Optical semiconductor device
The optical semiconductor device addresses chip size and broadbanding issues by using a donut-shaped mesa and groove structure for direct wire bonding and reduced capacitance, achieving compact size and improved bandwidth.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MITSUBISHI ELECTRIC CORP
- Filing Date
- 2024-12-13
- Publication Date
- 2026-06-18
AI Technical Summary
Conventional optical semiconductor elements face challenges in reducing chip size and achieving broadbanding due to the need for a large electrode pad region and increased capacitance caused by forming pads on insulating films with higher dielectric constants.
The optical semiconductor device features a donut-shaped mesa centered on the waveguide with electrode pads on the mesa and a groove below, allowing direct wire bonding and reducing capacitance.
This design reduces chip size and enables broadbanding by minimizing the chip width and capacitance, while preventing wire contact with the waveguide.
Smart Images
Figure JP2024044291_18062026_PF_FP_ABST
Abstract
Description
Optical semiconductor device 【0001】 The present disclosure relates to an optical semiconductor device. 【0002】 In a conventional optical semiconductor element, wire bonding was performed on an electrode pad drawn out beside a waveguide (see, for example, Patent Document 1). 【0003】 Japanese Patent Application Laid-Open No. 2012-23065 【0004】 However, since it was necessary to secure a region of about 50 μm in diameter for forming the electrode pad beside the waveguide, the chip width was increased. Further, since the electrode pad was formed via an insulating film on a mesa composed of a semiconductor having a higher dielectric constant than air, the capacitance of the electrode pad became large and broadbanding could not be realized. 【0005】 The present disclosure has been made to solve the above-described problems, and an object thereof is to obtain an optical semiconductor device capable of reducing the chip size and realizing broadbanding. 【0006】 The optical semiconductor device according to the present disclosure includes a substrate, a semiconductor layer formed on the substrate and having a waveguide and a mesa formed in a donut shape centered on the waveguide in a plan view, a groove being formed between the waveguide and the mesa, an upper surface electrode formed on the waveguide and connected to the semiconductor layer, and an electrode pad formed on the mesa via an insulating film and connected to the upper surface electrode. 【0007】 In the present disclosure, a mesa is formed in a donut shape centered on the waveguide in a plan view, and an electrode pad is formed on the mesa. Thereby, since wire bonding can be performed directly above the waveguide, the chip size can be reduced. Further, since there is a groove between the waveguide and the mesa below the wire, the capacitance of the electrode pad can be reduced and broadbanding can be realized. 【0008】This is a top view showing an optical semiconductor device according to Embodiment 1. This is a cross-sectional view of an optical modulator along line I-II in Figure 1. This is a top view showing an optical semiconductor device according to a comparative example. This is a cross-sectional view along line I-II in Figure 3. This is a cross-sectional view showing a modified example of the optical semiconductor device according to Embodiment 1. This is a top view showing an optical semiconductor device according to Embodiment 2. This is a cross-sectional view along line I-II in Figure 6. This is a cross-sectional view showing an optical semiconductor device according to Embodiment 3. This is a top view showing an optical semiconductor device according to Embodiment 4. This is a cross-sectional view of a laser diode along line I-II in Figure 9. 【0009】 The optical semiconductor device according to the embodiment will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repetition of the description may be omitted. 【0010】 Embodiment 1. Figure 1 is a top view showing an optoelectronic device according to Embodiment 1. This optoelectronic device is an electro-absorption modulator integrated laser diode (EML) that monolithically integrates a distributed feedback type laser diode 1 and an electro-absorption type optical modulator 2. The optical modulator 2 has a waveguide 3 and a mesa 4 that is formed in a donut shape centered on the waveguide 3 in a plan view. The mesa 4 is divided into two parts and is arranged on opposite sides of the waveguide 3. The width of the mesa 4 is about 10 μm. The width of the mesa 4 is adjusted according to the ultrasonic vibration intensity and load during wire bonding to prevent the mesa 4 from being damaged. 【0011】 Figure 2 is a cross-sectional view of an optical modulator along line I-II in Figure 1. A semiconductor layer 6 is formed on a substrate 5. The semiconductor layer 6 has a waveguide 3 and a mesa 4. Grooves 7 are formed between the waveguide 3 and the left and right mesa 4. Since the mesa 4 can be formed at the same time as the waveguide 3, forming the mesa 4 does not increase the manufacturing process. 