WO2008013368A1

WO2008013368A1 - Mems-based light projection engine and associated method of manufacture

Info

Publication number: WO2008013368A1
Application number: PCT/KR2007/003334
Authority: WO
Inventors: Sung Hoon Kwon
Original assignee: Sung Hoon Kwon
Priority date: 2006-07-28
Filing date: 2007-07-10
Publication date: 2008-01-31
Also published as: WO2008013368A9; KR100815440B1; KR20080010752A

Abstract

Provided are a MicroElectroMechanical Systems (MEMS)-based light projection engine and a method of manufacturing the same. The light projection engine includes: a light source; a first optical scanner for scanning at least one light beam emitted from the light source in a first direction and including a waveguide capable of moving in the first direction; and a second optical scanner for scanning the at least one light beam transmitted from the f irst optical scanner in a second direction not parallel to the first direction.

Description

[DESCRIPTION]

[Invention Title]

MEMS-BASED LIGHT PROJECTION ENGINE AND ASSOCIATED METHOD OF MANUFACTURE [Technical Field]

The present invention relates to a light projection system, and more particularly, to a MicroElectroMechanical Systems (MEMS)-based light projection engine and a method of manufacturing the same. [Background Art]

Current projection display technology is roughly classified into 2 categories of Digital Micromirror Devices (DMDs) and Liquid Crystal Displays (LCDs). Both technologies use a light projection engine including separate devices for a number of respective image pixels. The light projection engine is generally illuminated by a high-power white-light lamp, e.g., a mercury lamp. A control unit modulates the respective image pixels to obtain a desired image' s brightness, contrast ratio and color. A projector may integrate color filter wheels to selectively project red, green and blue (three primary colors) images, or may use three separate light projection engines to project the three primary colors, respectively.

DMD- or LCD-based projectors have some drawbacks. First, when respective image pixels are displayed by separate pixel devices, a light projection engine must be large and complex, and thus requires high production costs. An extended Graphics Array (XGA) Digital Light Processing (DLP) device corresponds to, for example, 0.7 inches. Since the number of devices that can be produced per wafer is small, and the yield of perfectly operating devices is low, the unit price of the devices steeply increases together with the number of pixels. Second, a DMD- or LCD-based projector is optimized for only one image format, i.e., the number of horizontal and vertical pixels. Other image formats can be supported but require comprehensive image processing, e.g., interpolation, and also numerous image artifacts will be seen, e.g., aliasing. Third, since respective image pixels are projected from separate pixel devices, it can be seen that the image pixels are divided by dark lines when an image is observed in close proximity. Fourth, a DMD- or LCD-based projector requires numerous optical devices to uniformly illuminate them and thus is fundamentally large and complex. Fifth, in a DMD- or LCD-based projector, a light source must be constantly and perfectly turned on. A contrast ratio is generated by modulating separate pixel devices to discard a part of light. Efficiency obtained by discarding light determines an achievable contrast ratio. In particular, an LCD-based projector has poor efficiency and thus its contrast ratio is generally limited to about 500:1. [Disclosure]

[Technical Problem]

The present invention is directed to a light projection engine that can be manufactured at low cost and a method of manufacturing the same.

The present invention is also directed to a light projection engine that can support various image formats and a method of manufacturing the same. The present invention is also directed to a light projection engine that projects an image in which pixels are not separated by dark lines even when the image is observed in close proximity, and a method of manufacturing the light projection engine.

The present invention is also directed to a small and simple light projection engine and a method of manufacturing the same.

The present invention is also directed to a light projection engine having a high contrast ratio and a method of manufacturing the same.

