Technical Field

The invention relates to a radio frequency device

comprising a first substrate layer and a second substrate layer arranged at a distance towards each other, whereby the first and second substrate layer comprise electrically conductive transmission line elements on a first surface of the first substrate layer and on a second surface of the second substrate layer that allow for transmission of a radio frequency signal along a transmission direction defined by the transmission line elements parallel to the first surface of the first substrate layer or parallel to the second surface of the second substrate layer, and with an electrically conductive crossover between the first surface of the first substrate layer and the second surface of the second substrate layer that provides for an

electrically conductive connection of electrically

conductive transmission line elements on the first surface of the first substrate layer with the electrically

conductive transmission line elements on the second surface of the second substrate layer.

Background of the invention

Within many radio frequency devices, a radio frequency signal is transmitted along electrically conductive transmission line elements. Such transmission line elements can be arranged on a surface of a substrate layer.

Sometimes several transmission line elements forming a signal path for a radio frequency signal are arranged on two or more surfaces of at least two substrate layers that are itself arranged at a distance towards each other. Some of the transmission line elements are arranged on the opposing surfaces of the two substrate layers. The

transmission line elements enable the transmission of a radio frequency signal along a transmission direction that is defined by the design, the arrangement and the

orientation of the corresponding transmission line elements at the opposing surfaces, whereby the transmission

direction is parallel to at least one of the opposing surfaces of the two substrate layers. If both surfaces of the two substrate layers are arranged parallel towards each other, the transmission direction is parallel to both opposing surfaces.

For many devices the transmission line elements can be manufactured by well-known methods like e.g. surface micromachining or bulk micromachining including deposition methods, lithographic methods or etching methods. It is also possible to generate the transmission line elements by printing methods.

Many radio frequency devices require two electrodes forming transmission line elements at a distance towards each other, like e.g. microstrip lines. The surfaces of the two substrate layers with the respective transmission line elements must be arranged at a distance towards each other in order to avoid an unwanted electroconductive connection between the two surfaces and the respective transmission line elements. Usually, a solid dielectric material layer is arranged between the two substrate layers with the respective transmission line elements, resulting e.g. in a microstrip line arrangement of the respective transmission line elements. However, for some applications the volume between the two substrate layers is at least partially filled by a fluidic material like air or a liquid crystal material, whereby the mechanic characteristics of such a fluidic material cannot provide for or guarantee the required distance. For such devices, usually one or more spacer elements are arranged between the two substrate layers that define and provide for the distance between the two substrate layers. The volume between the two substrate layers that is not filled by spacer elements can be used for and filled by the fluidic material.

For some applications like e.g. thin film transistor display based radio frequency applications, the signal must be fed at some point from the transmission line elements on a first surface of a first substrate layer to corresponding transmission line elements on a second surface of a second substrate layer. Thin film transistor displays with a large number of picture elements named pixels comprise a

capacitor for each picture element for which the voltage that is applied to the corresponding capacitor can be controlled. Usually there is a common ground electrode for all picture elements on a first substrate layer, and dedicated control electrodes for each of the picture elements on a second substrate layer. The source voltage driver and most of the control elements are arranged on the same surface of the second substrate layer as the control electrodes. Thus, there is one electrically conductive crossover required to transfer the common ground electrode signal from the second surface of the second substrate layer to the first surface of the first substrate layer.

If at least one substrate layer easily allows for

manufacturing an opening into the substrate layer and for inserting an electroconductive connection element like e.g. a wire or a pin from the outside through the opening, this electroconductive connection element can be used for providing an electrically conductive crossover between transmission line elements on the two surfaces that are placed next to or around the opening.

However, for some devices the two substrate layers are made from a material like e.g. glass that does not easily allow for openings through the substrate layer. For such

substrate layers the electrically conductive crossover should not require openings within at least one of the substrate layers. Furthermore, if a fluidic dielectric material is used to fill the volume between the two

substrate layers, such an opening may promote or even create unwanted leakage of the fluidic material through the opening, resulting in the need for additional sealings that protect the opening.

In some cases, such an electrically conductive crossover can be achieved by making an electroconductive connection that is inserted from a lateral edge of the substrate layers to the transmission line elements on both surfaces, whereby the respective transmission line elements are contacted via the space between the two substrate layers from the outside of both substrate layers. However, for some applications and devices such an electroconductive connection is not possible or considered unfavorable.

