Packaging and connecting electrostatic transducer arrays
Embodiments of a method for packaging cMUT arrays allow packaging multiple cMUT arrays on the same packaging substrate introduced over a side of the cMUT arrays. The packaging substrate is a dielectric layer on which openings are patterned for depositing a conductive layer to connect a cMUT array to VO pads interfacing with external devices. Auxiliary system components may be packaged together with the cMUT arrays. Multiple cMUT arrays and optionally multiple auxiliary system components can be held in place by a larger support structure for batch production. The support structure can be made of an arbitrary size using inexpensive materials.
1. A method for packaging a capacitive micromachined ultrasonic transducer (cMUT) array, the method comprising:
fabricating the cMUT array on a cMUT fabrication substrate;
introducing a first dielectric packaging substrate layer over the cMUT array and the cMUT fabrication substrate;
forming a first pattern in the first dielectric packaging substrate layer, the first pattern having a first opening over the cMUT array;
introducing a first conductive layer patterned over the first dielectric packaging substrate layer to provide at least a first part of an interconnection for connecting the cMUT array to outside through the first opening; and
removing a portion of the cMUT fabrication substrate.
2. The method as recited in claim 1 , wherein the cMUT array has a plurality of cMUT elements, the first pattern in the first dielectric packaging substrate layer has a plurality of first openings, each over a respective one of the plurality of cMUT elements, and the first part of the interconnection provided by the first conductive layer comprises a plurality of interconnections connecting each cMUT element to the outside.
3. The method as recited in claim 1 , wherein the side of the cMUT array corresponds to a top side of the cMUT fabrication substrate on which the cMUT array is fabricated.
4. The method as recited in claim 1 , wherein:
the fabricating the cMUT array on the cMUT fabrication substrate comprises:
providing a cMUT fabrication substrate;
forming an opening pattern from a top side of the cMUT fabrication substrate to define a boundary of the cMUT array, wherein the opening pattern reaches only a partial depth in the cMUT fabrication substrate; and
forming the cMUT array on the top side of the cMUT fabrication substrate; and
the removing the portion of the cMUT fabrication substrate comprises removing a bottom portion of the cMUT fabrication substrate from a bottom side so that a remaining portion of the cMUT fabrication substrate forms a separate bottom electrode for the first cMUT array.
5. The method as recited in claim 4 , wherein the cMUT array comprises a plurality of cMUT elements fabricated on the cMUT fabrication substrate.
6. The method as recited in claim 5 , wherein the opening pattern also defines boundaries of each of the plurality of cMUT elements, and removing the bottom portion of the cMUT fabrication substrate forms a plurality of separate bottom electrode each for a respective one of the plurality of cMUT elements.
7. The method as recited in claim 4 , wherein removing the bottom portion of the cMUT fabrication substrate enables complete separation of the cMUT array from rest of the cMUT fabrication substrate.
8. The method as recited in claim 4 , wherein removing the bottom portion of the cMUT fabrication substrate comprises: thinning the cMUT fabrication substrate from the bottom side to reach the trench's deepest end.
9. The method as recited in claim 4 , wherein the cMUT fabrication substrate is an SOI wafer comprising a device layer, an insulation layer below the device layer, and a handle layer below the insulation layer, and the opening pattern reaches the insulation layer, and wherein removing the bottom portion of the cMUT fabrication substrate comprises removing the handle layer.
10. The method as recited in claim 4 , wherein the cMUT fabrication substrate comprises a device layer, an embedded cavity below the device layer, and a support layer below the embedded cavity, and the opening pattern reaches the embedded cavity, and wherein removing the bottom portion of the cMUT fabrication substrate comprises removing the support layer.
11. The method as recited in claim 4 , further comprising: at least partially filling the opening pattern with a dielectric filler material.
12. The method as recited in claim 4 , wherein forming the opening pattern takes place prior to forming the cMUT array.
13. The method as recited in claim 4 , wherein forming the opening pattern takes place after forming the cMUT array, and forming the opening pattern further comprises cutting through a top layer of the cMUT array.
14. The method as recited in claim 1 , wherein the first dielectric packaging substrate layer is flexible.
15. The method as recited in claim 1 , wherein the first part of the interconnection for connecting the cMUT array to the outside comprises at least one of a connection between the cMUT array and an I/O pad, a connection between the cMUT array and another cMUT, and a connection between the cMUT array and another system component.
16. The method as recited in claim 1 , wherein the first part of the interconnection for connecting the cMUT array to the outside comprises an I/O pad and at least one connection between the cMUT array and the I/O pad.
17. The method as recited in claim 1 , further comprising:
introducing a second dielectric packaging substrate layer over the first dielectric packaging substrate layer and the first conductive layer;
forming a second pattern in the second dielectric packaging substrate; and
introducing a second conductive layer patterned over the second dielectric packaging substrate layer to provide at least a second part of the interconnection for connecting the cMUT array to the outside.
18. The method as recited in claim 17 , wherein the second part of the interconnection for connecting the cMUT array to the outside comprises at least one of a connection between the cMUT array and an I/O pad, a connection between the cMUT array and another cMUT, a connection between the cMUT array and another system component, and a connection between the first conductive layer and the second conductive layer.
