Membrane-based microelectromechanical system (mems) device having ruthenium-based contact surface material built on a substrate

Abstract

Methods of fabricating and packaging ohmic microelectromechanical system (MEMS) switch devices can include constructing a switch device on an insulating substrate. The switch device can have contacts composed of a platinum group metal. The methods can also include forming an oxide layer of the platinum group metal on an outer surface of each of the one or more contacts. The methods can also include bonding an insulating cap to the insulating substrate to hermetically seal the switch device. The bonding can occur in an atmosphere having an oxygen proportion in a range of 0.5% to 30%, such that after the switch device has been hermetically sealed within a sealed cavity, the atmosphere within the sealed cavity has an oxygen proportion in a range of 0.5% to 30%. The platinum group metal can be ruthenium, and the oxide layer of the platinum group metal can be ruthenium dioxide.

Description

[0001] Related applications

[0002] This application is a continuation-to-file of U.S. Application No. 16 / 832,408, filed March 27, 2020. The entire teachings of the above application are incorporated herein by reference. Background Technology

[0003] Devices such as microelectromechanical systems (MEMS) switches typically require encapsulation to protect their microscale features from environmental contaminants. These packages are usually discrete or formed via wafer bonding processes. When exposed to uncontrolled operating environmental conditions, MEMS switches may not operate reliably and consistently. Moisture and contamination can lead to a lack of initial performance or an increase in premature device failure. Therefore, it is common practice to enclose such devices in protective packages that at least partially isolate the internal device environment from the external environment. The processes associated with encapsulating the device within a protective package are critical for creating reliable, durable, hermetically sealed switching devices.

[0004] For example, examples of prior art MEMS switches with RuO2 contacts can be found in U.S. Patent Nos. 7,968,364; 8,124,436; 9,583,294; 9,784,048; 10,388,468 and U.S. Patent Application Publication No. 2007 / 0115082, which are constructed on a silicon substrate and sealed in a hermetically sealed package. Summary of the Invention

[0005] Embodiments of the present invention are directed to hermetically sealed bonded wafer stacks comprising microelectromechanical systems (MEMS) switches, wherein the MEMS switches comprise ruthenium oxide (e.g., RuO2) contacts which are housed in a sealed, isolated environment containing oxygen, or a mixture of oxygen, nitrogen, and / or rare gases.

[0006] This document describes an example embodiment of a MEMS switching device fabricated on a substrate, using stoichiometric ruthenium dioxide (RuO2) with a ruthenium dioxide structure as the contact surface material. The MEMS switching device is hermetically sealed via a bonding process (e.g., thermocompression (TC) wafer bonding) in an environment containing trace amounts of oxygen (O2) and other inert gases (e.g., argon (Ar) and / or nitrogen (N2)). The contact material can be Ru, or a metal stack with Ru as both the top and exposed contact material, or a Ru alloy. The example embodiment also describes a process flow for creating a RuO2 (conductive oxide) contact surface formed during a pre-bonding, oxygen plasma ashing cleaning process on a glass substrate. Excited oxygen ions generated by the plasma effectively react with Ru atoms on the top surface of the contact material to create a high-quality thin layer of RuO2 generated during plasma ashing cleaning. The resulting RuO2 contacts enable the MEMS switching device to maintain low contact resistance values ​​throughout billions of switching cycles.

[0007] The example implementation also describes several device enhancement techniques. One technique involves encapsulating oxygen inside the cavity to reduce the accumulation of organic contaminants on the contact surfaces, which improves manufacturing yield and switching device life. Another enhancement technique is pre-bonded oxygen heat treatment to increase the thickness of the RuO2 contacts. Inert gases can be added to the sealed environment to further improve the switch life.

[0008] In example implementations, MEMS switching devices can be fabricated on wafer-based substrates, such as silicon, silicon dioxide (SiO2), fused silica, silica glass, quartz, sodium-doped glass, borosilicate glass, sapphire, SOI, etc. Prior to the thermocompression (TC) bonding process, the RuO2 contact surface material can be created by oxygen plasma ashing of the glass substrate and the deposition of Ru contact material. The typical expectation of oxygen plasma ashing is to clean any residual organic material on the substrate, including the contact surfaces. A clean, stoichiometric oxide contact surface results in low and stable contact resistance. Additional processing steps, such as introducing oxygen during the pre-bonding temperature ramping stage or during the mechanical bonding stage, will further solidify and thicken the RuO2 contact layer.

