Abstract:
An image projection system comprises a micro-electromechanical system (MEMS) package wherein the MEMS package further includes: a first substrate and a second substrate joined together at a joinder surface applied with a ponder material thereon to provide an internal space to contain and package a MEMS device therein, wherein at least one of the first and second substrate is configured to have a an inclined surface near the joinder surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application of a Provisional Application 61/197,717 and claims a Priority Date of Oct. 30, 2008. This application is also a Continuation-in-Part (CIP) application of a co-pending application Ser. No. 12/231,922 filed on Sep. 5, 2008 by common Applicants of this patent application. The application Ser. No. 12/231,922 is a non-provisional application of a U.S. Patent Provisional Application No. 60/967,811 filed on Sep. 6, 2007. The patent application Ser. No. 12/231,922 is a Continuation In Part (CIP) application of a pending U.S. patent application Ser. No. 11/121,543 filed on May 4, 2005 issued into U.S. Pat. No. 7,268,932. The application Ser. No. 12/231,922 is also a Continuation In Part (CIP) application of three previously filed applications. These three applications are 10/698,620 filed on Nov. 1, 2003, 10/699,140 filed on Nov. 1, 2003 now issued into U.S. Pat. No. 6,862,127, and 10/699,143 filed on Nov. 1, 2003 now issued into U.S. Pat. No. 6,903,860 by the Applicant of this patent applications. The disclosures made in these patent applications are hereby incorporated by reference in this patent application. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to the configuration and methods for manufacturing an image display system implemented with a micro electromechanical system (MEMS) device functioning as a spatial light modulator (SLM). More particularly, this invention relates to a technology used for packaging a MEMS device provided with electrical connections and optical configurations suitable to operate in the image display system. 
         [0004]    2. Description of the Related Art 
         [0005]    After the dominance of CRT technology in the display industry for over 100 years, Flat Panel Display (FPD) and Projection Display have gained popularity because of their space efficiency and larger screen size. Projection displays using micro-display technology are gaining popularity among consumers because of their high picture quality and lower cost. There are two types of micro-displays used for projection displays in the market. One is micro-LCD (Liquid Crystal Display) and the other is micro-mirror technology. Because a micro-mirror device uses un-polarized light, it produces better brightness than micro-LCD, which uses polarized light. 
         [0006]    Although significant advances have been made in technologies of implementing electromechanical micro-mirror devices as spatial light modulators, there are still limitations in their high quality images display. Specifically, when display images are digitally controlled, image quality is adversely due to an insufficient number of gray scales. 
         [0007]    Electromechanical micro-mirror devices have drawn considerable interest because of their application as spatial light modulators (SLMs). A spatial light modulator requires an array of a relatively large number of micro-mirror devices. In general, the number of required devices ranges from 60,000 to several million for each SLM. Referring to  FIG. 1A , an image display system  1  including a screen  2  is disclosed in a relevant U.S. Pat. No. 5,214,420. A light source  10  is used to generate light beams to project illumination for the display images on the display screen  2 . The light  9  projected from the light source is further concentrated and directed toward lens  12  by way of mirror  11 . Lenses  12 ,  13  and  14  form a beam columnator operative to columnate the light  9  into a column of light  8 . A spatial light modulator  15  is controlled by a computer through data transmitted over data cable  18  to selectively redirect a portion of the light from path  7  toward lens  5  to display on screen  2 .  FIG. 1B  shows a SLM  15  that has a surface  16  that includes an array of switchable reflective elements  17 ,  27 ,  37 , and  47 , each of these reflective elements is attached to a hinge  30 . When the element  17  is in an ON position, a portion of the light from path  7  is reflected and redirected along path  6  to lens  5  where it is enlarged or spread along path  4  to impinge on the display screen  2  to form an illuminated pixel  3 . When the element  17  is in an OFF position, the light is reflected away from the display screen  2  and, hence, pixel  3  is dark. 
         [0008]    The on-and-off states of the micromirror control scheme, as that implemented in the U.S. Pat. No. 5,214,420 and in most conventional display systems, impose a limitation on the quality of the display. Specifically, applying the conventional configuration of a control circuit limits the gray scale gradations produced in a conventional system (PWM between ON and OFF states), limited by the LSB (least significant bit, or the least pulse width). Due to the ON-OFF states implemented in the conventional systems, there is no way of providing a shorter pulse width than the duration represented by the LSB. The least intensity of light, which determines the gray scale, is the light reflected during the least pulse width. The limited levels of the gray scale lead to a degradation of the display image. 
         [0009]    Specifically,  FIG. 1C  exemplifies, as related disclosures, a circuit diagram for controlling a micromirror according to U.S. Pat. No. 5,285,407. The control circuit includes memory cell  32 . Various transistors are referred to as “M*” where “*” designates a transistor number and each transistor is an insulated gate field effect transistor. Transistors M 5 , and M 7  are p-channel transistors; transistors, M 6 , M 8 , and M 9  are n-channel transistors. The capacitances, C 1  and C 2 , represent the capacitive loads in the memory cell  32 . The memory cell  32  includes an access switch transistor M 9  and a latch  32   a  based on a Static Random Access switch Memory (SRAM) design. All access transistors M 9  on a Row line receive a DATA signal from a different Bit-line  31   a . The particular memory cell  32  is accessed for writing a bit to the cell by turning on the appropriate row select transistor M 9 , using the ROW signal functioning as a Word-line. Latch  32   a  consists of two cross-coupled inverters, M 5 /M 6  and M 7 /M 8 , which permit two stable states that include a state  1  when is Node A high and Node B low, and a state  2  when Node A is low and Node B is high. 
         [0010]    The control circuit, as illustrated in  FIG. 1C , controls the mirrors to switch between two states, driving the mirror to either an ON or OFF deflected angle (or position) as shown in  FIG. 1A . The minimum intensity of light controllable to reflect from each mirror element for image display, i.e., the resolution of gray scale of image display for a digitally controlled image display apparatus, is determined by the shortest length of time that the mirror is controllably held in the ON position. The length of time that each mirror is held an ON position is in turn controlled by multiple bit words. 
