EP2433343A1

EP2433343A1 - Heat sink for pulsed high-power laser diode

Info

Publication number: EP2433343A1
Application number: EP10721017A
Authority: EP
Inventors: Werner Herden; Hans-Jochen Schwarz; Wolfgang Pittroff
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2009-05-22
Filing date: 2010-05-18
Publication date: 2012-03-28
Also published as: JP2012527754A; DE102009026413A1; WO2010133572A1; US8891567B2; JP5843756B2; US20120106582A1

Abstract

The invention relates to a semiconductor laser module (100) comprising a substrate (110) and at least one semiconductor laser (120) arranged on the substrate (110), wherein the substrate (110) has a layer construction comprising at least one first primary layer (111), which realizes a thermal contact with the semiconductor laser (120). According to the invention, the semiconductor laser (120) is designed in such a way that the semiconductor laser emits heat pulses having a minimum specific heat of approximately 3 mJ per mm2, preferably approximately 5 mJ per mm2, and having a pulse duration of approximately 100 µs to approximately 2000 µs, and the primary layer (111) has a layer thickness (d1) that is between approximately 200 µm and approximately 2000 µm, preferably between approximately 400 µm and approximately 2000 µm.

Description

description

title

HEAT SINKS FOR PULSED HIGH-PERFORMANCE LASER DIODE

State of the art

The invention relates to a semiconductor laser module having a substrate and having at least one semiconductor laser arranged on the substrate, wherein the substrate has a layer structure consisting of at least one first primary layer, which realizes a thermal contact to the semiconductor laser.

The invention further relates to a production method for such a semiconductor laser module.

Disclosure of the invention

It is an object of the present invention to improve a semiconductor laser module and a manufacturing method of the type mentioned in that effective cooling of the semiconductor laser is given in a pulsed operation with a cost-effective structure.

This object is achieved in the semiconductor laser module of the type mentioned in the present invention in that the semiconductor laser is designed so that it emits heat pulses with a minimum specific heat amount of about 3 millijoules (mJ) per square millimeter (mm ² ), preferably about 5 mJ / mm ² , and having a pulse duration of about 100 microseconds (μs) to about 2000 μs, and that the primary layer has a layer thickness of between about 200 microns (μm) and about 2000 microns, preferably between about 400 microns and about 2000 microns. According to investigations by the Applicant, in such a coordination between the semiconductor laser and the primary layer provided for its cooling, optimum dissipation of the thermal energy released during the pulsed operation of the semiconductor laser is provided. In particular, due to the layer thickness of the primary layer selected according to the invention, it is ensured that at least a predominant proportion of a heat pulse emitted by the semiconductor laser can be absorbed by the primary layer, so that efficient and at the same time cost-effective cooling of the semiconductor laser is possible in its pulsed mode. In particular, in contrast to conventional systems, the principle according to the invention does not require any layer thicknesses for the primary layer which amount to significantly more than two millimeters, so that the semiconductor laser module according to the invention can be manufactured inexpensively.

In a preferred embodiment of the semiconductor laser module according to the invention, the pulse frequency of the heat pulses is less than approximately 400 Hertz (Hz), preferably less than approximately 100 Hz, so that the heat "buffered" in the primary layer can be dissipated to a heat sink during the pulse pauses cooled advantageous and is then ready again for fast absorption of a heat pulse generated by the semiconductor laser.

Pulse durations and pulse pauses of the aforementioned magnitude occur, in particular, when using the semiconductor laser for the optical pumping of other laser systems, especially of passively Q-switched laser systems, which are e.g. be used in laser spark plugs of internal combustion engines for generating laser ignition pulses. Therefore, the semiconductor laser module according to the invention is particularly suitable as a pump light source for laser-based ignition systems of internal combustion engines, in particular of motor vehicles or stationary large gas engines.

A further improved derivation of the heat pulses generated by the semiconductor laser is given according to an advantageous embodiment of the invention, when a second primary layer is provided, which is in thermal contact with the semiconductor laser, in particular with a surface of the semiconductor laser, which faces away from the first primary layer , In order to reduce thermo-mechanical stresses during the operation of the semiconductor laser, a further advantageous embodiment provides for the primary layer and a secondary layer of the substrate connected to the primary layer to be designed, in particular matched to one another, such that a resulting coefficient of thermal expansion of the two layers is in the range a surface facing the semiconductor laser is approximately equal to the thermal expansion coefficient of the semiconductor laser. Particularly preferably, the deviation of the respective thermal expansion coefficients from each other is at most about 20 percent, preferably about 10 percent.

