JP2001196818A - Antenna integrated element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground electrode configuration capable of being produced by a simple process, easily entering light and being effectively operated as a ground surface in an antenna integrated element in which an optical signal is entered from the backside of a substrate. SOLUTION: A backside entering type photodetector 3 and a planar antenna 2 electrically connected to the photodector 3 are formed on the front surface of the substrate 1, and a reticulated ground electrode 5 is formed on the backside of the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna integrated element in which a back-illuminated light receiving element and a planar antenna are integrated.

[0002]

2. Description of the Related Art Wireless technologies for transmitting signals as electromagnetic waves are widely used in various fields such as communication and broadcasting.

In recent years, a so-called “optical microwave” technique of transmitting light modulated by a microwave signal through an optical fiber, performing optical-electrical conversion at a base station, and radiating the microwave as a microwave from an antenna has attracted attention. I have.

[0004] The importance of an "antenna integrated element" in which a light receiving element (optical-electrical conversion element) and an antenna are integrated, which are essential parts in constructing such a system, is increasing.

As a configuration example of an antenna integrated element, a combination of a back-illuminated photodiode as a light receiving element and a planar antenna is suitable for mass production by applying a widely established semiconductor process technology.

However, when a planar antenna is used, the space (usually air) is directly above the antenna (usually a metal film) formed on the substrate, and in principle, radio waves have a higher refractive index than air. It is more strongly radiated in the back direction.

In order to avoid this and effectively radiate radio waves toward the substrate surface, it is necessary to devise a structure such as providing a ground electrode on the back surface of the substrate and reflecting the radio waves toward the substrate surface.

FIG. 4A is a sectional view of an example of a conventional antenna integrated element, and FIG. 4B is a bottom view.

A light receiving element 13 such as a photodiode and a planar antenna 12 made of a metal film are formed on a surface of a substrate 11 made of a semiconductor or the like. On the other hand, a ground electrode 15 made of a metal film is formed on the back surface of the substrate 11. A hole 16 is formed in the ground electrode 15 so that signal light enters the light receiving element 13 (that is, in order to prevent light from being blocked).
Are formed.

[0010]

In the conventional antenna integrated device shown in FIG. 4, the center position of the hole 16 of the ground electrode 15 needs to be substantially coincident with the center position of the light receiving element 13. Therefore, in the process of forming the ground electrode 15, it is necessary to accurately position the light receiving element 13 formed on the surface of the substrate 11. This required special equipment and procedures, and had problems in cost and productivity.

Usually, a configuration is used in which the incident signal light is narrowed down to the size of the light receiving element 13 using a lens.
It is considerably wider than the size of 3. Therefore, the size of the hole 16 formed in the ground electrode 15 needs to be considerably larger than the size of the light receiving element 13. This is particularly serious when the thickness of the substrate 11 is increased. In an extreme case, the size of the hole 16 becomes substantially the same as the wavelength of the radio wave, and the hole 16 does not substantially function as a ground plane. There was also a problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art. In an antenna integrated device having a structure in which an optical signal is incident from the back surface of a substrate, the antenna can be manufactured by a simple process and light incidence is easy. Another object of the present invention is to provide an antenna integrated element having a ground electrode configuration that effectively functions as a ground plane.

[0013]

In order to solve the above-mentioned problems, an antenna integrated element according to the present invention is provided on a front surface of a substrate and is electrically connected to the back-illuminated light-receiving element and the light-receiving element. And at least a planar antenna, and a mesh-like ground electrode is formed on the back surface of the substrate.

With such a configuration, light can be easily incident,
In addition, it is possible to provide an antenna integrated element that can manufacture a ground electrode that effectively functions as a ground plane by using a simple process without using a special device.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings described below, those having the same functions are denoted by the same reference numerals, and the repeated description thereof will be omitted.

FIG. 1A is a sectional view of an embodiment of the present invention, and FIG. 1B is a bottom view.

A light receiving element 3 such as a photodiode and a planar antenna 2 made of a metal film or the like are formed on a surface of a substrate 1 made of a semiconductor or the like. As the photodiode, for example, a high-output photodiode described in JP-A-9-275224 is suitable. Note that the step of forming the wiring 4 can be omitted by using a part of the metal film constituting the planar antenna 2 as the wiring.