         [0011]      FIG. 1D  shows the “binary time intervals” when controlling micromirrors with a four-bit word. As shown in  FIG. 1D , the time durations have relative values of 1, 2, 4, 8, which in turn define the relative brightness for each of the four bits where “1” is the least significant bit and “8” is the most significant bit. According to the control mechanism as shown, the minimum controllable differences between gray scales for showing different levels of brightness is a represented by the “least significant bit” that maintains the micromirror at an ON position. 
         [0012]    For example, assuming n bits of gray scales, one time frame is divided into 2 n −1 equal time periods. For a 16.7-millisecond frame period and n-bit intensity values, the time period is 16.7/(2 n −1) milliseconds. 
         [0013]    Having established these times for each pixel of each frame, pixel intensities are quantified such that black is a 0 time period, the intensity level represented by the LSB is 1 time period, and the maximum brightness is 2 n −1 time periods. Each pixel&#39;s quantified intensity determines its ON-time during a time frame. Thus, during a time frame, each pixel with a quantified value of more than 0 is ON for the number of time periods that correspond to its intensity. The viewer&#39;s eye integrates the pixel brightness so that the image appears the same as if it were generated with analog levels of light. 
         [0014]    For controlling deflectable mirror devices, the PWM applies data to be formatted into “bit-planes”, with each bit-plane corresponding to a bit weight of the intensity of light. Thus, if the brightness of each pixel is represented by an n-bit value, each frame of data has the n-bit-planes. Then, each bit-plane has a 0 or 1 value for each mirror element. According to the PWM control scheme described in the preceding paragraphs, each bit-plane is independently loaded and the mirror elements are controlled according to bit-plane values corresponding to the value of each bit during one frame. Specifically, the bit-plane according to the LSB of each pixel is displayed for 1 time period. 
         [0015]    Micro-electromechanical system (MEMS) devices, such as the above described micromirror device, tend to be sensitive to external environmental conditions, including temperature, humidity, fine particle dust, vibration, and shock. Therefore, a MEMS device requires a MEMS package to protect the device and so that it can operate normally. Many patents related to such a MEMS package have been disclosed. 
         [0016]      FIGS. 2A and 2B  are diagrams which together show the configuration of a MEMS package disclosed in U.S. Pat. No. 5,610,625. The configuration that is disclosed includes a ring  53  for retaining a window  52  so that the window is kept at a certain distance from the modulation array  51  placed on a substrate  50 . In this configuration, there are problems in that not only are the number of components and the number of connections associated with the ring  53  increased, but there is also a difficulty in preventing the adhesive materials from spreading out beyond the joinder areas thus adversely affects the light transmission and other performance characteristics of the device. 
         [0017]      FIG. 3  is a diagram showing the configuration of a MEMS package disclosed in U.S. Pat. No. 5,650,915. In this configuration, two package substrates  65  and  66 , which sandwich a lead finger  63  (i.e., a lead frame  64 ), are used in order to retain a cover member  62  a certain distance from a micro-circuit chip  61  placed on a heat spreader  60 . The aforementioned configuration includes the cover member  62  and heat spreader  60 , in addition to the two package substrates, making the structure more complex. 
         [0018]      FIG. 4  is a diagram showing the structure of a MEMS package disclosed in U.S. Pat. No. 6,624,921. The configuration uses beads  73  in order to retain a window  72  a certain distance from the micromirror device  71  of a micromirror device chip  70 . This configuration is also faced with the problem of an increase in the number of components due to including the beads  73 . 
       SUMMARY OF THE INVENTION 
       [0019]    With the situation as described above in mind, the present invention aims at providing a MEMS package simply configured by eliminating a dedicated spacer member used for securing the distance between the MEMS device and window substrate. 
         [0020]    A first embodiment of the present invention is an image projection system comprises a micro-electromechanical system (MEMS) package wherein the MEMS package further includes: a first substrate and a second substrate joined together at a joinder surface applied with a joinder material thereon to provide an internal space to contain and package a MEMS device therein, wherein at least one of the first and second substrate is configured to have a an inclined surface near the joinder surface. 
         [0021]    In another embodiment, the present invention discloses a method for manufacturing an image display device by implementing a micro-electromechanical system (MEMS) device contained in a package formed by joining together two substrates, the method comprising: forming an inclined surface on at least one of the two substrates; depositing a joinder material on a joinder surface near the inclined surface, joining together the two substrates to form a joined substrate by placing one of the substrates onto the joinder surface f another substrate deposited with the joinder material; and applying a dicing process to divide the joined substrate into individual MEMS packages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The present invention is described in detail below with reference to the following Figures. 
