Micro-electro mechanical switch designs

A capacitive RF switch and DC RF switch include a fixed electrode having a thin layer of metal and at least one pull-down electrode. A moving plate has a plurality of corrugations and a selective finger design. The capacitive switch includes a selective finger that comes into contact with the fixed electrode so as to minimize the stiction between the moving plate and the fixed electrode when the switch is closed. The DC switch comprises a plurality of dimples that are formed on the selective portion of the moving plate and are positioned to come into contact with the fixed electrode when the switch is closed so as to increase the contact force and lower the resistance between the moving plate and fixed electrode.

BACKGROUND OF THE INVENTION

The invention relates to the field of RF switches, and in particular to capacitive and DC types of RF switches having lower switch actuation thresholds, reduced field-induced stiction, and lower DC contact resistance.

A single RF capacitive switch in a coplanar waveguide can be comprised of a 200 μm long and 150 μm wide film of silicon dioxide and aluminum which forms a cantilever membrane. Stress is built into the membrane that causes it to curl upward away from a substrate. Moreover, the membrane includes a 50 μm long and 150 μm wide section at its end that forms one plate of a capacitor or moving plate. A voltage is applied between a buried electrode in the substrate and the membrane, which causes the membrane to pull and bring the moving plate into intimate contact with a similarly sized fixed electrode. This results in increasing the capacitance between the fixed electrode and moving plate.

A DC RF switch has a similar design except that the membrane is shorter, narrower, and has platinum contacts at the end of its curled up membrane. Also, the DC RF switch includes a platinum fixed contact on the surface of the substrate. With applied voltage, the moving platinum contact is brought in contact with the fixed platinum contact on the surface of the substrate, closing the DC circuit.

However, there is a need to have enhancements in both DC and capacitive switches that target lower switch actuation thresholds, reducing field-induced stiction, enabling x-y addressability in switch arrays, and dual-mode DC/capacitive switches.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a capacitive RF switch. The capacitive RF switch includes a fixed electrode and at least one pull-down electrode. A moving plate includes a plurality of corrugations and a selective finger design that is formed on a selective portion of the moving plate. The selective finger is configured so as to minimize the stiction between the fixed electrode and moving plate when the switch is closed.

According to another aspect of the invention, there is a provided a DC RF switch. The DC RF switch includes a fixed electrode having a thin layer of metal and at least one pull-down electrode. A moving plate includes a plurality of corrugations and a selective finger design. The moving plate includes at least one dimple that is formed on a selective portion of the moving plate. The at least one of the dimple is positioned to come into contact with the fixed electrode when the switch is closed so as to increase the contact force lowering the resistance between the moving plate and fixed electrode.

According to another aspect of the invention, there is provided an RF switch. The RF switch includes a fixed electrode having a thin layer of metal and at least one pull-down electrode. A moving plate includes a plurality of corrugations and a selective finger design. The moving plate also has a selective portion that comprises a capacitive switch and a DC switch. The moving plate comprises a selective finger that comes into contact with the fixed electrode so as to minimize the stiction between the moving plate and the fixed electrode when the switch is closed. The DC switch comprises at least one dimple that is formed on the selective portion of the moving plate and are positioned to come into contact with the fixed electrode when the switch is closed so as to increase the contact force and lower the resistance between the moving plate and fixed electrode.

According to another aspect of the invention, there is provided a method of forming a capacitive RF switch. The method includes providing a fixed electrode and at least one pull-down electrode. The method also includes providing a moving plate having a plurality of corrugations and a selective finger design that is formed on a selective portion of the moving plate. The selective finger is configured so as to minimize the stiction between the fixed electrode and moving plate when the switch is closed.

According to another aspect of the invention, there is a provided a method of forming a DC RF switch. The method includes providing a fixed electrode having a thin layer of metal and at least one pull-down electrode. In addition, the method includes providing a third electrode which is a moving plate having a plurality of corrugations and a selective finger design. The moving plate has at least one dimple that is formed on a selective portion of the moving plate. The dimples are positioned to come into contact with the electrode when the switch is closed so as to increase the contact force and lower resistance between the moving plate and fixed electrode.

