JPS62195907A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To improve the reliability and efficiency by providing a semiconductor layer including a hyper abrupt junction formed by an n(p) semiconductor and a p(n) semiconductor, a peizoelectric layer laminated on the semiconductor layer and >=2 electrodes formed on the piezoelectric layer. CONSTITUTION:The monolithic structure is provided, where the n(p) semiconductor layer 12, the p(n) semiconductor layer 14 and the piezoelectric layer 16 are arranged as layers in this order. Signal input and reference signal input interdigital electrode 20, 22 are arranged on the piezoelectric layer 16 in the lengthwise direction of the piezoelectric layer 16. The hyper abrupt junction 18 is formed between the semiconductor layers 12 and 14. A depletion layer capacitance (C) versus applied voltage (V) characteristic curve with a steep gradient is obtained from the junction 18, and since the depletion layer capacitance changes rapidly or remarkably when the applied electric field is changed slightly, the efficiency or sensitivity is improved. Since the monolithic structure is adopted, the high reliability is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a surface acoustic wave device, and particularly to a surface acoustic wave device that can be used in, for example, an acoustoelectric convolver, a parametric link oscillator, and the like.

(Prior Art) Surface acoustic wave elements are used in various ways, such as filters and oscillators, and one of their applications is, for example, spread spectrum (SS).
There is a surface acoustic wave (SAW) convolver used as a spreading demodulator in a 1Jll signal reception system. The sAw convolver uses, for example, an angular frequency ω generated by ink digital transducers (IDTs) on both ends of the substrate. Surface acoustic waves with wave numbers of , and - are propagated toward the center of the substrate and interact between the two transducers, and the wave number of O1 increases due to the nonlinear action of the piezoelectric material and semiconductor.
Angular frequency 2ω. This produces a weak electric field.

FIG. 6 is an illustrative view showing an example of a conventional elastic convolver which is the background of the present invention. The elastic convolver includes a signal input electrode 2 and a reference signal input electrode 3 arranged on a piezoelectric substrate 1, and the surface acoustic waves generated by these two input electrodes 2 and 3 are compressed by a beam width compressor 4 and output. A convolution signal is extracted from the output electrodes 5 and 6 by utilizing the nonlinear strain of the piezoelectric substrate 1 directly under the waveguide as the electrode 5.

FIG. 7 is an illustrative view showing an example of a conventional separation medium type convolver which is the background of the present invention. In the separation medium type convolver, a semiconductor 7 is placed above a piezoelectric substrate 1, which is a propagation medium for surface waves, with a slight air gap. An alternating current electric field leaks from the surface of the piezoelectric substrate 1 as the surface waves propagate from the two input electrodes 2 and 3, and the leaked alternating current electric field and the semiconductor 7
A convolution signal is extracted from the output electrodes 5 and 6 by interaction with carriers therein.

(Problems to be Solved by the Invention) In the elastic convolver shown in FIG. 6, the electric field generated by the weak nonlinearity of the piezoelectric substrate 1 is directly extracted by the metal electrodes 5 and 6 on the surface of the substrate, so the efficiency is very high. bad.

The separated medium type convolver shown in FIG. 7 utilizes the nonlinear effect of a semiconductor to extract an output signal from an electrode on the semiconductor, so its efficiency is high.

However, a minute air gear (
For example, on the order of 1,000 people, it is necessary to maintain uniformity, and manufacturing is not only difficult and expensive, but also susceptible to vibration and lacking in reliability.

Therefore, the main object of the present invention is to provide a reliable and efficient surface acoustic wave device.

(Means for Solving the Problems) Simply put, this invention consists of an n (p) type semiconductor and a p type semiconductor.
(n) type semiconductor, a piezoelectric layer laminated on the semiconductor layer, and a surface layer having two or more electrodes formed on the piezoelectric layer. It is an elastic wave element.

