JPS5835403B2 - Surface acoustic wave parametric device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave parametric device that functions as a variable frequency selection device, in which a pump electrode is divided into a plurality of parts along the propagation direction of the surface acoustic wave, and each divided pump electrode has a The frequency customization of the variable frequency selection device can be designed as desired by varying the value of the DC bias voltage in the applied Paran l-IJ rack interaction region forming voltage in accordance with the desired output frequency customization. The present invention relates to a parametric device designed to obtain a parametric device.

As previously disclosed in Japanese Patent Application No. 52-107271, the present applicant has invented a bullet synchronization device having a variable frequency selection function as shown in FIG.

In FIG. 1, reference numeral 1 denotes a semiconductor substrate, and an insulating film 2 and a piezoelectric layer 3 are sequentially laminated on this semiconductor substrate 1.
Further, on the piezoelectric layer 3, a rectangular pump electrode 4 for applying a DC bias voltage and a pump voltage, and input/output transducers 5, 6 are provided, respectively.

7 is a DC power supply for applying DC bias, 8 is an inductor for blocking AC, 9 is a high frequency power supply for applying pump voltage,
10 is a DC blocking capacitor, and 11,
12 is a surface acoustic wave absorbing material for preventing unnecessary surface acoustic waves from being reflected at the end face.

Then, a DC bias voltage is applied to the pump electrode 4 from the DC power source 7 to generate an appropriate space charge layer capacitance on the surface of the semiconductor substrate 1 directly under the pump electrode 4, and then a high frequency power source 9 is applied to the pump electrode 4 to generate a suitable space charge layer capacitance. A pump voltage with twice the frequency of 2f is similarly applied to the pump electrode 4 to excite the space charge layer capacitance at the frequency of 2f, thereby changing the space charge layer capacitance at the frequency of 2f.

〇On the other hand, when an electrical signal is input to the input quadrature transducer 5 having a broadband property, this input electrical signal is converted into a surface wave signal and the surface of the piezoelectric layer 3 is transmitted to the input quadrature transducer 5 as shown in FIG. It propagates to the left and right.

Then, in the process in which the signal component near the frequency f of the surface acoustic wave input signal 13 propagating to the right propagates through the operating region below the pump electrode 4, its piezoelectric potential is transferred to the space charge layer on the surface of the semiconductor substrate 1. A parametric interaction occurs with the pump voltage due to the capacitive nonlinear effect, and the amplified surface acoustic wave signal 14 is converted back into an electric signal by the output transducer 6 and output to the outside.

At the same time, from the pump electrode 4 towards the left side of the figure,
The bullet has a frequency fi corresponding to the magnitude of the surface wave input signal 13.
A surface acoustic wave signal 15 of (fi = 2 fo - fs, fs: frequency of input signal) is generated.

This surface acoustic wave signal 15 can also be appropriately outputted to the outside as an output signal.

Here, the frequency characteristics P414a, 15a, 14b, 15b of each of the above output surface acoustic wave signals 14, 15 are input to the input signal 1.
Figures 2 and 3 show the size of 3 as 1,
FIG. 2 shows a case where the pump voltage is relatively small, and FIG. 3 shows a case where the pump voltage is relatively large.

As shown in both figures above, in a surface acoustic wave device equipped with a rectangular pump electrode 4, the desired center frequency f is selected.

When the output at is determined, the response of the signal passband and the spurious response are almost determined.

For this reason, when using conventional surface wave devices as frequency selection devices, there was extremely little freedom in designing custom frequencies, and the width of the spurious response was not small enough for practical use. .

Here, the present invention provides a surface acoustic wave parametric device that can match the response of a signal passband to specifications and reduce spurious responses to a level that does not cause any practical problems when used as a frequency selection device. That's what I tried to do.

That is, the present invention was made based on the following theory.

According to current electric circuit theory, the output frequency % of a linear circuit is obtained by Fourier transforming the time response (time change) of the output end when an impulse is applied to the input end.

Therefore, by conversely finding a time response that has a Fourier transform relationship with the desired frequency customization, and configuring a linear circuit so that this time response and impulse response are equal, an output signal having the desired frequency customization can be obtained. .

