Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P3/00—Waveguides; Transmission lines of the waveguide type
  • H01P3/003—Coplanar lines
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P1/00—Auxiliary devices
  • H01P1/18—Phase-shifters
  • H01P1/184—Strip line phase-shifters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
  • H01P3/00—Waveguides; Transmission lines of the waveguide type
  • H01P3/003—Coplanar lines
  • H01P3/006—Conductor backed coplanar waveguides

Definitions

• radiofrequency refers to the field of millimeter or submillimeter waves, for example in a frequency range of 10 to 500 GHz.
• Trans lines ⁇ task connects these components, or the component, are an ele ⁇ base in an RF circuit.
• the quality factor is an essential parameter because it represents the insertion losses of a transmission line for a given phase shift.
• these lines must provide a determined phase shift and have a characteristic impedance determined for the frequency used.
• these transmission lines consist of a conductive ribbon having lateral dimensions of 10 to 50 ⁇ m and a thickness of about 1 ⁇ m (0.5 to 5 ⁇ m). depending on the technology used).
• This conductive ribbon is surrounded by one or more side conductors, upper or lower constituting ground planes for forming with the conductive ribbon a waveguide type structure.
• the conductive strip and the ground planes are made of metallization levels of elements formed over a semiconductor substrate.
• FIG. 1 shows a transmission line formed on an insulating substrate 100.
• This line comprises a central conductor ribbon 102 constituting the transmission line proper, surrounded by lateral coplanar mass ribbons 104, 106.
• This structure is commonly called a guide coplanar wave and designated by the acronym CPW (according to the terms CoPlanar Waveguide).
• a type of transmission line particularly per ⁇ forming is described in US Patent No. 6,950,590 of which Figure 4a is reproduced in Figure 2 attached.
• a lower shield plane 136 is formed on a silicon substrate 128 coated with metal levels separated by an insulator 127. divided into parallel strips of small width, for example of the order of 0.1 to 3 ⁇ m.
• a central conductive strip 122 constituting the transmission line itself, surrounded by coplanar lateral mass ribbons 124, 126.
• the dimensions of the various elements are optimized to obtain, at a given frequency, given phase characteristics as well as a given characteristic impedance. It is not possible to modify these characteristics once the line has been completed. For example, it is not possible to make a phase shifter having a given identical phase shift for several different frequencies, or an impedance adapter for adapting various impedances.
• An object of embodiments of the present invention is to provide a transmission line tunable substantially with control voltages of the order of a few volts.
• embodiments of the present invention combine the characteristics of ferroelectric layer-controlled CPW lines and S-CPW lines.
• the present invention provides a coplanar waveguide type transmission line particularly suitable for integration on microelectronic integrated circuits.
• various parameters of the waveguide are adjustable to optimize the phase shift at a chosen frequency and for a selected characteristic impedance, and to modify the parameters of the line in order to adapt to a different operating frequency or to a different frequency. different characteristic impedance.
• An embodiment of the present invention provides a high frequency transmission line comprising a conductive ribbon associated with at least one conductive shield plane, wherein at least a portion of the space between the shield plane and the ribbon conductor comprises a ferroelectric material.
• the line is of the slow wave coplanar waveguide type comprising two lateral ribbons extending on either side of the central ribbon.
• the ferroelectric material extends under all or part of the central ribbon and lateral ribbons.
• the line is associated with means for selective polarization (Vbias) of the central ribbon and / or lateral ribbons.
• Vbias means for selective polarization
• the lateral strips have their central portions formed with recesses above and are associated with means of MOVE ⁇ lateral electrostatic cements.
• FIG. 1, previously described, represents a transmission line of the SCW type
• Figure 2 previously described, is a reproduction of Figure 4a of US Patent 6,950,590;
• Figures 3A, 3B and 3C are respectively a sectional view, a perspective view and a top view of a transmission line according to an embodiment of the present invention;
• Fig. 4 is a sectional view of a transmission line according to another embodiment of the present invention.
• Figs. 5A and 5B are a top view and a sectional view of a transmission line according to an embodiment of the present invention.
• a substrate for example a semiconductor substrate, for example made of silicon
• metallization levels are formed separated by an insulating material 2.
• a shield plane divided into microstrip strips 4 similar to the structure 136 of FIG. 2.
• a central transmission tape 6 similar to the ribbon 122 and, on either side of this central ribbon , are formed lateral ribbons of mass 8 and 9 similar to the mass ribbons 124 and 126 of Figure 2.
• a ferroelectric material 10 (the layer of ferroelectric material 10 is not shown in Figures 3B and 3C for simplicity of represen tation ⁇ ).
• a ferroelectric material generally has a high dielectric constant and said dielectric constant can go to values well above if an electric field is applied ⁇ continuous stick.
• the dielectric constant changes from 100 to 300 for polarization voltages ranging from 0 to 5 volts. It will be noted that the capacitive component between the central ribbon 6 and the transverse ribbons 8 and 9 is negligible if we look at the lateral faces facing the central ribbon 6 and lateral ribbons 8 and 9.
