Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/32—Non-reciprocal transmission devices
  • H01P1/38—Circulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/10—Auxiliary devices for switching or interrupting
  • H01P1/12—Auxiliary devices for switching or interrupting by mechanical chopper
  • H01P1/127—Strip line switches
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H59/00—Electrostatic relays; Electro-adhesion relays
  • H01H59/0009—Electrostatic relays; Electro-adhesion relays making use of micromechanics

Definitions

• a telecommunication system mainly comprises a central signal processing part providing, in particular, AT attenuation and phase-shift D functions, which are typically implemented. implemented by digital electronic circuits (chips), associated with a transmitter stage E, a receiver stage R and an antenna A.
• the emitter E stage mainly comprises a DRA amplifier (for "Digital Research Amplifier"), a HPA amplifier (for "High Power Amplifier '', and an insulator I.
• An insulator is a special case of pump.
• a load is 50 ohms connected to one of the ports (usually port 3 by convention) Whatever the impedance of the circuit connected to the output on the second port p2, there is practically no return to the transmitter (port p1): most of the power returned or coupled is dissipated by the load connected at p3.
• An isolator is usually used to minimize signal feedback on the output of the HPA. Indeed, any signal arriving at the output of the HPA could cause a major malfunction or even the destruction of this component.
• the receiver stage R comprises a LIM bandwidth limiting circuit and a signal amplifier generally noted LNA (Low Noise Amplifier).
• a three-way circulator C (or ports) p1, p2, p3 controlled by an electronic activation circuit (not shown) makes it possible to transfer a radiofrequency signal supplied by the emitting stage to the antenna A
• the radio frequency circulator C must in particular have the following binding characteristics: have fast switching times; support the high radiofrequency power of the signals to be transmitted to the antenna; have limited insertion losses.
• the radiofrequency circulators used are voluminous structures with ferrite and permanent magnet which imposes a direction of electromagnetic gyration.
• These ferromagnetic circulators have different disadvantages. These are very expensive components. They are not easily reproducible because they require human intervention for proper adjustment. Their structure is very bulky. They occupy about 80% of the space in a telecommunication system. They consume a lot of electrical power, and therefore pose problems of heat dissipation. They introduce insertion losses (radiofrequency power losses in the coupling through the ferrite) of the order of 2 to 4 dB in their operating frequency band, which is otherwise narrow, of the order of 0.2 to 1. Gigahertz. For all these different reasons, we seek to replace the ferromagnetic circulators with components that do not have these disadvantages.
• the invention proposes an alternative solution for simplifying the production of circulators, reducing their manufacturing cost, and the area occupied, to reduce the dissipated electrical power.
• An idea underlying the invention is to use electromechanical micro-devices called MEMS (according to the acronym for Micro Electro Mechanical System), and more particularly microdevices of the capacitor type, functioning as switches, micro -devices called micro-switches in the following.
• Capacitor-type micro-switches are particularly appreciated in microwave applications, especially for their low response times combined with low control voltages ranging from a few volts to a few tens of volts. They are advantageously very small, of millimeter size (2 to 10 mm 2 ), which is on average 10 times smaller than a ferromagnetic circulator. They consume very little. They are inexpensive to produce because they use the usual fabrication techniques in microelectronics, from a substrate generally silicon and are very easily reproducible. Their insertion losses are very low, generally of the order of 0.1 to 0.2 dB over a very wide frequency band, 18 to 19 GigaHertz.
• series-type microswitches are concerned: an input signal line and an output signal line extending one from the other, separated by a switching zone, and electrically isolated, and above the switching zone, a flexible membrane resting on pillars.
• the switching zone is covered with a dielectric.
• the membrane is either in the rest position, high, the capacity formed by the switching zone, the dielectric and the membrane having a low Coff value, so that the two signal lines are isolated, or in the low position so that the two line portions are capacitively coupled, the capacitance formed by the switching zone, the dielectric and the membrane having a high Con value, allowing the transmission of a radiofrequency or microwave signal.
• the control of the membrane is a voltage control suitably applied in the switching zone, the membrane being brought to a reference potential (electrical ground) by the pillars.
• the switching performance depend in particular on the Con on Coff report which must be as high as possible.
• An idea underlying the invention is to take advantage of all the qualities of such a series-type micro-switch component for to realize a circulator adapted to radiofrequency telecommunication systems.