[0009] In one aspect, the present invention can be a method for manufacturing and packaging an ohmic microelectromechanical system (MEMS) switching device, the method comprising the steps of: constructing the ohmic MEMS switching device on a substrate. The ohmic MEMS switching device may have one or more contacts made of platinum group metals. In a first chamber, the method may further comprise the step of: forming an oxide layer of platinum group metals on the outer surface of each of the one or more contacts. In a second chamber, the method may further comprise the step of: bonding a cap to the substrate, thereby hermetically sealing the ohmic MEMS switching device within a sealed cavity formed by the cap and the substrate. This bonding may occur in a bonding atmosphere having an oxygen content in the range of 0.05% to 30%, such that after the ohmic MEMS switching device has been hermetically sealed within the sealed cavity, the cavity atmosphere within the sealed cavity has an oxygen content in the range of 0.05% to 30%.

[0010] In an embodiment, the substrate and the cover may each comprise an insulating material. The platinum group metal may be ruthenium (Ru), and the oxide layer of the platinum group metal may be ruthenium dioxide (RuO2). The steps of constructing the ohmic MEMS switching device may further include: forming the ohmic MEMS switching device on the substrate using a thin-film microfabrication process. The step of forming the platinum group metal oxide layer on the outer surface of each of the one or more contacts may include: performing an oxygen plasma ashing process on the ohmic MEMS switching device. The method may further include the step of: after forming the platinum group metal oxide layer on the outer surface of the one or more contacts, performing an oxygen plasma ashing cleaning process on the ohmic MEMS switching device to enhance the platinum group metal oxide layer on the outer surface of the one or more contacts.

[0011] The bonding atmosphere may have an oxygen content in the range of 0.05% to 30%. The step of bonding the cap to the substrate may further include: subjecting the cap and the substrate to a bonding temperature, and pressing the cap and the substrate together using a bonding force according to a profile representing the bonding temperature and bonding force over time.

[0012] The substrate may be one of a plurality of substrates on the first wafer, and the cover may be one of a plurality of covers on the second wafer. The step of bonding the cover to the substrate may further include: subjecting the first wafer and the second wafer to a bonding temperature, and pressing the first wafer and the second wafer together using a bonding force according to a distribution map characterizing the bonding temperature and bonding force relative to time. The bonding atmosphere may further include one or both of (1) nitrogen (N2) and (ii) an inert gas.

[0013] In another aspect, the present invention can be a switching device comprising: an ohmic microelectromechanical system (MEMS) switching device configured on a substrate. The ohmic MEMS switching device may have one or more contacts made of platinum group metals. The switching device may further include: an oxide layer of platinum group metals formed on the outer surface of each of the one or more contacts; and a cap disposed on the substrate and bonded to the substrate to form a hermetically sealed cavity enclosing the ohmic MEMS switching device. The cavity atmosphere may have an oxygen content in the range of 0.05% to 30%.

[0014] The substrate and the cover may each include an insulating material. The platinum group metal may be ruthenium (Ru), and the oxide layer of the platinum group metal may be ruthenium dioxide (RuO2). Ohmic MEMS switching devices can be formed on the substrate using thin-film microfabrication processes. An oxide layer of the platinum group metal can be formed on the outer surface of each of the one or more contacts on the ohmic MEMS switching device using an oxygen plasma ashing process. After the platinum group metal oxide layer has been formed on the outer surface of the one or more contacts, an oxygen plasma ashing cleaning process can be used on the ohmic MEMS switching device to enhance the platinum group metal oxide layer.

[0015] The cavity atmosphere within the sealed chamber can have an oxygen content ranging from 0.05% to 30%. To bond the cap to the substrate, the cap and substrate can be subjected to a bonding temperature, and the cap and substrate can be pressed together using bonding pressure, based on a time-dependent distribution map of bonding temperature and bonding pressure. The insulating substrate can be one of a plurality of insulating substrates on a first wafer, and the insulating cap can be one of a plurality of insulating caps on a second wafer.