19. The method as recited in claim 17 , wherein the second part of the interconnection for connecting the cMUT array to the outside comprises an I/O pad and at least one connection between the cMUT array and the I/O pad.
20. The method as recited in claim 17 , wherein the second pattern in the second dielectric packaging substrate has at least a second opening over the cMUT array, and the second part of the interconnection for connecting the cMUT array to the outside includes a connection to the second opening.
21. The method as recited in claim 1 , further comprising:
providing an auxiliary system component; and
placing the auxiliary system component adjacent to the cMUT array such that the first dielectric packaging substrate layer is introduced over a first side of the auxiliary system component, the first pattern in the first dielectric packaging substrate layer has at least a second opening over the auxiliary system component, and the first conductive layer is patterned over the first dielectric packaging substrate layer to provide at least part of the interconnection for connecting the cMUT array to outside through the first opening over the cMUT array and the second opening over the auxiliary system component.
22. The method as recited in claim 1 , further comprising: fabricating an additional electrical component on the first conductive layer after the first conductive layer has been introduced over the first dielectric packaging substrate layer, wherein the additional electric component includes at least one of: a transmission line, a capacitor, an inductor, a pressure sensor, a switch, or an IC chip.
23. A method for packaging a capacitive micromachined ultrasonic transducer (cMUT) array, the method comprising:
placing the cMUT array on a packaging support structure, wherein the packaging support structure includes a supporting substrate having a preformed cavity for receiving the cMUT array;
introducing a first dielectric packaging substrate layer over the cMUT array and the supporting substrate;
forming a first pattern in the first dielectric packaging substrate layer, the first pattern having a first opening over the cMUT array;
introducing a first conductive layer patterned over the first packaging substrate layer to provide at least a first part of an interconnection for connecting the cMUT array to outside through the first opening; and
removing the supporting substrate.
24. The method as recited in claim 23 , wherein the cMUT array has a plurality of cMUT elements, the first pattern in the first dielectric packaging substrate layer has a plurality of first openings, each over a respective one of the plurality of cMUT elements, and the interconnection provided by the first conductive layer comprises a plurality of interconnections connecting each cMUT element to the outside.
25. The method as recited in claim 23 , wherein the side of the cMUT array corresponds to a top side of a cMUT fabrication substrate on which the cMUT array is fabricated.
26. The method as recited in claim 23 , wherein the first dielectric packaging substrate layer is flexible.
27. The method as recited in claim 23 , wherein the cavity has a retaining member for securing the cMUT array when placed in the cavity.
28. The method as recited in claim 23 , wherein the cMUT array has a through-wafer interconnection accessible from a backside of the cMUT array, and attaching the cMUT array to the cMUT array holder comprises placing the cMUT array facedown onto the cMUT array holder with the backside of the cMUT array facing toward a top side of the packaging support structure to enable access to the through-wafer interconnection from the top side of the packaging support structure.
29. The method as recited in claim 23 , wherein the supporting substrate of the packaging support structure comprises a support base layer, and the cMUT array holder comprises the cavity preformed in a supplemental support layer placed over a top surface of the support base layer.
30. The method as recited in claim 23 , wherein the first part of the interconnection for connecting the cMUT array to the outside comprises at least one of a connection between the cMUT array and an I/O pad, a connection between the cMUT array and another cMUT, and a connection between the cMUT array and another system component.
31. The method as recited in claim 23 , wherein the first part of the interconnection for connecting the cMUT array to the outside comprises an I/O pad and at least one connection between the cMUT array and the I/O pad.
32. The method as recited in claim 23 , further comprising:
introducing a second dielectric packaging substrate layer over the first dielectric packaging substrate layer and the first conductive layer;
forming a second pattern in the second dielectric packaging substrate; and
introducing a second conductive layer patterned over the second dielectric packaging substrate layer to provide at least a second part of the interconnection for connecting the cMUT array to the outside.
33. The method as recited in claim 32 , wherein the second part of the interconnection for connecting the cMUT array to the outside comprises at least one of a connection between the cMUT array and an I/O pad, a connection between the cMUT array and another cMUT, a connection between the cMUT array and another system component, and a connection between the first conductive layer and the second conductive layer.
34. The method as recited in claim 32 , wherein the second part of the interconnection for connecting the cMUT array to the outside comprises an I/O pad and at least one connection between the cMUT array and the I/O pad.
35. The method as recited in claim 32 , wherein the second pattern in the second dielectric packaging substrate has at least a second opening over the cMUT array, and the second part of the interconnection for connecting the cMUT array to the outside includes a connection to the second opening.
36. The method as recited in claim 23 , further comprising:
providing an auxiliary system component; and
placing the auxiliary system component adjacent to the cMUT array such that the first dielectric packaging substrate layer is introduced over a first side of the auxiliary system component, the first pattern in the first dielectric packaging substrate layer has at least a second opening over the auxiliary system component, and the first conductive layer is patterned over the first dielectric packaging substrate layer to provide at least part of the interconnection for connecting the cMUT array to outside through the first opening over the cMUT array and the second opening over the auxiliary system component.
37. The method as recited in claim 23 , further comprising: fabricating an additional electrical component on the first conductive layer after the first conductive layer has been introduced over the first dielectric packaging substrate layer, wherein the additional electric component includes at least one of: a transmission line, a capacitor, an inductor, a pressure sensor, a switch, or an IC chip.