【0012】Waveguide 3 has an n-type cladding layer 8, an absorption layer 9, and a p-type cladding layer 10 stacked sequentially on a substrate 5 as a semiconductor layer 6. The substrate 5, n-type cladding layer 8, and p-type cladding layer 10 are made of, for example, InP, InGaAs, InGaAsP, AlGaInAs, etc. The absorption layer 9 is made of, for example, InGaAsP, AlGaInAs, etc. Note that the substrate 5 may be a semi-insulating substrate such as Fe-InP. Mesa 4 has an n-type cladding layer 8 and a p-type cladding layer 10. 【0013】 The sides of the waveguide 3, the top and sides of the mesa 4, and the bottom of the groove 7 are covered with an insulating film 11. The thickness of the insulating film 11 is about 1 to 2 μm. The insulating film 11 is made of, for example, SiN, SiO ２ It consists of BCBs, etc. The waveguide 3 has a width of about 5 μm, each mesa 4 has a width of about 10 μm, and the groove 7 has a width of about 10 μm. The inner surface of the groove 7 is covered with an insulating film 11, but there is an air gap inside that. 【0014】 An upper electrode 12 is formed on the waveguide 3 and connected to the p-type cladding layer 10. Electrode pads 13 are formed on the left and right mesa 4 via insulating films 11. The electrode pad 13 of one mesa 4 is connected to the upper electrode 12. This reduces capacitance compared to the case where the electrode pads 13 of both mesa 4 are connected to the upper electrode 12. A lower electrode 14 is formed on the lower surface of the substrate 5. The upper electrode 12, electrode pads 13, and lower electrode 14 are made of materials such as Au, Ti, Pt, AuGe, etc. 【0015】 The bonding portion at one end of the wire 15 is positioned directly above the waveguide 3 and bonded to the left and right electrode pads 13. The other end of the wire 15 is connected to a terminal on a mounting substrate on which the semiconductor device is mounted. This terminal on the mounting substrate is electrically connected to the output terminal of a driver IC for modulating and driving the EML. The wire 15 is made of, for example, Au. The donut-shaped mesa 4 is formed within a wire bonding region with a diameter of approximately 50 μm, which is about the same as the diameter of the wire 15. 【0016】Next, the effects of this embodiment will be explained in comparison with the comparative example. Figure 3 is a top view showing an optoelectronic device according to the comparative example. Figure 4 is a cross-sectional view taken along line I-II in Figure 3. In the comparative example, wires 15 are bonded to electrode pads 13 that are brought out to a mesa 4 next to the waveguide 3. However, because it is necessary to secure an area next to the waveguide 3 to form the electrode pads 13, the width of the chip becomes large. Also, because the electrode pads 13 are formed on a mesa 4 made of a semiconductor with a dielectric constant higher than air via an insulating film 11, the capacitance of the electrode pads 13 becomes large, and broadband cannot be achieved. 【0017】 In contrast, in this embodiment, a mesa 4 is formed in a donut shape centered on the waveguide 3, and an electrode pad 13 is formed on top of the mesa 4. As a result, wire bonding can be performed directly above the waveguide 3, eliminating the need to form the electrode pad 13 next to the waveguide 3, thus reducing the chip width. Consequently, the chip size can be reduced. Furthermore, there is a groove 7 between the waveguide 3 and the mesa 4 below the wire 15. Therefore, the capacitance of the electrode pad 13 can be reduced, enabling wider bandwidth. 【0018】 Furthermore, an insulating film 11 is formed on the mesa 4, but not on the waveguide 3. Therefore, the height of the electrode pad 13 on the mesa 4 is higher than the height of the upper electrode 12 on the waveguide 3 by the thickness of the insulating film 11. As a result, even if wire bonding is performed directly above the waveguide 3, the wire 15 will not come into contact with the upper electrode 12, and the waveguide 3 will not be damaged. If the thickness of the insulating film 11 is 1 μm or more, the wire 15 will not come into contact with the upper electrode 12. However, the thicker the insulating film 11, the longer it takes to form. Note that the mesa 4 is not limited to a circular donut shape in plan view, but may also be a square donut shape, an ellipse, a polygon, or a shape that combines curves and straight lines. 【0019】Figure 5 is a cross-sectional view showing a modified example of the optoelectronic device according to Embodiment 1. The height of the upper electrode 12 on the waveguide 3 is the same as the height of the electrode pad 13, and the wire 15 contacts not only the electrode pads 13 on the left and right mesa 4 but also the upper electrode 12 on the waveguide 3. As a result, the contact area of the wire 15 increases, and the bonding strength is increased. In addition, the upper electrode 12 and the electrode pad 13 are connected via the wire 15. Therefore, wiring connecting the upper electrode 12 and the electrode pad 13 is unnecessary, and the capacitance can be further reduced. 