Patent Application
20250202190
The present invention relates to a stacked laser arrangement and a method for generating such a laser array.
For various applications, including virtual reality or augmented reality, laser diodes are used to generate visual information, the light from which is guided to the user's eye via suitable optics. Various laser diodes are used for the red, green and blue color range by placing them on a corresponding carrier and, if necessary, aligning them precisely with the optics.
The conventional manufacturing techniques required for this are often complex and expensive. In addition, the laser diodes arranged on a circuit board require complex optics in order to display the different colors correctly on the user's lens. Although these so-called squint angles can be compensated for by suitable lenses, they are often larger. This is particularly the case if the optics are located outside the package, as the laser beams first expand to the optics. This increases the size, which is undesirable for smaller applications, e.g. for spectacles.
There is therefore a need to find a space-saving solution for laser arrangements, especially for the virtual reality or augmented reality sector, which can also be implemented cost-effectively.
This need is met by the objects of the independent patent claims. Further developments and embodiments of the proposed principle are given in the sub-claims.
The inventors propose stacking several laser devices on top of each other along one of their main sides in order to reduce the space required. These can then be contacted by various means, whereby on the one hand the different resonator lengths can be utilized. On the other hand, neighboring laser devices can also be connected to a common potential so that common contacting for the individual laser devices is possible in a simple manner. Stacking the laser device results in a particularly space-saving design, as the finished stack can be used as a single module. A further submount can therefore be omitted. In addition, various stacked devices can be produced in this way, i.e. laser devices with individual laser combs (single ridges) but also with several laser combs (multi-ridges). Depending on the desired light output power, the number of stacked laser arrangements of individual colors can be varied.
The relative position of the individual laser devices to each other is determined by the stacking. In particular, precise positioning in relation to each other is possible so that, on the one hand, the side surfaces of the devices are aligned flush with each other and, on the other hand, simpler lenses can be used for the optical path. It is possible to stack both individual laser devices and groups of devices up to wafer stacking. This enables the use of parallel processes in production. The resulting stacks require fewer assembly steps and only one burn-in process for the entire stack, so that further advantages can be realized.
Furthermore, some aspects take advantage of the fact that the side surfaces are exposed during production of the individual laser devices. These allow contact to be made with electrically conductive areas that lead to the active zone of the respective laser device.
Accordingly, in one possible embodiment, a stacked laser arrangement comprises a first and at least one second laser device. The first and at least one second laser device each comprise a resonator-forming semiconductor body with an active zone. This has a light-emitting side. Each of the laser devices has two main sides and two side surfaces extending perpendicularly thereto. The side surfaces of the two laser devices each have an insulating material. In this context, the term “main sides” refers to the sides of the laser device that extend essentially in the direction of growth of the semiconductor body. The light-emitting surface is essentially perpendicular to the main sides. In some embodiments, the laser comb extends parallel to the main side and is not necessarily centered on the light-emitting surface, but is offset from the center in the direction of one of the main sides.
The light emitted by the laser devices also has a non-rotationally symmetrical beam profile with a fast axis and a slow axis perpendicular to the fast axis. The beam profile is elliptical, with the large semi-axis, also known as the fast axis, running parallel to the side surfaces and the small or slow axis aligned parallel to the main sides.
According to the proposed principle, the light-emitting sides of the first laser device and of the at least one second laser device point in the same direction. In addition, the at least one second laser device is arranged on one of the main sides of the first laser device and is attached thereto. Conveniently, the two laser devices are the same width so that the side surfaces are flush with each other.
This achieves a very small design with the smallest possible distance between the respective laser combs. Electrical contact to the active zones of the first and at least one second laser device is now not made via the main side, but via at least one of their respective side surfaces, in that the insulating material is perforated in places. This aspect makes it possible to achieve electrical contact independently of the stacking of the individual laser devices.
In this way, a very compact design of a stack of laser devices is achieved. In one embodiment, electrical contacts are applied to the insulating material of the side surfaces, for example in the form of metallic surfaces. These can be vapor-deposited or sputtered onto the insulating material. In one example, a first electrical contact can be arranged on a first side surface and a second electrical contact on the second (opposite) side surface. The contacts are electrically connected through the insulating material of the side surfaces to the electrically conductive areas on the inside. In another example, the first and second electrical contacts are arranged on a common side surface. In this case, the two contacts are laterally spaced apart in order to avoid a possible short circuit.
In some aspects, a metallic layer is arranged on the side surfaces, which forms the contact surface in each case. In order to achieve easier contacting along this side surface, it may be provided to optionally extend the metallic layer over at least 50% of a length of the side surface, possibly also over the entire length of the side surface. The electrically conductive areas within a laser device are vertically spaced from each other, the spacing being determined by the epitaxial growth process and the manufacturing steps. Accordingly, in some aspects, the apertures on the side surfaces that contact the electrically conductive areas of the laser devices are laterally offset from each other. For example, with respect to the light emitting side and with respect to one of the main sides, an aperture through the insulating material on one side surface may be vertically offset from an aperture through the insulating material on the other side surface. In some embodiments, the openings may be at the same height but on different sides, for example if the electrically conductive areas within the laser device lead to the active zone.
During the production of the individual laser devices, the main sides can be provided with a dielectric layer. As a result, the two laser devices are electrically insulated from each other after stacking. An adhesive or an additional electrically insulating material can also be provided between the laser devices, which is particularly advantageous if one of the laser devices has no additional dielectric layer or only a very thin layer. This creates a special space-saving design. The adhesive layer can be an epoxy. In another aspect, the bonding layer can be metallic. It also makes sense to choose a material for the bonding layer with particularly high heat transfer properties. This allows any heat generated during operation of the stacked laser arrangement to be dissipated easily. The contacts, webs on the side surfaces or the side surfaces themselves can also be used in this context.
