Semiconductor laser device and heat sink used therein

A semiconductor laser device has a heat sink of which multiple laminated plates are constituted and a semiconductor laser element mounted on upper surface of the heat sink. The heat sink has a channel in which a coolant flows inside thereof. The heat sink includes a channel-forming plate portion that forms the channel and a mounting plate portion that forms an upper surface of the heat sink that comes into contact with the channel. The mounting plate portion is made of material having a thermal expansion coefficient, which is closer to that of the semiconductor laser element than that of the channel-forming plate portion.

The present invention contains subject matter related to Japanese Patent Application No. JP2005-115118 filed in the Japanese Patent Office on Apr. 12, 2005, the entire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor laser device and a heat sink used therein.

2. Description of Related Art

A semiconductor laser device in a range from several watts to a few tens watts has often used a water-cooled system therein in order to implement high-power and high-reliability. Micro channels are well known as heat sink structures because they increase heat-removing efficiency.

Fine interior channel structures such as micro channels are typically formed by etching a pattern onto thin metal plates and laminating the plates together. Diffusion bonding or brazing is generally used to bond the thin metal plates together. As Copper plates are commonly used as the thin metal plates because they have excellent thermal conductivity and easy machinability.

Copper has a thermal expansion coefficient of, 17*10−6/k while a substrate of gallium arsenide, which is generally used in a high-power semiconductor laser device, has a thermal expansion coefficient of, 5.9*10−6/k. This large difference between the thermal expansion coefficients causes a stress to occur when a semiconductor laser chip is fixed to a heat sink with solder and then they are cooled to the normal temperature.

It is known that, turning on electricity through the semiconductor laser chip with any stress occurring in the chip, accelerates the number of crystalline defects, thereby reducing the reliability of the laser.

In order to solve the problem, a soft solder, for example, indium solder is used or a sub mount made of copper tungsten or the like, which has a thermal expansion coefficient close to that of the semiconductor laser chip, is inserted into a position between the heat sink and the laser chip (see Japanese Patent Application Publication No. 2004-186527).

SUMMARY OF THE INVENTION

If the indium solder is used for bonding the semiconductor laser chip, the solder may weaken due to alloyed indium solder when turning on electricity through the semiconductor laser chip for a long time and hence, reliability of the chip deteriorates. If the sub mount is inserted into the position between the heat sink and the chip, heat-removing efficiency decreases based on the thermal resistance in the sub mount.

Heat sinks using micro channels have a structure such that by increasing a velocity of water flowing just under the chip, the heat removing efficiency is improved However, corrosion of the metal material may occur at this point, thereby causing water to leak therefrom.

If the semiconductor laser device is a stack type, such that multiple sets of water-cooled members are stacked, any corrosion that occurs electrically due to any difference in potential of the two adjacent heat sinks, thereby causes a part of the heat sink that is near the water channel to decrease in thickness due to corrosion and water to leak therefrom.

It is desirable to present a semiconductor laser device and a heat sink used therein that can prevent any stress from occurring without decreasing heat-removing efficiency.

According to an embodiment of the present invention, there is a semiconductor laser device having a heat sink including multiple laminated plates and a semiconductor laser element mounted on an upper surface of the heat sink. The heat sink has a channel in which a coolant, for example, water flows inside thereof. The heat sink includes a channel-forming plate portion that forms the channel and a mounting plate portion that forms an upper surface of the heat sink that comes into contact with the channel. The mounting plate portion is made of material having a thermal expansion coefficient, which is closer to that of the semiconductor laser element than that of the channel-forming plate portion.

According to another embodiment of the present invention, there is a heat sink including multiple laminated plates and a channel in which a coolant flows inside thereof. A semiconductor laser element is mounted on a surface of the heat sink. The heat sink includes a channel-forming plate portion that forms the channel and a mounting plate portion that forms an upper surface of the heat sink that comes into contact with the channel. The mounting plate portion is made of material having a thermal expansion coefficient, which is closer to that of the semiconductor laser element than that of the channel-forming plate portion.

According to any embodiments of the invention, heat generated when driving the semiconductor laser element is transferred to the heat sink. The heat sink having a channel in which a coolant, for example, water, flows inside thereof removes the heat received from the semiconductor laser element. This allows the semiconductor laser element to be cooled.

In the heat sink, the mounting plate portion on which the semiconductor laser element is mounted is made of material having a thermal expansion coefficient, which is closer to that of the semiconductor laser element than that of the channel-forming plate portion. This allows any stress generated in the semiconductor laser element to be reduced when expanding and contracting the semiconductor laser element and the mounting plate portion based on the heat generated from driving the semiconductor laser element.

Thus, according to any embodiments of the invention, any stress generated in the semiconductor laser element can be reduced, and hence, reliability of the semiconductor laser element can be improved. Since a whole upper surface of the heat sink can be made of a single type of material in any embodiments of the invention, it is possible to prevent a decrease in heat-removing efficiency based on the thermal resistance.

Since the mounting plate portion on which the semiconductor laser element is mounted is made of material, for example, insulating material, having a thermal expansion coefficient, which is closer to that of the semiconductor laser element, in the embodiment of the heat sink, it is possible to avoid any corrosion occurring on a part of the heat sink that is in contact with the channel, thus preventing water from leaking therefrom.

The concluding portion of this specification particularly points out and directly claims the subject matter of the present invention. However those skilled in the art will best understand both the organization and method of operation of the invention, together with further advantages and objects thereof, by reading the remaining portions of the specification in view of the accompanying drawing(s) wherein like reference characters refer to like elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe embodiments of semiconductor laser device and heat sink according to the invention with reference to the accompanying drawings.

(A Configuration of First Embodiment of Semiconductor Laser Device According to the Invention)

FIG. 1is an expanded view of a first embodiment of each of the semiconductor laser device and the heat sink used therein according to the invention for illustrating a configuration thereofFIG. 2is a sectional side elevation of the first embodiment of the semiconductor laser device according to the invention for illustrating a configuration thereof.

