JP2001102489A - Optical semiconductor device - Google Patents

Abstract

(57) [PROBLEMS] To provide an optical semiconductor device having good characteristics by eliminating the influence of a sub-substrate when driving an optical semiconductor element disposed on a sub-substrate made of a semiconductor at high speed. A linear electrode for microwave transmission (41, 42, 81, 82) is formed on one main surface of each of a base substrate 8 made of a dielectric and a sub-substrate 1 made of a semiconductor.
The optical semiconductor element 2 is connected and arranged to a part of the linear electrode formed on the sub-substrate 1, and the base substrate 8 and the sub-substrate 1
Are joined so that the linear electrodes formed on both sides are connected to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an optical fiber communication system for a wide band of 2.5 GHz or more. For example, an optical semiconductor device driven by a high-speed logic (logic gate) is provided on a semiconductor substrate. The present invention relates to an optical semiconductor device comprising:

[0002]

2. Description of the Related Art In recent years, practical use of optical fiber communication has started in the field of CATV and public communication. 2. Description of the Related Art Hitherto, high-speed and highly reliable optical semiconductor modules have been realized in a package shape called a coaxial type or a butterfly type, and these have already been put to practical use mainly in a region called a trunk line system.

On the other hand, recently, a Si (silicon) sub-substrate (a sub-mount placed in a package,
On the other hand, optical modules using technology for positioning and mounting an optical semiconductor element and an optical fiber with high accuracy only by mechanical accuracy on the optical module have been actively developed.
These are intended to be put to practical use mainly in an area called an access system, and are required to be reduced in size, height, cost, and the like. On the other hand, with the explosive increase in data transmission traffic in recent years, increasing the bandwidth in access systems has become an important issue.

A typical example of a conventional optical semiconductor device will be described below.

[Conventional Example 1] For example, as shown in FIG. 5A, the active layer of the semiconductor laser
Located on the i-sub-substrate 1 side, the semiconductor laser element 2 is aligned at a predetermined position on the input electrode 41 on the active layer side, and is joined by solder such as Au-Sn alloy. Further, the electrode on the surface of the semiconductor laser element 2 located on the opposite side to the active layer and the electrode 42 are electrically connected via the wire 6. An optical fiber (not shown) has a V-shaped groove 10.
By being mounted above, mechanical optical alignment is performed with the previously mounted semiconductor laser device 2.

As shown in FIG. 5C, the Si sub-substrate 1 is placed in the recess 8a of the multilayer alumina base substrate 8, and the input electrode 81 and the electrode 82 on the multilayer alumina base substrate 8 Each of the input electrode 41 and the electrode 42 of the Si sub-substrate 1 is connected. In the figure, 11 is a stopper groove of the optical fiber, and 83 is a ground electrode.

[Conventional Example 2] A so-called microstrip line is formed by forming a ground electrode on the lower surface of the above-mentioned Si sub-substrate and a linear electrode on the upper surface, and a part of the microstrip line. A method has been proposed in which a thin film resistor is used for impedance matching with a load (optical semiconductor element) (for example, US Pat.
937,660).

According to this method, impedance matching is performed on the Si sub-substrate immediately adjacent to the load, and there is an advantage that the loss at high frequencies can be reduced as compared with the above-mentioned conventional example 1.

Generally, the impedance of an optical semiconductor device such as a semiconductor laser device is typically around 5Ω, which is lower than 50Ω or 25Ω used in a transmission line from a signal source to a load. Therefore, it is a general technique that impedance matching is performed between a signal source and a load by an appropriate combination of circuit components such as a microstrip line and a reactance element. For example, it is described in JP-A-10-75003.

[0010]

However, in the above conventional example 1, since the wiring on the sub-board has no ground electrode,
Hardly matches the impedance of the signal source. For this reason, the reflection becomes large at a high frequency at which microwaves are transmitted, and a phenomenon occurs such that a signal is not transmitted at a higher frequency or a specific frequency is not transmitted due to multiple reflections, thereby limiting the bandwidth of the microwave signal. You. That is, the limitation of the bandwidth affects the rising and falling sharpness of the signal pulse and the characteristics of overshoot and undershoot, and the speed of the signal pulse is greatly limited.

In addition, the large dielectric loss tangent of Si causes a large dielectric loss at high frequencies, which is a major factor in limiting the bandwidth. Here, FIG.
Further, as shown in the isoelectric field distribution, the region L where the electromagnetic field is strong in the above-mentioned conventional example 1 is affected by a high dielectric loss tangent over a wide range around the input electrode.

Further, the base substrate and the sub-substrate, including the portion where the optical semiconductor element is provided, are sealed by covering them with a resin. However, external noise enters and the noise current increases.

