Optical module

Abstract

This optical module is provided with: an optical junction part; a sub-carrier and an optical semiconductor chip that are bonded to one surface of the optical junction part; and an light wave circuit that is bonded to the other surface of the optical junction part. A gap is provided between the sub-carrier and the optical semiconductor chip, and the optical semiconductor chip is in contact with the sub-carrier via a block electrode disposed on the upper surface of the optical semiconductor chip and along the light input / output surface of the optical semiconductor chip, and p-type electrodes and n-type electrodes sandwiching the block electrode and positioned on the opposite side of the light input / output surface.

Description

Optical Module

[0001] The present disclosure relates to optical modules.

[0002] Non-Patent Document 1 discloses a distributed feedback (DFB) laser chip with both p-type and n-type electrodes on its top surface. The chip is flip-chip mounted on a subcarrier, and an underfill agent is poured into the gap between the subcarrier and the chip to secure the chip, forming an optical module. The underfill agent prevents breakage of the electrode junction due to stress caused by the difference in thermal expansion coefficient between the chip and the subcarrier.

[0003] A. Marinins et. al., “Wafer-Scale Hybrid Integration of InP DFB Lasers on Si Photonics by Flip-Chip Bonding With sub-300 nm Alignment Precision,” J of Sel. In Quantum Electronics, vol. 29, no. 3, 8200311.

[0004] According to the optical module described in Non-Patent Document 1, it is necessary to pour an underfill agent into the gap for stress relief, etc. However, there are problems such as degradation of the high-frequency characteristics of the optical module due to loss of high-frequency signals caused by dielectric loss of the underfill agent, and shifting of the laser oscillation wavelength due to stress from the underfill agent.

[0005] The present disclosure has been made in view of the above-mentioned problems, and has an object to provide an optical module that has excellent high-frequency characteristics and wavelength stability without using an underfill agent.

[0006] In order to solve the above-mentioned problems, an optical module according to one aspect of the present disclosure includes an optical junction, a subcarrier and an optical semiconductor chip bonded to one side of the optical junction, and a lightwave circuit bonded to the other side of the optical junction. A gap is provided between the subcarrier and the optical semiconductor chip, and the optical semiconductor chip is in contact with the subcarrier via a block electrode arranged on the top surface of the optical semiconductor chip along the optical input / output surface of the optical semiconductor chip, and a p-type electrode and an n-type electrode located on the opposite side of the block electrode from the optical input / output surface.

[0007] According to the present disclosure, an optical module having excellent high frequency characteristics and wavelength stability can be provided without using an underfill agent.

[0008] Fig. 1 is a top view of an optical module according to a first embodiment of the present disclosure. Fig. 2 is a side view of the optical module according to the first embodiment of the present disclosure. Fig. 3 is a top view of an optical semiconductor chip included in the optical module according to the first embodiment of the present disclosure. Fig. 4 is a cross-sectional view of the optical semiconductor chip of Fig. 3 taken along line A-A. Fig. 5 is a top view of an optical semiconductor chip included in an optical module according to a second embodiment of the present disclosure.

[0009] Next, embodiments of the present disclosure will be described in detail with reference to the drawings. In the description, the same components are designated by the same reference numerals and redundant description will be omitted.

[0010] [Description of First Embodiment] Fig. 1 is a top view of an optical module according to a first embodiment of the present disclosure. Fig. 2 is a side view of the optical module according to the first embodiment of the present disclosure. The optical module includes an optical semiconductor chip 10, a subcarrier 20, an optical junction 30, and a lightwave circuit 40.

[0011] The optical semiconductor chip 10 is at least one of a directly modulated DFB laser chip and an electroabsorption optical modulator integrated laser chip. For example, the optical semiconductor chip 10 is a chip fabricated on an indium phosphide (InP) substrate. Light output from the optical semiconductor chip 10 (output light R1) is introduced into an optical waveguide in the lightwave circuit 40. The optical semiconductor chip 10 is not limited to the examples given here.

[0012] The subcarrier 20 incorporates wiring for supplying power to the optical semiconductor chip 10 or wiring for transmitting signals from the optical semiconductor chip 10. For example, the subcarrier 20 has an aluminum nitride substrate and a gold wiring pattern. The subcarrier 20 is not limited to the example given here.