• the capacitive component between the central ribbon 6 and the side ribbons 8 and 9 essentially correspond to the capacitance between the central ribbon and the shielding plane 4 in series with the two capacitors (in parallel) between the shielding plane 4 and the lateral ribbons 8 and 9.
• these three capacities have the same value, Cw, the overall capacity will be equal to 2Cw / 3.
• this overall capacity may vary in a factor of 1 to 3.
• an impedance between the bias voltage source and the central ribbon will be provided, preferably an inductance L but possibly also a high value resistor.
• a phase shift of the order of 5 ° is obtained for a bias voltage of 5 V for a line of 60 ym long at a frequency of 60 GHz.
• Similar simulations on a CPW line of the type of that of FIG. 1 have shown that only a phase shift of the order of 0.15 ° is obtained.
• the setting sensitivity of the S-CPW line is at least 30 times higher than that of the CPW line.
• the ferroelectric layer 10 is represented as occupying the entire gap between the shielding plane and the conductive strips 6, 8 and 9.
• This embodiment is capable of numerous variants.
• the ferroelectric layer does not necessarily go down to the lower shield plane and is optionally coated with an interface layer before the deposition of the metal strips 6, 8 and 9.
• ferroélec ⁇ stick layer 10 An alternative embodiment of the ferroélec ⁇ stick layer 10 is shown in Figure 4.
• the ferroelectric layer 10 instead of being present in the set of conductive traces is present in portions only in a part of these conductive ribbons. More party ⁇ cularly as shown in the figure, a portion of ferroelectric material 10A is disposed under the strip 6 and the ferroelectric material portions 10B and 10C are formed in the strips 8 and 9.
• the ferroelectric material is present only under the central ribbon or that under the lateral ribbons. This is likely to simplify the polarization control circuit because it will then be sufficient to apply a bias on the central ribbon or on the lateral ribbons.
• the change in polarization between the ribbons or 6, 8, 9 and the shielding plane 4 has the main effect of modi ⁇ proud the equivalent capacitance C e q of the transmission line.
• This causes a modification of the characteristic impedance Z (L ecr / C ecr ) 1/2 of the line, L eCf being the equivalent inductance of the line.
• C e q could be modified continuously by applying more or less significant differences in potential between the ribbon (s) 6, 8, 9 and the shielding plane 4. However, it may be preferable to act all or nothing by applying potentials such as the equivalent capacity takes one or more of several predetermined values.
• an embodiment of the present invention provides that the lateral distance between the lateral ground strips and the central ribbon is adjustable, which has the essential effect of modify the equivalent inductance L e q of the line.
• Figures 5A and 5B are respectively a top view and a sectional view along the plane B-B of Figure 5A.
• Figures 5A and 5B will be described collectively hereinafter.
• FIGS. 5A and 5B The structure of FIGS. 5A and 5B is a variant of that described with reference to FIGS. 3A to 3C.
• An electrical material 10A is disposed only under the central ribbon 6 between this ribbon and the shielding plane 4.
• a recess 18, 19 is formed under each of the lateral ribbons 8 and 9 so that these tapes can be moved laterally under the effect of a voltage difference between them and external lateral electrodes 21, 22.
• the lateral ribbons 8 and 9 are connected to studs 23-1, 23-2 and 24-1, 24-2 respectively formed on the insulator 2 by lamellae 25-1. , 25-2 and 26-1, 26-2.
• the lamellae 25-1, 25-2 and 26-1, 26-2 form a spring and allow movement of the ground strips 8 and 9 when they are attracted by the external electrodes 21, 22.
• Abutment systems may be provided for limiting the movement of the lateral strips and avoid a short circuit between these strips and the electrodes 21, 22 or the central conduc tor ⁇ 6. These stops may for example be formed of insulating layers deposited on the side faces of the various elements.
• the invention has been described in the context of a particular example of its application to an S-CPW type structure. However, it will be understood that it applies generally to other types of tape transmission lines whose parameters depend on the distance or distances between this ribbon and various ground planes.
• the attraction electrodes 21 and 22 and the mass ribbons 8, 9 may be coupled by interdigitated structures.
• the leaf springs 25-1, 25-2, 26-1, 26-2 may have various configurations, for example meandering shapes.
• One of the advantages of the structure described here is that it is well compatible with the usual techniques for forming metallization levels generally used for the realization of interconnections above a microelectronic integrated circuit.
• the recesses 18, 19 in each of the lateral ribbons 8 and 9 can be made by forming on the surface of the structure a sacrificial layer before depositing the metallizations 6, 8 and 9 and removing the sacrificial layer after the metallization Réali ⁇ Sees.
• the ferroelectric layer has a larger extent and it is covered with a sacrificed layer ⁇ cial before formation of conductors 6, 8, 9.

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• 2010
  • 2010-09-08 FR FR1057136A patent/FR2964499B1/fr not_active Expired - Fee Related
• 2011
  • 2011-09-08 EP EP11773052.3A patent/EP2614553A1/de not_active Withdrawn
  • 2011-09-08 WO PCT/FR2011/052058 patent/WO2012032269A1/fr active Application Filing
  • 2011-09-08 US US13/821,865 patent/US9136573B2/en not_active Expired - Fee Related

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