A first embodiment of the semiconductor laser device1A contains a heat sink2having a fine channel structure of micro channel type and a semiconductor laser chip3mounted thereon. This embodiment of the heat sink2includes laminated thin plates. In this embodiment, the heat sink2includes the following plates as five layers: a laser-chip-mounting plate4as a first layer; radiation-fin-forming plates5,6as second and fourth layers; and channel-forming plates7,8as third and fifth layers. The plates are bonded together using diffusion bonding or the like to form the heat sink2.

The laser-chip-mounting plate4is an example of the mounting plate portion. The laser-chip-mounting plate4is a thin plate on which the semiconductor laser chip3is mounted. The laser-chip-mounting plate4is made of material having a thermal expansion coefficient, which is closer to that of material of the semiconductor laser chip3. If the semiconductor laser chip3is made of substrate of gallium arsenide that is generally used, the laser-chip-mounting plate4is made of metallic material such as Kovar or copper-tungsten alloy or a ceramic such as aluminum nitride or silicon carbide.

If the laser-chip-mounting plate4is made of ceramic that is an insulating material, a metal layer4mis formed on a surface thereof using rolled gold so that the metal layer4mand an electrode formed on a lower surface of the semiconductor laser chip3can be connected electrically.

The radiation-fin-forming plate5is an example of the channel-forming plate portion. The radiation-fin-forming plate5is made of, for example, material having higher thermal conductivity. The radiation-fin-forming plate5has a radiation-fin-forming channel9therein.

The radiation-fin-forming plate6is an example of the channel-forming plate portion. The radiation-fin-forming plate6is made of, for example, material having higher thermal conductivity, similar to a case of the radiation-fin-forming plate5. The radiation-fin-forming plate6has a radiation-fin-forming channel10, a coolant-supply-channel-forming opening11, and a coolant-discharge-channel forming opening12therein. In this case, if the laser-chip-mounting plate4is made of ceramic, the radiation-fin-forming plates5,6are made of copper or the like that has excellent thermal conductivity and is capable of diffusion-bonding to the ceramic.

The radiation-fin-forming channel9is formed in the radiation-fin-forming plate5so that it passes through the radiation-fin-forming plate5in a vertical direction thereof. Plural radiation fins9fare arranged so as to be positioned under the semiconductor laser chip3and are projected in a line toward the inside of the channel9and hence, a coolant flows in a space between the radiation fins9fin the radiation-fin-forming channel9.

The radiation-fin-forming channel10is formed in the radiation-fin-forming plate6so that it passes through the radiation-fin-forming plate6in a vertical direction thereof. Multiple radiation fins10fare arranged so as to be positioned under the semiconductor laser chip3are projected in a line toward the inside of the channel10and hence, a coolant flows in a space between the radiation fins10fin the radiation-fin-forming channel10. The radiation-fin-forming channel10lengthens to form a coolant-supply channel10ifor supplying a coolant to the radiation fins10f.

The coolant-supply-channel forming opening11and the coolant-discharge-channel forming opening12are respectively formed in the radiation-fin-forming plate6so that they pass through the radiation-fin-forming plate6in a vertical direction thereof. These openings11,12are separately formed from the radiation-fin-forming channel10in the radiation-fin-forming plate6.

The channel-forming plate7is an example of the channel-forming plate portion. The channel-forming plate7is made of the same material as that of the laser-chip-mounting plate4. The channel-forming plate7has a circulation channel13, a coolant-supply-channel forming opening14, and a coolant-discharge-channel forming opening15therein.

The channel-forming plate8is an example of the channel-forming plate portion. The channel-forming plate8is made of the same material as that of the laser-chip-mounting plate4, similar to a case of the channel-forming plate7. The channel-forming plate8has a coolant-supply-channel forming opening16and a coolant-discharge-channel forming opening17therein. For example, if the laser-chip-mounting plate4is made of ceramic, the channel-forming plates7,8are made of ceramic.

The circulation channel13is formed in the channel-forming plate7so that it passes through the channel-forming plate7in a vertical direction thereof. The circulation channel13is formed so that it can be connected to the radiation-fin-forming channel9in the radiation-fin-forming plate5and the radiation-fin-forming channel10in the radiation-fin-forming plate6.

The coolant-supply-channel forming opening14is formed in the channel-forming plate7so that it passes through the channel-forming plate7in a vertical direction thereof. The coolant-supply-channel forming opening14is formed relative to its position and shape so that it can be connected to the coolant-supply-channel forming opening11in the radiation-fin-forming plate6and the coolant-supply channel10i.

The coolant-discharge-channel forming opening15is formed in the channel-forming plate7so that it passes through the channel-forming plate7in a vertical direction thereof. The coolant-discharge-channel forming opening15is formed relative to its position and shape so that it can be connected to the radiation-fin-forming channel9in the radiation-fin-forming plate5and the coolant-discharge-channel forming opening12in the radiation-fin-forming plate6.

The coolant-supply-channel forming opening16is formed in the channel-forming plate8so that it passes through the channel-forming plate8in a vertical direction thereof. The coolant-supply-channel forming opening16is formed so that it can be connected to the coolant-supply-channel forming opening11in the radiation-fin-forming plate6. The coolant-discharge-channel forming opening17is formed in the channel-forming plate8so that it passes through the channel-forming plate8in a vertical direction thereof. The coolant-discharge-channel forming opening17is formed so that it can be connected to the coolant-discharge-channel forming opening12in the radiation-fin-forming plate6.

To form the heat sink2, the laser-chip-mounting plate4, the radiation-fin-forming plate5, the channel-forming plate7, the radiation-fin-forming plate6, and the channel-forming plate8are bonded to each other using any diffusion bonding with the respective plates being stacked in turn.

