Abstract:
The invention is directed to the provision of an optical integrated device wherein provisions are made to be able to mount components on a substrate with high accuracy and high packing density without having to heat the components. The optical integrated device includes a substrate, an optical device optically coupled to a first device, and an electrical device mounted on top of the optical device or on top of a second device, wherein the optical device is bonded to the substrate by surface activated bonding via a first bonding portion formed from a metallic material on the substrate, and the electrical device is bonded to the optical device or the second device by surface activated bonding via a second bonding portion formed from a metallic material on the optical device or the second device.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an optical integrated device to be used as a laser light source in various kinds of apparatus such as an optical communication or compact projector apparatus, and more particularly to an optical integrated device constructed by integrating an optical device and an electrical device on the same substrate. 
       BACKGROUND 
       [0002]    It is known in the art to provide a module in which an optical device such as a laser device and an electrical device such as an IC are integrated together on the same substrate (for example, refer to patent document 1 in the list shown below). In the module disclosed in patent document 1, an optical device and an electrical device for controlling the optical device are mounted on a silicon or like substrate. Further, an optical waveguide which is optically coupled to the optical device, and which directs light to the outside, is formed on the same substrate. 
         [0003]    In the module disclosed in patent document 1, the optical device and the electrical device are both flip-chip mounted on the substrate. That is, the optical device and the electrical device, with bumps formed on their bottom faces, are placed on the substrate with the bumps contacting with electrodes, etc. formed on the substrate, and are pressed together under heat to accomplish metal bonding. 
         [0004]    There is also known a technique for bonding an optical device such as a laser device to a substrate by surface activated bonding (for example, refer to patent document 2 in the list shown below). Surface activated bonding is a technique that activates material surfaces by removing inactive layers such as oxides, contaminants, etc. covering the material surfaces by plasma or other means, and that bonds the surfaces together at low temperatures by causing atoms having high surface energy to contact each other and by utilizing the adhesion forces acting between the atoms. 
         [0005]    It is also known to provide a stacked-type semiconductor device which is constructed by stacking semiconductor chips one on top of another in order to increase the packing density of the semiconductor device (for example, refer to patent document 3). In the semiconductor device disclosed in patent document 3, a through-silicon via is formed in each semiconductor chip, and the stacked semiconductor chips are electrically connected together by the through-silicon vias and solder bumps. 
       PRIOR ART DOCUMENTS 
     Patent Documents 
       [0006]    Patent document 1: Japanese Unexamined Patent Publication No. 2007-72206 
         [0007]    Patent document 2: Japanese Unexamined Patent Publication No. 2005-311298 
         [0008]    Patent document 3: Japanese Unexamined Patent Publication No. 2010-56139 
       SUMMARY 
       [0009]    However, in the prior art integrated devices described above, since functional devices formed from dissimilar materials are mounted together on a base substrate in order to produce a high-functionality integrated device, deformation due to thermal history builds up in the case of a base substrate on which an optical waveguide is formed. Due to optical axis misalignment, etc. caused by such deformation buildup, it has not been possible to optically couple the optical device mounted on the substrate precisely to the waveguide formed on the substrate. In particular, as the number of optical devices and electrical devices to be mounted increases, increasing the number of process steps, the amount of buildup of deformation due to the thermal history of the base substrate increases, making it even more difficult to optically couple each optical device mounted on the substrate precisely to the optical waveguide formed on the substrate. That is, in order to achieve a precise optical coupling between the optical device and the optical waveguide, it is necessary to align the optical device with the optical waveguide with a submicron-order accuracy. However, it has been difficult to achieve such an accurate alignment. 
         [0010]    When the optical device and the optical waveguide are flip-chip mounted, as described in patent document 1, since the optical device, the optical waveguide, and the substrate are heated, there has been the problem that the component members may become displaced relative to each other because of differences in thermal expansion coefficients between the respective component members. 
         [0011]    In the case of bonding the optical device by surface activated bonding after flip-chip mounting the electrical device, as described in patent document 2, since the substrate is heated at high temperature when mounting the electrical device, the substrate warps, thus adversely affecting the positioning accuracy when bonding the optical device by surface activated bonding. 
         [0012]    A similar problem occurs when mounting chips, each having a through-silicon via, in three dimensions by using solders in order to increase the packing density of the semiconductor device, as described in patent document 3, because, in this case also, the chips and the substrate are heated at high temperature in soldering steps, etc. performed by reflowing the solder. As described above, in the prior art, it has been difficult to implement a device having an optical device with high accuracy and high packing density. 
         [0013]    It is an object of the present invention to provide an optical integrated device that can overcome the above deficiencies. 