(Function) A steep depletion layer capacitance-voltage characteristic curve is obtained by the super-step junction, and even when a weak alternating current electric field is applied, the depletion layer capacitance changes greatly. The change is extracted as an output signal.

(Effects of the Invention) According to the present invention, since it has a monolithic structure, it is highly reliable and easy to manufacture. A wave element can be obtained.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Example) FIG. 1 is an illustrative cross-sectional view showing one embodiment of the present invention.

The surface acoustic wave device 10 includes an n (p) type semiconductor layer 12 .
It has a monolithic structure in which the p (n) type semiconductor layer 14 and the piezoelectric layer 16 are stacked in this order.

The n (p) type semiconductor layer 12 and the p (n) type semiconductor layer 14 are made of a semiconductor material such as Si, for example. Furthermore, the piezoelectric layer 16 is made of, for example, ZnO. On this piezoelectric layer 16 is an ink digital electrode 20 for signal input.
Ink digital electrodes 22 for inputting a reference signal are arranged at both ends of the piezoelectric layer 16 in the length direction (SAW propagation direction) at intervals. Note that these electrodes 20 and 2
2 may be provided on the semiconductor layer 12 side.

n (p) type semiconductor layer 12 and p (n) type semiconductor layer 14
A super-step junction as shown in FIG. 2 is formed between the two. In this super-step junction 18, a characteristic curve of depletion layer capacitance (C) vs. applied voltage (V) with a steep slope is obtained. Therefore, when the applied electric field changes slightly, the depletion layer capacitance increases rapidly or significantly. Changes to Therefore, a surface acoustic wave element with higher efficiency or sensitivity than a conventional elastic convolver can be obtained.

FIG. 3 is an illustrative cross-sectional view showing another embodiment of the present invention. In this embodiment, the n (p) type semiconductor layer 12 is n”
(p”) type semiconductor N12a and the n layered on top of it
(p) type semiconductor layer 12b.

Then, the n (p) type semiconductor layer 12b has p” (n
o) Type semiconductors N14' are stacked or bonded.

As for the semiconductor regions other than the depletion layer capacitance, if the specific resistance is large, the loss will be large, so in this embodiment, in order to increase the conductivity, the n(p) type semiconductor layer 1
2, an n''(p'') type semiconductor layer 12a is provided. Also, if it is necessary to attach a ground electrode, n (p
) type semiconductors, this results in Schottky contact, which is undesirable, so in order to make ohmic contact, this n” (p
”) type semiconductor layer 12a is effective.

In addition, if the impurity concentration near the bonding surface is high, it is difficult to obtain a good super-step bond, so in this example, n"(p"
) type semiconductor layer 12a.
As b, a super-step junction 18 is formed by growing an epitaxial layer and implanting or diffusing positive ions and negative ions into the epitaxial layer.

Also in this embodiment of FIG. 3, the n (p) type semiconductor 11
2b and the p"(n") type semiconductor layer 14', the superstep junction 18 shown in FIG. The degree of change in layer capacitance becomes very large.

FIG. 5 is an illustrative view showing an example of an acousto-electric convolver as a preferred embodiment of the present invention. This convolver 1
00 has the same monolithic structure as the surface acoustic wave device 10 shown in FIG.
, n (p) type semiconductor layer 112 b, p” (n
) type semiconductor layer 114 and piezoelectric layer 116 are laminated in this order. Then, the n (p) type semiconductor layer 112b
and the p″(n″) type semiconductor layer 114 form a superstep junction 118. On the piezoelectric layer N116, an ink digital electrode 120 for signal input and an ink digital electrode 122 for inputting a reference signal are arranged at intervals on both ends of the piezoelectric layer 116 in the length direction (SAW propagation direction). be done. Between these two ink digital electrodes 120 and 122, a gate electrode 124 is formed on the piezoelectric layer 116, and an n+(p+
A ground electrode 126 is formed on the lower surface of the ) type semiconductor layer 112a.

