Abstract:
A method of making a micro electromechanical gyroscope. A cantilevered beam structure, first portions of side drive electrodes and a mating structure are defined on a first substrate or wafer; and at least one contact structure, second portions of the side drive electrodes and a mating structure are defined on a second substrate or wafer, the mating structure on the second substrate or wafer being of a complementary shape to the mating structure on the first substrate or wafer and the first and second portions of the side drive electrodes being of a complementary shape to each other. A bonding layer, preferably a eutectic bonding layer, is provided on at least one of the mating structures and one or the first and second portions of the side drive electrodes. The mating structure of the first substrate is moved into a confronting relationship with the mating structure of the second substrate or wafer. Pressure is applied between the two substrates so as to cause a bond to occur between the two mating structures at the bonding or eutectic layer and also between the first and second portions of the side drive electrodes to cause a bond to occur therebetween. Then the first substrate or wafer is removed to free the cantilevered beam structure for movement relative to the second substrate or wafer. The bonds are preferably eutectic bonds.

Description:
TECHNICAL FIELD The present invention relates to micro electromechanical (MEM) gyroscopes using dual wafers which are bonded together preferably eutectically.  
         [0001]    1. Related Applications  
           [0002]    This invention is related to other inventions which the subject of separate patent applications filed thereon. See: U.S. patent application Ser. No. ______ entitled “A Single Crystal, Dual Wafer, Tunneling Sensor or Switch with Silicon on Insulator Substrate and a Method of Making Same” (attorney docket 617965-3); U.S. patent application Ser. No. ______ entitled “A Single Crystal, Dual Wafer, Tunneling Sensor and a Method of Making Same” (attorney docket 617975-0); U.S. patent application Ser. No. entitled “A Single Crystal, Dual Wafer, Tunneling Sensor or Switch with Substrate Protrusion and a Method of Making Same” (attorney docket 617337-2); and U.S. patent application Ser. No. ______ entitled “A Single Crystal, Tunneling and Capacitive, Three-Axes Sensor Using Eutectic Bonding and a Method of Making Same” (attorney docket 617808-9), all of which applications have the same filing date as this application, and all of which applications are hereby incorporated herein by reference.  
           [0003]    2. Background of the Invention  
           [0004]    The present invention provides a new process of fabricating a single crystal silicon MEM gyroscopes using low-cost bulk micromachining techniques while providing the advantages of surface micromachining. The prior art, in terms of surface micromachining, uses e-beam evaporated metal that is patterned on a silicon dioxide (SiO 2 ) layer to form the control, self-test, and tip electrodes of a tunneling MEM sensor. A cantilevered beam is then formed over the electrodes using a sacrificial resist layer, a plating seed layer, a resist mold, and metal electroplating. Finally, the sacrificial layer is removed using a series of chemical etchants. The prior art for bulk micromachining has utilized either mechanical pins and/or epoxy for the assembly of multi-Si wafer stacks, a multi-Si wafer stack using metal-to-metal bonding and an active sandwiched membrane of silicon nitride and metal, or a dissolved wafer process on quartz substrates (Si-on-quartz) using anodic bonding. None of these bulk micromachining processes allow one to fabricate a single crystal Si cantilever (with no deposited layers over broad areas on the beam which can produce thermally mismatched expansion coefficients) above a set of tunneling electrodes on a Si substrate and also electrically connect the cantilever to pads located on the substrate. The fabrication techniques described herein provide these capabilities in addition to providing a low temperature process so that CMOS circuitry can be fabricated in the Si substrate before the MEMS sensors are added. Finally, the use of single crystal Si for the cantilever provides for improved process reproductibility for controlling the stress and device geometry.  
           [0005]    MEM gyroscopes may be used in various military, navigation, automotive, and space applications. Space applications include satellite stabilization in which MEM technology can significantly reduce the cost, power, and weight of the presently used gyroscopic systems. Automotive air bag deployment, ride control, and anti-lock brake systems provide other applications for MEM gyroscopes and/or sensor. Military applications include low drift gyros.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0006]    Generally speaking, the present invention provides a method of making a micro electro-mechanical (MEM) gyroscope wherein a cantilevered beam structure and a mating structure are defined on a first substrate or wafer and at least one contact structure and a mating structure are defined on a second substrate or wafer. The mating structure on the second substrate or wafer is of a complementary shape to the mating structures on the first substrate or wafer. A bonding or eutectic layer is provided on at least one of the mating structures and the mating structure are moved into a confronting relationship with each other. Pressure is then applied between the two substrates and heat may also be applied so as to cause a bond to occur between the two mating structures at the bonding or eutectic layer. Then the first substrate or wafer is removed to free the cantilevered beam structure for movement relative to the second substrate or wafer. The bonding or eutectic layer also provides a convenient electrical path to the cantilevered beam for making a circuit with the contact formed on the cantilevered beam.  