According to another aspect of the invention, there is a provided a method of forming an RF switch. The method includes providing a fixed electrode having a thin layer of metal and at least one pull-down electrode. In addition, the method includes providing a moving plate that has a plurality of corrugations and a selective finger design. The moving plate also has a selective portion that comprises a capacitive switch and a DC switch. The capacitive switch comprises a selective finger that comes into contact with the fixed electrode so as to minimize the stiction between the moving plate and the fixed electrode when the switch is closed. The DC switch comprises at least one dimple that is formed on the selective portion of the moving plate and is positioned to come into contact with the fixed electrode when the switch is closed so as to increase the contact force and lower the resistance between the moving plate and fixed electrode.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic of corrugations2used in accordance with the invention. Switches configured in accordance with the invention have corrugations2that are increased in size as compared to the prior art. Moreover, the design is meant to keep the cantilever membrane4flatter and therefore reduces the voltage threshold.

In particular,FIG. 1shows a cross-section of a membrane used with the invention. The membrane4includes several corrugations2of equal dimensions. In addition,FIG. 1illustrates two views (view1and view2) of the corrugations2. View1demonstrates the external dimensions of a corrugation and the view2demonstrates the internal dimensions of the same corrugation. View2divides a corrugation2into a first side region6, a second side region8, an elevated region10, and a bottom region12. The first side region6is sized at 1 μm and the second side region8is sized at also 1 μm. In addition, the elevated region10is sized at 3 μm and the bottom region12is sized at 3 μm.

View1divides the external regions of the corrugation in two regions, second elevated region16and second bottom region14. The second elevated region16is sized at 1.3 μm and second bottom region14at 0.3 μm. The dimensions demonstrated by view1and2can vary.

FIG. 2is a detailed schematic of a membrane18used in accordance with the invention. The membrane18includes a top layer20, a middle layer22, and a bottom layer24. The top layer20comprises silicon dioxide having a stress of −2.5×109dyne/cm2, and is sized at 0.1 μm. The middle layer22comprises aluminum having a stress of 3.5×109dyne/cm2, and is sized at 0.3 μm. The bottom layer24is comprised of silicon dioxide having a stress of −4.25×109dyne/cm2, and is sized at 0.1 μm. However, certain embodiments may not require the use of the top20and bottom24layers. Under these circumstances, other modifications to the switch are used to compensate for the removal of the top20and bottom24layers, which will be discussed more hereinafter. The thickness of the membrane18, in this embodiment, is approximately 0.5 μm. This value is also permitted to vary in other embodiments.

Furthermore, the threshold voltage applied to the membrane18can be adjusted by varying the amount of curl in the membrane18, which is controlled by the stress in the top20and bottom24layers and by varying the thickness of the membrane18.

FIGS. 3A–3Bare schematics of an RF capacitive switch26having a one-finger design used in accordance with the invention.FIG. 3Ashows a capacitive switch26that includes a curled membrane28comprising the materials described inFIG. 2. Moreover, the capacitive switch26includes a moving plate30also comprised of the materials ofFIG. 2and a fixed plate electrode32that is comprised of aluminum with an optional layer of silicon dioxide over it. The contact between the fixed electrode32and the moving plate30produces the overall capacitance in the switch26. Both the moving plate30and fixed electrode32are charged with a particular voltage source, which is not shown for clarity.

The moving plate30inFIG. 3Acan be designed to have to a particular geometric arrangement. In this embodiment, the moving plate30is designed to be a one-finger design. The one finger design implies that a single fixed electrode32and plate30are surrounded on three sides by the pull down electrode and the corrugations respectively. The electric field between the pull down electrode31and the corrugated membrane28and between the fixed32and moving plate30create the force necessary to establish contact between the moving30and fixed32plates. In other embodiments, there can be designs having more than one-finger in the moving plate30. For example, a moving plate30can have a two-finger design, which implies that two plates are used to form a capacitive switch where there could be corrugations between the plates. Furthermore, these extra corrugations can be designed into the moving plate30and combined with a corresponding pull down electrode to provide more efficient contact with the fixed electrode32.

