GB2194685A

GB2194685A - Ferromagnetic resonance devices

Info

Publication number: GB2194685A
Application number: GB08715560A
Authority: GB
Inventors: Yoshikazu Murakami; Takahiro Ogihara; Tsutomu Okamoto; Kanako Niikura
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1986-07-02
Filing date: 1987-07-02
Publication date: 1988-03-09
Anticipated expiration: 2007-07-02
Also published as: FR2602619B1; GB8715560D0; KR880002285A; DE3721923A1; GB2194685B; CA1271237A; KR960006463B1; FR2602619A1

Description

1 GB2194685A 1

SPECIFICATION

Ferromagnetic resonance devices This invention relates to ferromagnetic resonance devices.

It has been proposed for a magnetic resonance element for a microwave device, such as a filter or an oscillator, which utilises ferrimagnetic resonance of yttrium iron garnet (YIG), to employ a spherical body prepared from a bulk single crystal of Y1G. However, the lower limit of the resonance frequency of the spherical body is relatively high owing to a demagnetising field; for instance, the lower limit is 1680 MHz in the case of using an unsubstituted Y1G sphere having a saturation magnetisation of 1800 G (gauss). Thus, a microwave device capable of operating in a range down to the UHF band has not yet been attained. The lower limit of the resonance frequency may be reduced partially by substituting non-magnetic ions such as Ga3+ for Fe 3+ in the Y1G and thereby decreasing the saturation magnetisation. In this case, if the amount of subsititution is too large, the half width AH of resonance is increased, which causes deterioration in characteristics of the device.

According to another technique, it has been proposed that a microwave device utilising ferrimagnetic resonance be provided by forming a Y1G thin film on a gadolinium gallium garnet (GGG) substrate by liquid phase epitaxial (LPE) growth (hereinafter referred to as "LPE") and causing the thin film to adopt a desired pattern, such as a circular or rectangular shape, by photolithography. As such a microwave device may be prepared as a microwave integrated circuit (MIC) using a micro-strip line or the like for a transmission line, the device is easily mounted in a magnetic circuit for applying a d c bias magnetic field. Further, as the device is produced by using LPE and photolithography, mass-produceability is improved. Such ferromag netic resonance devices utilising Y1G thin films are disclosed in out US Patents Nos. 4 547 754, 25 4 626 800 and 4 636 756, and in our European Patent Applications Publications Nos. EP-A-0 157 216, EP-A-0 164 685, EP-A-0 196 918, EP-A-0 208 547 and EP-A-0 208 548. Addition ally, the use of a thin-film element can greatly reduce the lower limit of the resonance frequency as compared to the case in which a spherical element is employed. However, in such a magnetic resonance device using a Y1G thin film element, a detailed investigation intended to reduce the 30 lower limit of the resonance frequency to an ultimate value has not yet been reported.

While, as is mentioned above, an investigation into reducing the lower limit of the resonance frequency to an ultimate value has not yet been established, an exemplary method of reducing the lower limit to an ultimately low frequency is to strengthen connection between the Y1G thin film element and the transmission line and thereby sufficiently decrease an external Q (quality 35 factor) value of a resonator. That is, since an unloaded Q value of a Y1G resonator is lowered in a low frequency, it is necessary sufficiently to reduce the external Q value so as to enlarge to some extent a reflection amplitude in the case of a reflection type or a transmission amplitude in the case of a transmission type.