[0013] The optical joint 30 is made of, for example, an insulating adhesive, and fixes the optical semiconductor chip 10 and the subcarrier 20 to the lightwave circuit 40.

[0014] 1 and 2, the optical semiconductor chip 10 and the subcarrier 20 are bonded to one surface of the optical junction 30. The lightwave circuit 40 is bonded to the other surface of the optical junction 30. The relative positions of the optical semiconductor chip 10 and the lightwave circuit 40 are set so that light (e.g., output light R1) output from the optical waveguide WG of the optical semiconductor chip 10 is introduced into the optical waveguide in the lightwave circuit 40. The optical waveguide WG has a core portion CR, and both side surfaces of the core portion CR may be filled with a semi-insulating semiconductor.

[0015] 2, a gap is provided between the optical semiconductor chip 10 and the subcarrier 20. A block electrode EB, p-type electrodes EP1 and EP2, and n-type electrodes EN1 and EN2 are provided between the optical semiconductor chip 10 and the subcarrier 20, and the optical semiconductor chip 10 is in contact with the subcarrier 20 via these electrodes.

[0016] The block electrode EB, p-type electrodes EP1 and EP2, and n-type electrodes EN1 and EN2 are electrically connected to wiring built into the subcarrier 20 via electrode junctions. Here, the electrode junctions are made of at least one of solder, a conductive adhesive, and a metal.

[0017] For example, a conductive adhesive is applied to these electrodes of the optical semiconductor chip 10, and the optical semiconductor chip 10 is flip-chip mounted on the subcarrier 20. The block electrode EB, p-type electrodes EP1, EP2, and n-type electrodes EN1, EN2 are electrically connected to wiring built into the subcarrier 20. In addition to the conductive adhesive, electrical connection may also be achieved using solder, metal, or ultrasonic bonding.

[0018] Alternatively, the thermal expansion coefficient of the subcarrier 20 may be equal to that of the optical semiconductor chip 10. This prevents breakage of the electrode junction due to stress caused by the difference in thermal expansion coefficient between the optical semiconductor chip 10 and the subcarrier 20.

[0019] Fig. 3 is a top view of an optical semiconductor chip included in the optical module according to the first embodiment of the present disclosure. Fig. 4 is a cross-sectional view of the optical semiconductor chip taken along line A-A in Fig. 3. A block electrode EB, p-type electrodes EP1 and EP2, and n-type electrodes EN1 and EN2 are arranged on the top surface of the optical semiconductor chip 10.

[0020] The block electrodes EB are arranged along the light input / output surface of the optical semiconductor chip 10. In particular, the block electrodes EB are arranged parallel to the light input / output surface of the optical semiconductor chip 10. In Fig. 3, the light input / output surface of the optical semiconductor chip 10 is located at the left end of the optical semiconductor chip 10. The width of the optical junction portion 30 may be set smaller than the width of the block electrodes EB.

[0021] The p-type electrodes EP1, EP2 and the n-type electrodes EN1, EN2 are located on the opposite side of the block electrode EB from the light input / output surface of the optical semiconductor chip 10.

[0022] In order to confirm the effect of providing a gap between the optical semiconductor chip 10 and the subcarrier 20, an optical module was prepared as a comparative example in which an underfill agent was filled between the optical semiconductor chip 10 and the subcarrier 20. The optical module according to this embodiment was then compared with the comparative example.

[0023] As conditions for comparison, the optical semiconductor chip 10 was a chip fabricated on an InP substrate, and the width of the optical semiconductor chip 10 was 0.4 mm. The subcarrier 20 had an aluminum nitride substrate and a gold wiring pattern. In addition, a conductive adhesive was used for the electrode junction. The lightwave circuit 40 used had a silicon nitride core on a silicon substrate. A conductive adhesive was applied to the electrode portions of the optical semiconductor chip 10, and it was flip-chip mounted on the subcarrier 20.

