DE3536704A1 - ACOUSTIC SURFACE WAVES TRAINING SURFACE WAVE COMPONENT - Google Patents

Description

Surface acoustic wave component forming surface acoustic waves

The invention relates to a surface acoustic wave forming surface acoustic wave component with a semiconductor substrate / a piezoelectric film formed thereon and at least two input / output transducers, which are arranged near the outer ends of its surface, and in particular a surface acoustic wave device, that as a variable surface acoustic wave band-pass filter / that of a plurality of surface acoustic wave filters having different frequency bands, serving as a surface acoustic wave delay line, etc.

A surface acoustic wave filter is widely used as a Intermediate frequency filters in television receivers and as filters in various types of message connection devices related. However, it is usually used as a fixed frequency band filter.

Fig. 7 of the accompanying drawing shows in a perspective View the general shape of a common surface acoustic wave filter with a piezoelectric substrate 1, comb-shaped Electrodes 2 ', which form an input transducer 2, and comb-shaped electrodes 3', which form an output transducer 3 form.

Since the frequency band of such a filter is determined by the shape and number of the comb-shaped electrode pairs it is a constant that is specific to the surface acoustic wave filter and cannot be changed. Variable frequency band filter however, are for communication links in which the frequency band changes with time, and at various types of multi-channel message interconnection devices are highly desirable.

8a shows a plan view of an example of a surface acoustic wave filter with a variable frequency band, in which the same components as in the filter shown in FIG. In the surface acoustic wave filter shown in FIG. 8A, a plurality of individual filters are formed on a substrate in such a way that the frequency bands of the individual filters are adjacent to one another _/ and one of the frequency bands is selected by switching the external circuit 4. Fig. 8B is a graph showing the relationship between the frequency and the output signal when the contact of the switch in the switching circuit is switched to A, B, C, D and E in Fig. 8A in succession.

In such a known filter, an external circuit 4 for switching is inevitable, which in terms of Manufacturing costs and the saving of space is problematic. This filter also has the disadvantage that the Free space for the shape of the band pass is very small, as this is only controlled by switching it on and off.

An acoustic surface-wave-forming surface acoustic wave delay line is also used to signal processing in radar devices, and as a delay line ^in: a surface acoustic wave oscillator. In particular, it is desirable to develop an apparatus in which the delay time can be varied, since such apparatus can be applied to a variable frequency oscillator and to a device for suppressing ghosting in a television receiver.

20 and 21 of the accompanying drawings show known devices as surface acoustic wave delay lines with variable delay are used and a piezoelectric substrate 1, comb-shaped electrodes 2 ', which form an input transducer 2, comb-shaped electrodes 3A, 3B ..., which form output transducers 3, a circuit 4 with a switching function, an input terminal 5 and a Have output connection 6.

FIG. 20 shows a so-called delay line with taps, the substrate area of which can be very small, but the has the disadvantage that due to the reflections of the surface acoustic waves at each tap (comb-shaped output electrodes 3A, 3B ...) mutual interference occurs between the various taps. In the case of the FIG The device shown is the mutual interference between the comb-shaped output electrodes 3A, 3B ... small, on the other hand, a large piezoelectric substrate 1 is necessary. Furthermore, for both institutions an external circuit 4 is required for switching, which is thus in terms of manufacturing costs and space savings is problematic.

The invention is intended in particular to produce surface acoustic waves forming surface wave delay line with variable delay time are created, which does not require an external circuit and as a surface acoustic wave component works that is free from the disadvantages of conventional components described above.

The invention is intended in particular to produce surface acoustic waves forming surface acoustic wave filter with variable frequency band can be created, which no circuit with a switching function, as shown in Fig. 8, and which ensures great freedom of use.

To achieve this, the present invention includes acoustic Surface acoustic wave component metal electrodes between the input and output transducers on a piezoelectric film, a device that puts bias voltages between each metal electrode and laying the semiconductor substrate, and means for controlling these bias voltages.

The part on which the metal electrodes are arranged has a structure in the form of a so-called monolithic MIS semiconductor. A surface acoustic wave propagating in such a structure changes significantly their propagation loss as a function of the bias voltages that exist between the metal electrodes and the Semiconductors are present. Fig. 9 shows an example of the relationship between the propagation loss and the bias voltage with the temperature as a parameter. As shown in Fig. 9, the propagation loss increases greatly in a given one Voltage range too. The area in which the acoustic surface wave is strongly attenuated corresponds to a voltage range, in which the surface of the semiconductor (interface between the piezoelectric substrate and the semiconductor body) is strongly inverted. Fig. 10 shows a comparison of the capacitance-voltage characteristic (curve b) with the Loss of propagation (curve a). It can be seen from Fig. 10 that the propagation loss greatly increases when the semiconductor surface is strongly inverted (area to the left of the dashed line).

By creating a strongly inverted area, generating a large bias voltage to the metal electrode, it is thus possible to reduce the surface acoustic wave in this Interrupt area. Since this also has the effect of a variable damping depending on the preload, if the applied bias is not so great, it is possible to have a band characteristic with greater freedom to achieve and to continuously change the propagation loss of the surface acoustic waves by the fact that the

bias voltage lying on each metal electrode is changed.

Particularly preferred exemplary embodiments of the invention are described in greater detail below with reference to the accompanying drawings described:

1 shows a perspective view of a surface acoustic wave filter which forms surface acoustic waves with a variable frequency band according to an embodiment of the invention.

Fig. 2 is a diagram showing the relationship between the output signal and the frequency.

3 shows a plan view of a surface acoustic wave forming surface acoustic wave filter according to a further embodiment of the invention,

4 show partial plan views of surface acoustic wave filters according to FIG three further embodiments of the invention.

Fig. 7 shows a perspective view of a known surface acoustic wave forming surface wave fliter with a fixed frequency band.

Fig. 8 shows a plan view of a known surface acoustic wave forming surface wave filter with variable frequency band and a diagram showing the relationship between the output signal and the frequency shows.

Fig. 9 is a graph showing the relationship between the propagation loss and the bias with temperature as a parameter.

Fig. 10 graphically shows the relationship between the bias and the propagation loss as well as the high frequency capacity.

11 shows a perspective view of a

Surface acoustic wave delay line forming surface acoustic waves with a variable delay time according to an embodiment of the invention.

Fig. 12 shows a plan view of a surface acoustic wave delay line with a variable delay time according to a further embodiment of the invention.

13 show partial plan views of surface waves bis 16 delay lines with variable delay times corresponding to four other different ones Embodiments of the invention.

17 show cross-sectional views from surfaces to 19 wave delay lines with variable delay time according to three further exemplary embodiments of the invention.

Fig. 20 show in plan views two known surface and 21 wave delay lines with variable delay time.

1 shows, in a perspective view, an example of a surface acoustic wave filter which forms surface acoustic waves with a variable frequency band as an embodiment of the surface acoustic wave component according to the invention, In Fig. 1, the same components as in Fig. 8 are the same

Provided with reference numerals. A semiconductor substrate 7 and a piezoelectric film 8 arranged thereon form a piezoelectric substrate 1. On the other outer surface of the semiconductor substrate 7 opposite the piezoelectric film 8, a rear side electrode 9 is arranged, which is grounded. At one end of the surface of the piezoelectric substrate 1 there are comb-shaped electrodes 2 ¹ , which form the input transducer 2, while at the other end, comb-shaped electrodes 3A, 3B, 3C and 3D, which form the output transducer 3, are designed so that each electrode is only responds to surface acoustic waves which lie in the corresponding one frequency band of the mutually different frequency bands. All of the comb-shaped output electrodes 3A, 3B, 3C, 3D are connected to the output terminal 6. Metal electrodes 10A, 10B, 10C and 10D are arranged between the comb-shaped input electrodes 2 'and the comb-shaped output electrodes 3A, 3B, 3C and 3D. For each filter, one of the bias voltages V,., Ν _{β /} V ^, V is between each metal electrode and the rear side electrode 9. The frequency band of the entire filter is changed by controlling each bias voltage. If the bias voltages V-, V ", V ^ and V_ applied to the metal electrodes 10A, 10B, 10C and 10D are changed, the propagation loss due to the interposition of each of the filters changes, so that the entire bandpass pass through a different combination of the Biases can be set differently.

Fig. 2 shows the change in the propagation loss due to the interposition of the filters in the frequency bands A, B, C and D as a function of frequency for different bias voltages. These biases can be set arbitrarily so that, for example, an output characteristic as shown by a solid line can be obtained is.

In the component shown in FIG. 1, the output transducer is 3 divided into a plurality of comb-shaped electrode pairs, so that the total output power as a sum the parallel output power is removed, but a structure is also possible as shown in Fig. 3 is shown.

