rest of the etch stop layer 210. The coupling transmission structure thinning process can be performed by applying and imaging a coupling transmission structure mask 275 to the substrate 230 exposing only the portions of the substrate 230 that cover the portion of the etch stop layer 210 that is covering the coupling transmission structures extending from the individual ICs, as shown in FIG. 10i, followed by etching the substrate 230 to remove all the substrate 230 material that is covering the portion of the etch stop layer 210 covering the coupling transmission structures and removing the coupling transmission structure mask 275 covering the substrate 230, as shown by FIG. 10j. 
In FIGS. 10k and 10l, a disjoin process is performed on the substrate 230, the etch stop layer 210 and circuitry layer 225. Upon completion of the disjoin process the individual ICs 205 and 206 on the wafer will be disjoined from each other. The disjoin process can be performed by: applying and imaging an integrated circuit mask 280 to the substrate 230 exposing only the portions of the substrate 230 that are between the individual ICs, as shown by FIG. 10k; etching through the substrate 230, the etch stop layer 210 and circuitry layer 225; and removing the integrated circuit mask 280, as shown by FIG. 10l. 
Alternatively, the process of disjoining the individual ICs from the wafer can be accomplished by a laser die cutting process instead of masking and etching. The laser cutter is guided to where the cutting is to be performed. Upon completion of the laser die cutting process the individual ICs 205 and 206 will be disjoined from each other, as shown by FIG. 10l. 
Finally, removing the wax or other suitable material 235 enables removal of the individual ICs 205 and 206 from the support substrate 240, as shown by FIG. 10l. The wax 235 can be removed with Tetra-chloro-ethylene (TCE).
The embodiments described in detail for exemplary purposes are, of course, subject to many different variations in structure, design and application. Since many varying and different embodiments may be made within the scope of the inventive concepts herein taught, and since many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the detailed embodiments provided above are to be interpreted as illustrative and not in a limiting sense.

## Claims

1. A monolithic microwave integrated circuit (MMIC) comprising:
a) a substrate with a first surface and a second surface, the first surface containing a first surface main area and one or more first surface protruding areas, the second surface containing a second surface main area and one or more second surface protruding areas; and
b) a circuit substantially disposed above and in contact with the first surface main area, the circuit containing one or more coupling transmission structures, the one or more coupling transmission structures extending on to the first surface protruding areas and being disposed above and in contact with the first surface protruding areas;
wherein the first surface and the second surface are in a spaced relationship there between, the first surface protruding areas are narrower than the first surface main area and the second surface protruding areas are narrower than the second surface main area.

2. The MMIC of claim 1, wherein the first surface main area is substantially parallel to the second surface main area.

3. The MMIC of claim 2, wherein the first surface protruding areas are substantially parallel to the second surface protruding areas.

4. The MMIC of claim 1, wherein the first surface is disposed substantially above the second surface.

5. The MMIC of claim 1 wherein at least one of the one or more coupling transmission structures is used as an onboard antenna.

6. The MMIC of claim 1 wherein at least one of the one or more coupling transmission structures is used as an onboard probe.

7. The MMIC of claim 1 wherein a protruding area distance between the first surface protruding areas and the second surface protruding areas is less than a main area distance between the first surface main area and the second surface main area.

8. The MMIC of claim 7, wherein the second surface is a staggered surface.

9. The MMIC of claim 8, wherein the first surface main area is substantially parallel to the second surface main area.

10. The MMIC of claim 8, wherein the first surface protruding areas are substantially parallel to the second surface protruding areas.

11. The MMIC of claim 7, wherein the first surface is disposed substantially above the second surface.

12. The MMIC of claim 7 wherein at least one of the one or more coupling transmission structures is used as an onboard antenna.

13. The MMIC of claim 7 wherein at least one of the one or more coupling transmission structures is used as an onboard probe.

14. The MMIC of claim 7 further comprising an etch stop layer disposed between the circuit and the second surface, the etch stop layer containing an etch stop layer main area and one or more etch stop layer protruding areas, wherein the first surface, the second surface and the etch stop layer are in a spaced relationship there between.

15. The MMIC of claim 14 wherein the protruding area distance is zero.

16. The MMIC of claim 1 wherein a protruding area distance between the first surface protruding areas and the second surface protruding areas decreases.

17. The MMIC of claim 16 wherein the protruding area distance decreases from a main area distance to a final protruding area distance, wherein the main area distance is between the first surface main area and the second surface main area and the final protruding area distance ranges from the main area distance to zero.

18. The MMIC of claim 1 wherein a protruding area distance between the first surface protruding areas and the second surface protruding areas decreases from the second surface main area.

