Patent Application
20160187643
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The present disclosure relates generally to micro-electromechanical systems (MEMS) and, more particularly, to MEMS devices and methods for packaging the same.
2. Description of the Related Art
Recently, MEMS devices have been widely used in many applications as replacements for conventional components because of their compact size, light weight, reliability, and relatively lower cost of manufacturing. In some imaging applications that employ optical scanning systems, for example, oscillating MEMS mirror devices have been used to replace traditional rotating polygon minors as MEMS minors provide potential advantages of higher scanning speeds, smaller sizes and weights, and reduced costs, among others.
A MEMS mirror device typically includes a mirror fabricated on a semiconductor die using microfabrication techniques. In operation, energy is applied to the MEMS mirror device to allow its mirror to oscillate at a particular frequency. A light source illuminates a light beam on the mirror such that as the mirror oscillates, the light beam is scanned bidirectionally in both forward and reverse directions across a target image plane surface, such as photosensitive member in electrophotographic imaging devices.
The extent of motion or oscillation of a MEMS mirror device in response to a given drive energy is determined at least in part by the mirror device's quality factor (Q). One source of reduction in quality factor (Q) is the damping effect of air resistance induced by the mirror's oscillation. As the mirror becomes larger and/or oscillates faster, reduction of Q may result in greater drive energy and greater jitter for a given oscillation angle. To reduce this damping effect, some MEMS mirror devices are operated at very low air pressures by packaging them in an inert atmosphere or vacuum.
In some existing package designs, a MEMS mirror die is mounted within a vacuum sealed package. In order to drive the mirror, direct electrical connections between the MEMS mirror die and external drive electronics are typically established. Ceramic substrates may be used in or as part of MEMS mirror packages because its thermal expansion characteristics closely match that of a semiconductor material, such as silicon typically used to fabricate a MEMS die, and because vacuum tight electrical connections can be achieved through the ceramic substrate. However, ceramic substrates are generally expensive and the processes involved for establishing complex structures, such as the electrical connections through the ceramic substrate, require complex fabrication techniques that are often difficult to manufacture at low costs. To some extent, this has prevented or discouraged use of MEMS devices in various applications.
Example embodiments of the present disclosure provide a cost-efficient means for packaging MEMS devices.
In one example embodiment, a scanning device includes an enclosure maintaining a substantially fixed pressure level therein and having a window for allowing light to enter and exit the enclosure. A MEMS mirror for reflecting light incident thereon is disposed within the enclosure. The scanning device further includes a transformer having a first wire coil disposed outside the enclosure, and a second wire coil disposed within the enclosure and electrically coupled to the MEMS mirror. The transformer is used deliver electrical power to the MEMS mirror to drive the MEMS mirror.
In another example embodiment, an assembly for a micro-electromechanical system (MEMS) device includes a sealed enclosure, a MEMS component disposed within the sealed enclosure, and a transformer arrangement. The transformer arrangement has a first wire coil disposed outside the sealed enclosure, and a second wire coil disposed within the sealed enclosure and coupled to the MEMS component, the first and second wire coils being mutually inductively associated with each other. In operation, applying energy to the first wire coil outside the sealed enclosure induces electrical energy in the second wire coil within the sealed enclosure for use by the MEMS component.
The above-mentioned and other features and advantages of the disclosed example embodiments, and the manner of attaining them, will become more apparent and will be better understood by reference to the following description of the disclosed example embodiments in conjunction with the accompanying drawings, wherein:
It is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings.
Spatially relative terms such as “top”, “bottom”, “front”, “back” and “side”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. Terms such as “first”, “second”, and the like, are used to describe various elements, regions, sections, etc. and are not intended to be limiting. Further, the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.
Furthermore, and as described in subsequent paragraphs, the specific configurations illustrated in the drawings are intended to exemplify embodiments of the disclosure and that other alternative configurations are possible.
Reference will now be made in detail to the example embodiments, as illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.
During image formation, the surface of photoconductive member 112 is charged to a specified voltage, such as −800 volts, for example, by a charge roller 118. At least one light beam LB from a laser scanning unit (LSU) 120 is directed to the surface of photoconductive member 112 and discharges those areas it contacts to form a latent image thereon. In one example embodiment, areas on the photoconductive member 112 illuminated and impinged by the light beam LB are discharged to approximately −100 volts. The developer unit 106 then transfers toner to photoconductive member 112 to form a toner image thereon. The toner is attracted to the areas of the surface of photoconductive member 112 that are discharged by the light beam LB from LSU 120. In one example embodiment, a positive voltage field formed in part by transfer member 115 attracts the toner image from photoconductive member 112 to the media sheet between the photoconductive member 112 and transfer member 115.
A fuser assembly 124 is disposed downstream of toner transfer area 103 and receives media sheets with the unfused toner images superposed thereon. In general terms, fuser assembly 124 applies heat and pressure to the media sheets in order to fuse toner thereto. After leaving fuser assembly 124, a media sheet is either deposited into output media area 126 or enters duplex media path 128 for transport to toner transfer area 103 for imaging on a second surface of the media sheet.
