Abstract:
Disclosed therein is a magnetostatic wave device that employs a single-crystal thin film of magnetic garnet (which contains iron) characterized in that the magnetic garnet has incorporated indium or tin in an amount of about 10 to 3000 ppm (by weight).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetostatic wave device. 
     2. Description of the Related Art 
     A magnetostatic wave device employs single-crystal thin film of magnetic garnet which has conventionally been YIG (yttrium iron garnet) represented by Y 3  Fe 5  O 12 . YIG is characterized most by its extremely small ferromagnetic half-width (ΔH). This leads to the fact that a magnetostatic wave device that employs a single-crystal thin film of magnetic garnet has little difference between its input signals and output signals. Another feature of YIG is that it becomes saturated upon application of input signals of comparatively small power. These characteristic properties permit a single-crystal thin film of YIG (as well as other iron-containing garnets) to be used widely for magnetostatic wave devices such as limiters and noise filters. 
     SUMMARY OF THE INVENTION 
     Recent electronic machines with a less power consumption than before need a new version of YIG which becomes saturated upon application of a very small input power. 
     Accordingly, it is a first object of the present invention to provide a high-performance magnetostatic wave device which becomes saturated upon application of a very small input power. 
     The fact that YIG becomes saturated upon application of input signals leads to a transient response, namely the phenomenon that saturation does not occur immediately after application of input signals, with input signals being outputted as such, and saturation takes place after a lapse of time. This transient response adversely affects the performance of the magnetostatic wave device. 
     Accordingly, it is a second object of the present invention to provide a high-performance magnetostatic wave device which is free from transient response (the phenomenon that input signals are outputted as such and saturation takes place with lapse of time). 
     The first aspect of the present invention resides in a magnetostatic wave device that employs a single-crystal thin film of magnetic garnet (which contains iron) characterized in that the magnetic garnet incorporates indium in an amount of about 10 to 3000 ppm (by weight), preferably at least about 500 ppm and more preferably at least about 1000 ppm. 
     The second aspect of the present invention resides in a magnetostatic wave device that employs a single-crystal thin film of magnetic garnet (which contains iron), characterized in that the magnetic garnet incorporates tin in an amount of about 10 to 3000 ppm (by weight), preferably at least about 500 ppm and more preferably at least about 1000 ppm. 
     It turned out that input power for saturation can be very small if a single-crystal thin film of YIG (as well as iron-containing magnetic garnet) for the magnetostatic wave device has incorporated indium in an amount of about 10 to 3000 ppm (by weight). 
     It also turned out that transient response can be minimized if single-crystal thin film of YIG (as well as iron-containing magnetic garnet) for the magnetostatic wave device has incorporated tin in an amount of about 10 to 3000 ppm (by weight). 
     The first aspect of the present invention is designed to make best use of YIG&#39;s capability of becoming saturated upon application of a very small input power, thereby providing a high-performance magnetostatic wave device. 
     The second aspect of the present invention makes best use of YIG&#39;s feature that saturation takes place without delay upon application of input signals of small power. This makes it possible to minimize the transient response, thereby enhancing the performance of the magnetostatic wave device. 
     These and other objects, advantages, and features of the invention may be readily ascertained by referring to the accompanying drawing and the following detailed description of embodiments and 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view showing one embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective view showing one embodiment of the present invention, which is a magnetostatic wave device 10. It is composed of a rectangular substrate 12 of Gd 3  Ga 5  O 12  and a rectangular single-crystal thin film 14 of magnetic garnet formed on one surface thereof. The magnetic garnet contains iron. On the surface of the single-crystal thin film 14 of magnetic garnet are placed an input terminal 16 and an output terminal 18 which are parallel to each other. These terminals have their ends grounded. 
     The magnetic garnet has a composition represented by (Y 3-x1-x2  R&#39; x1  R&#34; x2 ) (Fe 5-y1-y2  M&#39; y1  M&#34; y2 )O 12 , wherein 0≦x1≦3, 0≦x2≦3, 0≦x1+x2≦3, 0≦y1&lt;5, 0≦y2≦3, 0≦y1+y2&lt;5, and x2=y2; 
     R&#39; is at least one member selected from Sc, Bi, and La series; 
     R&#34; is at least one member selected from the Mg, Ca, Sr, and Ba; 
     M&#39; is at least one member selected from Al, Ga, and In; and 
     M&#34; is at least one member selected from Si, Ti, Zr, Hf, and Ge. 
     The first aspect of the present invention is demonstrated by Examples 1 to 3, and the second aspect of the present invention is demonstrated by Examples 4 to 6. 
     EXAMPLE 1 
     A garnet thin film was formed by liquid phase epitaxy (LPE) on a GGG substrate (gadolinium gallium garnet--Gd 3  Ga 5  O 12 ) in the following manner. First, Fe 2  O 3  and Y 2  O 3  as the raw materials of the garnet were mixed with InO 2  as an additive and PbO-B 2  O 3  as a flux. Then the mixture was placed in a platinum crucible held in a vertical electric furnace and melted and homogenized at about 1200° C. The melt was cooled to and kept at about 900° C. so that garnet became supersaturated. Into this melt was dipped the GGG substrate, which was rotated for a prescribed period of time for crystal growth. Finally, the substrate was raised from the melt and then spun rapidly to remove the excess melt by centrifugal force. Thus was obtained the desired garnet thin film. 
     For comparison, the same procedure as above was repeated without the addition of the indium. 
     The thus obtained garnet thin film was fabricated into the magnetostatic wave device as shown in FIG. 1. The device was measured for the amount of input power (at 2 GHz) required for the device to become saturated. Also, the garnet film underwent chemical analysis to determine the content of indium. The results are shown in Table 1. 
     