         [0014]    It is also an object of the present invention to provide an optical integrated device wherein provisions are made to be able to mount components on a substrate with high accuracy and high packing density without having to heat the components. 
         [0015]    According to the present invention, there is provided an optical integrated device includes a substrate, an optical device optically coupled to a first device, and an electrical device mounted on top of the optical device or on top of a second device, wherein the optical device is bonded to the substrate by surface activated bonding via a first bonding portion formed from a metallic material on the substrate, and the electrical device is bonded to the optical device or the second device by surface activated bonding via a second bonding portion formed from a metallic material on the optical device or the second device. 
         [0016]    Preferably, in the optical integrated device, the first device is a laser diode, and the optical device is a wavelength conversion device that outputs light by wavelength-converting laser light emitted by the laser diode. 
         [0017]    Preferably, in the optical integrated device, the electrical device is a temperature controlling IC that controls the temperature of the wavelength conversion device, and the temperature controlling IC is bonded to the wavelength conversion device by surface activated bonding via the second bonding portion formed on the wavelength conversion device. 
         [0018]    Preferably, in the optical integrated device, the electrical device is a first IC that performs electrical processing, the second device is a second IC that performs another electrical processing, and the first IC is bonded to the second IC by surface activated bonding via the second bonding portion formed on the second IC. 
         [0019]    Preferably, in the optical integrated device, the first device is a laser diode, the optical device is a wavelength conversion device that outputs light by wavelength-converting laser light emitted by the laser diode, the first IC is a driver IC for driving the laser diode, and the second IC is a temperature controlling IC that controls the temperature of the wavelength conversion device. 
         [0020]    Preferably, in the optical integrated device, the first device is a laser diode, and the optical device is a wavelength conversion device that outputs light by wavelength-converting laser light emitted by the laser diode, wherein the optical integrated device further comprises a spacer placed between the laser diode and the substrate. 
         [0021]    Preferably, in the optical integrated device, a micro-bump structure of Au for bonding the laser diode and a solid pattern of Au for equalizing pressing force applied from above the spacer are formed on an upper surface of the spacer. 
         [0022]    Preferably, in the optical integrated device, the first and second bonding portions each have a micro-bump structure of Au. 
         [0023]    Preferably, in the optical integrated device, the bonding accomplished by the surface activated bonding serves not only to electrically connect the electrical device to the substrate, but also to firmly secure the electrical device in position. 
         [0024]    In the optical integrated device, all the devices constituting it are bonded by surface activated bonding via bonding portions formed from a metallic material, and at least two of these devices are stacked one on top of the other and bonded together by surface activated bonding. It thus becomes possible to mount the components on the substrate with high accuracy and high packing density, while eliminating the need to heat the components as in the prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is an external view of an optical integrated device  1 . 
           [0026]      FIG. 2  is a cross-sectional view taken along line AA′ in  FIG. 1 . 
           [0027]      FIG. 3(   a ) is a perspective view for explaining how a wavelength conversion device  30  is bonded to an Si platform  10 . 
           [0028]      FIG. 3(   b ) is a side view for explaining how the wavelength conversion device  30  is bonded to the Si platform  10 . 
           [0029]      FIG. 4(   a ) is a perspective view for explaining the external appearance of an alternative optical integrated device  2 . 
           [0030]      FIG. 4(   b ) is a perspective view for explaining the structure of the alternative optical integrated device  2  in which bare-chip electrical devices laminated and bonded together are sealed with a sealing member. 
           [0031]      FIG. 5  is a cross-sectional view taken along line BB′ in  FIG. 4(   b ). 
           [0032]      FIG. 6  is a cross-sectional view of a further alternative optical integrated device  3 . 
           [0033]      FIG. 7  is a diagram for explaining how an LD device  25  is mounted by bonding. 
           [0034]      FIG. 8(   a ) is a diagram ( 1 ) for explaining the steps for bonding the LD device  25 . 
           [0035]      FIG. 8(   b ) is a diagram ( 2 ) for explaining the steps for bonding the LD device  25 . 
           [0036]      FIG. 8(   c ) is a diagram ( 3 ) for explaining the steps for bonding the LD device  25 . 
           [0037]      FIG. 9(   a ) is a diagram ( 1 ) for explaining the bonding portion formed on an Si spacer  50 . 
           [0038]      FIG. 9(   b ) is a diagram ( 2 ) for explaining the bonding portion formed on the Si spacer  50 . 
       
    
    
     DESCRIPTION 
       [0039]    An optical integrated device will be described below with reference to the drawings. It will, however, be noted that the technical scope of the present invention is not limited by any particular embodiment described herein, but extends to the inventions described in the appended claims and their equivalents. The following description is given by taking as an example an optical integrated device, etc. on which a wavelength conversion device for converting light emitted by an LD device into its second harmonic is mounted together with an electrical device. 