In the second conventional example, as in the first conventional example, there is a problem that the dielectric loss increases at high frequencies due to the high dielectric loss tangent of Si. That is, since most of the electromagnetic field is confined between the linear electrode on the upper surface of the Si sub-substrate and the ground electrode on the lower surface of the Si sub-substrate and microwaves propagate,
i is strongly affected by the dielectric loss tangent.

Further, it is necessary to form a through hole from the lower surface to the upper surface of the Si substrate. However, the mechanical strength of the substrate is weakened by the through hole. In particular, in the case of the Si substrate, cracks start from the through hole. Easy to enter and break. Further, it is necessary to perform a pattern forming process on both the upper and lower main surfaces, and there is a problem that the process is complicated.

The present invention has been proposed in view of the above-mentioned conventional problems, and eliminates the influence of the sub-substrate when driving an optical semiconductor device disposed on a sub-substrate made of a semiconductor at high speed. It is an object of the present invention to provide an optical semiconductor device having good characteristics.

[0016]

In order to achieve the above object, an optical semiconductor device according to the present invention is characterized in that a linear substrate for microwave transmission is formed on one main surface of each of a base substrate made of a dielectric and a sub-substrate made of a semiconductor. An electrode is formed, an optical semiconductor element is connected and arranged on a part of the linear electrode formed on the sub-substrate, and the base substrate and the sub-substrate are connected so that the linear electrodes formed on both are connected. It is characterized by being joined.

Further, the linear electrodes formed on the sub-substrate and the base substrate are formed stepwise so that the characteristic impedance becomes uniform in the traveling direction of the microwave. The conductivity of the sub-substrate is 0.1 S / cm or more.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an optical semiconductor device according to the present invention will be described below in detail with reference to the drawings. FIGS. 1A and 1B schematically show an example of an optical semiconductor device according to the present invention. FIG. 1A is an exploded perspective view, and FIG. 1B is a perspective view of a completed product. FIG. 2 is a schematic partial cross-sectional view of the optical semiconductor device M. FIG. 3 is an end view in FIG. 2 for explaining the width of a linear electrode for microwave transmission to be connected to the optical semiconductor element 2. FIG. 3A is an end view along line AA ′.
(B) is an end view taken along the line BB ', and (c) is an end view taken along the line CC'.

1 (a), 1 (b) and 2 show a sub-substrate 1 made of a semiconductor such as a single crystal of Si (having a resistivity of 10 kΩ · cm or less) and capable of anisotropic etching. Reference numeral 2 denotes a light emitting device (semiconductor laser) which is an optical semiconductor device for making light incident on an optical waveguide such as an optical fiber or an optical waveguide, and 10 denotes a V-groove for mounting an optical waveguide such as an optical fiber 3. , 41, and 42 are an input electrode and a terminal electrode (4, respectively) which are linear electrodes for microwave signal input.
If one of the electrodes 1 and 42 is an input electrode, the other is a terminal electrode. 5 (shown in FIG. 2) is a dielectric layer made of silicon oxide or the like. 6 is a bonding wire (lead wire).
Numeral 7 includes package leads 7, 8 a base substrate made of a ceramic such as alumina or the like and having a dielectric (resistivity greater than 10 kΩ · cm), 81 an input-side electrode, 8
2 is an output electrode, 83 is a ground electrode formed on the back side of the base substrate 8 shown by oblique lines, 84 is a conductor formed in a through hole connecting the output electrode 82 and the ground electrode 83, and 9 is hermetically sealed. Stop resin 11 is a dicing groove for a stopper of the optical waveguide.

As described above, the optical semiconductor device M has a linear electrode 41 for microwave transmission on one main surface of each of the base substrate 8 having a concave portion 74 made of a dielectric and the sub-substrate 1 made of a semiconductor. 42, 81, and 82 are formed. An optical semiconductor element (semiconductor laser 2) is connected to a part of the linear electrode 41 formed on the sub-substrate 1, and both the base substrate 8 and the sub-substrate 1 are connected. The semiconductor laser 2 is joined so that the linear electrodes formed on the semiconductor laser 2 are connected to each other and the semiconductor laser 2 is accommodated in the recess 74. Then, as shown in FIG. 2, the base substrate 8 is hermetically sealed with a sealing resin such as an epoxy resin so as to completely cover the sub-substrate 1.

Here, in particular, the sub-substrate 1 and the base substrate 8
Are formed stepwise so that the characteristic impedance becomes uniform in the traveling direction of the microwave, as described later. The conductivity of the sub-substrate 1 is 0.1
S / cm or more.

