EP2024986B1 - Radiofrequency or hyperfrequency micro switch structure and method for producing one such structure - Google Patents

Abstract

The invention relates to a micro switch structure comprising: a substrate (1) covered by a passivation layer (2), a first signal line LS-IN and a second signal line LS-OUT being each located in the extension of the other and separated by a switching region (10); a control electrode (3) arranged in said region, a frequency-invariant dielectric material (4) with high relative permittivity being arranged on the control electrode such that the control electrode is wider on both sides and in the orthogonal direction, between the two signal lines, and the dielectric overlaps on both sides of the control electrode and lies on the passivation layer; and parallel mass lines arranged symmetrically either side of the signal lines and on a topological level separated from that of the signal lines by at least one insulating layer in a material different from that of the passivation layer.

Description

The field of the invention is that of microsystem components also called MEMS (acronym for Micro Electro Mechanical Systems) and more particularly microsystems radiofrequency or microwave. The main application areas are wireless telecommunications systems and radars.

In the following we use generically the term radio frequency or RF, to understand as covering both microwave and radio frequencies.

According to the state of the art of RF MEMS microswitches, the RF switching is obtained by varying the capacitance of a capacitor whose armatures consist on the one hand of a membrane and on the other hand of an electrode control, a dielectric being provided between the two frames generally on the electrode. The capacity then varies from a Con value to a Coff value. The dielectric used may be silicon nitride. In other embodiments, the dielectric is PZT or BZT, or other material with a high relative permittivity, which makes it possible in particular to increase the Con / Coff ratio, and thus improves the transmission and isolation qualities of the micro- switch, as well as its characteristic times of switching between the two states on and off.

RF microswitches are increasingly used to improve the functionality of radio frequency circuits used especially in telecommunication systems. It is a question of obtaining better performances in terms of losses, noise, linearity, consumption. They are also used to obtain high component compactness and the lowest possible manufacturing costs.

There are two types of microswitches providing a radiofrequency signal switching function on a transmission line: the microswitches in series with the radiofrequency transmission line and the microswitches in parallel with the radiofrequency transmission line.

When the microswitches are of the series type, the application of an activation voltage under the membrane changes it from a state of rest off, open, to state on, closed. The configuration of a microswitch in series with a radiofrequency line is as follows: the line is cut in the switching zone, above which one has the membrane. The membrane is isolated from the electrical mass. The membrane does not have to support the radiofrequency power over its entire surface, its role not being to short circuit the signal to ground but simply to connect two lines together by capacitive effect.

When the microswitches are of parallel type, the application of a voltage on the control electrode moves it from a state of rest on, closed, to an open off state. The configuration of a microswitch in parallel with a radiofrequency line is as follows: the RF line is not cut in the switching zone, above which one has the membrane. The membrane is connected to the electrical earth and must be able to withstand the power of the radiofrequency signal.

The operation is as follows: in the rest position, the microswitch is in the on state, closed, which results in a very weak capacitance C, which does not affect the radiofrequency signal transmission. When it is in the low state, under the effect of an activation voltage under the membrane, the capacity increases in a significant ratio, 100 for example. The capacitor then induces a sufficiently weak impedance between the line and the ground to shunt the radiofrequency line to the electrical ground: the radiofrequency signal then flows from the line bringing the RF signal to the electrical mass via the membrane. The two portions of lines, before and after the membrane, are then isolated: the microswitch is in the off state.

• Les techniques de réalisation, qui sont dérivées des technologies classiques de fabrication de circuits intégrés électroniques. Elles permettent de simplifier la réalisation et l'intégration et par conséquent, d'obtenir des coûts de fabrication faibles comparés à ceux d'autres technologies, tout en garantissant une fiabilité élevée ;
• Les très faibles puissances électriques consommées, quelques nanojoules étant nécessaires à l'activation ;
• L'encombrement. On réalise ainsi un micro-commutateur dans une surface de l'ordre du dixième de millimètre carré, permettant d'atteindre une forte capacité d'intégration ;
• Les performances en utilisation hyperfréquence. Ce type de micro-commutateur présente des pertes d'insertion très faibles, de l'ordre du dixième de déciBel, bien inférieures à celles de dispositifs assurant les mêmes fonctions.