         [0040]      FIG. 1  is an external view of an optical integrated device  1 , and  FIG. 2  is a cross-sectional view taken along line AA′ in  FIG. 1 . 
         [0041]    As shown in  FIG. 1 , optical devices, i.e., a laser diode  20  (hereinafter abbreviated to LD) formed from a material such as GaAs, GaN, or the like and a wavelength conversion device  30  having a waveguide of lithium niobate (PPLN, LiNbO3), are positioned relative to each other and bonded onto the upper surface of a silicon substrate  10  (hereinafter called the Si platform) to form the optical integrated device  1 . A temperature controlling IC  40  is mounted on top of the wavelength conversion device  30  by bonding. The optical integrated device  1  forms an optical-electrical hybrid integrated circuit that contains both optical and electrical devices to achieve increased packing density. The Si platform  10  includes interconnection patterns, lands, logic LSI, temperature sensor, etc. formed on the silicon substrate, and further includes waveguides, etc. that form optical interconnects, circuits, etc. on the silicon substrate. 
         [0042]    The LD device  20  and the temperature controlling IC  40  are electrically connected to the Si platform  10  by bonding wires  201  and  401 , respectively, via which power is supplied. The LD device  20  and the wavelength conversion device  30  are positioned with their optical axes aligned such that the light emitted from the LD device  20  is aligned with a submicron-order accuracy with the entrance face of the optical waveguide formed within the wavelength conversion device  30 . 
         [0043]    The operation of the optical integrated device  1  will be briefly described below. When drive power is supplied from the Si platform  10  via the bonding wires  201 , the LD device  20  emits infrared light L 1  of wavelength 1064 nm. The wavelength conversion device  30  converts the infrared light L 1  introduced through the entrance face of the optical waveguide into light at its harmonic wavelength as the light propagates through the optical waveguide, and outputs green laser light L 2 . The above combination of the LD device  20  and the wavelength conversion device  30  is only one example, and other devices or other device combinations may be used. That is, by changing the combination of the LD device  20  and the wavelength conversion device  30 , the optical integrated device  1  can produce laser light of various colors. 
         [0044]    The temperature controlling IC  40  mounted directly on the wavelength conversion device  30  by bonding includes a heater and a temperature sensor. The temperature controlling IC  40  is supplied with drive power from the Si platform  10  via the bonding wires  401 , and performs temperature control (electrical processing) so as to maintain the temperature of the wavelength conversion device  30  at 40° C.±10° C. With this temperature control, the wavelength conversion device  30  can maintain high harmonic wavelength conversion efficiency and stable laser light output at the harmonic wavelength. 
         [0045]    Since the temperature controlling IC  40  is mounted on the wavelength conversion device  30  in three dimensions, not only can the temperature of the wavelength conversion device be controlled directly, but the packing density can be also increased, thus achieving the compact design of the optical integrated device  1 . 
         [0046]    As shown in  FIG. 2 , a silicon dioxide film  101  is formed on the upper surface of the Si platform  10 . The silicon dioxide film  101  serves as an insulating film and provides insulation to the interconnection patterns, etc. except the land portion where the electrical devices can be electrically connected. A bonding portion  501  containing micro bumps  511  of Au is formed in the region on the Si platform  10  where the LD device  20  is to be bonded. An Au film  601  is formed on the lower surface of the LD device  20 . The Au film  601  formed on the LD device  20  is bonded to the Au micro bumps  511  by surface activated bonding. 
         [0047]    An Au film  602  formed on the lower surface of the wavelength conversion device  30  is bonded by surface activated bonding to Au micro bumps  512  (bonding portion  502 ) formed on the Si platform  10 . The bonding portion  502  is not bonded over the entire lower surface of the wavelength conversion device  30 . If a metallic material such as Au is present near the optical waveguide, the characteristics of the optical waveguide will be adversely affected; therefore, the wavelength conversion device  30  is bonded to the Si platform  10  at portions excluding at least the portion corresponding to the width of the optical waveguide and extending longitudinally along the length of the optical waveguide. 
         [0048]    The temperature controlling IC  40  is bonded to the wavelength conversion device  30  by lamination bonding to increase the packing density, and the temperature of the wavelength conversion device is directly controlled by the temperature controlling IC  40  which includes the heater and temperature sensor. A bonding portion  503  containing Au micro bumps  513  is formed in the region where the temperature controlling IC  40  is bonded to the wavelength conversion device  30 . The Au micro bumps  513  are bonded by surface activated bonding to an Au film  603  formed on the lower surface of the temperature controlling IC  40 . 