• the invention therefore relates to a circulator with at least three ports, a first input port for receiving a radiofrequency or microwave signal to be transmitted to a second port intended to be connected to a transmitting / receiving antenna, a third output port capable of being connected to a receiver device of a radiofrequency or microwave signal.
• the system is characterized in that it comprises two identical electromechanical microswitches of the series type according to the invention, formed on the same substrate, a first microswitch being arranged to allow the transmission of a radiofrequency or microwave signal from said an input port to the port for connection to an antenna, a second micro-switch being arranged to allow signal transmission between said second port to said output port, and in that it is associated with a signal circuit; impedance matching connected between the second port and the antenna, said circuit having the function of acting as a virtual obstacle to the transmission of a radiofrequency or microwave signal from said second port to the first port.
• the circulator has at least three ports, an input port for receiving a radiofrequency signal to be transmitted to a port intended to be connected to a transmitting / receiving antenna, an output port adapted to be connected to a device receiver or charge. It comprises two identical series electromechanical microswitches formed on the same substrate.
• a first micro-switch is arranged to allow the transmission of a radiofrequency or microwave signal from said input port corresponding to the first signal line of said first micro-switch to the port to be connected to an antenna, corresponding to the second signal line of said first micro-switch, a second micro-switch is arranged to allow signal transmission between the port to be connected to an antenna, corresponding to the first signal line of said second micro-switch to said port of output corresponding to the second signal line of said second micro-switch.
• the circulator includes at least first and second contact pads for applying control voltages to the on or off state on at least one of the control electrode parts of the first microswitch and the second microswitch.
• the activation voltages are of the order of volts to a few tens of volts.
• the microswitches can be simultaneously controlled in the off state, or one in the on state and the other in the off state.
• the structure of the microswitches of such a circulator must be very well matched in impedance so that the radiofrequency power transmission is significant.
• a micro-switch structure or topology is sought which is able to withstand the high radiofrequency power to be transmitted to the antenna (in transmission), with good radiofrequency and microwave transmission and isolation properties, low losses through insertion, low latency (switchover time in the off state and in the on state), and keeping low control voltage levels of the order of a few volts to a few tens of volts.
• each micro-switch of the circulator is formed on a base substrate covered with a passivation layer, and is characterized in that it comprises:
• a mobile metal diaphragm forming a bridge over a switching zone between a first signal line and a second signal line isolated between them.
• the first and second signal lines are arranged in the extension of one another and said membrane comprises at least one layer of a metallic material selected from Al, Au or Cu, a voltage control electrode made of a material resistive conductor on the passivation layer, in said switching zone, and comprising two electrically insulated parts, one in contact with the first signal line and the other in contact with the second signal line, a relative permittivity dielectric greater than one hundred and frequency invariant, disposed on said control electrode, and having a shape such that in the direction of the two signal lines, said control electrode is wider on both sides, and next the orthogonal direction, the dielectric material protrudes on both sides of said control electrode, and comes into contact with said passivation layer.
• the membrane rests at least one end on a conductive pillar, said conductive pillar and the signal lines being made on said passivation layer.
• the circulator comprises two parallel coplanar mass lines, arranged symmetrically with respect to said first and second signal lines, said ground lines being separated from said ground lines by an insulating layer made of a material different from that of the first passivation layer of the substrate.
• the impedance matching circuit is advantageously formed by two series-type micro-switches made on the same substrate, used in variable capacities, each disposed between two sections of a signal line which is intended to be connected to one end. the port of the circulator for receiving the antenna, and at another end, to be connected to the antenna, the capacity of each micro-switch being defined by the voltage applied to a respective control electrode and the geometric characteristics of the membrane, the inductance of each cell being defined by the geometric dimensions of a corresponding signal line section.
• the invention also relates to a radiofrequency telecommunication system comprising a transmitting antenna, an amplifier transmitting circuit, an amplifier receiving circuit and a first circulator according to the invention with a first port connected to the output of the circuit. a second port connected to the antenna, a third port connected to the receiving circuit.