           [0023]      FIGS. 1A and 1B  are, respectively, a functional block diagram and a top view of a portion of a micromirror array implemented as a spatial light modulator used in a conventional display system disclosed in a prior art patent; 
           [0024]      FIG. 1C  is a circuit diagram showing a prior art circuit for controlling a micromirror under the ON and OFF states of a spatial light modulator; 
           [0025]      FIG. 1D  is diagram showing the binary time intervals for a four-bit gray scale; 
           [0026]      FIGS. 2A and 2B  are top and side view diagrams showing the configuration of a MEMS package according to a conventional technique; 
           [0027]      FIG. 3  is a diagram showing the configuration of another MEMS package according to a conventional technique; 
           [0028]      FIG. 4  is a diagram showing the configuration of yet another MEMS package according to a conventional technique; 
           [0029]      FIG. 5  is a diagram, as viewed from a diagonal perspective, showing an exemplary configuration of a MEMS package according to a first preferred embodiment of the present invention; 
           [0030]      FIG. 6  is a cross-sectional diagram showing an exemplary configuration of a MEMS package according to the first embodiment of the present invention; 
           [0031]      FIG. 7  is a flow chart exemplifying the process of the package substrate as a part of the production process of a MEMS package, according to the first embodiment of the present invention; 
           [0032]      FIGS. 8A through 8G  are diagrams for describing each process of the flow chart shown in  FIG. 7 ; 
           [0033]      FIG. 9  is a flow chart exemplifying the production process of a MEMS package according to the first embodiment of the present invention; 
           [0034]      FIGS. 10A through 10F  are diagrams for describing each process of the flow chart shown in  FIG. 9 ; 
           [0035]      FIG. 11  is a diagram showing an exemplary modification of a method for applying an adhesive included in a MEMS package according to the first embodiment of the present invention; 
           [0036]      FIG. 12  is a diagram exemplifying the relation between the reflection light reflected by an inclined surface in a MEMS package, according to the first embodiment of the present invention, and the reflection light reflected by a mirror device; 
           [0037]      FIGS. 13A and 13B  are diagrams together showing an exemplary configuration of a MEMS package according to a second preferred embodiment of the present invention; 
           [0038]      FIG. 14  is a diagram showing an exemplary configuration of a MEMS package according to a third preferred embodiment of the present invention; 
           [0039]      FIG. 15  is a diagram showing an exemplary configuration of a MEMS package according to a fourth preferred embodiment of the present invention; 
           [0040]      FIG. 16  is a diagram showing an exemplary configuration of a MEMS package according to a fifth preferred embodiment of the present invention; 
           [0041]      FIG. 17  is a diagram showing an exemplary configuration of a MEMS package according to a sixth preferred embodiment of the present invention; 
           [0042]      FIG. 18  is a diagram showing an exemplary configuration of a MEMS package according to a seventh preferred embodiment of the present invention; 
           [0043]      FIG. 19  is a diagram showing an exemplary configuration of a MEMS package according to an eighth preferred embodiment of the present invention; 
           [0044]      FIG. 20  is a diagram showing an exemplary configuration of a MEMS package according to a ninth preferred embodiment of the present invention; 
           [0045]      FIG. 21  is a diagram showing an exemplary configuration of a MEMS package according to a tenth preferred embodiment of the present invention; 
           [0046]      FIG. 22  is a diagram showing an exemplary configuration of a MEMS package according to an eleventh preferred embodiment of the present invention; and 
           [0047]      FIG. 23  is a diagram showing an exemplary configuration of a MEMS package according to a twelfth preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0048]    The following is a description, in detail, of the preferred embodiment of the present invention with reference to the accompanying drawings. 
       First Embodiment 
       [0049]      FIGS. 5 and 6  are diagrams showing an exemplary configuration of a MEMS package  1000  that packages a MEMS device inside the package.  FIG. 5  is a diagonal view diagram of the MEMS package  1000 , showing the package substrate  110  and the window substrate  200  separated, for better comprehension of the internal structure of the MEMS package  1000 .  FIG. 6  is a cross-sectional diagram showing the layer structure of the MEMS package  1000 . 
         [0050]    As exemplified in  FIGS. 5 and 6 , the MEMS package  1000  comprises a MEMS device  100 , a package substrate  110  on which the MEMS device  100  is placed, an electrical connection unit  130 , bonding wires  150 , and a window substrate  200 . For simplicity of description, the term, “MEMS package  1000 ” in this description includes the MEMS device  100  inside the packaging. Further, the term, “inside of package” indicates the space enclosing the MEMS device  100 . In  FIG. 6 , for example, the space surrounded by the package substrate  110  and window substrate  200  is “inside of package”, as opposed to space “outside of package”. 
         [0051]    The following is a brief description of the role of an individual constituent component. 
         [0052]    To begin with, the MEMS device  100  is the object of the packaging and is, for example, a micromirror device in which a plurality of micromirror elements is arranged in an array (simply noted as “arrayed” hereinafter). 
         [0053]    The micromirror device is a kind of spatial light modulator used for an image display apparatus and is capable of deflecting an illumination light incident from a light source using micromirror elements corresponding to the respective pixels of an image, thereby projecting a desired image. 
         [0054]    Each micromirror element includes a mirror supported by an elastic hinge. The mirror is tilted by an electrostatic force generated between the mirror and an electrode placed under the mirror, in accordance with an electric signal from an external control circuit. The tilt angle of the mirror is, for example, between −12 degrees and +12 degrees, with the initial state of the mirror being zero (“0”) degrees. In this case, when the tilt angle of the mirror is +12 degrees, the mirror is in an ON state, deflecting the illumination light in the direction of a projection optical system. When the tilt angle of the mirror is −12 degrees, the mirror is in an OFF state, deflecting the illumination light away from the projection optical system. 
         [0055]    The MEMS device  100  is positioned on the package substrate  110 . The package substrate  110  includes a cavity for placing the MEMS device  100  and an inclined surface  120  used for joining the window substrate  200 . A metalized layer  160 , which is used for joining together the MEMS device  100  and package substrate  110 , is formed inside of the cavity. The MEMS device  100  may be joined onto the metalized layer  160  by soldering. Alternatively, an adhesive, such as an epoxy-series adhesive and an ultraviolet hardening adhesive, and a low-melting point glass such as a fritted glass may be used for joining the MEMS device  100 . Meanwhile, the cavity as shown in the figure is not necessarily required, and the MEMS device  100  may be placed instead within a step formed by the inclined surface  120 . 
         [0056]    The electrical connection unit  130  is formed as a pattern on the package substrate  110  and is utilized for securing an electrical connection between the inside and outside of the package. An internal electrode pad  131 , used as the electrical connection point to the MEMS device  100 , and an external electrode pad  132 , used as the electrical connection point to the device external to the MEMS package  1000 , are equipped on both sides of the electrical connection unit  130 . In addition, the electrical connection unit  130  also radiates the heat from inside of the package to the outside. Alternatively, a thermal conductive member may be equipped, in addition to the electrical connection unit  130 , so as to separate the function of electrical connection from that of heat transfer. These members are preferably made of aluminum, copper, gold, silver, tungsten magnesium, titanium, and the like. 