In this embodiment, for simplicity, the simplest example in which a light emitting element is provided on the sub-substrate 1 has been described. However, a monitoring light receiving element for controlling light emission of the light emitting element is provided near the light emitting element. May be provided, and
A plurality of optical waveguides may be provided, or a light receiving element for reception and an optical waveguide may be provided on any one of the front and back main surfaces of the sub-substrate 1. Further, the portion where the semiconductor laser 2 is provided on the sub-substrate 1 side is formed in a concave shape,
The sub-substrate 1 and the base substrate 8 may be joined.

In order to optically couple the semiconductor laser 2 to the optical waveguide mounted on the surface layer of the sub-substrate 1, its active layer side electrode is arranged on the sub-substrate 1 side and aligned at a predetermined position on the input electrode 41. And joined by solder such as Au-Sn alloy. The electrode on the back side of the active layer and the terminating electrode 42 are electrically connected by the wire 6. Also, the input electrode 41
The terminal electrode 81 is insulated from the sub-substrate 1 via the dielectric layer 5 (for example, a thermal oxide film having a thickness of about 1 μm). Since the optical waveguide is mounted on the V-groove 10, mechanical optical alignment with the previously mounted semiconductor laser 2 is performed with high precision.

The sub-substrate 1 is placed on the base substrate 8 with the electrode forming surface facing down. At this time, the input electrodes 41 and 81 and the terminal electrodes 42 and 82 are connected to each other via a thin solder layer (not shown) made of, for example, an Sn-Pb alloy or the like so as to be electrically connected. The thickness of this solder layer is, for example, one more than the electrode width at the intersection of the electrodes 41 and 81 and the electrodes 42 and 82 or the distance between these electrodes and the ground electrode 83.
By setting the ratio to / 10 or less, a step is prevented from occurring at the connection portion.

The input electrodes 41 and 81 and the termination electrodes 42 and 8
2. The ground electrode 83, the base substrate 8, and the air layer 12 constitute a microstrip line. In the microstrip line, the input electrodes 41 and 81 and the termination electrodes 42 and 82 are arranged in substantially the same plane parallel to the ground electrode 83, and the width of the electrodes is adjusted according to the relative permittivity and shape of the surrounding dielectric material. The characteristic impedance of the electric system is controlled to match 25Ω or 50Ω. At this time, the ground electrode 83 is on the rear surface of the base electrode 8 (the surface opposite to the surface on which the sub-substrate 1 is mounted).
Alternatively, it may be formed inside the base electrode 8.

A circuit component 13 such as a small chip resistor is used for a part of the microstrip line in order to perform impedance matching with a load. As a result, the terminal electrodes 42 and 13 and the ground electrode 83 are connected.

Thus, the microwave signal is transmitted to the electrodes 41,
The electromagnetic field is almost completely confined between 42 and the ground electrode 83, and can be distributed in the dielectric of the base substrate 8 and in the air layer 12. Therefore, the structure is not affected by the high dielectric loss tangent of Si, and has an effect of greatly reducing the dielectric loss as compared with the conventional configuration.

As shown in FIG. 3, the width W1 of the linear electrode
By setting W3 to, for example, W2 <W1 <W3, the characteristic impedance of the microstrip line can be made uniform up to the terminal end in the direction of microwave propagation, and the bandwidth can be expanded to, for example, about 40 GHz or more. Has the effect of doing

In the conventional structure shown in FIG. 6, when the base substrate and the sub-substrate are sealed with resin, the relationship between the conductivity of the sub-substrate, the transmission loss, and the noise current is as shown by a broken line in FIG. However, according to the present invention, the conductivity of the sub-substrate 1 is set to 0.1 to prevent the transmission loss of the microstrip line formed below the sub-substrate 1 from being affected.
When the substrate is a Si substrate having a resistivity of 1.0 to 1.0 S / cm (resistivity of 1 to 10 Ω · cm), the noise current can be suppressed extremely low (one digit or more), and the transmission loss is lower than before (2 dB / cm or less).
It turns out that you can. In this case, the high frequency was 4.5 GHz and the transmission distance was 1.5 mm to 3 mm.

This has the effect of attenuating electromagnetic waves entering from the outside and suppressing superimposition of noise that interferes with communication on the microstrip line.

[0031]

Next, more specific examples will be described.

First, a substrate having a thickness of 0.35 mm and a resistivity of 10 Ω · cm was used as the Si sub-substrate 1 in FIG. The outer shape of the Si sub-substrate 1 is 1.6 mm × 4.0 mm, and the length of the V groove 10 on which the optical fiber 3 is mounted is 3 mm.
And The base substrate 8 is made of KYOCERA A473 alumina (dielectric constant ε = 9.8) and has an outer shape of 10 mm × 6 mm,
The one having an 8-pin lead having a thickness of 0.5 mm and a pitch of 2.54 mm was used.