Image forming device 100 is depicted in
Image forming device 100 further includes a controller 130 and memory 132 communicatively coupled thereto. Though not shown in
Referring to
Light source 140 may emit a light beam LB and may be implemented, for example, using a laser diode or any other suitable device for generating a beam of light. LSU 120 may also include driver circuitry (not shown) communicatively coupled to controller 130 for receiving video/image information and/or control data that may be utilized to set and/or vary the laser power used by light source 140. In the example embodiment illustrated in
Pre-scan optics 142 may include a collimating lens 150 for collimating light beam LB emitted by light source 140, and/or a pre-scan lens 152 to direct and focus the collimated light beam LB towards scanning device 145.
Scanning device 145 may include at least one reflective surface for receiving and reflecting light incident thereon. In the example shown, scanning device 145 comprises a bidirectional scanning oscillator, such as a torsion oscillator or resonant galvanometer, controlled to operate bidirectionally at a scanning frequency to scan light beam LB emitted by light source 140 and create scan lines on the surface of photoconductive member 112 in both forward direction 154A and reverse direction 154B along a main scan direction.
Post-scan optics 147 may include a post-scan lens 156 used to focus light beam LB onto the surface of photoconductive member 112. It will be appreciated, though, that other optical elements may be included downstream scanning device 145, relative to the optical path of light beam LB, such as mirrors, other lenses, and sensors used for synchronization.
During an imaging operation, image data corresponding to an image to be printed may be converted by controller 130 into modulation data. The modulation data may be utilized by the driver circuitry to modulate light source 140 so that LSU 120 outputs modulated light beam LB. Light beam LB emitted from light source 140 may be collimated by collimation lens 150 and pass through pre-scan lens 152 so that light beam LB converges to strike the reflective surface of scanning device 145. Scanning device 145 may direct portions of light beam LB modulated with image data toward the surface of photoconductive member 112 through a scan angle 170 defined by scan positions 170A and 170B. Post-scan lens 156 may transform the rotational scan of light beam LB reflected from scanning device 145 into a substantially linear scan of light beam LB at the surface of photoconductive member 112, with substantially linear scan velocity, and with substantially uniform light beam spot size along the surface of photoconductive member 112.
As photoconductive member 112 rotates, a plurality of scan lines may be formed, creating a latent image on the surface of photoconductive member 112. In the example embodiment, the plurality of scan lines may comprise alternating forward and reverse scan lines occurring in the forward and reverse directions 154A and 154B, respectively, due to the nature of scanning using a bidirectional scanning oscillator.
According to example embodiments, scanning device 145 may be implemented as a MEMS device having a MEMS mirror component or die that is fabricated on a semiconductor wafer.
A number of actuation methods may be used to drive the mirror 210 to oscillate about the axis defined by extensions 220 to bidirectionally scan light beam LB across the surface of photoconductive member 112, such as, for example, magnetic, or thermal actuation. Accordingly, MEMS mirror die 200 may include other electrical circuitries or components used for actuation which may be fabricated using different conventional integrated circuit (IC) fabrication methods. Further, MEMS mirror die 200 may also include other electronics and components for receiving and/or transforming energy into a form suitable for driving oscillation of the mirror 210.
In order to achieve an operating environment with a relatively very low air pressure so as to reduce damping effects on MEMS mirror die 200, MEMS mirror die 200 may be packaged within an enclosure sealed near or at vacuum pressure. In accordance with example embodiments of the present disclosure, MEMS mirror die 200 may be packaged in a manner that bypasses the need to pierce through the sealed enclosure when establishing electrical connections with an external drive circuitry.
As shown, MEMS mirror assembly 300 is disposed in a package 302 which includes a sealed enclosure 305. Pressure level within the sealed enclosure 305 may be kept near or at vacuum conditions so as to allow the MEMS mirror die 200 to operate with substantially reduced damping effect. In another example embodiment, a gas, such as Argon gas, is placed in sealed enclosure 305 so that pressure is maintained at a substantially constant level, but not necessarily at or near vacuum. Such an implementation provides an advantage of providing a substantially constant pressure, dust free environment for MEMS mirror assembly 300, without stressing package 302 as seen in maintaining vacuum conditions. A power source in the form of external drive circuitry 310 may be used to provide energy to MEMS mirror assembly 300 to drive the mirror 210 of MEMS mirror die 200 to oscillate. To avoid having to pierce through any wall of the sealed enclosure 305 for power delivery, power may be delivered into the sealed enclosure via mutual inductance. In particular, a first coil 315 may be disposed outside the sealed enclosure 305 and a second coil 320 may be disposed within sealed enclosure 305. The first coil 315 is electrically coupled to drive circuitry 310 to receive energy therefrom. The second coil 320 within the sealed enclosure 305 is arranged to be mutually inductively associated with the first coil 315 such that current variations introduced by the drive circuitry 310 in the first coil 315 induces a voltage V across the ends of the second coil 320 through electromagnetic induction. As such, the first coil 315 and the second coil 320 may form a transformer arrangement with the first coil 315 acting as a primary winding of the transformer and providing electrical power to the MEMS mirror die 200 via the second coil 320. The ratio between the number of turns of the first coil 315 to the numbers of turns of the second coil 320 may be used to either boost or reduce the voltage V presented to the MEMS mirror die 200, depending on the design contemplated. The induced voltage V may be applied to the MEMS mirror die 200 which in turn may use the applied voltage to drive its mirror to oscillate. MEMS mirror die 200 may include additional circuitry for converting the induced voltage V into a form suitable for driving its mirror to oscillate.
