Optical semiconductor module

Abstract

A light semiconductor module is provided. A light semiconductor module of one embodiment includes a temperature control element including a temperature control surface; a first substrate including a first surface and a second surface opposite to the first surface, and placed on the temperature control element with the first surface in contact with the temperature control surface; a semiconductor laser element placed on the second surface; a second substrate including a third surface and a fourth surface opposite to the third surface, and placed on the second surface of the first substrate; and a housing that accommodates the temperature control element, the first substrate, the second substrate, and the semiconductor laser element. The second substrate includes a wiring on the fourth surface. The wiring is connected to the housing by a first lead wire, and connected to the semiconductor laser element by a second lead wire. The thermal conductivity of the second substrate is lower than the thermal conductivity of the first substrate.

Description

Technical Field

[0001] This disclosure relates to optical semiconductor modules.

[0002] This application claims priority based on Japanese Application No. 2020-186792, dated November 9, 2020, and invokes all the contents set forth in the aforementioned Japanese application. Background Technology

[0003] Japanese Patent Application Publication No. 2016-180779 discloses the optical circuit of a box-type TOSA module. The module internally includes a thin plate called a sub-plate. A wiring pattern is formed on the sub-plate by metallization or vapor deposition of a dielectric material. A laser diode, an optical modulator, a resistor, and a capacitor are mounted on the sub-plate. The module also has a tray housing the sub-plate, and a thermoelectric cooling element (TEC) is mounted below the tray. The tray and TEC are housed within the module's casing. Heat generated on the components on the sub-plate is absorbed by the TEC and dissipated from the bottom of the casing. The module includes a modulation signal power supply wiring that runs from the outside of the casing to the inside. The modulation signal power supply wiring and the sub-plate are electrically connected to each other via wire or strip gold wire. Summary of the Invention

[0004] The optical semiconductor module disclosed herein comprises: a temperature control element having a temperature control surface; a first substrate having a first surface and a second surface opposite to the first surface, and mounted on the temperature control element with the first surface in contact with the temperature control surface; a semiconductor laser element mounted on the second surface; a second substrate having a third surface and a fourth surface opposite to the third surface, and mounted on the second surface of the first substrate; and a housing housing the temperature control element, the first substrate, the second substrate, and the semiconductor laser element. The second substrate has wiring on the fourth surface. The wiring is connected to the housing via a first lead and to the semiconductor laser element via a second lead. The thermal conductivity of the second substrate is lower than that of the first substrate. Attached Figure Description

[0005] Figure 1 This is a top view schematically illustrating the internal structure of the optical semiconductor module in an embodiment.

[0006] Figure 2 This is a top view schematically representing the semiconductor laser element, the second substrate, and the leads of the optical semiconductor module.

[0007] Figure 3 This is a schematic side view showing the temperature control element, first substrate, second substrate, semiconductor laser element, and leads of the optical semiconductor module.

[0008] Figure 4 This is a side view showing an example of a layer structure between a first substrate and a second substrate.

[0009] Figure 5 This is a side view showing another example of a layer structure between a first substrate and a second substrate.

[0010] Figure 6 This is a schematic side view of the temperature control element, substrate, and semiconductor laser element of a comparative example optical semiconductor module. Detailed Implementation

[0011] Specific examples of optical semiconductor modules according to embodiments of the present disclosure will be described with reference to the accompanying drawings. Furthermore, the present invention is not limited to these examples, but is intended to include all modifications within the scope equivalent to the scope of the claims, as indicated by the claimed scope. In the description of the drawings, the same or equivalent elements are labeled with the same reference numerals, and repeated descriptions are omitted where appropriate. For ease of understanding, some parts of the drawings are depicted in a simplified or exaggerated manner, and the dimensions, ratios, etc., are not limited to what is shown in the drawings.