Here, the case where the above theory is applied to the conventional device shown in FIG. 1 will be described in more detail with reference to FIGS. 4A to 7B.

The bullet shown in Fig. 1 is created using a surface wave parametric device, with the parametric interaction set to not be very strong, and with the ideal duration O as shown in Fig. 4A in the input quadrangle juicer 5. Impulse e at time 1=0
Suppose you input it with

At this time, the two bullets output from the pump electrode 4 to the left and right take a time response ■1 with respect to the output signal 15 (frequency fi) which travels in the opposite direction to the input surface acoustic wave 13 among the surface wave signal outputs. The result shown in FIG. 4B is obtained.

Here, in FIG. 4B, time t1 is the time required for the surface acoustic wave signal to travel back and forth between the input quadrature transducer 5 and the front end 4' of the pump electrode 4, and time t2 is the time required for the surface acoustic wave signal to travel back and forth between the input quadrature transducer 5 and the front end 4' of the pump electrode 4. It shows the time required for the surface wave signal to travel back and forth between the inlet transducer 5 and the rear end 4 of the pump electrode 4.

To explain the input impulse e1 and the output time response 11 in more detail, an ideal impulse response includes infinite frequency components.

When this impulse e is input from the input quadrature transducer 5, only the 0 signal component near the frequency f (when the pump frequency is 2f) among the above infinite frequency components mainly undergoes parametric interaction. The input bullet is output as a backward surface acoustic wave signal 15 traveling in the opposite direction to the surface wave 13.

The envelope when the frequency component in this output signal is subjected to AM detection is the output time response 1 shown in FIG. 4B.

On the other hand, instead of impulse e, input quadrangle user 5
FIG. 5B shows the frequency spectrum 15c of the backward wave elastic table same-wave output signal 15 when a signal e having a constant amplitude and a frequency f as shown in FIG. 5A is applied.

Incidentally, the frequency spectrum 15c in FIG. 5B corresponds to the custom-made output frequency indicated by reference numeral 15a in FIG.

Here, the above frequency spectrum 15c corresponds to the Fourier transform of the above-mentioned time response (1). Therefore, if the frequency spectrum 15c shown in FIG. 5B is a custom-made desired frequency, then this The time response ■1 shown in Figure 4B has a Fourier transform relationship with
The linear circuit exhibiting this time response (1), ie, the surface acoustic wave parametric device, is the device equipped with the rectangular pump electrode 4 shown in FIG.

However, the above-mentioned ideal impulse e is actually unrealizable.

Therefore, instead of this, a carrier frequency f as shown in FIG. 6A is used.

, an RF pulse e' of duration f (t<1-1) is used.

2 1 1 At this time, the time response ■1' for the backward wave output signal 15 is the 6th
What is shown in FIG. 4B is obtained, and when this is subjected to AM detection, the envelope is almost the same as that shown in FIG. 4B.

Incidentally, the carrier frequency of the time response output signal 1' shown in FIG. 6B is fi=2fo-fo=fo.

Also, regarding the signal e with a constant amplitude in FIG. 5A, the actual signal e' has a middle 6th frequency f as shown in FIG. 7A.

There is a tendency for the amplitude to attenuate at frequencies far away from .

However, even when such a signal e' is inputted from the transducer 5, the frequency spectrum 15c' of the backward wave output signal shown in FIG. 7B is obtained.

This frequency spectrum 150' is almost the same as that shown in FIG. 5B above.

Therefore, design a custom-made surface acoustic wave parametric device with a desired frequency (design of the parametric IJ interaction region)
In this case, the signals shown in FIG. 6A and FIG. 7A are actually used as impulses and constant amplitude signals, respectively.

Next, the present invention based on the above-mentioned technical method will be specifically explained with reference to the embodiments shown in the drawings.

In the following drawings, the same reference numerals as above are given to the same members as in FIG. 1.

In FIG. 8, reference numeral 1 denotes a semiconductor substrate made of silicon (Si) material, as an example.
An insulating film 2 and a piezoelectric layer 3 are sequentially laminated thereon to form a laminate.

The insulating film 2 acts as a stabilizing film on the surface of the semiconductor substrate 1, and is made of, for example, a silicon dioxide film (S+02
).

Further, the piezoelectric layer 3 is formed of a piezoelectric material such as zinc oxide (ZnO) or aluminum nitride (AlN).

Next, an input juicer 5 and an output juicer 6 are respectively disposed near both left and right ends of the laminate in the figure.

The man-made output juicers 5 and 6 are formed to have a sufficiently wide and custom-made area.

A plurality of divided pump electrodes M12M2, . . . are disposed on the propagation path of the surface waves between the input and output fluid reducers 5 and 6.

The shape of these pump electrodes M12M2... is as follows:
As an example, it is formed into a rectangular shape, and its long sides are parallel to each other and arranged along the propagation direction of the surface acoustic wave.
etc., and each pump electrode M, , M2...
...The gap length between each pump electrode M12M
2. It is also selected to correspond to a desired frequency custom order in connection with the DC bias voltage value to be described later.

And each of the above pump electrodes Ml j M2...
, an AC blocking inductor L1. L2...
DC power supply E for applying DC bias separately through...
Connect 1E2゜E3...

This DC power supply E7. E2. E3...... is a semi-fixed variable power source, and each pump electrode M1゜M22M3...
... so that DC bias voltages of different values can be applied to each of them.

In addition, each pump electrode M12M2...... has a DC blocking capacitor C1, C2, C3...
A high frequency power source 9 for applying a common pump voltage is connected via.

Reference numerals 11 and 12 designate surface wave absorbing materials at the end faces for preventing unwanted surface waves from being reflected.

Incidentally, when applying DC bias voltages of different values to the pump electrodes M02M22M3, . . . , one DC power source E may be shared as shown in FIG. 9.

In this case, the DC power source E is connected to each pump electrode M1. M2
, M3... are connected to each other.

Each of the above voltage regulating means includes - for example, resistors R1 and R2,
It is constituted by a voltage dividing circuit each consisting of a combination of two resistors, such as R3 and R4, or R5 and R6, etc.

Further, when the voltage adjusting means consisting of a resistor circuit is provided as described above, it is arranged as shown in FIG. 10, as an example, so that the apparatus as a whole can be easily constructed.

That is, each resistor R1, R2, R3... is formed of a thin film resistor, and these thin film resistors are placed on the piezoelectric layer 3, that is, on the surface where each pump electrode M12M22M3... is disposed. Mixed accumulation on the same level.

In addition, in the case of Fig. 10, each of the DC blocking capacitors C1, C2, C3...
The dielectric thin film 17 and the upper electrode 18 are integrally integrated in the 12M22M3 portion.

Reference numerals 19 and 19' indicate membrane wiring layers. Next, based on the above-mentioned technical method, a procedure for setting the DC bias voltage value etc. to be applied to the IJ rack interaction area, that is, each pump electrode M12M2, etc. in Paragraph 7) will be explained.

Now let us assume that the desired frequency custom-made is an ideal bandpass filter with a bandwidth B as shown in FIG.

At this time, if we calculate the time response I2 that has a Fourier transform relationship with this frequency custom E2, we will get 5l as shown in Figure 12.
In the nx//x-shaped diagram, it extends infinitely to the left and right.

Here, the magnitude of the bullet surface wave output signal 5AW3 generated by the impulse e1 is related to the strength of the parametric interaction region, and one of the main factors determining the strength of this parametric interaction is the semiconductor surface space charge. There is a nonlinear magnitude of layer capacitance.

Furthermore, the magnitude of this nonlinearity varies significantly depending on the DC bias voltage applied to the pump electrode.

This is illustrated for an n-type semiconductor substrate in FIG. 14, which shows the bias voltage dependence ratio of capacitance C (FIG. 13) when looking at the device stack from the pump electrode, and further differentiates dC. /dV is a custom-made drawing.

When the parametric interaction is relatively weak, the square of the magnitude of dc/dV shown in FIG. 14 is approximately proportional to the impulse response.