           [0007]    In another aspect, the present invention provides an assembly or assemblies for making a single crystal silicon MEM sensor therefrom. A first substrate or wafer is provided upon which is defined a beam structure and a mating structure. A second substrate or wafer is provided upon which is defined at least one contact structure and a mating structure, the mating structure on the second substrate or wafer being of a complementary shape to the mating structure on the first substrate or wafer. A pressure and heat sensitive bonding layer is disposed on at least one of the mating structures for bonding the mating structure defined on the first substrate or wafer with the mating structure on the second substrate in response to the application of pressure and heat therebetween.  
           [0008]    In operation, a Coriolis force is produced normal to the plane of the device by oscillating the beam laterally across the substrate. The side drive electrodes are preferably fabricated with the cantilevered beam on the first substrate and are bonded to the second substrate at the same time that the cantilevered beam is attached. This provides for high alignment accuracy between the cantilevered beam and the side electrodes. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0009]    [0009]FIGS. 1A through 6A depict the fabrication of a first embodiment of the cantilevered beam forming portion of a MEM gyroscope;  
         [0010]    [0010]FIGS. 1B through 6B correspond to FIGS.  1 A- 6 A, but show the cantilevered beam forming portion, during its various stages of fabrication, in plan view:  
         [0011]    [0011]FIGS. 7A through 11A show, in cross section view, the fabrication of the base portion of the gyroscope;  
         [0012]    [0012]FIGS. 7B through 11B correspond to FIGS.  7 A- 9 A but show the fabrication process for the base portion in plan view;  
         [0013]    [0013]FIGS. 12 and 13 show the cantilevered beam forming portion and the base portion being aligned with each other and being bonded together preferably by eutectic bonding; and  
         [0014]    [0014]FIGS. 14A and 15 show the completed MEM gyroscope in cross sectional view, FIG. 15 being enlarged compared to FIG. 14A;  
         [0015]    [0015]FIG. 14B shows the completed MEM gyroscope in plan view;  
         [0016]    [0016]FIGS. 16 and 17 show a modification of the cantilevered beam forming portion wherein the beam is formed on an etch stop layer and also shown the base portion being aligned therewith and being bonded thereto preferably by eutectic bonding;  
         [0017]    [0017]FIGS. 18A and 18 b  show the completed MEM gyroscope in cross sectional view and plan views; and  
         [0018]    [0018]FIG. 19 shows a modification wherein a relatively small ribbon conductor is provided on the cantilevered beam. 
     
    
     DETAILED DESCRIPTION  
       [0019]    Several embodiments of the invention will be described with respect to the aforementioned figures. The first embodiment will be described with reference to FIGS. 1A through 15. A second embodiment will be discussed with reference to FIGS. 16 through 18B. Further modifications are described thereafter.  
         [0020]    The MEM gyroscope shown in the accompanying figures is not drawn to scale, but rather are drawn to depict the relevant structures for those skilled in this art. Those skilled in this art realize that these devices, while mechanical in nature, are very small and are typically manufactured using generally the same type of technology used to produce semiconductor devices. Thus a thousand or more devices might well be manufactured at one time on a silicon wafer. To gain an appreciation of the small scale of these devices, the reader may wish to turn to FIG. 15 which includes size information for the first embodiment of a MEM gyroscope utilizing the present invention. The figure numbers with the letter ‘A’ appended thereto are section views taken as indicated in the associated figure numbers with the letter ‘B’ appended thereto, but generally speaking only those structures which occur at and immediately adjacent the section are shown and not structures which are well behind the section. For example, in FIG. 2A, the portion of the mask  14  which forms the upper arm of the letter E shaped structure seen in FIG. 2B does not appear in FIG. 2A since it is located spaced from the plane where the section is taken; however, the opening  14 - 3  behind the section line which is used to help define one of the two side drive electrodes of the gyroscope is shown. The section views are thus drawn for ease of illustration.  
