EP1153478A2 - Substrate lamina made of langasite or langatate - Google Patents

Abstract

The invention relates to a substrate lamina made of langasite or langatate. Said lamina has a crystal cut (x1, x2, x3) for langasite in an area around the Euler angle combination (10 DEG , 140 DEG , 166 DEG ) or the Euler angle combinations equivalent thereto or special angle combinations of the langatate.

Description

description

Langasite or Langatat substrate plates

The invention relates to a substrate plate for, in particular, also frequency-stable surface waves (SAW) components, the substrate plate consisting of a single crystal of langasite or langatate and the surface of the substrate plate provided for the component being such a crystal cut with which this SAW component, based on this surface, has a high electromechanical coupling factor and low propagation speed for surface waves, and in particular also guarantees frequency stability of the SAW component that is independent of temperature changes.

Langasite and langatate are also used as crystal material such as quartz, lithium niobate, lithium tantalate and the like. used for surface wave devices as substrate platelets. Before surface wave components serve as (high-frequency) filters, delay lines, identification marks and sensors for various applications. For such a component, electrode structures of a predetermined type and design are applied to the at least one flat surface of the substrate plate. By means of transducer electrode structures, when the electrical signal is impressed, acoustic waves can be generated in the flat surface of the crystal which, depending on the prevailing boundary conditions, have respective wave forms, in particular are Rayleigh waves, shear waves or the like. Such a wave runs on the surface at a material-specific speed which is dependent on the crystal cut and which can also depend on the respective temperature of the crystal. If these electrode structures form an electroacoustic resonance system, the frequency stability of such a surface wave component is also temperature-dependent. For a particular crystal cut, the crystal material can have the property that the selected structure of the transducer system has a particular main wave propagation direction actually pivoted by a beam steering angle.

From Jpn. J.Appl. Phys. 37 (1998) 2909 and DE 195 32 602 Cl, are already known for certain applications as selected or selected crystal sections for SAW substrate platelets. In particular, the second-mentioned publication specifies the temperature property of individual crystal cuts of the langasite. These are crystal cuts which, particularly for temperature sensors, have a particularly high temperature dependence of the electrical component values. Special crystal cuts for filters and the like are described in WO 97/25776 AI with Euler angles λ = -15 ° to + 10 °, μ = 120 ° to 165 ° and θ = 20 ° to 45 °. For Langatat on IEEE Frequ. Control. Symp. (1998) 742.

The object of the invention is to find such crystal cuts for substrate platelets for surface acoustic wave components, regardless of already known crystal cuts for langasite and langatate, which have the greatest possible coupling factor, low propagation speed of the (selected) surface wave and as close as possible to zero have outgoing beam steering angles. If possible, this should be the case for all of these three properties in the crystal cut sought / found. In particular, surface wave components with these crystal sections should also be temperature-stable, preferably temperature-invariant, and have high frequency stability as resonance components. With a high coupling factor, a large filter bandwidth can be achieved. In particular, in the case of a crystal cut according to the invention, the propagation speed of a bulk wave in this material with a crystal cut according to the invention is to be significantly greater than the low propagation speed for the respective surface wave provided in the crystal cut or of the surface wave component. This object is achieved with crystal cuts with Euler angle combinations in accordance with the details of the claims. Further embodiments of the invention are the subject of dependent claims.

Langasite and langatate, roughly with the composition La ₃ Ga ₅ SiOi ₄ or La ₃ Ga5.5Tao, sOi ₄ , each form a trigonal crystal or have a crystal unit cell with trigonal symmetry with oblique x, y , z coordinate system with the angles 120 °, 90 °, 90 ° of these axes to each other. A right-angled coordinate system, here designated X, Y and Z, is assigned to this crystal coordinate system as the basis for recording and specifying the individual material sizes and their further use. The Z-axis are defined as coincident with the z-axis and the X-axis as coincident with the x-axis or in each case parallel to one another. Reference is also made to Standards on Piezoelectric Crystals (1949) and Nye, Physical Properties of Crystals, Oxford Science Publications, CLARENDON Press Oxford (1985), Appendix B, in particular pages 276 to 281.

There is a choice of the orientation with which a substrate plate with a specific surface is cut out of a langasite single crystal to achieve the above-mentioned object and which direction is provided on this specific surface for the excitation of a surface wave. To identify this crystal cut and this direction, the surface of the substrate plate is assigned its own right-angled axis system, here designated xl, x2 and x3. The clear relation of the right-angled crystal coordinate system X, Y, Z and this axis system Xi, x ₂ , x of the crystal section to one another is defined in a known manner by the respective specification of the Euler angles λ, μ and θ and can be clearly quantified. For a substrate wafer of a surface wave component or for the surface provided with the structures, the xl direction is defined as the main wave propagation direction determined by the transducer structure (with beam steering angle = 0).

The figures are also included for further explanation.

FIG. 1 shows a schematic representation of a piezoelectric surface wave component or its substrate plate.

Figure 2 shows the already rectangular coordinate system X, Y, Z of the crystal and the position of the Euler angles.