         [0057]    The bonding wire  150  is a wire used to connect the electrode pad equipped on the top surface of the device substrate  101  of the MEMS device  100  to the internal electrode pad  131  equipped on the electrical connection unit  130 . The bonding wire  150  secures the electrical connection between the device substrate  101  and electrical connection unit  130  and also conducts the heat of the device substrate  101 . Also in this comprisal, a thermal conduction-use member may be separately placed, or the heat may be conducted by way of the above described metalized layer  160 . 
         [0058]    The window substrate  200  is joined to the package substrate  110  and is an optically transparent substrate tightly sealing the inside of the package. An anti-reflection coating is applied, commonly with MgF 2 , to the surface of the window substrate  200  in order to prevent extraneous light from influencing the display image. In addition to the reflection prevention method utilizing the difference in the refractive indexes of the MgF 2 , a method of preventing reflection by forming a fine micro-structure with pitch between the structural elements less than the wavelength of light has been recently proposed. While having a function as the gateway, i.e., the entrance and exit, for the light to and from the MEMS device  100 , the window substrate  200  has the primary function of protecting the MEMS device  100  from dust and debris, which is generated in the substrate dicing process. 
         [0059]    A joinder material  140  is placed on the inclined surface  120  of the package substrate  110 . The joinder material  140  joins together the package substrate  110  and window substrate  200  without intervening directly on the joinder surface. 
         [0060]    Note that while the configuration shown in  FIG. 5  has the joinder surface that is formed as a rectangle surrounding inside of the package, such a configuration is arbitrary. The joinder surface may also be formed as a circular shape surrounding the inside of the package. 
         [0061]    Note that the present specification document labels the contact surface between the package substrate  110  or window substrate  200  and the joinder material  140  as the “adhesion surface” and further labels the contact surface between the package substrate  110  and the window substrate  200  as the “joinder surface”. 
         [0062]    Next is a description of the production process of the MEMS package  1000  according to the present embodiment. 
         [0063]      FIG. 7  is a flow chart exemplifying the process of the package substrate  110  as a part of the production process of the MEMS package  1000 .  FIGS. 8A through 8G  are diagrams for describing each process of the flow chart shown in  FIG. 7 . The following is a description of the production process of the package substrate  110 , in detail, with reference to  FIG. 7  and  FIGS. 8A through 8G . 
         [0064]    First, in step S 101 , a package substrate  110  is prepared (refer to  FIG. 8A ). The package substrate  110  is composed of, for example, a glass substrate, a silicon substrate and a ceramic substrate. To prevent the MEMS device  100  from peeling off or breaking due to thermal expansion, the package substrate  110  is preferably composed of a material in which the coefficient of linear expansion is approximately the same as the material constituting the MEMS device  100 . Further, in consideration of the above described thermal conduction, the package substrate  110  is preferably composed of a material with high thermal conductivity. 
         [0065]    In S 102 , the inclined surface  120  is formed on the prepared package substrate  110  (refer to  FIG. 8B ). Specifically, the package substrate  110  is processed so as to leave a hill-like protrusion part (noted as “protrusion part” hereinafter) on both sides of a region (noted as “cavity part” hereinafter) in which a cavity is formed in step S 103 . The protrusion part plays the role of a spacer that is used for adjusting the distance between the MEMS device  100  and window substrate  200 . The inclined surface  120  is formed as the two side surfaces of the protrusion part. The cavity side of each protrusion part is labeled the inside inclined surface  121 , and the other inclined surface  120  is labeled as the outside inclined surface  122 . Note that the inclined surface  120  can be formed by various methods such as grinding, sand blasting, chemical etching, and ultrasonic process (e.g., a honing). The method may be selected in consideration of the material used for the package substrate  110 , the productivity of the method, and other factors. 
         [0066]    In S 103 , a cavity for placing the MEMS device  100  between the two protrusion parts that have been formed in S 102  is formed (refer to  FIG. 8C ). Note that the cavity may also be formed by using various methods such as sand blasting, chemical etching, ultrasonic processing, or the like, as in the case of forming the inclined surface  120 . 
         [0067]    In S 104 , a thin, electric conductive film is formed on the package substrate  110  as the precursor to forming the electrical connection unit  130  (refer to  FIG. 8D ). The thin film (simply noted as “film” hereinafter) is made of, for example, aluminum (Al). The film may be made of tungsten (W), aluminum (Al), gold (Au), silver (Ag), copper (Cu), magnesium (Mg), titanium (Ti), or other material with high thermal conductivity. The film may be formed by means of a physical vapor deposition vacuum deposition (PVD) such as a sputtering method and a vacuum deposition method. 
         [0068]    In S 105 , the film formed in S 104  is etched to form the pattern of the electrical connection unit  130  (refer to  FIG. 8E ). First, a photoresist is coated on the film by means of, for example, a spin coating method. Other methods include a spray method and a dipping method. Next, an etching mask is formed by exposing the photoresist using a mask for transferring the pattern of the electrical connection unit  130 . Lastly, the pattern of the electrical connection unit  130  is formed by etching the etching mask. 
         [0069]    Note that the protrusion part plays the role of a spacer used for supporting the window substrate  200  while maintaining the distance between itself and the MEMS device  100 , as described above. Therefore, the side surfaces of the protrusion part may be configured to be a vertical surface. The MEMS package  1000  according to the present embodiment, however, is configured to form the side surface of the protrusion part as an inclined surface  120 . The reason for it is to ease the transfer of the pattern onto the side surface. 
         [0070]    Meanwhile, the height of the protrusion part is preferably as small as possible, since a variation in the distance between the mask and electrical connection unit  130  increases with the height of the protrusion part, thus decreasing the accuracy of transfer and of the pattern. 
         [0071]    Next, in S 106 , a metalized layer  160  used for joining the MEMS device  100  onto the bottom surface of the cavity is formed (refer to  FIG. 8F ). 