[Technical Solution] One aspect of the present invention provides a MicroElectroMechanical Systems (MEMS)-based light projection engine. The example light projection engine may be configured to support requirements of various resolutions, colors, frame rates, contrast ratios and brightness values. The light projection engine comprises a light source and two optical scanners, and a first one of the two optical scanners includes at least one steerable waveguide scanning at least one light beam in a first direction. The first optical scanner may include a plurality of waveguides, which may be spatially connected with each other (directly or indirectly by, for example, position feedback and a means for dynamic control) to provide synchronized movement of a plurality of scan beams. The second optical scanner may include a moving mirror, a lens or another appropriate scanner to scan in a second direction. The first and second directions may be not parallel but, for example, perpendicular to each other. The two scanners may be monolithical Iy manufactured on a single semiconductor wafer die, and may be electrostatically driven through comb-tooth structures. The two scanners may scan light beams in perpendicular directions corresponding to the horizontal and vertical directions of a desired image.

The second optical scanner may include a scanning mirror monolithical Iy integrated and/or consisting of mirror galvanometers. In addition, the second optical scanner may include a scanning lens. The scanning lens may include glass, polysilicon, a polymer or another appropriate material. The first and/or second optical scanner may be driven in resonant or non-resonant motion and may move magnetically, electrostatically, thermally and/or piezoelectrically. Optical devices, such as a lens, a prism, a mirror, a polarizer, a filter, a diffraction grating, etc., are well-known in this field and may be additionally included in a part of the engine.

The light source may include at least one monochromatic Light Emitting

Diode (LED), Laser Diode (LD), or another appropriate light source. The LED and/or LD may be monolithical Iy integrated in the light projection engine, or may be separately implemented and connected to one of the optical scanners through, for example, an optical fiber and/or a waveguide. Additionally, a light combiner may be included to align light beams of a plurality of colors, e.g., red, green and blue, in the first optical scanner, or to increase the total intensity of light. The light combiner may be monol ithical Iy integrated in the first optical scanner.

A controller may be further included to control an operation, e.g., an operation of the first and second optical scanners and light emission of the optical source for performing a well-known raster scanning method, of the light projection engine. In addition, the controller may use a technique such as sinusoidal scan compensation, (capacitive) scan position feedback, stitching alignment feedback, and light source emission intensity feedback.

Another aspect of the present invention provides a method of manufacturing a light projection engine. The method comprises the step of monolithically forming two optical scanners on a single semiconductor wafer die. In particular, conventional Silicon-On-Insulator (SOI) MEMS technology and flip-chip bonding may be used to form the two perpendicular optical scanners on a single chip. In addition to the two optical scanners, an optical source and/or an optical device may be additionally integrated in the single chip.

Still another aspect of the present invention provides a method of operating a light projection engine having a first optical scanner for scanning in a first direction and a second optical scanner for scanning in a second direction. The method comprises the step of controlling a scanner to generate a desired image. The first optical scanner may operate to project separate lines of the image, and the second optical scanner may stagger the separate lines in separate frames of the image. A scan rate may be, for example, about 30 kHz for the first optical scanner (horizontal scanner) and 30 Hz for the second optical scanner (vertical scanner). Additionally, various techniques such as sinusoidal scan compensation, (capacitive) scan position feedback, stitching alignment feedback, and light-source emission intensity feedback may be used for controlling the two optical scanners to generate the desired image.

The example devices described here can be advantageously manufactured at low price with low complexity to produce a small-sized high-resolution display. For example, an example light projection engine can be used in various projection systems, such as a portable projector, a small projector, e.g., a computer-mouse size, a front/rear projection television, and a heads-up display. The example light projection engine can be integrated in a small projector, can wirelessly communicate with a laptop computer, a Personal Digital Assistant (PDA), etc., and can project an image having a diagonal length up to, for example, 4 feet at an Ultra extended Graphics Array (UXGA) resolution. As a new application, the example light projection engine may be integrated to be used in a cellular phone, a digital camera, a PDA, a laptop computer, a Moving Picture Experts Group (MPEG) layer 3 (MP3) player, etc. [Advantageous Effects]

According to a light projection engine of the present invention and a method of manufacturing the same, the light projection engine can be manufactured at low cost.

Also, various image formats can be simply supported. In addition, pixels are not divided by dark lines even when an image is observed in close proximity.