         [0049]    Since the bonding temperature associated with the above surface activated bonding is 150° C. at highest and is thus within the normal temperature range, no positional displacement occurs during the bonding of the LD device  20  and the wavelength conversion device  30  which requires an extremely high optical axis alignment accuracy. After the bonding, if the temperature controlling IC  40  is bonded by lamination bonding, no positional displacement occurs between the LD device  20  and the wavelength conversion device  30  due to heating, nor does any problem such as functional degradations due to thermal stresses to the devices occur. 
         [0050]      FIG. 3(   a ) is a perspective view for explaining how the wavelength conversion device  30  is bonded to the Si platform  10 , and  FIG. 3(   b ) is a side view for explaining how the wavelength conversion device  30  is bonded to the Si platform  10 . In  FIGS. 3(   a ) and  3 ( b ), the same component elements are designated by the same reference numerals, and any description once given will not be repeated. 
         [0051]    As shown in the upper part of each of  FIGS. 3(   a ) and  3 ( b ), the bonding portion  502  formed on the upper surface of the Si platform  10  has a micro-bump structure that contains numerous cylindrically shaped Au micro bumps  512 . For example, the micro bumps  512  are each 5 μm in diameter and 2 μm in height, and are arranged at a pitch of 10 to 25 μm. On the other hand, the Au film  602  is formed on the lower surface of the wavelength conversion device  30 , that is, the surface to be bonded to the Si platform  10 . 
         [0052]    First, the Si platform  10  and the wavelength conversion device  30  are placed in an atmosphere evacuated to about 6 to 8 Pa, and surface activation is performed using argon plasma to remove inactive layers, such as oxides, contaminants (dirt), etc., that cover the Au film  602  of the wavelength conversion device  30  and the surfaces of the micro bumps  512  on the Si platform  10 . 
         [0053]    Next, as shown in the lower part of each of  FIGS. 3(   a ) and  3 ( b ), the wavelength conversion device  30  is placed on the Si platform  10  and pressed together by applying a load (for example, 5 to 10 Kgf/mm 2 ) in an atmosphere held at normal temperature not higher than 150° C. The micro bumps  512  are slightly crushed and deformed in the thickness direction under the applied load, but the Si platform  10  and the wavelength conversion device  30  are securely bonded together by the covalent bonding of Au atoms. 
         [0054]    In this way, the bonding by the surface activated bonding can be accomplished within the normal temperature range not higher than 150° C., and even if components such as optical and electrical devices are laminated and bonded together, the devices do not suffer any problems such as positional displacement, functional degradation due to thermal stresses, or component breakage due to residual stresses arising from differences in thermal expansion coefficient. 
         [0055]      FIG. 4(   a ) is a perspective view for explaining the external appearance of an alternative optical integrated device  2 , and  FIG. 4(   b ) is a perspective view for explaining the structure of the optical integrated device  2  in which bare-chip electrical devices laminated and bonded are sealed with a sealing member.  FIG. 5  is a cross-sectional view taken along line BB′ in  FIG. 4(   b ). 
         [0056]    Unlike the optical integrated device  1  that emits monochromatic light, the alternative optical integrated device  2  is an optical integrated device capable of emitting three different colors, for example, three primary colors such as used in a compact projector or the like. 
         [0057]    As shown in  FIG. 4(   a ), in common with the optical integrated device  1 , the optical integrated device  2  is constructed by integrating various kinds of components such as optical devices and electrical devices on an Si platform  11 . The Si platform  11  has an electrical configuration comprising a CPU, a CMOS LSI (integrated circuit) such as a memory, interconnection patterns, lands, temperature sensors, heaters, etc. 
         [0058]    formed thereon. Further, the Si platform  11  has an optical configuration comprising a waveguide  112  formed thereon as an optical circuit that combines RGB lights emitted from wavelength conversion devices  31 ,  32 , and  33  and that guides the combined light through to a port  111 . 
         [0059]    Three LD devices  21 ,  22 , and  23  are mounted on the Si platform  11 . Three laser lights emitted from the respective LD devices  21  to  23  are converted into the R, G, and B lights corresponding to the three primary colors of light by the three wavelength conversion devices  31  to  33 , respectively. However, the wavelength conversion device  31  for the R light may be omitted, and the R component light emitted from the LD device  21  may be directly introduced. 
         [0060]    In the optical integrated device  2 , a plurality of ICs for performing electrical processing are mounted one on top of another on the Si platform  11 ; that is, a driver IC  41 , a video controller IC  42 , and a temperature controlling IC  43  are stacked one on top of another in the order named. Since the packing density is increased by stacking the three kinds of electrical devices in three dimensions, the optical integrated device  2  can be reduced in size. 
