Abstract:
Briefly, embodiments of the present invention provide an electro-mechanical device, for example, a Micro-Electro-Mechanical Systems (MEMS) device, for example, a low-loss Film Bulk Acoustic Resonators (FBAR) filter, and a process to produce the same.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Electro-mechanical devices, for example, Micro-Electro-Mechanical Systems (MEMS) devices may include ultra-small mechanical components.  
         [0002]     Certain MEMS devices, for example, Film Bulk Acoustic Resonator (FBAR) Radio Frequency (RF) filters, may include a membrane attached to a substrate, for example, a Silicon substrate. One or more cavities may be formed in the substrate, for example, to allow freedom of movement of the membrane and/or to reduce loss of RF energy during operation.  
         [0003]     A conventional process for producing such MEMS devices may include depositing the membrane and/or other layers on top of the substrate, and then forming the cavities in the substrate. Since access to the substrate is obscured by the membrane and/or other layers, release holes may be created in the device to allow injection of etching material to form the cavities in the substrate by a dry or wet-etching process.  
         [0004]     Thus, the cavities may be fluidically connected, for example, via the release holes, with an environment surrounding the MEMS device, for example, before the MEMS device is packaged. This may result in contamination of the cavities and/or stiction of the membrane, i.e., the membrane sticking to the surface of the cavity, for example, as a result of the wet-etching process and/or due to environmental humidity.  
         [0005]     Contamination of the cavities and/or stiction of the membrane may affect the operation of the MEMS device.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with features and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanied drawings in which:  
         [0007]      FIG. 1  is a schematic illustration of a Micro-Electro-Mechanical Systems (MEMS) device in accordance with exemplary embodiments of the present invention;  
         [0008]      FIG. 2  is a schematic flowchart depicting a process for producing a MEMS device in accordance with exemplary embodiments of the present invention; and  
         [0009]      FIGS. 3A-3I  are schematic illustrations of a MEMS device at different stages in the process of  FIG. 2 .  
         [0010]     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits may not have been described in detail so as not to obscure the present invention.  
         [0012]     Although some exemplary embodiments of the invention may refer to a Micro-Electro-Mechanical Systems (MEMS) device, it will be appreciated by those skilled in the art that aspects of the present invention may be applicable to any other electro-mechanical device, for example, a Nano-Electro-Mechanical Systems (NEMS) device.  
         [0013]     Although the present invention is not limited in this regard, the term “MEMS device” as used herein may be understood to include, among other things, any suitable Micro-Electro-Mechanical Systems device, for example, a Film Bulk Acoustic Resonator (FBAR) filter, a FBAR Radio Frequency (RF) filter, a RF switch, a varactor, a tunable capacitor, or any other MEMS device where it may be relevant to apply the principles of the present invention. Although an exemplary embodiment of the present invention may include a FBAR RF filter, it is presented herein only as an example of applying the principles of the present invention to a MEMS device; the present invention is not limited in this regard, and its principles may be applied to other suitable MEMS devices.  
         [0014]     It will be appreciated that the terms “top” and “bottom” may be used herein for exemplary purposes only, to illustrate the relative positioning or placement of certain components, and/or to indicate a first and a second component. The terms “top” and “bottom” as used herein do not necessarily indicate that a “top” component is above a “bottom” component, as such directions and/or components may be flipped, rotated, moved in space, placed in a diagonal orientation or position, placed horizontally or vertically, or similarly modified.  
         [0015]     It will be appreciated that the term “sealed cavity” as used herein may refer to a cavity being isolated, i.e., fluidically disconnected, from an environment, for example, air surrounding an element containing the cavity, such that any contents of the sealed cavity may not be in direct contact with the environment.  
         [0016]     Reference is made to  FIG. 1 , which schematically illustrates a MEMS device  100  in accordance with exemplary embodiments of the present invention.  
         [0017]     According to some exemplary embodiments of the invention, device  100  may be used, for example, as a FBAR RF filter, as is known in the art. Device  100  may include a membrane  112  attached to a support structure  101  including at least one sealed cavity  116 , as described in detail below.  
         [0018]     According to some exemplary embodiments of the invention, device  100  may further include one or more bottom conductors  106  associated with membrane  112  and/or support structure  101 . Device  100  may also include one or more top conductors  110  associated with membrane  112 . Optionally, device  100  may include one or more wafer vias  108 .  
         [0019]     According to exemplary embodiments of the invention, support structure  101  may include a cap layer  114  having a first, for example, top, surface  107  attached to membrane  112  and a second, for example, bottom, surface  109  attached to a base structure  103 . Sealed cavity  116  may be encapsulated between surface  109  and base structure  103 .  