This enables the radiation-fin-forming channel9in the radiation-fin-forming plate5and the radiation-fin-forming channel10in the radiation-fin-forming plate6to be connected to each other through the circulation channel13in the channel-forming plate7. This also enables the coolant-discharge-channel forming opening15in the channel-forming plate7, the coolant-discharge-channel forming opening12in the radiation-fin-forming plate6, and the coolant-discharge-channel forming opening17in the channel-forming plate8to be connected to each other to form a discharge channel18. The discharge channel18is connected to the radiation-fin-forming channel9in the radiation-fin-forming plate5.

This further enables the coolant-supply-channel forming opening14in the channel-forming plate7, the coolant-supply-channel forming opening11in the radiation-fin-forming plate6, and the coolant-supply-channel forming opening16in the channel-forming plate8to be connected to each other to form a supply channel19. The supply channel19is connected to the coolant-supply channel10iof the radiation-fin-forming channel10in the radiation-fin-forming plate6.

Thus, in the heat sink2, formed is a channel20for a coolant in which the supply channel19is connected to the discharge channel18via the radiation-fin-forming channel10in the radiation-fin-forming plate6, the circulation channel13in the channel-forming plate7, and the radiation-fin-forming channel9in the radiation-fin-forming plate5.

Since the heat sink2has the five-layer-structure as described above, the laser-chip-mounting plate4as the first layer, the uppermost layer, the channel-forming plate7, as the third layer, and the channel-forming plate8as the fifth layer, the lowermost layer are made of one and the same material. The radiation-fin-forming plate5as the second layer and the radiation-fin-forming plate6as the fourth layer are made of one and the same material. This allows the heat sink to have a configuration that is laminated in a symmetrical manner.

Thus, even when the temperature of the plates return to the normal temperature after they have been diffusion-bonded at high temperature, it is difficult for the heat sink2to be bent due to any differences in the thermal expansion coefficients of the laser-chip-mounting plate4as the first layer, the channel-forming plates7,8as the third and fifth layers, and the radiation-fin-forming plates5,6as the second and fourth layers.

The semiconductor laser chip3is an example of the semiconductor laser element. The semiconductor laser chip3has a structure such that multiple light-emitting parts are arranged in a line. The laser-chip-mounting plate4of the heat sink2is mounted to the semiconductor laser chip3with solder.

When the laser-chip-mounting plate4is made of ceramic, the metal layer4mis formed on an upper surface of the laser-chip-mounting plate4as described above. The metal layer4mis electrically connected to the electrodes, which are not shown, provided on the undersurface of the semiconductor laser chip3. Electrodes provided on an upper surface of the semiconductor laser chip3, which are not shown, and the metal layer4mare respectively connected to any separate driver devices, which are not shown, electrically by bonding wires or the like.

The semiconductor laser chip3mounted on the laser-chip-mounting plate4is positioned above the multiple radiation fins9fformed in the radiation-fin-forming plate5and the multiple radiation fins10fformed in the radiation-fin-forming plate6.

Since the laser-chip-mounting plate4of the heat sink2is made of material having a thermal expansion coefficient, which is closer to that of the semiconductor laser chip3, as described above, the laser-chip-mounting plate4and the semiconductor laser chip3have an almost identical rate of expansion and contraction by heat. This prevents any stress from occurring in the semiconductor laser chip3when the heat sink2bonds the semiconductor laser chip3with solid solder such as alloy of gold and tin.

Thus, according to this embodiment, the heat sink2can bond the semiconductor laser chip3with solid solder such as alloy of gold and tin, thereby avoiding any deterioration in the solder even if electricity flows for long time. This enables the semiconductor laser device to maintain reliability for long time.

(Description of the First Embodiment of the Semiconductor Laser Device According to the Invention)

The following describes the first embodiment of the semiconductor laser device1A.

In the semiconductor laser device1A, the supply channel and the discharge channel18are connected to a circulation device, which is not shown, for supplying and discharging a coolant, so-called “chiller”.

In the heat sink2, when the supply channel19receives the coolant, the coolant flows through the channel20. The supply channel19is connected to the discharge channel18via the radiation-fin-forming channel10in the radiation-fin-forming plate6, the circulation channel13in the channel-forming plate7, and the radiation-fin-forming channel9in the radiation-fin-forming plate5.

Thus, the coolant received by the supply channel19flows through the coolant-supply channel10iin the radiation-fin-forming plate6to the radiation-fin-forming channel10. In the radiation-fin-forming channel10, the coolant flows in a space between the radiation fins10fto the radiation-fin-forming channel9in the radiation-fin-forming plate5via the circulation channel13in the channel-forming plate7. In the radiation-fin-forming channel9, the coolant flows in a space between the radiation fins9fto the discharge channel18from which the coolant is discharged.

The semiconductor laser chip3receives an electric signal from the driver device, which is not shown, and converts it to an optical signal to output. Any heat occurring at driving the semiconductor laser chip3is transferred to the heat sink2through the laser-chip-mounting plate4. Since the coolant flows in the channel20of the heat sink2, as described above, the heat transferred from the semiconductor laser chip3can be removed. This enables the semiconductor laser chip3to be cooled.

In the heat sink2of this embodiment, the radiation fins9f,10fare positioned under the mounted semiconductor laser chip3. The radiation fins9f,10fcan increase the area in contact with the coolant. The radiation fins9f,10fcan generate turbulent flows. This enables any heat transferred from the semiconductor laser chip3to be efficiently removed.

Since the coolant flows fast under the semiconductor laser chip3in the heat sink2of micro channel type, it is possible to implement higher heat-removing efficiency because fast-flowing coolant is in contact with the undersurface of the laser-chip-mounting plate4on which the semiconductor laser chip3is mounted.

In this embodiment, the laser-chip-mounting plate4on which the semiconductor laser chip3is mounted and the undersurface which is in contact with the coolant is made of ceramic. The channel-forming plates7,8are also made of ceramic. This prevents deterioration of the metal material by corrosion thereof from occurring at the points where the fast-flowing coolant is in contact with the undersurface of the laser-chip-mounting plate4and prohibits water from being leaked therefrom.

Further, since in this embodiment, the radiation-fin-forming plates5,6are made of a metallic material that has good thermal conductivity, such as copper, it is possible to increase the heat-removing efficiency. If the radiation-fin-forming plates5,6are further provided with a suitable corrosion proof region, the whole of the heat sink2can prevent the coolant from leaking.

In this embodiment, the laser-chip-mounting plate4on which the semiconductor laser chip3is mounted is made of ceramic. The channel-forming plate7between the radiation-fin-forming plates5,6and the channel-forming plate8under the radiation-fin-forming plate6are made of ceramic. This configuration prohibits current for driving the semiconductor laser chip3from flowing in the radiation-fin-forming plates5,6made of metallic material. This prevents corrosion caused by stray current by any potential difference due to internal resistance from occurring.

In the heat sink2of this embodiment, it is possible to bond the semiconductor laser chip3to the upper surface of the heat sink2directly with solid solder. This enables thermal resistance and electric resistance to decrease in contrast with a case where any sub mount made of another material is inserted into a mounted position of the semiconductor laser chip3.

In this embodiment, the laser-chip-mounting plate4, the upper surface of the heat sink2, has a relatively low thermal conductivity in contrast with copper or the like of which the radiation-fin-forming plates5,6are made. If the laser-chip-mounting plate4is made of the same material and has the same thickness as the laser-chip-mounting plate4when the sub mount is used, it is possible to decrease at least the total of thermal resistance.

(A Configuration of Second Embodiment of Semiconductor Laser Device According to the Invention)

FIG. 3is a sectional side elevation of a second embodiment of a semiconductor laser device according to the invention for illustrating a configuration thereof.

This semiconductor laser device1B in the second embodiment is a semiconductor laser device a of stacked type in which, for example, two semiconductor laser devices1A in the first embodiment are stacked in a vertical direction thereof.

It is to be noted that although two semiconductor laser devices have been stacked in this embodiment, this invention is not limited to this. For example, twenty semiconductor laser devices can be stacked, thereby implementing any high-power semiconductor laser device.

The semiconductor laser device1B in this embodiment has an upper heat sink2A and a lower heat sink2B each having a fine channel structure of micro channel type. The semiconductor laser chips3A and3B are mounted on heat sinks2A and2B respectively.

FIG. 4is an expanded view of the second embodiment of the invention for illustrating a configuration of upper sink2A.

The upper heat sink2A has the same configuration as that of the first embodiment of the heat sink2shown inFIG. 1and includes laminated thin plates. In this embodiment, the upper heat sink2A includes the following plates as layers: a laser-chip-mounting plate4A as a first layer; radiation-fin-forming plates5A,6A as second and fourth layers; and channel-forming plates7A,8A as third and fifth layers. The plates are bonded to each other using the diffusion bonding or the like to form the upper heat sink2A.

The laser-chip-mounting plate4A is made of a material, for example, ceramic, having a thermal expansion coefficient, which is closer to that of material of the semiconductor laser chip3A. If the laser-chip-mounting plate4A is made of ceramic that is an insulating material, a metal layer4Am is formed on a surface thereof using rolled gold so that the metal layer4Am and electrodes formed on a lower surface of the semiconductor laser chip3A can be connected electrically to each other.

The radiation-fin-forming plates5A and6A are made of material having higher thermal conductivity, for example, copper. The radiation-fin-forming plate5A has a radiation-fin-forming channel9A therein. The radiation-fin-forming plate6A has a radiation-fin-forming channel10A, a coolant-supply-channel-forming opening11A, and a coolant-discharge-channel-forming opening12A therein. In this case, the radiation-fin-forming channel9A, the radiation-fin-forming channel10A, the coolant-supply-channel-forming opening11A, and the coolant-discharge-channel-forming opening12A are formed in the respective plates similar to those of the first embodiment of the heat sink2shown inFIG. 1.

The channel-forming plates7A,8A are made of same material as that of the laser-chip-mounting plate4A. The channel-forming plate7A has a circulation channel13A, a coolant-supply-channel-forming opening14A, and a coolant-discharge-channel-forming opening15A therein. The channel-forming plate8A has a coolant-supply-channel-forming opening16A and a coolant-discharge-channel-forming opening17A therein. In this case, the circulation channel13A, the coolant-supply-forming opening14A, the coolant-discharge-channel-forming opening15A, the coolant-supply-channel-forming opening16A and the coolant-discharge-channel-forming opening17A are formed in the respective plates similar to those of the first embodiment of the heat sink2shown inFIG. 1.

In the upper heat sink2A, the semiconductor laser chip3A is mounted with solder. A spacer plate21is bonded to the laser-chip-mounting plate4A on a portion thereof except for a portion where the semiconductor laser chip3A is mounted. The spacer plate21is made of the same material, for example, ceramic, as that of the laser-chip-mounting plate4A. A metal layer21mis formed on an upper surface of the spacer plate21using rolled gold or the like.

When the laser-chip-mounting plate4A is made of ceramic, the metal layer4Am is formed on an upper surface of the laser-chip-mounting plate4A as described above. The metal layer4Am is electrically connected to the electrodes, which are not shown, on the undersurface of the semiconductor laser chip3A. Electrodes provided on an upper surface of the semiconductor laser chip3A, which are not shown, and the metal layer21mare connected electrically by bonding wires22.

FIG. 5is an expanded view of the second embodiment of the invention for illustrating a configuration of the lower heat sink2B.