Fig. 10 of the accompanying drawings shows the structure of a previously proposed Y1G thin 40 film resonance device of a Y1G thin film resonance device of a Y1G thin film type band-pass filter. In this structure, a dielectric substrate 1 (for example an alumina substrate) has a ground conductor 2 formed on one principal plane (hereinafter referred to as--thefirst principal plane") and first and second parallel micro-strip lines 3 and 4 (acting as input and output transmission lines, respectively) formed on another principal plane (hereinafter referred to as---thesecond principal plane---). the micro-strip lines 3 and 4 are connected at their ends through first and secon ' d connecting conductors 5 and 6, respectively, to the ground conductor 2. First and second Y1G thin film elements 7 and 8, acting as magnetic resonance elements, are arranged on the second principal plane of the substrate 1 and are electromagnetically connected to the first and second micro-strip lines 3 and 4, respectively. The Y1G thin film elements 7 and 8 are 50 prepared by forming a Y1G thin film on one of the principal planes of a non-magnetic GGG substrate 9 by the above-mentioned thin film forming technique and making the thin film take up a desired pattern, such as a circular shape, by selective etching using a photolithography technique, for example. A third micro-strip line 10, acting as a connecting transmission line for electromagnetically connecting together the first and second Y1G thin film elements 7 and 8, acting as the first and second magnetic resonance elements, is formed on the other principal plane of the GGG substrate 9. The third micro strip 10 is connected at its ends through third and fourth connecting conductors 11 and 12, respectively, to the ground conductor 2. The structure shown in Fig. 10 is placed in a d c bias magnetic field applied perpendicularly to a major surface of the Y1G thin film elements. (The bias magnetic field applying structure is not 60 shown in Fig. 10).

Since the connection between the microstrip lines and the Y1G thin film elements is not strong, the external Q value cannot be reduced to such an extent as is required for low frequency operation. In a case in which the Y1G thin film elements 7 and 8 had a diameter of 2.5 mm and a thickness of 25 micrometres, an external G value Qel due to the connection 2 GB2194685A 2 between the YIG thin film elements 7 and 8 and the input and output transmission lines 3 and 4 was 200, while an external Q value Qe2 due to the connection between the YIG thin film elements 7 and 8 and the connecting transmission line 10 was 250. In order further to reduce these external Q values, it is necessary to enlarge the volume of the YIG thin film elements 7 and B. However, if the diameter of the elements 7 and 8 were made as large in comparison with the width of the microstrip lines as the transmission lines, a spurious characteristic would be deteriorated. Further, if the thickness of the elements 7 and 8 were increased, the resonance frequency would (disadvantageously) be increased.

According to a first aspect of the present invention there is provided a ferromagnetic reso- nance device comprising a yttrium iron garnet (YIG) thin film element formed on a non-magnetic 10 substrate, the YIG thin film element having a major surface formed as a (100) plane, a transmission line coupled to the YIG thin film element, and a bias magnetic field means for applying a bias magnetic field means for applying a bias magnetic field perpendicularly to said major surface.

According to a second aspect of the present invention there is provided a ferromagnetic 15 resonance device comprising a YIG thin film element formed on a non- magnetic substance, the YIG thin film element having a major surface formed as a (111) plane and having a uniaxial magnetic anisotropy constant which is smaller than a uniaxial magnetic anisotropy constant of a pure YIG thin film element formed on a gadolinium-gallium-garnet (GGG) substrate, a transmission line coupled to the YIG thin film element, and a bias magnetic field means for applying a bias 20 magnetic field perpendicularly to said major surface.

Preferred ferromagnetic resonance devices embodying the invention and described hereinbelow are suitable, for example, for use with a microwave filter or a microwave oscillator.

The preferred ferromagnetic resonance devices can be designed to be operable at an ex tremely low resonance frequency limit and/or to be operable over a wide frequency range.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of a filter device, utilising ferromagnetic resonance, according to a preferred embodiment of the present invention; Figure 2 is an exploded perspective view of a body of the device shown in Fig. 1; Figure 3 is a graph showing filter characteristics (with respect of frequency) of the preferred embodiment; Figure 4 is a sectional view of another embodiment of the present invention; Figure 5 is a graph showing filter characteristics (with respect to frequency) of the embodi- ment shown in Fig. 4; Figure 6 is a graph showing a relationship between a dernagnetisation factor NT' and an aspect ratio a; Figure 7 is a graph showing a relationship between a quantity NT'47r!Vls and the aspect ration Figure 8 is a graph showing a relationship between a resonance frequency and an unloaded Q 40 value; Figure 9 is a graph showing a relationship between an external magnetic field and the resonance frequency; and Figure 10 is a perspective view of the above-described previously proposed ferromagnetic resonance device.

According to embodiments of the present invention described below, by using a YIG thin film element having a major surface which is formed as a (100) plane, or as an (111) plane having a reduced Ku (uniaxial anisotropy constant) value, a lower limit O)min of the resonance frequency may be reduced.