                       TABLE 1______________________________________    Content of indium inSample   garnet thin film                  Amount of input powerNo.      (ppm by weight)                  for saturation (mW)______________________________________ 1*        0           3.2 2*        5           3.03         10           1.54         500          1.35        1000          1.26        1500          1.07        3000          0.9 8*      3100          **______________________________________ *Samples not conforming to the invention. **No satisfactory thin film was obtained. 
    
     According to the present invention, the content of indium in the garnet is specified as above because a content less than about 10 ppm (by weight) is not enough to effectively contribute to saturation (as in Sample No. 2 which is similar to Sample No. 1 containing no indium) and a content in excess of about 3000 ppm (by weight) is unfavorable to the formation of good single-crystal thin film (as in Sample No. 8). 
     EXAMPLE 2 
     A garnet thin film was formed by LPE on a GGG substrate (Gd 3  Ga 5  O 12 ) in the following manner. First, Fe 2  O 3 , Y 2  O 3 , Ga 2  O 3 , and La 2  O 3  as the raw materials of the garnet were mixed with InO 2  as an additive and PbO-B 2  O 3  as a flux. The mixture was placed in a platinum crucible held in a vertical electric furnace and then melted and homogenized at about 1200° C. The melt was cooled to and kept at about 900° C. so that garnet became supersaturated. Into this melt was dipped the GGG substrate, which was rotated for a prescribed period of time for crystal growth. Finally, the substrate was raised from the melt and then spun rapidly to remove the excess melt by centrifugal force. Thus there was obtained the desired garnet thin film. 
     For comparison, the same procedure as above was repeated without the addition of indium. 
     The thus obtained garnet thin film was fabricated into the magnetostatic wave device as shown in FIG. 1. The device was measured for the amount of input power (at 2 GHz) required for the device to become saturated. Also, the garnet film underwent chemical analysis to determine the content of indium. The results are shown in Table 2. 
     
                       TABLE 2______________________________________                Content of indium                            Amount of inputSample               in garnet thin film                            power forNo.   Composition    (ppm by weight)                            saturation (mW)______________________________________ 9*   Y.sub.2.96 La.sub.0.04 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                  0         2.910*   Y.sub.2.96 La.sub.0.04 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                  5         2.811    Y.sub.2.96 La.sub.0.04 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                 10         1.412    Y.sub.2.96 La.sub.0.04 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                 500        1.313    Y.sub.2.96 La.sub.0.04 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                1000        1.214    Y.sub.2.96 La.sub.0.04 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                1500        1.015    Y.sub.2.96 La.sub.0.04 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                3000        0.916*   Y.sub.2.96 La.sub.0.04 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                3100        **______________________________________ *Samples not conforming to the invention. **No satisfactory thin film was obtained. 
    