         [0021]    Turning to FIG. 1A and 1B, a starting wafer for the fabrication of the cantilever is depicted. The starting wafer includes a wafer of bulk n-type silicon (Si)  10  upon which is formed a thin layer of doped p-type silicon  12 . The silicon wafer  10  is preferably of a single crystalline structure having a &lt;100&gt; crystalline orientation. The p-type silicon layer  12  is preferably grown as an epitaxial layer on silicon wafer  10 . The layer  12  preferably has a thickness of in the range of 1 to 20 micrometers (μm), but can have a thickness anywhere in the range of 0.1 μm to 800 μm. Generally speaking, the longer the cantilevered beam is the thicker the beam is. Since layer  12  will eventually form the cantilevered beam, the thickness of layer  12  is selected to suit the length of the beam to be formed.  
         [0022]    Layer  12  in this embodiment is with Boron such that its resistivity is reduced to less than 0.05 Ω-cm and is preferably doped to drop its resistivity to the range of 0.01 to 0.05 Ω-cm. The resistivity of the bulk silicon wafer or substrate  10  is preferably about 10 Ω-cm. Boron is a relatively small atom compared to silicon, and therefore including it as a dopant at the levels needed (10 20 ) in order to reduce the resistivity of the layer  12  tends to induce stress which is preferably compensated for by also doping, at a similar concentration level, a non-impurity atom having a larger atom size, such as germanium. Germanium is considered a non-impurity since it neither contributes nor removes any electron carriers in the resulting material.  
         [0023]    Layer  12  shown in FIGS. 1A and 1B is patterned using well known photolithographic techniques to form a mask layer  14 , patterned as shown, preferably to assume the shape of a capital letter ‘E’, with mesas  14 - 3 , which will be used to help define side drive electrodes for the gyroscope. While the shape of the capital letter ‘E’ is preferred, other shapes can be used. In this embodiment, the outer peripheral portion of the E-shape will form a mating and supporting structure which will be used to join the cantilever portion of the sensor to the base portion and to support the cantilevered beam above the base portion.  
         [0024]    After the mask layer  14  has been patterned as shown in FIGS. 2A and 2B, the wafer is subjected to a plasma etch in order to etch through the exposed thin layer of p-type doped silicon  12  and also to over etch into the silicon wafer  10  by a distance of approximately 500 Å. This etching step defines the outer peripheral portion of the E-shape in layer  12 , a cantilevered beam having a thick portion  12 - 2  and a thin elongated portion  12 - 5  (see FIG. 4B) as well as portions  12 - 3  of the side drive electrodes.  
         [0025]    The mask  14  shown in FIGS. 2A and 2B is then removed and another photoresist layer  16  is applied, which is patterned as shown in FIGS. 3A and 3B by providing two openings therein  16 - 1 ,  16 - 2  plus two openings labeled  16 - 3  which align with the two small portions  12 - 3  of layer  12  which remain due to the aforementioned etching step. Opening  16 - 1  basically follows the outer perimeter of the ‘E’ shape of the underlying thin layer of p-type silicon  12  while opening  16 - 2  is disposed at or adjacent an end of the thick portion  12 - 2  (FIG. 4B) of the interior leg of the ‘E’-shaped p-type silicon layer  12 . The interior leg  12 - 2 ,  12 - 5  will become to the cantilevered beam.  
         [0026]    Layers of Ti/Pt/Au are next deposited over mask  16  and through openings  16 - 1 ,  16 - 2  and  16 - 3  to form a post contact  18 - 1 , a tunnelling tip contact  18 - 2  and two side drive electrode contacts  18 - 3 . The Ti/Pt/Au layers preferably have a total thickness of about 2000 Å. The individual layers of Ti and Pt may have thicknesses in the ranges of 100-200 Å and 1000-2000 Å, respectively. After removal of the photoresist  16 , the wafer is subjected to a sintering step at approximately 520° C. to form an ohmic Ti—Si juncture between contacts  18 - 1  and  18 - 2  and the underlying layer  12 . As will be seen with reference to FIG. 19, the sintering step can be eliminated if a metal layer, for example, is used to connect contacts  18 - 1 ,  18 - 2  and  18 - 3 .  