For some devices like e.g. phased array antennas a large number of antenna elements, e.g. several hundred or several thousand antenna elements are arranged within a small area. Each antenna element requires at least one phase shifting element and connecting lines formed by transmission lines that connect the antenna element with the respective phase shifting element and with a feeding network. In order to allow for a compact phased array antenna device, it is considered favorable to make use of transmission line elements on two substrate layers that are arranged at a distance towards each other, whereby transmission line elements for connection lines or for phase shifting

elements are arranged at two surfaces of the two substrate layers that face towards each other. Furthermore, if the electroconductive crossover does not allow for openings in at least one of the two substrate layers, the electrically conductive crossover should be formed by means different that pins or wires that connect the two surfaces of the two substrate layers.

Accordingly, there is a need for a cost-effective and space-saving arrangement and design of an electrically conductive connection that allows for connecting

transmission line elements arranged on two opposing

surfaces of two substrate layers that are arranged at a distance towards each other.

Summary of the invention The present invention relates to a radio frequency device as described above, whereby more than one electrically conductive crossover is arranged between the first and second substrate layers. Even though the manufacture of more than one electrically conductive crossover may require more efforts and costs than the manufacture of a single electrically conductive crossover that is connected to all transmission line elements that require such a connection, the use of several electrically conductive crossovers facilitates the triggering and control of several

transmission line elements that are not combined or

integrated into a single electric component of the radio frequency device, but related to e.g. many different phase shifting elements.

According to a preferred embodiment of the invention, at least one phase shifting region of the radio frequency device comprises corresponding regions of the respective first and second surfaces of the first and second substrate layers with electrically conductive transmission line elements that are used for forming several radio frequency phase shifting elements that are arranged inside of a boundary of the at least one phase shifting region, whereby all electrically conductive crossovers are arranged outside of the at least one phase shifting region of the radio frequency device, and whereby each electrically conductive crossover outside of the at least one phase shifting region is electrically connected to a respective phase shifting element inside of the at least one phase shifting region.

By spatially separating the electrically conductive

crossovers from the surface region that is required by the phase shifting elements and by other components like e.g. radiation emitting elements or coupling elements that couple the radio frequency signal to radiating elements outside of the substrate layers, a very dense spatial arrangement of the phase shifting elements and the

radiating elements within the phase shifting region, i.e. inside of the boundary of the phase shifting region is possible. For example, when designing a phased array antenna, the shape and distance of radiating elements and the arrangement of corresponding phase shifting elements can be designed in order to allow for the best advantage of the radiation characteristics of the phased array antenna. The area within the phase shifting region that is

surrounded and defined by the boundary can be fully used for phase shifting elements as well as corresponding radiating elements. Due to the arrangement of the

electrically conductive crossovers outside of the phase shifting region the available space for each of the

electrically conductive crossovers can be maximized without interfering or limiting the phase shifting region. Thus, a large footprint of each electrically conductive crossover is possible, which facilitates the manufacturing of the electrically conductive crossover as well as increases the reliability of the electrically conductive crossover.

The footprint of the electrically conductive crossover can be circular or rectangular. It is also possible to make best use of the available space outside of the phase shifting region by designing electrically conductive crossovers with different shape and dimension of the corresponding footprint. According to an advantageous aspect of the invention a number of electrically conductive crossovers are arranged along a straight line along a border of a phase shifting region of the radio frequency device. Arranging the

electrically conductive crossovers next to the border of a phase shifting region allows for short distances between the electrically conductive crossover and the corresponding phase shifting element.

Preferably a number of electrically conductive crossovers are arranged along several straight lines parallel to each other along a border of a phase shifting region of the radio frequency device. Furthermore, for many radio

frequency devices it is advantageous to arrange one or more straight lines along two or more straight-lined or curved borders of the phase shifting region. If the radio

frequency device comprises two substrate layers with a rectangular shape that are stacked, the electrically conductive crossovers can be arranged along one, several or all borders of the stacked two substrate layers, creating a large rectangular phase shifting region within an inner region of the two substrate layers. For many applications like, e.g. phased array antennas, a matrix-like arrangement of a large number of antenna elements with respective phase shifting elements and radiating elements within a

rectangular shaped phase shifting region allows for space saving construction of the phased array antenna and for advantageous emission or reception characteristics of the phased array antenna.

According to an advantageous embodiment of the invention the respective electrically conductive crossovers of a first straight line are arranged at a distance in direction of the first straight line with respect to the adjacent electrically conductive crossovers of a second straight line. The shifted position of the electrically conductive crossovers of a second straight line with respect to the adjacent first straight line allows for a very compact design of the connection lines that connect the

electrically conductive crossovers with the dedicated phase shifting element inside the phase shifting region.

Preferably, an electrically conductive crossover comprises a first crossover electrode on the first substrate layer, a second crossover electrode on the second substrate layer, whereby the first crossover electrode on the first

substrate layer at least partially overlaps the second crossover electrode on the second substrate layer. The first and second crossover electrodes can be manufactured together with the corresponding phase shifting elements and connection lines using the same manufacturing method and usually within the same manufacturing step. For example, the first crossover electrode, the respective part of the connection lines and of the phase shifting elements on the first surface of the first substrate layer can be

manufactured by printing or etching or by any other

microelectronic manufacturing method.

The first and second crossover electrodes define the footprint of the electrically conductive crossover.

Usually, the first and second crossover electrodes are of identical shape and dimension, and are arranged in a stack to fully overlap each other. However, for some devices it might be advantageous to allow for first and second crossover electrodes of different shape or dimension or both. It is also possible to arrange the first and second crossover electrodes on the respective first surface of the first substrate layer and on the second surface of the second substrate layer in a manner that the first and second crossover electrodes only partially overlap.

According to an advantageous embodiment of the invention an electroconductive material is arranged between at least a part of the overlapping area of the first and second crossover electrode, whereby the electroconductive material electrically connects the first crossover electrode on the first substrate layer with the second crossover electrode on the second substrate layer. The electroconductive material can comprise e.g. gold-plated plated particles that are electrically conductive and typically dispersed in a binder to form anisotropic conductive adhesive materials such as anisotropic conductive films or anisotropic

conductive paste which can be employed in the connection of the first and second crossover electrode. It is also possible to make use of nickel conductive spacers that are known from coatings, adhesives, printing ink, plastics, and rubber, to provide for the electrically conductive

connection between the first and second crossover

electrode .

In yet another embodiment of the invention, the

electroconductive material comprises electroconductive particles dispersed within a nonconductive matrix material. There are several different conductive particles or

conductively coated particles, electrooptical materials or anisotropic particles dispersed in a polymeric matrix available that are suitable for use as the

electroconductive material which electrically connects the first and second crossover electrodes.

It is also possible that the electroconductive material comprises electroconductive particles with a large enough mean diameter to provide for an electroconductive contact with the first crossover electrode and with the second crossover electrode. According to a preferred embodiment of this aspect of the invention, the diameter of the

electroconductive particles equals the distance between the first and second crossover electrode. For manufacture of such an electrically conductive crossover, the

electroconductive particles can be embedded into a suitable matrix material. The matrix material can be a photoresist. The embedded electroconductive particles and arranged on the first or second crossover electrode. Afterwards, the matrix material can be removed which leaves the

electroconductive particles in between the first and second crossover electrode. The position of the electroconductive particles with respect to the first and second crossover electrode can be secured by pressing the first and second substrate layer towards each other, resulting in a gripping force that prevents the electroconductive particles from moving away.

In case that the mechanical characteristics of the chosen electroconductive material provide for sufficient

mechanical stability, the electroconductive material between the two crossover electrodes can be designed to also provide for a spacer element that guarantees the distance between the first and second substrate layer. In this case, it is advantageous to arrange electrically conductive crossovers along all lateral edges of the two substrate layers, thus providing for the mechanical stability of the layer sandwich of two substrate layers at a distance towards each other and with a fluidic material layer in between.

According to yet another aspect of the invention, the first crossover electrode of the first substrate layer or the second crossover electrode on the second substrate layer or both is partially or fully covered by an electroconductive mechanical protection layer. The electroconductive

mechanical protection layer can be made of e.g. gold or copper, or of any suitable electroconductive material with sufficient mechanical stability or with sufficient

thickness, or with both, to provide for a mechanical protection layer on top of the first and second crossover electrode. Then the first and second crossover electrodes can be made of a less mechanically stable material that is also used for the transmission lines including the phase shifting elements and that might provide for advantageous characteristics of the transmission lines or the

manufacture of the transmission lines. For example, some or all of the transmission lines and the first and second crossover electrodes can be made of a thin metal like e.g. indium-tin-oxide ITO.

The electroconductive crossover can be formed by

electroconductive material that is placed between the two electroconductive mechanical protection layers. In yet another embodiment of the invention the electrically conductive crossover is formed by the electroconductive material of the mechanical protection layer that

electrically connects the first crossover electrode on the first substrate layer with the second crossover electrode on the second substrate layer.