[0012] Figure 1 This is a top view schematically illustrating the internal structure of the optical semiconductor module 1 according to an embodiment. The optical semiconductor module 1 includes, for example, a rectangular housing 2 and a plurality of external terminals 3 disposed at one end of the housing 2 along its length direction (direction D1). The plurality of external terminals 3 are arranged along the width direction (direction D2) of the housing 2 at one end along direction D1. Direction D2 is a direction intersecting direction D1. The plurality of external terminals 3 include, for example, terminals for receiving high-speed electrical signals from the outside, terminals for receiving drive current from a laser diode, terminals for receiving drive current from a TEC, monitoring terminals for detecting the temperature of the laser diode, and terminals for providing a ground potential (reference potential). The signals exchanged with the outside via the plurality of external terminals 3 include high-speed signals and low-speed signals. Low-speed signals include DC signals. The housing 2 has an inner wall 2b that divides the internal space S of the housing 2. At the end of the housing 2 along direction D1, opposite to the external terminals 3, a light output section 4 for outputting light L (optical signal) is provided.

[0013] The optoelectronic semiconductor module 1 has, for example, a transmission line 5, a pad 6 as a DC pad, and a TEC (Thermo Electric Cooler) 7 as a temperature control element in the internal space S of the housing 2. Figure 2 This is a schematic top view of the enlarged upper structure of the TEC7. Figure 3 This is a schematic side view representing the upper structure of the TEC7. (Example) Figure 2 and Figure 3As shown, the optical semiconductor module 1 includes a TEC7, an AlN (Aluminum Nitride) substrate mounted on the TEC7 (i.e., a first substrate 8), a quartz substrate mounted on the first substrate 8 (i.e., a second substrate 9), and a semiconductor laser element 10. Transmission lines 5 and pads 6 are formed on the inner surface of the housing 2. The transmission lines 5 and multiple pads 6 are connected to multiple external terminals 3 via wiring penetrating the inner wall 2b. The wiring connecting the transmission lines 5 and multiple pads 6 to the multiple external terminals 3 is formed, for example, by metal plating or vapor deposition. The transmission lines 5 include signal lines 5s extending in one direction at a distance from the parallel grounding wiring 5g.

[0014] The first substrate 8 is a high thermal conductivity substrate with a higher thermal conductivity than the second substrate 9. The second substrate 9 is a low thermal conductivity substrate with a lower thermal conductivity than the first substrate 8. The thickness T1 of the first substrate 8 is, for example, 600 μm or less, and the thickness T2 of the second substrate 9 is 50 μm or more. In the case where the first substrate 8 is an AlN substrate formed of AlN and the second substrate 9 is a quartz substrate formed of quartz, for example, the thickness T1 of the AlN substrate 8 is 250 μm, and the thickness T2 of the quartz substrate 9 is 150 μm. For example, the thermal conductivity of the AlN substrate 8 is 170 W / m·K (the thermal resistance of the AlN substrate 8 with a thickness of 250 μm is 1.47 × 10⁻⁶). －6 [m 2 The thermal conductivity of the quartz substrate 9 is 1.48 W / m·K (the thermal resistance of the quartz substrate 9 with a thickness of 150 μm is 1.01 × 10⁻⁶). -4 [m 2 The thermal conductivity of AlN substrate 8 is more than 100 times greater than that of quartz substrate 9. As an example, the thermal resistance of AlN substrate 8 is less than 1 / 50 of that of quartz substrate 9.