An important feature of this design is that by having the fixed and moving plates surrounded on three sides by the pull down electrode and corrugations respectively, the moving and fixed plates are brought into intimate contact without necessarily having to apply a voltage between the two plates. In this design the fixed plate is quite flat while the moving plate tends to be flexable and slightly curved in a slight bowl shape with the bottom of the bowl touching first during actuation. By having the surrounding pullin field the moving plate is flattened against the fixed plate.

FIG. 3Bshows a more detailed section ofFIG. 3Aand the corrugations in the membrane33. The membrane33includes two sets of corrugations, such as the plate corrugations36and the standard corrugations34. The standard corrugations34are formed in the membrane33using standard prior art techniques. In this embodiment, the standard corrugations34are 8 μm in period. However, the period for the standard corrugations34can vary for different embodiments. The plate corrugations36are formed on the moving plate35. In this case,FIG. 3Bshows3plate corrugations36, however, that number can vary in other embodiments. The length and width of the corrugations along with the size of the plate and the oxide thickness determines the amount of capacitance in the switch. Also, the plate corrugations36do not necessarily cover the entire width of the membrane33, usually a selective portion of the width. The standard corrugations34cover the entire width of the membrane33and portions of the width not covered by the plate corrugations36.

In all one-finger designs, the fixed plate electrode of a switch is surrounded on at least three sides by a membrane and pull-down electrodes. This geometry can be designed so that the pull down voltage is sufficient to provide enough pressure at the edges so that a membrane is kept flat across a fixed plate electrode without having to apply a voltage between the fixed and moving plates.

In the prior art, the pull-down voltage was applied to both the pull down electrodes and to the fixed electrode relative to the membrane. This was necessary for intimate contact between a fixed electrode and moving plate, and maximizing the closed-state capacitance. The theory is that high fields between a fixed plate electrode and moving plate slowly breaks down the insulator, builds up charge, which causes stiction. The one-finger capacitance switches have the feature that a membrane can be pulled flat using a reduced DC voltage applied between a fixed plate electrode and moving plate of the capacitor. By having no voltage or perhaps a very low voltage between a fixed electrode and moving plate, the field-induced stiction should be eliminated or greatly reduced.FIG. 3Cshows a lengthwise cross section of a switch where the actuation of the switch is simulated.

FIG. 3Cis a cross sectional drawing of one embodiment off the capacitive switch using the membrane ofFIG. 3A and 3B.FIG. 3Cis a stop action simulation of the switch membrane during the switching action.

FIGS. 4A–4Bare schematics of another embodiment of the inventive capacitive switch38.FIG. 4Ashows the top view of the capacitive switch38. For purposes of illustration,FIG. 4Aillustrates the use of carbonized resists40throughout the capacitive switch38during fabrication. The carbonized resists40are used to form the corrugations on the membrane39. These resists40in this embodiment are sized at 1 μm thick and 5 microns wide, and one can refer to resists40as “thick”, and are removed after release from the membrane39. The corrugations could also be formed using other materials such as molybdenum instead of carbonized resist. The capacitive switch also includes a moving plate42having three plate corrugations44. The plate corrugations44rest on a fixed plate50before release. Note that the switch has a one-finger design. It also incorporates the advantages described inFIGS. 3A–3Bregarding a one-finger capacitive switch.

FIG. 4Bis a cross-sectional view of the capacitive device38, which is shown after release in its closed or rolled out position. A slight gap is shown between the membrane and the substrate and fixed plate for clarity. In actual operation the membrane contacts the fixed surface over significant areas. The membrane39includes a layer of silicon dioxide sized at 100 nm thick, aluminum sized at 300 nm thick, and silicon dioxide sized at 100 nm thick. Note thatFIG. 4Bassumes that the carbonized resists are removed. Also, the capacitive switch38includes bottom pull-down electrodes48. These electrodes48are high resistance to make them transparent to RF and are made from tantalum nitride and are contained in the oxide layer52of the capacitive device38. Moreover, the pull-down electrodes48are continuous and provide the necessary potential to pull, or actuate, the membrane39down onto the fixed oxide surface and onto the fixed plate50. In this embodiment, the fixed plate50is comprised of aluminum. However, the fixed plate50can be comprised of other materials, such as gold or copper. The capacitive switch38includes a pull-back region46where electrode48is not present. The pull-back region is sized to control the threshold voltage for actuation of the membrane.