Moreover, it is possible to provide a small and simple light projection engine. Furthermore, it is possible to provide a light projection engine having a high contrast ratio. [Description of Drawings]

FIG. 1 is a plan view (a) and a side view (b) of a light projection engine according to a first exemplary embodiment of the present invention;

FIG. 2 shows a light combiner that can be employed in the light projection engine of FIG. 1, and can combine first and second input light beams to output the combined light beam;

FIG. 3 is a perspective view (a) and a plan view (b) of an actually manufactured first optical scanner that can be employed in the light projection engine of FIG. 1;

FIG. 4 shows a conventional pixel-based display (a) in which a resolution is limited by a pixel size, and analog optical scanning (b) and (c) using the light projection engine shown in FIG. 1; FIG. 5 is a plan view (a) and a cross-sectional view (b) of a light projection engine according to a second exemplary embodiment of the present invention;

FIG. 6 shows in detail a microlens that can be employed in the light projection engine of FIG. 5; FIGS. 7 to 20 show a method of manufacturing first and second scanners for a light projection engine according to an exemplary embodiment of the present invention;

FIG. 21 shows a structure of a light projection engine manufactured by the method according to an exemplary embodiment of the present invention; and FIG. 22 shows a method of pre-tilting a vertical scan mirror using a push-down pin wafer and plastic deformation of silicon according to an exemplary embodiment of the present invention.

* Description of Major Symbols in the above Figures 10, 10' : Light source 11: Solid-state light source

20, 20' : Light combiner 21: Color-light combiner

30, 30' : First optical scanner 31, 31' : waveguide 32, 32' , 42, 49, 81: Comb-tooth structure 33: Spring structure 34: Anchor

40, 40' : Second optical scanner 41: Mirror

46: Microlens 47: Static etched mirror

48: Silicon ring 50: Transparent packaging cover

51: Projection lens 60: Controller 71: SOI substrate 71A: Lower silicon layer

71B: Buried oxide layer 71C: Upper silicon layer

72: Trench 73, 75: Si licon nitride layer

74, 77: Silicon oxide layer 76: Electrical contact location

78: Open region 79: Interconnection 80: Fiber

82: Moving comb-tooth device of a mirror

83: Inner mirror 84: Fixed comb-tooth device

85: External frame 90: Push-down pin wafer

91: Fork 92, 93: Push-down pin [Modes for Invention]

Hereinafter, exemplary embodiments of the present invention will be described in detail. However, the present invention is not limited to the exemplary embodiments disclosed below, but can be implemented in various types. Therefore, the present exemplary embodiments are provided for complete disclosure of the present invention and to fully inform the scope of the present invention to those ordinarily skilled in the art.

According to an exemplary embodiment of the present invention described here, a steerable waveguide is used to project a light beam to a surface, e.g., a screen or another appropriate surface, thereby performing high-speed high-resolution line scanning onto at least 2000 dividable spots without digitizing an image, using a mirror or an electronic device, e.g., a Digital Light Processing (DLP) device and a Liquid Crystal Display (LCD). The resolution of a light projection engine according to an exemplary embodiment of the present invention will increase in comparison with a conventional system, e.g., DLP technology of a 10 μm-mirror compared with a 1 μm-waveguide aperture of the exemplary embodiment. An on-chip MicroElectroMechanical Systems (MEMS) micro-optics, e.g., a scan mirror or a microlens, is used to stably refresh a frame. An original image is coded by direct modulation of a light source. An appropriate light source includes a Light-Emitting Diode (LED), a Laser Diode (LD) or other solid-state light sources, e.g., a 100W- white light lamp compared with a lW-sol id-state light source, enabling reduced power consumption. In this specification, the terminologies "horizontal" and

"vertical" are used as examples for indicating a first scan direction and a second scan direction. Those skilled in the art may find another configuration of first and second scanners for scanning in the first and second directions, which may be non-parallel with each other. FIG. 1 is a plan view (a) and a side view (b) of a light projection engine according to a first exemplary embodiment of the present invention. Referring to FIG. 1, the light projection engine comprises a first optical scanner 30 and a second optical scanner 40 integrated in a single chip.