How this is achieved will now be describe in detail.

The lower limit (Omin of the resonance frequency of a ferrimagnetic single crystal depends on two factors, namely the dernagnetising field and the anisotropy field. Therefore, in order to reduce the-lower limit (Omin to an ultimate value, it is necessary to consider both these factors.

First, the dernagnetising field will be considered. For the sake of simplicity, a spheroid sample is considered. When the sample is arranged in a d c magnetic field Ho in such a manner that the magnetic field Ho lies in the axial direction of the sample, an internal d c magnetic field Hi that is obtained can be expressed as follows:

Hi=Ho-Nz.41rMs (1), where Nz is a demagnetisation factor in the axial direction and 47ZMS is a saturation magnetisation. The resonance frequency co of or in this sample is given by Kittel's equation as follows:

co=y[Ho-(Nz-N,).47rMs]. (2), 1 3 GB2194685A 3 where y is a gyromagnetic ratio and NT is a demagnetisation factor in a transverse direction. The following equation can be derived from Equations (1) and (2):

o)=y(Hi+NT.47tMs) (3).

in this case, unless magnetisation of the sample is saturated, a single magnetic domain is not provided and, accordingly, a magnetic resonance loss is rapidly increased. Therefore, a condition for saturating the sample, that is the internal d c magnetic field Hi>O, is required. Even if the internal magnetic field required for saturating the sample is ignored, the resonance frequency is 10 not lowered below the following value:

comi,,=yNT.47tMs (4).

In case of a spherical Y1G resonance element, NT 1/3 applies, and the lower limit of the resonance frequency is 1680 MHz (y=2.8 MHz/0e) for unsubstituted Y1G having a saturation magnetisation of 1800 G, and is 560 MHz when trivalent non-magnetic Ga ions Ga 3 + are partially substituted for trivalent Fe ions Fe3,1- so as to reduce the saturation magnetisation to 600 G.

In the case of a circular Y1G thin film disc, since the shape of the disc is not a complete spheroid, and the internal d c magnetic field is not uniform, the operation is different than in the 20 above case. However, a resonance frequency obtained from a magnetostatic mode theory (cf., Y. Ikusawa and K. Abe; -Resonant Modes of Magnetostatic Waves in a Normally Magnetized Disc-, Japan Applied Physics 48, 3001 (1977)) can be expressed in the same fashion as in Equation (2). In this case, Nz-NT depends upon the aspect ratio (thickness/diameter ratio) of the thin film disc. The internal d c magnetic field Hi is at a minimum at the centre of the disc. 25

Suppose that the minimum value of Hi is expressed as follows:

Hi=Ho-Nz'.47rMs (5), where W' denotes an effective demagnetising factor at the centre of the disc. The lower limit 30 0)min of the resonance frequency is given from Equations (2) and (5) as follows:

COmin=y[Nz'-(Nz-N,)].47rMs=NT'.4Ms (6).

Fig. 6 shows the dependency of NT' upon the aspect ration or, and Fig. 7 shows values of -NT' a= 1 X 10-2 47rMs when 47rMs is 1800 G. Typical values of yN,'47rMs are 63 MHz when (diameter: 2 mm; thickness: 20 micrometers) and 125 MHz when (;= 2 x 10- 2. It is appreciated that these values are very small as compared with the above case of the spherical YIG element.

Next, the effect of the anisotropy field will be considered.

Magnetic anisotropy of a YIG thin film formed by LPE includes crystal magnetic anisotropy and 40 uniaxial magnetic anisotropy. Conditions for a YIG thin film having a (100) crystal plane for the principal plane and for a YIG thin film having a (111) crystal plane for the principal plane are given by the following equations, as influenced by the afore-mentioned anisotropy field (cf., J.

Smit and H.P.J. Wijn, "Ferrites", Chap. 6, John Wiley & Sons, Inc., New York, 1959, and J.0.