FIGS. 5A–5Bare schematics of a third embodiment of the inventive capacitive switch54.FIG. 5Ashows the top view of the capacitive switch54which is the same asFIG.4Aexcept for the pull down electrode64. In this embodiment the pull down electrode64is segmented to form strips lying under the resist corrugations, all the strips64being connected together at the top and bottom edges. The pull down electrode strips64beside the plate region are short and do not cross under the fixed plate, and end just short of the plate.

FIG. 5Bis a cross-sectional view of the capacitive device54, which is the same asFIG. 4Bexcept for the pull down electrode64. The membrane55includes a layer of silicon dioxide sized at 100 nm, aluminum sized at 300 nm, and silicon dioxide sized at 100 μm. Note thatFIG. 5Bassumes that the carbonized resists are removed. The capacitive switch54includes a pull-back region62that does not include any pull down electrodes. The segmented pull down electrode is shown in cross section. In this embodiment the pull down electrode64is closer to the surface than the pull down electrode48isFIG. 4B. The pull down electrode64could also be on the surface without any oxide covering. The design of the strips of the pull down electrode is to make their width substantially less than the width of and centered to the corrugations. When the membrane bottom surface comes in contact with the top surface of the substrate there will be an air gap between the bottom electrode strips and the membrane electrode. This air gap can help to reduce stiction.

It should be noted here that the plate electrode is shown to be rectangular and has square corners. The plate in these designs could be nonrectangular and have rounded corners, and indeed could be generally round if desired, perhaps reducing the RF losses.

FIG. 6is a schematic of a fifth embodiment of the inventive capacitive switch86.FIG. 6shows the top view of the capacitive switch86having a one-finger design. This device has the same description as the device ofFIGS. 5A&Bexcept for an additional electrode70. This additional electrode70covers the bottom surface of the membrane87everywhere except in the area of the plate. The membrane87now has two electrodes one63on top of the other66separated by and oxide layer65which insulates the two layers63,66. This additional electrode70is used together with the pull down electrode64to actuate the switch86. The switch86has a total of four electrodes63,65,70, and64, two thicker ones for RF conduction and two thinner layers for actuation. Therefore, the switch86is a four terminal device where the actuation electrodes are separated from the RF electrodes.

The membrane87includes a layer of silicon dioxide sized at 100 nm, aluminum sized at 300 nm, and silicon dioxide sized at 100 nm. There is an ultra thin layer of aluminum below the 100 μm layer of silicon dioxide to form the additional electrode70. Other materials could be used instead of the ultra thin aluminum such as tantalum nitride. Tantalum nitride could also be used for the pull down electrode for any of the embodiments described. In another embodiment one could extend the thin electrode70and the pull down electrode64over the plate region to provide better contact in the plate region when the switch is actuated.

The ultra-thin layer70of aluminum can be used for pull-down electrodes and for routing signals in an x-y device array. This ultra-thin layer70connects out through the region where the membrane attaches to the substrate, and connects to either the bottom or top electrode high resistance layers, where it is isolated from the RF signal. Furthermore, the ultra-thin aluminum layer provides a way to do the x-y addressing required in some switch array applications.

FIG. 7is an additional embodiment of the capacitive switch100. This switch100is like the one finger design ofFIG. 6Bexcept that the membrane has the aluminum conductor removed in two strips, or cuts101, separating the moving electrode into three electrodes. Only the aluminum part of the membranes is cut so that the silicon dioxide part of the membrane still connects. The side electrodes, which during operation would be connected together electrically externally, together with the pull down electrode, provide the force to bring the moving plate into contact with fixed capacitor plate. By providing the cuts, and connecting together the side electrodes, once again as inFIG. 6a 4 terminal device results. A four terminal device has the advantage that no additional bias connections to the RF lines are necessary.

FIG. 8is a schematic of a fifth embodiment of an inventive capacitive112switch.FIG. 8shows the top view of the capacitive switch112having a one-finger design. This design is the same as the first embodiment,FIG. 4A, except that there is a latch added at the end of the cantilever. The latch is created by having a hole or slot124at the far end of the plate120and the pull down electrode is placed in this opening. The pull down electrode provides extra force at the end of the cantilever holding it down with a lower voltage. There are a wide variety of possible latch designs, for example the opening could be wider or narrower, there could be several openings etc.