The first optical scanner 30 includes at least one waveguide 31 scanning along a single plane parallel to a substrate (in a horizontal direction). The plurality of waveguides 31 may be spatially fixed to each other. For example, the waveguides 31 may be stacked or electrically synchronized. The first optical scanner 30 shown here includes two waveguides 31 that are spatially fixed to each other for synchronized motion. The waveguides 31 of the first optical scanner 30 may be driven in resonant or non-resonant motion and may move magnetically, electrostatically, thermally and/or piezoelectrical Iy. The waveguides 31 of the first optical scanner 30 shown here are moved electrostatically. To this end, the first optical scanner 30 includes a comb-tooth structure 32 horizontally moving the waveguides 31. The first optical scanner 30 transmits at least one light beam to the second optical scanner 40.

The second optical scanner 40 includes a pre-tilted moving scan mirror 41. To receive the light beam from the first optical scanner 30, an angle between the radiated light beam and the plane of the mirror 41 must be larger than the maximum rotation angle. However, after an initial process, the plane of the mirror 41 and the horizontal beam become parallel to the substrate. Pre-ti Iting of the scan mirror 41 makes an initial angle between the horizontal scanning beam and the mirror 41 larger than a rotation angle of the mirror 41, thereby allowing the first and second optical scanners 30 and 40 to be monolithically integrated in the single chip. In addition, pre- tilting of the scan mirror 41 redirects a light beam toward an external projection lens 51 disposed above the mirror 41. The external projection lens 51 can be readily implemented on a transparent packaging cover 50. The scan mirror 41 rotates to perpendicularly scan the at least one light beam transmitted from the first optical scanner 30. Thus, the first optical scanner 30 rapidly generates horizontal lines of an image, and the second optical scanner 40 rapidly staggers the lines to project the desired image. In one example, the light projection engine including the two waveguides 31 is integrated in the single chip, and the transparent packaging cover 50 includes the projection lens 51 or another optical device, thereby setting a direction of a generated light beam and/or a condition. In the second optical scanner 40, the mirror 41 is rotated by a comb-tooth structure 42 that is connected to the mirror 41 and electrostatically moved. Instead of the mirror 41, a moving lens or prism may be used in the second optical scanner 40.

Lastly, scanned light travels toward the projection lens 51 to be projected onto a screen. The projection lens 51 may perform an autofocus operation.

The light projection engine may additionally include a light source 10 including at least one solid-state light source 11, e.g., an LED or an LD. The light source 10 may include at least one set of, for example, three primary colors, and will be used to generate a complete color image, e.g., Red, Green and Blue (RGB), Cyan, Yellow and Magenta (CYM), etc. An LED and/or an LD may be monolithically integrated in the light projection engine, or separately implemented and connected to the first optical scanner 30 through an optical fiber and/or a waveguide.

To align a plurality of color light sources, the light projection engine may include a light combiner (a light wave combiner) 20. A micromachined color-light combiner 21 combines light beams from respective sets of the light sources 11 to generate a perfect color image. The light combiner 20 guides the combined light to the first optical scanner 30. As shown in FIG. 1, the light combiner 20 may be monolithically integrated in the first optical scanner 30.

The light projection engine may include a controller 60. The controller 60 controls modulation of the light source 10 for image encoding, horizontal scanning of the first optical scanner 30, and vertical scanning of the second optical scanner 40. The light source 10, the light combiner 20 and the first optical scanner 30 may be integrated on a single chip, or may be separate devices connected with, for example, an optical fiber, an optical waveguide, etc.