That is, when looking only at the positive direction bias voltage in the same figure,
Increasing the bias voltage reduces the magnitude of the impulse response.

Therefore, in order to equalize the time response (2) and the impulse response, each pump electrode M1. M2゜M3...
The values of the DC bias voltages applied to . . . may be made different depending on the waveform of the time response (2).

However, in order to correspond to the ideal bandpass filter (Fig. 11), as in waveform 2 of Fig. 12, pump electrodes M12M2... groups are arranged infinitely in the left and right direction. , we must create a parametric interaction region up to this infinite position.

Therefore, the shape and dimensions of the laminate must be increased accordingly, which poses a practical problem.

For this reason, custom-made filters (custom-made frequency selection) must be designed to optimize the number of pump electrodes, DC bias voltage, etc. for application to the device, while making some sacrifices to the extent that there is no practical problem. Must be.

Therefore, a design example of the parametric interaction region, in other words, the number of pump electrodes, the DC bias voltage value applied thereto, etc., will be described below, taking practical considerations into account.

FIG. 15 shows the impulse response ■3 corresponding to the time response of the Sln\C type shown in FIG. 3, each pump electrode M12M22M3
. . . FIG. 16 shows the DC bias voltage values applied to each of them.

As shown in FIG. 8 above, E1, R2+ R
3...En are Ml, M2, M3 respectively
・・・・・・Indicates a DC power supply connected to the bottom.

The number M of pump electrodes is a finite number that can be arranged on the stack.

When the number of pump electrodes and the DC bias voltage values applied to them as shown in FIG. 16 above are applied to the device shown in FIG. The desired result can be obtained as shown in FIG.

When this custom-made frequency E3 is compared with the ideal bandpass filter E2 shown in Fig. 11, there is a deterioration in the shoulder characteristics of the filter, but when compared with that of the conventional example shown in Fig. 2, there is a spurious response. has decreased significantly to the extent that there is no problem in practical use.

Therefore, each pump electrode M1. shown in FIG. M2゜M
3...The manner of applying DC bias voltage to the pigeon is as follows:
It can be applied as a DC bias voltage application mode of a surface acoustic wave parametric device that generates 1'1EE3 at a desired frequency.

Next, Figures 18 and 19 show each pump electrode M12M2゜M.
This figure shows another design example of the DC bias voltage value to be applied to
The pump electrodes M1, M2, M3 and M3 are each in the form of a Gaussian function of 2π f, and the time response (4), which is in a Fourier transform relationship with this, is equal to the impulse response.
...This shows each DC bias voltage setting value applied to the pigeon.

In this case as well, when compared with the ideal bandpass filter custom-made E2, there is a slight deterioration in the shoulder characteristics of the filter, but the spurious response has been eliminated, and the pump electrode M12M2... The number etc. can be set within a practical range, and it can be applied as a DC bias voltage application mode of the surface acoustic wave parametric device shown in FIG.

The two design examples described above with reference to FIGS. 15 to 20 are both cases in which the pump voltage is reduced.

If the pump voltage is set to high and the Paran l-IJ rack interaction is large, the impulse response and each pump electrode M12M2
The setting mode of the DC bias voltage value applied to ...... will be slightly different from the case where the pump voltage is small.

However, if the effect of this deviation is taken into account, even when the pump voltage is set to 100%, it is possible to set the application mode of the DC bias voltage to obtain the desired frequency customization in almost the same way as in the design example above. be.

In addition, in all of the above design examples, the surface acoustic wave output is
Although we have described the case in which the backward wave output indicated by the reference numeral 5AW3 in the figure is extracted, the bullet 5AW2, which is an output wave in the same direction as the input surface acoustic wave 5AW1, can be designed in the same way for the case in which the surface wave is extracted. be.

However, with respect to the surface acoustic wave 5AW2, since signal components of frequencies that do not cause parametric interaction are output as they are without being changed, the effect of improving the spurious response is somewhat reduced.

A surface acoustic wave parametric device according to an embodiment of the present invention is constructed as described above and operates as follows.