Particularly preferably, the primary layer comprises copper and / or gold and / or silver and / or further materials with comparable heat capacity and comparable thermal conductivity. Ductile materials are preferably used to form the primary layer to enable efficient microstructuring of the surface facing the semiconductor laser, with the aim of producing plastically deformable microstructures on the surface which, upon assembly of the components, provide improved positive engagement and hence lower thermal resistance ,

As a further solution of the object of the present invention, a method according to claim 7 is given. The method according to the invention for producing a semiconductor laser module having a substrate and having at least one semiconductor laser arranged on the substrate, wherein the substrate has a layer structure consisting of at least one first primary layer, which realizes thermal contact with the semiconductor laser, is characterized by the following steps:

Producing a primary layer having a layer thickness of between about 200 μm and about 2000 μm, preferably between about 400 μm and about 2000 μm, connecting the semiconductor laser to the primary layer. - A -

In order to ensure a preferably low-heat form-fitting transition of an epitaxial side of the semiconductor laser to the primary layer, it is proposed in a further variant of the method according to the invention that the step of connecting the semiconductor laser to the primary layer is carried out by:

Hard or soft soldering with a solder layer thickness that is less than about 40 μm, preferably about 10 μm,

- Alloying the components using a liquid metal layer, in particular a gallium indium tin eutectic, friction welding, bonding by means of ultrasound, thermal bonding,

Clamping, in particular with insertion of a liquid metal layer, in particular a gallium indium tin eutectic, between the components.

In a further advantageous embodiment of the method according to the invention, it is provided that prior to the joining step, at least one surface of the two components to be joined is subjected to microstructuring which generates regular and / or randomly distributed, preferably plastically deformable, microstructures on the surface. This advantageously provides the possibility of realizing a tolerance compensation with respect to the positive connection of the surfaces to be joined, because the plastically deformable microstructures are plastically deformed when the semiconductor laser is connected to the primary layer and can thus compensate for irregularities in the surfaces involved. This results in an optimized positive connection and thus a lower thermal resistance of the connection between the semiconductor laser and the primary layer.

A further improved connection between the semiconductor laser and the primary layer according to the invention is given by the fact that the surfaces to be joined together are coated with a gold layer or a gold-nickel layer. Alternatively to the microstructuring of the primary layer or of the semiconductor laser itself, the surfaces of which can also be coated with a suitable microstructurable material, such as a gold layer, and the microstructure according to the invention is produced in the gold layer, for example by electronic removal with pulsed current.

Other features, applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures of the drawing. All described or illustrated features, alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing.

In the drawing shows:

FIG. 1a shows a first embodiment of the invention

Semiconductor laser module during an active phase of the pulse operation of the semiconductor laser,

FIG. 1b shows the semiconductor laser module according to FIG. 1a with a deactivated one

Semiconductor laser,

2a, 2b show a further embodiment of the semiconductor laser module according to the invention in different operating modes,

3a, 3b show a further embodiment of the semiconductor laser module according to the invention in different operating modes,

FIG. 4 shows yet another embodiment of the invention

Semiconductor laser module,

FIG. 5 schematically shows a side view of an embodiment of the semiconductor laser module according to the invention before the semiconductor laser is connected to the primary layer receiving it, and FIG. 6 shows a simplified flowchart of an embodiment of the method according to the invention.

FIG. 1a schematically shows a side view of a first embodiment of the semiconductor laser module 100 according to the invention in a first operating state. The semiconductor laser module 100 has a semiconductor laser 120 connected to a substrate 110. In the first operating state, preferably in a pulsed mode, the semiconductor laser 120 generates laser radiation 200, which i.a. for optical pumping of other laser systems (not shown) can be used.

The substrate 110 serves, in addition to the mechanical support of the semiconductor laser 120, primarily for the temperature control, in particular cooling, of the semiconductor laser 120.

For this purpose, the substrate 110 has a primary layer 111 receiving the semiconductor laser 120, which is in good thermal contact with the semiconductor laser 120. The primary layer 111 is connected to a secondary layer 112 on its surface facing away from the semiconductor laser 120. The secondary layer 112 in turn is disposed on a heat sink 113, which is formed for example as a heat sink and / or as a Peltier element and / or as a heat pipe ("heat pipe").

The primary layer 111 is preferably formed of silver and / or gold and / or copper, while the secondary layer 112 is preferably made of a ceramic material, such as e.g. Aluminum nitride, AIN, is formed or also comprises material systems of copper and diamond.

The semiconductor laser 120 is optimized for use in pulsed operation, in particular pulse operation as required for optically pumping other laser devices (not shown). For example, the semiconductor laser 120 can emit pump light pulses 200, with which optical devices with passive Q-switching are optically pumped. Such systems are preferably suitable for use in laser-based ignition systems of internal combustion engines, for example of motor vehicles. According to the invention, the semiconductor laser 120 is designed to emit heat pulses having a minimum specific heat amount of about 3 mJ per mm ² , preferably about 5 mJ per mm ² , the pulse duration being from about 100 μs to about 2000 μs.

A thickness d1 of the primary layer 111 is selected according to the invention to be about 200 μm to about 2000 μm, preferably between about 400 μm and about 2000 μm.

In the configuration according to the invention described above, according to investigations by the Applicant, an optimized derivation of the heat pulses generated by the semiconductor laser 120 during its pulsed operation into the primary layer 111, cf. the unspecified arrows in Figure 1a. In particular, in the choice of the layer thickness d1 according to the invention, it is advantageously ensured that the primary layer 111 can absorb a complete heat pulse emitted by the semiconductor laser 120 before it reaches the secondary layer 112 arranged underneath in FIG. 1a. That is, the primary layer 111 according to the invention operates as a kind of local buffer for the heat pulses to be dissipated by the semiconductor laser 120.

With the relatively long pulse pauses, which result from a preferred pulse frequency of the heat pulses of less than about 400 Hz, preferably less than about 100 Hz, it is ensured that the heat is removed from the primary layer 111 via the secondary layer 112 to the heat sink 113 can. This operating state is shown in FIG. 1 b, cf. the unspecified arrows that indicate the heat transfer during a pulse break from the primary layer 111 to the heat sink 113.

In comparison with conventional semiconductor laser modules, which are usually designed for continuous wave (cw) applications, the semiconductor laser module 100 according to the invention has a particularly cost-effective design, since the principle according to the invention provides an intermediate storage of the heat pulses generated by the semiconductor laser 120 in the primary layer 111, combined with a subsequent, during a pulse pause, heat dissipation 111 via the secondary layer 112 to the heat sink 113th This means that the semiconductor laser module 100 according to the invention can be operated with comparatively high pulse powers, without at the same time requiring considerably more extensive cooling due to a corresponding formation of the substrate 110, as is known from conventional systems.

As a result, economical production of the semiconductor laser module 100 according to the invention is possible. In particular, for the secondary layer 112, a material may be chosen that has a lower thermal conductivity than the material of the primary layer 111, because the heat conduction through the secondary layer 112, the relatively long pulse pauses are used.

FIGS. 2a, 2b depict another embodiment 100a of the semiconductor laser module according to the invention. The semiconductor laser module 100a has two primary layers 111, 111 ', whereby a heat storage capacity of the primary layers 111, 111' is increased compared to the embodiment according to FIGS. 1a, 1b. This variant of the invention enables operation of the semiconductor laser 120 with higher pulse powers.

FIG. 2 a once again illustrates a first operating state of the semiconductor laser module 100 a with an active semiconductor laser 120 which emits a laser pulse 200. The resulting heat pulse is illustrated by the outgoing from the semiconductor laser 120 in the primary layers 111, 111 'arrows.

FIG. 2b shows a further, corresponding to a pulse pause, operating state of the semiconductor laser module 100a according to the invention, in which the semiconductor laser 120 is deactivated and the previously (Figure 2a) in the primary layers 111, 111 'registered heat via the semiconductor laser 120, the secondary layer 112 and the heat sink 113 is removed.

3a, 3b show a further embodiment of the semiconductor laser module according to the invention, in which a combination of a primary layer 111, 111 'and a secondary layer 112, 112' assigned to it is provided on both sides of the semiconductor laser 120. The heat sink 113 is arranged in the present embodiment on the left in Figure 3a end faces of the substrate layers 111, 112, 111 ', 112'.