         [0027]    As another alternative, which does rely on the aforementioned sintering step occurring, post contact  18 - 1  may be formed by layers of Ti and Au (i.e without Pt), which would involve an additional masking step to eliminate the Pt layer from post contact  18 - 1 . However, in this alternative, the sintering would cause Si to migrate into the Au to form an Au/Si eutectic at the exposed portion of post contact  18 - 1  shown in FIGS. 4A and 4B. As a further alternative, the exposed portion of the post contact  18 - 1  shown in FIGS. 4A and 4B could simply be deposited as Au/Si eutectic, in which case the Pt layer in the post contact  18 - 1  could be optionally included. Post contact  18 - 1  may be eliminated if the subsequently described bonding between the cantilevered beam forming portion  2  and the base portion  4  occurs non-eutectically.  
         [0028]    As a result, the exposed portion of the post contact  18 - 1  and the exposed portions  18 - 3  of the side drive electrodes  12 - 2 ,  18 - 3  shown in FIGS. 4A and 4B are formed preferably either by Au or by Au/Si. When the cantilevered beam forming portion  2  and the base portion  4  are mated as shown and described with reference to FIGS. 12 and 13 (and with reference to FIGS. 16 and 17 for a second embodiment) , one of the exposed mating surfaces is preferably a Au/Si eutectic while the other is preferably Au. Thus, exposed mating surfaces  18 - 1 ,  18 - 3  can preferably be either Au and Au/Si if the exposed mating surface on the base portion  4  is the other material, i.e., preferably either Au/Si or Au so that a layer of Au/Si confronts a layer of Au.  
         [0029]    The structures shown in FIGS. 4A and 4B are then covered with a layer of photoresist  20  which, as shown in FIG. 5A, is patterned as shown in FIGS. 5A and 5B, with a opening  20 - 2  therein over tunnelling tip contact  18 - 1 . Those skilled in the art will appreciate that the size of the openings  16 - 1 ,  16 - 2 ,  16 - 3  and  20 - 2  are not drawn to scale on the figures and that openings  16 - 2  and  20 - 2  would tend to be significantly smaller than would be openings  16 - 1  and  16 - 3 - 1 . As such, when a rather thick layer of Au  26 , preferably having a thickness of about 15,000 Å, is deposited on the wafer, it basically clogs opening  20 - 2  (see FIG. 5A). Those skilled in the art will appreciate that there is fill-in at the sides of a mask when a layer such as Au layer  26  is deposited because of an increasing overhang which occurs at the edges of opening  20 - 2  as the deposition process proceeds. Since opening  20 - 2  is rather narrow, the deposited Au  26 , as shown at numeral  26 - 2 , assumes a pyramidal-like or conical-like shape as the opening is clogged with Au. The thickness of the deposition of Au layer  26  is sufficiently thick to assure that layer  26  will close across the top of opening  20 - 2  during the deposition process and so that structure  26 - 2  assumes its pointed configuration.  
         [0030]    The photoresist  20  is then dissolved lifting off the layer  26  formed thereon and leaving the structures depicted by FIGS. 6A and 6B.  
         [0031]    The fabrication of the base portion  4  of this embodiment of the MEM gyroscope will now be described with reference to FIGS. 7A through 11B. Turning to FIGS. 7A and 7B, a wafer  30  of silicon is shown upon which a layer of photoresist has been deposited and patterned (i) to assume preferably the outerperipheral shape of a capital letter ‘E’  50 - 1  complementary to the outer peripheral shape of patterned mask layer  14  (FIG. 2B) and (ii) to define mesas  50 - 3  complementary to the size, shape and location of the first portions  12 - 3 ,  18 - 3  of the side drive electrode formed on the cantilevered beam forming portion  2 . The exposed silicon is then subjected to an etch, etching it back approximately 20,000 Å, to define a protruding portion  30 - 1  of wafer  30  under the patterned mask  50 - 1  of the photoresist and protruding portions  30 - 3  under mesas  50 - 3 . The photoresist mask  50  is then removed and wafer  30  is oxidized to form layers of oxide  52 ,  54  on its exposed surfaces. The oxide layers are each preferably about 1 μm thick. Of course, the end surfaces shown in FIG. 8A are not shown as being oxidized because it is assumed that the pattern shown in FIG. 8A (and the other figures) is only one of a number of repeating patterns occurring across an entire wafer  30 . The oxide includes protruding portions  52 - 1  and  52 - 3  thereof on protruding portions  30 - 1  and  30 - 3  of the wafer  30 .  