The lower heat sink2B has the same configuration as that of the first embodiment of the heat sink2except for a connection part thereof to the upper heat sink2A and includes laminated thin plates.

In this embodiment, the lower heat sink2B includes the following plates as layers: a laser-chip-mounting plate4B as a first layer; radiation-fin-forming plates5B,6B as second and fourth layers; and channel-forming plates7B,8B as third and fifth layers. The plates are bonded to each other using the diffusion bonding or the like to form the lower heat sink2B.

The laser-chip-mounting plate4B is made of a material, for example, ceramic, having a thermal expansion coefficient, which is closer to that of material of the semiconductor laser chip3B. The laser-chip-mounting plate4B has a coolant-supply-channel-forming opening23and a coolant-discharge-channel-forming opening24therein.

The coolant-supply-channel-forming opening23and the coolant-discharge-channel-forming opening24are formed in the laser-chip-mounting plate4B so that they pass through the laser-chip-mounting plate4B in a vertical direction thereof. The coolant-supply-channel-forming opening23is positioned so that it can be connected to the coolant-supply-channel-forming opening16A of the upper heat sink2A. The coolant-discharge-channel-forming opening24is positioned so that it can be connected to the coolant-discharge-channel-forming opening17A of the upper heat sink2A.

If the laser-chip-mounting plate4B is made of ceramic that is an insulating material, a metal layer4Bm is formed on a surface thereof using rolled gold so that the metal layer4mand electrodes formed on a lower surface of the semiconductor laser chip3B can be connected electrically to each other. It is to be noted that the coolant-supply-channel-forming opening23and the coolant-discharge-channel-forming opening24are formed so that they pass through the metal layer4Bm.

The radiation-fin-forming plates5B,6B are made of material having higher thermal conductivity, for example, copper. The radiation-fin-forming plate5B has a radiation-fin-forming channel9B and a coolant-supply-channel-forming opening25therein. The radiation-fin-forming plate6B has a radiation-fin-forming channel10B, a coolant-supply-channel-forming opening11B, and a coolant-discharge-channel-forming opening12B therein.

The radiation-fin-forming channel9B is formed in the radiation-fin-forming plate5B so that it passes through the radiation-fin-forming plate5B in a vertical direction thereof. Multiple radiation fins9fare arranged so as to be positioned under the semiconductor laser chip3B and are projected in a line toward the inside of the channel9B and hence, the coolant flows in a space between the radiation fins9fin the radiation-fin-forming channel9B. The radiation-fin-forming channel9B is positioned so that it can be connected to the coolant-discharge-channel-forming opening24in the laser-chip-mounting plate4B.

The radiation-fin-forming channel10B is formed in the radiation-fin-forming plate6B so that it passes through the radiation-fin-forming plate6B in a vertical direction thereof. Multiple radiation fins10fare arranged so as to be positioned under the semiconductor laser chip3and are projected in a line toward the inside of the channel10B and hence, the coolant flows in a space between the radiation fins10fin the radiation-fin-forming channel10B. The radiation-fin-forming channel10B lengthens to form a coolant-supply channel10ifor supplying a coolant to the radiating fins10f.

The coolant-supply-channel-forming opening11B and the coolant-discharge-channel-forming opening12B are respectively formed in the radiation-fin-forming plate6B so that they pass through the radiation-fin-forming plate6B in a vertical direction thereof. These openings11B,12B are separately formed from the radiation-fin-forming channel10B in the radiation-fin-forming plate6B.

The channel-forming plates7B,8B are made of same material, for example, ceramic, as that of the laser-chip-mounting plate4B. The channel-forming plate7B has a circulation channel13B, a coolant-supply-channel-forming opening14B, and a coolant-discharge-channel-forming opening15B therein. The channel-forming plate8B has a coolant-supply-channel-forming opening16B and a coolant-discharge-channel-forming opening17B therein.

The circulation channel13B is formed in the channel-forming plate7B so that it passes through the channel-forming plate7B in a vertical direction thereof. The circulation channel13B is formed so that it can be connected to the radiation-fin-forming channel9B in the radiation-fin-forming plate5B and the radiation-fin-forming channel10B in the radiation-fin-forming plate6B.

The coolant-supply-channel forming opening14B is formed in the channel-forming plate7B so that it passes through the channel-forming plate7B in a vertical direction thereof. The coolant-supply-channel forming opening14B is formed relative to its position and shape so that it can be connected to the coolant-supply-channel forming opening25in the radiation-fin-forming plate5B, the coolant-supply-channel forming opening11B in the radiation-fin-forming plate6B, and the coolant-supply channel10i.

The coolant-discharge-channel forming opening15B is formed in the channel-forming plate7B so that it passes through the channel-forming plate7B in a vertical direction thereof. The coolant-discharge-channel forming opening15B is formed relative to its position and shape so that it can be connected to the radiation-fin-forming channel9B in the radiation-fin-forming plate5B and the coolant-discharge-channel forming opening12B in the radiation-fin-forming plate6B.

The coolant-supply-channel forming opening16B is formed in the channel-forming plate8B so that it passes through the channel-forming plate8B in a vertical direction thereof. The coolant-supply-channel forming opening16B is formed so that it can be connected to the coolant-supply-channel forming opening11B in the radiation-fin-forming plate6B. The coolant-discharge-channel forming opening17B is formed in the channel-forming plate8B so that it passes through the channel-forming plate8B in a vertical direction thereof. The coolant-discharge-channel forming opening17B is formed so that it can be connected to the coolant-discharge-channel forming opening12bin the radiation-fin-forming plate6B.

In the lower heat sink2B, if the laser-chip-mounting plate4B on which the semiconductor laser chip3B is mounted is made of ceramic and the channel forming plates7B,8B are made of ceramic, to make the heat sink have a configuration that is laminated in a symmetrical manner, the radiation-fin-forming plates5B,6B are made of material having excellent thermal conductivity, for example, copper that is diffusion-bonded to the ceramic.

In the lower heat sink2B, the semiconductor laser chip3B is mounted to the laser-chip-mounting plate4B with solder or the like. A spacer plate26is bonded on the laser-chip-mounting plate4B on a portion thereof except for a portion where the semiconductor laser chip3B is mounted. The spacer plate26is made of the same material, for example, ceramic, as that of the laser-chip-mounting plate4B. A metal layer26mis formed on an upper surface of the spacer plate26using rolled gold or the like.

The spacer plate26has a coolant-supply-channel forming opening27and a coolant-discharge-channel forming opening28therein. The coolant-supply-channel forming opening27is formed so that it can be connected to the coolant-supply-channel forming opening23in the laser-chip-mounting plate4B. The coolant-discharge-channel forming opening28is formed so that it can be connected to the coolant-discharge-channel forming opening24in the laser-chip-mounting plate4B.

When the laser-chip-mounting plate4B is made of ceramic, the metal layer4Bm is formed on an upper surface of the laser-chip-mounting plate4B as described above. The metal layer4Bm is electrically connected to the electrodes, which are not shown, on the undersurface of the semiconductor laser chip3B. Electrodes on an upper surface of the semiconductor laser chip3B, which are not shown, and the metal layer26mare connected electrically by bonding wires29.

To form the upper heat sink2A, the laser-chip-mounting plate4A, the radiation-fin-forming plate5A, the channel-forming plate7A, the radiation-fin-forming plate6A, and the channel-forming plate8A are bonded to each other using any diffusion bonding with the respective plates being stacked in turn. In the upper heat sink2A, the spacer plate21is bonded to the laser-chip-mounting plate4A.

This enables the radiation-fin-forming channel9A in the radiation-fin-forming plate5A and the radiation-fin-forming channel10A in the radiation-fin-forming plate6A to be connected to each other through the circulation channel13A in the channel-forming plate7A in the upper heat sink2A. This also enables the coolant-discharge-channel forming opening15A in the channel-forming plate7A, the coolant-discharge-channel forming opening12A in the radiation-fin-forming plate6A, and the coolant-discharge-channel forming opening17A in the channel-forming plate8A to be connected to each other to form a discharge channel18A. The discharge channel18A is connected to the radiation-fin-forming channel9A in the radiation-fin-forming plate5A.

This further enables the coolant-supply-channel forming opening14A in the channel-forming plate7A, the coolant-supply-channel forming opening11A in the radiation-fin-forming plate6A, and the coolant-supply-channel forming opening16A in the channel-forming plate8A to be connected to each other to form a supply channel19A. The supply channel19A is connected to the coolant-supply channel10iof the radiation-fin-forming channel10A in the radiation-fin-forming plate6A.

To form the lower heat sink2B, the laser-chip-mounting plate4B, the radiation-fin-forming plate5B, the channel-forming plate7B, the radiation-fin-forming plate6B, and the channel-forming plate8B are bonded to each other using any diffusion bonding with the respective plates being stacked in turn. In the lower heat sink2B, the spacer plate26is bonded to the laser-chip-mounting plate4B.

This enables the radiation-fin-forming channel9B in the radiation-fin-forming plate5B and the radiation-fin-forming channel10B in the radiation-fin-forming plate6B to be connected to each other through the circulation channel13B in the channel-forming plate7B in the lower heat sink2B.

This also enables the coolant-discharge-channel forming opening28in the spacer plate26, the coolant-discharge-channel forming opening24in the laser-chip-mounting plate4B, the radiation-fin-forming channel9B in the radiation-fin-forming plate5B, the coolant-discharge-channel forming opening15B in the channel-forming plate7B, the coolant-discharge-channel forming opening12B in the radiation-fin-forming plate6B, and the coolant-discharge-channel forming opening17B in the channel-forming plate8B to be connected to each other to form a discharge channel18B.

This further enables the coolant-supply-channel forming opening27in the spacer plate26, the coolant-supply-channel forming opening23in the laser-chip-mounting plate4B, the coolant-supply-channel forming opening25in the radiation-fin-forming plate5B, the coolant-supply-channel forming opening14B in the channel-forming plate7B, the coolant-supply-channel forming opening11B in the radiation-fin-forming plate6B, and the coolant-supply-channel forming opening16B in the channel forming plate8B to be connected to each other to form a supply channel19B. The supply channel19B is connected to the radiation-fin-forming channel10B in the radiation-fin-forming plate6B via the coolant-supply-channel forming opening14B in the channel-forming plate7B and the coolant-supply channel10iof the radiation-fin-forming plate6B.

Thus, the upper heat sink2A and the lower heat sink2B are bonded with the discharge channels18A,18B and the supply channels19A,19B being sealed by O-ring30. This enables the upper heat sink2A and the lower heat sink2B to be connected to each other, thereby forming a channel31.

Since the upper heat sink2A includes the five-layer-structure as described above, the laser-chip-mounting plate4A as the first layer, the uppermost layer thereof, the channel-forming plate7A as the third layer, and the channel-forming plate8A as the fifth layer, the lowermost layer thereof are made of one and the same material. The radiation-fin-forming plate5A as the second layer and the radiation-fin-forming plate6A as the fourth layer are made of the same material. This allows the heat sink2A to have a configuration that is laminated in a symmetrical manner.

Since the lower heat sink2B includes the five-layer-structure as described above, the laser-chip-mounting plate4B as the first layer, the uppermost layer thereof, the channel-forming plate7B as the third layer, and the channel-forming plate8B as the fifth layer, the lowermost layer thereof are made of the same material. The radiation-fin-forming plate5B as the second layer and the radiation-fin-forming plate6B as the fourth layer are made of one and the same material. This allows the lower heat sink2B to have a configuration that is laminated in a symmetrical manner.

Thus, even when the temperature of the plates return to the normal temperature after they have been diffusion-bonded at high temperature, it is difficult for the upper and lower heat sinks2A,2B to be bent due to any differences in the thermal expansion coefficients of the respective plates constituting the layers.

Relative to electric connection of the semiconductor laser chip3in the semiconductor laser device1B, in the upper heat sink2A, the metal layer21mof the spacer plate21that is connected to the upper electrodes, which is not shown, of the semiconductor laser chip3A is connected to the power supply of the driver device32or the like. In the lower heat sink2B, the metal layer4Bm of the laser-chip-mounting plate4B that is connected to the lower electrodes, which is not shown, of the semiconductor laser chip3B is also connected to the power supply of the driver device32or the like.

Further, the metal layer4Am of the laser-chip-mounting plate4A that is connected to the lower electrodes, which is not shown, of the semiconductor laser chip3A in the upper heat sink2A and the metal layer26mof the spacer plate26that is connected to the upper electrodes, which is not shown, of the semiconductor laser chip3B in the lower heat sink2B are connected to each other by bonding wires33.

This enables electric current to flow in the upper and lower semiconductor laser chips3A,3B in series from the driver device32.

The laser-chip-mounting plate4A of the upper heat sink2A is made of material having a thermal expansion coefficient, which is closer to that of the semiconductor laser chip3A. This prevents any stress from occurring in the semiconductor laser chip3A when the upper heat sink2A bonds the semiconductor laser chip3A with solid solder such as alloy of gold and tin. Thus, according to this embodiment, it is possible to avoid any deterioration in the solder even if electricity flows for long time. This enables the semiconductor laser device to maintain reliability for long time.

Similarly, the laser-chip-mounting plate4B of the lower heat sink2B is made of material having a thermal expansion coefficient, which is closer to that of the semiconductor laser chip3B. This prevents any stress from occurring in the semiconductor laser chip3B when the lower heat sink2B bonds the semiconductor laser chip3B with solid solder such as alloy of gold and tin. Thus, according to this embodiment, it is possible to avoid any deterioration in the solder even if electricity flows for long time. This enables the semiconductor laser device to maintain reliability for long time.

(Description of the Second Embodiment of the Semiconductor Laser Device According to the Invention)

The following will describe the second embodiment of the semiconductor laser device1B.

In the semiconductor laser device1B, the supply channel19B and the discharge channel18B in the lower heat sink2B are connected to a circulation device, which is not shown, for supplying and discharging a coolant.

In the lower heat sink2B, when the supply channel19B receives the coolant, a portion of the coolant flows toward the radiation-fin-forming channel10B in the radiation-fin-forming plate6B via the coolant-supply channel10itherein. In the radiation-fin-forming channel10B, the coolant flows in a space between the radiation fins10fto the radiation-fin-forming channel9B in the radiation-fin-forming plate5B via the circulation channel13B in the channel-forming plate7B. In the radiation-fin-forming channel9B, the coolant flows in a space between the radiation fins9fto the discharge channel18B from which the coolant is discharged.

When the supply channel19B receives the coolant, the other portion of the coolant passes through the supply channel19B to reach the supply channel19A in the upper heat sink2A. When the supply channel19A receives the coolant, this portion of the coolant flows toward the radiation-fin-forming channel10A in the radiation-fin-forming plate6A via the coolant-supply channel10itherein. In the radiation-fin-forming channel10A, the coolant flows in a space between the radiation fins10fto the radiation-fin-forming channel9A in the radiation-fin-forming plate5A via the circulation channel13A in the channel-forming plate7A. In the radiation-fin-forming channel9A, the coolant flows in a space between the radiation fins9ffrom the discharge channel18A to the discharge channel18A of the lower heat sink2B from which the coolant is discharged.

Each of the semiconductor laser chips3A,3B receive an electric signal from the driver device32and converts it to an optical signal to output it. It is to be noted that a lens, which is not shown, condenses the optical signal irradiated from any of the semiconductor laser chips3A,3B to make incident on an optical fiber, for example, thereby obtaining an optical signal with high-power.

Any heat occurring at driving the semiconductor laser chip3A is transferred to the upper heat sink2A through the laser-chip-mounting plate4A. Since the coolant flows in the channel31, as described above, in the upper heat sink2A, the heat transferred from the semiconductor laser chip3A can be removed. This enables the semiconductor laser chip3A to be cooled.

Similarly, any heat occurring at driving the semiconductor laser chip3B is almost transferred to the lower heat sink2B through the laser-chip-mounting plate4B. Since the coolant flows in the channel31, as described above, in the lower heat sink2B, the heat transferred from the semiconductor laser chip3B can be removed. This enables the semiconductor laser chip3B to be cooled.

In this embodiment, the coolant flows fast under the semiconductor laser chips3A and/or3B in the upper and lower heat sinks2A,2B of micro channel type and hence, it is possible to increase heat-removing efficiency.

In the upper heat sink2A, the laser-chip-mounting plate4A which is contact with the semiconductor laser chip3A is mounted and the undersurface of which is in contact with the coolant is made of ceramic as well as the channel-forming plates7A,8A are made of ceramic. This prevents deterioration of the metal material by corrosion thereof from occurring at the points where the fast-flowing coolant is in contact with the laser-chip-mounting plate and prohibits water from being leaked therefrom.

Further, in this embodiment, the radiation-fin-forming plates5A,6A are made of metallic material that has good thermal conductivity such as copper, and hence, it is possible to increase heat-removing efficiency. If the radiation-fin-forming plates5A,6A are further provided with a suitable corrosion proof region, the whole of the upper heat sink2A can prevent the coolant from leaking.