         [0061]    A sealing material (for example, epoxy-based resin) is applied by potting using a dispenser from above the plurality of electrical devices mounted in the form of bare chips as shown in  FIG. 4(   a ), and the material is cured at normal temperature to form the sealing member  44  as shown in  FIG. 4(   b ). The driver IC  41 , the video controller IC  42 , and the temperature controlling IC  43  are not only firmly secured in position but also hermetically sealed and protected by the sealing member  44 . 
         [0062]    Signals supplied from an apparatus (for example, a compact projector) incorporating the optical integrated device  2  are converted by the video controller IC  42  into graphic processed signals. Based on the thus converted signals, the driver IC  41  supplies drive power to the LD devices  21  to  23  acting as light sources for the RGB lights. 
         [0063]    The LD devices  21  to  23  output laser lights based on the supplied drive power, and the output lights of the LD devices  21  to  23  are wavelength-converted by the respective wavelength conversion devices  31  to  33  into the R, G, and B lights for output. The R, G, and B lights output from the wavelength conversion devices  31  to  33  are combined in the waveguide  112  formed on the Si platform  11 , and the combined light is emitted from the port  111 . The wavelength conversion devices  31  to  33  are controlled within a prescribed temperature range to achieve excellent conversion efficiency and stability, by the temperature sensors and heaters formed in the Si platform  11  and the temperature controlling IC  43  which controls the heaters based on the signals from the temperature sensors. 
         [0064]    As shown in  FIG. 5 , the wavelength conversion devices  31  to  33  are bonded to the Si platform  11  by surface activated bonding in the same manner as described for the optical integrated device  1 . More specifically, the bonding portions  502 , each having micro bumps  512 , formed on the Si platform  11  and the Au films  602  formed on the respective wavelength conversion devices  31  to  33  are bonded together by surface activated bonding at portions excluding the portions at and near the respective optical waveguides  311 ,  312 , and  313 . 
         [0065]    The heater  113  and the temperature sensor, not shown, are formed in the Si platform  11  under each bonding portion  502 , and the temperature controlling IC  43  performs temperature control so that the wavelength conversion devices  31  to  33  are maintained at optimum temperature. 
         [0066]    A silicon dioxide film  101  is formed on the upper surface of the Si platform  11 , and as in the case of the optical integrated device  1 , the silicon dioxide film  101  serves as an insulating film and provides insulation to the interconnection patterns, etc. except the land portion  114  where the electrical devices can be electrically connected. Further, the silicon dioxide film  101  together with a silicon nitride film, not shown, forms the waveguide  112  (see  FIG. 4 ) as an optical circuit. 
         [0067]    The driver IC  41 , the video controller IC  42 , and the temperature controlling IC  43 , mounted in three dimensions on the Si platform  11 , are formed with through-silicon vias by which the plurality of chips can be electrically interconnected. 
         [0068]    A plurality of bonding portions  504  are formed in the land portion  114  in the region where the driver IC  41  is mounted on the Si platform  11 , and each bonding portion  504  is formed with Au micro bumps  514 . Au films  604  formed at positions where the electrodes and the through-silicon via  614  are respectively located on the lower surface of the driver IC  41  are bonded to the micro bumps  514  of the respective bonding portions  504  by surface activated bonding. The bonding portions between the Si platform  11  and the driver IC  41  not only provide electrical connections, but also serve to firmly secure them in position. 
         [0069]    The driver IC  41  and the video controller IC  42  are also bonded together in a similar manner. That is, a plurality of bonding portions  505  are formed in the electrode portions (not shown) in the region where the video controller IC  42  is mounted on the driver IC  41 , and each bonding portion  505  is formed with Au micro bumps  515 . Au films  605  formed at positions where the electrodes and the through-silicon via  615  are respectively located on the lower surface of the video controller IC  42  are bonded to the micro bumps  515  of the respective bonding portions  505  by surface activated bonding. The bonding portions between the driver IC  41  and the video controller IC  42  not only provide electrical connections, but also serve to firmly secure them in position. 
         [0070]    The video controller IC  42  and the temperature controlling IC  43  are also bonded together in a similar manner. That is, a plurality of bonding portions  506  which also serve as electrodes are formed on the video controller IC  42 , and each bonding portion  506  is formed with Au micro bumps  516 . Au films  606  formed at positions where the electrodes are located on the lower surface of the temperature controlling IC  43  are bonded to the micro bumps  516  of the respective bonding portions  506  by surface activated bonding. The bonding portions between the video controller IC  42  and the temperature controlling IC  43  not only provide electrical connections, but also serve to firmly secure them in position. 
