Patent Grant
7310175
Microelectromechanical systems or MEMS devices include micromachined substrates integrated with electronic microcircuits. Such devices may form, for example, microsensors or microactuators which operate based on, for example, electromagnetic, electrostrictive, thermoelectric, piezoelectric, or piezoresistive effects. MEMS devices have been formed on insulators or other substrates using micro-electronic techniques such as photolithography, vapor deposition, and etching.
An example of a MEMS device includes a micro-mirror device. The micro-mirror device can be operated as a light modulator for amplitude and/or phase modulation of incident light. One application of a micro-mirror device is in a display system. As such, multiple micro-mirror devices are arranged in an array such that each micro-mirror device provides one cell or pixel of the display.
A conventional micro-mirror device includes an electrostatically actuated mirror supported for rotation about an axis of the mirror. As such, rotation of the mirror about the axis may be used to modulate incident light by directing the incident light in different directions. To direct the incident light in different directions, the mirror may include a reflective surface which reflects the incident light. Unfortunately, variations in the reflective surface may lower the reflectivity of the mirror and/or produce light interference, thereby lowering or diminishing a contrast ratio of the mirror.
For these and other reasons, there is a need for the present invention.
One aspect of the present invention provides a method of forming a MEMS device, The method includes depositing a conductive material on a substructure, forming a first sacrificial layer over the conductive material, including forming a substantially planar surface of the first sacrificial layer, and forming a first element over the substantially planar surface of the first sacrificial layer, including communicating the first element with the conductive material through the first sacrificial layer. In addition, the method includes forming a second sacrificial layer over the first element, including forming a substantially planar surface of the second sacrificial layer, forming a support through the second sacrificial layer to the first element after forming the second sacrificial layer, including filling the support, and forming a second element over the support and the substantially planar surface of the second sacrificial layer. As such, the method further includes substantially removing the first sacrificial layer and the second sacrificial layer, thereby supporting the second element relative to the first element with the support.
In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
In one embodiment, as described below, micro-mirror device 10 is formed so as to minimize or reduce variations in a reflective surface of the device. For example, in one embodiment, a reflective element of micro-mirror device 10 is formed with a substantially planar surface over an entirety thereof. As such, reflectivity of micro-mirror device 10 may be enhanced and/or light interference from micro-mirror device 10 may be reduced. Thus, a contrast ratio of micro-mirror device 10 may be improved.
In one embodiment, as illustrated in
In one embodiment, actuating element 40 is actuated so as to move between a first position 47 and a second position 48 relative to substrate 20 and plate 30. Preferably, actuating element 40 moves or tilts at an angle about an axis of rotation. As such, first position 47 of actuating element 40 is illustrated as being substantially horizontal and substantially parallel to substrate 20 and second position 48 of actuating element 40 is illustrated as being oriented at an angle to first position 47. Movement or actuation of actuating element 40 relative to substrate 20 and plate 30 is described in detail below.
Preferably, plate 30 is a transparent plate 32 and actuating element 40 is a reflective element 42. In one embodiment, transparent plate 32 is a glass plate. Other suitable planar translucent or transparent materials, however, may be used. Examples of such a material include quartz and plastic.
Reflective element 42 includes a reflective surface 44. In one embodiment, reflective element 42 is formed of a uniform material having a suitable reflectivity to form reflective surface 44. Examples of such a material include polysilicon or a metal such as aluminum. In another embodiment, reflective element 42 is formed of a base material such as polysilicon with a reflective material such as aluminum or silver disposed on one or more sides of the base material. In addition, reflective element 42 may be formed of a non-conductive material or may be formed of or include a conductive material.
As illustrated in the embodiment of
The direction of output light 14 is determined or controlled by the position of reflective element 42. For example, with reflective element 42 in first position 47, output light 14 is directed in a first direction 14a. However, with reflective element 42 in second position 48, output light 14 is directed in a second direction 14b. Thus, micro-mirror device 10 modulates or varies the direction of output light 14 generated by input light 12. As such, reflective element 42 can be used to steer light into, and/or away from, an optical imaging system.
In one embodiment, first position 47 is a neutral position of reflective element 42 and represents an “ON” state of micro-mirror device 10 in that light is reflected, for example, to a viewer or onto a display screen, as described below. Thus, second position 48 is an actuated position of reflective element 42 and represents an “OFF” state of micro-mirror device 10 in that light is not reflected, for example, to a viewer or onto a display screen.