On the rear side of the component shown in FIG. 3, a rear side electrode is arranged which is connected to ground, as is the case in the previous exemplary embodiment. ^{Bias voltages v} _A > ^v _B ' ^v r / ^V _D ^un ^ ^v w are applied to the metal electrodes 10A, 10B, 10C, 10D and 10E in the same way as in the previous exemplary embodiment. The only difference between the component shown in FIG. 3 and the component shown in FIG. 1 is that the output transducer 3 consists only of a pair of comb-shaped electrodes 3 ¹ , and that the distance between the teeth of the comb-shaped electrodes 3 'is continuously in a Direction perpendicular to the direction of propagation of the surface acoustic waves changes. Each electrode spacing corresponds to one of the frequency bands A, B, C, D, E, so that the component shown in FIG. 3 operates in the same way as the component shown in FIG. The advantage of this design is that the frequency bands can be subdivided more finely and fewer connections for leading the output power to the outside are required.

Further, when the metal electrodes 10 are formed so that they are arranged finer and closer to each other and when the pitch of the comb-shaped electrodes 3 ¹ changes continuously in a direction perpendicular to the direction of propagation of the surface acoustic waves, it is possible to arbitrarily set the bandpass filter by the distribution of the prestresses is chosen accordingly. The semiconductor substrate in the construction shown in Fig. 1, 3 and 4

elements has an insulating film / e.g. an oxide film / a nitride film, etc. obtained thereby is / that its surface is oxidized or nitrided.

The material of the metal electrodes can furthermore be the same as that of the comb-shaped electrodes, and at The metal electrodes can be manufactured using the same process (photolithographic process) as the comb-shaped electrodes are formed simultaneously with the comb-shaped electrodes.

Although the input transducer shown in Figs. 1, 3 and 4 consists only of a pair of comb-shaped electrodes which common to all filters, it can be selected from a multitude of filters of pairs of comb-shaped electrodes 2A, 2B, 2C and 2D with the same input characteristic, as shown in FIG Fig. 5 is shown.

The input transducer can further comprise a plurality of pairs of comb-shaped electrodes 2A, 2B, 2C and 2D different input characteristics exist. In this case, however, each pair of comb-shaped electrodes using separate matching circuits 11A, 11B, 11C, 11D can be adjusted.

It is also desirable to form one end face of the metal electrodes 10A, 10B ... so that they are with respect to the direction of propagation of the surface acoustic waves runs obliquely, since in this way influences from reflections of surface waves at the end face can be reduced.

11 shows a perspective view of an acoustic Surface wave delay line forming surface waves with a variable delay time according to an embodiment of the invention.

A semiconductor 7 and a piezoelectric film 8, the arranged thereon form a piezoelectric substrate 1. On the other, the piezoelectric film 8 opposite A rear-side electrode 9, which is connected to ground, is arranged on the outer surfaces of the semiconductor substrate 7. At one end of the surface of the piezoelectric substrate

1 comb-shaped electrodes 2 ¹ are arranged, which form the input transducer 2, and at the other end there are comb-shaped electrodes 3A, 3B, 3C, 3D, which form the output transducer 3. The distances between electrodes 3A, 3B, 3C and 3D and the comb-shaped input electrodes

2 are different, so that the time it takes for the surface acoustic waves output from the transducer 2 to reach the output transducers 3A, 3B, 3C, 3D is different. All electrodes 3A, 3B, 3C, 3D are connected to the output terminal 6. Metal electrodes 10A, 10B, 10C and 1OD are provided in the propagation paths of surface acoustic waves from the input transducer 2 to the electrodes 3A, 3B, 3C and 3D, respectively, and bias voltages V 1, V _β , V _ and V _D are applied to these metal electrodes, respectively. If, according to the operating principle described above, the bias ^{voltages V} A ' ^V B' ^V C ^V D are ^so f ^ tsel ^ t that the surface of the semiconductor substrate is strongly inverted, the surface acoustic waves that are in the areas under the metal electrodes 10A, 10B , 10C and 10D propagate, heavily attenuated. By defining the bias voltages such that the surface of the semiconductor substrate is in a depletion state or forms a barrier layer or is slightly inverted or is in a sufficiently charged state, it is also possible, in contrast, to reduce the attenuation of the surface acoustic waves to a sufficiently low level keep. By controlling the bias voltages ^V A ' ^V B' ^V C ^V D 'applied ^{to the metal electrodes} 10A, 10B, 10C and 10D, it is consequently possible to switch on and off the surface acoustic waves which the comb-shaped output electrodes 3A, 3B, 3C , Achieve 3D. Since it is still possible to continuously reduce the propagation loss of the surface acoustic waves by changing the preload

To change voltages V _A , V, V _c and V _D , the output signal level of each delay line can be appropriately controlled.

