High-frequency substrate

Abstract

In the present invention, a high-frequency substrate (100) comprises: a ceramic substrate (12) which has a surface (12a) on which a semiconductor laser (20) is mounted, and which is formed from a heat-dissipating material; and a low-dielectric-constant substrate (11), which has a surface (11a) on which a signal line (13) for transmitting a high-frequency signal to the semiconductor laser 20 is provided, and which is formed of a material having a dielectric constant lower than the dielectric constant of the ceramic substrate (12). A side surface (11b) of the low dielectric constant substrate (11) and a side surface (12b) of the ceramic substrate (12) are butt-joined.

Description

High-frequency board

[0001] The present disclosure relates to high frequency substrates.

[0002] Patent Document 1 discloses an optical semiconductor module, in which a semiconductor laser and a signal line for transmitting a high-frequency signal to the semiconductor laser are provided on an AlN substrate.

[0003] Japanese Patent Application Laid-Open No. 2022-76389

[0004] In the optical semiconductor module disclosed in Patent Document 1, the signal line for transmitting a high-frequency signal is provided on an AIN substrate, which has a relatively high dielectric ratio, which causes degradation in the pass characteristics of the high-frequency signal transmitted through the signal line, resulting in attenuation of the high-frequency signal.

[0005] To solve this problem, it is conceivable to change from the AlN substrate to a low-dielectric-constant substrate made of a low-dielectric-constant material. However, low-dielectric-constant substrates have lower thermal conductivity than AlN substrates, which may result in a decrease in heat dissipation from the semiconductor laser.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a high-frequency substrate that can dissipate heat from a semiconductor laser and suppress attenuation of high-frequency signals transmitted through signal lines.

[0007] The high-frequency substrate according to the present disclosure comprises a first substrate having a first surface on which a semiconductor laser is mounted and formed of a material having heat dissipation properties, and a second substrate having a second surface on which a signal line for transmitting a high-frequency signal to the semiconductor laser is provided and formed of a material having a dielectric constant lower than that of the first substrate, and the side surfaces of the first substrate and the second substrate are butt-joined.

[0008] According to the present disclosure, it is possible to dissipate heat from a semiconductor laser and suppress attenuation of a high-frequency signal transmitted through a signal line.

[0009] FIG. 2 is a perspective view of a laser beam output device to which a high-frequency substrate according to a first embodiment is applied. FIG. 2 is a front view showing an example of bonding two substrates. FIG. 2A is a view showing a state before two substrates are bonded. FIG. 2B is a view showing a state after the two substrates have been bonded. FIG. 2C is a view showing a state after a first wire 31 has been wire-bonded to the two bonded substrates. FIG. 2B is a view showing a comparison result of an S21 characteristic simulation when the high-frequency substrate material is aluminum nitride and quartz. FIG. 2C is a perspective view of a laser beam output device to which a high-frequency substrate according to a second embodiment is applied. FIG. 2D is a perspective view of a laser beam output device to which a high-frequency substrate according to a third embodiment is applied. FIG. 2E is a perspective view of a laser beam output device to which a conventional high-frequency substrate is applied.

[0010] In order to explain the present disclosure in more detail, embodiments of the present disclosure will be described below with reference to the accompanying drawings.

[0011] First Embodiment A high-frequency substrate 100 according to a first embodiment will be described with reference to FIGS. 1 to 3 and 6. FIG.

[0012] First, the configuration of a laser beam output device to which a high-frequency substrate 100 according to the first embodiment is applied will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a perspective view of a laser beam output device to which a high-frequency substrate 100 according to the first embodiment is applied. Fig. 2 is a front view showing an example of joining two substrates 11 and 12.

[0013] As shown in FIG. 1, the laser light emitting device according to the first embodiment includes a high-frequency substrate 100, signal lines 13 and 14, a GND 15, a termination resistor 16, a semiconductor laser 20, a first wire 31, and a second wire 32.

[0014] The high-frequency substrate 100 is composed of a low-dielectric-constant substrate 11 and a ceramic substrate 12. The low-dielectric-constant substrate 11 and the ceramic substrate 12 are joined together with their side surfaces 11b and 12b butting against each other. This will be described later.

[0015] The low-dielectric-constant substrate 11 is formed in a plate shape. The low-dielectric-constant substrate 11 is made of a low-dielectric-constant material having a low dielectric constant. Specifically, the dielectric constant of the low-dielectric-constant substrate 11 is lower than the dielectric constant of the ceramic substrate 12 described below. The low-dielectric-constant substrate 11 is made of, for example, quartz. The low-dielectric-constant substrate 11 constitutes a second substrate, and its surface 11a constitutes a second surface.

[0016] The ceramic substrate 12 is formed in a plate shape. The ceramic substrate 12 is made of a material with high thermal conductivity or heat dissipation. Specifically, the thermal conductivity or heat dissipation of the ceramic substrate 12 is higher than that of the low dielectric constant substrate 11. The ceramic substrate 12 is made of, for example, aluminum nitride. The ceramic substrate 12 constitutes a first substrate, and its surface 12a constitutes a first surface.

[0017] The signal lines 13 and 14 are provided on the surface 11a of the low-dielectric-constant substrate 11. By providing the signal lines 13 and 14 on the surface 11a of the low-dielectric-constant substrate 11, which has a low dielectric constant, the signal lines 13 and 14 can improve the passing characteristics of high-frequency signals and increase the speed of the high-frequency signals. In other words, attenuation of high-frequency signals passing through the signal lines 13 and 14 is suppressed. The signal lines 13 and 14 are, for example, coplanar lines.

[0018] The GND 15 is provided across the surface 11a of the low dielectric constant substrate 11 and the surface 12a of the ceramic substrate 12. The GND 15 is composed of a GND 15a provided on the surface 11a and a GND 15b provided on the surface 12a. The GND 15a constitutes the second GND, and the GND 15b constitutes the first GND.

[0019] GND 15a is disposed so as to surround signal line 13 disposed at a corner of surface 11a. GND 15a is formed so as to bend at a substantially right angle midway toward surface 12a, and the tip of the bent portion is connected to GND 15b. GND 15b is formed linearly and is provided on the side of signal line 13 along the longitudinal direction of signal line 13.

[0020] Therefore, the GNDs 15a and 15b are arranged to surround the signal line 13. Specifically, the GND 15a covers two sides of the signal line 13, and the GND 15b covers one side of the signal line 13.

[0021] The terminating resistor 16 is provided on the surface 11a of the low dielectric constant substrate 11. The terminating resistor 16 is electrically connected to the signal line 14. The terminating resistor 16 terminates a modulated signal from a semiconductor laser 20, which will be described later.

[0022] The semiconductor laser 20 is, for example, an EML (Electro-absorption modulator laser). The semiconductor laser 20 is mounted, for example, by soldering or the like, on a GND 15b provided on the surface 12a of the ceramic substrate 12. By providing the semiconductor laser 20 on the surface 12a of the ceramic substrate 12 in this manner, heat generated by the semiconductor laser 20 is dissipated to the ceramic substrate 12.

[0023] The semiconductor laser 20 has a laser light source 21 and a modulator 22. The laser light source 21 receives power supply and generates laser light. The modulator 22 modulates the laser light generated by the laser light source 21 and emits the modulated laser light. An arrow L shown in Fig. 1 indicates the emission direction of the laser light.

[0024] The laser light source 21 is configured by, for example, a distributed feedback laser diode (DFB-LD) and is formed so that the length in the direction D1, which is the longitudinal direction of the laser light source 21, is about 500 μm.

[0025] The modulation unit 22 modulates the laser light generated by the laser light source 21 based on a modulation signal from a drive circuit (not shown). The modulation unit 22 is located forward of the laser light source 21 in the D1 direction. The modulation unit 22 intensity-modulates the laser light generated by the laser light source 21 based on, for example, a voltage change in the modulation signal from the drive circuit, and emits the modulated laser light in the D1 direction from one end of the ceramic substrate 12 along the surface 12a of the ceramic substrate 12. The modulation unit 22 is configured, for example, by an electro-absorption modulator (EAM). In addition, in order to reduce parasitic capacitance, the modulation unit 22 is formed so that its length in the D1 direction is approximately 100 μm, which is shorter than the length of the laser light source 21 in the D1 direction.

[0026] The first wire 31 and the second wire 32 are, for example, conductive metal wires. The first wire 31 electrically connects the signal line 13 and the modulation section 22 of the semiconductor laser 20. One end of the first wire 31 is wire-bonded to the signal line 13. The other end of the first wire 31 is wire-bonded to the modulation section 22 of the semiconductor laser 20. The second wire 32 electrically connects the modulation section 22 of the semiconductor laser 20 and the signal line 14. One end of the second wire 32 is wire-bonded to the modulation section 22 of the semiconductor laser 20. The other end of the second wire 32 is wire-bonded to the signal line 14.

[0027] Therefore, the high-frequency signal is transmitted through the signal line 13 and then through the first wire 31 to the modulator 22 of the semiconductor laser 20. The high-frequency signal (modulated signal) output from the modulator 22 of the semiconductor laser 20 is then transmitted through the second wire 32 to the signal line 14 and then terminated at the termination resistor 16.