The main advantages of these types of serial or parallel microswitches are essentially:

• The realization techniques, which are derived from conventional technologies of manufacturing electronic integrated circuits. They simplify the realization and integration and therefore, to obtain low manufacturing costs compared to other technologies, while ensuring high reliability;
• The very low electric powers consumed, some nanojoules being necessary for the activation;
• Congestion. A micro-switch is thus produced in a surface of the order of one tenth of a square millimeter, making it possible to achieve a high integration capacity;
• Performance in microwave use. This type of micro-switch has very low insertion losses, of the order of one-tenth of decibel, much lower than those of devices providing the same functions.

The search for higher switching speeds, larger RF power outages equal to or greater than ten watts, wideband operation of at least 18 GigaHertz, the lowest compactness possible and always at a lower cost, of duration increasingly important life (number of switches), of the order of 10 ¹¹ at least to respond to the evolution and the need of the market, including civil markets such as mobile telephony, leads to search for structures and processes optimized fabrication, the known structures of micro-switches imperfectly meet these needs.

The invention thus relates to a structure and a method of manufacturing a micro-switch that can meet all of these different needs. It applies to both serial and parallel microswitches.

A structure of a capacitor-type microswitch, according to the preamble of claim 1, is known from the document FR 284 5075 .

• l'électrode de commande est formée sur ladite couche de passivation,
• la couche de matériau diélectrique est à forte permittivité relative supérieure à une centaine.

As characterized by the invention therefore concerns the structure of a capacitor-type radio frequency or microwave microswitch with a first armature comprising a voltage control electrode arranged in a switching zone between a first conductive line called an input signal line. and a second conductive line called an output signal line arranged in the extension of one another, separated by the switching zone, a second armature being a flexible membrane disposed above said switching zone, the two armatures being separated by a vacuum or gas thickness and at least one layer of a dielectric material, two parallel ground lines being arranged symmetrically with respect to the signal lines, said structure being formed on an insulating substrate covered with a layer of passivation. The structure is such that:

• the control electrode is formed on said passivation layer,
• the layer of dielectric material has a high relative permittivity greater than one hundred.

• la couche de matériau diélectrique est déposée sur ladite électrode de commande, en sorte que suivant la direction des lignes d'entrée et de sortie, ledit matériau diélectrique ne repose que sur ladite électrode de commande et suivant la direction orthogonale, ledit matériau diélectrique déborde de chaque côté et vient en contact avec ladite couche de passivation du substrat,
• la membrane flexible est conductrice et comporte au moins une couche d'un matériau conducteur.
• au moins une couche d'isolant dans un matériau différent de celui de la couche de passivation sépare le niveau des lignes de masse du niveau des lignes signal.

According to the invention:

• the layer of dielectric material is deposited on said control electrode, so that in the direction of the input and output lines, said dielectric material rests only on said control electrode and in the orthogonal direction, said dielectric material overflows with each side and comes into contact with said substrate passivation layer,
• the flexible membrane is conductive and comprises at least one layer of a conductive material.
• at least one insulating layer in a material different from that of the passivation layer separates the level of the ground lines from the level of the signal lines.

Said high-permittivity material is preferably PZT (Lead Zirconium Titanate, PbZrTiO ₃ ).

According to one embodiment of the invention, the metal membrane comprises a lower layer of a resistive material, typically a titanium-tungsten alloy and a low-resistivity layer, of a material capable of withstanding mechanical stress, selected from Al, Au, Cu, preferably Al.

For use as a variable capacitor, in which it seeks to control the movement of the membrane between the rest position and a maximum position between the dielectric and the rest position, the membrane is formed of a single layer of aluminum.