         [0032]    Turning to FIGS. 9A and 9B, a layer of photoresist  56  is applied having (i) an opening therein  56 - 1  which again assumes the outerperipheral shape of a capital letter ‘E’, as previously described and (ii) a pair of openings  56 - 3  to aid in the formation of the second portion of the side electrode on wafer  30 . Then, a layer of Ti/Pt/Au  58 , preferably having a thickness of 2,000 Å, is deposited through openings  56 - 1 ,  56 - 3  followed by the deposition of a layer  60  of an Au/Si eutectic preferably with a 1,000 Å thickness. Layers  58 - 1 ,  58 - 3  of Ti/Pt/Au and layers  60 - 1 ,  60 - 3  of the Au/Si eutectic are thus formed. Layers  58 - 1  and  60 - preferably follow the outerperipheral shape of a capital letter ‘E’, as can be clearly seen in FIG. 9B, while layers  58 - 3  and  60 - 3  disposed on the oxided protrusion  52 - 3  define the second portions of the side drive electrodes. The second portions of the side drive electrodes will be mated with the first portions thereof formed on cantilevered beam forming portion  2  in due course. Of course, if the post contact  18 - 1  and the side electrode contacts  18 - 3  (see FIG. 4A) are either formed of an Au/Si eutectic or has an Au/Si eutectic disposed thereon, then layers  60 ,  60 - 1 ,  60 - 3  may be formed of simply Au or simply omitted due to the presence of Au at the exposed layers  58 - 1  and  58 - 3 .  
         [0033]    Photoresist layer  56  is then removed and a layer  62  of photoresist is applied and patterned to have (i) openings  62 - 2 ,  62 - 3 ,  62 - 4  and  62 - 6 , as shown in FIG. 10A, (ii) openings for pads  40 - 1  through  40 - 5  and their associated ribbon conductors  42 ; (iii) an opening for guard ring  44  and its pad, as depicted in FIG. 10B. For the ease of illustration, the opening for guard ring  44  is not shown in FIG. 10A. A layer  38  of Ti/Pt/Au is then deposited over the patterned photoresist layer  62  and through openings  62 - 2 ,  62 - 3 ,  62 - 4  and  62 - 6  therein forming contacts  38 - 2 ,  38 - 3 ,  38 - 4  and  38 - 6  and the photoresist  62  is removed to thereby arrive at the structure shown in FIGS. 11A and 11B. Those contacts are interconnected with their associated pads  40 - 2  through  44 - 4  by the aforementioned ribbon conductors  42 , which contacts  40  and ribbon conductors  42  are preferably formed at the same time as contacts  38 - 3 ,  38 - 4  and  38 - 2  are formed. The outerperipheral layers  58 - 1  and  60 - 1  are also connected with pad  40 - 1  by an associated ribbon conductor  42 . The protrusion  30 - 1 , which preferably extends approximately 20,000 Å high above the adjacent portions of wafer  30 ′, and the relatively thin layers  58 - 1  and  60 - 1  form the mating structure for the base portion  4 .  
         [0034]    Contacts  38 - 6  are preferably triangularly shaped with their hypotenuses confronting each other and positioned such that the hypotenuses will lie under a centerline of the elongated cantilevered beam  12 - 5  when the cantilevered beam forming portion  2  is joined to the base portion  4 .  
         [0035]    Pad  40 - 1  is connected to layers  58 - 1  and  60 - 1  and provides a pad for a beam bias voltage. Pad  40 - 2  is connected to tip contact  38 - 2  and provides a pad for the tip contact  38 - 2 . Pad  40 - 3  is connected to contacts  38 - 3  and provides a pad for the side drive electrodes  38 - 5 ,  58 - 3  and  60 - 3  (when the two portions  2 ,  4  are bonded together). Pad  40 - 4  is connected to contact  38 - 4  and provides a pad for device testing. Pad  40 - 5  is connected to contact  38 - 5  and provides a pad for a pull down voltage. Pads  40 - 6  are connected to the two side sense contacts  38 - 6  and provides pads for the side sense contacts  38 - 6 .  