First, each pump electrode M1. M2. M3...... and each DC power supply El t E2 j E3...
For example, each set voltage as shown in FIG. 16 is applied from . A distribution state of the layer capacitance is generated, and a pump voltage having a frequency 2fo which is twice the center frequency f in a desired frequency selection band is applied from the high frequency power source 9 to each pump electrode Ml 2M2 j M3... , the space charge layer capacitance is excited at a frequency of 2fo to change the space charge layer capacitance at a frequency of 2f.

〇On the other hand, the input electric signal applied to the broadband input quadrature transducer 5 is converted into a surface acoustic wave and propagates on the surface of the piezoelectric layer 3 toward the left and right of the input quadrature transducer 5 in FIG. do.

Of the surface acoustic wave input signal 5AW1 propagating to the right, the signal component near the frequency f is the pump electrode group Ml,
M2. M3...In the process of propagating through the lower parametric interaction region, the piezoelectric potential is amplified by parametric interaction with the pump voltage due to the space charge layer capacitance nonlinear effect on the surface of the semiconductor substrate 1, In the output bullet, a surface wave is generated from the pump electrode M portion to the left and right in FIG.

The input bullet travels in the same direction as the surface wave 5AW1, and the output bullet, the surface wave 5AW2, is converted back into an electrical signal by the output transducer 6 and output to the outside.

On the other hand, the output surface acoustic wave 5AW3 traveling in the opposite direction to the input surface acoustic wave 5AW1 can be generated by using the input quadrature transducer 5 or by using other appropriate means (for example, Japanese Patent Application No. 54-64923, etc. Similarly, the signal can be output as an electric signal to the outside using an output means equipped with a multi-strike IJ coupler as disclosed in .

If the surface acoustic wave 5AW3 traveling in the opposite direction is to be extracted as an output, at least only the input quadrature juicer 5 of the input quadrature juicer 5 and the output fluid juicer 6 is installed, and this is input/output. It can also be used as a dual-purpose transducer.

And as mentioned above, surface acoustic waves 5AW2 and 5AW3
In the process of outputting, the pump electrode of the IJ rack interaction area forming section is divided, and each divided pump electrode M02M22M3... is applied with each DC bias voltage corresponding to the desired custom frequency. is applied to the input bullet, only the signal component of the frequency corresponding to the desired frequency customization among the surface waves 5AW1 of the input bullet is selectively outputted as the surface waves 5AW2 or 5AW3.

That is, for example, the output surface acoustic wave 5AW3 in the opposite direction to the input surface acoustic wave 5AW1 is output as a signal having a custom desired frequency as shown in FIG. 17 or FIG. The wave parametric device functions as the desired bandpass filter.

In addition, the output bullet in the same direction as the input surface acoustic wave 5AW1 is the surface wave 5AW2. Although the above output bullet is inferior to the surface wave 5AW3 in terms of spurious response, it can be used as a signal with a desired frequency customization in the same way as above. Output.

As detailed above, according to the present invention, the pump electrode is divided into a plurality of parts along the propagation direction of the surface acoustic wave, and the value of the DC bias voltage applied to each pump electrode is adjusted to the desired value of the output surface acoustic wave. Since each surface acoustic wave parametric device is made to be different depending on the frequency customization, when the surface acoustic wave parametric device is used as a variable frequency selection device (bandpass filter), the output frequency can be designed as desired according to the specifications, which is an extremely excellent effect. Demonstrate.