• FIGS. 1a and 1b illustrate two modes of signal transmission in a circulator
• FIG 2 is a simplified diagram of a wireless telecommunications system comprising a circulator according to the state of the art
• FIG. 3 schematically illustrates, in plan view, a microswitch circulator according to the invention
• FIGS. 4a to 4c illustrate in top view and in section the structure of a series microswitch according to the invention, specially adapted for a circulator according to the invention;
• FIGS. 5a and 5b are illustrative of the radiofrequency signal transmission modes in the circulator according to the invention, with corresponding activation voltages indicated by way of example;
• FIGS. 6 and 7 illustrate a capacitor adaptation circuit according to the invention;
• FIG. 8 is a simplified diagram of a micro-switch impedance dynamic matching circuit according to the invention.
• FIG 9 is a simplified diagram of a wireless telecommunications system according to the invention.
• FIGS. 10a and 10b to 16a and 16b, 17, 18a, 18b and 19 illustrate topological phases of a method of manufacturing a microswitch as illustrated in FIGS. 4a to 4c.
• a CMEMS circulator according to the invention is described with reference to FIGS. 3 to 9.
• the CMEMS circulator comprises two identical series-type microswitches.
• a first micro-switch MEMSI is arranged to allow the transmission of a radiofrequency or microwave signal from an input port p1 by a signal line Ls1 to a port p2 intended to be connected to an antenna, by a second signal line Ls2.
• a second micro-switch MEMS2 is arranged to allow the transmission of signal from the second port p2, by the signal line Ls2 to an output port p3, by a third signal line Ls3.
• the entire circulator, including the microswitches and signal lines, is made on the same base substrate.
• Each series-type microswitch generally comprises a membrane-dielectric material-control electrode assembly that forms a variable capacitor whose membrane and electrode constitute the armatures.
• the control electrode is disposed in a switching zone between the two signal lines associated with the microswitch and has a two-part shape, isolated, preferably interdigitated, each part contacting a signal line. It is covered with a dielectric.
• the membrane is disposed above the switching zone.
• the dielectric is chosen to have a high relative permittivity, greater than one hundred. It is preferably PZT, whose relative permittivity, determined during the manufacture of the PZT to be equal to 150 in the case that interests us, is advantageously invariant with the frequency.
• a capacitor is thus constituted whose armatures are on the one hand the membrane and on the other hand the control electrode opposite.
• the capacitance of the capacitor thus formed varies between a low value Coff corresponding to an off state, open micro-switch and a high value Con corresponding to a state on, closed micro-switch.
• the capacity Coff of the capacitor is weak of the order of ten femtofarads. This very low capacitance induces a sufficiently important impedance between the two conducting lines so that no signal can pass from one line to the other.
• the micro-switch is open.
• each MEMSI, MEMS2 microswitch of a CMEMS circulator is as illustrated in FIGS. 4a, 4b and 4c, respectively in plan view, in section 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 made on the passivation layer 2, arranged coplanar in the extension of one another, separated by a switching zone 10.
• an electrode 3 is formed between the two signal lines in two electrically isolated parts: 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 in the direction along the signal lines, the control electrode is wider of the two sides, and in the orthogonal direction, it overflows each side of the control electrode 3, on the passivation layer 2.
• the dielectric 4 must meet the constraints of high radio frequency or microwave power: in transmission in the state one passing (membrane in downwardly bent position, in contact with the dielectric), and in isolation in the off state or open (membrane in the initial high position).
• the dielectric 4 is preferably PZT, which combines the advantages of having a high relative permittivity greater than 100 invariant with the frequency, of being able to work in the microwave, up to 100 GigaHertz, and of supporting the power, because of its monocrystalline nature.
• a PZT with a relative permittivity equal to 150, determined during its manufacture, is used.
• the gap separating the two parts of the control electrode to 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 a known manner, such a shape makes it possible to significantly increase the dielectric capacity of the capacitor formed by the membrane m, the control electrode 3 and the dielectric 4.
• control electrode is made of a Platinum / Gold alloy 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.
• the micro-switch structure is of the coplanar type: ground lines LM 1 and LM 2 are formed on the same face of the substrate as the signal lines LS-IN and LS-OUT. 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.
• This insulator is typically silicon nitride. 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 rise very high in frequency, typically up to at least 100 GigaHertz.
• the pillars, the signal lines and the ground lines typically comprise a first resistive hung layer shown in thick black in FIGS. 4b and 4c 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.
• at least one contact pad (not shown on the Figures 4a to 4c) 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 the pad and at least one signal line.
