# Patent

## Title
Micro-optical device packaging system

## Abstract

According to one embodiment, a micro-optical device includes an electro-optical circuit and an annular frame disposed on a surface of a substrate. The electro-optical circuit has an active region that is encapsulated by a window and an interconnect region adjacent at least one edge of the electro-optical circuit. The annular frame extends around an outer periphery of the window and is separated from the window by a gap, the annular frame and the electro-optical circuit form a cavity for placement of a plurality of bonding wires the interconnect that electro-optical circuit to the substrate.

## Background
This application is a Divisional of application Ser. No. 12/345,421, filed 29 Dec. 2008 and issued as U.S. Pat. No. 7,936,033 on 3 May 2011.


TECHNICAL FIELD OF THE DISCLOSURE
This disclosure generally relates to optical devices, and more particularly, to a micro-optical device packaging system and a method of fabricating the same.
BACKGROUND OF THE DISCLOSURE
Light modulators, such as micro-optical-electromechanical systems (MOEMSs) or liquid crystal display (LCD) devices typically have a plurality of reflective elements for generating two-dimensional images. These devices modulate a light beam into pixels corresponding to the arrangement of reflective elements configured on the light modulator. Some light modulators, such as digital micro-mirror devices (DMDs), may be fabricated on semi-conductor materials using known planar processing techniques.
SUMMARY OF THE DISCLOSURE
According to one embodiment, a micro-optical device includes an electro-optical circuit and an annular frame disposed on a surface of a substrate. The electro-optical circuit has an active region that is encapsulated by a window and an interconnect region adjacent at least one edge of the electro-optical circuit. The annular frame extends around an outer periphery of the window and is separated from the window by a gap, the annular frame and the electro-optical circuit form a cavity for placement of a plurality of bonding wires the interconnect that electro-optical circuit to the substrate.
Some embodiments of the disclosure may provide numerous technical advantages. For example, some embodiments of the micro-optical device may be manufactured without requiring physical contact with electro-optical circuit or the window disposed outwardly from the active region. Thus, attachment of the annular frame may be provided during an assembly stage of manufacture that may be external to a clean room environment. An additional advantage that may be provided by certain embodiments is a gap that equalizes pressure between the cavity and the ambient environment due to periodic changes in barometric pressure.
Some embodiments may benefit from some, none, or all of these advantages. Other technical advantages may be readily ascertained by one of ordinary skill in the art.



BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of embodiments of the disclosure will be apparent from the detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a side elevational view of one embodiment of an electro-optical device according to the teachings of the present disclosure;
FIG. 2 is a top view of the electro-optical device of FIG. 1;
FIG. 3 is an exploded view of the electro-optical device of FIG. 1 showing a lens housing that may be secured to the annular frame; and
FIG. 4 is a flowchart showing a series of actions that may be performed to manufacture the electro-optical device of FIG. 1.



DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
Various types of imaging devices, such as image sensors, light modulators, and image generators, may be manufactured using known integrated circuit (IC) processing techniques. These imaging devices are typically formed on a surface of a semiconductor material, such as silicon or gallium-arsenide having an active region for manipulation of light, such as from an external light source. These imaging devices are generally formed of a plurality of elements that may be arranged as a two-dimensional array over the active region of the imaging device.
Elements forming the active region are relatively small in size and thus may be sensitive to contamination by dust or other airborne debris. Fabrication of image devices is therefore, often performed in clean rooms to control the level of contaminants that may be potentially harmful to these elements. Prior to leaving the clean room, a transparent window may be placed over the active region for protection during normal use.
Integrated circuit manufacturing techniques typically involve manufacture of numerous imaging devices on a wafer followed by an assembly process in which each imaging device is separated from the wafer and mounted in a suitable package. Due to the relatively sensitive nature of its active region, the assembly process of many imaging devices must also be performed in the sanctity of the clean room.
FIGS. 1 and 2 show a side view and a top view, respectively, of one embodiment of a micro-optical device 10 according to the teachings of the present disclosure. Micro-optical device 10 includes an electro-optical circuit 12 and an annular frame 14 attached to a surface 16 of a substrate 18. Electro-optical circuit 12 has an active region 20 configured to generate, receive, or modulate light through a window 22. A cavity 24 is formed between annular frame 14 and electro-optical circuit 12 for encasing a plurality of bonding wires 26. Annular frame 14 extends around the outer periphery of window 22 and is separated from window 22 by a gap 28.
Certain embodiments incorporating a gap 28 between window 22 and annular frame 14 may provide numerous benefits. For example, gap 28 may equalize pressure variations between cavity 24 and the ambient environment due to changes in barometric pressure. Gap 28 may also provide a fabrication procedure for micro-optical device that may not require physical contact with electro-optical circuit 12, window 22, and/or bonding wires 26 during its assembly. Thus, attachment of annular frame 14 to substrate 18 may be provided during an assembly stage of production that may be external to a clean room environment.
Electro-optical circuit 12 may be any electrical device that manipulates or receives light, such as, for example, a micro-optical-electromechanical system (MOEMS) device, or a charge coupled display (CCD) device that generates an electrical signal representative of an image. In one embodiment, electro-optical circuit 12 is a light modulator, such as a digital micro-mirror device (DMD) that modulates light generated by an external source into a two-dimensional image. The digital micro-mirror device has a plurality of relatively small mirrors arranged in an M×N configuration on active region 20 and adapted to selectively reflect light emanating from the external source to or away from a planar surface. When coordinated together, the plurality of mirrors modulate light from the light source to create an image on the planar surface.
Electro-optical circuit 12 has an interconnect region 30 that provides electrical connection of the various elements of active region to substrate 18 using bonding wires 26. Interconnect region 30 covers a portion of the surface of electro-optical circuit 12 adjacent its edge. In the particular embodiment shown in which electro-optical circuit 12 is rectangular in shape, interconnect region 30 may be disposed adjacent any one or more if its edges. Bonding wires 26 are relatively thin and thus may be susceptible to damage if not sufficiently protected. Annular frame 14 provides protection for bonding wires 26 by inhibiting physical access to bonding wires 26 from objects external to micro-optical device 10.
Window 22 is generally transparent to light and configured outwardly from active region 20. Window 22 protects the various elements of active region 20 while allowing light to pass through freely. Window 22 is disposed outwardly from the surface 16 of substrate 18 at a height HW that may be specified according to its thickness and its desired distance from active region 20. In one embodiment, annular frame 14 has a height HF from the surface 16 that is approximately similar to the height HW of window 22 for protection of the edges of window from physical damage. In other embodiments, the height HF of annular frame 14 may be less or greater than the height HW of window 22. For example, a particular height HF of annular frame 14 that is less than height HW of window 22 may provide enhanced optical clearance of the light path through window 22 while a height HF greater than height HW may provide enhanced protection of window 22 in some embodiments.
Annular frame 14 may be formed of any suitable material, such as plastic, having a generally rigid shape for protection of bonding wires 26 from the external environment. Gap 28 formed between annular frame 14 and window 22 may have any width that provides sufficient protection for bonding wires 26 due to normal use and provides ample clearance for ease of assembly. In one embodiment, the width of gap 28 is approximately 180 microns. In some embodiments, gap 28 may have any width that is between 0 and 1000 microns.
Substrate 18 may be made of any suitable material, such as ceramic, that has a planar surface 16 for attachment of electro-optical circuit 12 and annular frame 14. Electro-optical circuit 12 and annular frame may be bonded to surface 16 using any suitable adhesive material. In one embodiment, annular frame 14 may be free of any mechanical bond to window 22. In this manner, flexure or strain of the annular frame 14 due to external forces may not be transferred to window 22 and thus to electro-optical circuit 12. In another embodiment, annular frame 14 is bonded to window 22 with an adhesive such that cavity 24 is hermetically sealed from the outside environment.
A hole 38 may optionally be provided for filling cavity 24 with a potting material, such as an epoxy compound having a relatively low working viscosity. In other embodiments, the gap 28 may be sufficiently wide to provide insertion of potting material through gap 28. Annular frame 14, therefore, may serve as a dam for containment of potting material during its curing phase.
FIG. 3 is an exploded view of the micro-optical device 10 of FIGS. 1 and 2. In the particular embodiment shown, annular frame 14 has several mechanical alignment features 32 for releasable securement of a lens housing 34 to its surface at a specified position and orientation relative to electro-optical circuit 12. Mechanical alignment features 32 include ridges formed in annular frame 14 such that its outer contour is complementary to an inner contour 36 of lens housing 34. In other embodiments, mechanical alignment features 32 may have any physical shape that maintains lens housing in a specified position and orientation relative to electro-optical circuit 12.
Modifications, additions, or omissions may be made to micro-optical device 10 without departing from the scope of the disclosure. The components of micro-optical device 10 may be integrated or separated. For example, electro-optical circuit 12 may be implemented on multiple semiconductor substrates and attached over varying regions of substrate 18 such that each semiconductor substrate is interconnected to one another via bonding wires. Moreover, the operations of micro-optical device 10 may be performed by more, fewer, or other components. For example, electro-optical circuit 12 may include other electrical components, such as line conditioning circuits, timing circuits, and/or control circuits for manipulating the manner in which elements of active region 20 are used. As used in this document, “each” refers to each member of a set or each member of a subset of a set.
FIG. 4 is a flowchart showing one embodiment of a series of actions that may be performed to manufacture the micro-optical device 10 of FIG. 1. In act 100, the process is initiated.
In act 102, electro-optical circuit 12 is attached to the surface 16 of substrate 18. Electro-optical circuit 12 may be attached using any suitable approach, such as with a suitable adhesive or using a solder process in which various electrical connections are formed that rigidly constrain electro-optical circuit 12 to the surface 16 of substrate 18. In one embodiment, electro-optical circuit 12 is a digital micro-mirror device that modulates light from an external source into an image that may be displayed on a generally planar surface.
In act 104, electro-optical circuit 12 is electrically coupled to substrate 18 using bonding wires 26. In one embodiment, electrical coupling of electro-optical circuit 12 is performed external to a clean-room environment. A clean-room environment generally describes a type of environment in which particulate matter, such as dust or other airborne debris, is regulated to a relatively low level. Certain embodiments incorporating electro-optical circuit 12 having a window 22 for encapsulation of active region 20 may provide an assembly procedure for micro-optical device 10 that may not need to be conducted in a clean-room environment.
In act 106, annular frame 14 is attached to the surface 16 of substrate 18. In one embodiment, annular frame 14 is attached to surface 16 using a suitable adhesive. In another embodiment, annular frame 14 has tabs, detents, or other similar type of structural features for attaching annular frame 14 to surface 16 using a snap fit type action. In another embodiment, annular frame 14 may be configured with one or more metallic pads over a portion of its surface for attachment to surface 16 using solder. Annular frame 14 may be made of any generally rigid material, such as plastic, for protection of bonding wires 26. In one embodiment, a gap 28 is formed between annular frame 14 and window 22 for ease of assembly. In one embodiment, annular frame 14 is attached to substrate 18 external to a clean-room environment for reasons cited above.
In act 108, cavity 24 formed between annular frame 14 and electro-optical circuit 12 is optionally filled with a potting material. Annular frame 14 serves as a dam for containment of potting material while in its uncured state thus allowing the use of potting materials having relatively low working viscosity in some embodiments.
In act 110, a lens housing 34 is secured on annular frame 14. Annular frame 14 has one or more mechanical alignment features 32 that maintains lens housing 34 in a fixed position and orientation relative to electro-optical circuit 12. Using mechanical alignment features 32, lens housing 34 may be secured to micro-optical device 10 during fabrication processes for other devices that incorporate electro-optical device 10, such as camera phones, which may alleviate costs and complexity associated with camera assembly procedures for incorporation of these devices in some embodiments.
Modifications, additions, or omissions may be made to the method without departing from the scope of the disclosure. The method may include more, fewer, or other acts. For example, electrical coupling of bonding wires 26 and/or attachment of annular frame 14 to substrate may be conducted within or external to a clean room. The arrangement of annular frame 14 and window 22 provides a manufacturing process whereby assembly in a relatively high controlled environment, such as a clean room may not be necessary.
Although the present disclosure has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present disclosure encompass such changes, variations, alterations, transformation, and modifications as they fall within the scope of the appended claims.

## Claims

1. A micro-optical device comprising:
a substrate;
an electro-optical device supported by the substrate;
an electrical connection between the substrate and the electro-optical device; and
a frame attached to the substrate and forming a cavity around the electrical connection, wherein the frame extends towards the electro-optical device above the cavity in a lip region, and wherein the frame is separated from the electro-optical device in the lip region by a gap.

2. The device of claim 1, wherein the substrate is ceramic.

3. The device of claim 1, wherein the frame is plastic.

4. The device of claim 1, wherein the electrical connection is one or more bond wires.

5. The device of claim 1, wherein the frame has alignment features formed therein.

6. The device of claim 1, wherein the electro-optical device comprises a micro-optical-electromechanical system.

7. The device of claim 1, wherein the electro-optical device comprises a charge coupled device.

8. The device of claim 1, wherein the electro-optical device comprises a light modulator.

9. The device of claim 1, wherein the electro-optical device comprises a micromirror device.

10. The device of claim 1, wherein the electro-optical device comprises a window having a surface opposite the substrate at a first distance relative to a surface of the substrate, wherein a surface of the frame has a second distance relative to the surface of the substrate and the first distance is less than the second distance.

11. The device of claim 1, wherein the electro-optical device comprises a window having a surface opposite the substrate at a first distance relative to a surface of the substrate, wherein a surface of the frame has a second distance relative to the surface of the substrate and the first distance is greater than the second distance.

12. The device of claim 1, wherein the electro-optical device comprises a window having a surface opposite the substrate at a first distance relative to a surface of the substrate, wherein a surface of the frame has a second distance relative to the surface of the substrate and the first distance is approximately the same as the second distance.

13. The device of claim 1, wherein the frame is separated from the electro-optical device in the lip region by a gap approximately 180 microns wide.

14. The device of claim 1, wherein the frame is separated from the electro-optical device in the lip region by a gap 1000 microns, or less, wide.

15. The device of claim 1, comprising a potting material in at least a portion of the cavity region.

16. The device of claim 1, comprising an epoxy material in at least a portion of the cavity region.

17. The device of claim 1, comprising a lens housing engaging the frame.