In FIG. 1, 10 denotes the langasite or langatate crystal plate of the surface wave component 1. A surface wave structure 12 is shown on the selected surface 11, which (simplified) comprises a transducer structure 112 and a reflector structure 212.

By means of the transducer structure 112, an acoustic wave 13 can be generated in the surface 11 in the case of an corresponding electrical signal, which (again at the beam steering angle = 0) proceeds in the main wave propagation direction indicated by the axis xl. By orthogo ^¬ nal the other axes are x and x ₃ oriented. This axis system x, x, x ₃ characterizes the crystal cut of the surface 11.

In Figure 2, the axes X, Y and Z of the crystal are shown in a perspective view. The axes xi to x _{3 of} the crystal section of the surface 11 of FIG. 1 are additionally entered in this crystal coordinate system. This orientation of the crystal cut axes to the crystal axes X, Y, Z is clearly described by the Euler angles λ, μ and θ. From the crystal coordinate system X, Y, Z, the three win- core rotations λ, μ and θ the orientation of the axis system xi, x ₂ , x. For this purpose, the plane of the axes X and Y is first rotated around the axis Z by the angle λ. This results in

Intermediate stage the axis system xi, x, x ₃ . Then the plane with the Z-axis and the x ₂ 'axis is rotated about the axis xi by the angle μ. This results in the axis arrangement xi '= xi ", x ₂ ", x ₃ "". With the third Euler angle θ, the plane with the axes xi "and x ₂ " is now rotated about the axis x ₃ " and this results in the axis system xi, x ₂ , x _{3 of} the crystal cut, ie the surface 11.

Crystal sections with the high coupling factor and low, little temperature-dependent propagation speed of the acoustic surface wave 13 and thus with high frequency stability of a Langasit component are defined by Euler angles in the respective range from λ = 10 ° to 14 °, μ = 130 ° to 150 ° and θ = greater than 160 ° to 175 °. Crystal cuts ones with relating to those fields Euler angles and all equivalent thereto crystallographically such combina- have very low linear temperature coefficients of the addition also low propagation velocity v of about 2680 m / s of the acoustic wave 13 and to rela ^¬ tively high electroacoustic coupling factor of about 0.45 to 0.5%. Low speed of the wave makes it possible to implement a surface wave component with a predetermined property even with a comparatively short substrate plate, and such a component has a higher achievable frequency bandwidth with a comparatively low insertion loss due to the higher coupling factor.

Added to this is the fact that the beam steering angle is particularly small for a component with Euler angles of the crystal section falling within the mentioned angle ranges. A particularly favorable choice of a combination of Euler angles for Langasit with regard to the task and the advantages achieved by the invention is that with (λ, μ, θ) = (10 °, 140 °, 166 °) with a tolerance range of ± 5 ° for the angle μ and θ. The angle λ is to be maintained as far as possible within the manufacturing accuracy of the crystal cut.

To this end, the crystallographically equivalent combinations are crystallographic and therefore their properties are equivalent to a combination (λ, μ, θ). This applies again with the tolerance range specified above. In order to take into account the crystallographic equivalents of combinations for Euler angles, the statement that a crystal section is defined by a certain combination is to be interpreted in such a way that this crystal section corresponds to the specified combination or one of these crystallographically equivalent combinations as defined below.

The above-mentioned angle combination (10 °, 140 °, 166 °) is (lo, itio, to), where 1, m and t stand for λ, μ and θ.

Crystallographic equivalents to lo, πio, to are:

(lo, mc t ₀ + 180 °) = (10 °, 140 °, 346 °)

(lo, m ₀ + 180 °, 180 ° - t ₀ ) = (10 °, 320 °, 14 °)

(lo, m ₀ + 180 °, 360 ° - t ₀ ) = (10 °, 320 °, 194 °)

(lo + 120 °, m ₀ , t ₀ ) = (130 °, 140 °, 166 °) (1 ₀ + 120 °, m ₀ , t ₀ + 180 °) = (130 °, 140 °, 346 °)

(lo + 120 °, m ₀ + 180 °, 180 ° - t ₀ ) = (130 °, 320 °, 14 °)

(lo + 120 °, m ₀ + 180 °, 360 ° - t ₀ ) = (130 °, 320 °, 194 °)

and corresponding other combinations as indicated below: (250 °, 140 °, 166 °) (110 °, 140 °, 14 °)

(250 °, 140 °, 346 °) (110 °, 140 °, 194 °)

(250 °, 320 °, 14 °) (110 °, 320 °, 166 °)

(250 °, 320 °, 194 °) (110 °, 320 °, 346 °)

(230 °, 140 °, 14 °) (350 °, 140 °, 14 °) (230 °, 140 °, 194 °) (350 °, 140 °, 194 °) (230 °, 320 °, 166 °) (350 °, 320 °, 166 °)

(230 '320 °, 346 °) (350 °, 320 °, 346 °)

(50 °, 220 °, 14 °) (70 °, 220 °, 166 °

(50 °, 220 °, 194 °) (70 °, 220 °, 346o

(50 °, 40 °, 166 °) (70 °, 40 °, 14 °)

(50 °, 40 °, 346 °) (70 °, 40 °, 194 °

(170 °, 220 °, 14 °) (190 °, 220 °, 166 °)