Artmand, "Microwave Resonance in Anisotropic Tropic Single Crystal Ferrites" Proc. IRE, 44, 45 1284, 1956):

condition in the case of a (100) crystal plane:

co=y(Hi+2Ku/Ms-21K,I/Ms) (7) (Hi-21K,I/Ms=2Ku/Ms), and condition in the case of a (111) crystal plane:

co=7(Hi+2Ku/Ms+41K11/Ms (8), where K, is a primary cubic crystal magnetic anisotropy constant, which has a negative value in YIG, and Ku is a uniaxial anisotropy constant, which is inherent in a thin film of YIG rather than in bulk YIG. The uniaxial anisotropy constant Ku consists of magnetostriction anisotropy Ks generated because of mismatching between a lattic constant of the YIG thin film formed by LPE and a lattice constant of the GGG substrate, and growth induced magnetic anisotropy K, associated with non-uniform growth of the crystal of the YIG thin film. Actually, since the growth induced magnetic anisotropy K, is negligibly small, only the magnetostriction anisotropy 60 factor need be considered. Since the lattice constant of the unsubstituted YIG is smaller than that of the GGG substrate, and magnetostrictive constants A,,, and A,O, have negative values, the magnetostriction anisotropy Ks has a positive value. On the other hand, Y3-1- ions in YIG are partially substituted with La3 ions to thereby attain matching between the lattice constant of the YIG thin film and that of the GGG substrate. Thus, Ks may be made substantially zero and, as a 65 4 GB2194685A 4 result, Ku may be made substantially zero.

It will be appreciated from Equation (7) that perpendicular resonance of the (100) film can rise from a frequency of zero. Further, the lower limit frequency co,,in of perpendicular resonance of the (111) film becomes 149 MHz when Ku=0 and 11(11/Ms=40 Oe.

Summarising the above, the lower limit frequency of perpendicular resonance of the Y1G 5 thin film disc can be expressed as follows:

in the case of using a (100) plane for the principal plane:

6OgTlin=yN,'4nMs (9), and in the case of using a (111) plane for the principal plane:

o).i.=y(N4nMs+2Ku/Ms+41K11/3Ms) (10).

While a YIG thin film element used in a device according to one aspect of the present.

invention uses a (100) plane for the principal plane, Equation (9) may be established by suffici ently reducing the magnetostrictive anisotropy and the growth induced magnetic anisotropy and thereby making the uniaxial anisotropy constant Ku equal to or less than the absolute value of the primary cubic anisotropy constant K, Furthermore, when the aspect ratio is set to 5 X 10-2 or less, with reference to Fig. 6, the lateral dernagnetisation factor NT' may be reduced to 20 thereby reduce the lower limit frequency Omin to an ultimate value.

In another aspect, it is to be appreciated that (o,,, may be reduced in the case of the substituted YIG thin film element having a value of Ku smaller than that of unsubstituted YIG on a GGG substrate, and that (orr, may be further reduced to an ultimate value when Ku=O.

Further, as will be appreciated from Equation (9), the lower limit frequency 0)", may be reduced by partially substituting non-magnetic ions such as Ga3+ ions for Fe3+ ions in the YIG and thereby reducing the saturation. magnetisation 47rMs.

While the above description is directed to the case where the primary cubic anisotropy constant K, is negative, conditions of perpendicular resonance when K, is positive can be expressed as follows: condition in the case of a (100) crystal plane.

w=y(Hi+2Ku/Ms+2K,/Ms) (11), and condition in the case of a (111) crystal plane:

o)=y(Hi+2Ku/Ms-4K,/3Ms) (12) (Hi:4K,/3Ms-2Ku/Ms).

As will be apparent from Equations (11) and (12), COmin may be reduced by Making Ku equal to 40 or less than (2/3)K1 when using the (111) crystal plane.

Further, as was mentioned previously, the unloaded G value may be increased by reducing the lower limit of the resonance frequency. Fig. 8 shows how the unloaded Q valve Qu changes with frequency. As is apparent from Fig. 8, Qu is proportional to frequency CO, and Qu is zero at co---. Qu may be expressed as follows..

Qu=(w-comj/7AH (13).

As will be appreciated from Equation (13), the unloaded Q value may be increased by greatly reducing co,n when the frequency o) is fixed, thus improving characteristics. This effect is 50 especially marked at frequencies of lower than 1 GHz.

In ferromagnetic resonance devices embodying the invention using Y1G thin film elements, the operation frequency.may be reduced to an ultimately low frepency by reducing the external Q value Qe. This effect will now be described in detail.

First, in the case of using a reflection type resonance device such as a Y1G tuned oscillator, a 55 reflection factor S, is given by the following equation, where the unloaded Q value, the external Q value and the resonance frequency of the Y1G element are denoted by Qu, Qe and wo, respectively:

E GB2194685A 5 l/Qe - l/Qu - J ( W/Gi o - W o/#j) S11 --- (14) l/Qe + 1Qu + j (W 1w o - W o/W) Qu/Qe - 1 - jQu (0 1W o - W o/ti) Qu/Qe + 1 + jQu (W 1W o - W olw) ....... (15).

As will be appreciated from Equation (15), the reflection factor is -1 when Co is sufficiently separated from coo, and becomes equal to (Qu/Qe1)/(Qu/Qe+ 1) when (o=(oo. When Qu>Qe, 15 the YIG resonance element comes into an over-coupled condition, and the reflection factor describes a large loop in the vicinity of a)o. On the other hand, since Qu is small at an ultimately low frequency, as will be apparent from Equation (13), Qe must be reduced to a very low value so as to establish the relationship Qu>Qe.

Next, in the case of using a transmission type resonance device such as a band-pass filter, a 20 transmission factor S21 of a one-stage band-pass filter is given by the following equation:

2/JQe1Qe2 S21 l/Qu + l/Qel + l/Qe2 + J ((A/w o - t4 o1W) Substituting Qel=Ge2 into Equation (16) for the sake of simplicity, the following equation can be 30 obtained:

S21 = 2Qu/Qe . (17).

(2Qu/Qe + 1 + jQu (W /W o - W 0/W) As will be appreciated from Equation (17), the transmission factor is zero when Co is sufficiently separated from (oo, and becomes equal to (2Qu/Qe)/(2Qu/Qe+l) when co=(Oo. Accordingly, unless Qe is made sufficiently small in association with a reduced value of Qu at an ultimately low frequency, the transmission amplitude at =o cannot be large to a certain extent. in other words, the operation frequency may be reduced to an ultimately low value by sufficiently decreasing the external Q.value Qe.

A detailed description of the construction of embodiments of the invention will be be given. A

YIG thin film disc having a diameter of 2.5 mm and a thickness of 50 micrometres was prepared with its principal plane formed or specified as a (100) plane, and a perpendicular resonance frequency was measured when an external d c magnetic field applied in the direction of the thickness of the YIG thin film disc was varied. The results of measurement are shown in Fig. 9 by plotted blank (empty) circles. The lower limit of the resonance frequency was 140

MHz. Another YIG thin film disc having a diameter of 2.5 mm and a thickness of 50 micrometres was prep ared with its principal plane formed or specified as a (111) plane. Resonance frequencies obtained in this case are shown by solid circles plotted in Fig. 9. In this case, the lower limit of the resonance frequency was 270 MHz. These lower limits almost coincide with theoretical values of 125 MHz and 274 MHz obtained from Equations (9) and (10). A curved solid line shown in Fig. 9 is a theoretical value curve drawn by using a 47TMs= 1800 G, K,=-5.7x 103 erg/M3, and Ku=0.7 X 103 erg/cm3 (provided that Ku is applied to the (100) plane only). It will be appreciated that the condition that Ku<K1 is satisfied in this example.

Figs. 1 and 2 shows an example of a two-stage band-pass filter device of YIG thin film construction and embodying the present invention, the device comprising a body 19 and a bias magnetic field applying means 20 applying a d c bias magnetic field to the body 19.

A transmission system in this example comprises a so-called suspended substrate strip line. That is, the body 19 includes a first conductor 21 and a second conductor 22, between which a non-magnetic GGG substrate 25 and a dielectric substrate 29 are interposed. The nonmagnetic GGG substrate 25 is provided with first and second disc-like YIG thin film elements 23 and 24. The dielectric substrate 29 has first and second strip lines 26 and 27, acting as input 6 GB2194685A 6 and output strip lines, respectively, formed on one surface thereto, and has a third connecting strip line 28 formed on another surface thereof.

The strip lines 26 and 27 are so arranged as to be offset from the second conductor 22 in a position relatively near the same, so as to increase a high-frequency magnetic field between the strip lines and the second conductor 22. The YIG thin film elements 23 and 24 are so arranged 5 as to contact the strip lines 26 and 27 so as to strengthen the connection therebetween.

The first and second YIG thin film elements 23 and 24 are simultaneously prepared by forming a YIG thin film having a (100) crystal plane, or a substituted YIG thin film having a (111) crystal plane, as a principal plane by LPE on an entire surface of the non- magnetic GGG substrate 25 opposed to the dielectric substrate 29, and then etching off an unnecessary portilon of the thin 10 film by photolithography to obtain a desired size, shape and arrangement.

The dielectric substrate 29 is formed of a ceramic or ceramics such as alumina. The first and second strip lines 26 and 27 are deposited on a surface of the substrate 29 opposed to the YIG thin-fiJm elements 23 and 24 at positions facing the elements 23 and 24. The third strip line 28 is deposited on the other surface of the substrate 29 in such a manner as to intersect the strip lines 26 and 27 in opposed relationship thereto. Opposed ends 26a and 27a of the first and second micro-strip lines 26 and 27 and both ends 28a and 28b of the third micro-strip line 28 are designed to act as ground or earth terminals. The substrates 25 and 29 are interposed between the first and second conductors 21 and 22 to contact the conductor 21 and 22.

The first conductor 21 is formed at its lower surface with a relatively deep recess 30 to define a relatively large space at portions opposite to the first and second YIG thin film elements 23 and 24, the electromagnetically connected portion between the first and second strip lines 26 and 27 and the elements 23 and 24, and the connected portion between the third strip line 28 and the first and second strip lines 26 and 27.

The second conductor 22 is formed at its upper surface with a relatively shallow recess 31 to receive the superimposed substrates 25 and 29. Spacers 32 are located at opposite ends of the bottom surface of the recess 31 so as to maintain a desired relatively small gap between the conductor 22 and portions of the YIG thin film elements 23 and 24 opposed to the strip lines 26 and 27.

The ground terminals at or constituted by the ends 28a and 28b of the third micro-strip line 28 are designed to contact the lower surface 21a of the first conductor 21, while the ground terminals at or constituted by the ends 26a and 27a of the first and second microstrip lines 26 and 27 are designed to contact base portions 22a of the second conductor 22 located in the recess 31.

The bias magnetic field applying means 20 comprises a pair of barrel cores 41 and 42 surrounding the body 19 of the device. The barrel cores 41 and 42 have respective central magnetic poles 41A and 42A opposed to each other in such a manner as to interpose the body 19 therebetween. A coil 43 is wound around at least one of the central magnetic poles 41A and 42A. When the coil 43 is supplied with current, a d c bias magnetic field is generated 40 between the central magnetic poles 41A and 42A. The strength of the d c bias magnetic field may be varied by selecting the current supplied to the coil 43.

With the arrangement desribed above, magnetic connection between the YIG thin film ele ments 23 and 24 and the input and output strip lines 26 and 27 is strenghthened to thereby sufficiently reduce the external Q value Qe. Accordingly, the operation frequency may. be re- duced. For instance, in the case of using YIG thin film elements 23 and 24 having a diameter of 2.5 mm and a thickness of 25 micrometres, the external Q value Qel due to the connection between the input and output strip lines 26 and 27 and the YIG thin film elements 23 and 24 is 70, and the external Q value Qe2 due to the connection between the connecting strip line 28 and the YIG thin film elements 23 and 24 is 325. Fig. 3 shows results of measqrment of filter 50 characteristics, in which curves 61, 62 and 63 represent insertion loss, reflection loss and 3 dB bandwidth, respectively. As is apparent from Fig. 3, the foregoing arrangement can be designed to provide a variable frequency YIG band-pass filter which may be operated in a frequency range of from 400 MHz to 2 GHz.