[0016] To bond the insulating cap to the insulating substrate, the first and second insulating wafers can be subjected to a bonding temperature, and the first and second insulating wafers can be pressed together using bonding pressure, based on a distribution map of bonding temperature and bonding pressure relative to time. The cavity atmosphere may also include one or both of (1) nitrogen (N2) and (ii) inert gases.

[0017] In another aspect, the present invention can be a method for manufacturing and packaging an ohmic microelectromechanical system (MEMS) switching device, the method comprising the steps of: constructing the ohmic MEMS switching device on a fused silica substrate using a thin-film microfabrication process. The ohmic MEMS switching device may have one or more contacts made of ruthenium (Ru). The method may further comprise the steps of: forming a ruthenium dioxide (RuO2) layer on the outer surface of each of the one or more contacts in a first chamber, and bonding a fused silica cap to the fused silica substrate in a second chamber, thereby hermetically sealing the ohmic MEMS switching device within a sealed cavity formed by the cap and the substrate. This bonding may occur in a bonding atmosphere having an oxygen content in the range of 0.05% to 30%, such that after the ohmic MEMS switching device has been hermetically sealed within the sealed cavity, the cavity atmosphere within the sealed cavity has an oxygen content in the range of 0.05% to 30%. The method may further include the following steps: after RuO2 is formed on the outer surface of the one or more contacts, an oxygen plasma ashing process is performed on the ohmic MEMS switching device to enhance the RuO2 on the outer surface of the one or more contacts. Attached Figure Description

[0018] This patent or application document contains at least one drawing executed in color. A copy of the patent or application disclosure with color illustrations is provided by the Patent Office upon request and payment of the necessary fees.

[0019] The foregoing will become apparent from the following more detailed description of the exemplary embodiments illustrated in the accompanying drawings, in which the same reference numerals refer to the same parts throughout the different views. The drawings are not necessarily drawn to scale, but rather focus on illustrating the embodiments.

[0020] Figure 1A A detailed cross-section of an exemplary embodiment of the switching device according to the present invention is shown.

[0021] Figure 1B It shows Figure 1A An isolated view of the substrate portion of the switching device shown.

[0022] Figure 1C It shows Figure 1A An isolated view of the cover portion of the switch device shown.

[0023] Figure 1D It shows Figure 1A An enlarged view of the contact area of ​​the switching device shown.

[0024] Figure 2An example implementation of the process flow for fabricating and bonding a glass substrate wafer and a glass cover wafer for hosting MEMS switches is described.

[0025] Figure 3 An example embodiment of the thermally compressed (TC) bond distribution map according to the present invention is shown.

[0026] Figure 4A An example embodiment according to the invention is shown, which includes allowing an oxygen-containing gas to flow into the bonding chamber.

[0027] Figure 4B An example embodiment according to the invention is shown, which includes the inflow of a nitrogen-containing gas into the bonding chamber.

[0028] Figure 4C An example embodiment according to the invention is shown, which includes the inflow of a gas containing a rare inert gas into the bonding chamber.

[0029] Figure 5A , Figure 5B and Figure 5C An example embodiment of the invention is shown, which involves a pretreatment step to form a RuO2 contact layer. Detailed Implementation

[0030] The following is a description of an example implementation.

[0031] All patents, published applications, and teachings cited in this article are incorporated by way of their entirety.

[0032] Ruthenium (Ru) has been used as a contact material and ruthenium dioxide (RuO2) as a contact surface material in various mechanical relays and reed switches since the 1960s. In addition to low and stable contact resistance, RuO2 contacts exhibit desirable mechanical properties such as extremely high hardness, good corrosion resistance, and abrasion resistance. In thermal switching applications (i.e., opening or closing switch contacts when transmitting signals), RuO2 demonstrates resistance to high-intensity arc discharges and resistance to adhesion or pitting corrosion. Although the example embodiments described herein depict Ru contacts with RuO2 contact surface material, other embodiments may utilize contacts comprising any platinum group metal (e.g., Ru, Rh, Pd, Os, Ir, or Pt) and corresponding oxide layers of platinum group metals.