The microstrip line is wired on the Si sub-substrate 1 with a length of 0.65 mm from the mounting portion of the semiconductor laser 2 toward the outer periphery of the substrate, and further extended on the base substrate 8 with a length of 2.15 mm. I wired it. The microstrip line has a dielectric layer 5 made of silica having a thickness of 1 μm on the sub-substrate 1, and a dielectric layer 5 having a thickness of 4 μm thereon.
Width w1 = 250 μm, w2 = 235 μm, w3 = 255
μm Cr / Au (lower / upper) electrode layer 41,
42 and 3 μm thick and 250 μm wide M on the base substrate 8.
It was composed of o / Au electrode layers 81 and 82. The connection between the package lead 71 and the microstrip line is 200 μm.
The connection was made via a through-hole electrode formed on the base substrate 8 of φ.

Accordingly, the bandwidth of the transmission line from the input-side package lead to the end of the termination electrode 42 is set to 40 GHz.
And could be.

[0035]

As described above, according to the optical semiconductor device of the present invention, the following effects can be expected.

When transmitting microwaves on a sub-substrate made of a semiconductor, dielectric loss due to the sub-substrate can be suppressed as much as possible, and transmission loss at high frequencies can be drastically suppressed, so that the bandwidth is increased. A wide band optical semiconductor device can be provided. In addition, the wiring length on the sub-substrate can be increased.

When wiring is performed for a plurality of elements, the capacitance between the wirings can be reduced, and grounding to the base substrate can be easily performed.

Good matching of the electromagnetic field between the transmission line on the sub-substrate and the transmission line on the base substrate made of a dielectric material, which can also contribute to the expansion of the bandwidth.

A precise optical connection by a sub-substrate and a base substrate precisely formed by ceramic technology;
Good electrical connection by a base substrate made of a multilayer ceramic or the like can be combined, whereby an optical semiconductor device excellent in optical connection and high-frequency characteristics can be provided on one base substrate.

By using a common ground electrode on the base substrate, no ground electrode is required on the sub-substrate, which simplifies the process of forming the sub-substrate and simplifies assembly and mounting on the base substrate.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams schematically illustrating an example of an optical semiconductor device according to the present invention. FIG. 1A is an exploded perspective view showing an assembled state, and FIG. 1B is a perspective view of a completed product.

FIG. 2 is a partial cross-sectional view schematically illustrating an example of an optical semiconductor device according to the present invention.

FIG. 3 is an end view in FIG. 2, wherein (a) is AA ′
Line end view, (b) is BB 'line end view, (c) is C-
It is a C 'line end elevation.

FIG. 4 is a schematic diagram for explaining an electrode width of the optical semiconductor device according to the present invention.

FIG. 5 is a diagram showing the relationship between the conductivity of the present invention and a conventional substrate, transmission loss, and noise current.

6A and 6B are diagrams schematically illustrating a conventional optical semiconductor device, wherein FIG. 6A is a perspective view of a sub-substrate, FIG. 6B is a sectional view taken along line DD in FIG. 6A, and FIG. It is a perspective view of an apparatus.

[Explanation of symbols]

 1: Sub-substrate 2: Semiconductor laser (optical semiconductor element, light-emitting element) 3: Optical fiber 5: Dielectric layer 6: Wire 7: Package lead 8: Base substrate 9: Sealing resin 10: V groove 11: Dicing groove 12 : Air layer 13: Terminating resistor 41: Sub-board input electrode (linear electrode) 42: Sub-board terminating electrode (linear electrode) 71: Package lead input electrode 81: Base substrate input electrode (linear electrode) 82: terminal electrode of base substrate (linear electrode) 83: ground electrode M: optical semiconductor device

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryuji Yoneda 3-5-chome, Seika-cho, Soraku-gun, Kyoto Prefecture Inside the Central Research Laboratory, Kyocera Corporation (72) Inventor Yutaka Kuyoshi 3-chome, Seika-cho, Soraku-gun, Kyoto 5 Kyocera Corporation Central Research Laboratory F term (reference) 5F073 BA01 EA14 FA07 FA13 FA15 FA18 FA29

Claims (3)

[Claims] A linear electrode for microwave transmission is formed on one main surface of each of a base substrate made of a dielectric and a sub substrate made of a semiconductor, and a part of the linear electrode formed on the sub substrate An optical semiconductor device, wherein the base substrate and the sub-substrate are joined so that linear electrodes formed on both are connected to each other. 2. The method according to claim 1, wherein the linear electrodes formed on the sub-substrate and the base substrate are formed in a step shape so that a characteristic impedance becomes uniform in a traveling direction of the microwave. An optical semiconductor device according to item 1. 3. The optical semiconductor device according to claim 1, wherein the conductivity of the sub-substrate is 0.1 S / cm or more.