         [0020]     According to some exemplary embodiments of the invention, base structure  103  may include two or more protrusions  104  attached to a base substrate  102  and separating between base substrate  102  and cap layer  114 . Base substrate  103  may be formed of any suitable material, for example a semiconductive material, for example, Silicon. Protrusions  104  may be formed of any suitable material, for example, an insulating material, for example, Silicon Oxide. Although the present invention is not limited in this regard, in exemplary embodiments of the present invention protrusions  104  may have a thickness of between 0.05 and 10 micrometers.  
         [0021]     According to other embodiments, base substrate  102  and protrusions  104  may be integrally formed, for example, from Silicone.  
         [0022]     According to exemplary embodiments of the invention, membrane  112  may be formed of any suitable material, for example, Aluminum Nitride, which may be suitable for FBAR devices, any other piezoelectric material, for example, Zinc Oxide, or any other suitable material. Although the present invention is not limited in this regard, in exemplary embodiments of the present invention membrane  112  may have a thickness of between 0.05 and 100 micrometers. Furthermore, in embodiments of the present invention, membrane  112  may be constructed in any suitable shape or form, and may include any suitable components, as may be required in accordance with specific implementations and/or designs.  
         [0023]     According to exemplary embodiments of the invention, cap layer  114  may be formed of a selectively permeable material, for example, Aluminum Nitride, which may be permeable only to certain materials under predetermined conditions, for example, as described below.  
         [0024]     According to some exemplary embodiments of the invention, cap layer  114  may be formed of a piezoelectric material, for example, Aluminum Nitride or Zinc Oxide, similar to the material of membrane  112 . However, according to other embodiments cap layer  114  may be formed of any other suitable material e.g., similar to or different than the material of membrane  112 .  
         [0025]     Conductors  106  and/or  110  may be formed of any suitable conductive material, for example, Aluminum. In an embodiment of the present invention, conductors  106  and/or  110  may be used, for example, to electrically connect device  100  to other components and/or circuits of a device and/or a system incorporating device  100 , using electrical contacts (not shown), vias  108  and/or other conducting elements (not shown). Vias  108  may include any suitable conductive, for example, metallic, via.  
         [0026]     It will be appreciated by persons skilled in the art that, in exemplary embodiments of the present invention, sealed cavity  116  may be isolated, i.e., fluidically disconnected, from the environment, for example, the environment surrounding device  101 .  
         [0027]     Accordingly, it will be appreciated by persons skilled in the art, that cavity  116  may be protected from undesired conditions of the environment, for example, humidity, in contrast to conventional unsealed cavities which are fluidically connected to the environment, for example, via one or more release holes.  
         [0028]     It will also be appreciated by persons skilled in the art that, although the above description with reference to the schematic illustration of  FIG. 1  may depict a generally planar MEMS device and/or components placed generally parallel to each other, the present invention is not limited in this regard. Embodiments of the present invention may include MEMS devices that are not planar, and/or components that are not parallel or generally parallel to each other.  
         [0029]     Reference is made to  FIG. 2 , which schematically illustrates a flowchart of a process for producing a MEMS device, for example, device  100  ( FIG. 1 ) according to exemplary embodiments of the invention, and to  FIGS. 3A-3I , which schematically illustrate exemplary stages in the process of  FIG. 2  and exemplary components useful in understanding the process.  
         [0030]     Although the present invention is not limited in this regard, the term “producing” as used herein with reference to an item, may be understood to include, inter alia, manufacturing or assembling the item, providing a pre-fabricated item, or processing a partly formed item.  
         [0031]     According to exemplary embodiments of the invention, the process may include producing a base structure including one or more recesses, as indicated at block  202  of  FIG. 2 . As shown in  FIG. 3A , according to some exemplary embodiments of the invention, a base structure  242  may include one or more recesses  245  formed between two or more protrusions  243 , for example, formed of silicon Oxide, attached to a base substrate  244 , for example, formed of a semiconductive material, for example, Silicon. Producing the base structure may include depositing a layer of, for example, Silicone Oxide onto base substrate  244 , for example, using any suitable method, for example, a Plasma Enhanced Chemical Vapor Deposition (PECVD) method or a sputtering method, as are known in the art. Producing the base structure may also include forming recesses  245  using any material removing method, for example, any suitable photolithographic and/or etching process, for example, a dry etching process, as are known in the art.  