Since in this case it is possible for the The component according to the invention has to control surface acoustic waves merely by changing the bias voltages the advantage that the circuit provided for it, compared with that of a conventional known component can be simplified in which the switching of the surface acoustic waves by switching high-frequency signals is effected. Furthermore, since the semiconductor substrate is lower in cost and large-sized substrate in view are more readily available on the piezoelectric body, the substrate in the component according to the invention can be manufactured at a lower cost than the substrate used in known corresponding components will.

Although the component shown in FIG. 11 is the output transducer 3 is divided into a plurality of comb-shaped electrode pairs 3A, 3B, 3C, 3D and the final output signal removed in the form of the resulting output signal from a large number of circuits connected in parallel the structure shown in FIG. 12 is also possible.

In the component shown in FIG. 12, there is the output transducer a pair of comb-shaped electrodes 3 ', which are designed in the shape of a staircase in such a way that the distance between the input transducer and the comb-shaped output electrodes in the direction of propagation of the surface acoustic waves is discontinuous in the direction perpendicular changes to the direction of propagation of the surface acoustic waves. It should be understood that that shown in FIG

The device operates entirely in the same manner as the device shown in FIG.

The comb-shaped output electrodes 3 'can also do so be designed as shown in FIG.

In the components shown in FIGS are the comb-shaped electrodes 3 'of the output transducer 3 arranged so that the distance between the comb-shaped electrodes 2 'of the input transducer 2 and the comb-shaped Electrodes 3 'of the output transducer 3 are discontinuous or continuous in a direction perpendicular to the direction of propagation of surface acoustic waves changes. In this way it is possible to obtain the advantage that the delay time can be regulated more finely and fewer connections are required to pick up the output signal to the outside will.

The input transducer 2 may similarly be divided into a plurality of electrodes 2A, 2B, 2C and 2D, such as it is shown in FIG. However, only one pair of electrodes can be used 2 'be designed in the shape of a staircase, as shown in FIG. 15, or the electrodes can be inclined be arranged with respect to the propagation path of the surface acoustic waves, as shown in FIG.

Furthermore, it is desirable that the end faces of the metal electrodes 1OA, 10B ... run obliquely with respect to the direction of propagation of the surface acoustic waves, since in this Way influences of the reflection of surface acoustic waves at the end faces can be reduced.

The semiconductor substrate which is used for the formation according to the invention can be covered by an insulating film 11 such as an oxide film, a nitride film, etc.

which is formed by oxidizing or nitriding the substrate surface as shown in FIG is.

In the piezoelectric substrate shown in FIG 1, the propagation path of surface acoustic waves can be divided into two areas, one of where metal electrodes 10A, 10B, ... for controlling the propagation of the surface acoustic waves are arranged and in the other of which a metal film 12 on the Interface between the piezoelectric film 8 and the semiconductor substrate 7 or the insulating film 11 is provided. With such a structure, in the area where the metal film 12 is present, the potential is the acoustic Surface waves are shielded so that the semiconductor substrate and the surface acoustic waves do not mutually interfere disturb. This structure is particularly advantageous when a long delay time is required because the Attenuation of the surface acoustic waves is extremely low.

As shown in Fig. 19, it is also possible to use a different substrate structure in which the piezoelectric film in the area in which the comb-shaped Electrodes 2 "and the metal electrodes 10A, 10B, ... are present and is not provided in the propagation paths of surface acoustic waves therebetween. This Structure similar to the structure shown in Fig. 18 has an advantage when long delay times are required, since the surface acoustic waves propagate through the crystal semiconductor substrate 7 when the piezoelectric Film 8 is not present, so that the attenuation of the surface acoustic waves there is extremely small.

As described above, according to the invention, a space saving and a reduction in cost can be achieved the known surface acoustic wave filter can be achieved with a variable frequency band, since it is not necessary to switch elements

to be arranged separately for each of the individual filters for arbitrarily choosing an output signal. Since the invention Component a function equivalent to switching can be realized in that only the biases are switched on and off, the circuit itself is simplified. Since continues the propagation loss for each frequency band can be changed in an analogous manner by controlling the biases as a whole in an analogous manner a frequency band characteristic can be obtained with great freedom.

Surface acoustic wave filters producing surface acoustic waves according to the invention can be used in all types of devices in which surface acoustic wave filters to be used. However, they are particularly useful for messaging devices that have the Frequency band changes over time, such as in community antenna systems, communication satellites, relay, Radio and multichannel messaging devices are suitable.

