JPH05129879A - Surface acoustic wave amplifier - Google Patents

Abstract

PURPOSE:To obtain the surface acoustic wave amplifier whose structure is simple to offer ease of manufacture in which a large gain is obtained. CONSTITUTION:The amplifier is roughly formed by a P-channel piezoelectric semiconductor substrate 2, a couple of interdigital electrodes 3,4 provided on the upper side of the substrate 2 and a power supply 12. A P-channel GaAs or a P-channel CdS or the like whose impurity concentration is 10<15>-10<16> particles/cm<3> is employed for the material of the P-channel piezoelectric semiconductor substrate 2. Let the mobile velocity of positive holes being the carrier be V(d) and propagation velocity of a surface acoustic wave 15 be V(s), then a high DC electric field is applied between interdigital electrodes 3,4 with the power supply 12 so as to satisfy the relation of V(d)>V(s) to amplify the surface acoustic wave 15. Since the impurity concentration of the P-channel piezoelectric semiconductor substrate 2 is high, the number of the carriers is increased more than that of a conventional amplifier and the amplified surface acoustic wave 15 is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave amplifier.

[0002]

2. Description of the Related Art It is known that a filter having an amplifying function can be obtained by applying an appropriate DC electric field to a surface acoustic wave filter made of a piezoelectric semiconductor material such as GaAs or CdS. A conventional piezoelectric semiconductor material is an n-type piezoelectric semiconductor having a low impurity concentration (for example, about 10 ¹⁴ pieces / cm ³ ), and an effective gain can be obtained only in a limited DC electric field, and the gain is 40 dB / cm. It was about the level (in the case of GaAs having an impurity concentration of 10 ¹⁴ / cm ³ ).

In addition to this, in order to obtain a high gain, a surface acoustic wave amplifier having a structure in which a piezoelectric body having a large electromechanical coupling coefficient and a semiconductor having a large carrier mobility are bonded together has also been proposed. However, this amplifier has a problem in that the structure and manufacturing process are complicated. Therefore,
The problem of the present invention is that the structure is simple and easy to manufacture, and
An object is to provide a surface acoustic wave amplifier that can obtain a large gain.

[0004]

In order to solve the above problems, a surface acoustic wave amplifier according to the present invention comprises (a) a P-type piezoelectric semiconductor substrate having a high impurity concentration, and (b) a surface of the piezoelectric semiconductor substrate. And a power source for applying a DC electric field between the interdigital transducers (c). As the P-type piezoelectric semiconductor having a high impurity concentration, P-type GaAs or P-type CdS having an impurity concentration of 10 ¹⁵ to 10 ¹⁶ pieces / cm ³ is used.

[0005]

In the above structure, when a DC electric field is applied between the interdigital electrodes by the power source, the DC electric field causes P
The holes, which are carriers of the piezoelectric semiconductor, move parallel to the propagation direction of the surface acoustic wave. The moving speed of this hole is V
(D) If the propagation velocity of the surface acoustic wave is V (s), if the strength of the DC electric field is increased so that the relationship of V (d)> V (s) is satisfied, the holes become surface acoustic waves. Combined with the accompanying electric field, the surface acoustic wave is amplified. Since the P-type piezoelectric semiconductor has a high impurity concentration, the number of carriers is larger than that of the conventional amplifier. Therefore, the amplification amount of the surface acoustic wave also increases.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the surface acoustic wave amplifier according to the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, the surface acoustic wave amplifier 1 includes a P-type piezoelectric semiconductor substrate 2, an input interdigital electrode 3, an output interdigital electrode 4, and a comb-shaped electrode provided on the upper surface of the P-type semiconductor substrate 1. Electrodes 3,4
It is composed of a power supply 12 for applying a DC electric field therebetween.
The material of the piezoelectric semiconductor substrate 2 has an impurity concentration of 10 ¹⁵
P-type GaAs of 10 / cm ³ and 10 ¹⁶ / cm ³ are used. The interdigital electrodes 3 and 4 have an electro-mechanical energy conversion function and also have an electrode function for applying a DC electric field to the piezoelectric semiconductor substrate 2 in parallel with the propagation direction of the surface acoustic wave 15. Aluminum or the like is used as a material for the interdigital electrodes 3, 4 and is formed by means such as a photoetching method. Electrode pitch d of the interdigital electrodes 3 and 4
Is designed to satisfy d = (n + 1/2) λ (n = 0,1,2,3 ...), where λ is the wavelength of the surface acoustic wave 15. Table 1 shows design values of the electrode pitch d of the interdigital electrodes 3 and 4 of this example. The average tolerance of the electrode pitch d required during manufacturing is about ± λ
/ 4.