[0033] When Ru is exposed to an O2-containing environment, it will grow a naturally occurring, self-inhibiting oxide surface layer. If the oxidation temperature exceeds a certain threshold (reported in most literature as above 200 °C), a stoichiometric ruthenium dioxide (RuO2) layer will form, instead of other types of Ru oxides (e.g., RuO, RuO3, and RuO4). Stoichiometric RuO2 has a molecular weight of approximately 3.5–4.6 × 10⁻⁶. -5 Conductive oxide materials with intrinsic resistivity of Ω·cm. This value is greater than 6.71 to 7.16 × 10⁻⁶. -6 The intrinsic resistivity of Ru is Ω·cm, but much lower than that of other forms of Ru oxide. At room temperature and in a gaseous environment, the oxidation process of Ru on its surface exhibits high self-limitation. The surface RuO2 has a dense lattice structure that restricts O2 penetration to form more RuO2 underneath, leading to other types of Ru oxides. It has been found that contacts dominated by non-stoichiometric RuO2 will have a contact resistance 5 to 10 times higher than those dominated by stoichiometric RuO2, and this resistance increases with the duration of switching operation, while stoichiometric RuO2 exhibits a stable low contact resistance.

[0034] Other methods for forming RuO2 include oxygen plasma treatment, direct sputtering of RuO2 onto a surface in an Ar / O2 mixed environment, chemical vapor deposition (CVD), or atomic layer deposition (ALD). Sputtering methods can produce oxide layers that are much thicker than other methods. For these reasons, MEMS switches can be fabricated using Ru as the contact material, rather than using gold, silver, copper, aluminum, or other highly conductive metals.

[0035] MEMS switches are typically fabricated on semiconductor substrates (e.g., silicon) because MEMS manufacturing has historically originated from silicon CMOS processing technology. Therefore, most MEMS device fabrication infrastructure is based on the use of silicon substrates. Consequently, it is expected / predicted that, looking ahead, the commercialization of MEMS switch technology will primarily be achieved on silicon-based substrates. MEMS switch devices used only for specific applications (e.g., microwave technology) are fabricated on substrates other than silicon.

[0036] Hard materials such as Ru can be coated onto gold (Au) MEMS switch contacts to extend switch life. However, the hard material used as the contact itself does not prevent early failure during switching cycle operation, typically less than a few million cycles. Failure mechanisms can include wear, micro-soldering, surface roughening due to fracture, and accumulation of organic / polymer contaminants on the surface. Oxidation of the Ru contact surface or direct deposition of RuO2 as the contact material can significantly improve the thermomechanical properties of MEMS switches and reduce organic accumulation on the contact surface. MEMS switching devices are typically packaged in a sealed, clean environment to ensure device performance over a long lifespan, a method widely used in traditional mechanical switches and relays to avoid moisture and contact contamination.

[0037] The exemplary embodiments described herein present a MEMS ohmic contact switch that can be fabricated on an insulating substrate, such as silicon dioxide, fused silica, silica glass, quartz, sodium-doped glass, and borosilicate glass, although other non-insulating substrate materials (e.g., silicon) may be alternatively used. In the exemplary embodiments, fused silica may be chosen as the base substrate material due to its extremely low electrical losses. This characteristic is advantageous for the switching device to have excellent low insertion losses for RF and microwave applications, as well as excellent isolation for use as a high-power DC and / or RF or microwave switch. In the exemplary embodiments, RuO2 can be formed on both the top and bottom MEMS switch contact surfaces, which helps to extend the switching lifespan to over billions of cycles. Figure 1A A detailed cross-section of an exemplary embodiment of the switching device 100 according to the present invention is shown. Figure 1B , Figure 1C as well as Figure 1D Examples Figure 1A Detailed views of certain parts of the depicted switching device.

[0038] Reference Figure 1A Example switching device 100 includes Figure 1B The substrate portion 104 shown in isolation and Figure 1C The cover portion 106 is shown in isolation. Figure 1D The contact area 102 of the switching device 100 is shown in isolation and magnified view.

