Abstract:
A method for applying anti-stiction material to a micro device on a substrate includes introducing anti-stiction material on a surface of an encapsulation device or a surface of the substrate and sealing at least a portion of the encapsulation device to the surface of the substrate to form a chamber to encapsulate the micro device and the anti-stiction material. The micro device includes a first component and a second component. The first component is moveable and is configured to contact the second component. The method also includes vaporizing the anti-stiction material and depositing the anti-stiction material on a surface of the first component or a surface of the second component after vaporizing the anti-stiction material to prevent stiction between the first component and the second component.

Description:
BACKGROUND 
       [0001]    The present disclosure relates to the micro devices. 
         [0002]    Assuring reliability and yield are two critical tasks for the manufacturing of micro devices, such as integrated circuits and micro electromechanical systems (MEMS). Typically, in manufacturing micro devices, multiple micro devices are fabricated on a semiconductor wafer. The semiconductor wafer is then separated into individual dies each containing one or more individual micro devices. The electrical and optical performance of the micro devices are often tested for quality assurance on the individual dies in an ambient environment. For testing purposes, electrical and optical signals need to be properly input into the circuits in each micro device. Output electric and optical signals from the micro devices need to be properly detected and measured to analyze the functional performance of the micro devices. During testing and handling of the micro devices, the micro devices must not be contaminated by dust and pollutants in the ambient environment. Electrical and optical input and output, as well as protecting the micro devices from the environment, all need to be considered when designing packaging for the micro devices. Given the increased complexity of the micro devices and the testing requirements, a need exists for improved die packaging for the micro devices. 
         [0003]    A common problem for MEMS is stiction between components that can contact each other during operations. For example, a micro mirror built on a substrate can include a tiltable mirror plate. The micro mirror can be driven by electrostatic forces to tilt about an axis. The mirror plate can tilt to two positions: an “on” position, wherein the micro mirror plate directs incident light to a display device, and an “off” position, wherein the micro mirror plate directs incident light away from the display device. The mirror plate can be stopped by mechanical stops at the “on” or the “off” positions so that the orientation of the mirror plate can be precisely defined at these two positions. For some micro mirror devices, the mirror plate stopped at the “on” or the “off” position must be able to overcome stiction between the mirror and the stop. A delay in the response of the mirror plate can be less than optimum in environments that require that the mirror respond quickly. 
       SUMMARY 
       [0004]    In one general aspect, the present invention relates to a method for applying anti-stiction material to a micro device on a substrate. The method includes introducing anti-stiction material on a surface of an encapsulation device or a surface of the substrate, wherein the micro device comprises a first component and a second component, and the first component is moveable and is configured to contact the second component; sealing at least a portion of the encapsulation device to the surface of the substrate to form a chamber to encapsulate the micro device and the anti-stiction material; vaporizing the anti-stiction material; and after vaporizing the anti-stiction material, depositing the anti-stiction material on a surface of the first component or a surface of the second component to prevent stiction between the first component and the second component. 
         [0005]    Implementations of the method may include one or more of the following. The step of sealing can include applying an adhesive to the encapsulation device or to the surface of the substrate; after applying the adhesive, bringing the encapsulation device and the surface of the substrate together with the adhesive therebetween; and after bringing the encapsulation device and the surface of the substrate together, curing the adhesive. Alternatively, the step of sealing can include bonding at least a portion of the encapsulation device to the surface of the substrate by plasma surface activated bonding. The step of sealing can include sealing at least a portion of the encapsulation device to the surface of the substrate in a vacuum environment to form an at least partially evacuated chamber to encapsulate the micro device and the anti-stiction material. The step of vaporizing can include heating the anti-stiction material. The step of vaporizing can be after the sealing step. The step of depositing the anti-stiction material can include depositing the anti-stiction material on substantially all the surfaces of the micro device. 
         [0006]    In another general aspect, the present invention relates to a micromechanical system including: a substrate; a micro device on the substrate, wherein the micro device comprises a first component and a second component, and the first component is moveable and is configured to contact the second component; anti-stiction material coated on a surface of the first component or a surface of the second component to prevent stiction between the first component and the second component; and an encapsulation device bonded with the surface of the substrate to form a chamber to encapsulate the micro device. The anti-stiction material can be vaporized at a temperature below 450° C. The anti-stiction material can be vaporized at a temperature below 300° C. The step of vaporizing can include evaporating the anti-stiction material, subliming the anti-stiction material, or a combination thereof. 