According to an aspect of the invention a sealant surrounds either some or each of the electrically conductive

crossovers, or in that a sealant surrounds some part or all of the region comprising the electrically conductive crossovers, or in that a sealant surrounds some part or all of the phase shifting region. The sealant protects the electrically conductive crossovers from interference with material or external conditions that originate from the volume between the two substrate layers, e.g. from

interference with a liquid crystal material that is used for controlling and manipulating the phase shifting

elements within the phase shifting region.

Brief description of the drawings

The present invention will be more fully understood, and further features will become apparent, when reference is made to the following detailed description and the

accompanying drawings. The drawings are merely

representative and are not intended to limit the scope of the claims. In fact, those of ordinary skill in the art may appreciate upon reading the following specification and viewing the present drawings that various modifications and variations can be made thereto without deviating from the innovative concepts of the invention. Like parts depicted in the drawings are referred to by the same reference numerals . Figure 1 illustrates a sectional view of an electrically conductive crossover between a first and a second substrate layer,

Figure 2 illustrates a schematic top view of a first substrate layer with a number of electrically conductive crossovers, each connected to a phase shifting element and then to a radiating element,

Figure 3 illustrates a sectional view of the substrate layer shown in Figure 2 along line III-III in Figure 2,

Figure 4 illustrates a perspective view of a first

substrate layer with a number of electrically conductive crossovers arranged outside of a phase shifting region along the lateral edge of the first substrate layer,

Figure 5 illustrates a schematic top view of a first substrate layer with a number of electrically conductive crossovers arranged along two straight lines along a lateral edge of the first substrate layer,

Figure 6 illustrates a schematic top view of a first substrate layer with a number of electrically conductive crossovers arranged along two straight lines along a lateral edge of the first substrate layer, whereby the position of the electrically conductive crossovers of the first straight line is shifted with respect to those of the second straight line, Figure 7 illustrates a sectional view of another embodiment of an electrically conductive crossover between a first and a second substrate layer,

Figure 8 illustrates a sectional view of yet another embodiment of an electrically conductive crossover between a first and a second substrate layer, and

Figure 9 illustrates a sectional view of yet another embodiment of an electrically conductive crossover between a first and a second substrate layer.

Detailed description of the invention

Figure 1 shows a sectional view of a first embodiment of an electrically conductive crossover 1 between a first

substrate layer 2 and a second substrate layer 3 of a radio frequency device 4. The electrically conductive crossover 1 between the first and second substrate layer 2, 3 comprises a first crossover electrode 5 arranged on a first surface 6 of the first substrate layer 2, and a second crossover electrode 7 arranged on a second surface 8 of the second substrate layer 3. The two substrate layers 2, 3 are arranged in parallel and with the first surface 6 of the first substrate layer 2 facing the second surface 8 of the second substrate layer 3. Both substrate layers 2, 3 are made of glass.

The volume between the first crossover electrode 5 and the second crossover electrode 7 is filled with an

electroconductive material 9 that provides for an

electroconductive connection between the first crossover electrode 5 and the second crossover electrode 7. The first crossover electrode 5 is connected to transmission line elements 10 on the first surface 6 of the first substrate layer 2, and the second crossover electrode 7 is connected to transmission line elements 11 on the second surface 8 of the second substrate layer 3. The electrically conductive crossover 1 provides for an electrically conductive

connection between transmission line elements 10 on the first surface 6 of the first substrate layer 2 and

transmission line elements 11 on the second surface 8 of the second substrate layer 3. No opening or drill hole is required in the first substrate layer 2 or in the second substrate layer 3.

Figures 2 and 3 illustrate an exemplary embodiment of a radio frequency device 4 with several phase shifting elements 20 and with several coupling structures 21 that are arranged on the first surface 6 of the first substrate layer 2 and on the second surface 8 of the second substrate layer 3. Each coupling structure 21 couples a radio

frequency signal to a corresponding radiating element that is arranged outside of the first and second substrate layer 2, 3. Each phase shifting element 20 is formed by one or more transmission line elements 10' on the first surface 6 of the first substrate layer 2 and by one or more

transmission line elements 11' on the second surface 8 of the second substrate layer 3. Each phase shifting element 20 is at one side electrically conductively connected via a connection line 14 to a dedicated electrically conductive crossover 1 that provides for a bias voltage that operates and controls the corresponding phase shifting element 20. The phase shifting element 20 is at another side electrically conductively connected via a connection line 14 to a dedicated coupling structure 21 which couples a radio frequency signal to a corresponding radiating

element. Thus, for each signal path of a radio frequency signal that is transmitted via a phase shifting element 20 to a coupling structure 21 and thus to a corresponding radiating element, a dedicated electrically conductive crossover 1 facilitates the triggering and control of the phase shifting element 20 resulting in individual phase control of the corresponding radiating elements so that the superposed beam of a phased array antenna can be steered in two dimensions, e.g. in azimuth and elevation. The volume between the first and second substrate layer 2, 3 is filled with a tunable dielectric material, namely with a liquid crystal material 19 that can be used to control the

respective phase shift that is created by the corresponding phase shifting devices 20.