• 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 makes it possible to have metal 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.
• the metallic membrane comprises:
• the tungsten titanium preferably has a proportion of 80% of titanium and 20% of tungsten to 1 or 2%, as indicated previously.
• a highly conductive layer in a material selected from
• the membrane must be able to deform to come into contact with the dielectric 4 without breaking (state on), and return to its state initial (off state).
• aluminum is used, whereby the best results are obtained in terms of switching speed and resistance to mechanical stress.
• the section of the signal lines has a width Is 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.
• the layer 4 of PZT has a thickness e4 less than one micron per 0.4 micron example. The thickness of the mass lines results from the technological process used.
• the mobile part of the membrane that is to say off pillars, is in a rectangular parallelepiped shape, the dimensions of which are advantageously: a width Im 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 dielectric PZT overflows on the length of the order of 20 microns on the passivation layer, on each side.
• the micro-switch which has just been described has good radio frequency and microwave performance in particular for the transmission of radio frequency power signals or significant microwave frequency, of the order of ten watts.
• FIG. 5a is a simplified circuit diagram of the circulator, in a state corresponding to the transmission of a radiofrequency signal from port p1 (RF input) to port p2 (Antenna).
• the micro-switch MEMSI must then be controlled in the closed state (Con), and the micro-switch MEMS2 must then be controlled in the open state (Coff). This is achieved as illustrated in FIG.
• each microswitch by applying to each microswitch a reference voltage (electrical ground) on the membrane m and an appropriate activation voltage on the control electrode ec.
• Membrane m of the second micro-switch MEMS2 is isolated (no voltage applied) and the voltage Vc2 applied to the control electrode ec is equal to 0 volts.
• a circulator according to the invention has excellent performance, particularly in terms of insertion losses, of the order of a tenth of a dB to a few tenths of a dB, and a very significant space gain, with a component ten times smaller. than ferromagnetic circulators and a wider operating frequency band, about 18 to 19 GigaHertz approximately.
• the circulator which has just been described in relation to FIG. 4 is a passive component. It is typically an SPDT component (Single pole,
• Double Throw which has the disadvantage of allowing the passage of the radio frequency signal in both directions: the signal transmission between the ports p1 and p2 and between the ports p2 and p3 can potentially operate in both directions, switches not seeing the difference.
• a part of the radiofrequency power picked up by the antenna can be reflected towards the transmitting port
• a two-cell LC type impedance matching circuit ADAPT is advantageously connected between the antenna A and the port p 2 antenna A must be connected.
• Such an impedance matching circuit acts as a virtual obstacle with respect to the input port p1, which then sees an infinite impedance.
• the impedance returned by the antenna at the output p2 of the system circulator is denoted Zrc.
• Zrs is the impedance brought back from the circulator to the input of the antenna.
• a first LC 1 cell comprising an inductor L 1 and a capacitor Ci and a second cell LC 2 comprising an inductor L 2 and a capacitor C 2 are connected in series between the output p 2 of the circulator and the antenna A: the inductances Li and L 2 are connected in series between p2 and A.
• the capacitor Ci is connected between the midpoint between the two inductors, and the ground.
• the capacitor C 2 is connected between the point of connection between the inductor L 2 and the antenna A and grounded.
• ADAPT circuit is thus a two-pole filter.
• this impedance matching circuit is a passive filter: the elements of the cells LC 1 and LC 2 are pre-configured (or sized) for a given application, c for a given antenna: frequency, antenna impedance.
• a preferred embodiment of such an impedance matching circuit is based on microswitches comparable to those used for the circulator, with the difference that the membrane is formed of a single thick layer of aluminum, to form a rigid structure, which can be controlled in steps, according to the amplitude of the activation voltage applied to the control voltage. This voltage then defines the displacement of the rigid membrane, between the rest position and a maximum, predefined position.
• the membrane has a thickness of the order of 2.5 microns.
• the microswitches have the same structure as that described with reference to FIGS. 4a to 4c, with the exception of the structure of the membrane as indicated above.
• the inductances are then produced by the signal line portions between the microswitches, as illustrated in FIG. 7.