         [0036]    Turning to FIG. 12, the cantilevered beam forming portion  2  is now bonded to base portion  4 . As is shown in FIG. 12, the two wafers  10  and  30  are brought into a confronting relationship so that their mating structures  18 - 1 ,  30 - 1 ,  58 - 1  and  60 - 1  are in alignment and so the first and second portions of the side drive electrode are in alignment and so that (i) layers  18 - 1  and  60 - 1  properly mate with each other and (ii) layers  18 - 3  and  60 - 3  properly mate with each other. Pressure and heat (preferably by applying a force of 5,000 N at 400° C. between three inch wafers  2 ,  4  having 1000 sensors disposed thereon) are applied so that eutectic bonding occurs between layers  18 - 1  and  60 - 1  and between layers  18 - 3  and  60 - 3  as shown in FIG. 13. Thereafter, silicon wafer  10  is dissolved so that the MEM sensor structure shown in FIG. 14 is obtained. The p-type silicon layer  12  includes a portion  12 - 2  which serves as the cantilevered beam and another portion which is attached to the base portion  4  through the underlying layers. The gold contact  26 - 2  is coupled to pad  40 - 1  by elements  18 - 2 ,  12 - 2 ,  12 - 1 ,  18 - 1 ,  60 - 1 ,  58 - 1  and its associated ribbon conductor  42 . If the bonding is done non-eutectically, then higher temperatures will be required.  
         [0037]    Protrusion  30 - 1  and layers  18 - 1 ,  60 - 1 , and  58 - 1  have preferably assumed the shape of the outerperpherial edge of a capital letter ‘E’ and therefore the cantilevered beam of the MEM gyroscope is well protected by this physical shape. After performing the bonding, silicon layer  10  is dissolved away to arrive at the resulting MEM sensor shown in FIGS. 14A and 14B. The silicon can be dissolved with ethylenediamine pyrocatechol (EDP). This leaves only the Boron doped silicon cantilevered beam  12  with its associated contact  26 - 2  and its supporting or mating structure  18 - 1  bonded to the base structure  4 . Preferable dimensions for the MEM sensor are given on FIG. 15. The beam as preferably has a length of 200 to 300 μm (0.2 to 0.3 mm).  
         [0038]    [0038]FIG. 15 is basically identical to FIG. 14, but shows the MEM sensor in somewhat more detail and the preferred dimensions of the MEM sensor are also shown on this figure.  
         [0039]    Instead of using EDP as the etchant, plasma etching can be used if a thin layer  11  of SiO 2  is used, for example, as an etch stop between layer  12  and substrate  10 . FIGS. 16, 17,  18 A and  18 B are similar to FIGS. 12, 13,  14 A and  14 B, respectively, but differ in that a thin layer of SiO 2  is shown being utilized as an etch stop between layer  12  and substrate  10 . Such a thin layer  11  of SiO 2  can be formed by the implantation of oxygen so that layer  12  retains the same crystalline structure of wafer  10 . In this case the layer  12  may be undoped or may be doped with Boron or other dopants. The plasma etch in this case is a two step process. A first etch, which preferentially etches silicon, removes substrate  10  and a second etch, which preferentially etches SiO 2 , removes the etch stop layer  11  to arrive at the structure shown in FIGS. 18A and 18B. If layer  12  is undoped or nor sufficiently doped to provide proper conductivity (for example, to a level less than 0.05 Ω-cm), then a thin ribbon conductor  18 - 4  should be affixed to layer  12  as shown in FIG. 19 to interconnect contacts  18 - 1 ,  18 - 2  and  18 - 3 . Generally speaking, it is preferred to use the conductivity in the cantilevered beam, by sufficiently doping same, to interconnect contacts  18 - 1 ,  18 - 2  and  18 - 3  rather than a separate ribbon conductor  18 - 4  since the existence of a ribbon conductor on the beam  12  may interfere with its freedom of movement in response to acceleration events which a gyroscope should detect. If a ribbon conductor  18 - 4  is used, then is should be kept as small as practicable in both height and width to minimize its effect on the cantilevered beam. It will be recalled that in the embodiment of FIGS.  1 A- 15 , that after the layer of Ti/Pt/Au  18  was applied forming contacts  18 - 1 ,  18 - 2  and  18 - 3 , they were sintered in order to form an ohmic bond with Boron-doped cantilever  12 . It was noted that sintering could be avoided by providing a ribbon conductor between the contacts. The just-described ribbon conductor  18 - 4  has the advantage of omitting any steps needed to form ohmic contacts with the beam.  