Figure 4 shows a perspective view of the first substrate layer 2 with a number of electrically conductive crossovers 1 arranged outside of a phase shifting region 12. A

boundary 22 of the phase shifting region 12 is indicated by a dot and dash line and that is located in an inner area of the respective first and second substrate layer 2,3. In order to demonstrate the arrangement of the electrically conductive crossovers 1 on the first substrate layer 2, the second substrate layer 3 that is mounted above the first substrate layer 2 is only indicated by dashed lines. Inside the phase shifting region 12 phase shifting elements 20 and coupling structures 21 of a phased array antenna are located. Outside of the phase shifting region 12 a number of electrically conductive crossovers 1 is arranged along lateral edges 13 of the first substrate layer 2. By

separating the electrically conductive crossovers 1 from the phase shifting region 12 that comprises the phase shifting elements 20 and the coupling structure 21, both the phase shifting elements 20 and the coupling structures 21 can be arranged to optimize the emission and reception characteristics of the phased array antenna without need of taking into account the space requirement for the

electrically conductive crossovers 1. Furthermore, the footprint of the electrically conductive crossovers 1 can be large enough to provide for a reliable electrically conductive connection between the first and second

substrate layer 2, 3 without interfering with the design and arrangement of the phase shifting elements and the coupling structures 21 or the radiating elements. The electrically conductive crossovers 1 are arranged along a straight line parallel to the lateral edges 13. They are conductively connected to the phase shifting elements inside the phase shifting region 12 via connection lines 14.

Figure 5 illustrates a schematic top view of the first substrate layer 2 according to another embodiment of the invention, with a number of the electrically conductive crossovers 1 arranged along two straight lines along the lateral edge 13 of the first substrate layer 2. The

connection lines 14 of the electrically conductive

crossovers 1 of the first straight line that is adjacent to the phase shifting region 12 are directed towards the phase shifting region 12. The connection lines 14 of the

electrically conductive crossovers 1 of the second straight line that is more distant to the phase shifting region 12 are converged at the side opposite to the phase shifting region 12, and each two connection lines 14 are directed through the two straight lines of electrically conductive crossovers 1 towards the phase shifting region 12.

Figure 6 illustrates a schematic top view of the first substrate layer 2 according to another embodiment of the invention, with a number of electrically conductive

crossovers 1 arranged along two straight lines along a lateral edge 13 of the first substrate layer 2. The

position of the electrically conductive crossovers 1 of the first straight line is shifted with respect to those of the second straight line. Thus, for all electrically conductive crossovers 1 the connection lines 14 can be directed towards the phase shifting region 12. The total length of all connection lines 14 of this embodiment is less than the total length of all connection lines 14 of the embodiment shown in Figure 5.

Figure 7 shows a sectional view of another embodiment of the electrically conductive crossover 1 between the first and a second substrate layer 2, 3. The first and second crossover electrodes 5, 7 as well as the adjoining

connection lines 14 are made of indium-tin-oxide ITO. Both, the first and second crossover electrode 5, 7 are covered by an electroconductive mechanical protection layer 15, 16 made of gold or copper.

Figure 8 shows a sectional view of yet another embodiment of the electrically conductive crossover 1 between the first and second substrate layer 2, 3. Instead of a

separate electroconductive material 9, the volume between the first and second crossover electrodes 5, 7 is filled with the material 17 of the electroconductive mechanical protection layer 15, 16, i.e. filled by gold or copper or any other electrically conductive material suitable for providing mechanical protection. In order to establish the electrically conductive connection. The additional material 17 of the electroconductive mechanical protection layer 15, 16 can be added in a single manufacturing step e.g. by additive manufacturing methods, as indicated on the bottom side of the electrically conductive crossover 1, or can be added in a separate manufacturing step, as indicated on the top side of the electrically conductive crossover 1.

Figure 9 shows a sectional view of yet another embodiment of the electrically conductive crossover 1 between the first and second substrate layer 2, 3. The electrically conductive crossover 1 is surrounded by a sealant 18 that prevents any direct contact of the electroconductive material 9 with any other material like liquid crystal material 19 that is filled between the first and second substrate layer 2, 3.