FIG. 9is a schematic of a fourth embodiment of the inventive two-finger capacitive switch192.FIG. 9shows the top view of the capacitive switch192having a two-finger design. This embodiment is very similar toFIG. 4Aexcept that it has two fingers. For purposes of illustration, the carbonized resists194are used to form the corrugation on the membrane. These resists194are sized at 1 μm thick, and are removed after release from the membrane196. The capacitive switch also includes a moving plate197having two fingers198,200, where each finger198,200has a set of 3-RF zone corrugations202,204. The two fingers rest on a fixed plate electrode196, and each includes a thin layer of resist on its sides201,203. Furthermore, a significantly large distance separates the fingers198,200. The range distance between fingers could be from one micron to hundreds of microns.

The membrane includes196, a layer of silicon dioxide, sized at 100 nm, aluminum sized at 300 nm, and silicon dioxide sized at 100 nm. Also, the capacitive switch192includes bottom pull-down electrodes, which are positioned below the oxide layer195of the capacitive device192. Moreover, these pull-down electrodes are continuous and provide the necessary potential to pull the membrane196on the fixed plate electrode193.

FIG. 10is a schematic of a varactor502formed in accordance with the invention. The varactor502is similar to the two finger capacitive device ofFIG. 10except that it includes several segmented pull-down electrodes510which are connected to separate voltage sources and can be arranged to pull the membrane down to the surface of the substrate in stages. With the voltage applied to the first electrode504the cantilever moves to contact the first electrode and therefore increases the capacitance by a specified a amount. The second506, third508, and fourth512electrodes similarly can be used to increase the capacitance in steps, hence a varactor502. In other designs one could have a different number of electrodes where the membrane design is adjusted accordingly to provide a finer or courser capacitance variation with voltage. By adjusting the voltages it is possible to create an analog variation of capacitance with voltage.

FIG. 11is a schematic of an additional embodiment of a capacitive switch210having an additional pull-down electrode on its end, which one can call the latch. The capacitive switch210includes a moving plate214having a one-finger design, where the one finger210includes plate corrugations216in the membrane as in earlier embodiments. However in this case the corrugations begin again at the end of the plate and there are no corrugations along the sides of the plate.

Having a pull down electrode219in switch210at the end of the cantilever membrane has the advantage of requiring a somewhat lower voltage to hold the membrane in the rolled out position compared with previous designs. This latch structure could also be combined within the other designs described herein for example a latch could be incorporated into the switch ofFIG. 5at the moving end of the cantilever.

FIG. 12is a cross sectional schematic of the capacitive switch210having pull-down electrodes228on its end. In this embodiment, the segmented pull-down electrodes228,225are placed above the oxide layer223of the switch222. The switch222is broken up into three regions, the latch region224, RF pad or fixed plate electrode226, and pull-down electrodes228. The voltage for the pull down and the latch regions can be the same so they can be connected together to form one electrode. A small voltage and can be optionally applied between the plates to provide more intimate contact and a higher capacitance.

FIG. 13is a schematic of an embodiment of a DC switch232.FIG. 13shows the top view of the DC switch232which includes a moving membrane having a plate at the end. The plate contains the contact dimples. The switch also includes the fixed contact directly under the moving plate. For purposes of illustration,FIG. 13illustrates the use of carbonized resists234throughout the DC switch232during fabrications. The carbonized resists234are used to form the corrugations on the membrane233. These resists are sized at 1 μm thick, and are removed after release from the membrane233. Other materials could be used instead of the carbonized resist such a molybdenum. Furthermore, the moving plate236includes raised and depressed regions that form dimples237. These dimples237are used to provide the electrical contact between the membrane233and fixed plate electrode235, and the size and number, along with the plate area, will effect the contact force and contact area which will be described more below. The contact resistance with the switch closed will generally be smaller if there is a larger number of contacts and if there is a larger force holding the contacts together. The larger force can be brought about using a larger voltage, resulting in a larger electric field, and a larger membrane pull down area around the contacts.