19. The MMIC of claim 1 wherein the MMIC is within a waveguide.

20. An integrated circuit (IC) comprising:
a) a substrate with a first surface and a second surface, the first surface containing a first surface main area and one or more first surface protruding areas, the second surface containing a second surface main area and one or more second surface protruding areas; and
b) a circuit substantially disposed above and in contact with the first surface main area, the circuit containing one or more coupling transmission structures, the one or more coupling transmission structures extending on to the first surface protruding areas and being disposed above and in contact with the first surface protruding areas;
wherein the first surface and the second surface are in a spaced relationship there between, the first surface protruding areas are narrower than the first surface main area and the second surface protruding areas are narrower than the second surface main area.

21. The IC of claim 20, wherein the first surface main area is substantially parallel to the second surface main area.

22. The IC of claim 21, wherein the first surface protruding areas are substantially parallel to the second surface protruding areas.

23. The IC of claim 20, wherein the first surface is disposed substantially above the second surface.

24. The IC of claim 20 wherein at least one of the one or more coupling transmission structures is used as an onboard antenna.

25. The IC of claim 20 wherein at least one of the one or more coupling transmission structures is used as an onboard probe.

26. The IC of claim 20 wherein a protruding area distance between the first surface protruding areas and the second surface protruding areas is less than a main area distance between the first surface main area and the second surface main area.

27. The IC of claim 26, wherein the second surface is a staggered surface.

28. The IC of claim 27, wherein the first surface main area is substantially parallel to the second surface main area.

29. The IC of claim 27, wherein the first surface protruding areas are substantially parallel to the second surface protruding areas.

30. The IC of claim 26, wherein the first surface is disposed substantially above the second surface.

31. The IC of claim 26 wherein at least one of the one or more coupling transmission structures is used as an onboard antenna.

32. The IC of claim 26 wherein at least one of the one or more coupling transmission structures is used as an onboard probe.

33. The IC of claim 26 further comprising an etch stop layer disposed between the circuit and the second surface, the etch stop layer containing an etch stop layer main area and one or more etch stop layer protruding areas, wherein the first surface, the second surface and the etch stop layer are in a spaced relationship there between.

34. The IC of claim 33 wherein the protruding area distance is zero.

35. The IC of claim 20 wherein a protruding area distance between the first surface protruding areas and the second surface protruding areas decreases.

36. The IC of claim 35 wherein the protruding area distance decreases from a main area distance to a final protruding area distance, wherein the main area distance is between the first surface main area and the second surface main area and the final protruding area distance ranges from the main area distance to zero.

37. The IC of claim 20 wherein a protruding area distance between the first surface protruding areas and the second surface protruding areas decreases from the second surface main area.

38. The IC of claim 20 wherein the IC is within a waveguide.

39. The integrated circuit of claim 20 wherein the integrated circuit is a monolithic microwave integrated circuit.

40. The MMIC of claim 1, wherein the circuit is an integrated circuit.

41. A monolithic microwave integrated circuit (MMIC) comprising:
a) a substrate with a first surface and a second surface, the first surface containing a first surface main area and one or more first surface protruding areas, the second surface containing a second surface main area and one or more second surface protruding areas; and
b) a circuit substantially disposed on the first surface main area, the circuit containing one or more coupling transmission structures, the one or more coupling transmission structures extending on to the first surface protruding areas;
c) an etch stop layer disposed between the circuit and the second surface, the etch stop layer containing an etch stop layer main area and one or more etch stop layer protruding areas, wherein the first surface, the second surface and the etch stop layer are in a spaced relationship there between;
wherein the first surface protruding areas are narrower than the first surface main area, the second surface protruding areas are narrower than the second surface main area, and the one or more etch stop layer protruding areas are narrower than the etch stop layer main area, and
wherein a protruding area distance between the first surface protruding areas and the second surface protruding areas is less than a main area distance between the first surface main area and the second surface main area.

42. An integrated circuit (IC) comprising:
a) a substrate with a first surface and a second surface, the first surface containing a first surface main area and one or more first surface protruding areas, the second surface containing a second surface main area and one or more second surface protruding areas; and
b) a circuit substantially disposed on the first surface main area, the circuit containing one or more coupling transmission structures, the one or more coupling transmission structures extending on to the first surface protruding areas;
c) an etch stop layer disposed between the circuit and the second surface, the etch stop layer containing an etch stop layer main area and one or more etch stop layer protruding areas, wherein the first surface, the second surface and the etch stop layer are in a spaced relationship there between;
wherein the first surface protruding areas are narrower than the first surface main area, the second surface protruding areas are narrower than the second surface main area, and the one or more etch stop layer protruding areas are narrower than the etch stop layer main area, and
wherein a protruding area distance between the first surface protruding areas and the second surface protruding areas is less than a main area distance between the first surface main area and the second surface main area.