     According to the present invention, the content of indium in the garnet is specified as above because a content less than about 10 ppm (by weight) is not enough to effectively contribute to saturation (as in Sample No. 10 which is similar to Sample No. 9 containing no indium) and a content in excess of about 3000 ppm (by weight) is unfavorable to the formation of good single-crystal thin film (as in Sample No. 16). 
     EXAMPLE 3 
     A garnet thin film was formed by LPE on a GGG substrate (Gd 3  Ga 5  O 12 ) in the following manner. First, Fe 2  O3, Y 2  O 3 , Ga 2  O 3 , and Bi 2  O 3  as the raw materials of the garnet were mixed with InO 2  as an additive and PbO-B 2  O 3  as a flux. The mixture was placed in a platinum crucible held in a vertical electric furnace and then melted and homogenized at about 1200° C. The melt was cooled to and kept at about 900° C. so that garnet became supersaturated. Into this melt was dipped the GGG substrate, which was rotated for a prescribed period of time for crystal growth. Finally, the substrate was raised from the melt and then spun rapidly to remove the excess melt by centrifugal force. Thus there was obtained the desired garnet thin film. 
     For comparison, the same procedure as above was repeated without the addition of indium. 
     The thus obtained garnet thin film was fabricated into the magnetostatic wave device as shown in FIG. 1. The device was measured for the amount of input power (at 2 GHz) required for the device to become saturated. Also, the garnet film underwent chemical analysis to determine the content of indium. The results are shown in Table 3. 
     
                       TABLE 3______________________________________                Content of indium                            Amount of inputSample               in garnet thin film                            power forNo.   Composition    (ppm by weight)                            saturation (mW)______________________________________ 17*  Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.55 Ga.sub.0.45 O.sub.12                  0         3.0 18*  Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.55 Ga.sub.0.45 O.sub.12                  5         2.819    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.55 Ga.sub.0.45 O.sub.12                 10         1.420    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.55 Ga.sub.0.45 O.sub.12                 500        1.321    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.55 Ga.sub.0.45 O.sub.12                1000        1.222    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.55 Ga.sub.0.45 O.sub.12                1500        1.123    Y.sub.2.8 Bi.sub.02 Fe.sub.4.55 Ga.sub.0.45 O.sub.12                3000        1.0 24*  Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.55 Ga.sub.045 O.sub.12                3100        **______________________________________ *Samples not conforming to the invention. **No satisfactory thin film was obtained. 
    
     According to the present invention, the content of indium in the garnet is specified as above because a content less than about 10 ppm (by weight) is not enough to effectively contribute to saturation (as in Sample No. 18 which is similar to Sample No. 17 containing no indium) and a content in excess of about 3000 ppm (by weight) is unfavorable to the formation of good single-crystal thin film (as in Sample No. 24). 
     EXAMPLE 4 
     A garnet thin film was formed by liquid phase epitaxy (LPE) on a GGG substrate (gadolinium gallium garnet--Gd 3  Ga 5  O 12 ) in the following manner. First, Fe 2  O 3  and Y 2  O 3  as the raw materials of the garnet were mixed with SnO 2  as an additive and PbO-B 2  O 3  as a flux. The mixture was placed in a platinum crucible held in a vertical electric furnace and then melted and homogenized at about 1200° C. The melt was cooled to and kept at about 900° C. so that garnet became supersaturated. Into this melt was dipped the GGG substrate, which was rotated for a prescribed period of time for crystal growth. Finally, the substrate was raised from the melt and then spun rapidly to remove the excess melt by centrifugal force. Thus there was obtained the desired garnet thin film. 
     For comparison, the same procedure as above was repeated without the addition of tin. 
     The thus obtained garnet thin film was fabricated into the magnetostatic wave device as shown in FIG. 1. The device was measured for time required for saturation to take place (at 2 GHz). Also, the garnet film underwent chemical analysis to determine the content of tin. The results are shown in Table 4. 
     
                       TABLE 4______________________________________       Content of tin in                   Time required for       garnet thin film                   saturation to takeSample No.  (ppm by weight)                   place (ms)______________________________________ 1*           0         124 2*           5         1233            10         804            500        685           1000        616           1500        557           3000        48 8*         3100        **______________________________________ *Samples not conforming to the invention. **No satisfactory thin film was obtained. 
    