         [0007]    Implementations of the system may include one or more of the following. The anti-stiction material can include one or more of 3,3,3 trifluoro-propylmethyldichlorosilane (PMDCS), tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS), heptadecafluoro-1,1,2,2, -tetrahydrodecyltrichlorosilane (FDTS), dodecyltrichlorosilane (DDTCS), dimethyldichlorosilane (DDMS), vinylundecyltirchlorosilane (V11TCS), aminopropyltrimethoxysilane (APTMS), epoxides, methacroloxy, maleimide-polyethylene glycol (mPEG), or mercaptosilane. 
         [0008]    The second component can be stationary relative to the substrate. The first component can be a tiltable micro mirror plate that is configured to tilt in response to an external electric signal. The encapsulation device can include an encapsulation cover. At least a portion of the encapsulation cover can be transparent to visible light. The encapsulation device can include a plurality of spacer walls each of which extends from the encapsulation cover and comprises at least one surface configured to be sealed to the surface of the substrate. 
         [0009]    Implementations may also include one or more of the following advantages. A potential advantage of the disclosed systems and methods is simplification of the fabrication process of the micro-device. Anti-stiction material can be applied to a plurality of micro devices after the micro devices are packaged on a semiconductor wafer (i.e. in situ). The anti-stiction material can be introduced on the inside surfaces of an encapsulation device or the upper surface of the substrate before the encapsulation of the micro device. The encapsulation device is then sealed to the upper surface of the substrate to form a chamber to encapsulate the anti-stiction material and the micro device. The anti-stiction material in the chamber can be evaporated or sublimed by heating. The evaporated anti-stiction material can be deposited on the surfaces of the micro devices to prevent stiction between components that can contact each other in the operation of the micro device. In contrast, anti-stiction material is conventionally deposited on the surface of the components during the fabrication of the micro devices. The in situ application of anti-stiction material disclosed in the present specification reduce the device development and testing times, and thus enable shorter time to the market. 
         [0010]    The disclosed methods and systems may be useful for providing anti-stiction materials on contact areas that are hidden in a micro device. For example, the contact surfaces between a tiltable mirror plate and a landing tip on a substrate can be hidden underneath the mirror plate. The contact surfaces are often formed at the final stage of the device fabrication. The disclosed methods and system can provide a way to isotropically deposit anti-stiction material on the contact surfaces that are hidden by other components of the micro device. 
         [0011]    Another potential advantage of the disclosed systems and methods is that anti-stiction materials can be applied to a plurality of micro devices outside of a vacuum environment. The anti-stiction materials can be applied to the micro devices after they are encapsulated in micro chambers formed by an encapsulation cover sealed to the semiconductor wafer. The semiconductor wafer containing the encapsulated micro devices can be diced to form separate dies. 
         [0012]    Yet another potential advantage of the disclosed system and methods is increased flexibility in selection and method of application of the anti-stiction material to micro devices. The disclosed methods can be applicable to small and large micro devices with no or minimal incremental cost in scaling up the device sizes. The disclosed methods may also be applicable to different types of devices without being affected by the detailed fabrication process. 
         [0013]    Although the invention has been particularly shown and described with reference to multiple embodiments, it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The following drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles, devices and methods described herein. 
           [0015]      FIG. 1  is a cross-sectional view of a substrate having one or more micro devices encapsulated by a encapsulation device. 
           [0016]      FIG. 2A  is a plan view of an encapsulation device. 
           [0017]      FIG. 2B  is a cross-sectional view of the encapsulation device of  FIG. 2A . 
           [0018]      FIG. 3  is a flowchart for encapsulating micro devices on a semiconductor wafer. 
           [0019]      FIG. 4  is a cross-section view of an exemplified micro device mirror in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  is a cross-sectional view of a substrate having encapsulated micro devices.  FIGS. 2A and 2B  are a plan view and a cross-sectional view of an encapsulation device.  FIG. 3  is a flowchart for encapsulating micro devices on a semiconductor wafer. 