In one embodiment, MEMS die 404 is a MEMS torsion mirror device as described above with respect to MEMS mirror die 200, for use as a resonant oscillator in an optical system such as LSU 120. It is understood that MEMS die 404 may be an electrostatic, piezoelectric, or electromagnetic MEMS device. MEMS assembly 400 may be used in optical systems other than LSU 120. In this regard, MEMS die 404 may be any optical MEMS device that diffracts, refracts and/or reflects light. For example, MEMS die 404 may be a deformable MEMS mirror. A deformable MEMS mirror allows for the divergence/convergence of a reflected beam of light to be changed. Because deformable MEMS mirrors and other MEMS optical devices are well known, a detailed discussion thereof will not be presented for reasons of simplicity. Though the discussion hereinbelow is described with respect to MEMS mirror die 200 and MEMS mirror assembly 300, it is understood that MT MS die 404 and MEMS assembly 400 may be similarly employed.
Sealed enclosure 305 may comprise a receptacle 340 and a window 345. Receptacle 340 includes a base 340A and side walls 340B. Window 345, on the other hand, may be sized to cover the open surface of receptacle 340 in sealing engagement with the top rim 340C of side walls 340B to form or define a volume under reduced pressure, relative to atmospheric pressure, or partial vacuum. MEMS mirror die 200 and the second coil 320 may be disposed within the sealed volume defined by receptacle 340 and window 345. The second coil 320 may be positioned within receptacle 340 to be mutually inductively associated with the first coil 315 to complete the transformer arrangement therewith.
In the example shown, second coil 320 is formed by winding a conductive wire on a film, substrate, or circuit board 355 in a substantially parallel relation relative to the first coil 315 and sufficiently close thereto so that magnetic flux produced by the first coil 315 may inductively link with the second coil 320. Alternatively, second coil 320 is disposed within enclosure 305 without an underlying film, substrate or circuit board. In
With further reference to
Window 345 allows light to enter sealed enclosure 305 and exit therefrom after being reflected off by mirror 210 of MEMS mirror die 200. Window 345 may be made of substantially transparent material over a predetermined range of wavelengths, such as glass, and may be adhesively attached to the top rim 340C of receptacle 340 to complete the enclosure of MEMS mirror die 200 and second coil 320 and provide an environment thereto near or at vacuum conditions. In other alternative embodiments, window 345 may be coated with or made of a different material from receptacle 340. Top rim 340C of receptacle 340 may be formed in a planar manner to provide a substantially planar surface for application of adhesive, and window 345 may be oversized, relative to the perimeter of the top rim 340C, to allow a low-precision alignment of window 345 to receptacle 340. Since window 345 is outside of receptacle 340, ambient air pressure present may force window 345 against receptacle 340, which may increase the reliability of the seal between window 345 and receptacle 340.
In an example embodiment, window 345 may be arranged in a tilted manner relative to the position of mirror 210 about extensions 220 of MEMS mirror die 200. For example, receptacle 340 may be formed in a manner such that a side wall 340B of receptacle 340 is taller than an opposite side wall 340B thereof, resulting in window 345 being attached to receptacle 340 at an angle θ, as shown in
With the above example embodiments, a simple and cost-efficient way of packaging MEMS devices is provided, which supports the mechanical rigors of low-cost manufacturing processes. Example embodiments also introduce notions of rendering use of ceramic substrates to support MEMS components unnecessary in order to reduce cost, eliminating the need to pierce through walls of sealed enclosures within which MEMS components are disposed in order to simplify manufacturing and packaging processes, and delivering power into and/or out of sealed enclosures using one or more transformer configurations.
The description of the details of the example embodiments have been described in the context of electrophotographic imaging devices. However, it will be appreciated that the teachings and concepts provided herein are applicable to other systems employing optical scanners for scanning light beams. In addition, it will also be appreciated that teachings and concepts provided herein are applicable to other types of MEMS devices or any optical component that may benefit from being in a dust-free, pressure controlled environment, such as those used in the field of active optics.
The foregoing description of several example embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise steps and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.