• a).Formation de l'électrode de commande;
• b).Formation du diélectrique, sur ladite électrode de commande,
• c).Dépôt sur toute la surface d'une première couche conductrice résistive et d'une deuxième couche conductrice peu résistive, et gravure de la deuxième couche, pour former les lignes signal d'entrée/sortie et des plots de contact,
• d).Dépôt sur toute la surface d'une couche d'isolant, dans un matériau différent de celui de la couche de passivation, puis ouverture sur les lignes signal, des plots de contact et sur le diélectrique,
• e).Dépôt sur toute la surface d'une première couche conductrice résistive et d'une deuxième couche conductrice peu résistive, et gravure de la deuxième couche, pour former les lignes de masse, f).Dépôt d'une épaisseur déterminée de résine sur toute la surface et recharge localisée à concurrence de la hauteur de résine du matériau de ladite deuxième couche conductrice peu résistive des lignes signal et de masse,
• g).Gravure localisée sous l'emplacement de la membrane de la première couche conductrice déposée à l'étape e).
• h).Formation de la membrane ;
• i). Libération de la membrane, par suppression de la couche de résine de l'étape f).

The invention also relates to a method for manufacturing a radio-frequency or microwave microswitch of such a microswitch on an insulating substrate covered with a passivation layer, characterized in that it comprises at least the succession of following steps :

• a) .Training of the control electrode;
• b) .Training of the dielectric on said control electrode
• c) .Deposit on the entire surface of a first resistive conductive layer and a second non-resistive conductive layer, and etching of the second layer, to form the input / output signal lines and contact pads,
• d) .Deposit over the entire surface of an insulating layer, in a material different from that of the passivation layer, then opening on the signal lines, contact pads and on the dielectric,
• e) .Deposit on the entire surface of a first resistive conductive layer and a second non-resistive conductive layer, and etching of the second layer, to form the ground lines, f) .Deposit of a determined thickness of resin over the entire surface and localized charging up to the resin height of the material of said second conductive layer of low resistive signal and mass lines,
• g). Localized etching under the location of the membrane of the first conductive layer deposited in step e).
• h). Formation of the membrane;
• i). Release of the membrane, by removing the resin layer of step f).

• les figures 1 a à 1c illustrent une structure de commutateur série selon l'invention;
• les figures 2a à 2c illustrent une structure de commutateur parallèle selon l'invention;
• la figure 3a et les figures suivantes jusqu'à la figure 12 illustrent des étapes d'un procédé selon l'invention.

The invention will be better understood and other advantages will become apparent on reading the description which follows, given by way of non-limiting example and thanks to the appended figures among which:

• the figures 1 a to 1c illustrate a serial switch structure according to the invention;
• the Figures 2a to 2c illustrate a parallel switch structure according to the invention;
• the figure 3a and the following figures until the figure 12 illustrate steps of a method according to the invention.

A radiofrequency or microwave microswitch structure according to the invention is illustrated on the figures 1 a to 1 d, for a series-type microswitch or on Figures 2a to 2c for a parallel-type microswitch.

A structure according to the invention comprises on a substrate 1 covered with a passivation layer 2, a first signal line LS- _IN and a second signal line LS- _OUT arranged in the extension of one another, separated by a switching zone 10; a control electrode 3 in said zone, a dielectric material 4 with a high relative invariant frequency permittivity, arranged on the control electrode so that between the two signal lines, the control electrode is wider on both sides and in the orthogonal direction, the dielectric overflows both sides of the control electrode, and rests on the passivation layer; parallel ground lines arranged symmetrically on either side of the signal lines and made on a topological level separated from that of the signal lines by at least one insulating layer 6 in a material different from that of the passivation,

The insulating material is advantageously silicon nitride Si ₃ N ₄ .

The dielectric material is advantageously PZT whose relative permittivity is equal to 150, and is independent of the frequency, which contributes to increasing the width of the operating frequency band of the micro-switch. In addition, the PZT which has a monocrystalline structure resists well to significant RF powers.

A series-type microswitch structure will be described in more detail. The figure 1 a represents a top view of such a micro-switch and the Figures 1b and 1c are sectional views respectively along AA, and following BB.

This structure is made by superposition of layers on a base substrate 1, typically a highly resistive silicon substrate, covered with a passivation layer 2, typically silicon oxide SiO ₂ .

It comprises two signal lines LS- _IN and LS- _OUT arranged coplanar in the extension of one another, separated by a switching zone 10. In the switching zone, a control electrode 3 is formed between the two lines signal, in two parts electrically isolated: each part contacts a signal line. A dielectric 4 with a high relative permittivity greater than one hundred and invariant with the frequency is deposited on the control electrode 3. It has a shape such that that in the direction following the signal lines, the control electrode is wider on both sides, and in the orthogonal direction, it overflows on either side of the control electrode 3, on the passivation layer 2.

The dielectric 4 must make it possible to respond to the constraints of high radiofrequency or microwave powers: in on-state transmission, passing (membrane in downwardly bent position, in contact with the dielectric), and in isolation in the off or open state. (membrane in initial high position).

The dielectric 4 is preferably PZT, which combines the advantages of having a high relative permittivity greater than one hundred (typically 150), invariant with the frequency, of being able to work in the microwave, up to 100 GigaHertz, and to support the power, because of its monocrystalline nature.

In practice, the gap separating the two parts of the control electrode has a width g of the order of 10 microns. The cut between the two parts may be straight section. It is advantageously such that the two parts are interdigitated. In known manner, such a shape makes it possible to significantly increase the dielectric capacitance of the capacitor formed by the membrane m, the control electrode 3 and the dielectric 4.

Preferably, the control electrode is made of a titanium platinum alloy surmounted by a platinum / gold layer and this for technological needs.

The membrane m rests at each end, on a conductive pillar 5a, 5b. It is also possible to consider only one conductive pillar on the two that support the membrane.

Ground lines LM1 and LM2 are formed on the same surface of the substrate as the LS- _IN and LS- _OUT signal lines. These coplanar ground lines are made on a topological level separated from the level of the input / output signal lines by an insulating layer 6, in a material different from that used for the passivation layer. In this way, it is certain that there will not be a short circuit between a signal line and a ground line, via the substrate. This has the technical effect that the micro-switch structure according to the invention can be very high in frequency, typically up to at least 100 GigaHertz. The insulation used is advantageously silicon nitride.

The pillars, the signal lines and the ground lines typically comprise a first resistive conductive conducting layer, represented in thick black on the Figures 1b and 1c and a second, weakly resistive layer, typically gold. The first layer is sufficiently resistive to prevent the propagation of a radiofrequency or microwave signal. It is typically a layer of tungsten titanium, preferably 80% titanium and 20% tungsten to 1 or 2%, by which the best radiofrequency and microwave performance are obtained.

The titanium-tungsten layer 7 of the signal lines and pillars also serves for the realization of connection lines through which an activation voltage of the microswitch can be applied in the switching zone. In practice, at least one contact pad (not shown on the Figures 1a to 1c ) is made in the same way as the signal line and the pillars, on the same topological levels and a connection line is formed between this pad and at least one signal line. Preferably the contact pad is connected to the two signal lines LS- _IN and LS- _OUT , so that the voltage is found on the two parts of the control electrode 3. The arrangement in interdigitated fingers allows to have a part substantially in the middle under the membrane. These two combined characteristics make it possible to obtain a maximum electrostatic field substantially in the middle of the membrane, which ensures optimum on and off switching times.

• une couche conductrice d'accroche, résistive, typiquement en titane-tungstène, faisant face à la zone de commutation. Cette couche est suffisamment résistive pour empêcher la propagation d'un signal radiofréquence ou hyperfréquence. Le titane tungstène a de préférence une proportion de 80 % de titane et 20% de tungstène à 1 ou 2 % près, comme indiqué précédemment;
• et une couche très conductrice. Ce peut être un diélectrique. De préférence, on choisit un matériau métallique, sélectionné parmi, Al, Cu et Au, pour leur faible résistivité électrique et leur capacité à résister à un stress mécanique supérieur à 30 mégapascals : la membrane doit pouvoir se déformer pour venir en contact du diélectrique 4 sans se casser (état on), et revenir dans son état initial (état off). De préférence, c'est l'aluminium qui est utilisé, par lequel les meilleurs résultats sont obtenus en terme de rapidité de commutation et de résistance au stress mécanique.

The conductive membrane comprises:

• a conductive, resistive conductive layer, typically made of titanium-tungsten, facing the switching zone. This layer is sufficiently resistive to prevent the propagation of a radiofrequency or microwave signal. The tungsten titanium preferably has a proportion of 80% of titanium and 20% of tungsten to 1 or 2%, as indicated previously;
• and a very conductive layer. It can be a dielectric. Preferably, a metal material selected from Al, Cu and Au is chosen for their low electrical resistivity and their ability to withstand mechanical stress greater than 30 megapascals: the membrane must be capable of deform to come into contact with the dielectric 4 without breaking (state on), and return to its initial state (off state). Preferably, aluminum is used, whereby the best results are obtained in terms of switching speed and resistance to mechanical stress.