【0020】 Embodiment 2. Figure 6 is a top view showing an optoelectronic device according to Embodiment 2. Figure 7 is a cross-sectional view taken along line I-II in Figure 6. A double concentric mesa 4 is formed in a region with a diameter of approximately 50 μm, which is about the same as the wire diameter, centered on the waveguide 3. The width of each mesa 4 is approximately 5 μm. An electrode pad 13 is formed on each mesa 4. The upper electrode 12 of the waveguide 3 is connected to the electrode pad 13 formed on the right inner mesa 4. In this embodiment, the inner mesa 4 is positioned close to the waveguide 3 to support the wire 15, thus further reliably preventing contact between the wire 15 and the upper electrode 12. Other configurations and effects are the same as in Embodiment 1. Note that the mesa 4 is not limited to a double concentric shape, but may be formed in a triple or more multiple concentric shape, or it may be an ellipse, a polygon, or a combination thereof. 【0021】 Embodiment 3. Figure 8 is a cross-sectional view showing an optoelectronic device according to Embodiment 3. Below the wire 15, the groove 7 between the waveguide 3 and the mesa 4 is filled with an insulator 16. For example, SiN, SiO ２ After forming the insulating film 11 by CVD, the groove 7 is filled with an insulator 16 made of BCB (Benzocyclobutene). The left and right mesa 4 and waveguide 3 become one large block via the insulator 16, making them more resistant to ultrasonic vibrations during wire bonding. Furthermore, by using a material with a lower dielectric constant than the semiconductor layer 6 as the insulator 16, the capacitance can be reduced compared to conventional technology where the entire area under the pad is semiconductor. Other configurations and effects are the same as in Embodiment 1. 【0022】Embodiment 4. Figure 9 is a top view showing an optoelectronic device according to Embodiment 4. No optical modulator 2 is formed, and a directly modulated laser diode 1 is formed. Figure 10 is a cross-sectional view of the laser diode along line I-II in Figure 9. An active layer 17 is formed in the waveguide 3 instead of an absorption layer 9. The active layer 17 is made of, for example, InGaAsP, AlGaInAs, etc. A mesa 4 is formed in a donut shape around the waveguide 3 of the laser diode 1, and an electrode pad 13 is formed on the mesa 4. The other configurations and effects are the same as in Embodiment 1. The mesa 4 may be made of multiple concentric circles as in Embodiment 2, or the space between the waveguide 3 and the mesa 4 may be filled with an insulator 16 as in Embodiment 3. Also, the optoelectronic device is not limited to a modulator or a laser diode, but may be, for example, an SOA, etc. 【0023】 1. Laser diode, 2. Optical modulator, 3. Waveguide, 4. Mesa, 5. Substrate, 6. Semiconductor layer, 7. Groove, 11. Insulating film, 12. Top electrode, 13. Electrode pad, 15. Wire, 16. Insulator
Claims
1. An optoelectronic semiconductor device comprising: a substrate; a semiconductor layer formed on the substrate, having a waveguide and a mesa formed in a donut shape centered on the waveguide in a plan view, with a groove formed between the waveguide and the mesa; an upper electrode formed on the waveguide and connected to the semiconductor layer; and an electrode pad formed on the mesa via an insulating film and connected to the upper electrode.
2. The optoelectronic device according to claim 1, further comprising a wire positioned directly above the waveguide and bonded to the electrode pad.
3. The optical semiconductor device according to claim 2, characterized in that the height of the electrode pad is greater than the height of the upper electrode, and the wire is not in contact with the upper electrode.
4. The optical semiconductor device according to claim 2, characterized in that the wire is in contact with the upper electrode, and the upper electrode and the electrode pad are connected via the wire.
5. The optoelectronic device according to any one of claims 1 to 4, characterized in that the mesa is formed in a multi-layered concentric circular pattern.
6. The optical semiconductor device according to any one of claims 1 to 5, characterized in that the groove is a void.
7. The optical semiconductor device according to any one of claims 1 to 5, characterized in that the groove is filled with an insulator.
8. The optical semiconductor device according to claim 7, characterized in that the dielectric constant of the insulator is lower than the dielectric constant of the semiconductor layer.
9. The optical semiconductor device according to any one of claims 1 to 8, characterized in that the optical semiconductor device is an optical modulator.
10. The optical semiconductor device according to any one of claims 1 to 8, characterized in that the optical semiconductor device is a laser diode.