         [0021]    A plurality of micro devices  290  are provided on a semiconductor wafer  200 , as shown in  FIG. 1 . The semiconductor wafer  200  includes a substrate  115  and a circuit layer  230 . The micro devices  290  are located on the circuit layer  230 . The circuit layer  230  includes electronic circuits that process input signals received at electric terminals  245  and send the signals to the micro devices  290 . One or more components in the micro device  290  can move under the control of the input signal and to come to contact with another component in the micro device  290 . Output signals from the micro devices  290  can also be transmitted to the electric terminals  245  via an electric circuit in the circuit layer  230 . The semiconductor wafer  200  can also include a plurality of electric terminals  245  for receiving input signals for the micro devices  290  or output signals from the micro devices  290 . 
         [0022]    One or more droplets of an anti-stiction material  260  are on the lower surface of the encapsulation cover  210  on the upper surface  235  of the substrate  115 . The anti-stiction material can be anywhere within a chamber formed by the encapsulation cover  210  and the substrate  115 . The anti-stiction material  260  can include one or more of 3,3,3 trifluoro-PMDCS, tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS), heptadecafluoro-1,1,2,2,-tetrahydrodecyltrichlorosilane (FDTS), dodecyltrichlorosilane (DDTCS), dimethyldichlorosilane (DDMS), vinylundecyltirchlorosilane (V11 TCS), aminopropyltrimethoxysilane (APTMS), epoxides, methacroloxy, maleimide-polyethylene glycol (mPEG), mercaptosilane, or other suitable molecular films, which are available from Applied MicroStructures, Inc. located at San Jose, Calif. The anti-stiction materials are capable of reducing adhesion or stiction at the contact interface between two objects. The anti-stiction materials can be applied, for example, using an applicator for polymer materials. This droplet is then used to form a layer of anti-stiction material on the micro device, as described further below. 
         [0023]    Referring to  FIG. 3 , an encapsulation device is formed (step  310 ). An exemplary encapsulation device  205  is shown in  FIGS. 2A and 2B . The encapsulation device  205  can include an encapsulation cover  210  that has an upper surface and a lower surface and a plurality of spacer walls  221  that are connected with the lower surface of the encapsulation cover  210 . The encapsulation cover  210  and spacer walls  221  can be an integral piece or be separate pieces joined together. 
         [0024]    The encapsulation cover  210  can be made of a transparent material, such as glass or silicon dioxide, which allows visual and microscopic examinations of the micro devices  290  after the encapsulation of the micro device  290 . The transparent encapsulation cover  210  also allows optical communications with micro devices  290  that are opto-electrical devices, such as micro-mirror based spatial modulation devices. Antireflective layers  212  and  211  can be coated on the top and lower surfaces of the encapsulation cover  210 , respectively. The antireflective layers  212  and  212  can reduce intensity loss in the incident light and output light at the surfaces of the encapsulation cover  210 . Optionally, the encapsulation layer  210  is coated with one or more antireflective layers. 
         [0025]    In general, the anti-reflective layers  211  and  212  can be a thin film made of dielectric or metallic materials, which may include a single layer of multiple layers of such materials. The materials for the ant-reflective layer  211  and  212  can include metal oxide, silicon oxides, such as TiO x /SiO x , NbO x /SiO x , TaO x /SiO x , and MgF 2 /SiO x . The anti-reflective layers  211  and  212  can be made of the same or different materials. The ant-reflective layer  211  and  212  can be deposited by physical vapor deposition (PVD), chemical vapor deposition (CVD), or molecular beam epitaxy (MBE) in the vacuum environment. 
         [0026]    The anti-reflective layers  211  and  212  reduce the light reflectance and thereby increase the light transmittance at the two surfaces of the encapsulation layer  210 . The anti-reflective layers  211  and  212  create two interfaces on each side of the anti-reflective layer  211  or  212 : the air/anti-reflective-layer interface and the anti-reflective-layer/encapsulation-cover interface. The light transmittance is increased by constructive interference between the transmitted light at the two interfaces. The light reflectance is decreased by destructive interference between the reflected light at the two interfaces. The reflections from the two interfaces are 180 degrees out of phase (thus creating destructively interference with each other) if the coating is a quarter wavelength thickness and the index of refraction of the anti-reflective layer is less than that of the glass. 