[0028] 1, the length of the low dielectric constant substrate 11 in the D1 direction is the same as the length of the ceramic substrate 12 in the D1 direction. The thickness of the low dielectric constant substrate 11 is the same as the thickness of the ceramic substrate 12. As shown in FIG. 2A, the low dielectric constant substrate 11 has a side surface 11b extending in the D1 direction. The ceramic substrate 12 has a side surface 12b extending in the D1 direction.

[0029] When the low dielectric constant substrate 11 and the ceramic substrate 12 are butt-bonded, the side surface 11b of the low dielectric constant substrate 11 and the side surface 12b of the ceramic substrate 12 are arranged to face each other, as shown in Fig. 2A. Next, as shown in Fig. 2B, the side surfaces 11b and 12b are butt-bonded using solder 41. Next, as shown in Fig. 2C, for example, a first wire 31 is wire-bonded between the signal line 14 and the modulation section 22 of the semiconductor laser 20.

[0030] In this way, the low dielectric constant substrate 11 and the ceramic substrate 12 are connected to each other to form a single rectangular high frequency substrate 100 as a whole. In this case, the surface 11a of the low dielectric constant substrate 11 and the surface 12a of the ceramic substrate 12 are flush with each other, with no step between them. In addition, the outer peripheral surfaces of the low dielectric constant substrate 11 and the ceramic substrate 12 are flush with each other, with no step between them.

[0031] Alternatively, the low-dielectric-constant substrate 11 having the signal lines 13, 14, GND 15a, and termination resistor 16 provided on the surface 11a may be butt-joined to the ceramic substrate 12 having the GND 15b and semiconductor laser 20 provided on the surface 12a, and then the first wire 31 and the second wire 32 may be joined. Alternatively, the low-dielectric-constant substrate 11 and the ceramic substrate 12 may be butt-joined, the signal lines 13, 14, GND 15a, and termination resistor 16 may be provided on the surface 11a, and the GND 15b and semiconductor laser 20 may be provided on the surface 12a, and then the first wire 31 and the second wire 32 may be joined.

[0032] Next, the effects of the high frequency substrate 100 according to the first embodiment will be described in comparison with those of a conventional high frequency substrate.

[0033] Fig. 6 is a perspective view of a laser beam emitting device to which a conventional high-frequency substrate is applied. In Fig. 6, components having the same functions as those described in the first embodiment are denoted by the same reference numerals, and their description will be omitted.

[0034] The only high-frequency substrate applied to the laser light emission device shown in Fig. 6 is the ceramic substrate 12. Signal lines 13 and 14, a GND 15, a termination resistor 16, and a semiconductor laser 20 are provided on a surface 12a of the ceramic substrate 12. A first wire 31 electrically connects the signal line 13 to the modulation section 22 of the semiconductor laser 20. A second wire 32 electrically connects the modulation section 22 of the semiconductor laser 20 to the signal line 14.

[0035] Generally, in order to reduce parasitic capacitance, the modulation section 22 is formed so that its length in the D1 direction is approximately 100 μm, which is shorter than the length of the laser light source 21 in the D1 direction. In contrast, in order to obtain a high output, the laser light source 21 is formed so that its length in the D1 direction is approximately 500 μm. Therefore, the length of the signal line 13 in the D1 direction needs to be longer than 500 μm. However, if the length of the signal line 13 in the D1 direction is made longer than 500 μm, the signal line 13 may resonate at high frequencies, degrading the high-frequency characteristics.

[0036] 1 , the high-frequency substrate 100 according to the first embodiment has the signal line 13 provided on the surface 11 a of the low-dielectric-constant substrate 11, thereby shortening the electrical length of the high-frequency signal transmitted through the signal line 13. Therefore, the high-frequency substrate 100 can shift the resonance frequency occurring near the high-frequency substrate 100 to the higher frequency side, thereby improving the high-frequency characteristics. As a result, the high-frequency substrate 100 eliminates band limitations due to high-frequency resonance, and can obtain a good optical waveform in high-baud-rate modulation requiring a bandwidth exceeding 60 GHz, such as 100 GBaud PAM4, which is a promising modulation method for next-generation Ethernet.

[0037] 3 shows the comparison results of S21 characteristic simulations when the high-frequency substrate material is aluminum nitride (ε = 8.8) and quartz (ε = 3.8). In Fig. 3, the results when the signal line is provided on the high-frequency substrate made of aluminum nitride are shown by a two-dot chain line, and the results when the signal line is provided on the high-frequency substrate made of quartz are shown by a solid line. It can be seen that when the signal line is provided on the high-frequency substrate made of quartz, the electrical length of the high-frequency signal is shortened, thereby suppressing resonance and improving the characteristics of the 3 dB band.