A bias voltage is applied to the gate electrode 124, and therefore a depletion layer capacitance is generated in the superstep junction 118.

When signals are input from the two input interdigital electrodes 120 and 122 in this state, the depletion layer capacitance changes due to the surface acoustic waves transmitted to ZnO as the piezoelectric layer 116. A voltage corresponding to this change in depletion layer capacitance is extracted from the gate electrode 122 through the coupling capacitor.

That is, excited from the input electrodes at both ends of the piezoelectric layer,
For example, the angular frequency ω. When surface acoustic waves with wave numbers of , and - pass each other on the piezoelectric layer directly under the gate electrode, the angular frequency is 2ω due to the nonlinear action of the piezoelectric layer. , a convolution signal with a wave number of 0 is generated, but this is a very weak electric field, so if it is extracted directly, the efficiency is very low. Therefore, a reverse bias is applied to the hyperstaircase junction to create a depletion layer.

An electric field of a convolution signal generated in the piezoelectric layer is applied thereto, and the change in depletion layer capacitance is extracted as an output signal from the gate electrode using the steep CV characteristic curve of the hyperstep junction.

Note that, as in this embodiment, Zn is used as the piezoelectric layer 116.
When O is used, a piezoelectric layer with a Sezawa wave or a Rayleigh wave with a large electromechanical coupling coefficient of 2 and a large nonlinear coupling coefficient can be realized, and therefore a wide bandwidth and a large T product can be obtained.

[Brief explanation of drawings]

FIG. 1 is an illustrative cross-sectional view showing one embodiment of the present invention. FIG. 2 is a diagram showing the impurity concentration distribution of the embodiment shown in FIG. FIG. 3 is an illustrative cross-sectional view showing another embodiment of the present invention. FIG. 4 is a diagram showing the impurity concentration distribution of the embodiment shown in FIG. FIG. 5 is a perspective view showing an example of an acoustoelectric convolver as a preferred embodiment of the present invention. FIG. 6 is an illustrative view showing an example of an elastic convolver which is the background of the present invention. FIG. 7 is an illustrative view showing an example of a separation medium type convolver which is the background of the present invention. In the figure, 10 is a surface acoustic wave element, 12 is an n (p) type semiconductor layer, 12a, 112a are n + (p''') type semiconductor regions, 12b, 112b are n (p) type semiconductor regions,
14 is a p (n) type semiconductor layer, 14', 114 are p'' (
n'') type semiconductor layer, 16.116 is a piezoelectric layer, 18,1
18 is a super step junction, 20, 22, 120, 122 are interdigital electrodes, 100 is an acoustoelectric convolver, 12
4 is a gate electrode, and 126 is a ground electrode. Patent applicant Murata Manufacturing Co., Ltd. Agent Patent attorney Yama 1) Yoshito (and 1 other person) Figure 1

Claims (1)

[Claims] 1. A semiconductor layer including a super-step junction formed by an n(p) type semiconductor and a p(n) type semiconductor, a piezoelectric layer laminated on the semiconductor layer, and the piezoelectric layer A surface acoustic wave device comprising at least two or more electrodes formed thereon. 2. The n(p) type semiconductor is stacked on the n^+(p^+) type semiconductor, and the p(n) type semiconductor is layered on the p^+(n^+) type semiconductor.
) type semiconductor, the surface acoustic wave device according to claim 1. 3. The surface acoustic wave device according to claim 2, wherein the n(p) type semiconductor and the p^+(n^+) type semiconductor include an epitaxial layer. 4. Claim 1, wherein the piezoelectric layer contains ZnO
The surface acoustic wave device according to any one of Items 1 to 3. 5. The electrode has a comb-shaped structure,
A surface acoustic wave device according to any one of claims 1 to 4. 6. According to any one of claims 1 to 5, wherein a gate electrode is formed on the piezoelectric layer between at least two of the electrodes, thereby forming an acoustoelectric convolver. The surface acoustic wave device described above.