         [0072]    In S 107 , the MEMS device  100  is joined onto the metalized layer  160  using a solder (refer to  FIGS. 8F and 8G ). 
         [0073]    In S 108 , an environment adjustment material  170  is placed inside of the cavity (refer to  FIG. 8G ). The environment adjustment material  170  absorbs the out-gas generated from the moisture inside of the cavity and from the joinder material  140 . The environment adjustment material  170  is not limited to any particular material, and may be composed of a moisture absorption material, such as zeolite. 
         [0074]    The last step, S 108 , is a wire bonding process. The electrode pad equipped on the top surface of the device substrate  101  is connected to an internal electrode pad  131  (not shown in drawing) equipped on the electrical connection unit  130  using the bonding wire  150  (refer to  FIG. 8G ). The bonding wire  150  is preferably made of gold (Au). The present embodiment shows the structure using a wire bonding; alternatively, the connection may use a land grip or ball grip, obtaining an electrical connection using a bump by extending the electrical connection unit to the outer edges of the cavity. With the above described process, the production process of the package substrate  110  is completed. 
         [0075]    The following description labels the product, resulting from the above described processes in which the MEMS device  100  is placed on the package substrate  110  and the electrical connection unit  130  is formed, as the package substrate assembly  180 . 
         [0076]    Note that the initial form of the package substrate  110  is flat. However, this is arbitrary. Alternatively, a package substrate  110 , for which a protrusion part is already formed by a molding or a sintering, may be prepared in S 101 . In such a case, the process for forming the inclined surface  120  (in S 102 ) may be eliminated. 
         [0077]    Further,  FIG. 8G  shows the diagram of only one piece of the MEMS device  100  joined onto the package substrate  110  for simplicity of description. In the actual production process, however, the package substrate  110  is designed to be a large scale substrate base so that a single substrate can produce a plurality of device-use package substrates, and thereby the productivity is improved. 
         [0078]      FIG. 9  is a flow chart exemplifying the production process of the MEMS package  1000  of joining together the package substrate assembly  180  and window substrate  200 .  FIGS. 10A through 10F  are diagrams for describing each process of the flow chart shown in  FIG. 9 . The following is a description, in detail, of the production process of the MEMS package  1000  with reference to  FIG. 9  and  FIGS. 10A through 10F . 
         [0079]    First, in S 201 , an optically transparent window substrate  200  is prepared. The material of the window substrate  200  is, for example, glass. Further, the top and bottom surfaces of the window substrate  200  may be coated with an anti-reflection (AR) coating produced by vapor-depositing magnesium fluoride, or the like, so as to eliminate extraneous reflection. 
         [0080]    In S 202 , a groove  210  is formed on the window substrate  200  (refer to  FIG. 10A ). The groove  210  is utilized for positioning the joinder material  140  and plays the role of preventing failure when the window substrate  200  and package substrate assembly  180  are joined together, such as a positional shift, and preventing the joinder material  140  from touching an extraneous area. The groove  210  is formed at a position corresponding to the outside inclined surface  122  of the package substrate  110  when it is joined. Note that the groove  210  may also be formed at a position that is slightly shifted to the outside of the package from the upper position of the outside inclined surface  122 . Such a configuration prevents the joinder material  140  from flowing to the joinder surface (i.e., the flat part of the protrusion part of the package substrate  110 ) between the window substrate  200  and package substrate  110 , and instead allows the joinder material  140  to spread along the outside inclined surface  122 . 
         [0081]    In S 203 , an air outlet hole  220  is bored in the window substrate  200  on an as needed basis (refer to  FIG. 10A ). The air outlet hole  220  is formed as an air path between the substrates in order to ease the joining together of the package substrate assembly  180  and window substrate  200 . 
         [0082]    In S 204 , the joinder material  140  is placed in the groove  210  that has been formed in S 202  (refer to  FIGS. 10A and 10B ). The joinder material  140  may be constituted by, for example, fritted glass, epoxy resin-series adhesive, solder, and the like. If the MEMS device  100  is a micromirror device, and if extraneous reflection occurs on the border surface between the window substrate  200  and joinder material  140 , the reflection causes the contrast of the projected image to be reduced. Therefore, the refraction indexes of the joinder material  140  and window substrate  200  are preferably the same, in order to prevent extraneous reflection on the border surface. For example, if the window substrate  200  is made of a glass substrate, the joinder material  140  is preferably composed of fritted glass. Alternatively, the color of the joinder material  140  is preferred to be a dark color, such as black, for absorbing extraneous light. 
         [0083]    In S 205 , the package substrate assembly  180  and window substrate  200  are joined together by using the joinder material  140  (refer to  FIG. 10C ). The joinder material  140 , for example, fritted glass, is melted to become semi-liquid and is spread under pressure from the inclined surface  122  toward the outside as a result of the joinder material  140  coming in contact with the package substrate  110 . The joinder material  140  does not intervene on the joinder surface between the package substrate  110  and window substrate  200 . With this configuration, it is possible to prevent a shift in the distance between the MEMS device  100  and window substrate  200 , caused by the joinder material  140  intervening on the joinder surface. Further, the air between the package substrate  110  and window substrate  200  is ventilated through the air outlet hole  220 . Therefore, there is no possibility of the joinder position being shifted by extraneous pressure applied to both substrates during the process of being joined together. 
         [0084]    After joining the window substrate  200 , the air outlet hole  220  equipped in S 203  is sealed. The sealant uses fritted glass, epoxy resin, ultraviolet hardening resin, or other similar material. 
         [0085]    In S 206 , the joinder material  140  spread on the inclined surface  120  is hardened to fix the joined state of the package substrate assembly  180  and window substrate  200 . 
         [0086]    Step S 207  is the first stage of the dicing process, in which only the window substrate  200  is cut (refer to  FIG. 10D ). The present embodiment is configured to equip the outside of the protrusion part with the outside inclined surface  122 , and therefore, a space is created between the package substrate  110  and window substrate  200  on the outside of the package. This fact makes it possible cut only the window substrate  200  without damaging the electrical connection unit  130  on the package substrate  110 . This configuration enables the window substrate  200  to be joined to the entire MEMS device  100  as one piece of wafer, instead of being joined onto individual MEMS device  100  on the package substrate  110  one by one, and to be divided into individual MEMS devices  100  after the aforementioned joinder. 