The membrane is made in the form of a grid, that is to say that it has holes passing through it from one side to the other. This configuration contributes to facilitating the production of the membrane, as will be seen in connection with the manufacturing process, because it facilitates the passage of solvents or gases to remove the sacrificial resin layer which serves as a plane support for producing the membrane. This configuration also contributes to improving the flexibility of the membrane. Finally, the grid shape is well known in the form of a performant in the radio frequency and microwave domain.

In a preferred embodiment, the serial micro-switch has the following sizing characteristics:

The section of the signal lines has a width ls of 80 microns, and the distance d between each side of the signal line of the ground line is 120 microns.

The gold layer e9 signal lines and pillars has a thickness of about 3 microns. The control electrode has a thickness of about 0.7 microns. The thickness of the ground lines is not an important parameter. It is substantially equal to that of the signal lines, from 0.2 to 0.4 microns, the negligible difference arising from the technological process. The layer 4 of PZT has a thickness e4 less than one micron, for example 0.4 micron. The width of the overhang on each side of the dielectric is of the order of 20 microns.

The mobile part of the membrane, that is to say off pillars, is part of a rectangular parallelepiped, the dimensions of which are advantageously: a width lm of 100 microns, in the direction of the signal lines, and a length wm between the two pillars, of the order of 280 microns. The total thickness e em of the membrane is of the order of 0.7 microns, the first layer of tungsten titanium being of less thickness than the second layer. In one example, the tungsten titanium layer has a thickness of 0.2 microns.

The structure of a parallel microswitch according to the invention is illustrated on the Figures 2a (view from above), 2b and 2c (views in sections respectively AA and BB), which use the same references as in the Figures 1a to 1c . The structure is substantially identical to that of the serial micro-switch. The differences are due to the specificities of the parallel type compared to the series type. In particular, the membrane resting directly on the ground lines, there are no pillars 5a, 5b, and the control electrode has a continuous shape and contacts each side a signal line. For these reasons, the foregoing description made in relation to the Figures 1a to 1c applies in the same way, with the reservations that have just been made.

The preferred dimensioning characteristics of a parallel microswitch according to the invention are identical to those indicated above for the series structure.

In a variant applicable both to the series and parallel mode, the membrane is made of a single aluminum layer, preferably with a thickness of the order of 2.5 microns, making it possible to produce a capacitor with variable capacitance, the voltage activation then defining the value of the capacitance, as a function of the displacement imposed on the membrane.

The series and parallel microswitches according to the invention have good radio frequency and microwave performance, in particular for the transmission of radiofrequency or microwave significant power signals of the order of about ten watts or more.

A method of manufacturing a micro-switch advantageously used in the invention, as described in connection with the Figures 1a to 1c will now be described. It is illustrated by the figures 3a and following, which show different stages.

Beforehand, each conductive element: signal lines, ground lines, contact pads, and membrane are made by a first highly resistive conductive layer and a second non-resistive conductive layer.

Preferably, the first layer is a tungsten titanium alloy in a proportion of 80% of titanium and 20% of tungsten to 1 or 2%, and the second layer is gold, this choice making it possible to obtain the best performances. In the description of the process steps, for simplicity, we speak directly of tungsten titanium and gold, but other materials such as copper and aluminum, for example, could be used without departing from the scope of the invention.

Step 1, figures 3a (view from above) and 3b (section along X). We have a substrate 100, preferably highly resistive silicon (or GaAs, GaN ...). This substrate 100 is deposited on a passivation layer made of silicon oxide SiO ₂ (relative permittivity 4). The control electrode 102 is formed, with its shape in two isolated parts a, b, preferably as illustrated, interdigitated. The width g of the gap between the two parts is typically 10 microns. The control electrode is for example made of a titanium / platinum alloy surmounted by a gold / platinum layer.

2nd step, Figures 4a and 4b . The PZT dielectric 103 is formed on the control electrode in the prescribed form, typically by a sol-gel or sputtering method: narrower in the Ds direction of the signal lines and wider on both sides in the orthogonal direction , coming to rest on the layer 101 of passivation.