         [0071]    Since the plurality of electrical devices thus laminated and bonded together are bare chips exposed to the outside environment, the sealing member  44  is formed to firmly secure the electrical devices in position and to hermetically seal and protect them against the outside environment. The video controller IC  42  may be omitted, and the temperature controlling IC  43  may be bonded to the driver IC by surface activated bonding. 
         [0072]    The electrical devices are bonded to the Si platform  11  by surface activated bonding at near normal temperatures. Accordingly, even when the electrical devices are laminated and bonded together (mounted in three dimensions) after the optical devices have been bonded to the Si platform  11  by aligning the optical axis of each LD device with the optical axis of the corresponding wavelength conversion device with a submicron-order accuracy, the devices do not suffer any problems such as positional displacement between the optical devices, functional degradation of the optical devices due to thermal stresses, or breakage of the optical devices due to residual stresses arising from differences in thermal expansion coefficient. 
         [0073]    If the order of the bonding steps is reversed, and the electrical device lamination bonding step (three-dimensional mounting step) is performed first, the Si platform  11  as the substrate suffers hardly any distortion or deformation, since the bonding is accomplished by surface activated bonding at near normal temperatures. Accordingly, the optical devices can be bonded to the Si platform  11  by aligning the optical axis of each LD device with the optical axis of the corresponding wavelength conversion device with a submicron-order accuracy. 
         [0074]      FIG. 6  is a cross-sectional view of a further alternative optical integrated device  3 . 
         [0075]    Like the optical integrated device  1 , the optical integrated device  3  is an optical integrated device that emits monochromatic light. In the optical integrated device  3 , a lidded wavelength conversion device  60  is used in place of the wavelength conversion device  30  used in the optical integrated device  1 . The lidded wavelength conversion device  60  is made up of a wavelength conversion portion  61  and a lid portion  62 , and an optical waveguide is formed along the interface between the wavelength conversion portion  61  and the lid portion  62 . In the optical integrated device  3 , the same component elements as those of the optical integrated device  1  are designated by the same reference numerals, and the description of such component elements will not be repeated here. 
         [0076]    Because of the use of the lidded wavelength conversion device  60 , the position of the optical waveguide moves from the surface of the Si platform  10  to a position above the surface (for example, about 0.5 mm above it), and as a result, the position to which the laser light from the LD device  25  is to be projected has to be moved to a corresponding position above the surface. Therefore, in the optical integrated device  3 , a height adjusting Si spacer  50  is placed on the Si platform  10 , and the LD device  25  is mounted on the Si spacer  50 . Thus, in the optical integrated device  3 , the optical alignment between the LD device  25  mounted on the Si spacer  50  and the lidded wavelength conversion device  60  can be accomplished with a submicron-order accuracy. 
         [0077]    The operation of the optical integrated device  3  will be briefly described below. When drive power is supplied directly from the Si platform  10  via the bonding wires (not shown), the LD device  25  mounted on the Si spacer  50  emits infrared light L 1  of wavelength 1064 nm. The lidded wavelength conversion device  60  converts the infrared light L 1  introduced through the entrance face of the optical waveguide into light at its harmonic wavelength as the light propagates through the optical waveguide, and outputs green laser light L 2 . The above combination of the LD device  25  and the lidded wavelength conversion device  60  is only one example, and other devices or other device combinations may be used. That is, by changing the combination of the LD device  25  and the lidded wavelength conversion device  60 , the optical integrated device  3  can produce laser light of various colors. 
         [0078]    As shown in  FIG. 6 , a silicon dioxide film  101  is formed on the upper surface of the Si platform  10 . 
         [0079]    The silicon dioxide film  101  serves as an insulating film and provides insulation to the interconnection patterns, etc. except the land portion where the electrical devices can be electrically connected. A bonding portion  553  containing micro bumps  563  of Au is formed in the region on the Si platform  10  where the Si spacer  50  is to be bonded. An Au film  653  is formed on the lower surface of the Si spacer  50 . The Au film  653  formed on the Si spacer  50  is bonded to the Au micro bumps  563  by surface activated bonding. 
         [0080]    An Au film  652  formed on the lower surface of the lidded wavelength conversion device  60  is bonded by surface activated bonding to Au micro bumps  562  (bonding portion  552 ) formed on the Si platform  10 . In the lidded wavelength conversion device  60 , since the optical waveguide is formed along the interface between the wavelength conversion portion  61  and the lid portion  62 , the entire lower surface of the lidded wavelength conversion device  60  is bonded to the Si platform  10 , unlike the optical integrated device  1 . 
