JPS5824259A - Manufacture of surface acoustic wave correlator - Google Patents

Abstract

PURPOSE:To reduce the manufacturing cost of a surface acoustic wave correlator by using one kind of photomask, and manufacturing a surface acoustic wave correlator capable of respondence for an optional phase code signal. CONSTITUTION:On a piezoelectric substrate 1, the 1st reed screen type electrodes for generating (or receiving) a surface acoustic wave and electrodes 3 for a tap transducer for receiving (or generating) a surface acoustic wave are formed previously. Then, to obtain tap electrodes 11a, 11b-1Na, and 1Nb by encoding the polarity of the electrodes 3 according to a prescribed code, electric short circuits of the tape electrodes 11a, 11b-1Na, and 1Nb to pad electrodes 4 and 5 are disconnected at one-side points 21a, 21b-2Na, and 2Nb. Thus, one kind of photomask is used to manufacture a surface acoustic wave corellator.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a surface acoustic wave correlator used for generating or detecting phase encoded (PSK) signals.

BACKGROUND ART In recent years, as the demand for communications has increased significantly, efficient use of frequencies has been particularly sought after in the field of wireless communications. As a countermeasure against this problem, there is a spread spectrum communication system, and with recent advances in various parts, the above communication system is becoming a reality. As the name suggests, this spread spectrum communication system performs primary modulation to put information on a carrier wave, as well as secondary modulation to spread the frequency spectrum. Secondary modulation can be roughly divided into the die reflex) O sequence method and the frequency hopping method, but the most important issue in either method is how to detect such a signal. The former direct sequence method uses a two-phase phase encoded (P8K) signal, and a surface acoustic wave correlator is useful for detecting this signal.

Various forms of spread spectrum communication systems are possible, but if a fixed code is assigned to each communication device, signal detection using a surface acoustic wave correlator with a tapped delay line structure is efficient and effective. It has features that can be realized at low cost. In a typical configuration of a tapped delay line that uses surface acoustic waves, an input/output converter that mutually converts an electric signal and a surface acoustic wave is provided on a piezoelectric substrate, and one converter is a normal one. This is a tap converter in which several interdigital electrodes and tap electrodes with a relatively small number of logarithms are arranged side by side on the other hand. When an electrical impulse is applied to the interdigital electrode, a surface wave pulse corresponding to the pattern of the interdigital electrode is excited, which propagates through the substrate and is converted into an electrical signal again at each tap electrode. is encoded into a predetermined hood, so the overall output signal of the tap converter is a phase-encoded (P8K) signal. That is, such a device has the function of a phase-encoded signal generator. If a coded electrical signal conjugate to the code sequence of the tap electrode is applied to the interdigital transducer, a correlation signal can be obtained from the tap transducer.

That is, the above-mentioned device has a signal detection function in P8.

In a typical surface acoustic wave device, a desired pattern is created on a photomask and transferred onto a piezoelectric substrate using photolithography technology to create the required electrode pattern. However, in the case of surface acoustic wave correlators used in actual spread spectrum communications, there is very little need to manufacture a large number of correlators that have exactly the same pattern, that is, generate or detect exactly the same encoded signal. Therefore, the method of creating 7 otomasks for each encoded code and using these for transcription increases device cost and may not be used in an actual device.

An object of the present invention is to provide a method for manufacturing a surface acoustic wave correlator having an arbitrary tap coding sequence using the same 7# mask. 1. The manufacturing method of the present invention includes a first step in which a transducer-like electrode for generating (or receiving) a surface acoustic wave and a tap transducer electrode for receiving (or generating) the surface acoustic wave are formed in advance on a piezoelectric substrate. and a step of encoding the polarity of the tap converter electrode according to a predetermined code to form a tap electrode.

Next, the present invention will be explained with reference to the drawings. 1st
wi shows an embodiment of a method for manufacturing a surface acoustic wave correlator OIl according to the present invention. In the figure, 1 is a piezoelectric substrate, and on its front surface there are interdigital electrodes 2 that convert electrical signals into surface acoustic waves.
And a tap converter electrode 3 for converting surface acoustic waves into electrical signals is formed. These electrode patterns have extremely small line widths ranging from micrometers to several tens of micrometers, and are usually formed using photo-ring roughing technology. Since the production process is well known, detailed explanation will be omitted.
The outline is as follows. First, a thin metal film such as Muj or MuU, which is an electrode material, is formed on a piezoelectric substrate by vapor deposition or sputtering. The film thickness is determined depending on the operating frequency of the device and is usually in the range of several hundred to several thousand. Next, a photoresist film No. 7 is applied, dried, and then exposed using an exposure machine by overlapping it with a photomask having a desired pattern. Soak this in resist developer,
The resist streaks other than the resist film portion covering the metal material region to be left as an electrode pattern are removed.

Next, soak the electrode material in etching solution to remove unnecessary gold #. The membrane region is removed to obtain an electrode pattern as shown in FIG. At this stage, each electrode finger lla, llb, 12a constituting the tap converter 3.