Fig. 4 shows another embodiment which may reduce the external Q value more than in the case of the previous embodiment. Referring to Fig. 4, the arrangment of this embodiment is similar to that of the previous embodiment, as shown in Figs. 1 and 2, except that a conductor layer 50 is formed on the whole of the surface of the non-magnetic GGG substrate 25 on the opposite side to the YIG thin film elements 23 and 24, that is on the surface of the substrate 25 opposed to the second conductor 22, which surface includes a portion opposed to at least 60 the YIG thin,film elements 23 and 24. The conductor layer 50 is kept in a floating condition where it is not electrically connected to the first and second conductors 21 and 22. Parts in Fig.

4 corresponding to parts in Fig. 1 are designated by the same reference numerals as in Fig. 1 and an explanation thereof is not repeated.

Fig. 5 shows results of measurement of filter characteristics of the embodoment of Fig. 4 with 65 7 GB2194685A 7 respect to frequency, in which curves 64, 65 and 66 designate insertion loss, reflection loss and 3 dB bandwidth, respectively. The insertion loss (the curve 64) in this case is not very different from that shown in Fig. 3 since the filter of the previous embodiment shown in Figs. 1 and 2 is originally low in insertion loss. In contrast, the 3 dB bandwidth (the curve 66) of Fig. 5 is increased so as to about 5 MHz more than that of Fig. 6. This result is due to the fact that the 5 external Q value in Fig. 4 is reduced more.

Although the above embodiments employ a suspended substrate strip line arrangement, em bodiments of the present invention may include modified arrangements such as an infinite open type suspended substrate strip line arrangement where the first conductor 21 is sufficiently spaced away from the dielectric substrate 29, or an inverted micro-strip line arrangement.

The embodiments of the present invention described above enable provisionof a ferromag netic resonance device of a YIG thin film type which may be operated from an ultimately low frequency. Furthermore, the lower limit of the resonance frequency may be reduced. As a result, an unloaded Q value may be increased at the same frequency to thereby improve characteristics.

The effect is particularly marked at frequencies of lower than 1 GHz.

Moreover, as described with reference to Figs. 1 and 2 and Fig. 4, the conductors 21 and 22 of the body 19 surround the resonance element to exhibit a shielding effect. Accordingly, when the body 19 is mounted in the gap between the magnetic poles 41A and 42A of the magnetic circuit of the bias magnetic field applying means 20, a change in characteristics due to isolation deterioration may be avoided by the shielding effect. Further, since the strip lines are formed on 20 the dielectric substrate 29, and the YIG thin film elements 23 and 24 are formed on the non magnetic substrate 25, the forma tion of the strip lines may be carried out independently of the formation of the YIG thin film elements, thereby simplifying the production process and improv ing yield.

Claims

1. A ferromagnetic resonance device comprising a yttrium iron garnet (YIG) thin film element formed an a non-magnetic substrate, the YIG thin film element having a major surface formed as a (100) plane, a transmission line coupled to the YIG thin film element, and a bias magnetic field means for applying a bias magnetic field perpendicularly to said major surface.

2. A ferromagnetic resonance device comprising a YIG thin film element formed on a non magnetic substrate, the YIG thin film element having a major surface formed as a (111) plane and having a uniaxial magnetic anisotropy constant which is smaller than a uniaxial magnetic anisotropy constant of a pure YIG thin film element formed on a gadolinium-gallium-garnet (GGG) substrate, a transmission line coupled to the YIG thin film element, and a bias magnetic field means for applying a bias magnetic field perpendicularly to said major surface.

3. A device according to claim 1 or claim 2, wherein the YIG thin film element is disc shaped.

4. A device according to claim 3, wherein the YIG thin film element has an aspect ratio which is not greater than F) X 10 2.

5. A ferromagnetic resonance device comprising:

a non-magnetic substrate, a ferrimagnetic thin film element formed on a magor surface of the non- magnetic substrate, a strip line disposed on the non-magnetic substrate and electromagnetically coupled to the ferrimagnetic thin film element, a conductive wall connected or connectable to ground potential, the wall facing the strip line and being spaced at a predetermi ' ned distance therefrom, an end of the trip line being connected to said conductive wall, and bias magnetic field means for applying a d c magnetic field to the ferrimagnetiQ thin film perpendicularly to said major surface of the substrate, the ferrimagnetic thin film element being a YIG thin film having a major surface formed as a (100) plane.