         [0040]    It can be seen that the Si layer  12  formed on silicon wafer  10  may be (i) doped with Boron or (ii) may be either undoped or doped with other impurities. If doped with Boron, layer  12  is preferably formed by epitaxial growth. If layer  12  is either undoped or doped with other impurities, it is preferably formed by methods other than epitaxial growth on substrate  10  and a thin etch stop layer  11  is then preferably formed between the thin Si layer  12  and the silicon substrate or wafer  10 . This configuration is called Silicon On Insulator (SOI) and the techniques for making an SOI structure are well known in the art and therefor are not described in detail herein. The etch stop layer  11 , if used, is preferably a layer of SiO 2  having a thickness of about 1-2  82  m and can then be made, for example, by the implantation of oxygen into the silicon wafer  10  through the exposed surface so as to form the etch stop layer  11  buried below the exposed surface of the silicon wafer  10  and thus also define, at the same time, the thin layer of silicon  12  adjacent the exposed surface. This etch stop layer  11  is used to release the cantilevered beam from wafer  10  by the aforementioned two step plasma etch process. If layer  12  is doped with Boron, it is doped to reduce the resistivity of the epitaxial layer  12  to less than 1 Ω-cm. At that level of Boron doping the epitaxial layer  12  can resist a subsequent EDP etch used to release the cantilevered beam from wafer  10  and thus an etch stop layer is not needed. Preferably, the level of doping in layer  12  reduces the resistivity of layer  12  to less than 0.05 Ω-cm.  
         [0041]    The structures shown in the drawings has been described in many instances with reference to a capital letter ‘E’. However, this shape is not particularly critical, but it is preferred since it provides good mechanical support for the cantilevered structure formed primarily by beam portion of layer  12 . Of course, the shape of the supporting and mating structure around cantilever beam  12  can be changed as a matter of design choice and it need not form the perimeter of the capital letter ‘E’, but can form any convenient shape, including circular, triangular or other shapes as desired.  
         [0042]    This description includes references to Ti/Pt/Au layers. Those skilled in the art will appreciate that this nomenclature refers to a situation where the Ti/Pt/Au layer comprises individual layers of Ti, Pt and Au. The Ti layer promotes adhesion, while the Pt layer acts as a barrier to the diffusion of Si from adjacent layers into the Au. Other adhesion layers such as Cr and/or other diffusion barrier layers such as a Pd could also be used or could alternatively be used. It is often desirable to keep Si from migrating into the Au, if the Au forms a contact, since if Si diffuses into an Au contact it will tend to form SiO 2  on the exposed surface and, since SiO 2  is a dielectric, it has deleterious effects on the ability of the Au contact to perform its intended function. As such, a diffusion barrier layer such as Pt and/or Pd is preferably employed between an Au contact and adjacent Si material. However, an embodiment is discussed wherein the diffusion barrier purposefully omitted to form an Au/Si eutectic.  
         [0043]    The nomenclature Au/Si or Au—Si refers a mixture of Au and Si. The Au and Si can be deposited as separate layers with the understanding that the Si will tend to migrate at elevated temperature into the Au to form an eutectic. However, for ease of manufacturing, the Au/Si eutectic is preferably deposited as a mixture except in those embodiments where the migration of Si into Au is specifically relied upon to form Au/Si.  
         [0044]    Many different embodiments of a MEM device have been described. Many more embodiments can certainly be envisioned by those skilled in the art based the technology disclosed herein. But in all cases the base structure  4  is united with the cantilevered beam forming structure  2  by applying pressure and preferably also heat, preferably to cause an eutectic bond to occur between the then exposed layers of the two structures  2  and  4 . The bonding may instead be done non-eutectically, but then higher temperatures must be used. Since it is usually desirable to reduce and/or eliminate high temperature fabrication processes, the bonding between the two structures  2  and  4  is preferably done eutectically and the eutectic bond preferably occurs between confronting layers of Si and Au/Si.  
         [0045]    In operation, the side electrodes are used to create a force on the cantilevered beam that then oscillates laterally across the substrate in response thereto. When the gyroscopic sensor is rotated about its axis (i.e. the axis of the cantilevered beam), a Coriolis force is produced normal to the plane of the substrate. This force is detected as an oscillating tunneling current by the control electrodes in a servo loop. The servo loop responds by oscillating the control electrode voltage for force rebalancing operation at the lateral resonant frequency of the cantilevered beam. The side drive electrodes are preferably fabricated with the cantilevered beam on the first substrate and are bonded to the second substrate at the same time that the cantilevered beam is attached. This provides for high alignment accuracy between the cantilevered beam and the side electrodes.  
         [0046]    Having described the invention with respect to certain preferred embodiments thereof, modification will now suggest itself to those skilled in the art. The invention is not to be limited to the foregoing description, except as required by the appended claims.