[0039] Reference Figure 1BIn the illustrated example embodiment, the substrate portion 104 of the switching device 100 may include a substrate (e.g., fused silicon) 108. An electrically insulating material layer 110 may be deposited on one or both of the top and bottom surfaces of the insulating substrate 108. Both the first bonding site 112 and the second bonding site 114 include bonding metals used to mechanically and electrically connect the switching device substrate 104 to its corresponding 106. Various metals and metal stacks may be used for metal compression or metal eutectic bonding methods. (Metal stacks may be used for metal compression bonding or metal eutectic bonding). The bonding metals of both the first bonding site 112 and the second bonding site 114 may be formed on an adhesive layer 116 deposited on the insulating material layer 110. During the bonding process described herein, the first bonding site 112 and the second bonding site 114 may be bonded to corresponding metal bonding sites on the cap portion 106. This bonding defines a cavity 111a surrounding the switching element (e.g., the beam, gate, and switch contact described herein) (see...). Figure 1A This cavity isolates the switching element from the external environment 111b of the switching device 100. The environment within the cavity 111a may differ from the environment 111b surrounding the bonded switching device in terms of pressure and gas composition.

[0040] A first end of beam 118 can be anchored to a conductive trace electrically connected to bonding site 112 and mechanically coupled to substrate 108. A first contact arrangement 126 can be disposed at a second end of beam 118. The first contact arrangement 126 may include: a Ru layer 130 mechanically coupled to the underside of beam 118 and electrically connected to the beam; and a RuO2 layer 132 formed on the outer surface of the Ru layer 130. A second and corresponding contact arrangement 134 may include: a Ru layer 136 deposited on an extension of the conductive trace electrically connected to bonding site (114) and mechanically adhered to substrate 108; and a RuO2 layer 138 formed on the outer surface of the Ru layer 136. The second contact 134 should be located below the beam and have similar X and Y coordinates to the first contact 126, such that when the beam is actuated by gate electrode 140 and pulled toward the substrate, the first contact surface and the second contact surface contact and are electrically connected. Although in the example embodiment, the Ru layer 136 is deposited on an extension of the second bonding site 114, other embodiments may have a Ru layer deposited on a site different from the bonding site. For example, in some embodiments, additional circuitry may be located between the third contact arrangement 134 and the bonding site 114.

[0041] The gate structure 140 may include a conductive metal layer 142 deposited on an insulating substrate 108. The gate structure 140 may be used to generate an electromotive force on a beam 118 that causes the beam to bend until the RuO2 layer 132 of the first contact arrangement 126 makes electrical contact with the RuO2 layer 138 of the second contact arrangement 134.

[0042] Reference Figure 1C The cover portion 106 of the switching device 100 may include an insulating cover 150 comprising an insulating material, such as fused silica or other such insulating materials known in the art. A third bonding site 152 and a fourth bonding site 154 (both comprising a bonding material such as gold (Au)) may be formed in locations on an adhesive layer 156, such as tantalum (Ta), deposited on the insulating cover 150, that facilitate bonding with the first bonding site 112 and the second bonding site 114. At least one conductive, hermetically sealed glass via (TGV) 158 may be provided in the insulating cover 150, facilitating the conduction of electrical signals to and / or from components of the switching device 100, which are sealed within a cavity formed after the cover portion 106 is bonded to the substrate portion 104.

[0043] In contrast to methods that use oxygen processes to oxidize Ru contact surfaces or directly sputter RuO2 material in wafer bonding equipment, this embodiment employs an oxygen plasma ashing process prior to thermal compression (TC) bonding for two purposes. The first purpose of the oxygen plasma ashing process is to remove organic contaminants from the contact surfaces. The second purpose is to deactivate the Ru contact surfaces to form RuO2. Subsequent bonding processes are performed in an environment containing between 0.05% and 30% oxygen, although for the example embodiment, the oxygen content may not exceed 20%. In other embodiments, the bonding environment may be supplemented with oxygen using one or more other gases (e.g., nitrogen (N2) and / or rare inert gases such as argon (Ar)).

