SE527452C2 - Method and apparatus for microwave switching - Google Patents

Abstract

A method is disclosed for obtaining a device for control and switching of microwave or radio frequency signals on a substrate material generally adapted for microwave or RF operation. Typically the substrate may be a plate of quarts or similar material, on which an area of a trivalent 'rare earth' metal or an alloy thereof is deposited. This area is subjected to hydrogen and will act as a metal or as a semiconductor depending on the amount of hydrogen present. The area of the trivalent metal then acts as a switch for a microwave or radio frequency signal. An arrangement with hydrogen is provided for switching the trivalent metal area between its states of dihydride conducting metal state and a trihydride semiconducting state. A device for control and switching of Megaherz and Gigahertz radio signals is formed on a substrate for instance provided with strip-lines or corresponding surfaces of gold connecting a trivalent area acting as the switching or controlling element. The opposite surface of the substrate is typically having a deposited layer of a highly conducting metal forming a ground plane. The device will constitute a switched antenna, filter, stub, capacitance, resistor and similar microwave or radio frequency component, respectively.

Description

527 452 Metal hydrides change from a metallic state to a semiconducting or insulating state with increasing hydrogen content. DC resistivity increases and optical properties change from being reflective metallic to transparent semiconductor. Thin layers of these metals can be reversibly switched between a metallic and a semiconducting or insulating state. Most metal hydrides in the aqueous state are best attributed to semiconductors and that terminology will be used hereinafter.

Yttrium is a metal that can be used. When yttrium is exposed to hydrogen, it changes to yttrium dihydride, which is a metal with lower resistance than yttrium. Additional exposure to hydrogen gives yttrium trihydride, which is a semiconductor with a large band gap. Yttrium dihydride has a resistivity of 3> <10-7 Qm and yttrium trihydride has a resistivity of 7x10'4 Qm [1]. The optical properties change from strongly re-reflecting for yttrium dihydride, which is typical for a metal, to transparent, typically for a semiconductor with a large band gap. The transition between yttrium dihydride and trihydride is reversible and this property is used in optical * switches.

Several metallic materials can form metal hydrides and have been found to possess switchable optical and electrical properties. 1) Trivalent metals such as yttrium (Y), scandium (Sc), lanthanum (La), or alloys thereof. i 2) The rare earth metals with atomic numbers 58 - 71 (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) [2]. 3) Mg and alloys of Mg with rare earth metals [3], [4], [l2]. 4) Multilayer stacks, with layer thicknesses of 1 - 2 nm, of a trivalent metal and magnesium (Mg) [4]. g 5) Alloys of Mg and a transition metal [5).

Below we discuss yttrium, but any metal can be used, unless otherwise explicitly stated. 52? 452 Table 1 illustrates the change in resistivity of some switchable metal hydrides between their metallic and semi-leaky states.

The layer thicknesses and the cover layers with a catalytically active metal are also given.

D stands for deuterium.

Table 1 Metal <-> Resistivity Layer thickness Mist layer Reference Semiconductor [mQçm] [nm] YH2 <- + YHs 0.03 -> 5 300 Pd, 15 [6] flm YH1.9 <-> YH2_9 0.025 -> 50 Pd, 10 [1 ] 70 * nm YD1.9 <-> YD2_9 0.035 - + 50 Pd, 10 [1] 90 * 'nm LaMg <-> 0.07 -> 5 584 Pd, AlOx [3] LaMgHzß MggNi H 0.06 -> 9 232 _ Pd , 2nm - [7] Mg2NiH4 LaH2 <-> LaI-'Ia 0¿04 -> 32 500 Pd, 20nm [8] * Values compensated for the resistivity of the cover layer The switching of the metal hydrides between on and off depends on the exchange of hydrogen. If yttrium is exposed to molecular hydrogen at room temperature and atmospheric pressure, yttrium hydride is formed. First, yttrium dihydride, which is metallic, is formed, and with further hydrogenation, yttrium trihydride, which is a semiconductor, is formed.