         [0027]    The spacer walls  221  can include materials such as an oxide, such as silicon oxide, silicon, or a metal. Each spacer wall  221  can include one or more side faces  223  and a base face  222 . The spacer walls  221  can be formed by first depositing a layer of spacer material followed by selective removal of the spacer material using standard photolithography and etching. 
         [0028]    Anti-stiction material is deposited on the encapsulation device or on a surface of the substrate (step  320 ). Alternatively, the anti-stiction material can be placed on the micro device itself. 
         [0029]    An adhesive material such as a polymer epoxy can be applied to the encapsulation device, such as to the base face  222  of the spacer walls  221  or to the surface areas surrounding each micro device  290  on the substrate  115  (step  330 ). The encapsulation device  205  is then placed on the substrate with the adhesive therebetween (step  340 ) so that the base face  222  of the spacer walls  221  come to contact and seal to the upper surface  235  of the substrate  115 . If necessary, the encapsulation device  205  and substrate  115  are pressed together. The adhesive is then cured, such as by heat or UV irradiation (step  350 ) to form a seal the micro device under the encapsulation device. The bond can be a semi-hermetic bond between the spacer walls  221  and the encapsulation cover  210 . A chamber  250  formed by the spacer walls  221  and the encapsulation cover  210  encloses a micro device  290  and the anti-stiction material  260  previously applied to the lower surface of the encapsulation cover  210  or the upper surface  235  of the substrate  115  (in step  320 ). The application and the subsequent curing of the adhesive can be conducted in a vacuum environment so that the chamber is at least partially evacuated. 
         [0030]    Alternatively, the encapsulation device  205  can be bonded directly to the upper surface  235  of the substrate to encapsulate the micro device  290 . For example, hermetic bonding can be made by plasma surface activated bonding. The vacuum or partial vacuum environment in the chamber  250  can be maintained by the air-tight seal between the base faces  222  of the spacer walls  221  and the upper surface  235  of the substrate  115  and the bond between the spacer walls  221  and the encapsulation cover  210 . 
         [0031]    In some embodiments, the encapsulation device  205  does not have spacer walls. The micro device is in a recessed area on the substrate  115 . The height of the micro device does not exceed the upper surface  235  of the substrate  115 . The encapsulation device  205  is a flat. An anti-stiction material  260  can be disposed on the lower surface of the encapsulation device  205  or on the upper surface  235  in the recessed area of the substrate  115 . The lower surface of the encapsulation cover  210  can be sealed or bonded to the upper surface  235  of the substrate  115  to encapsulate the micro device in a cavity formed by the recessed upper surface  115  and the encapsulation cover  210 . 
         [0032]    The encapsulation cover  210  can include a plurality of openings  215  that are located outside of the chamber  250 . The openings  215  allow access to the electric terminals  245  for the micro devices  290  on the semiconductor wafer  200  so that the micro devices on the semiconductor wafer  200  can be tested electronically before the semiconductor wafer  200  is diced into dies. 
         [0033]    After the micro device  290  and the anti-stiction material  260  are encapsulated in a chamber  250 , the anti-stiction material  260  is vaporized in the chambers  250  (step  360 ) to deposit the material on the surfaces of the micro devices  290 . The evaporation or the sublimation temperatures can be caused by heating, for example, by placing the semiconductor wafer  200  in an oven or using a laser beam to locally heat the anti-stiction material  260 . The anti-stiction material  260  can be in a liquid or solid state before the heating. The anti-stiction material  260  can also be in the form of a viscous polymer melt. In some embodiments, the anti-stiction materials  260  can be vaporized at a temperature lower than 450° C. The vaporization can occur in an evaporation process or a sublimation process. The evaporation or the sublimation temperatures of the anti-stiction materials  260  are lower than 450° C. Thus, if the circuit layer  230  includes a CMOS circuit, when the anti-stiction materials are heated to evaporate the materials from a liquid or sublime the materials from a solid state, the heating will not damage the CMOS circuit. In some embodiments, the evaporation temperature or the sublimation temperatures of the anti-stiction material  260  is below 300° C., for example, 150° C. 