         [0032]     As indicated at block  204  of  FIG. 2 , the process may also include depositing a layer of a sacrificial material onto base structure  242 , for example, using a suitable spin coating process, as is known in the art. According to some exemplary embodiments of the invention, the sacrificial material may include the Unity™ sacrificial polymer available from Promerus Electronic Materials of Ohio, USA, or any other suitable sacrificial material, e.g. polymer. As shown in  FIG. 3B , a resulting part  250  of the above operations may include a layer  251  of the sacrificial material filling recesses  245 . Layer  251  may additionally cover at least some of protrusions  243 . According to exemplary embodiments of the invention, the process may also include performing a solvent flash process including, for example, heating part  250  to a temperature of approximately 100° C. for approximately 5 seconds, for example, by placing part  250  on a hotplate. The process may also include performing a cure process, for example, as is known in the art, to prevent oxidation of layer  251 . The cure process may include, for example, heating part  250 , for example, in a N 2  atmosphere, to a temperature of approximately 300° C. for approximately two hours.  
         [0033]     As indicated at block  206  of  FIG. 2 , the process may further include removing an excess part of layer  251  above protrusions  243 , for example, using any suitable polishing method as is known in the art As shown in  FIG. 3C , a resulting part  255  of the above operations may include base structure  242  having recesses  245  substantially filled with the sacrificial material and having substantially none of the sacrificial material on a top surface  256  of part  255 .  
         [0034]     As indicated at block  208  of  FIG. 2 , the process may continue with depositing a cap layer on top of part  255 , for example, using a suitable deposition process, as is known in the art. According to some exemplary embodiments of the invention, the cap layer may be formed of a generally non-permeable material, which may be selectively permeable to the sacrificial material under predetermined conditions, for example, of temperature and/or pressure as described below. For example, the cap layer may be formed of Aluminum Nitride or Zinc Oxide. As shown in  FIG. 3D , a resulting part  260  of the above operations may include a cap layer  261  attached to protrusions  243  such that the sacrificial material is encapsulated between layer  261  and base structure  242 .  
         [0035]     As indicated at block  210  of  FIG. 2 , the process may continue with removing the sacrificial material encapsulated between layer  261  and base structure  242 . In exemplary embodiments of the present invention, removing the sacrificial material may include causing at least part of the sacrificial material to permeate through selectively permeable cap layer  261 . Although the present invention is not limited in this regard, causing at least part of the sacrificial material to permeate through the cap layer may include, for example, heating part  260 . For example, part  260  may be placed in a furnace, for example, a Nitrogen or Hydrogen Quartz tube furnace as is known in the art, at a temperature suitable for transforming the sacrificial material into a gaseous form. For example, part  260  may be heated to a temperature of approximately 400° C. if a Unity™400 sacrificial polymer is used. It will be appreciated that any other suitable methods may be implemented for removing at least most of the sacrificial material, for example, if a different sacrificial material, cap layer and/or base substrate are used. As shown in  FIG. 3E , a resulting support structure  265  of the above operations may include one or more sealed cavities  262  encapsulated between cap layer  261  and base structure  242 .  
         [0036]     As indicated at block  212  of  FIG. 2 , the process may continue with forming at least one bottom conductor  271  on a top surface  272  of support structure  265 . Forming the at least one conductor may include using any depositing and/or patterning methods, for example, sputtering, etching and/or photolithography, as are known in the art. As shown in  FIG. 3F , a resulting part  270  of the above operations may include at least one conductor  271  attached to surface  272 .  
         [0037]     As indicated at block  214  of  FIG. 2 , the process may continue with applying a membrane  276  to surface  272 . The membrane may be applied using any depositing and/or patterning methods, as are known in the art. As shown in  FIG. 3G , a resulting part  275  of the above operations may include membrane  276  attached to surface  272 .  
         [0038]     As indicated at block  216  of  FIG. 2 , the process may continue with forming at least one top conductor  278  on top of a surface  281  of membrane  276 . The at least one conductor may be formed using any depositing and/or patterning methods, for example, sputtering, etching and/or photolithography, as are known in the art. As shown in  FIG. 3H , a resulting part  280  of the above operations may include at least one conductor  278  attached to membrane  276 .  
         [0039]     As indicated at block  218  of  FIG. 2 , the process may continue with creating at least one via  289  in membrane  276 , for example, using any suitable method, as is known in the art. According to some exemplary embodiments, one or more conductors  291  may be formed on top of conductors  278  and/or on top of surface  281 , for example, after creating vias  289 . As shown in  FIG. 3I , a resulting MEMS device  290  of the above operations may include conductors  271 ,  278  and/or  291  associated with, for example, at least partially attached to, membrane  276 .  
         [0040]     It will be appreciated that sealed cavities  262  may be isolated from the environment surrounding device  290 .  
         [0041]     It is noted that embodiments of the present invention may include units and/or sub-units, which may be separate of each other or combined together, and may be implemented using specific, multi-purpose or general devices as known in the art.  
         [0042]     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents may occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.