If the yttrium trihydride is not exposed to hydrogen, but for example to air, the hydrogen concentration will decrease. The yttrium trihydride will be changed back to yttrium dihydride. This process will go faster if the sample is heated.

The molecular hydrogen must be dissociated into atomic hydrogen. A cover layer of a catalytically active metal can be used on top of the metal film to smooth the dissociation.

The catalytic metal can be palladium (Pd), platinum (Pt), nickel (Ni), cobalt (Co) or alloys of these metals [4].

A layer of alumina in the nanometer tube can be used between the metal and the catalytic layer. With the alumina layer, the thickness of the catalytically active metal layer can be reduced to 1 nm.

The alumina layer prevents the catalytically active metal from diffusing into the metal hydride and prevents the latter from being oxidized, which increases the life of the yttrium hydride [9].

The thickness of the yttrium layer in optical switches is typically 100 - 1000 nm [2], but values up to 2000 nm have been mentioned [4]. The switching time between the metallic and semiconducting states changes with film thickness and longer for thicker films. For a few hundred nanometers, the switching time is tens of seconds. Micrometer-thick films can have switching times of fl minutes. Using an alloy of a rare earth metal with magnesium in the metal hydride can increase the switching speed [4].

The hydrogen can be supplied not only from the gas phase but also from a 'surface electrolyte [6]' or a solid electrolyte [10]. The hydrogen could also be supplied from a hydrogen plasma or from another metal hydride [4]. The exchange of hydrogen can be in heat-controlled, or diffusion-driven, voltage-controlled, combinations thereof. 10 20 25 30 527 452 n o. 4 and coon. g, z u I 9 z 'o 0 i'. , n n I 0. ,. e n en o a o '' e o n o o o I 'g: 2 I.' , .. sno oo A yttrium film can be deposited using conventional methods such as sputtering, vacuum evaporation, chemical gas phase deposition (CVD), laser ablation or electroplating. A catalytically active layer can be deposited using the same conventional methods.

The substrate for optical couplers would generally be glass or quartz.

SUMMARY OF THE INVENTION A method is shown for obtaining a device for controlling and switching microwave or radio signals. To begin with, a substrate is provided with electrical properties adapted for the use of microwave or radio frequencies (RF). The substrate can typically be a thin quartz plate or a similar material, on which a surface of, for example, a trivalent metal is created. This surface is exposed to hydrogen in a preferred embodiment and acts as a metal or semiconductor depending on the amount of hydrogen present. The surface, for example of a trivalent metal, can function as a high frequency control device or switch, when used in microwave or radio frequency circuits. In addition, the device for controlling or switching microwave or radio frequency signals is provided with a tool for switching such a trivalent metal surface between its metallic dihydridulis stripe and its high trihydric state.

A typical trivalent metal to use among the rare earth metals is, for example, a deposited layer of yttrium, exposed to hydrogen gas or to an electrolyte containing hydrogen, which with the trivalent metal forms either the dihydride or trihydride state. Alloys with other lanthanides or rare earth metals can also be candidates for a switchable layer for RF or microwaves.