The membrane233includes a layer of silicon dioxide sized at 100 nm, aluminum sized at 300 nm, and silicon dioxide sized at 100 nm. There is a thin layer of platinum at the bottom of the dimples and also on the top of the fixed plate in the contact area. With the switch pulled down the two platinum surfaces provide the electrical contact. The platinum is a good contact material because it does not easily form an insulating oxide which can interfere with current conduction between the contacts. Other materials could be used instead of platinum, such as gold or iridium or ruthenium or rhenium or palladium etc. or alloys of these materials etc. The DC switch232can include a small pull-back region. Also, the DC switch232includes a pull-down electrode, which is positioned below the oxide layer231between the membrane contact edge and the fixed contact232. Moreover, this pull-down electrode is continuous and provides the necessary potential to pull the membrane233on the fixed plate electrode235. Of course the pull down electrode could also be segmented as was described for the capacitive switch.

FIG. 14is a schematic diagram of another embodiment of a DC switch238formed in accordance with the invention.FIG. 14shows a cross-sectional view of the DC switch238. This switch has a similar design for the membrane233and with dimples237similar to the previous embodiment. In this case however the pull down electrode241is formed on two sides of the dimples. The advantage of this geometry is that it is possible to have a greater force on the contacts with the same or lower hold down voltage.

FIG. 15is a schematic diagram of an additional embodiment of the DC switch with the detail of the dimple and the finger electrode described herein.FIG. 15shows a top view of an exemplary switch, showing a dimple254described inFIG. 15. There is a finger structure250etched into the plate during fabrication which forms around the fixed contact249sitting on the surface. The dimple254is embossed directly in top of the fixed contact249on the moving plate finger256which is directly on top of the fixed plate finger250of a DC switch. The length of the finger of the moving plate is 20 μm. In addition, the width of the membrane is 25 μm. The overall length of the membrane251between the edge of attachment252and the end is 67.5 microns.

The fabrication can be arranged however so that the fixed contact250is embedded in the oxide surface. In this case there would be no visible finger structure in the moving plate250and there would only be a dimple. The dimple is in the center over the end of the finger structure of the fixed contact. The pull down electrode is not shown and is placed around the fixed contact finger under the membrane. The size of the dimple is 2 microns in diameter and could be in the range of 0.1 to 10 microns. The finger length is 10 microns, the width is 6 microns and these dimensions will vary depending on the design and the amount of force to be applied to the contact.

FIGS. 16A–16Bare schematics of a DC switch326having one finger and dimple.FIG. 16Ashows the top view of the DC switch326, andFIG. 16Bshows a cross-sectional view of the same switch326. The carbonized resists328are used to form the corrugations on the membrane330and there are four corrugations333in the moving plate. These resists328are sized at 1 μm thick, and are removed after release from the membrane330. The DC switch326also includes a moving plate332. In addition, the moving plate332is designed with a dimple334as described herein. The regions336surrounding the dimple334are coated with a thin layer of resist for forming the one finger design.

FIG. 16Bis a cross-sectional view of the switch326, which is in its closed position. The membrane330includes a layer of silicon dioxide sized at 100 nm, aluminum sized at 300 nm, and silicon dioxide sized at 100 nm. The DC switch326includes a pull-back region338that does not include any electrodes. Also, the switch326includes bottom pull- down electrodes341which are positioned below the oxide layer335of the switch326. Moreover, these pull-down electrodes341are continuous and provide the necessary potential to pull the moving plate330on the fixed plate340. In this embodiment, the dimple334is placed over the fixed plate340, and also includes a thin platinum contact329on its bottom-most portion that comes into contact with the thin platinum contact327of the fixed plate340. Other materials can be used in place of the platinum contacts327,329of the dimple334and the fixed plate340, such as aluminum.

FIGS. 17A–17Bare schematics of the DC switch342having a one-finger design and three dimples352,354,356. The structure of this switch342is similar to that described inFIGS. 16A–16B. However, this switch342includes three dimples352,354,356of which dimple354is used to form the one finger design with mechanical and electrical contact, and the other two dimples352,356are used to establish mechanical contact only. Moreover, the switch342also includes upper segmented down electrodes358, which are contained in the oxide layer362. The modifications done to this switch342are consistent with other switches described herein, thus it operates as its counterpart described inFIGS. 16A–16B. The extra mechanical contact dimples352,356inFIGS. 17A–17Bprovide a stiffer structure after the dimples come into contact allowing the membrane to maintain its gap to the substrate at high electric fields.