• the inductance and capacitance parameters of each cell are defined by the geometry of the membranes (width lc 1; Ic 2 , length wc-i , wc 2 ) and signal lines Li and L 2 : width IL- I , IL 2 , and length w ⁇ _i, w ⁇ _ 2 and the activation voltages applied to the control electrodes. These tensions of activation define the height of displacement of the membrane and consequently the value of the capacity.
• the value of the capacitance is then defined, for predetermined dimensions, by the value of the activation voltage applied to each control electrode: V1 for the first capacitor C1 and V2 for the second capacitor C2 . It is the voltages that determine the position of the membrane in each microsystem, in operating mode, for a given application.
• the representation that is given corresponds to a microstrip type circuit structure: the substrate adapted to this technology is provided on the rear face with a ground plane.
• coplanar ground lines symmetrically arranged on both sides of the signal lines are then produced, by diverting the shape of the signal lines and the membranes. so as to be distant from everywhere of a determined break value, typically 80 microns.
• the impedance matching circuit is active, allowing a dynamic adaptation of impedance. It includes variable capabilities that allow its filtering characteristics to be adjusted dynamically with the impedance variation seen at the output. We then have a device that is particularly suitable for use with so-called active antennas or with reconfigurable antenna arrays used in certain systems, for example in radar systems.
• FIG. 8 A preferred embodiment of such a dynamic impedance matching circuit resumes the embodiment described with reference to FIG. 6, with a difference for the activation voltage of the control electrodes.
• This embodiment is illustrated in FIG. 8.
• Another variable capacitance micro-switch C3 is used to control the voltage Vadapt applied to the control electrodes of the variable capacitors C1 and C2.
• the control electrode ec3 of FIG. this variable capacitance C3 being connected to the contact pad PA intended to be connected to the antenna A.
• the current or the voltage at this point is a function of the actual impedance of the antenna.
• self-adaptive impedance matching to the impedance variation brought by the antenna which is of particular interest to active antenna systems or networks. It can be realized in microstrip or coplanar technology.
• the elements of the LC cells are then dimensioned (inductance, capacitance) to respond to a given frequency band, corresponding to a frequency band, the voltage control according to the invention allowing the dynamic self-adaptation in operational mode.
• the impedance matching circuit ADAPT is made separately from the circulator. It is thus possible to adapt the circuit and the circulator according to the telecommunication system in question and the characteristics of the antenna.
• FIG. 9 illustrates the configuration of a telecommunication system that can be realized according to the invention, with an IMEMS isolator, a CMEMS circulator and an ADAPT impedance matching circuit connected between port p2 and an antenna A.
• L The IMEMS isolator is placed between the emitter E, on its input port p1 and the input port of the circulator, connected to its port p2, with a load of 50 ohms connected to the port p3.
• FIGS. 3a to 3c A method of manufacturing a micro-switch advantageously used in the invention, as described with reference to FIGS. 3a to 3c, will now be described. It is illustrated by Figures 10a and following, which show different steps 1 to 10 characteristics.
• Step 1 Figures 10a (top view) and 10b (section along X).
• a passivation layer 101 is 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.
• Step 2 Figures 11a and 11b.
• FIGS. 13a and 13b 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 two parts of the control electrode), and a contact pad and a pillar to put the membrane at a voltage reference (electrical ground).
• a voltage reference electrical ground
• Step 5 Figures 14a and 14b.
• the surface layer is this layer 106 of insulation.
• Step 6 Figures 15a and 15b.
• the surface layer is titanium / tungsten layer 107.
• Step 7 Figures 16a and 16b. Localized removal of tungsten titanium in an area f under the location of the membrane.
• Step 8 Figure 17. Localized refill of gold, by prior resin deposition on the whole surface and by current injection via the contact pads and the connection lines.
• the height of gold thus obtained is controlled by the resin thickness.
• the thickness (or height) of gold signal lines and pillars reaches 3 microns.
• the resin achieves the same level everywhere, which ensures the flatness of the membrane which is achieved in the next step.
• Figures 18a and 18b Formation of the membrane. For a microswitch used as a switch as in the circulator and as described in connection with Figures 3a to 3c, deposition of tungsten titanium and then deposition of aluminum (or gold, or copper), and etching of the membrane.
• a thickness of 0.2 micron tungsten titanium and a thickness of 0.5 microns gold is preferred.
• Step 10 Figure 19: 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 latency and provides better radio and microwave performance.

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