A functional embodiment of the device for controlling or switching microwave or radio frequency signals is created on a substrate, which is for instance provided with 'strip-lines' or corresponding surfaces of gold, which connect a trivalent surface which functions as the switching or controlling element, to a suitable one. input or output. The opposite surface of the substrate typically has a deposited layer of a well-conducting metal, such as gold, which forms a ground plane. Thus, the device will constitute a control device or switch for, for example, an antenna, a filter, a stub element, a capacitance, a resistor or a similar microwave or radio frequency component.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, and its further objects and advantages, may best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic view seen from above of a device for controlling or switching radio frequency and microwave transmission characteristics, FIG. 2 is a schematic cross-section of the device of FIG. 1, FIG. 3 is a schematic top view of a simple microwave device for impedance matching or for forming a tunable antenna device by a switchable metal hydride, FIG. 4 shows the amplitude in the spreading parameter S21 against frequency f of the switchable device in FIG. 1 with the layer in its metallic phase (bold solid line) and in its semiconducting phase (bold dashed line) in comparison with an unbroken transmission line of gold (thin solid line) and broken transmission line with an air gap of the same length as the metal hydride (thin dashed line). ) for the experimental frequency range 10 MHz to 40 GHz, FIG. 5 shows an enlarged part of FIG. 4 in the frequency range 20 to 40 GHz, 10 20 25 30 527 452 FIG. 6 shows the amplitude of scattering parameter S11 against frequency of the device in FIG. 1 with the layer in its metallic phase (bold solid line) and in its semiconducting phase (bold dashed line) in comparison with an unbroken transmission line of gold (thin solid line) and a broken transmission line with an air gap of the same length as the metal hydride (thin dashed line) ) for the experimental frequency range 10 MHz to 40 GHz, FIG. 7 shows the amplitude of the scattering parameter S21 in dB against time in seconds during hydrogenation at a frequency of 5 GHz, FIG. 8 shows the arriplitude of the spreading parameter S11 against frequency of the switchable device in FIG. 3 with the metal hydride in the metallic state (solid line), in the semiconductor phase (dotted line) and two intermediate phases1 (dashed line and dotted line), and FIG. 9 shows the amplitude of the scattering parameter S21 against frequency of the switchable device in FIG. 3 with the metal hydride in the metallic state (solid line), in the semiconductor phase (dotted line) and two intermediate phases (dashed line and dotted line).

DETAILED DESCRIPTION OF THE INVENTION A method and apparatus are shown for controlling and switching signal transmission characteristics within the radio and microwave frequency ranges.

It is based on the change between a metallic state and a semiconducting state, which occurs in metal hydrides when hydrogen is replaced.

Figure 1 illustrates an embodiment of a device in accordance with the present inventive method. The device can be used for control or switching of radio frequency and microwave signal propagation.

The substrate 4 is a 1 mm thick quartz plate. On top of the substrate there are two strips of gold, 1 and 2, which connect to a central surface part 3. In the illustrative embodiment, the width of the strips is 2.4 mm. Both strips have a length of 23.4 mm and a thickness of 10 μm. Between the two gold strips 1 and 2 there is a yttrium hydride layer 3. The width of the yttrium hydride layer is 2.4 mm, the length is 3.7 mm and the thickness is 1 μm. Strips 1 and 2 form a transmission line, which has different properties depending on the state of the yttrium hydride in the short strip 3. On top of the yttrium hydride layer there is a 5 nm cover layer of a catalytic metal, in this case palladium.

Figure 2 shows a cross section of the switchable device in Figure 1.

Reference numerals 1, 2, 3 and 4 refer to the same parts as in Figure 1.

The bottom of the substrate is 5 years a ground plane of gold. The transmission lines were designed to have a characteristic impedance of 50..

During the measurement, a 10 MHz - 40 GHz analyzer was connected to the connection ends of strips 1 and 2 in Figure 1 and Figure 2.

A slightly more complicated device is shown in Figure 3. It is similar to that described in Figure 1 and Figure 2, but the pattern in the metal layer is not that for a simple transmission line, but rather a pattern intended to give a strong frequency dependence in a narrower frequency range, compared with the device in Figure 1. Reference numbers 1, 2, 3 and 4 correspond to those in Figure 1 and Figure 2. Reference numbers 1 and 2 again show the connections where the analyzer for 10 MHz - 40 GHz was connected for the word measurement.

The amplitude of the scattering parameter S21 (transmission coefficient) of the switchable device in Figure 1 is illustrated in Figure 4. When the metal hydride is in its metallic state, the device acts as a general transmission line. The transmission decreases for frequencies above 10 GHz. The same behavior is seen for the transmission line of pure gold, and consequently not due to losses in the metal hydride, but rather in the experimental setup. Thus, the frequency range of an application would not be limited to those presented here. When the metal hydride is in its semiconductor state, the transmission decreases significantly over the entire frequency range. The maxima and minima seen in all the curves depend on the geometry of the sample rather than material properties.