         [0087]    Step S 208  is the second stage of the dicing process, in which the package substrate  110  is cut to make a chip from the MEMS package  1000  (refer to  FIG. 10E ). The area in which the package substrate  110  is cut is a part of the area in which the electrical connection unit  130  is exposed by cutting the window substrate  200  in S 207 . 
         [0088]    In S 209 , ball grids  190  are formed on the external electrode pad  132  of the electrical connection unit  130  in order to connect to an external device (refer to  FIG. 10F ). 
         [0089]    Lastly in S 210 , the operation testing on each MEMS package  1000  is performed. This process completes the production process for the MEMS package  1000 . The MEMS package  1000  according to the present embodiment is produced by the above described process. 
         [0090]    Note that the joinder material  140  is deposited on the window substrate  200  in  FIG. 10A ; however, it is not required for the joinder material  140  to be deposited on the side of the window substrate  200 . Alternately, the joinder material  140  may be deposited on the inclined surface  120  of the package substrate  110 , as shown in  FIG. 11 . 
         [0091]    Further, if the MEMS device  100  is a micromirror device, the design of the inclined surface  120  needs to take into consideration the reflection of the illumination light incident to the inclined surface  120 , as shown in  FIG. 12 . Specifically, the reflected light must be directed towards a direction other than the projection light path so that the reflection light reflected from the inclined surface  120  is not projected. Commonly, the ON light modulated by a micromirror is reflected perpendicularly to the package substrate, and the micromirror is in the maximum deflection state in this situation. Therefore, for example, if the inclination angle of the inclined surface  120  is configured to be no smaller than the maximum tilt angle of the mirror of the micromirror element, the extraneous light reflected on the inclined surface  120  will be reflected towards the illumination light path and not the projection light path. 
         [0092]    The MEMS package  1000  according to the present embodiment is configured to form the protrusion part on the package substrate  110 , thereby eliminating a spacer that is conventionally provided as a separate member from the substrate to secure the distance between the MEMS device  100  and window substrate  200 . This configuration makes it possible to decrease the number of components and reduce the cost related to producing the package. 
         [0093]    Further, the MEMS package  1000  according to the present embodiment is configured to form the side surface of a protrusion part as the inclined surface  120  and utilize it as the adhesion surface for the joinder material  140 . This configuration separates the joinder surface from the adhesion surface. Since the joinder material  140  is not on the joinder surface, the distance between the MEMS device  100  and window substrate  200  can be accurately maintained. As a result, the top surface of the window substrate  200  can also be utilized as the surface for positioning the optical axis direction. 
         [0094]    Further, the MEMS package  1000  according to the present embodiment is configured to use the inclined surface  120  as an adhesion surface, thereby making it possible to enlarge the area in which the joinder material  140  comes into contact with the package substrate  110 . This configuration makes it possible to attain a strong joinder. 
         [0095]    The MEMS package  1000  according to the present embodiment is configured to equip the window substrate  200  with the groove  210  used for positioning when depositing the joinder material  140 . Further, the inclined surface  120  of the package substrate  110  makes it possible to manage the direction of the joinder material  140  spreading. This configuration stabilizes the positioning of the joinder material  140 , making it possible to minimize variation in the joinder state between individual components. 
       Second Embodiment 
       [0096]      FIGS. 13A and 13B  are diagrams for describing a second preferred embodiment. In contrast to the first embodiment, the present embodiment is configured to form a light-blocking layer  230  on the window substrate  200 , used for preventing extraneous light inside of the package. Otherwise the configuration is similar to that of the first embodiment. The following describes the differences between the second embodiment and the first embodiment, with reference to  FIGS. 13A and 13B . 
         [0097]    As shown in  FIGS. 13A and 13B , the light-blocking layer  230  is formed on some areas of the window substrate  200  which are not part of the designated light path. This configuration makes it possible utilize other areas not covered by the light-blocking layer  230  as a groove  210 , utilized for positioning the joinder material  140 , as opposed to actively forming a groove  210  by processing the window substrate  200  in the first embodiment, as described above. 
         [0098]    Note that the material used for the light-blocking layer  230  may vary and may be selected in consideration of cost, durability, productivity, or other factors. Specifically, the material may be, for example, metallic thin film, painted film, resin film or a composite of them. 
         [0099]    Further, the method for forming the light-blocking layer  230  may also vary. Possible methods includes a sputtering method, a vacuum deposition method, a screen printing method, and a method of adhesively attaching a separately produced light-blocking member onto a window substrate  200 . 
         [0100]    As described above, in addition to deriving the benefits of the first embodiment, the present embodiment prevents an increase in the temperature inside of the package caused by extraneous light entering the package and also prevents degradation in the contrast of an image due to extraneous light incident to the projection optical system. 
       Third Embodiment 
       [0101]      FIG. 14  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to a third preferred embodiment. The present embodiment results from changing the placement of the joinder material  140  in the first embodiment. Otherwise, it is similar to the configuration of the first embodiment. The following describes the difference from the first embodiment, with reference to  FIG. 14 . 
         [0102]    The present embodiment is configured to join the package substrate assembly  180  and window substrate  200  using the joinder material  140  placed on the inside inclined surface  121  within the package. 
         [0103]    As such, the present embodiment provides similar benefits as the first embodiment. Furthermore, modifications similar to the second embodiment can also be applied to the present embodiment. 
         [0104]    By substituting a black, opaque adhesive for the joinder material  140 , reflection of extraneous light coming from the nearby surface of the micromirror device inside of the package can be prevented, and thus a further benefit is realized. 