         [0081]    The LD device  25  is bonded to the Si spacer  50  by lamination bonding. A bonding portion  551  containing Au micro bumps  561  is formed in the region where the LD device  25  is bonded to the Si spacer  50 . The Au micro bumps  561  are bonded by surface activated bonding to an Au film  651  formed on the lower surface of the LD device  25 . The bonding between the Si spacer  50  and the Si platform  10  and the bonding between the Si spacer  50  and the LD device  25  are both accomplished by surface activated bonding. This makes it possible to highly accurately maintain the position of the LD device  25  above the Si platform  10  (in the height direction). 
         [0082]    The temperature controlling IC  40  is bonded to the lidded wavelength conversion device  60  by lamination bonding to increase the packing density, and the temperature of the wavelength conversion device is directly controlled by the temperature controlling IC  40  which includes a heater and a temperature sensor. A bonding portion  503  containing Au micro bumps  513  is formed in the region where the temperature controlling IC  40  is bonded to the lidded wavelength conversion device  60 . The Au micro bumps  513  are bonded by surface activated bonding to the Au film  603  formed on the lower surface of the temperature controlling IC  40 . 
         [0083]    Since the bonding temperature associated with the above surface activated bonding is 150° C. at highest and is thus within the normal temperature range, no positional displacement occurs during the bonding of the Si spacer  50  and the lidded wavelength conversion device  60 , which requires an extremely high optical axis alignment accuracy. After the bonding, if the LD device  25  and the temperature controlling IC  40  are respectively bonded by lamination bonding, no positional displacement occurs between the LD device  25  and the lidded wavelength conversion device  60  due to heating, nor does any problem such as functional degradation due to thermal stresses to the devices occur. 
         [0084]    In the optical integrated device  3 , three optical integrated devices may be mounted on a single Si platform in order to emit the R, G, and B lights, as in the case of the optical integrated device  2 . 
         [0085]      FIG. 7  is a diagram for explaining how the LD device  25  is mounted by bonding. 
         [0086]    When mounting the LD device  25  by bonding, first the LD device  25  may be bonded to the Si spacer  50  by lamination bonding, and then the component fabricated by bonding the LD device  25  to the Si spacer  50  may be bonded to the Si platform  10 .  FIG. 7  is a schematic diagram illustrating such a bonding process. 
         [0087]    The LD device  25  is bonded to the Si spacer  50  by displacing its center from the center of the Si spacer  50  (see  FIG. 9(   a )). That is, the light-emitting face of the LD device  25  is positioned slightly past the end of the Si spacer  50  in order to bring the LD device  25  closer to the wavelength conversion device  60  and to prevent the Si spacer  50  from interfering with the light emitted from the LD device  25 . This may cause a problem when mounting the component fabricated by bonding the LD device  25  to the Si spacer  50  onto the Si platform  10  by bonding. As earlier described, pressure needs to be applied using a pressing head  700  (see  FIG. 8(   a )) from above the structure in order to bond the Si spacer  50  to the micro bumps  563  formed on the Si platform  10 . However, the pressing force exerted on the Si platform  10  varies depending on where on the Si spacer  50  the LD device  25  is placed. For example, in the case of  FIG. 7 , the pressing force C 1  is smaller than the pressing force C 2 . If an uneven load is applied to the Si spacer  50 , the bonding between the Si spacer  50  and the Si platform  10  may be adversely affected. 
         [0088]      FIGS. 8(   a ) and  8 ( b ) are diagrams for explaining the steps for bonding the LD device  25 . 
         [0089]    As shown in  FIG. 8(   a ), using mounting equipment or the like, the Si spacer  50  is placed on the Au micro bumps  563  of the bonding portion  553 . The Au film  653  is formed on lower surface of the Si spacer  50 , while the Au micro bumps  561  of the bonding portion  551  and a solid pattern  565  of Au are formed on the upper surface of the Si spacer (see  FIG. 9(   b )). 
         [0090]    Next, the pressing head  700  is pressed against the Si spacer  50  from above so that the Au micro bumps  563  and the Au film  653  are bonded together by surface activated bonding. Since the lower surface of the pressing head  700  is formed from glass, the lower surface will not bond to the micro bumps  561 , the solid pattern  565 , etc. formed on the upper surface of the Si spacer. Further, the micro bumps  561 , the solid pattern  565 , etc. are formed so as to have the same height and so as to cover the entire upper surface of the Si spacer  50  (see  FIG. 9(   b )). Accordingly, when the pressing head  700  is pressed against the Si spacer  50  from above, the bonding between the Si spacer  50  and the Si platform  10  will not be adversely affected, since the load is applied evenly on the Si spacer  50 . That is, in the step shown in  FIG. 8(   a ), the problem described with reference to  FIG. 7  does not occur. 