(170 °, 220 °, 194 °) (190 °, 220 °, 346 °)

(170 °, 40 °, 166 °) (190 °, 40 °, 14 °)

(170 °, 40 °, 346 °) (190 °, 40 °, 194 °)

(290 °, 220 °, 14 °) (310 °, 220 °, 166 °)

(290 °, 220 °, 194 °) (310 °, 220 °, 346 °)

(290 °, 40 °, 166 °) (310 °, 40 °, 14 °)

(290 °, 40 °, 346 °) (310 °, 40 °, 194 °)

The Langatat monocrystalline material for Substratplätt ^¬ surfaces for surface acoustic wave elements has for the solution dersel ^¬ object above ben other combinations of Euler angles which are given below. Langatat crystal sections with high coupling factor and particularly low

Propagation speed and at least almost zero beam steering angle (λo, μo ^ θo) are as follows:

(0 °, 80 ° to 110 °, 0 °) with tolerance range ± 5 ° for λ and θ, (0 °, 20 ° to 80 °, 32.5 ° ± 5 °)

(0 ° to 20 °, 130 ° to 150 °, 155 ° to 180 °) (30 °, 60 °, 0 °) with ± 5 ° angle tolerance each (10 ° ± 5 °, 35 ° ± 10 °, 26 ° ± 5 °) (20 ° ± 5 °, 30 ° to 70 °, 17 ° ± 5 °) and, for these combinations, the associated crystallographic equivalents, such as are defined above.

In particular, the combination (0 °, 90 °, 0 °) (with the associated tolerance range) is characterized by a particularly low propagation speed for surface waves with little more than 2200 m / s and a coupling factor of 0.54% for Langatat. This property can be used in particular to prevent the substrate wafer additionally occurring bulk waves influence on the property of the Oberflächenwel ^¬ len device, such as a resonator have. The combinations mentioned above on two ter and third place are characterized particularly by the fact that the frequency-nearest bulk wave is far away from the frequency of a surface acoustic wave and thus precisely these sections particularly ge ^¬ are suitable for surface-wave filter with a particularly large usable bandwidth. A particularly high coupling factor of even 0.7%, and this with a disappearing beam steering angle, has in particular a crystal cut with the combination (10 °, 140 °, 167.5 °) with a wave propagation speed of approx. 2540 m / s. The beam steering angle is not to be neglected for Langgate, because it is more than 9 ° for the angle combination (40 °, 40 °, 0 °), for example.

The only rotated cuts with the Euler angle λ = 0 ° are advantageous because these cuts are easier to make than other so-called double-rotated cuts.

However, some of the double-rotated cuts have particularly favorable properties for Langatat substrate platelets. The combination (30 °, 60 °, 0 °) is characterized by a negligible influence of the nearest volume wave. Their speed of propagation is more than 200 m / s different from that of a surface wave with the same coupling factor of about 0.52 °. A combination on within the combination (10 °, 25 ° to 45 °, 26 °), especially with μ = 30 °, with a high coupling factor of 0.53% has a surface wave propagation speed of only approx. 2320 m / s. With this combination, too, the large distance between the frequency of the next bulk wave ensures a high usable bandwidth as a surface wave component (compared to the combination (0 °, 90 °, 0 °)). A combination of the range (20 °, 30 ° to 70 °, 17 °), especially the combination (20 °, 60 °, 16 °), has a very low propagation speed of only 2300 m / s.

Claims

claims 1. Substrate platelets (10) made of langasite with a crystal cut (λ, μ, θ) with a high coupling factor and low surface wave propagation speed, to be used for an electronic surface wave component with an oriented (xi, x ₂ , x ₃ ) substrate - Surface (11) for the surface wave structure (12) with surface wave propagation provided in the direction _x , characterized in that this surface (11) by Euler angle λ in the range from 10 ° to 14 °, μ in the range from 130 ° up to 150 ° and θ in the range from 160 ° to 175 °. 2. The substrate plate according to claim 1, characterized in that the surface (11) by a combination (λ, μ, θ) = (10 °, 140 °, 166 °) with a respective tolerance range of the angles μ and θ of ± 5 ° is. 3. Langatat substrate plate (10) with a crystal cut (λ, μ, θ) with a high coupling factor and low surface wave propagation speed, to be used for an electronic surface wave component with an oriented (xi, x, x ₃ ) substrate surface (11) wound for the surface wave structure (12) with xi laid in the direction ^¬ surface wave propagation, characterized in that this surface (11) is defined as follows by a combination (λo, microhm _f θo) of Euler angles as: (0 ° ± 5 °, 80 ° to 110 °, 0 ° ± 5 °) (0 °, 20 ° to 80 °, 32.5 ° ± 5 °) (0 ° to 20 °, 130 ° to 150 °, 155 ° to 180 °) (30 ° ± 5 °, 60 ° ± 5 °, 0 ° ± 5 °) (10 ° ± 5 °, 25 ° to 45 °, 26 ° ± 5 °) (20 ° ± 5 °, 30 ° to 70 °, 17 ° + 5 °).