Patent ID: 12249468

DETAILED DESCRIPTION OF THE INVENTION

FIGS.1a-cshow a diagram of a switch according to the invention in top view. The first RF line3is electrically connected to the MEMS membrane5by anchors51, thus allowing an RF signal passing through the MEMS membrane5to propagate in the first RF line3. The second RF line4has a first section41in contact with the face21of the substrate2and a second section42partially covering the dome6. These two sections are electrically connected to one another, thus allowing an RF signal passing through the first section41to propagate in the second section42(FIG.1a).

The stack comprising the MEMS membrane5, the dielectric (comprising the dielectric layer of the dome as well as any layer of air between the membrane5and the dielectric layer of the dome if the membrane5is not completely deflected), and the second section42of the second RF line4forms the capacitance. The signal propagates from one RF line to the other through this stack. When the membrane5is deflected toward the RF line4and comes into contact with the dielectric dome, the capacitance is higher. The switch according to the invention can therefore be used as switched capacitance. In this particular case, the activation of the membrane is done by the RF line.

The dome6ofFIGS.1aand1bincludes opposite faces61,62and comprises at least one dielectric layer and is covered by a layer of metal that can be discontinuous, the component patterns of which are connected to the first RF line3(FIG.1b). The component metal of the RF lines3and4makes it possible to guarantee the hermiticity of the cavity.

The dome6has several anchor points63on the planar face21of the substrate2and three openings64,65able to allow the elimination of sacrificial layers S1, S2having been used to develop the MEMS membrane5and the dome6(cf. description ofFIGS.7aand7bbelow): two openings64closed by the first RF line3(visible inFIGS.1aand1b) and an opening65closed by the second RF line4(visible inFIGS.1aand1c). As shown inFIG.1b(for the opening64) andFIG.1c(for the opening65), these openings are lateral openings, which are not across from the upper face52of the MEMS membrane5.

FIG.2shows a schematic sectional view of a switch according to the invention in the case where it is used as capacitance and where the second RF line4is inserted partially into the dielectric layer of the dome6. In this particular case, the second section42of the second RF line4is still separated from the MEMS membrane by at least one dielectric layer8. The more deeply the RF line is inserted into the dome6, the higher the maximum capacitance is, obtained when the MEMS membrane5comes into contact with the dome6.

FIG.3shows a schematic sectional view of a switch according to the invention in the case where it is used as capacitance and where a metal layer8is arranged below the dielectric layer. The advantage of this method is allowing nearly perfect reproducibility of the switched capacitance subject to a slight degradation of the quality factor.

FIGS.4aand4bshow a schematic sectional view of a switch according to the invention in the case where it is used as ohmic contact and has upper71and central72electrodes. In this particular case, each of the upper activation electrodes71is connected to a central electrode72by a metal via75passing through the dome6(FIG.4a). The activation electrodes are essential in the case of the ohmic contact, the activation of the membrane not being able to be done via the RF lines that come into contact.

The ohmic contact ofFIG.4is done via a metal contact pin91passing through the dome and being in contact with the second RF line4. When the membrane is deflected, it comes back into contact with said metal pin and allows the RF currents to pass between the two RF lines (RF lines3and4).

FIG.5shows a schematic sectional view of a switch according to the invention in the case where it is used as variable capacitance and where it has lower electrodes73and a stop pin9. This pin here may either be placed below the MEMS membrane5and in contact with said membrane or on the face21of the substrate2and in contact with said face. When the membrane is deflected toward the lower electrodes73, the pin limits the deflection of the MEMS membrane5toward the lower electrodes73, leaving an air gap between the MEMS membrane5and the lower electrodes73. Without said pin, the lower electrodes73could come into contact with the membrane, which would charge the membrane5and cause the device to fail.

FIG.6shows a schematic sectional view along line AA′ of a switch according to the invention in the case where it is used as ohmic contact and has central72and lower73electrodes. The activation electrodes71,73cannot deflect the membrane5toward them. Thus, adding lower electrodes73makes it possible to deflect the membrane5toward the substrate2and increase the amplitude of the variations in electric properties of the device.

FIGS.7aand7bshow schematic views of the different successive steps a) to g) to produce a switch according to the invention, with a sectional view along line AA′ (FIG.7a) and a sectional view along line BB′ (FIG.7b).

InFIGS.7aand7b, the diagrams corresponding to step (a) show a first sacrificial layer S1deposited on the substrate2after shaping thereof.

InFIGS.7aand7b, the diagrams corresponding to step (b) show a first metal layer M1deposited on the first sacrificial layer S1. This first metal layer M1is shaped by etching (dry or wet) to create the first RF line3and the MEMS membrane5, these two components being electrically connected to one another by the anchors51of the MEMS membrane.

InFIGS.7aand7b, the diagrams corresponding to step (c) show the second sacrificial layer S2after shaping thereof.

InFIGS.7aand7b, the diagrams corresponding to step (d) show the dielectric layer after shaping thereof to create the dome6. The dome6is anchored in the substrate2and allows the first RF line3to pass in order to allow the connection with the MEMS membrane5.

The openings64,65allow the dry etching or wet etching of the sacrificial layers, wet etching requiring an additional step for critical point dryer.

InFIGS.7aand7b, the diagrams corresponding to step (e) show the result of the step for eliminating the sacrificial layers.

InFIGS.7aand7b, the diagrams corresponding to step (f) show that step f) is a step for depositing a second metal layer M2, said layer being intended to serve as a base for forming the different patterns of the following step.

As illustrated in the diagrams corresponding to step (g) ofFIGS.7aand7b, said second metal layer M2is shaped by lift-off and/or etching (dry or wet) in order to create the second RF line4and to close the openings64,65formed during the preceding step, in a manner. This second RF line4is broken down into a first section41in contact with the planar face21of the substrate2, and a second section42adjacent to the first section41(i.e., that is electrically connected to it). At least one of said second RF line4and said first RF line3closes the lateral openings64,65, thus creating a hermetic cavity C that encapsulates the MEMS membrane.