FIG. 2 shows a light combiner that can be employed in the light projection engine of FIG. 1, and can combine first and second input light beams to output the combined light beam. For example, a passive waveguide light combiner combines light beams from a plurality of LEDs or LDs. In the field of optical communication, light combiners are well known as devices increasing electrical power for laser pumping. A waveguide light combiner may be formed of plastic, silica, silicon and/or another appropriate material confining and transmitting light of a desired wavelength. The light combiner may be formed using well-known MEMS technology, or by printing or stamping a polymer on a substrate to form, for example, a waveguide. Due to the coherent property of laser light, a laser waveguide is cautiously designed to avoid interference between laser beams using a well-known principle and algorithm. However, in an example including an incoherent LED as a light source, a waveguide design is relatively simple. In addition, use of the MEMS process technology allows a light combiner and an optical scanner to be monolithically integrated in a single chip, thereby reducing optical loss and packaging cost .

FIG. 3 is a perspective view (a) and a plan view (b) of an actually manufactured first optical scanner that can be employed in the light projection engine of FIG. 1. In FIG. 3, an electrostatically driven comb- tooth structure 32' provides power to move a waveguide 31' along a plane. A spring structure 33 is included to support the waveguide 31' and stabilize horizontal movement of the waveguide 31' . In addition, a reference numeral 34 functions as an anchor for the moving structure.

The light projection engine described with reference to FIG. 1 advantageously scans using an analog method and is not limited by a pixel size and position. FIG. 4 shows a conventional pixel-based display (a) in which a resolution is limited by a pixel size, and analog optical scanning (b) and (c) using the light projection engine shown in FIG. 1. As shown in FIG. 4, when a scanning frequency increases, the resolution of the light projection engine of FIG. 1 generally increases in comparison with the conventional digital pixel-based display. The light projection engine of FIG. 1 rapidly scans at least one light beam onto a screen, thereby projecting pixels not in parallel but in series. The operation is similar to a method of a Cathode Ray Tube (CRT) scanning an electron beam onto a fluorescent screen. In addition, while a DLP device and an LCD use separate pixel devices for respective several thousands to several millions of pixels projected in parallel, the light projection engine of FIG. 1 uses only 2 moving devices, i.e., the first and second optical scanners.

In the first exemplary embodiment, the first optical scanner includes a plurality of waveguides to form a plurality of horizontal scanning beams. The light projection engine is controlled to vertically scan the horizontal scanning beams onto a plurality of tiles, i.e., complete image sections. For example, two waveguides form 2 sets of parallel beams scanned by a mirror to form 2 tiles of the final rectangular image. In this method, an image can be refreshed at high speed with less motion. In one example, a micromachined light projection engine, including a Steerable Waveguide Array Transmitter (SWAT) and a plurality of fixed waveguides, is integrated with a polymer lens/mirror scanner capable of performing 30 Hz vertical scanning and thereby can perform 36 kHz horizontal scanning. In another example, a light projection engine may perform 15 to 120 kHz scanning in a first direction and 15 to 120 Hz scanning in a second direction. Needless to say, other scanning rates may be used.

FIG. 5 is a plan view (a) and a cross-sectional view (b) of a light projection engine according to a second exemplary embodiment of the present invention. The light projection engine of FIG. 5 is similar to that of FIG. 1 except that a microlens 46 is used instead of the moving micromirror 41. In FIG. 5, a static etched mirror 47 deflects a light beam from a waveguide to the microlens 46. The microlens 46 is controlled to operate in the plane of a first optical scanner and vertically scans a light beam according to what a user wants.