[0015] For example, AlN substrate 8 and quartz substrate 9 are sequentially mounted on TEC7 along direction D3, which is the height direction. Direction D3 is a direction that intersects with directions D1 and D2. Housing 2 houses TEC7, AlN substrate 8, quartz substrate 9, and semiconductor laser element 10 within internal space S. TEC7 has a heat dissipation surface 7a and a temperature control surface 7b. TEC7 is mounted on housing 2 with heat dissipation surface 7a in contact with housing 2. Temperature control surface 7b is located opposite to heat dissipation surface 7a in direction D3. For example, heat dissipation surface 7a and temperature control surface 7b are planes parallel to directions D1 and D2. AlN substrate 8 is mounted on temperature control surface 7b in contact with temperature control surface 7b. AlN substrate 8 has a first surface 8a as its lower surface and a second surface 8b as its upper surface. First surface 8a is in surface contact with temperature control surface 7b. Second surface 8b is the surface opposite to first surface 8a. The AlN substrate 8 has a second surface 8b on the side opposite to the TEC7, on which a quartz substrate 9 and a semiconductor laser element 10 are mounted. The quartz substrate 9 is arranged side-by-side with the semiconductor laser element 10 on the second surface 8b. The semiconductor laser element 10 is, for example, an electric-absorption modulator integrated laser (EML). For example, the semiconductor laser element 10 includes a laser diode 10b and a modulator 10c. For example, when a predetermined current flows through the TEC7, heat is absorbed on the temperature control surface 7b, and the absorbed heat is discharged on the heat dissipation surface. At this time, the semiconductor laser element 10 is cooled via the AlN substrate 8. For example, when a current flows through the TEC7 in the opposite direction to the predetermined current, heat is absorbed on the heat dissipation surface 7a, and the absorbed heat is discharged on the temperature control surface 7b. At this time, the semiconductor laser element 10 is heated via the AlN substrate 8. By reducing the thermal resistance of the AlN substrate, the heating / cooling of the semiconductor laser element 10 by the TEC7 can be performed efficiently.

[0016] The quartz substrate 9 is formed, for example, to include a coplanar waveguide. The quartz substrate 9 has a third surface 9a as its lower surface and a fourth surface 9b as its upper surface. The third surface 9a faces the AlN substrate. The fourth surface 9b is the surface opposite to the third surface 9a. The quartz substrate 9 has a wiring 11 on the fourth surface 9b, opposite to the AlN substrate 8. The fourth surface 9b is, for example, a plane parallel to directions D1 and D2. As an example, the quartz substrate 9 may be transparent. The wiring 11 includes a high-frequency wiring 11b extending in one direction while maintaining a certain distance from a parallel ground wiring 11c. For example, the ground wiring 11c includes a first ground wiring portion 11d and a second ground wiring portion 11f, which houses a die 12, a chip 13, and a resistor 14. When viewed from the high-frequency wiring 11b, the second ground wiring portion 11f is located opposite to the first ground wiring portion 11d. In other words, the high-frequency wiring 11b is disposed between the first ground wiring portion 11d and the second ground wiring portion 11f in direction D2. Furthermore, the first ground wiring portion 11d and the second ground wiring portion 11f are interconnected between the high-frequency wiring 11b and the light output portion. The high-frequency wiring 11b extends, for example, from one end of the quartz substrate on the external terminal 3 side toward the other end of the quartz substrate on the light output portion side in the longitudinal direction D1 of the quartz substrate 9. The high-frequency wiring 11b extends in direction D1 at a certain distance from the ground wiring 11c. Thus, a coplanar waveguide is formed by the high-frequency wiring 11b extending on the fourth surface 9b at a certain distance from the adjacent ground wiring 11c. The quartz substrate 9 may also be formed with a microstrip line instead of a coplanar waveguide. Microstrip lines will be described later. Furthermore, the ground wiring 11c may not be a wiring extending in one direction like the high-frequency wiring 11b, but may be a wiring pattern with a wider width. The die 12 is, for example, a die capacitor. The die capacitor has parallel, plate-shaped electrodes. One electrode is connected to the fourth surface 9b of the quartz substrate 9. The other electrode is connected to a lead W1. The die capacitor is capable of storing charge between the two electrodes.

[0017] Leads W1, W2, W3, and W4 extend from die 12, first ground wiring portion 11d, high-frequency wiring portion 11b, and second ground wiring portion 11f, respectively. For example, the opto-semiconductor module 1 further includes lead W5 connecting die 12 and laser diode 10b, lead W6 connecting one end of resistor 14 and modulator 10c, and lead W7 connecting high-frequency wiring portion 11b and modulator 10c. The diameters of leads W1, W2, W3, W4, W5, W6, and W7 are, for example, 18 μm, 25 μm, or 50 μm. The diameters of leads W1, W2, W3, W4, W5, W6, and W7 can all be the same value or different values. Leads W1, W2, W3, W4, W5, W6, and W7 can also be strip wires instead of bond wires. Striplines, for example, do not have a circular cross-section like bond wires, but rather a flat cross-section. For instance, in striplines, the transverse width of the cross-section is more than twice the thickness of the cross-section.