[0007]

[Table 1]

The interdigital electrodes 3 and 4 are electrically connected to the input-side CR parallel circuit 5 and the output-side CR parallel circuit 6 by the extraction electrodes 3a, 3b, 4a and 4b, respectively. Further, the input side CR parallel circuit 5 is electrically connected to the AC pulse generator via the high frequency transformer 9. Output side C
The R parallel circuit 6 is electrically connected to the receiver via a high frequency transformer 10. Power supply 12 between input side and output side
Are electrically connected, and an appropriate DC electric field is applied between the interdigital electrodes 3 and 4.

The amplifying action of the surface acoustic wave amplifier 1 was evaluated using the apparatus having the above-mentioned structure. By applying a DC pulsed electric field of 10 KV / cm between the interdigital electrodes 3 and 4 by the power source 12, the moving speed V (d) of holes which are carriers of the P-type piezoelectric semiconductor substrate 2 is the propagation speed of the surface acoustic wave 15. V
(S) The state becomes larger than that. Under this condition, an electric signal is supplied from the AC pulse generator to the input interdigital transducer 3. The electric signal is converted into surface acoustic waves 15, and the surface acoustic waves 15 cover the surface portion of the piezoelectric substrate 2 with the interdigital transducer 4.
Propagate toward. The holes are coupled to the electric field associated with the surface acoustic wave 15, and the surface acoustic wave 15 is amplified. In particular,

[0010]

[Equation 1]

The maximum amplification gain is obtained at the angular frequency ω of the surface acoustic wave 15 which satisfies the relationship of Furthermore, in the conventional surface acoustic wave amplifier using the n-type piezoelectric semiconductor,

[0012]

[Equation 2]

A large gain cannot be obtained unless the relational expression of is satisfied. However, in the case of using the P-type piezoelectric semiconductor having a high impurity concentration as in this example, a large amplification gain was obtained without satisfying the expression (2). Table 2 shows the evaluation results. The surface acoustic wave 15 has a resonance angular frequency ω
It is amplified at (P). In addition, in Table 2, the electrode pitch d of the interdigital electrodes 3 and 4 produced based on the design values in Table 1 is shown.
The actual measurement value and the average error of are also shown.

[0014]

[Table 2]

As shown in Table 2, the gain of the conventional surface acoustic wave amplifier is about 40 dB / cm.
The surface acoustic wave amplifier has a gain of 100 to 300 dB / cm.
It is above, and it is recognized that it has remarkably improved.
The surface acoustic wave amplifier according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the gist thereof.

[0016]

As is clear from the above description, according to the present invention, since the P-type piezoelectric semiconductor having a high impurity concentration is used as the material of the piezoelectric semiconductor substrate, the P-type piezoelectric semiconductor is compared with the conventional surface acoustic wave amplifier. A surface acoustic wave amplifier having an increased number of carriers and an improved amplification function can be obtained. Moreover, in manufacturing, it is only necessary to adopt a P-type piezoelectric semiconductor having a high impurity concentration as the material of the piezoelectric semiconductor substrate, and the structure and manufacturing process are simpler than those of a surface acoustic wave amplifier in which a piezoelectric body and a semiconductor are bonded together. Will be things.

If the application direction of the DC electric field is reversed,
Surface acoustic waves can be attenuated and a switching function can be provided.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a surface acoustic wave amplifier according to the present invention.

[Explanation of symbols]

 1 ... Surface acoustic wave amplifier 2 ... P-type piezoelectric semiconductor 3, 4 ... Interdigital electrode 12 ... Power supply

Claims (1)

[Claims] 1. A P-type piezoelectric semiconductor substrate having a high impurity concentration, a pair of interdigital electrodes provided on the surface of the piezoelectric semiconductor substrate, and a power supply for applying a DC electric field between the interdigital electrodes. A surface acoustic wave amplifier characterized by: