Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
2001-04-09
2003-03-11
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C385S014000, C385S033000, C385S034000, C385S035000, C359S201100, C359S224200, C359S850000
Reexamination Certificate
active
06531767
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the fabrication and packaging of optical microelectro-electromechanical devices (MEMS or MOEMS), carrying tiltable mirrors integrated on substrates; and improved MEMS structures and devices provided thereby, being more particularly directed to the precise alignment or tiling of such devices or dies on single packaging transparent optical substrates and the like, without restriction on the size of, or the layout upon, the substrate, and with ready adaptability for large scaling.
BACKGROUND
The present invention, as above stated, generally relates to the packaging of electronic integrated circuits, and more specifically to the packaging of MEMS devices with optical components, such as tiltable or orientable mirrors; being primarily concerned with the means by which optical and electrical inputs and outputs are made, utilizing packaging substrates, and how such packaging can monolithically employ general-purpose optical components.
Recent attention, however, has been paid to making multichip modules (MCM), systems-on-chip (SOC) and microscale optomechanical devices for a variety of applications. The MCMs are devoted to miniaturization of electronic systems into one packaged module where many hybrid technologies may be employed; while the SOC has focused on the integration of many electronic functions, (analog, digital and RF, etc.), monolithically onto a single VLSI die. Optoelectronic devices are beginning to follow along the MCM route where many optical components, such as lenses, beams splitters, lasers, detectors, and fiber optics and the like, are integrated onto MCM-like carrier substrates.
The present invention falls under the particular purview of the so-called flip-chip (FC) bonded multichip modules (MCM) that employ substrates that act not only as a mechanical attachment and electrical wiring point, but also as an optical interface. Typical MCMs incorporate an insulating or non-conductive substrate resembling a printed circuit board (PCB) where metalization is placed for the creation of interconnection circuitry. The substrates have regions where VLSI dies are attached, face-up to the substrate; and, following attachment to the substrate, are then wirebonded to complete the electrical connection. An example of such structures is disclosed in U.S. Pat. No. 6,147,876, creating a special substrate for die potting. Other forms of substrates, interconnection methodologies, materials, and architectures have also been proposed for face-up VLSI MCMs.
More recently, the previously mentioned flip-chip bonding of dies to substrates and of dies-to-dies for face-to-face solder attachments have also been proposed as in, for example, U.S. Pat. No. 6,150,724, illustrating die-on die/die-on-wafer flip-chip bonding. In such cases, solder is used to attach, align and electrically connect the VLSI to another die or a sub-wafer package. By utilizing surface tension while the solder is in its liquid state, the floating die placed face down onto the target substrate is drawn laterally until minimal misalignment between the target substrate and the die is achieved. Such techniques are shown, as a further example, in U.S. Pat. No. 6,151,173, employing solder microballs to achieve 1 micron alignment. In this case, the solder microballs are utilized to control the solder coating thickness, which plays an important role in alignment accuracy. In the field of MEMS or MOEMS, the use of such flip-chip bonding has been employed to mix differently processed die substrates in order to achieve hybrid integration of MEMS components for an optomechanical device, such as an optical scanner of Xerox Corporation, employing flip chip process for MEMS applications in silicon optical bench integration. In addition, flip-chip bonding has also been used for the self-alignment of optical fiber arrays to substrates that have waveguide components monolithically integrated, as described at http://www.rereth.ethz.ch/phys/ quantenelectomik/ melchior/pj.17.html. In this case, the surface tension of the solder bond draws the fiber arrays into alignment relative to the substrate.
In much of the prior art, the attach substrate has been opaque or not at all considered for optical interconnection functions or its optical properties. Recently, however, some consideration has been given to the use of the attach substrates as an optical path. VLSI dies with detectors or transmitters, for example, have been bonded to an optical substrate that provides an optical path for interconnection, as illustrated in U.S. Pat. No. 6,097,857, describing optical and electrical interconnections using such a substrate with integrated holograms, wherein VLSI chips are flip-chip bonded to the optical substrate. As another illustration, transmission through a VLSI substrate has also been considered for optical interconnection as in U.S. Pat. No. 6,052,498.
Up until the present invention, however, it does not appear that the prior art has taken into full account the problem of integrating many MEMS dies with high alignment accuracy onto an optically transmissive substrate that provides not only electrical connectivity but also simultaneously provides means to integrate passive or active optical components (as later discussed). MCM and flip-chip approaches heretofore only covered the many die-to-single substrate attachments. One of the purposes of this invention, on the other hand, is to create a substrate that provides both electrical and optical interconnection to optical MEMS-integrated circuits and components requiring critical alignment, say as low as +/−1 micron. The present state-of-the-art of VLSI processing, unfortunately, does not pragmatically provide a mechanism for creating die sizes beyond 20 mm on a side without defects. Sizes exceeding 20 mm on a side, indeed, require stitching of stepper repeated masks—a process that encompasses more defects per area that often result in defective mirrors or electronics, increasing the risk of unacceptable dies and producing wafers with very poor yield.
As a result, very large arrays of MEMS devices, sizes exceeding 40 mm on a side, have not heretofore been possible with the stitched stepper mask approach, for example, on a single silicon die, particularly where the die is approaching the wafer sizes. In addition, the scalability of the MEMS devices, typically on the order of 1 square mm in area, to thousands of devices, is currently seriously limited. To combat these problems, known good - die approaches have been the industry standard; that is, VLSI dies and correspondingly MEMS dies, are tested, and only known good parts are selected out for packaging. To effectively use known good dies in the creation of a larger optical MEMS array, however, a precise alignment of MEMS die-to-MEMS die is necessary in order to maintain beam integrity, requiring a high-accuracy tiling approach. In addition, while lens arrays can be used over the MEMS array to reduce the overall size of the MEMS and increase the amount of real estate available for integrated electronics and interconnections, a critically tight alignment of the lens arrays to the center of the MEMS mirror is required to avoid misfocusing of the optical beams.
In accordance with the present invention, these and other problems of tiling many MEMS have now been successfully addressed by using a custom-fabricated optically (for example, visible or near-infrared band) transmissive substrate. This substrate may have monolithically integrated optical components, such as lenses, diffractive gratings, optical absorbers, and transmission filters, and the like; and its MEMS chips are flip-chip-bonded onto support pillars or posts that act as the electrical and mechanical connections and also provide the mechanism for self-alignment. Instead of creating MCMs with standard VLSI dies and an optical substrate, or MCMs on non-optical substrates, the technique of the present invention rather builds an optical MCM (OMCM) with MEMS devices. This invention allows for physically integrated means to set the o
Analog Devices Inc.
Nelms David
Rines and Rines
Tran Mai-Huong
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