[0018] Leads W2, W3, and W4 correspond to the first leads that connect wiring 11 and housing 2. For example, leads W2, W3, and W4 are connected to the transmission line 5 of housing 2. Lead W7 corresponds to the second lead that connects wiring 11 and semiconductor laser element 10. For example, the distance (shortest distance) between the connection point S1 of the first lead (each of leads W2, W3, and W4) on the fourth surface 9b and the semiconductor laser element 10 is longer than the distance (shortest distance) between the connection point S2 of the second lead (lead W7) on the fourth surface 9b and the semiconductor laser element 10. Connection point S1 is located on high-frequency wiring 11b or ground wiring 11c. More specifically, connection point S1 is located near one end of the quartz substrate on the side of external terminal 3. Connection point S2 is located on high-frequency wiring 11b. More specifically, connection point S2 is located near the other end of the quartz substrate on the side of light output section. For example, in direction D1, connection point S1 is located between external terminal 3 and connection point S2. Additionally, in direction D1, connection point S2 is located between connection point S1 and the light output section.

[0019] For example, both the second surface 8b of the AlN substrate 8 and the third surface 9a of the quartz substrate 9 are metallized. A semiconductor laser element 10 is mounted on the metallized second surface 8b. The quartz substrate 9, for example, has a hollowed-out part 9d on a surface 10d opposite to the AlN substrate 8 that exposes the semiconductor laser element 10. The shape of the quartz substrate 9 is concave when viewed from the stacking direction of the AlN substrate 8 and the quartz substrate 9, i.e., direction D3. Specifically, the hollowed-out part 9d is formed as a portion of one side of the light output portion 4 of the quartz substrate 9 recessed in direction D1. The hollowed-out part 9d is formed, for example, by a side surface 9f opposite to the semiconductor laser element 10. The side surface 9f is, for example, metallized. Thus, the ground wiring 11c of the quartz substrate 9 is electrically connected to the ground wiring of the second surface 8b of the AlN substrate 8, enabling the formation of a high-frequency return path. For example, the side surface 9f includes a first side surface 9g opposite to the semiconductor laser element 10 along direction D1 and a pair of second side surfaces 9h opposite to the semiconductor laser element 10 along direction D2. For example, by providing a grounding wiring on the second surface 8b below the high-frequency wiring 11b, a microstrip line can be formed on the high-frequency wiring 11b. For example, the first side surface 9g is a plane perpendicular to direction D1. For example, the second side surface 9h is a plane perpendicular to direction D2. When viewed from direction D3, three of the four directions surrounding the semiconductor laser element 10 are surrounded by the first side surface 9g and a pair of second side surfaces 9h, leaving only one of the four directions open (without any obstruction). That is, when viewed from direction D3, the semiconductor laser element 10 is arranged in an exposed portion contained within the quartz substrate 9. When operating, the semiconductor laser element 10 emits a beam in the open direction.

[0020] Figure 4 This diagram illustrates an example of the layer structure of the AlN substrate 8 and the quartz substrate 9. (See diagram below.) Figure 4 As shown, for example, the AlN substrate 8 may also have a metallized portion 8c on its second surface 8b. The quartz substrate 9 may also have a metallized portion 9k on its third surface 9a. The quartz substrate 9 can be fixed to the AlN substrate 8 by an adhesive 15. The adhesive 15 may be made of, for example, gold-tin (AuSn). In this case, the adhesive 15 is located between the metallized portion 8c of the AlN substrate 8 and the metallized portion 9k of the quartz substrate 9. The metallized portion 8c and the metallized portion 9k are formed, for example, by metal plating or vapor deposition. As described above, by connecting the metallized portion 8c to the ground wiring 11c via the metallized side surface 9f, the metallized portion 8c can be provided on the high-frequency wiring 11b as a ground wiring (ground layer).