In one embodiment, reflective element 42 is moved between first position 47 and second position 48 by applying an electrical signal to an electrode 60 formed on substrate 20. In one embodiment, electrode 60 is formed on surface 22 of substrate 20 adjacent an end or edge of reflective element 42. Application of an electrical signal to electrode 60 generates an electric field between electrode 60 and reflective element 42 which causes movement of reflective element 42 between first position 47 and second position 48. Preferably, when the electrical signal is removed from electrode 60, reflective element 42 persists or holds second position 48 for some length of time. Thereafter, restoring forces of reflective element 42 pull or return reflective element 42 to first position 47.
In one embodiment, a conductive via 26 is formed in and extends through post 24. Conductive via 26 is electrically coupled to reflective element 42 and, more specifically, conductive material of reflective element 42. As such, reflective element 42 is moved between first position 47 and second position 48 by applying an electrical signal to electrode 60 and reflective element 42. More specifically, electrode 60 is energized to one polarity and the conductive material of reflective element 42 is energized to an opposite polarity. Thus, application of an electrical signal of one polarity to electrode 60 and an electrical signal of an opposite polarity to reflective element 42 generates an electric field between electrode 60 and reflective element 42 which causes movement of reflective element 42 between first position 47 and second position 48.
In another embodiment, reflective element 42 is moved between first position 47 and second position 48 by applying an electrical signal to reflective element 42. More specifically, the electrical signal is applied to conductive material of reflective element 42 by way of conductive via 26 through post 24. As such, application of an electrical signal to reflective element 42 generates an electric field which causes movement of reflective element 42 between first position 47 and second position 48.
Additional embodiments of actuation of micro-mirror device 10 are described, for example, in U.S. patent application Ser. No. 10/136,719, filed on Apr. 30, 2002, entitled “Micro-Mirror Device”, assigned to the assignee of the present invention and incorporated herein by reference.
In one embodiment, a pair of hinges 86 extend between inner portion 84 and outer portion 80. Hinges 86 extend from opposite sides or edges of inner portion 84 to adjacent opposite sides or edges of outer portion 80. Preferably, outer portion 80 is supported by hinges 86 along an axis of symmetry. More specifically, outer portion 80 is supported about an axis that extends through the middle of opposed edges thereof. As such, hinges 86 facilitate, movement of reflective element 42 between first position 47 and second position 48, as described above (
In one embodiment, hinges 86 include torsional members 88 having longitudinal axes 89 oriented substantially parallel to reflective surface 44. Longitudinal axes 89 are collinear and coincide with an axis of symmetry of reflective element 42. As such, torsional members 88 twist or turn about longitudinal axes 89 to accommodate movement of outer portion 80 between first position 47 and second position 48 relative to inner portion 84.
In one embodiment, reflective element 42 is supported relative to substrate 20 by support or post 24 extending from surface 22 of substrate 20. More specifically, post 24 supports inner portion 84 of reflective element 42, and outer portion 80 of reflective element 42 is supported by hinges 86 extending from inner portion 84. In one embodiment, post 24 is formed by conductive via 26 extending through inner portion 84 to a conductive layer of substrate 20.
As illustrated in the embodiments of
In one embodiment, reflective element 142 extends over and is supported from hinge element 141 by a support 124 and hinge element 141 extends over and is supported from substrate 20 by a support 125. In one embodiment, supports 124 and 125 constitute conductive vias extended between reflective element 142 and hinge element 141, and hinge element 141 and substrate 20, respectively.
In one embodiment, as illustrated in
Actuation of micro-mirror device 100 is similar to that of micro-mirror device 10, as described above, with the exception that both hinge element 141 and reflective element 142 of actuating element 140 are actuated. As such, hinge element 141 and reflective element 142 are both moved between a first position 147 and a second position 148 by applying an electrical signal to electrode 60 formed on substrate 20. Application of an electrical signal to electrode 60 generates an electric field between electrode 60 and hinge element 141 and/or reflective element 142 which causes movement of hinge element 141 and reflective element 142 between first position 147 and second position 148.
In one embodiment, as illustrated in
In one embodiment, substructure 200 includes a dielectric layer 214 formed on first side 212 of base material 210. As such, conductive layer 220 of substructure 200 is formed over dielectric layer 214. Dielectric layer 214 includes, for example, a silicon oxide such as tetraethylorthosilicate (TEOS). In one embodiment, deposited layers of substructure 200 including, for example, dielectric layer 214 are planarized during formation of substructure 200 to create a substantially planar substrate for micro-mirror device 10.
In one embodiment, conductive material of conductive layer 220 forms an electrical contact area 202 of substructure 200 and an actuating area 204 of substructure 200. Electrical contact area 202 defines an area where electrical connection to micro-mirror device 100 is to be made, and actuating area 204 defines an area where actuating element 140 of micro-mirror device 100 is to be formed, as described below. As such, conductive layer 220 of substructure 200 constitutes an interconnect level of the CMOS circuit.