       Fourth Embodiment 
       [0105]      FIG. 15  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to a fourth preferred embodiment. As compared to the third embodiment, the present embodiment is configured to expand the surface area of adhesion using a joinder material  140 . Otherwise, the configuration is similar to that of the third embodiment. The following describes the difference from the third embodiment, with reference to  FIG. 15 . 
         [0106]    The present embodiment is configured to deposit the joinder material  140  inside of the package, as in the case of the third embodiment, and the joinder material  140  is deposited so that it spreads to the bonding wires  150 . As a result, the bonding wires  150  are sealed by the joinder material  140 , which is the difference from the third embodiment. 
         [0107]    As such, in addition to deriving the benefits of the third embodiment, the present embodiment prevents the bonding wire  150  from peeling off or from contacting the window substrate  200 , and also prevents extraneous light caused by the bonding wire  150 . Furthermore, a modification that is similar to the second embodiment can also be applied to the present embodiment. 
       Fifth Embodiment 
       [0108]      FIG. 16  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to a fifth preferred embodiment. The present embodiment is configured to further add an adhesion surface to the configuration of the first embodiment. Otherwise, the configuration is similar to that of the first embodiment. The following is a description of the difference from the first embodiment, with reference to  FIG. 16 . 
         [0109]    The present embodiment is configured to place a joinder material  140  on the inside inclined surface  121 , in addition to the outside inclined surface  122 , as shown in  FIG. 16 . 
         [0110]    Note that, for the present embodiment, the joinder material  140  may be initially deposited on both the inside inclined surface  121  and the outside inclined surface  122 , or may initially be deposited on the flat part on top of the protrusion part. If the joinder material  140  is placed on the flat part, the two substrates are pressed together with sufficient pressure to spread the joinder material  140  over both inclined surfaces  120 , so as to prevent the joinder material  140  from remaining on the flat part after the joinder material  140  is hardened. 
         [0111]    As such, the present embodiment is configured to expand the adhesion surface area, thereby making it possible to strengthen the adhesion between the package substrate assembly  180  and window substrate  200 , while also deriving the benefits of the first embodiment. Furthermore, a modification that is similar to the second embodiment can also be applied to the present embodiment. 
       Sixth Embodiment 
       [0112]      FIG. 17  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to a sixth preferred embodiment. In the present embodiment, the form of the protrusion part is different from that of the first embodiment. Otherwise, the configuration is similar to that of the first embodiment. The following is a description of the difference from the first embodiment, with reference to  FIG. 17 . 
         [0113]    The present embodiment is configured such that the side surfaces of the protrusion part formed on the package substrate  110  is concavely curved, instead of being a flat surface. This difference increases the surface area of the outside inclined surface  122  (i.e., the inclined surface  120 ) to be utilized as an adhesion surface. 
         [0114]    As such, the present embodiment makes it possible to more strongly join together the package substrate assembly  180  and window substrate  200  by virtue of the expanded adhesion surface area, while deriving the benefits of the first embodiment. Furthermore, a modification that is similar to the second embodiment can also be applied to the present embodiment. 
         [0115]    Note that the side surface of the protrusion part formed on the package substrate  110  may alternatively be convexly curved, in contrast to the configuration shown in  FIG. 17 . Such a modification improves the accuracy in the pattern forming of the electrical connection unit  130  on the inclined surface  120 . 
       Seventh Embodiment 
       [0116]      FIG. 18  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to a seventh preferred embodiment. In the present embodiment, the form of the protrusion part and the placement of the joinder material  140  is different from those of the first embodiment. Otherwise, the configuration is similar to that of the first embodiment. The following is a description of the difference from the first embodiment, with reference to  FIG. 18 . 
         [0117]    The present embodiment is configured to form two straight-line protrusion parts on both sides of the cavity part, as shown in  FIG. 18 . Further, the joinder material  140  is placed in the space between the two protrusion parts and also the window substrate  200 . 
         [0118]    As such, in the present embodiment, there are actually four adhesion surfaces on the package substrate  110 , i.e., two for both sides of the cavity part. This configuration provides a more stable adhesion between the package substrate assembly  180  and the window substrate  200 , while also deriving the benefits of the first embodiment. The number of protrusion parts is arbitrary, and the forming of a plurality thereof makes it possible to derive a similar benefit. Furthermore, a modification that is similar to the second embodiment can also be applied to the present embodiment. 
       Eighth Embodiment 
       [0119]      FIG. 19  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to an eighth preferred embodiment. In the present embodiment, the form of the side surface of the protrusion part is different from that of the seventh embodiment. Otherwise, the configuration is similar to that of the seventh embodiment. The following is a description of the difference from the seventh embodiment, with reference to  FIG. 19 . 
         [0120]    As shown in  FIG. 19 , the present embodiment is configured such that the two facing side surfaces of the protrusion parts are concavely curved, instead of being a flat surface. Such a change enlarges the surface area of an inclined surface  120  to be utilized for an adhesion surface. 
         [0121]    As such, while also realizing the benefits of the seventh embodiment, the present embodiment is configured to enlarge the adhesion surface area, thereby providing a stronger adhesion between the package substrate assembly  180  and window substrate  200 . Furthermore, a modification that is similar to the second embodiment can also be applied to the present embodiment. 
       Ninth Embodiment 
       [0122]      FIG. 20  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to a ninth preferred embodiment. The protrusion part of the first embodiment is changed to a step having an inclined surface  120  in the present embodiment. Otherwise, the configuration is similar to that of the first embodiment. The following is a description of the difference from the first embodiment, with reference to  FIG. 20 . 
         [0123]    The present embodiment is configured to form a step having only one inclined surface  120  on the package substrate  110 , instead of a protrusion part with two inclined surfaces, as in the first embodiment. Further, the joinder material  140  is placed on the inclined surface  120  that forms the step. Such a change makes it possible to simplify the processing of the package substrate  110 . 