In addition to the above-mentioned effects, the surface acoustic wave parametric device inherently has the following effects: it has custom variable tuning over a wide frequency range, and the stability of the output center frequency depends on the stability of the external pump power supply. and S
This bullet can combine various effects such as good /N, and can provide a surface wave parametric device which is extremely excellent when used as a variable frequency selection device.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing a conventional example, Figures 2 and 3 are custom-made views showing the same custom-made output frequency, Figure 2 shows a case where the pump voltage is relatively small, and Figure 3 shows a case where the pump voltage is relatively low. Figure 4A is a waveform diagram showing an ideal impulse used in the design of the parametric interaction area, and Figure 4B is a waveform diagram of the time response when the same impulse is applied to the device in Figure 1. A custom-made diagram showing an example. Figure 5A is a custom-made frequency diagram of an ideal input surface acoustic wave. Figure 5B is a backward wave surface acoustic wave output when the same input bullet is applied to the device shown in Figure 1. Figure 6A is a waveform diagram showing an example of a practical RF pulse in place of Figure 4A, and Figure 6B is a diagram showing the frequency spectrum of the same RF pulse as shown in Figure 1. A special diagram showing an example of the time response, Figure 7A is a custom-made frequency diagram of the input surface acoustic wave used in place of Figure 5A, and Figure 7B is the same as above. FIG. 8 is a custom-made diagram showing the frequency spectrum of the surface wave output when applied to a backward wave projectile. FIG. Therefore, FIG. 9 is a perspective view showing another example of the arrangement of the DC power supply in the same device as above, with some parts omitted, and FIG. FIG. 11 is an enlarged perspective view with some parts omitted, and FIG. 11 is a characteristic diagram showing the frequency characteristics of an ideal bandpass filter.
Figure 2 is a custom-made diagram showing the time response related to the above customization and Fourier transform, Figure 13 is a custom-made diagram showing the bias voltage dependence of capacitance when looking at the device stack from the pump electrode, and Figure 14 is the same as above. Figure 15 is a custom-made diagram that further differentiates the custom-made dC/d■.
Figure 16 is a percentage diagram showing an impulse response with waveform parts other than π removed; Figure 16 is a setting curve diagram showing an example of setting the DC bias voltage applied to each pump electrode corresponding to the same impulse response; Figure 17. 18 is a custom diagram showing an example of a custom output frequency when the same setting example as above is applied to Figure 8.
19 is a custom-made diagram showing another example of the impulse response applied to the present invention, FIG. 19 is a setting curve diagram showing an example of setting the DC bias voltage applied to each pump electrode corresponding to the above impulse response, and The figure is a characteristic diagram showing custom output frequency when the above setting example is applied to FIG. 8. 1: Semiconductor substrate, 2: Insulating film, 3: Piezoelectric layer, 5: Input quadrature reducer, 6: Output transducer, 9: High frequency power supply, 1L12: Surface acoustic wave absorber, 17: Dielectric thin film, 18 Second upper electrode, CCC...: Capacitor, E, El, R2...152 Fu3...: DC power supply, Ll, L2, L3...
・：Inductance, M02M22M3・・・・・・：
Pump electrode, R1I R2JR3...: Resistance.

Claims (1)

[Scope of Claims] 1. In a laminate including a semiconductor and a piezoelectric body, at least an input quadrature juicer and a plurality of pump electrodes are arranged on the piezoelectric body of the piezoelectric body. Furthermore, the value of the DC bias voltage in the parametric interaction region forming voltage applied to each pump electrode is made to be different for each output bullet in accordance with the desired frequency customization of the surface wave. Surface acoustic wave parametric device. 2. The surface wave parametric device according to claim 1, wherein each pump electrode is formed in a rectangular shape, and the long sides of the rectangular pump electrodes are arranged in parallel. 3 Claims 1 or 2 in which silicon is used as a semiconductor and zinc oxide is used as a piezoelectric material
Surface acoustic wave Paran I-IJ rack arrangement as described in section. 4. The surface acoustic wave parametric device according to claim 1 or 2, which uses silicon as the semiconductor and aluminum nitride as the piezoelectric material. 5. The bullet according to any one of claims 1 to 4, wherein a DC power supply is connected to each pump electrode separately when applying DC bias voltages of different values to each pump electrode. Surface wave parametric device. 6. In applying DC bias voltages of different values to each pump electrode, a common DC power source is used, and this common DC power source is applied to each of the pump electrodes through voltage adjustment means consisting of a resistor circuit. The bullet according to any one of claims 1 to 4 is a surface wave parametric device. 7. The surface acoustic wave parametric device according to claim 6, wherein the resistance in the resistance circuit is formed of a membrane resistor, and the membrane resistor is integrated on the same plane as each pump electrode arrangement surface.