[0024] Next, with the laser of the optical semiconductor chip 10 emitting light, the power of the light passing through the optical waveguide on the lightwave circuit 40 was measured, and at the position where the peak value was reached, the optical semiconductor chip 10 and the subcarrier 20 were fixed to the lightwave circuit 40 via an insulating adhesive. The width of the joint of the insulating adhesive was set to 0.25 mm.

[0025] With the optical module according to the comparative example, the 3 dB bandwidth was 30 GHz. In contrast, with the optical module according to this embodiment, the 3 dB bandwidth was 33 GHz. Furthermore, with the optical module according to the comparative example, the laser oscillation wavelength shifted 0.5 nm toward the long wavelength side after mounting compared to before mounting, whereas with the optical module according to this embodiment, the shift in the laser oscillation wavelength after mounting compared to before mounting was 0.1 nm or less.

[0026] From the above results, it was confirmed that the optical module according to this embodiment has high wavelength stability and a structure with excellent high frequency characteristics compared to the optical module according to the comparative example.

[0027] [Description of Second Embodiment] Fig. 5 is a top view of an optical semiconductor chip included in an optical module according to a second embodiment of the present disclosure. Compared to Fig. 3, the optical semiconductor chip included in the optical module according to this embodiment is an optical signal receiving chip. Light (input light R2) input to the optical waveguide WG of the optical semiconductor chip 10A is light introduced from the optical waveguide in the lightwave circuit 40.

[0028] In order to confirm the effect of providing a gap between the optical semiconductor chip 10A and the subcarrier 20, an optical module was prepared as a comparative example in which an underfill agent was filled between the optical semiconductor chip 10A and the subcarrier 20. The optical module according to this embodiment was then compared with the comparative example.

[0029] As a condition for comparison, the optical semiconductor chip 10A was a chip fabricated on an InP substrate, and the width of the optical semiconductor chip 10A was 0.3 mm. The subcarrier 20 had an aluminum nitride substrate and a gold wiring pattern. Gold-tin solder was used for the electrode junction. The lightwave circuit 40 used had a silicon nitride core on a silicon substrate. Gold-tin solder was formed at the point where it would contact the electrode of the subcarrier 20, and the optical semiconductor chip 10A was flip-chip mounted to that point.

[0030] Next, with the optical power input from the lightwave circuit 40 kept constant, the current of the optical semiconductor chip 10A was monitored, and at the position where the current was at its maximum, the optical semiconductor chip 10A and the subcarrier 20 were fixed to the lightwave circuit 40 via an insulating adhesive. The width of the joint of the insulating adhesive was set to 0.2 mm.

[0031] The optical module according to the comparative example had a 3 dB bandwidth of 40 GHz, whereas the optical module according to the present embodiment had a 3 dB bandwidth of 45 GHz.

[0032] From the above results, it was confirmed that the optical module according to this embodiment has high wavelength stability and a structure with excellent high frequency characteristics compared to the optical module according to the comparative example.

[0033] [Effects of the Embodiment] As described above in detail, the optical module according to the present embodiment includes an optical junction, a subcarrier and an optical semiconductor chip joined to one side of the optical junction, and a lightwave circuit joined to the other side of the optical junction. A gap is provided between the subcarrier and the optical semiconductor chip, and the optical semiconductor chip comes into contact with the subcarrier via a block electrode arranged on the top surface of the optical semiconductor chip and aligned with the optical input / output surface of the optical semiconductor chip, and a p-type electrode and an n-type electrode located on the opposite side of the block electrode from the optical input / output surface.

[0034] This makes it possible to provide an optical module with excellent high-frequency characteristics and wavelength stability without using an underfill agent. In particular, by leaving a gap between the subcarrier and the optical semiconductor chip without using an underfill agent, it is possible to suppress high-frequency signal loss caused by the dielectric loss of the underfill agent and improve the high-frequency characteristics of the optical module. Furthermore, stress from the underfill agent is reduced, making it possible to suppress deviations in the laser oscillation wavelength of the optical semiconductor chip.