         [0091]      FIG. 9(   a ) is a schematic diagram for explaining the upper surface of the Si spacer  50  shown in  FIG. 7 , and  FIG. 9(   b ) is a schematic diagram for explaining the upper surface of the Si spacer  50  shown in  FIG. 8(   a ). In  FIGS. 9(   a ) and  9 ( b ), the upper part shows the relationship between the Si spacer  50  and the pressing head  700 , and the lower part shows a top plan view of the Si spacer  50 . 
         [0092]    As previously described with reference to  FIG. 7 , when the LD device  25  is bonded off center to the Si spacer  50 , the pressing force being applied by the pressing head  700  (not shown) to the Si spacer  50  varies from position to position. Such variations in pressing force may adversely affect the bonding between the Si spacer  50  and the Si platform  10 . One possible method to address this problem would be to first bond the Si spacer  50  to the Si platform  10  and then bond the LD device  25  onto the Si spacer  50 . 
         [0093]    However, as shown in  FIG. 9(   a ), the micro bumps  561  are formed on the Si spacer  50  only in the portion indicated by dashed lines where the LD device  25  is to be bonded. As a result, when mounting the Si spacer  50  first, if the pressing head  700  is pressed against the Si spacer  50  from above, the micro bumps  561  may be crushed under pressure, rendering the micro bumps  561  unusable when mounting the LD device  25  subsequently. 
         [0094]    In the example shown in  FIG. 9(   b ), not only the micro bumps  561 , but also the solid patterns of Au,  565 ,  567 , and  568 , are formed on the upper surface of the Si spacer  50 . Since the micro bumps  561  and the Au solid patterns  565 ,  567 , and  568  are formed so as to have the same height, the pressing force from the pressing head  700  is exerted evenly on the Si spacer  50 . This serves to reduce the chance of crushing the micro bumps  561  under pressure when mounting the Si spacer  50 . 
         [0095]    Further, the Au solid patterns  565 ,  567 , and  568  can be formed simultaneously with the Au micro bumps  561  (Au thin film deposition step and etching step), and there is no need to add an extra fabrication step. The solid patterns shown in  FIG. 9(   b ) are only examples, and their sizes, positions, etc. may be appropriately determined according to the position at which the micro bumps  561  are formed to match the size and position of the LD device  25  to be bonded. The solid patterns need not necessarily be provided at three places, but may be provided at one or two places, as long as the pattern or patterns are formed so that the pressing force from the pressing head  700  can be applied substantially evenly. 
         [0096]    As shown in  FIG. 8(   b ), after the Si spacer  50  has been bonded to the Si platform  10 , the LD device  25  is placed, using mounting equipment or the like, onto the Au micro bumps  561  formed in the bonding portion  551 . The Au film  651  is formed on the lower surface of the LD device  25 . 
         [0097]    As shown in  FIG. 8(   c ), the pressing head  700  is pressed against the LD device  25  from above so that the Au micro bumps  561  and the Au film  651  are bonded together by surface activated bonding. Since the LD device  25  is not placed on the solid patterns  565  to  568 , but placed on the Au micro bumps  561 , the presence of the solid patterns  565  to  568  on the upper surface of the Si spacer  50  does not affect the bonding between the LD device  25  and the Si spacer  50 . 
         [0098]    After the step of  FIG. 8(   c ), the lidded wavelength conversion device  60  and the temperature controlling IC  40  are bonded together in the same manner as previously described for the optical integrated device  1 , to complete the fabrication of the optical integrated device  3 . 
         [0099]    As described above, according to the optical integrated devices  1  to  3 , since all optical and electrical devices as components formed from dissimilar materials are bonded by surface activated bonding, the components can be easily laminated and mounted at low temperatures. As a result, even components such as optical and electrical devices between which the difference in thermal expansion coefficient is great can be mounted on the same substrate with high accuracy by suppressing warping of the substrate and eliminating any concern about their thermal histories. 
         [0100]    Furthermore, since optical and electrical devices having different functions can be mounted together on the same substrate, the functionality of the optical integrated device can be increased, and the number of substrates needed to construct an apparatus that uses the optical integrated device can be reduced; as a result, the overall size and cost of the apparatus can be reduced, while increasing its reliability. 
         [0101]    The optical integrated devices  1  to  3  have each been described above as having a laser diode and a wavelength conversion device as optical devices. However, the optical devices are not limited to these particular devices, but a prism, lens, mirror, beam former, diffraction grating, optical combiner, filter, interference device, etc. may be used as the optical devices, and such devices may be bonded by surface activated bonding via bonding portions formed from a metallic material capable of suitably deforming and having good electrical conductivity (for example, Au, Cu, or In).