Step 3, figures 5a (view from above) and 5b (section along YY '). Formation of the LS- _IN and LS- _OUT signal lines, contact pads Pc, and PI pillars, by deposition of a Titanium / Tungsten layer 104, deposition and etching of a gold layer 105. surface is then layer 104.

Step 4, Figures 6a and 6b etching of the titanium / tungsten layer 104, to form connection lines, between a contact pad and one or both signal lines (to bring an activation voltage to one or both parts of the control electrode ), and between a contact pad and a pillar, which allows to put the membrane to a reference potential (an electrical ground, which is not the mass of the circuit microswitch). As a surface layer, apart from the elements made, the passivation layer 101 is found.

Step 5, Figures 7a and 7b . Deposition of the silicon nitride insulator layer Si ₃ N ₄ , then opening O on the signal lines, and the contact pads, the pillars and the dielectric 103, according to the dashed lines. The surface layer is this layer 106 of insulation.

Step 6, Figures 8a and 8b . Depositing a layer 107 of titanium / tungsten and depositing and etching a layer of gold 109, to form the lines of mass L _M1 and L _M2 . The surface layer is titanium / tungsten layer 107.

Step 7, Figures 9a and 9b . Localized removal of tungsten titanium in an area f under the location of the membrane.

Step 8, figure 10 . Localized refill of gold, by prior resin deposition on the whole surface and by injection of current via the contact pads and the connecting lines. The height of gold thus obtained is controlled by the resin thickness. In practice the thickness (or height) of gold signal lines and pillars reaches 3 microns. The thickness of the mass lines is substantially equal, with in practice a negligible difference of the order of 0.2 to 0.4 microns (less). The resin achieves the same level everywhere, which ensures the flatness of the membrane which is achieved in the next step.

Step 9, Figures 11a and 11b . Formation of the membrane by deposition of tungsten titanium then deposition of Aluminum (or Gold, or Copper), and etching of the membrane. Preferably, a tungsten titanium thickness of 0.2 microns and a gold thickness of 0.5 microns is used. For a micro-switch used as variable capacitor as in the impedance matching circuit, this step 9 comprises the deposition of a single layer, aluminum, with a thickness of about 2.5 microns and etching.

Step 10, figure 12 : release of the membrane by removing the resin layer of step 8, for example by solvents. This operation is facilitated by a membrane which is pierced with holes. Such a membrane structure also has the effect of making the membrane less rigid, which contributes to improving the latency.

This method also applies to parallel-type switches which differ from serial microswitches simply in that there are no pillars, the membrane resting directly on the ground lines, and by the continuous form, without cutting off the control electrode between the two signal lines.

The succession of the steps of the method just described, leads to a micro-switch structure whose radio frequency performance in transmission, isolation, switching time, the service life, the width of the frequency band are substantially improved.

Claims (20)

1. A radio-frequency or hyper-frequency micro-switch structure of the capacitor type with a first armature comprising a voltage control electrode (3) disposed in a switching zone (10) between a first conducting line, referred to as input signal line (LS-_IN), and a second conducting line, referred to as output signal line (LS-_OUT), disposed in the extension of one or other, separated by the switching zone (10), a second armature being a flexible membrane (m) disposed above said switching zone, the two armatures being separated by a vacuum or a gas thickness and at least one layer of a dielectric material, two parallel ground lines (LM1, LM2) being disposed symmetrically relative to the signal lines, said structure being made on an insulating substrate (1) that is coated with a passivation layer (2), and such that:

   - said control electrode (3) is formed on said passivation layer (2);

   - said layer of dielectric material (4) has a high relative permittivity that is greater than one hundred;

   characterised in that:

   - the layer of dielectric material (4) is deposited onto said control electrode (3) so that, along the direction of the input and output lines, said dielectric material only rests on said control electrode and along the orthogonal direction said dielectric material protrudes on each side and makes contact with said passivation layer (2) of the substrate;

   - the flexible membrane is conducting and comprises at least one layer of a conducting material;