In addition, the light projection engine of FIG. 5 is similar to that of FIG. 1 but also includes a SWAT 30' , which is a kind of a first optical scanner. The SWAT 30' controls 8 horizontal beams directed toward the etched mirror 47. 8 waveguides included in the SWAT 30' are fixed to each other during movement so that beam steering is synchronized. Image encoding may be performed by the SWAT 30' . In addition, the SWAT 30' is combined with a light source 10' and a light combiner 20' . FIG. 6 shows in detail a microlens that can be employed in the light projection engine of FIG. 5. The microlens may include a support and a lens 46 formed of an ultraviolet (UV) cured polymer. The microlens support may be manufactured using well-known Si Iicon-On-Insulator (SOI) MEMS technology. In particular, a released silicon ring 48 is manufactured, and then the UV cured polymer is inserted into the ring 48. The liquid UV cured polymer may essentially be formed into a sphere lens shape due to surface tension at the edge of the ring 48. Translation of the microlens may be made by an electrostatic comb-tooth structure 49 shown herein, or another well-known MEMS device. Various aspects and characteristics of a light projection engine according to an exemplary embodiment of the present invention that can be used separately or in association with others will be summarized below. However, the summary does not limit the present invention, and those skilled in the art will understand that various modifications and additions can be made.

1. Light beam:

- The light projection engine may use one or more light beams.

- A light beam may be monochromatic or polychromatic. - An arbitrary number of light beams may be turned on simultaneously or sequentially.

- While scanning from left to right, from right to left, from up to down, or from down to up, an arbitrary number of light beams or all light beams may be turned on.

- An arbitrary number of light beams may scan in parallel, converge or diverge.

2. Light combiner:

- A light combiner may be formed of a polymer or a standard material for semiconductor manufacturing.

- A plurality of color-light combiners may be monolithically integrated in a first optical scanner.

- A plurality of color-light combiners may be connected with a plurality of waveguides of a first optical scanner. - A light combiner may combine an arbitrary number of colors.

- A light combiner combines an arbitrary number of similar or the same colors, thereby increasing the intensity of an output beam.

3. Horizontal and vertical scanning:

- As a first optical scanner, a waveguide scanner may be used. - When there are a plurality of waveguides, they are strongly combined with each other, thereby enabling synchronized movement.

- When there are a plurality of waveguides, they can separately move, but their movements are synchronized by a sensing means, e.g., a capacitive sensing means, and a control mechanism. - As a second optical scanner, a mirror and/or a lens scanner may be used.

- A vertical scanning mirror may be monolithically integrated and/or may consist of mirror galvanometers. - A vertical scanning lens may be formed of glass, polysilicon, a polymer or another appropriate material.

- First and second optical scanners may be driven in resonant or non- resonant motion. - An optical scanner may move magnetically, electrostatically, thermally and/or piezoelectrical Iy.

- A vertical scanning mirror and/or a microlens may have an initial offset at a scan angle to direct a light beam toward a projection lens disposed above an optical scanner. - At least one static mirror or other optical devices may be used to increase a scan range.

- Static mirrors may be separately and/or monolithically integrated.

- A projection lens may be separately and/or monolithically integrated.

- A projection lens may be included in a transparent packaging cover. - A projection lens may be included in a transparent packaging cover.

- A projection lens may perform an autofocus operation.

- Light projection may be performed by a combination of scanning from left to right, from up to down, from right to left, or from down to up.

- To turn off a light source for safety when scanning fails, scanning may be monitored at the edge of a scan range, for example, using a photodiode.

4. Light source^

- A light source may be a combination of red, green and blue LDs, LEDs and/or other light sources such as a laser.

- To obtain a desired total optical power, a plurality of light sources may be used for a color.

- A desired output wavelength may be obtained using a crystal, etc., or by an LD operating at its unique frequency, e.g., 532 nm-green light may be obtained by doubling the wavelength of 1064 ran infrared light.

Claims

- The power of a light source may be monitored, for example, using a photodiode, and may be adjusted on the basis of a factor such as an image color, image brightness, and ambient lighting to provide a desired image intensity and fidelity to an original image. - The intensity of a light source may be modulated pixel by pixel to obtain a desired image contrast ratio, brightness and color.

- A light source may be separated from the light projection engine or monolithically integrated in the same.

- A light source may be connected with a horizontal scanner through an optical fiber and/or a waveguide.

- Optical fibers and/or waveguides may be separated or monolithically integrated.