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Claims (12)

7 (Patent Attorneys Dipl. ^ Iog. H. We: ickman ν -, - Dipl.-Phys. Dr. K. Fincke Dipl - In-g] RA ^ We-ickman-n, "Dipl.-Chem. B. Huber ^ Dr.-Ing.H. Liska, Dipl.-Phys. Dr. J. Prechtel 8000 MUNICH 86 1 5th OKf. 1S85 - ■ ■ ■ POST BOX 860 820 -rnn / MÖHLSTRASSE22 OD ö D / 1) 4 TELEPHONE ( 089) 98 03 52 TELEX 522621 TELEGRAM PATENTWEICKMANN MÜNCHEN P / ht. CO., LTD. 35-2, Hakusan 5-chome, Bunkyo-ku Tokyo / Japan Surface wave component forming acoustic surface waves PATENT CLAIMS ( 1. Surface acoustic wave component forming surface acoustic waves, characterized by a semiconductor substrate (7), a piezoelectric film (8) formed on the semiconductor substrate (7) is arranged, an input and an output transducer (2, 3), which at the two outer ends on the piezoelectric Film (8) are arranged a plurality of metal electrodes (10A, B, C, D) between the input and the Output transducers (2, 3) are arranged, means for applying bias voltages to each metal electrode (10A, B, C, D) and means for varying the bias voltages. 2. Component according to claim 1, characterized in that the input converter (2) has at least one pair of comb-shaped inputs comprises output electrodes (2 ¹ ) and the output transducer (3): comprises several pairs of comb-shaped output electrodes (3A, B, C, D) which are arranged so that each pair of electrodes corresponds to a metal electrode (10A, B, C, D) . 3. Component according to claim 1, characterized in that the input and output transducers (2, 3) each consist of a pair of comb-shaped electrodes (2 ¹ , 3 ¹ ), the comb-shaped electrodes (3 ¹ ) of the output transducer (3) are designed so that the electrode spacing dis- ~ continuously changes in a direction perpendicular to the direction of propagation of the surface acoustic wave. 4. The component according to claim 1, characterized in that the input and the output transducer (2, 3) each consists of a pair of comb-shaped electrodes (2 ¹ , 3 '), the Metal electrodes (10) are finely and densely arranged and the comb-shaped electrodes (3 ¹ ) of the output transducer (3) are designed so that the electrode spacing changes continuously in a direction perpendicular to the direction of propagation of the surface acoustic wave. 5. The component according to claim 1, characterized in that the input transducer (2) consists of a plurality of pairs of comb-shaped input electrodes (2A, B, C, D) with identical There is input characteristic, which are arranged so that each pair of electrodes is one of the metal electrodes (10A, B, C, D). 6. Component according to claim 1, characterized in that that the input transducer (2) from a plurality of pairs of comb-shaped input electrodes (2A, B, C, D) with different There is input characteristic arranged so that each pair of electrodes is one of the metal electrodes (10A, B, C, D) corresponds to, each pair of comb-shaped Input electrodes (2A, B, C, D) via a matching circuit (11A, B, C, D) is supplied with input signals. 7. The component according to claim 1, characterized in that the input transducer (2) has at least one pair of comb-shaped Comprises electrodes and the output transducer (3) from a plurality of pairs of comb-shaped output electrodes consists, which are arranged so that each pair of electrodes corresponds to one of the metal electrodes (10), wherein the propagation paths of the surface acoustic wave between the comb-shaped input and output electrodes are different from each other. 8. The component according to claim 1, characterized in that the input and output transducers (2, 3) each comprises at least one pair of comb-shaped input and output electrodes and the comb-shaped output electrodes are arranged so that the distance between the input and output electrodes is continuous or discontinuous changes in a direction perpendicular to the direction of propagation of the surface acoustic waves. 9. Component according to claim 1, characterized in that - that the end face of each metal electrode (10A, B, C, D) so is designed to be inclined with respect to the direction of propagation the surface acoustic wave runs. 10. Component according to claim 1, characterized in that that an insulating film (11) between the semiconductor substrate (7) and the piezoelectric film (8) is arranged. 11. Component according to claim 10, characterized in that that a metal film (12) between the metal electrodes (10A, B, C, D) and the output transducer (3) on the insulating film (11) is arranged. 12. Component according to claim 10, characterized in that that the piezoelectric film (8) in an area between the metal electrodes (10A, B, C, D) and the Output converter (3) is removed.