         [0034]    The vaporized anti-stiction material  260  deposits on the surfaces of the micro device  290  and forms a thin film coating on the surfaces of the micro device  290 . The anti-stiction material is coated on the surfaces of the micro device  290  that come into contact with each other. Because the vaporized anti-stiction material can diffuse within the chamber  250 , the anti-stiction material can also be isotropically deposited on the surfaces that are not in contact with other components during the operations of the micro device. In some embodiments, a film of anti-stiction material coated on the surfaces of the micro device  290  is one or more molecular monolayer thick. The thickness of the coated anti-stiction material can be 0.3 nanometer or thicker. In some embodiments, the anti-stiction film is thicker than 1.0 nanometer. 
         [0035]    An example of a micro device  290  is a spatial light modulation device that includes one or more tiltable micro mirrors.  FIG. 4  illustrates a cross section of such a tiltable micro mirror  400  on a substrate  410 . The tiltable micro mirror  400  includes a mirror plate  402  that has a flat reflective upper layer  403   a  that provides the mirror surface, a middle layer  403   b  that provides mechanical strength to the mirror plate, and a bottom layer  403   c . The upper layer  403   a  can be formed of a reflective material, such as, a thin reflective metallic layer. For example, aluminum, silver, or gold can be used to form the upper layer  403   a . The layer thickness can be in the range of 200 to 1000 angstroms, such as about 600 angstroms. The middle layer  403   b  can be made of a silicon based material, for example, amorphous silicon, typically about 2000 to 5000 angstroms thick. The bottom layer  403   c  can be built from an electrically conductive material that allows the electric potential of the bottom layer  403   c  to be controlled relative to the step electrodes  421   a  or  421   b . For example, the bottom layer  403   c  can be made of titanium and have a thickness in the range of 200 to 1000 angstrom. 
         [0036]    The mirror plate  402  includes a hinge  406  that is connected to the bottom layer  403   c  and is supported by a hinge post  405  that is rigidly connected to a substrate  410 . The mirror plate  402  can include two hinges  406  connected to the bottom layer  403   c . Each hinge  406  defines a pivot point for the mirror plate  402 . The two hinges  406  define an axis about which the mirror plate  402  tilts. The hinges  406  extend into cavities in the lower portion of mirror plate  403 . For ease of manufacturing, the hinge  406  can be fabricated as part of the bottom layer  403   c.    
         [0037]    Step electrodes  421   a  and  421   b , landing tips  422   a  and  422   b , and a support frame  408  can also be fabricated over the substrate  410 . The step electrode  421   a  is electrically connected to an electrode  431  whose voltage Vd can be externally controlled. Similarly, the step electrode  421   b  is electrically connected with an electrode  432  whose voltage Va can also be externally controlled. The electric potential of the bottom layer  403   c  of the mirror plate  402  can be controlled by electrode  433  at potential Vb. 
         [0038]    The micro mirror plate  402  can be selectively controlled among an array of micro mirror plates by an electric circuit. Bipolar electric pulses can be applied individually to the electrodes  431 ,  432 , and  433 . Electrostatic forces can be produced on the mirror plate  402  when electric potential differences are created between the bottom layer  403   c  on the mirror plate  402  and the step electrodes  421   a  or  421   b . An imbalance between the electrostatic forces on the two sides of the mirror plate  402  causes the mirror plate  402  to tilt from one orientation to another. When the mirror plate  402  is tilted to the “on” position as shown in  FIG. 4 , the flat reflective upper layer  402  reflects the incident light  430  to produce the reflected light  440  along the “on” direction. The incident light  430  is reflected to the “off” direction when the mirror plate  402  is tilted to the “off” position. 
         [0039]    The multiple steps in the step electrodes  421   a  and  421   b  narrow the air gap between the mirror plate  402  and the step electrodes  421   a  or  421   b , and can increase the electrostatic forces experienced by the mirror plate  402 . The height of the step electrodes  421   a  and  421   b  can be in the range from about 0.2 microns to 3 microns. 