As a preferred combination, a light projection engine includes a first optical scanner and a second optical scanner, e.g., monolithically, integrated on the first optical scanner. The first and second optical scanners may be connected with at least one optical source. The second optical scanner may include a moving mirror. To connect the light source with the optical scanners, the light projection engine may additionally include a separate or integrated waveguide light combiner and/or waveguide. This example can reduce packaging complexity by monolithic integration and optical alignment complexity by self-alignment of the waveguide of the first optical scanner and the mirror of the second optical scanner in a lithographic step.

As another preferred combination, a light projection engine includes a light source and two optical scanners integrated on a single chip, and a first one of the two optical scanners includes at least one waveguide. The light source includes a plurality of integrated LDs formed together with the chip. The scanners include a plurality of waveguides for scanning in a first direction and a moving mirror for scanning in a second direction. Here, the second direction is different from the first direction, e.g., perpendicular to the first direction.

As yet another preferred combination, a light projection engine includes two optical scanners, and a first one of the two optical scanners is a plurality of SOI waveguide scanners that scan a plurality of beams in a first direction using a synchronization method. A plurality of SOI waveguide scanners may be used in, for example, the above-described various projection engines.

Various methods of manufacturing an MEMS-based light projection engine according to an exemplary embodiment of the present invention will be described below. In one example, conventional SOI MEMS technology and flip- chip bonding will be used to manufacture an optical instrument, first and second optical scanners, and a light source integrated on a single chip, thereby producing a small price-efficient MEMS 2-axis optical scanner. In another example, a light projection engine may be included in a volume of less than 5 mm x 2.5 mm x 2 mm. Thus, an example micromachined waveguide and microlens/microscanner allows miniaturization, mass production and price reduction. In yet another example, more or less components may be integrated in a single chip. For example, first and second scanners may be combined in the single chip and connected with a light source and/or a light combiner.

FIGS. 7 to 20 show a method of manufacturing first and second scanners for a light projection engine according to an exemplary embodiment of the present invention. FIG. 21 shows a structure of a light projection engine manufactured by the method according to an exemplary embodiment of the present invention, and will be referenced together with FIGS. 7 to 20. Here, the terminology "pattern" generally indicates a pattern formed by etching followed by photolithography to form an etch mask. Those skilled in the art will know that a sequence in which, for example, processes of etching, masking, deposition, etc., are described, as well as various materials and the described processes are merely examples. A variety of other processes and sequences in which the processes are performed may be used to obtain a simi lar result .

FIG. T- An example process is performed using an SOI substrate 71 having a diameter of 4" to 8" , including a lower silicon layer 71A, an upper silicon layer 71C, and a buried oxide layer 71B interposed between the upper and lower silicon layers 71C and 71 A. The upper SOI silicon layer 71C is a device layer, and the relatively thick lower silicon layer 71A is a handle wafer. The buried oxide layer 71B functions as an etch-stop layer and prevents electrical leakage through the handle wafer 71A.

FIG. 8: Trench etching, e.g., Deep Reactive-Ion Etching (DRIE) that exposes the oxide layer 71B is performed to insulate an electrical connection between a moving part and a non-moving part of a comb-tooth structure of the next step. In the next step, trenches 72 are backfilled with a dielectric material, such as silicon nitride, etc. The backfill material electrically insulates 2 structures in the upper silicon layer 71C from each other, and also allows the 2 structures to be mechanically connected. In this example, the 2 structures are moving protrusions and fixed protrusions in the comb- tooth structure of a mirror. FIG. 9: A low stress silicon nitride layer 73 is formed by Low Pressure Chemical Vapor Deposition (LPCVD) to backfill the previously formed trenches 72. The low stress silicon nitride layer 73 may also function as a lower cladding layer of a horizontally moving waveguide of the first optical scanner . FIGS. 10 and 11: Silicon dioxide is deposited by LPCVD, and the pattern of a waveguide core 74 is formed using, for example, reactive ion etching (RIE). The refractive index of silicon dioxide is smaller than that of silicon nitride, which satisfies requirements of the waveguide core 74 and the cladding layer 73.