     According to the present invention, the content of tin in the garnet is specified as above because a content less than about 10 ppm (by weight) is not enough to affect the time required for saturation to take place (as in Sample No. 2 which is similar to Sample No. 1 (YIG film) containing no tin) and a content in excess of about 3000 ppm (by weight) prevents saturation itself (as in Sample No. 8), making the magnetostatic wave device inoperable. 
     EXAMPLE 5 
     A garnet thin film was formed by LPE on a GGG substrate (Gd 3  Ga 5  O 12 ) in the following manner. First, Fe 2  O 3 , Y 2  O 3 , Ga 2  O 3 , and La 2  O 3  as the raw materials of the garnet were mixed with SnO 2  as an additive and PbO-B 2  O 3  as a flux. The mixture was placed in a platinum crucible held in a vertical electric furnace and then melted and homogenized at about 1200° C. The melt was cooled to and kept at about 900° C. so that garnet became supersaturated. Into this melt was dipped the GGG substrate, which was rotated for a prescribed period of time for crystal growth. Finally, the substrate was raised from the melt and then spun rapidly to remove the excess melt by centrifugal force. Thus there was obtained the desired garnet thin film. 
     For comparison, the same procedure as above was repeated without the addition of tin. 
     The thus obtained garnet thin film was fabricated into the magnetostatic wave device as shown in FIG. 1. The device was measured for time required for saturation to take place (at 2 GHz). Also, the garnet film underwent chemical analysis to determine the content of tin. The results are shown in Table 5. 
     
                       TABLE 5______________________________________                Content of tin in                            Time requiredSample               garnet thin film                            for saturation toNo.   Composition    (ppm by weight)                            take place (ns)______________________________________ 9*   Y.sub.2.95 La.sub.0.05 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                  0         122 10*  Y.sub.2.95 La.sub.0.05 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                  5         12111    Y.sub.2.95 La.sub.0.05 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                 10         7812    Y.sub.2.95 La.sub.0.05 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                 500        7013    Y.sub.2.95 La.sub.0.05 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                1000        6014    Y.sub.2.95 La.sub.0.05 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                1500        5415    Y.sub.2.95 La.sub.0.05 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                3000        49 16*  Y.sub.2.95 La.sub.0.05 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                3100        **______________________________________ *Samples not conforming to the invention. **No satisfactory thin film was obtained. 
    
     According to the present invention, the content of tin in the garnet is specified as above because a content less than about 10 ppm (by weight) is not enough to affect the time required for saturation to take place (as in Sample No. 10 which is similar to Sample No. 9 containing no tin) and a content in excess of about 3000 ppm (by weight) prevents saturation itself (as in Sample No. 16), making the magnetostatic wave device inoperable. 
     EXAMPLE 6 
     A garnet thin film was formed by LPE on a GGG substrate (Gd 3  Ga 5  O 12 ) in the following manner. First, Fe 2  O 3 , Y 2  O 3 , Ga 2  O 3 , and Bi 2  O 3  as the raw materials of the garnet were mixed with SnO 2  as an additive and PbO-B 2  O 3  as a flux. The mixture was placed in a platinum crucible held in a vertical electric furnace and then melted and homogenized at about 1200° C. The melt was cooled to and kept at about 900° C. so that garnet became supersaturated. Into this melt was dipped the GGG substrate, which was rotated for a prescribed period of time for crystal growth. Finally, the substrate was raised from the melt and then spun rapidly to remove the excess melt by centrifugal force. Thus there was obtained the desired garnet thin film. 
     For comparison, the same procedure as above was repeated without the addition of tin. 
     The thus obtained garnet thin film was fabricated into the magnetostatic wave device as shown in FIG. 1. The device was measured for time required for saturation to take place (at 2 GHz). Also, the garnet film underwent chemical analysis to determine the content of tin. The results are shown in Table 6. 
     
                       TABLE 6______________________________________                Content of tin in                            Time required forSample               garnet thin film                            saturation to takeNo.   Composition    (ppm by weight)                            place (ns)______________________________________ 17*  Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                  0         125 18*  Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                  5         12219    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                 10         7920    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                 500        7021    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                1000        5622    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                1500        5023    Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                3000        46 24*  Y.sub.2.8 Bi.sub.0.2 Fe.sub.4.6 Ga.sub.0.4 O.sub.12                3100        **______________________________________ *Samples not conforming to the invention. **No satisfactory thin film was obtained. 
    
     According to the present invention, the content of tin in the garnet is specified as above because a content less than about 10 ppm (by weight) is not enough to affect the time required for saturation to take place (as in Sample No. 18 which is similar to Sample No. 17 containing no tin) and a content in excess of about 3000 ppm (by weight) prevents saturation itself (as in Sample No. 24), making the magnetostatic wave device inoperable.