On the other hand, a ground electrode 5 made of a metal film or the like is formed on the back surface of the substrate 1. As the metal film, a two-layer structure composed of a low-resistance Au (upper layer) and a thin Ti film (lower layer) for improving adhesion to a substrate was used. The configuration of the metal film may use another metal species having low resistance as long as it does not affect the characteristics. This ground electrode 5 is processed into a mesh-like pattern as shown in FIG. If the size of the gap of this mesh pattern is approximately 1/10 or less of the wavelength of the radio wave used, it works as a complete ground plane. For example, when the effective refractive index of the substrate 1 is 3, the wavelength of a signal having a frequency of 10 GHz is about 1 cm.
The gap may be about 1 mm or less. On the other hand, with respect to the metal part constituting the ground electrode 5, it is necessary that each part is continuously connected, but regarding the width thereof,
For example, if a low-resistance metal such as gold is used, the thickness can be reduced to about 1 μm. Therefore, the area ratio between the portion covered with the metal and the portion not covered with the metal can be approximately 1: 500. That is, the substrate 1
Even if the ground electrode 5 is present, only about 0.2% of the incident signal light from the rear surface of 1 is blocked, so that the reduction in efficiency can be substantially ignored. In other words, it is possible to configure the ground electrode 5 which functions almost completely as a ground plane and has no problem in light transmittance. Since the light transmittance of the ground electrode 5 is the same in any part of the ground electrode 5, the light receiving element 3 formed on the surface of the substrate 1
There is no need to consider the relative positional relationship between the substrate and the mesh-like ground electrode 5 formed on the back surface of the substrate 1. In other words, the formation of the ground electrode 5 on the back surface of the substrate 1 does not require positioning with respect to the light receiving element 3 formed on the front surface of the substrate 1, so that there is no need to use a special device. What is necessary is just to form simply by the lift-off method using. If a slight decrease in efficiency due to the blocking of the incident light is not a problem, the width of the gap between the ground electrodes 5 is reduced or the width of the ground electrode 5 is increased, so that the exposure accuracy becomes further unnecessary. And the yield is improved. For example, the gap width of the mesh-like ground electrode 5 is set to 20
Even when the width is narrowed to 0 μm and the electrode width is widened to 3 μm, the ratio of blocking incident light is at most about 3%, and does not cause any substantial problem. As described above, the dimensions of the gap may be appropriately designed according to the frequency of the radio wave to be used.

FIGS. 2 and 3 show another example of the pattern of the ground electrode 5, respectively.

FIG. 2 uses a hexagonal repetition, and FIG. 3 uses a combination of an octagon and a quadrangle.

Even when these patterns are used, the same effects as those of the above embodiment can be obtained. Further, it goes without saying that other combinations of various shape patterns can be used.

Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and it is needless to say that various modifications can be made without departing from the gist of the present invention. It is.

For example, in the above-described embodiment, an example has been described in which a photodiode is used as a light receiving element. However, another light receiving element such as a phototransistor may be used.
Further, the light receiving element 3 may be one that is epitaxially grown on the substrate 1 or one that is hybrid-formed.

The substrate 1 is made of InP, GaAs
Various semiconductor substrates such as s, Si, and Ge can be used, and insulating substrates such as sapphire and ceramics can be used.

As a film constituting the planar antenna 2, a conductive film such as graphite may be used in addition to the metal film.

[0026]

As described above, according to the antenna integrated device of the present invention, the antenna can be manufactured by a simpler process than the conventional one, light can be easily incident, and the ground can effectively work as a ground plane. An antenna integrated element having electrodes can be realized.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view of an antenna integrated device according to an embodiment of the present invention, and FIG. 1B is a bottom view.

FIG. 2 is a diagram showing another example of the ground electrode pattern of the present invention.

FIG. 3 is a diagram showing still another example of the ground electrode pattern of the present invention.

FIG. 4A is a cross-sectional view of an example of a conventional antenna integrated element, and FIG. 4B is a bottom view.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Planar antenna, 3 ... Light receiving element, 4 ... Wiring, 5 ... Ground electrode, 11 ... Substrate, 12 Planar antenna, 1
3: light receiving element, 14: wiring, 15: ground electrode.

Claims (1)

[Claims] 1. A backlit type light receiving element formed on a surface of a substrate and a planar antenna electrically connected to the light receiving element, and a mesh-like pattern is formed on the backside of the substrate. An antenna integrated element, wherein a ground electrode is formed.