The high electric fields and the stiffened structure can be used to apply a larger force to the contact. If the design is such that during actuation the mechanical contact dimples come into contact before metal electrical contact dimple, the force from the electric field must be enough to bend the outer part of the switch membrane between the dimples to make electrical contact. This will reduce the closure contact force somewhat, but will increase the force for opening the electrical contact. This increase in opening force can be useful for reducing stiction. One additional way to stiffen the membrane would be to add a thicker gold plate instead of or in addition to the aluminum plate.

FIG. 18is a schematic of another embodiment of a DC switch390having a two-finger design. Except for the two contacts the switch390is similar to that described inFIGS. 17A–17B. However, this switch390includes segmented top electrodes392, which are contained in the oxide layer of the switch390. This switch will operate similar to those described in FIGS.15and17A–17B. The advantage of two contacts is that they provide a more stable landing avoiding the possible tipping to one side. The mechanical contact dimples and gold plate could be used as a possible enhancement for this design for stiffening the membrane during actuation similar to the effects described inFIGS. 17A–17B.

FIGS. 19A &19Bare schematics of a third embodiment of a DC switch394having a two-finger design. The switch394is similar to that described inFIG. 18. The difference is the cantilever membrane400which also includes an ultra-thin layer of aluminum402as an additional electrode. The ultra-thin layer can be used for x-y addressing, as described inFIG. 6for the capacitive switch. The thin aluminum electrode layer can be used together with the pull down electrode, to actuate the switch. This will allow for isolation between the actuation circuit and the RF circuit. The switch inFIG. 19is a four terminal device.

FIG. 20is an additional embodiment of the DC switch having a two finger design which is also a4terminal device. Instead of the thin aluminum ofFIG. 19as the actuation electrode on the bottom of the membrane containing the RF electrode, one can have the membrane becoming the pulldown electrode with the gold bars408on top of the membrane becoming the RF electrodes.FIG. 20is similar toFIGS. 17A & 17Bbut now gold bars have been added on top of the membrane362. The gold bars408are insulated from the aluminum in the pulldown electrode by the top oxide layer of the membrane406. The gold bars408are connected to or become the contacts410by being fabricated in an opening412through the aluminum pulldown electrode406.

FIG. 21is a schematic of a DC switch416having a three-finger design. It is possible to have devices with arbitrary numbers of contacts418by placing fingers side by side. Multiple fingers will give lower resistance due to the parallel contacts as long as sufficient pressure is available from the electric field for each contact418.

FIG. 22is a schematic of a switch444having a one-finger capacitor and two-finger DC switch design. This switch is a combination of the capacitor and DC switches which were described earlier. In particular,FIG. 22shows the top view of the switch444. The switch444also includes a moving plate448having three RF zone corrugations445. The RF corrugations445form the basis of the one-finger capacitor switch design. In addition, the moving plate448is designed with the dimples454as described herein. The regions447surrounding the dimples454are coated with a thin layer of resist for forming the two-finger DC design.

The cantilever membrane446includes a layer of silicon dioxide sized at 100 nm, aluminum sized at 3000 nm, and silicon dioxide sized at 100 nm. Also, the switch444includes bottom pull-down electrodes, which are positioned below the oxide layer of the switch444. Moreover, these pull-down electrodes provide the necessary potential to pull the moving plate448toward a fixed plate456having a thin layer contact of platinum. In this embodiment, the dimples454are placed over the fixed plate456, and also include a thin platinum contact on their bottom-most portion that comes into contact with the thin platinum contact of the fixed plate456. Other materials can be used in place of the platinum contacts of the dimple454and fixed plate456, such as gold, pladium or iridium or their alloys.

The switch444provides the capabilities wanted in both a capacitive switch and DC switch. In addition, as the DC part of the switch opens, there is still a capacitive component across the contacts associated with the capacitive part of the switch.