         [0124]    Further, in the present embodiment there is no space between the package substrate  110  and window substrate  200  on the outside of the package. Therefore, it is necessary to apply a dicing process to the window substrate  200  before the substrates are joined together, unlike the case of the first embodiment. In this case, it is possible to obtain a larger number of window substrates  200  from one piece of wafer than when dicing after the substrates are joined together, decreasing the unit price of the component associated with the window substrate  200 . 
         [0125]    As such, the present embodiment also provides similar benefits as the first embodiment. Further, a modification that is similar to the second embodiment can also be applied to the present embodiment. 
       Tenth Embodiment 
       [0126]      FIG. 21  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to a tenth preferred embodiment. In the present embodiment, the position where the joinder material  140  is deposited is different from the ninth embodiment. Otherwise, the configuration is similar to that of the ninth embodiment. The following is a description of the difference from the ninth embodiment, with reference to  FIG. 21 . 
         [0127]    The present embodiment is configured to deposit the joinder material  140  outside of the package. Such a change makes it possible to deposit the joinder material  140  after the package substrate  110  and window substrate  200  are in contact with each other. Note that in this case, a dicing process needs to be applied to the window substrate  200  before the substrates are joined together. 
         [0128]    The present embodiment also makes it possible to eliminate the spacer member, thus reducing the cost related to producing the package since there is a decrease in the number of components. 
         [0129]    In addition, in this embodiment, there is no joinder material  140  on the surface between the package substrate  110  and window substrate  200 , and therefore, the distance between the MEMS device  100  and window substrate  200  can be accurately secured. This, in turn, prevents problems, such as the bonding wire  150  coming in contact with the window substrate  200 . Further, the present embodiment may equip a light-blocking layer  230  on the window substrate  200 . 
       Eleventh Embodiment 
       [0130]      FIG. 22  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to an eleventh preferred embodiment. The protrusion part of the first embodiment is changed to a two-stage step having two inclined surfaces  120  in this present embodiment. Otherwise, the configuration is similar to that of the first embodiment. The following is a description of the difference from the first embodiment, with reference to  FIG. 22 . 
         [0131]    The present embodiment is configured with a two-stage step having two inclined surfaces  120  on the package substrate  110 , in place of the protrusion part in the first embodiment. Further, the window substrate  200  is supported by part of the flat surface between the two inclined surfaces  120 , and the joinder material  140  is deposited on the other part of the flat surface. Such a change makes it possible to deposit the joinder material  140  after placing the window substrate  200  on the package substrate  110 . Further, the joinder material  140  is actually surrounded by three surfaces: the flat surface formed between the two inclined surfaces  120 , the side surface of the window substrate  200  and the upper inclined surface  120 . This configuration makes it possible to stabilize the placement position of the joinder material  140  and to secure a larger surface area for adhesion. 
         [0132]    The present embodiment is further configured to bury the window substrate  200  in the package substrate  110 . Therefore, it is necessary to apply a dicing process to the window substrate  200  before the substrates are joined, unlike the case of the first embodiment. In this case, it is possible to obtain a larger number of window substrates  200  from one piece of wafer than when dicing the window substrate  200  after the substrates are joined together, decreasing the unit price of components associated with the window substrate  200 . 
         [0133]    As described above, also the present embodiment eliminates the spacer member and decreases the number of components, thereby making it possible to reduce the cost related to producing the package. 
         [0134]    In addition, there is no joinder material  140  intervening on the surface between the package substrate  110  and window substrate  200 , and therefore, the distance between the MEMS device  100  and window substrate  200  can be accurately secured. This, in turn, prevents problems such as the bonding wire  150  contacting the window substrate  200 . Further, increasing the adhesion surface area makes it possible to more securely and adhesively join together the package substrate assembly  180  and window substrate  200 . Also, the present embodiment may equip a light-blocking layer  230  on the window substrate  200 . Note that the present embodiment may also be applied to a configuration in which wireless bonding is employed. 
       Twelfth Embodiment 
       [0135]      FIG. 23  is a diagram showing the structure of joining together a package substrate assembly  180  and a window substrate  200  according to a twelfth preferred embodiment. In the present embodiment, the protrusion part of the first embodiment is changed to a step having an inclined surface  120  and electrically connected to an electrical connection unit formed on the lower surface of the package substrate through a hole. Otherwise, the configuration is similar to that of the first embodiment. The following is a description of the difference from the first embodiment, with reference to  FIG. 23 . 
         [0136]    The present embodiment is configured to form a step having only one inclined surface  120  on the package substrate  110 , as shown in  FIG. 23 . Such a change simplifies the processing of the package substrate  110 . 
         [0137]    Further, electrical connection units  130  are placed in two areas, on a flat surface, including the internal electrode pad  131 , on the top surface of the package substrate  110  and on a flat surface of the bottom surface (i.e., the surface to which the window substrate  200  is not joined) of the package substrate  110 . The electrical connection between the electrical connection unit  130  inside of the package and the electrical connection unit  130  outside of the package is secured through a hole  195  near the internal electrode pad  131 . In this configuration, the electrical connection unit  130  is formed only on flat surfaces, improving the transfer accuracy of a mask when forming the electrical connection unit  130  and improving the pattern accuracy of the electrical connection unit as a result. 
         [0138]    Further, in the present embodiment, there is no space between the package substrate  110  and window substrate  200  on the outside of the package, unlike the case of the first embodiment. However, there is no electrical connection unit  130  intervening between the package substrate  110  and window substrate  200  and therefore, even if the package substrate  110  and window substrate  200  are joined together, there is no possibility of damaging the electrical connection unit  130  when a dicing process is applied to the window substrate  200 . Therefore, the package substrate  110  and window substrate  200  can be joined together in units of wafer, as in the case of the first embodiment, and thereby, the production process can be simplified. 
         [0139]    As such, the present embodiment provides similar benefits as the first embodiment. Further, a modification similar to that of the second embodiment can also be applied to the present embodiment. 
         [0140]    The present invention is configured to eliminate a dedicated spacer member used for securing the distance between a MEMS device and a window substrate, thereby enabling a more simply configured MEMS package. 
         [0141]    Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.