[0021] Figure 5 These are diagrams illustrating other examples of the layer structures of the AlN substrate 8 and the quartz substrate 9. (Example...) Figure 5As shown, at least one of the AlN substrate 8 and the quartz substrate 9 may not have a metallized portion. The quartz substrate 9 can be directly fixed to the AlN substrate 8 by an adhesive 16. For example, the adhesive 16 may also be composed of silver (Ag) paste or ultraviolet (UV) curable resin.

[0022] Next, the effects obtained from the optical semiconductor module 1 of this embodiment will be explained. In the optical semiconductor module 1, as... Figure 3 As illustrated, the TEC7 has a temperature control surface 7b, and the AlN substrate 8 is mounted on the TEC7 in contact with the temperature control surface 7b. A quartz substrate 9 is mounted on the second surface 8b of the AlN substrate 8, opposite to the TEC7. The TEC7, AlN substrate 8, quartz substrate 9, and semiconductor laser element 10 are housed within the internal space S of the housing 2. Wiring 11 is formed on the fourth surface 9b of the quartz substrate 9, opposite to the AlN substrate 8. The TEC7 is mounted such that its heat dissipation surface 7a, opposite to the temperature control surface 7b, contacts the inner surface of the housing 2. For example, the inner surface of the housing 2 in contact with the heat dissipation surface 7a of the TEC7 is formed of a material with good thermal conductivity, such as a metal.

[0023] Leads W2, W3, and W4 connect the wiring 11 formed on the fourth surface 9b of the quartz substrate 9 to the housing 2. Lead W7 connects the wiring 11 to the semiconductor laser element 10. The thermal conductivity of the quartz substrate 9 is lower than that of the AlN substrate 8. That is, the thermal resistance of the quartz substrate 9 is greater than that of the AlN substrate 8. Therefore, the thermal resistance between the fourth surface 9b of the quartz substrate 9 and the second surface 8b of the AlN substrate 8, which are connected to the housing 2 via leads W2, W3, and W4, is greater than that of the AlN substrate 8, thus increasing the thermal resistance between the AlN substrate 8 and the housing 2. For example, the path of heat conduction from the housing 2 to the AlN substrate 8 passes through leads W2, W3, and W4, through wiring 11, and through leads W6 and W7, becoming a path through the semiconductor laser element 10 in direction D3. Alternatively, the following path exists: through lead W1, through the upper surface of die 12, through lead W5, and through the semiconductor laser element 10 in direction D3. Lead W1 is, for example, a single bond wire, while leads W2, W3, and W4 consist of five bond wires. Therefore, the heat flowing in and out via lead W1 is less than one-fifth less than the heat flowing out via leads W2, W3, and W4. Thus, the heat flow between the semiconductor laser element 10 and the housing 2 primarily occurs via leads W6 and W7, thereby suppressing the effect of TEC7 on the heating / cooling of the semiconductor laser element 10.

[0024] Figure 6 The optical semiconductor module 101 is shown as a comparative example. Optical semiconductor module 101 and... Figure 1Compared to the optical semiconductor module 1 of the illustrated embodiment, it does not have a quartz substrate 9, and a semiconductor laser element 10, a die 12, and a chip 13 are mounted on the second surface 8b of an AlN substrate 8. In this case, since the leads W2 (W3, W4) extending from the housing 2 are thermally connected to the TEC7 via the AlN substrate 8, it is impossible to suppress the flow of heat from the housing 2 to the temperature control surface 7b of the TEC7 via the thermally conductive AlN substrate 8. For example, when cooling the semiconductor laser element 10 by making the temperature of the temperature control surface 7b of the TEC7 lower than the external temperature of the optical semiconductor module 101, heat flows into the housing 2 via the leads W2 (W3, W4), so the TEC7 requires additional power to dissipate this heat. In addition, for example, when heating the semiconductor laser element 10 by making the temperature of the temperature control surface 7b of the TEC7 higher than the external temperature of the optical semiconductor module 101, heat flows out to the housing 2 via the leads W2 (W3, W4), so the TEC7 requires additional power to supply this heat. Thus, the outflow and inflow of heat between the leads W2 (W3, W4) and the housing 2 increases the power consumption of TEC7, thereby reducing the efficiency of temperature control of the semiconductor laser element 10.

[0025] In contrast, such as Figure 3 As shown, when the leads W2 (W3, W4) extending from the housing 2 are thermally connected to the temperature control surface 7b of the TEC7 via the quartz substrate 9 and the AlN substrate 8, the thermal conductivity of the quartz substrate 9 is less than 1 / 100 of that of the AlN substrate 8. Therefore, compared to the comparative example, the heat outflow and inflow between the housing 2 and the temperature control surface 7b of the TEC7 can be significantly suppressed. Thus, the increase in power consumption of the TEC7 can be suppressed, and the temperature control of the semiconductor laser element 10 can be efficiently performed. For example, in Figure 6 In the process of cooling the semiconductor laser element 10 by absorbing heat from the temperature control surface 7b of the TEC7, if the thermal resistance between the housing 2 and the temperature control surface 7b is small (when the temperature of the housing is higher than the target temperature of the semiconductor laser element), then more current needs to flow through the TEC7 to absorb the heat flowing in from the housing 2. For example, in Figure 3 In the process of cooling the semiconductor laser element 10 by absorbing heat from the temperature control surface 7b of TEC7, and with Figure 6 In contrast, the thermal resistance between housing 2 and temperature control surface 7b is greater. Therefore, the heat flowing into housing 2 is significantly reduced, decreasing the current required for temperature control of TEC7. This, in turn, improves the efficiency (electrical efficiency) of temperature control for the semiconductor laser element 10.

[0026] As described above, the quartz substrate 9 and the semiconductor laser element 10 are arranged side by side on the second surface 8b of the AlN substrate 8, opposite to the TEC7. Therefore, since the semiconductor laser element 10 is mounted on the second surface 8b of the AlN substrate 8, which has a thermal conductivity more than 100 times greater than that of the quartz substrate 9, temperature control (cooling and heating) of the semiconductor laser element 10 via the AlN substrate 8 through the TEC7 can be performed more efficiently.

[0027] The quartz substrate 9 can be fixed to the AlN substrate 8 via adhesive 15 or adhesive 16. In this case, the quartz substrate 9, which has a lower thermal conductivity than the AlN substrate 8, can be fixed to the AlN substrate 8 via adhesive 15 or adhesive 16.

[0028] The distance between the connection point S1 of each of leads W2, W3, and W4 on the fourth surface 9b and the semiconductor laser element 10 is longer than the distance between the connection point S2 of lead W7 on the fourth surface 9b and the semiconductor laser element 10. Therefore, by making the distance between the connection point S1 of each of leads W2, W3, and W4 connected to the housing 2 and the semiconductor laser element 10 longer than the distance between the connection point S2 of lead W7 and the semiconductor laser element 10, the thermal resistance between the housing 2 and the temperature control surface 7b can be further increased. Moreover, the outflow and inflow of heat between the housing 2 and the temperature control surface 7b of the TEC7 can be suppressed more reliably.

[0029] The thickness T1 of the AlN substrate 8 can be 600 μm or less, and the thickness T2 of the quartz substrate 9 can be 50 μm or more. In this case, by making the thickness T1 of the AlN substrate 8 600 μm or less, the thermal resistance of the AlN substrate 8 to heat conduction along the direction D3 can be further reduced, and temperature control of the semiconductor laser element 10 via the TEC7 through the AlN substrate 8 can be performed more efficiently. By making the thickness T2 of the quartz substrate 9 50 μm or more, the thermal resistance of the quartz substrate 9 to heat conduction along the direction D3 can be further increased, and heat outflow and inflow via the quartz substrate 9 relative to the housing 2 can be suppressed. Therefore, temperature control of the semiconductor laser element 10 can be performed more efficiently. For example, by making the thickness T1 of the AlN substrate 8 600 μm or less and the thickness T2 of the quartz substrate 9 50 μm or more, the thermal resistance between the housing 2 and the semiconductor laser element 10 can be reliably greater than the thermal resistance between the semiconductor laser element 10 and the temperature control surface 7b. Thus, for example, it is possible to reduce heat other than that generated by the heating of the semiconductor laser element 10 that flows into the temperature control surface 7b from the housing 2.

[0030] The embodiments of the optical semiconductor module disclosed herein have been described above. However, the present invention is not limited to the above embodiments. That is, those skilled in the art will readily recognize that the present invention can be modified and altered in various ways within the scope of the spirit described in the claimed scope. For example, in the above embodiments, an example of mounting a die 12, a chip 13, and a resistor 14 on the wiring 11 has been described. However, the types and quantities of components mounted on the wiring 11 are not limited to the above examples and can be appropriately modified.

[0031] In the above embodiments, an example of an EML (Electro-Mechanical Laser) semiconductor laser element 10 was described. However, the semiconductor laser element may also be a semiconductor laser element other than an EML. In the above embodiments, an example of an AlN substrate for the first substrate 8 and a quartz substrate for the second substrate 9 mounted on the first substrate 8 was described. However, the material of the first substrate may also be a material other than AlN. For example, the first substrate may also be a metal plate formed of a metallic material. For example, the first substrate may be a copper plate. Copper has a thermal conductivity of approximately 400 W / m·K, which is greater than that of AlN. The first substrate may also be a substrate formed of silicon nitride (Si3N4) (silicon nitride substrate). The thermal conductivity of silicon nitride is, for example, 85 W / m·K. The second substrate may also be made of alumina, epoxy glass, or polyimide. For example, alumina has a thermal conductivity of 32 W / m·K, which is less than 1 / 5 smaller than that of AlN. For example, epoxy glass has a thermal conductivity of approximately 0.5 W / m·K, which is even smaller than that of alumina. For example, in the case of polyimide, a material with a lower thermal conductivity than epoxy glass can be selected. For example, when a silicon nitride substrate is used as the first substrate and an alumina substrate is used as the second substrate, the thermal conductivity of the first substrate is approximately 2.6 times that of the second substrate. That is, the first and second substrates can also be substrates other than AlN substrates or quartz substrates, and the materials of the first and second substrates are not particularly limited.

Claims

1. An optical semiconductor module, wherein, have: A temperature control element having a temperature control surface; A first substrate has a first surface and a second surface opposite to the first surface, and is placed on the temperature control element such that the first surface is in contact with the temperature control surface; A semiconductor laser element is mounted on the second surface; The second substrate has a third surface and a fourth surface opposite to the third surface, and is placed on the second surface of the first substrate; and The housing contains the temperature control element, the first substrate, the second substrate, and the semiconductor laser element. The second substrate has wiring on the fourth surface. The wiring is connected to the housing via a first lead and to the semiconductor laser element via a second lead. The thermal conductivity of the second substrate is lower than that of the first substrate. The second substrate is disposed side-by-side with the semiconductor laser element on the second surface of the first substrate. The second substrate has an exposed portion in which the semiconductor laser element is disposed when viewed from a direction perpendicular to the fourth surface.

2. The optical semiconductor module according to claim 1, wherein, The second substrate is fixed to the first substrate by an adhesive.

3. The optical semiconductor module according to claim 1, wherein, The shortest distance between the connection point of the first lead on the second surface and the semiconductor laser element is longer than the shortest distance between the connection point of the second lead on the second surface and the semiconductor laser element.

4. The optical semiconductor module according to claim 1, wherein, The thickness of the first substrate is less than 600 μm. The thickness of the second substrate is 50 μm or more.

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