   - at least one insulating layer (8), made from a different material from that of the passivation layer (2), separates the level of the ground lines from the level of the signal lines.
2. The structure according to claim 1, characterised in that said dielectric material (4) is PZT.
3. The structure according to claim 1 or 2, characterised in that said insulator (8) is silicon nitride Si₃N₄.
4. The micro-switch structure according to claim 1 or 2, characterised in that the thickness of the signal lines is of the order of 3 microns and the thickness of the control electrode is of the order of 0.7 microns.
5. The micro-switch structure according to claim 1 or 2, characterised in that the signal lines and the ground lines include a lower layer with high resistance and an upper layer with low resistance.
6. The micro-switch structure according to any one of the preceding claims, characterised in that the membrane comprises a lower layer with high resistance (m1) facing the switching electrode that is made from titanium-tungsten, and an upper layer that is made from a material that is selected from Al, Cu or Au.
7. The structure according to any one of claims 1 to 5, characterised in that the membrane is formed from a single layer of aluminium with a thickness of the order of 2.5 microns, for use as a variable capacitor.
8. The micro-switch structure according to claim 5 or 6, characterised in that said lower layer is a layer of titanium-tungsten that is an alloy with a proportion of 80% titanium and 20% tungsten, with a tolerance of 1 or 2%.
9. The micro-switch structure according to claim 6, characterised in that the total thickness of the membrane is of the order of 0.7 microns, the thickness of the upper layer being of the order of 0.5 microns.
10. The micro-switch structure according to any one of the preceding claims, characterised in that the thickness of the dielectric material (4) is of the order of 0.4 microns.
11. The micro-switch structure according to any one of the preceding claims, characterised in that the width (ls) of the signal lines is 80 microns and the distance (d) to each ground line is 120 microns.
12. The micro-switch structure of the series type according to any one of the preceding claims, characterised in that said control electrode (3) comprises at least two separate parts, each in contact with one of the signal lines, a gap zone between the two parts being substantially located in the middle of the switching zone, and in that said membrane (m) rests at each end on a post (5a, 5b) that is disposed between the signal lines and a ground line.
13. The structure according to claim 12, characterised in that said parts of the control electrode are interdigitated.
14. The micro-switch structure of the parallel type according to any one of claims 1 to 11, the membrane resting at each end on a ground line and the control electrode having a unit form connecting the signal lines on each side.
15. The structure according to any one of claims 11 to 13, characterised in that the part of the membrane that is outside of the posts falls substantially within a rectangular parallelepiped having a length between the posts of the order of 280 microns and a width of the order of 100 microns.
16. The structure according to any one of claims 12 to 15, characterised in that the length of each protrusion of the dielectric material (4) on the passivation layer (2) is of the order of 20 microns.
17. A method for manufacturing a radio-frequency or hyper-frequency micro-switch according to claim 1 on an insulating substrate (100) coated with a passivation layer (101), characterised in that it at least comprises the following succession of steps:

    - a) forming the control electrode (102);

    - b) forming the dielectric material (13) on said control electrode;

    - c) depositing over the entire surface a first resistive conducting layer (104) and a second low-resistance conducting layer (105), and etching the second layer so as to form the input/output lines and contact pins;

    - d) depositing over the entire surface an insulating layer (106) made from a different material from that of the passivation layer (12), then opening onto the signal lines, contact pins (105) and onto the dielectric material (103);

    - e) depositing over the entire surface a first resistive conducting layer (107) and a second low-resistance conducting layer (108) and etching the second layer so as to form the ground lines;

    - f) depositing a determined thickness of resin over the entire surface and locally refilling up to the level of the resin with the material (Au) of said second low-resistance conducting layer (15, 108) for the signal and ground lines;

    - g) locally etching under the location of the membrane of the first conducting layer (107) deposited during step e);

    - h) forming the membrane (m);

    - i) releasing the membrane by removing the resin layer of step f).
18. The manufacturing method according to claim 17, characterised in that the layer of dielectric material is deposited by a sol-gel or cathode sputtering method.
19. The manufacturing method according to claim 17, characterised in that the membrane is perforated with holes.
20. The manufacturing method according to any one of claims 17 to 19 for a series type micro-switch, characterised in that in step c) posts are also formed, to which step f) for localised refilling is applied, the membrane formed in step i) resting at each end on said posts.

Images