6. A filter device utilizing ferromagnetic reasonance, the device comprising:

a non-magnetic substrate, first and second ferrimagnetic thin film elements formed on a major surface of the non- 55 magnetic substrate, a first strip line electromagnetically coupled to the first ferrimagnetic thin film element, a second strip line electromagnetically coupled to the second ferrimagnetic thin film element, a conductive wall connected or connectable to ground potential, the wall facing each of the first and second strip lines and being spaced at a predetermined distance therefrom, an end of the first strip line being connected or connectable to an input circuit, and another end of the first strip line being terminated at said conductive wall, an end of the second strip line being connected or connectable to an output circuit, and another end of the second strip line being terminated at said conductive wall, said first and second ferrimagnetic thin film elements being magnetically coupled with each 65 i 8 GB2194685A 8 other, and bias magnetic field means for applying a d c bias magnetic field to the ferrimagnetic thin films perpendicularly to said major surface of the substrate, at -least one of the ferrimagnetic thin film elements being a YIG thin film having a major surface formed as a (100) plane.

7. A device according to claim 5 or 6, comprising a conductive layer formed on a surface of 5 the substrate opposite to said major surface of the substrate.

8. A ferromagnetic resonance device comprising a non-magnetic substrate, a ferrimagnetic thin film element formed on a major surface of the nonmagnetic substrate, a strip line disposed on the non-magnetic substrate and electromagnetically coupled to the 10 ferrimagnetic thin film element, a conductive wall connected or connectable to ground potential, the wall facing the strip line and being spaced at a predetermined distance therefrom, an end of the strip line being connected to said conductive wall, and bias magnetic field means for applying a d c magnetic field to the ferrimagnetic thin film 15 perpendicularly to said major surface of the substrate, the ferrimagnetic thin element being a YIG thin film having a major surface formed as a (111) plane and having a uniaxial magnetic anisotropy constant smaller than a uniaxial anistropy constant of a pure-YIG thin film element form on a GGG substrate.

9. A filter device utilising ferromagnetic resonance, the device comprising:

a non-magnetic substrate, first and second ferrimagnetic thin film elements formed on a major surface of the non magnetic substrate, a first strip line electromagnetically coupled to the first ferrimagnetic thin film element, a second strip line electromagnetically coupled to the second ferrimagnetic thin film element, 25 a conductive wall connected or connectable to ground potential, the wall facing each of the first and second strip lines and being spaced at predetermined distance therefrom, an end of the first strip line being connected or connectable to an input circuit, and another end of the first strip line being terminated at said conductive wall, an end of the second strip line being connected or connectable to an output circuit, and 30 another end of the second strip line being terminted at said conductive wall, said first and second ferrimagnetic thin film elements being magnetically coupled with each other, and bias magnetic field means for applying a d c bias magnetic field to the ferrimagnetic thin films perpendicularly to said major surface of the substrate, at least one of the ferrimagnetic thin film elements being a YIG thin film having a major surface formed as a (111) plane and having a uniaxial magnetic anisotropy constant smaller than a uniaxial magnetic anisotropy constant of a pure YIG thin film element formed on a GGG substrate.

10. A device according to claim 5 or claim 6, comprising a conductive layer formed on a 40 surface of the substrate opposite to said major surface of the substrate.

11. A device according to claim 6 or claim 9, wherein the first and second ferrimagnetic thin film elements are magnetically coupled by a transmission line.

12. A device according to claim 6 or claim 9, wherein the first and second ferrimagnetic thin film elements are magnetically coupled by a third ferrimagnetic thin film element provided be- 45 tween and adjacent to the first and second ferrimagnetic thin film elements.

13. A ferrimagnetic resonance device substantially as herein described with reference to Figs.

1 to 3 and 6 to 9 of the accompanying drawings.

14. A ferrimagnetic resonance device substantially as herein described with reference to Figs.

4 to 9 of the accompanying drawings.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may He obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RQ. Printed by Burgess & Son (Abingdon) Ltd. Con. 1187.