         [0040]    The landing tips  422   a  and  422   b  can have the same height as that of second step in the step electrodes  421   a  and  421   b  for manufacturing simplicity. The landing tips  422   a  and  422   b  provide a gentle mechanical stop for the mirror plate  402  after each tilt movement. The landing tips  422   a  and  422   b  can also stop the mirror plate  402  at a precise angle. Additionally, the landing tips  422   a  and  422   b  can store elastic strain energy when they are deformed by electrostatic forces and convert the elastic strain energy to kinetic energy to push away the mirror plate  402  when the electrostatic forces are removed. The push-back on the mirror plate  402  can help separate the mirror plate  402  and the landing tips  422   a  and  422   b , which helps to overcome the stiction of the mirror plate to the substrate, a well known challenge for micro mirror devices. 
         [0041]    The evaporation or the sublimation of the anti-stiction material  260  in the chambers  250  can result in the deposition and coating of the anti-stiction material on essentially all the surfaces of the micro mirror  400 , including a layer of anti-stiction material  450  on the lower surface of the mirror plate  402  and layers of anti-stiction materials  451   a  and  451   b  on the upper surface of the landing tips  422   a  and  422   b  (for clarity of viewing, the anti-stiction layers are not shown on other surfaces of the micro mirror  400  in  FIG. 4 ). The anti-stiction material  450 ,  451   a  and  451   b  can reduce adhesion and stiction at these surfaces when the mirror plate  402  comes to contact with the upper surfaces of the landing tip  422   a  or  422   b , which allows timely separation between the mirror plate  402  and the landing tip  422   a  or  422   b  when the mirror plate  402  needs to tilted to a new orientation. 
         [0042]    In accordance with another aspect of the present invention, the anti-stiction material  260  can coat a thin and clear film on the surfaces of the micro devices  203  such as the micro mirror  400 . The clear film can be coated on the lower surface of the mirror plate  402  and the upper surface of the landing tips  422   a  and  422   b . The coating can occur on the surface of the reflective upper layer  403   a  of the micro mirror  400  and the side surfaces of the landing tips  422   a  and  422   b . The clear film on the upper surface of the reflective upper layer  403   a  will not substantially alter the reflectivity of the reflective upper layer  403   a.    
         [0043]    After the anti-stiction material is coated on the one or more surfaces of the micro device  290 , the micro device  290  can be tested in situ within the enclosed chamber  250  (step  370 ). For example, external electric signals can be applied to the electric terminals  245  to create an electric voltage between the bottom layer  403   c  of the mirror plate  402  and the step electrodes  421   a  or  421   b . The resultant electrostatic force can tilt the mirror plate  402  to different orientations when the mirror plate  402  comes to contact with a landing tip  422   a  or  422   b . The landing tips  422   a  and  422   b  are stationary relative the substrate  410 . The mirror plate  402  can reflect incident light  430  to form the reflected light  440  in different directions before and after the tilt movement. The reflected light  440  can be measured to evaluate the performance of the micro device  290 . Proper electric signals can also be applied to reverse the tilt movement of the mirror plate  402 . The coated anti-stiction material helps the separation between the mirror plate  402  and the landing tip  422   a  or  422   b . The functionality of the anti-stiction material can be confirmed by measuring the rate of mirror tilt by detecting the reflected light  440 . After the testing of each of the micro devices, the semiconductor wafer  200  can be separated, such as by cutting, dicing, etching or breaking, into individual dies each containing one or more micro devices  290  (step  380 ). Further testing and packaging may be conducted on the individual dies. 
         [0044]    Although multiple embodiments have been described, it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope of the ideas presented herein. For example, the micro devices can be fabricated over the wafer substrate in different configurations depending on the specific function and application of the micro devices. A micro device can include electric circuits having a substantially planar surface, or a three dimensional micro-electrical mechanical structure, such as a hinged and tiltable micro mirror for spatial light modulation. The configurations and materials for the encapsulation device can be varied and selected to be best suitable to each application. 
         [0045]    It is understood that the disclosed systems and methods are compatible with other configurations of LEDs, optical fibers, and the micro mirrors. For example, the micro devices may reside in a flat area or on a step instead of a recessed area over the substrate. Multiple micro devices can be in an encapsulated recess or flat region. The sealing between the encapsulation cover and the upper surface of the substrate can be realized by many techniques and is not limited by plasma surface activated bonding. The disclosed system and methods are also compatible with different numbers and configurations of the electronic pads for input and output signals to the micro devices. The numbers and the locations of the air-tight closed loop interfaces and air-tight cross interfaces can also be varied without deviating from the spirit of the present specification.