[0035] Furthermore, because the block electrodes are provided along the optical input / output surfaces of the optical semiconductor chip, it is possible to prevent the adhesive that forms the optical joint from penetrating between the optical semiconductor chip and the subcarrier 20 due to capillary action. As a result, it is possible to suppress high-frequency signal loss due to dielectric loss of the adhesive that forms the optical joint, and improve the high-frequency characteristics of the optical module. Furthermore, it is possible to reduce stress from the penetrating adhesive, and it is possible to suppress deviations in the oscillation wavelength of the laser of the optical semiconductor chip.

[0036] In the optical module according to this embodiment, the optical semiconductor chip may be at least one of a directly modulated DFB laser chip, an electro-absorption modulator integrated laser chip, and an optical signal receiving chip, which can improve the high-frequency characteristics and increase wavelength stability of the directly modulated DFB laser chip, the electro-absorption modulator integrated laser chip, and the optical signal receiving chip.

[0037] Furthermore, in the optical module according to this embodiment, the optical joint may be an insulating adhesive, which allows the optical semiconductor chip and the subcarrier to be fixed to the lightwave circuit 40. Furthermore, insulation between the optical semiconductor chip, the subcarrier, and the lightwave circuit can be ensured.

[0038] In the optical module according to this embodiment, the block electrode, p-type electrode, and n-type electrode are electrically connected to the wiring built in the subcarrier via electrode junctions, which may be made of at least one of solder, conductive adhesive, and metal, thereby ensuring electrical connection between the electrodes of the optical semiconductor chip 10 and the wiring built in the subcarrier.

[0039] Furthermore, in the optical module according to this embodiment, the thermal expansion coefficient of the subcarrier and that of the optical semiconductor chip may be equal. This reduces stress caused by the difference in thermal expansion coefficients between the optical semiconductor chip and the subcarrier when the optical semiconductor chip is mounted on the subcarrier. As a result, breakage of the electrode joint between the optical semiconductor chip and the subcarrier is suppressed.

[0040] In the optical module according to this embodiment, the width of the optical junction may be smaller than the width of the block electrode. This makes it possible to provide an optical module with excellent high-frequency characteristics and wavelength stability. It also improves the optical transmission efficiency between the optical semiconductor chip and the lightwave circuit.

[0041] Although the contents of the present disclosure have been described above based on the embodiments, the present disclosure is not limited to these descriptions, and various modifications and improvements are possible, which will be apparent to those skilled in the art. The descriptions and drawings that form part of this disclosure should not be understood as limiting the present disclosure. Various alternative embodiments, examples, and operating techniques will be apparent to those skilled in the art from this disclosure.

[0042] Of course, the present disclosure includes various embodiments not described herein. Therefore, the technical scope of the present disclosure is defined only by the invention-specifying matters according to the scope of the claims that are appropriate from the above description.

[0043] CR Core portion EN1, EN2 n-type electrodes EB Block electrode EP1, EP2 p-type electrodes R1 Output light R2 Input light WG Optical waveguide 10, 10A Optical semiconductor chip 20 Subcarrier 30 Optical junction 40 Lightwave circuit

Claims

1. An optical module comprising: an optical junction; a subcarrier and an optical semiconductor chip joined to one side of the optical junction; and a lightwave circuit joined to the other side of the optical junction, wherein a gap is provided between the subcarrier and the optical semiconductor chip, and the optical semiconductor chip is in contact with the subcarrier via a block electrode arranged on the top surface of the optical semiconductor chip and aligned with the optical input / output surface of the optical semiconductor chip, and a p-type electrode and an n-type electrode located on the opposite side of the optical input / output surface with the block electrode in between.

2. The optical module according to claim 1, wherein the optical semiconductor chip is at least one of a directly modulated DFB laser chip, an electric field absorption type optical modulator integrated laser chip, and an optical signal receiving chip.

3. The optical module according to claim 1, wherein the optical joint is an insulating adhesive.

4. The optical module described in claim 1, wherein the block electrode, the p-type electrode, and the n-type electrode are electrically connected to wiring built into the subcarrier via electrode junctions, and the electrode junctions are at least one of solder, conductive adhesive, and metal.

5. The optical module according to claim 1, wherein the thermal expansion coefficient of said subcarrier is equal to that of said optical semiconductor chip.

6. An optical module according to any one of claims 1 to 5, wherein the width of said optical junction is smaller than the width of said block electrode.

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