For the sake of clarity, a detail of the data presented in Figure 4 is shown in Figure 5, in which S21 (transmission coefficient) is given against frequency in the range 20 - 40 GHz. Although the data is noisy and there is structure due to geometric effects, there is a clear difference between the metallic and semiconducting states of the metal hydride. The switchable properties are similar to those seen between a pure gold line and a transmission line with an air gap, which is also illustrated in Figure 5.

The amplitude of the scattering parameter S11 (response coefficient) versus frequency is shown in Figure 6. When the metal hydride is in its metallic state, the response is almost as low as that of the transmission line of gold. In its semiconductor state, the reaction increases dramatically and is similar to that of a transmission line with an air gap.

The device depicted in Figures 1 and 2 can be switched between the metallic and the semiconducting state of the metal hydride, and consequently, the microwave transmission and reaction can be switched as shown in Figure 4, Figure 5 and Figure 6.

The amplitude of the scattering parameter S21 (transmission coefficient) at a frequency of 5 GHz, during the introduction of hydrogen for the hydride, is shown in Figure, for the device depicted in Figure 1 and Figure 2. At t = _ Os, the metal hydride is in its metallic state and the microwave signal is normally transmitted of the device. For t> 400s, the metal hydride is in its semiconductor state and the microwave signal is no longer transmitted. Figure 7 'clearly shows that the transmission of microwaves can be controlled and tuned by a device such as that of Figure 1. The switching time between the metallic state and the semiconductor of this device is approximately 7 minutes.

In Figure 8, the amplitude of the scattering parameter S11 (response coefficient) is demonstrated against the frequency of the device in Figure 3.

The amplitude S21 of the scattering parameter (transmission coefficient) versus frequency of the device in Figure 3 is shown in Figure 9.

The amplitude of the scattering parameter S11, shown in Figure 8, has a strong minimum, the position of which can be controlled by hydrating the metal hydride in the device depicted in Figure 3. Thus, the device can be used to match the impedance. In addition, the device of FIG. 3 to be able to function as an antenna with tunable properties.

In the experiments, yttrium hydride was used and the switch was made between a metallic yttrium dihydride state and a semiconducting yttrium trihydride state. However, in switching I RF microwave devices, any metal, metal hydride or alloy that is possible to switch between a metallic conductive state and one such or insulating semiconducting state using, for example, hydrogen, could be used in accordance with the present invention. Such materials are found in the lanthanide group in the third group of the periodic table. Typical alloys could contain magnesium (Mg), for example. Additional trivalent metals from this third group in the Periodic Table such as scandium (Se), yttrium (Y), lanthanum (La) or alloys thereof will be possible candidates to use in accordance with the present invention.

The thickness of the metal hydride is not critical. However, it should not be thinner than 0.1 μm and could, for example, be 10 μm thick. The thickness of the catalytic layer is not critical. It could typically be between 2 nm and 25 nm.

In the current reported experiment, quartz substrate was used. In a switchable device, any substrate used for planar radio frequency transmission lines or integrated microwave circuits would be applicable.

The thickness and width of the planar conductor and the thickness of the substrate are not specific to the described invention, but could be those used in a specific circuit.

Gold was used for the conductive layer and the ground plane in the illustrative experiment. In a switchable device in accordance with the present invention, any conductive material could be used, for example copper, silver or aluminum. described Microstrip transmission line technology was used in that experiment. In a device in accordance with the present invention, any transmission technology could be used which is suitable for reasonably flat surfaces, for example strip-lines, coplanar, waveguides or slit conductors.

The hydrogen controlling the switching of the device in the described experiment was obtained from molecular hydrogen gas phase. Atomic hydrogen was obtained by dissociation of molecular hydrogen through the catalytic metal of the cover layer. In a switchable device, hydrogen could be obtained from a liquid or solid electrolyte or from a hydrogen plasma. For example, a solid electrolyte could be a proton conducting solid; for example zirconia. o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o. The devices described above are simple to demonstrate the new principle as clearly as possible. The tunable or switchable radio frequency or microwave characteristics of the metal hydride could obviously be used in other devices or circuits. They could be used either in individual components or as part of circuits such as RFIC or MMIC.

Switchable metal hydrides can be used to change the geometry of the metal layer for individual components or in circuits such as RFIC or MMIC.

Different applications would require different geometries of the switchable metal hydride and the rest of the metal layer used.

The frequency range for application using the present invention is not limited to that given in the presented experimental data. The geometries and properties of the materials used in a specific application set limits on the frequency range. Physically relevant frequency limits for the present invention for controlling the transmission characteristics of radio frequency or microwaves could be 50 kHz up to 3000 GHz.

One application would be variable dampers. If a transmission line has a part which is a switchable metal hydride, the attenuation can be changed continuously with the exchange of hydrogen. The frequency range of such a device is expected to be wide.

Another application would be impedance matching. The length of a matching stub element could be changed by having one or more parts of metal hydride at the end of the stub element, or in series along the stub element. By having the parts of metal hydride in the metallic or semiconducting state, the length of the stump element could be changed and thus the impedance of the stump element could be changed. Trimming could be done on an RFIC or on an MMIC by switching the metal hydride between its metallic and high-voltage stå nstands. i 10 20 25 30 527 452 ooo o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o A metal hydride - which is a material rather than an active device - is expected to exhibit small nonlinearities power level and with respect to the RF or microwave signal the power losses of the signal can be made relatively small.

One application could be phase shifting devices. By forming transmission lines of different lengths, the phase shift of a transmitted or rejected signal can be controlled; Another application could be tunable capacitors. By designing in one radio frequency circuit one or both sides of a parallel plate capacitor of metal hydride, the area of the capacitor, and consequently also the capacitance, can be controlled.

Another application could be tunable resistors. Because in a radio frequency or microwave circuit one or both sides of the contacts against a resistive layer are formed by metal hydride, the width of the contacts, and consequently also their resistance, can be controlled.

Additional applications could »be coupling devices. By changing the dimensions of the transmission lines forming the device, the frequency selectivity and switching ratio can be controlled.

Another typical application could be rnikrovågslter. These can be implemented in flat transmission lines. This can be done by using stub elements with definite characteristic impedances, or transmission lines with different widths and, thus, different characteristic impedances. Other alternatives are connected line filters or filters with capacitive gaps in the transmission line. In all these types of filters, the characteristic impedance of the elements of the filter can be switched or tuned by using a disconnectable metal hydride. Metal hydrides could thus be used for switching or trimming microwavers of flat transmission lines.

Another application could be antennas. Switchable metal hydrides could be used in flat or slit antennas to switch between different antenna geometries or to tune the antenna gain. Another antenna application could be the polarization of antennas. By forming different antenna patterns, the structure will connect to different types of polarization, either for receiving or transmitting radio frequency or microwave signals. Additional applications could be phase controlled group antennas. By forming different antenna patterns, specific antenna characteristics can be achieved, which focus the reception or transmission of the radio frequency or microwave signal in specific directions.

The particular advantage of the present invention is that the switching and control function can be performed by a non-electrical influence on the hydrogen content of a component which operates in accordance with the principle shown above. As far as the technology has developed so far, there is no instantaneous influence of the component, but many functions are not dependent on immediate influence, but rather a non-electric one. procedure for obtaining switching or control.

It will be appreciated by those skilled in the art that various modifications and changes may be made to the present invention without departing from its scope, which is defined by the appended claims. 20 [21 [31 * [41 [51 [61 [71 [81 [91 1101]

[11] 1121 527 452 o v ooo o o oo oooo o oo 0 0. l o o o o v u u o .I g _ g o o o o o o, o o o o o o o,. . ooo o o o o o o 0 0 o o o o o o. . o o o o o o o o o o I ß I 0 o o o o o o oo ooo oo ooo o o REFERENCE by Gogh et al., Physical Review Letters, vol. 83, pp. 4614 (1999).