As illustrated in the embodiment of
After dielectric layer 222 is formed over conductive layer 220, a conductive material 224 is deposited and patterned on dielectric layer 222. In one embodiment, conductive material 224 is deposited and patterned by photolithography and etching within actuating area 204 of substructure 200. As such, conductive material 224 defines electrodes 225 on dielectric layer 222. In one embodiment, conductive material 224 includes aluminum or an aluminum alloy such as an aluminum silicon alloy.
In one embodiment, conductive material 224 communicates with conductive layer 220 of substructure 200 by a conductive via 226 formed through dielectric layer 222. It is understood that
In one embodiment, as illustrated in
As illustrated in the embodiment of
After the material of sacrificial layer 230 is deposited over conductive material 224 and dielectric layer 222, the material is planarized to create a substantially planar surface 232 of sacrificial layer 230. In one embodiment, the material of sacrificial layer 230 is planarized by a chemical mechanical polishing (CMP) process.
Next, as illustrated in the embodiment of
In one embodiment, openings 234 through sacrificial layer 230 are formed by chemical etching. Thus, mask layer 240 is formed of a material which is resistant to the etchant used for etching openings 234. Examples of a material suitable for mask layer 240 include a hard mask material such as silicon dioxide or silicon nitride, or a photoimageable material such as photoresist. After openings 234 are formed, mask layer 240 is stripped or removed.
As illustrated in the embodiments of
As illustrated in the embodiment of
In one embodiment, conductive vias 251 form posts 125 (
In one embodiment, as illustrated in
Next, as illustrated in the embodiment of
In one embodiment, as illustrated in
As illustrated in the embodiment of
Next, as illustrated in the embodiment of
After the material of sacrificial layer 270 is deposited over hinge element 141, the material is planarized to create a substantially planar surface 272 of sacrificial layer 270. In one embodiment, the material of sacrificial layer 270 is planarized by a CMP process.
Next, as illustrated in the embodiment of
In one embodiment, opening 274 through sacrificial layer 270 is formed by chemical etching. Thus, mask layer 280 is formed of a material which is resistant to the etchant used for etching opening 274. Examples of a material suitable for mask layer 280 include a hard mask material such as silicon dioxide or silicon nitride, or a photoimageable material such as photoresist. After opening 274 is formed, mask layer 280 is stripped or removed.
As illustrated in the embodiments of
In one embodiment, as illustrated in
As illustrated in the embodiment of
In one embodiment, plug material 294 includes, for example, silicon, an oxide, such as TEOS, a metal, such as aluminum, copper, titanium, or tungsten, or photoresist. In one exemplary embodiment, when sacrificial layers 230 and 270 are formed of silicon, a suitable material for plug material 294 includes silicon, an oxide, a metal, or photoresist. In another exemplary embodiment, when sacrificial layers 230 and 270 are formed of photoresist, a suitable material for plug material 294 includes photoresist.
Next, as illustrated in the embodiment of
As illustrated in the embodiments of
In one embodiment, as illustrated in
In one embodiment, material 300 constitutes reflective material of reflective element 142 and forms reflective surface 144 of reflective element 142. Thus, material 300 includes a reflective material. In one embodiment, for example, material 300 includes aluminum.
As illustrated in the embodiment of
In one embodiment, as illustrated in
As illustrated in the embodiment of
Next, as illustrated in the embodiment of
In one embodiment, sacrificial layers 230 and 270 are removed by a chemical etch process. As such, conductive layer 220, dielectric layer 222, conductive material 224, and the materials of actuating element 140 are selected so as to be resistant to the particular etchant used for removing sacrificial layers 230 and 270. In one embodiment, the etch process for removing sacrificial layers 230 and 270 is a dry etch, such as a plasma-based fluorinated etch using, for example, SF6, CF4, C2F6, or a combination of gases.
While the above description refers to the formation of a micro-mirror device, it is understand that the above processes are also applicable to the formation of other MEMS devices, including multi-layer MEMS devices. In addition, it is understood that
In one embodiment, as illustrated in
In one embodiment, light processor 514 receives image data 518 representing an image to be displayed. As such, light processor 514 controls the actuation of micro-mirror devices 10 and the modulation of light received from light source 510 based on image data 518. The modulated light is then projected to a viewer or onto a display screen 520.
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
This application is a divisional of Ser. No. 10/677,539, filed Oct. 2, 2003, now U.S. Pat. No. 6,861,277, which is hereby incorporated by reference.
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| Number | Date | Country | |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 10677539 | Oct 2003 | US |
| Child | 11019780 | US |