In the lower heat sink2B, similar to a case of the upper heat sink2A, the laser-chip-mounting plate4B on which the semiconductor laser chip3B is mounted and the undersurface which is in contact with the coolant is made of ceramic as well as the channel-forming plates7B,8B are made of ceramic. This prevents deterioration of the metal material by corrosion thereof from occurring at the points where the fast-flowing coolant is in contact with the undersurface of the laser-chip-mounting plate and prohibits water from being leaked therefrom.

Further, in this embodiment, the radiation-fin-forming plates5B,6B are made of metallic material that has good thermal conductivity such as copper, and hence, it is possible to enhance heat-removing efficiency. If the radiation-fin-forming plates5B,6B are further provided with a suitable corrosion proof region, the whole of the lower heat sink2B can prevent the coolant from leaking.

The upper heat sink2A and the lower heat sink2B are bonded with the discharge channels18A,18B and the supply channels19A,19B being sealed by O-ring30. This may prevent the coolant from leaking out of the whole of heat sink.

In the upper heat sink2A, the laser-chip-mounting plate4A on which the semiconductor laser chip3A is mounted is made of ceramic that is insulating material and the metal layer4Am on the laser-chip-mounting plate4A is electrically connected to the semiconductor laser chip3A. The channel-forming plate7A provided between the radiation-fin-forming plates5A,6A and the channel-forming plate8A provided under the radiation-fin-forming plate6A are made of ceramic that is insulating material. This configuration prohibits current for driving the semiconductor laser chip3A from flowing in the radiation-fin-forming plates5A,6A made of metallic material.

Similarly, in the lower heat sink2B, the laser-chip-mounting plate4B on which the semiconductor laser chip3B is mounted is made of ceramic that is insulating material and the metal layer4Bm on the laser-chip-mounting plate4B is electrically connected to the semiconductor laser chip3B. The channel-forming plate7B between the radiation-fin-forming plates5B,6B and the channel-forming plate8B under the radiation-fin-forming plate6B are made of ceramic that is insulating material. This configuration prohibits current for driving the semiconductor laser chip3B from flowing in the radiation-fin-forming plates5B,6B made of metallic material.

This enables electric potential of each of the radiation-fin-forming plates5A,6A of the upper heat sink2A and the radiation-fin-forming plates5B,6B of the upper heat sink2A is separated from each of the semiconductor laser chips3A,3B and fixed by the supplied coolant. This allows the respective radiation-fin-forming plates made of metallic material that is in contact with the coolant to become equipotential, thereby preventing electric corrosion due to any potential difference between the upper and lower heat sinks from occurring.

Thus, in this embodiment, it is possible to prevent the electric corrosion from occurring at the metallic plates without purifying the coolant, thereby managing the coolant easily, in contrast with a where the coolant, water, is purified and electric conductivity is decreased, thereby preventing the electric corrosion by potential difference of the upper and lower heat sinks from occurring.

In this embodiment, if the laser-chip-mounting plates4A,4B are made of ceramic and power is supplied to each of the semiconductor laser chips3A,3B through the metal layers4Am,4Bm provided on the laser-chip-mounting plates4A,4B, large amount of current can flow in such the thin metal layers4Am,4Bm, so that operation voltage of the semiconductor laser device is increased based on a voltage drop due to it.

If so, in this embodiment, the metal layers4Am,4Bm are made using rolled gold and thus, thickness thereof is increased so that no voltage drop may occur. Further, in this embodiment, the laser-chip-mounting plates4A,4B, and the channel-forming plates7A,8A,7B,8B can be made of ceramic and a metal layer can be formed on side surfaces of the upper and lower heat sinks2A,2B so that they can be connected to each other.

Additionally, the upper and lower heat sinks2A,2B can be connected to each other via any opening made in the upper and lower heat sinks2A and2B. If the upper and lower heats sinks2A and2B are connected, the radiation-fin-forming plates5A,5B,6A,6B that are in contact with the coolant become equipotential with the semiconductor laser chips3A,3B, thereby generating any potential difference between the upper and lower heat sinks2A,2B. This embodiment prevents deterioration of the metal material by corrosion thereof from occurring at points where the fast-flowing coolant is in contact with the undersurface of the laser-chip-mounting plate and prohibits water from being leaked therefrom when the laser-chip-mounting plates4A,4B are made of ceramic.

Still further, in this embodiment, the laser-chip-mounting plates4A,4B can be made of metallic material with electric conductivity. If so, the laser-chip-mounting plate4A,4B and the channel-forming plates7A,7B,8A,8B are made of material having higher electropositive potential than those of the radiation-fin-forming plates5A,5B,6A,6B. Since the laser-chip-mounting plate4A,4B can be made of metallic material, the radiation-fin-forming plates5A,5B,6A,6B that are contacted with the coolant become equipotential with the semiconductor laser chips3A,3B, thereby generating any potential difference between the upper and lower heat sinks2A,2B. In this embodiment, however, the laser-chip-mounting plates4A,4B are made of material having higher electropositive potential than those of the radiation-fin-forming plates5A,5B,6A,6B, so that the radiation-fin-forming plates5A,5B,6A,6B can become sacrifice electrodes, thereby preventing any corrosion from occurring at the lower portions of the laser-chip-mounting plates4A,4B to which fast-flown coolant is connected. In this case, inner sides of the radiation-fin-forming plates5A,5B,6A,6B can be corroded. If so, in this embodiment, the channel lasts longer than that of a case where the heat sink is made of metal only and hence, the portions of radiation-fin-forming plates5A,5B,6A,6B that are connected with the channels lasts longer so that resistance of the radiation-fin-forming plates5A,5B,6A,6B is increased to make current decreased, thereby enabling a degree of corrosion in the radiation-fin-forming plates5A,5B,6A,6B and the like to be reduced.

It is preferable to apply these embodiments to a high-power semiconductor laser device that is used for processing a welding, a disconnecting or the like.