FIG. 3a in turn indicates an operating state in which a heat pulse generated by the semiconductor laser 120 is stored in the primary layers 111, 111 ', while FIG. 3b shows the derivation of the previously stored heat pulse from the primary layers 111, 111' via the secondary layers 112, 112 '. to the heat sink 113 illustrated.

FIG. 4 shows a further particularly advantageous embodiment of the semiconductor laser module 100 according to the invention, in which the primary layer 111 and the secondary layer 112 are constituents of a direct copper bonded, DCB, substrate whose primary layer 111 consists of copper and has a layer thickness of approximately 400 μm, and its secondary layer 112 consists of aluminum nitride (AIN), which in the present case has a thickness of approximately 630 μm.

In order to achieve an optimized adaptation of the substrate receiving the semiconductor laser 120, a further layer 114 is assigned to the layer structure 111, 112, so that a configuration 111, 112, 114 of materials relative to the secondary layer 112 results with regard to their thermal expansion coefficient. The thermal expansion coefficient in the region of the contact surface to the semiconductor laser 120 resulting from the layer structure 111, 112, 114 is preferably matched to the coefficient of thermal expansion of the semiconductor laser 120 in order to prevent damage to the semiconductor laser 120 due to thermo-mechanical stresses occurring during the heating.

Instead of the substrate variant with a DCB substrate depicted in FIG. 4, it is also possible to use a DC40 substrate which has a layer structure 111, 112, 114 comprising a copper layer 111, a DC40 (copper-diamond) layer 112 and a copper layer 114 , Compared to the DCB substrate variant, this has the advantage that the DC40 material having secondary layer 112 due to their higher thermal conductivity allows better heat spreading than a layer containing aluminum nitride. The copper layers 111, 114 may preferably be bonded to the DC40 material 112, for example by thermocompression bonding, or soldered. The DC40 layer 112 may, for example, have a layer thickness of about 400 μm.

FIG. 5 schematically shows a side view of a semiconductor laser module according to the invention before the semiconductor laser 120 is connected to the primary layer 111 receiving it.

As can be seen from FIG. 5, the primary layer 111 has, on its surface 111a facing the semiconductor laser 120, a microstructure 111b which, for example, consists of regular or randomly distributed microstructures in the form of trenches and / or turrets and / or sponge-like structures. The microstructuring 111b preferably comprises plastically deformable microstructures which are plastically deformed when the semiconductor laser 120 is joined to the primary layer 111 and thereby ensure an optimized positive connection between the contact surfaces of the components 111, 120, which advantageously also reduces the thermal resistance of this connection.

In a preferred variant of the invention, the microstructures 111b comprise elements such as e.g. Turret whose largest dimension is perpendicular to the surface 111a in the range of about 5 microns to about 100 microns. The diameter of the turrets is preferably less than about 10 microns, more preferably less than about 2 microns, and an average distance between adjacent turrets should be less than about 4 microns, preferably about 0.5 microns.

FIG. 6 shows a simplified flow diagram of an embodiment of the method according to the invention. In a first step 300, the primary layer 111 according to the invention is produced with a layer thickness d1 (FIG. 1a) of approximately 200 μm to approximately 2000 μm, preferably approximately 400 μm to approximately 2000 μm. In a subsequent step 305, the microstructure 111b described above with reference to FIG. 5 is applied to at least one of the surfaces 111 a of the connection partners 111, 120.

Subsequently, the semiconductor laser 120 and the primary layer 111 are connected to one another, which takes place in step 310 and can be realized, for example, by clamping the components 111, 120. In this case, a sufficiently high pressure is exerted in order to deform the plastically deformable microstructures 111b, so that possibly existing surface defects of the connection partners 111, 120 are compensated.

Particularly preferably, the connection 310 of the semiconductor laser 120 to the primary layer 111, 111 'can also take place by:

- Alloying the components 111, 111 ', 120 using a liquid metal layer, in particular a gallium indium tin eutectic, friction welding, bonding by means of ultrasound, thermal bonding,

Clamping, in particular with insertion of a liquid metal layer, in particular a gallium indium tin eutectic, between the components 111, 111 ', 120.

The alloying of the components 111, 111 ', 120 preferably takes place at temperatures of less than or equal to approximately 150 ^° C.

A further improved connection between the semiconductor laser 120 and the primary layer 111 is given when the surface 111 a (FIG. 5) of the primary layer 111 is coated with a gold layer or a gold-nickel layer or the like.

In addition to the above-described microstructure 305 of the surface 111a (FIG. 5) of the primary layer 111, a conventional one can also be used Surface treatment done with the aim of the lowest possible surface roughness, for example by diamond milling or the like. The above-described measures according to the invention for connecting the surfaces or for reducing the respective thermal resistances can also be applied to one another or combined with one another on the layers 111, 112, 113.

Claims

claims

Claims 1. A semiconductor laser module (100) having a substrate (110) and at least one semiconductor laser (120) arranged on the substrate (110), the substrate (110) having a layer structure consisting of at least one first primary layer (111) having a thermal Contacting the semiconductor laser (120), characterized in that the semiconductor laser (120) is adapted to emit heat pulses having a minimum specific heat amount of about 3 mJ per mm ² , preferably about 5 mJ per mm ² , and with one Pulse duration of about 100 microseconds to about 2000 microseconds, and that the primary layer (111) has a layer thickness (dl) which is between about 200 microns and about 2000 microns, preferably between about 400 microns and about 2000 microns.

2. The semiconductor laser module (100) according to claim 1, characterized in that a pulse frequency of the heat pulses is less than about 400 Hz, preferably less than about 100 Hz.

3. The semiconductor laser module (100) according to any one of the preceding claims, characterized in that a second primary layer (111 ') is provided which is in thermal contact with the semiconductor laser (120), in particular with a surface of the semiconductor laser (120) of the first primary layer (111) is remote.

4. The semiconductor laser module (100) according to any one of the preceding claims, characterized in that a secondary layer (112, 112 ') on one of the semiconductor laser (120) facing away from the surface of the primary layer (111, 111') and thermally arranged with the primary layer (111 , 111 ') is connected.

5. The semiconductor laser module (100) according to claim 4, characterized in that the primary layer (111, 111 ') and the secondary layer (112, 112') are formed such that a resulting thermal expansion coefficient of the two layers (111, 112; In the Area of a semiconductor laser (120) facing surface approximately with the coefficient of thermal expansion of the semiconductor laser (120) coincides.

6. The semiconductor laser module (100) according to any one of the preceding claims, characterized in that the primary layer (111, 111 ') comprises copper and / or gold and / or silver.

7. A method for producing a semiconductor laser module (100) having a

Substrate (110) and with at least one semiconductor laser (120) arranged on the substrate (110), wherein the substrate (110) has a layer construction consisting of at least one first primary layer (111) which makes thermal contact with the semiconductor laser (120) characterized by the following steps:

Producing (300) a primary layer having a layer thickness (dl) which is between about 200 μm and about 2000 μm, preferably between about 400 μm and about 2000 μm,

Connecting (310) the semiconductor laser (120) to the primary layer

(100).

8. The method according to claim 7, characterized in that the step of

Connecting (310) the semiconductor laser (120) to the primary layer (111, 111 ') is effected by:

Hard or soft soldering with a solder layer thickness which is less than about 40 microns, preferably about 10 microns, - alloying together of the components (111, 111 ', 120)

Use of a liquid metal layer, in particular a gallium

Indium-tin eutectic,

friction welding,

Bonding by means of ultrasound, thermal bonding,

Clamping, in particular with insertion of a liquid metal layer, in particular a gallium indium tin eutectic, between the

Components (111, 111 ', 120).

9. Method according to one of claims 7 to 8, characterized in that before joining (310) at least one surface (111a) of the two components (111, 111 ', 120) is subjected to a microstructure (305) which regularly and / or or randomly distributed, preferably plastically deformable, microstructures (111b) on the surface (111a).

10. The method according to claim 9, characterized in that the

Microstructures (111b) have trenches and / or turrets and / or sponge-like structures whose maximum extent perpendicular to the surface (111a) in the range of about 5 microns to about 100 microns.

11. The method according to claim 9 or 10, characterized in that in the

Connecting (310) the components to be connected (111, 111 ', 120) are pressed together so that the microstructures (111 b) deform plastically.

12. The method according to any one of claims 9 to 11, characterized in that the surfaces to be joined together (111a) are coated with a gold layer or a gold-nickel layer.