[0038] As described above, the high-frequency substrate 100 according to the first embodiment can dissipate heat from the semiconductor laser 20 and suppress attenuation of the high-frequency signal transmitted through the signal line 13 .

[0039] Second Embodiment A high-frequency substrate 200 according to a second embodiment will be described with reference to Fig. 4. Fig. 4 is a perspective view of a laser light emission device to which the high-frequency substrate 200 according to the second embodiment is applied. Note that components having the same functions as those described in the first embodiment above are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0040] The high-frequency substrate 100 according to the first embodiment shown in Fig. 1 includes a single GND 15 extending across the surface 11a of the low-dielectric-constant substrate 11 and the surface 12a of the ceramic substrate 12. In contrast, the high-frequency substrate 200 according to the second embodiment shown in Fig. 4 electrically connects the GND 15a provided on the surface 11a of the low-dielectric-constant substrate 11 to the GND 15b provided on the surface 12a of the ceramic substrate 12 via a third wire 33. The third wire 33 is, for example, a conductive metal wire.

[0041] Therefore, the high-frequency substrate 200 does not need to have one GND 15 extending across the surface 11a of the low-dielectric-constant substrate 11 and the surface 12a of the ceramic substrate 12. As a result, the high-frequency substrate 200 can easily electrically connect the GNDs 15a and 15b regardless of the accuracy of butt-jointing between the low-dielectric-constant substrate 11 and the ceramic substrate 12.

[0042] Embodiment 3 A high-frequency substrate 300 according to embodiment 3 will be described with reference to Fig. 5. Fig. 5 is a perspective view of a laser light emission device to which the high-frequency substrate 300 according to embodiment 3 is applied. Note that components having the same functions as those described in embodiment 1 above are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0043] 1 according to the first embodiment includes a signal line 13 on the surface 11a of the low dielectric constant substrate 11, and a single GND 15 extending across the surface 11a of the low dielectric constant substrate 11 and the surface 12a of the ceramic substrate 12. In contrast, a high-frequency substrate 300 according to the third embodiment shown in FIG. 5 includes a signal line 13 on the surface 11a of the low dielectric constant substrate 11A, and a GND 15 only on the surface 12a of the ceramic substrate 12A.

[0044] Therefore, the high-frequency substrate 300 according to the third embodiment can simplify the manufacturing of the low-dielectric-constant substrate 11A and the ceramic substrate 12A.

[0045] It should be noted that within the scope of the present disclosure, the embodiments may be freely combined, or any component in each embodiment may be modified, or any component in each embodiment may be omitted.

[0046] The high-frequency substrate according to the present disclosure comprises a first substrate having heat dissipation properties and a second substrate having a low dielectric constant, thereby enabling heat dissipation from a semiconductor laser and suppressing attenuation of high-frequency signals transmitted through signal lines, and is suitable for use as a high-frequency substrate, etc.

[0047] 11, 11A low dielectric constant substrate, 11a surface, 11b side surface, 12, 12A ceramic substrate, 12a surface, 12b side surface, 13, 14 signal line, 15, 15a, 15b GND, 16 termination resistor, 20 semiconductor laser, 21 laser light source, 22 modulation unit, 31 first wire, 32 second wire, 33 third wire, 41 solder, 100, 200, 300 high frequency substrate.

Claims

1. A high frequency substrate comprising: a first substrate having a first surface on which a semiconductor laser is mounted and made of a material with heat dissipation properties; and a second substrate having a second surface on which a signal line for transmitting a high frequency signal to the semiconductor laser is provided and made of a material with a dielectric constant lower than that of the first substrate, wherein the side surfaces of the first substrate and the second substrate are butt-joined.

2. The high frequency board according to claim 1, characterized in that the first surface has a first GND on which the semiconductor laser is mounted, and the second surface has a second GND electrically connected to the first GND and a termination resistor at which the high frequency signal from the semiconductor laser terminates.

3. The high frequency board according to claim 2, wherein the signal line is surrounded by the first GND and the second GND.

4. A high frequency substrate according to claim 2 or 3, characterized in that the first GND and the second GND are integrally formed across the first surface and the second surface.

5. The high frequency board according to claim 1, wherein said first surface has a GND on which said semiconductor laser is mounted and a termination resistor at which a high frequency signal from said semiconductor laser terminates.

6. The high frequency board according to claim 5, wherein the signal line is surrounded by the GND.

7. The high frequency substrate according to any one of claims 1 to 6, wherein the first substrate is a ceramic substrate.

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