12b, --tNa, INb are electrically short-circuited to both pad electrodes 4.5 of the tap converter.

In this current state, the tap transducer electrode naturally does not operate as a transducer. Therefore, one of the electrical short circuits of each tap converter electrode to the pad electrode is cut by some means. In the figure, hatchback parts 2ja, 21b, 22m
, 22b, = 2Nm.

2Nb indicates the cutting point. This is because the phase of each tap electrode is determined by the connection state to the pad electrode.

For example, if the phase of the tap electrodes 11a and llb is defined as "0", the connection of the tap electrodes 13m and 13b to the pad electrodes is opposite to that of lla and llb, so the phase is "π".
It is.

Although there are several possible ways to perform the above-mentioned cutting in order to give each tap electrode the necessary sign, cutting by a laser trimmer device is preferred. This method allows the light to be focused on an extremely small spot,
In addition to being applicable to fine electrode patterns operating in relatively high frequency ranges, predetermined electrode encoding can be achieved automatically by controlling the reamer device (combined).

In the above embodiment, the interdigital electrode 2 has the number of electrode pairs necessary to generate a signal at the length P8 of one chip (for example, if one chip contains waves of M wavelengths, M pairs of electrode fingers are required; In the illustrated example, there are three pairs of tap electrodes), while the spacing of the tap electrodes constituting the tab transducer is equal to the length of one chip. Therefore, in this embodiment, there is no freedom to adjust the length of the l chip appropriately.

FIG. 2 shows another embodiment according to the invention. In this example, when photoetching is completed, the piezoelectric substrate 1
Each electrode finger of the input/output converter 2.3 formed above is connected to both pad electrodes 6, 7, . and 4.
5 is electrically shorted. Next, by cutting the part indicated by hatching in this figure using an appropriate means,
The same operation as the interdigital electrode 2 shown in FIG. 1 can be performed. If the number of pairs of these electrodes is M, then the number of wavelengths included in one chip that can be realized with one interdigital electrode can be arbitrarily selected up to M. In the figure, the hatched portions indicate the locations to be cut when M=4 and the number of waves included in one chip is 3. That is, the short circuit is cut so that the three pairs of electrode fingers near the tap transducer 3 are connected alternately to both pad electrodes 6.7, and the remaining electrode fingers 8m, 8b are connected at both ends so that they do not operate as transducers. It is cut at the section. On the other hand, when the photo-etching of the tab converter is completed, all the electrode fingers arranged at half-wavelength intervals are short-circuited to both pad electrodes 4.5. Then, tap electrodes are selected at the same period as the length of the input transducer (M=3 wavelengths in the figure), and encoding is performed according to a certain predetermined code. In the figure, 11a, llb, 12m, 12b, 13a, IB
b.

--+, INa, and INb are tap electrodes. Remaining electrode fingers lie, lid, lie, llf.

It is necessary to prevent the fingers 12c, 12d, 12e, 12f, etc. from contributing to the conversion operation, and for that purpose, it is possible to cut off both ends of each finger, but experiments have shown that the pads on the grounded side It has been found that a more desirable structure is to connect it to the electrode (5 in the case of WJ). That is, with such a structure, the periodicity of the tap electrode becomes less visible to the surface acoustic waves incident on the tap converter, and therefore reflections caused by it are suppressed.

In the embodiments described above, the period of the electrode fingers is two per wavelength at the operating frequency, which is a so-called "single electrode" structure, but this was used to avoid complication of the explanatory diagram; In order to suppress second-order effects, particularly reflections caused by acoustic impedance mismatch, it is more desirable to use a so-called "double electrode" structure in which each single electrode is divided into two.

As explained above, according to the present manufacturing method, one type of 7
Since it is possible to provide a surface acoustic wave correlator that can respond to any phase-encoded (P8K) signal by using the Oshimaster, the effect of reducing the manufacturing cost F is extremely large.

[Brief explanation of the drawing]

FIGS. 1 and 2 show an embodiment of a method for manufacturing a surface acoustic wave correlator according to the present invention. 1 is a piezoelectric substrate, 2 is an interdigital electrode, 3 is a tap transducer, 11a, llb, 12
m, 12b, = -INa, INb are each tap electrode, and the hatching part is cut after the electrode butter 71 is formed.
Part “show...”
Jin 1, 4. )

Claims (1)

[Claims] Negative) A tenth interdigital electrode that generates (or receives) surface acoustic waves and a first tap transducer electrode that receives (or generates) the surface acoustic waves are formed in advance on the piezoelectric substrate. and a second step of encoding the polarity of the tap converter electrode according to a predetermined code to form a tap electrode.
A method for manufacturing a surface acoustic wave correlator, comprising the steps of: (2) The first step is a step of forming an electrode for a tap converter in which each tap electrode constituting the electrode is electrically short-circuited to both pad electrodes provided at both ends thereof. 2. The method of manufacturing a surface acoustic wave correlator according to claim 1, wherein the second step of encoding each tap electrode is a step of cutting the electrical short circuit.