[0044] Because the RuO2 layer is formed during the oxygen plasma ashing process and before the cap is bonded to the substrate in the bonding chamber, the oxygen trapped within the sealed encapsulated device environment between the cap and substrate is not substantially depleted by the Ru contacts during the bonding process. Therefore, the oxygen content of the gas sealed within the device environment can be equal to or close to the oxygen content of the gas stream supplied during the bonding process. In the example environment, the oxygen content in the sealed device environment can be 20%, although other environments can exhibit oxygen contents between 0.05% and 30%.

[0045] Figure 2An example embodiment of a process flow 200 for fabricating and bonding a substrate wafer and a cover wafer capable of accommodating one or more MEMS switches is described. This example embodiment focuses on the use of a glass substrate wafer and a glass cover wafer, although other embodiments may utilize other insulating or non-insulating wafers. Furthermore, it should be understood that any cover with suitable mating surfaces for bonding to the substrate portion in the wafer bonding process can be used.

[0046] The process flow 200 may include: forming a 202 device (e.g., a MEMS switch) on a glass substrate (e.g., a MEMS wafer), releasing a 204 MEMS switch structure (i.e., eliminating the sacrificial support structure to allow the intended movable switch assembly to move freely, thereby exposing the Ru contact surface), and performing a 206 oxygen plasma ash cleaning procedure for at least 1 minute (4 minutes + / - 0.1 minutes in the example embodiment).

[0047] MEMS wafers are bonded to corresponding cap wafers to encapsulate the devices and enable them to be hermetically sealed in oxygen-containing environments. Cap wafers can be fabricated using typical microfabrication processes to include any electrical or mechanical layers. The cap wafer contains materials and features that facilitate bonding it to its corresponding MEMS device wafer, thereby hermetically sealing the device.

[0048] The substrate portion 104 and the cover portion 106 are aligned and loaded 208 into a thermal compression (TC) bonding chamber. Once the substrate portion 104 and the cover portion 106 are loaded into the bonding chamber, process 200 continues by flowing a gas with the desired composition into the bonding chamber 210 until the desired pressure is reached, raising the chamber temperature, and bonding 212 the substrate and cover wafers at a specific temperature and force. As the temperature decreases, the desired gas flow 214 continues to terminate the example bonding process.

[0049] In one embodiment, gas is introduced into bonding chamber 210 until a desired pressure is reached (described in more detail herein), a first bonding force (typically 20% or less of a subsequent second bonding force) is applied to contact the wafers (together), the temperature in the bonding chamber is raised, and a second and higher force (bonding force) is applied, thereby bonding cap portion 106 to substrate portion 104. The bonding chamber is maintained at its appropriate pressure using the desired gas, and the bonding force is reduced to the first bonding force (or a similarly low force), while the temperature in the bonding chamber is lowered.

[0050] In process flow 200, before loading the MEMS wafer into the thermocompression bonding apparatus, a conductive oxide contact surface (e.g., RuO2) can be formed during oxygen plasma ashing process step 206. Figure 3An example TC curve according to the invention is shown, in which the room temperature 302 (in °C) is shown together with the applied bonding force 304 (in kN). It should be understood that... Figure 3 The temperatures and pressures described are merely illustrative examples for descriptive purposes and not intended to be limiting. Typically, bonding temperature and pressure profiles can fall within ranges suitable for achieving bonding between a substrate and a cap as described herein. No special bonding treatment is required to accommodate oxidation of the Ru contact surfaces, except for standard bonding processes that do not perform Ru oxidation. The gas used to fill the bonding chamber can be an N2 / O2 mixture, or clean dry air (CDA), or an inert gas / O2 mixture, or an inert gas only, or any gas just mentioned mixed with one or more rare inert gases.

[0051] During oxygen plasma ash treatment, stoichiometric rutile oxide (RuO2) can be formed on the outer surface of the Ru contacts. Highly reactive O2 atoms can penetrate the surface of bulk Ru, but non-stoichiometric RuO2 can form beneath the surface. X (Where X is a positive real number). This RuO2 is annealed using O2. x The RuO2 is converted into RuO2. As a result, additional optional steps after O2 plasma ashing and before the wafer bonding stage can produce a thicker and higher percentage of RuO2 as a surface contact material. These options, for example, in... Figure 5A , Figure 5B It was also showcased in 5C.

[0052] Figure 4A An example implementation is shown, which includes: once the oxygen plasma ashing step has been performed and the substrate portion and the cover portion have been loaded into the bonding chamber, an oxygen-containing gas (O2) is allowed to flow into the 402 bonding chamber. Figure 4B An example implementation is shown in which, once the oxygen plasma ashing step has been performed and the substrate portion and the cover portion have been loaded into the bonding chamber, a nitrogen-containing gas (N2) (other than oxygen) is introduced into the 404 bonding chamber. Figure 4C An example embodiment is shown, which includes: once the oxygen plasma ashing step has been performed and the substrate portion and the cover portion have been loaded into the bonding chamber, a gas containing a rare inert gas is allowed to flow into the 406 bonding chamber. In other embodiments, the inert gas may be a combination of O2, N2, or both. In all three embodiments ( Figure 4A , Figure 4B as well as Figure 4C In the last step shown, the gas flow described in steps 402, 404, and 406 continues during the bonding between the substrate portion and the cover portion.

[0053] Figure 5A , Figure 5B as well as Figure 5C An example embodiment is shown that a pretreatment step is performed prior to the bonding process to form the RuO2 contact layer described herein. The RuO2 layer is formed in a chamber separate from the bonding chamber (e.g., an oven), rather than during oxygen plasma ashing. The RuO2 layer can be enhanced during oxygen plasma ashing. All three embodiments ( Figure 5A , Figure 5B as well as Figure 5C The diagram shows that after the MEMS device is loaded into the oven, the 502 oven is filled with oxygen-containing gas and the device is annealed at a temperature greater than 200°C for at least 10 minutes. Figure 5A , Figure 5B And 5C respectively show oxygen 504, nitrogen 506 or inert gas 508 flowing in the bonding chamber.

[0054] While several exemplary embodiments have been specifically shown and described, those skilled in the art will understand that various changes in form and detail may be made to these embodiments without departing from the scope of the embodiments covered by the appended claims.

Claims

1. A method for manufacturing and packaging an ohmic microelectromechanical system (MEMS) switching device, the method comprising the following steps: The ohmic microelectromechanical system (MEMS) switching device is constructed on a substrate, the ohmic MEMS switching device having one or more contacts made of platinum group metals; In the first processing chamber, an oxide layer of the platinum group metal is formed on the outer surface of each of the one or more contacts; In a second processing chamber separate from the first processing chamber, the cover is bonded to the substrate, thereby hermetically sealing the ohmic microelectromechanical system (MEMS) switching device within a sealed cavity formed by the cover and the substrate. The bonding occurs in a bonding atmosphere having an oxygen content in the range of 0.05% to 30%, such that after the ohmic MEMS switching device has been hermetically sealed within the sealed cavity, the cavity atmosphere within the sealed cavity is the same as the bonding atmosphere and has an oxygen content in the range of 0.05% to 30%.

2. The method according to claim 1, wherein, The substrate and the cover each include an insulating material.

3. The method according to claim 1, wherein, The platinum group metal is ruthenium (Ru), and the oxide layer of the platinum group metal is ruthenium dioxide (RuO2).

4. The method according to claim 1, wherein, The steps of constructing the ohmic microelectromechanical system (MEMS) switching device further include: forming the ohmic MEMS switching device on the substrate using thin-film microfabrication processes.

5. The method according to claim 1, wherein, The step of forming the oxide layer of the platinum group metal on the outer surface of each of the one or more contacts includes performing an oxygen plasma ashing process on the ohmic microelectromechanical system switching device.

6. The method according to claim 1, further comprising the following steps: Following the step of forming the oxide layer of the platinum group metal on the outer surface of the one or more contacts, an oxygen plasma ashing cleaning process is performed on the ohmic microelectromechanical system switching device to enhance the oxide layer of the platinum group metal on the outer surface of the one or more contacts.

7. The method according to claim 1, wherein, The bonding atmosphere has an oxygen content in the range of 0.05% to 30%.

8. The method according to claim 1, wherein, The step of bonding the cover to the substrate further includes: subjecting the cover and the substrate to a bonding temperature, and pressing the cover and the substrate together using the bonding force according to a distribution map characterizing the bonding temperature and bonding force relative to time.

9. The method according to claim 1, wherein, The substrate is one of a plurality of substrates on a first wafer, and the cover is one of a plurality of covers on a second wafer. The step of bonding the cover to the substrate further includes: subjecting the first wafer and the second wafer to a bonding temperature, and pressing the first wafer and the second wafer together using the bonding force according to a distribution map characterizing the bonding temperature and bonding force relative to time.

10. The method according to claim 1, wherein, The bonding atmosphere also includes (1) nitrogen (N2) and (ii) one or both of inert gases.

11. A switching device, the switching device comprising: Ohmic microelectromechanical system (MEMS) switching device, the ohmic MEMS switching device being constructed on a substrate, the ohmic MEMS switching device having one or more contacts made of platinum group metals; The oxide layer of the platinum group metal is formed on the outer surface of each of the one or more contacts. A cover, disposed on and bonded to the substrate, forms an airtight sealed cavity for enclosing the ohmic microelectromechanical system switching device, the cavity atmosphere having an oxygen content in the range of 0.05% to 30%.

12. The switching device according to claim 11, wherein, The substrate and the cover each include an insulating material.

13. The switching device according to claim 11, wherein, The platinum group metal is ruthenium (Ru), and the oxide layer of the platinum group metal is ruthenium dioxide (RuO2).

14. The switching device according to claim 11, wherein, The ohmic microelectromechanical system switching device is formed on the substrate using thin-film microfabrication technology.

15. The switching device according to claim 11, wherein, The oxide layer of the platinum group metal on the outer surface of each of the one or more contacts is formed on the ohmic microelectromechanical system switching device using an oxygen plasma ashing process.

16. The switching device according to claim 11, wherein, The platinum group metal oxide layer is enhanced by an oxygen plasma ashing cleaning process on the ohmic microelectromechanical system switching device after the platinum group metal oxide layer has been formed on the outer surface of the one or more contacts.

17. The switching device according to claim 11, wherein, The atmosphere within the sealed cavity has an oxygen content ranging from 0.05% to 30%.

18. The switching device according to claim 11, wherein, In order to bond the cap to the substrate, the cap and the substrate are subjected to a bonding temperature, and the cap and the substrate are pressed together using the bonding pressure according to a distribution map of the bonding temperature and bonding pressure relative to time.

19. The switching device according to claim 11, wherein, The substrate is one of a plurality of insulating substrates on a first insulating wafer, and the cover is one of a plurality of insulating covers on a second insulating wafer. In order to bond the cover to the insulating substrate, the first insulating wafer and the second insulating wafer are subjected to a bonding temperature, and the first insulating wafer and the second insulating wafer are pressed together using the bonding pressure according to a distribution map of the bonding temperature and bonding pressure relative to time.

20. The switching device according to claim 11, wherein, The cavity atmosphere also includes (1) nitrogen (N2) and (ii) one or both of inert gases.

21. A method for manufacturing and packaging an ohmic microelectromechanical system (MEMS) switching device, the method comprising the following steps: The ohmic microelectromechanical system (MEMS) switching device is fabricated on a molten silica substrate using a thin-film microfabrication process. The ohmic MEMS switching device has one or more contacts made of ruthenium (Ru). In the first processing chamber, a ruthenium dioxide (RuO2) layer is formed on the outer surface of each of the one or more contacts; In a second processing chamber separate from the first processing chamber, a molten silica cap is bonded to the molten silica substrate, thereby hermetically sealing the ohmic microelectromechanical system (MEMS) switching device within a sealed cavity formed by the cap and the substrate. The bonding occurs in a bonding atmosphere having an oxygen content in the range of 0.05% to 30%, such that after the ohmic MEMS switching device has been hermetically sealed within the sealed cavity, the cavity atmosphere within the sealed cavity is the same as the bonding atmosphere and has an oxygen content in the range of 0.05% to 30%.

22. The method according to claim 21, further comprising the step of: After the RuO2 is formed on the outer surface of the one or more contacts, an oxygen plasma ashing process is performed on the ohmic microelectromechanical system switching device to enhance the RuO2 on the outer surface of the one or more contacts.

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