R. Griessen et al., U.S. Pat. 5,635,729. and P. Duine, Patent Application WO 00/17706.

J. Isídorsson et al., Electrochimica Acta, vol. 46, pp. 2179 (2001).

T. J. Richardson, Patent Application WO 02/14921 E. S. Kooij et al., Journal of the Electrochemical Society, Vol. 146, pp.299o (1999y 1 _ J. Isídorsson et al., Applied Physics Letters, vol. 80, pp. 2305, (zoozy 1 JN Huiberts et al., Nature, vol. 380, pp. 231 (1996). van Gogh et al., Applied Physics Letters, vol. 77, pp. 815 (2000).

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Claims (14)

10 20 25 30 527 452 PATENT CLAIMS Method for obtaining a device for controlling or switching microwave or radio frequency signals, characterized by the steps of providing a substrate material (4) having electrical properties adapted for microwave or radio frequency use, creating an area (3) with a thin film of a material which will act as a conductor or as an insulating semiconductor depending on the amount of hydrogen present in the thin film, connecting the area (3) of the thin film in series with at least one connection (1) to a microwave or radio frequency coupling, and providing a tool for switching the area (3) of the thin film between a conductive metallic state and a semiconductive state by varying the hydrogen content. A method according to claim 1, characterized by the further steps of providing the thin film from a trivalent metal such as scandium (Se), yttrium (Y), lanthanum (La), or alloys thereof. A method according to claim 1, characterized in that the further step of depositing the thin film as a planar conductor to react with hydrogen to create either a conductive dihydride or an insulating semiconducting trihydride by the presence of hydrogen A method according to claim 1, characterized by the further step of using, for supplying hydrogen, an electrolyte material which supplies necessary hydrogen in an encapsulation for a switching and control function. 20 25 30 527 452 n i .5 '~. - A method according to claim 1, characterized by the further step of providing the substrate material with a well conductive ground plane on a lower side of the substrate opposite to a side which carries the area with thin film used for the switching and control function. Process according to claim 1, characterized by the further step using, as the thin film, a material from the group consisting of lanthanides, or an alloy thereof, which can be switched between a conductive state and an insulating semiconducting state by changing the hydrogen content of the metal film (3). Radio frequency switching and control device, characterized by g a substrate material (4), having electrical properties adapted for microwave or (RF) radio frequency use; an area of a thin elm (3), which with hydrogen will act as a conductor or as an insulating semiconductor depending on the amount of hydrogen present, where the area of the thin elm (3) is connected in series with at least one connection to a microwave or radio frequency switching; and an arrangement for hydrogen switching the thin film (3) between a conductive metallic state and an insulating semiconducting state. ' Device according to claim 7, characterized in that the thin film is a 'rare earth metal' or an alloy thereof, deposited on the substrate material (4) to react with hydrogen and create a conductive state of the thin film or an insulating semiconducting state of the thin ñlmen. 10 15 20 25 30 527 452 Device according to claim 7, characterized in that the substrate (4) is provided with a well-conducting ground plane (5) on the underside of the substrate opposite the side having the area with the thin film used for the switching and controlling function. Device according to claim 7, characterized in that the substrate (4) is provided with stripline conductor, or alternatively microstripline conductor, for using a microwave signal control function in the GHz frequency range. Device according to claim 7, characterized in that the thin film is of a trivalent metal such as scandium (Sc), yttrium (Y), lanthanum (La) or alloys thereof. Device according to claim 7, characterized in that a deposited trivalent thin metal fi lm is switched between a conductive dihydride state and a semiconductive trihydride state by the presence of hydrogen. Device according to claim 7, characterized in that a circuit component for microwave or radio frequencies is formed which provides a variable parameter value based on a variation of the hydrogen content. Device according to claim 7, characterized in that the thin film is magnesium (Mg) or an alloy of magnesium with a 'rare earth metal' or a transition metal deposited on the substrate material.