A further aspect results from subsequent processing of a stack of laser devices. Thus, in some aspects, it may be provided that the contacting takes place via a conductive web extending at least partially along the side surface of the respective laser device. This web is arranged on the insulating material of the side surface and, in some aspects, also extends at least partially over a side surface of the respective other laser device. This allows longer conductive webs to be formed, which lead along the side surfaces of different laser devices up to the contact. In other words, a laser device is contacted via metallic contact webs running along the side surfaces.
In some aspects, a metallic layer is provided that extends along a plurality of side surfaces and contacts electrically conductive regions of the first and the at least one second laser device on the same side. As a result, the metallic layer forms a common connection surface so that in an electrical operation the laser devices are at the same potential.
In some examples, the stacked laser arrangement is designed to emit light of different wavelengths. For this purpose, in some embodiments, the first laser device has a resonator length that differs from one of the at least one second laser device. It is expedient to stack the laser devices in such a way that the laser device with the greatest resonator length is at the bottom in relation to a later assembly.
In a further aspect, the stacked laser arrangement comprises a carrier with a number of contact surfaces, in particular contact surfaces arranged in a row.
The carrier can be a PCB board or a mount to which the laser array is attached. In other words, the stack is attached to the carrier rotated by 90° in this way. This also aligns the fast axis parallel to the carrier during operation.
In one embodiment, according to the proposed principle, the first and at least one second laser device are attached to the carrier in such a way that the electrical contacting of the side surface of at least one of the first and at least one second laser device is arranged on the contact surfaces. In this way, direct electrical contact is achieved, for example using suitable solders. At the same time, these contact surfaces can improve the mechanical stability and serve to dissipate heat during operation. In order to compensate for any tolerances, the contact surfaces can be slightly larger than the corresponding contacts on the side surfaces. In this context, it is envisaged in some aspects that all contact surfaces are arranged on one side.
In another aspect, it is intended to attach the side surface to a common surface in order to use it for heat transport. In this way, electrical contact can also be made via the side surface facing away from the carrier, for example by means of bonding wires that lead to electrical contacts on the surface of the carrier.
In another aspect, the laser arrangement comprises a carrier having a number of contact surfaces, in particular contact surfaces arranged in a row; wherein a main side of the first or at least one second laser device is arranged facing the carrier and a conductive web along the side surface of the first or at least one second laser device is electrically conductively connected to one of the contact surfaces. The web thus leads along one or more side surfaces to the contact for the laser device. This allows a particularly economical design, since bonding wires are not necessary and the through-plating of the webs and the contact surfaces is created.
In addition, the stacked laser arrangement can also be arranged on the carrier in such a way that the main sides are arranged parallel to a surface. For example, a main side of the first or at least one second laser device can be arranged facing the carrier, with a contact surface on one of the side surfaces of the first or at least one second laser device being electrically conductively connected to one of the contact surfaces, for example via a bonding wire.
Another aspect relates to a method for generating a stacked laser arrangement. Among other things, a first laser device with a light-emitting side and a semiconductor body forming a resonator with an active zone is provided. Likewise, at least one second laser device with a light-emitting side and a semiconductor body forming a resonator with an active zone is provided. The first and the at least one second laser device each have two main sides and side surfaces arranged substantially perpendicularly thereto. The laser devices are thus designed as already described above.
For example, they are produced epitaxially on a growth substrate and then separated. The manufacturing process is designed in such a way that the side surfaces of the respective laser devices have at least one electrically conductive area that makes electrical contact with the active zone.
The first and at least one second laser device are aligned with each other, for example stacked on top of each other. The tolerances can be as low as possible. After alignment, they are attached to each other so that a stack is formed that has flush side surfaces. Depending on the design, this can be done using an electrically insulating material, in particular an adhesive.
Then, at least one of the electrically conductive regions of the first and at least one second laser device is electrically contacted via at least one of their respective side surfaces, wherein an insulating material which is perforated in the region of the contacting is applied to the side surfaces. In some aspects, an electrically insulating layer is applied to the side surfaces for this purpose and then structured. Furthermore, an aperture is created in the electrically insulating layer so that the at least one electrically conductive region is exposed. An electrically conductive material is filled into this opening and the electrically conductive area is thus contacted. An electrical contact is then formed on the side surface. In this way, contact is made via the side surfaces, creating a space-saving arrangement.
There are several options for contacting the electrically conductive areas and connecting them to contacts on a carrier. In one aspect, an electrically conductive web is formed as a contact on the side surface. The electrically conductive web can extend along the length of the side surface, e.g. of the resonator. However, it is also possible to form the web substantially vertically, i.e. over the side surfaces of the stack. In some aspects, it is conceivable to provide the web as a metallic layer extending at least partially over the side surface of a plurality of webs. The metallic layer can serve as a contact when the stacked laser arrangement is placed on a carrier.
In another aspect, the electrical contact is created by forming a sequence of layers with an insulating material. One or more openings can be made in the layer sequence, for example by etching, laser drilling or similar. The openings are filled with an electrically conductive material. The layer sequence can be created separately and only connected to the stacked laser arrangements in a subsequent step. A metallic layer can also be deposited on the layer sequence, which contacts the electrically conductive material and thus serves as a contact.
In a further aspect, the layer sequence is now attached to the side surfaces of the first and at least one second laser device so that the apertures are in contact with the electrically conductive areas. In this way, the electrically conductive areas are guided outwards onto the side surfaces.
Some other items concerning various aspects of stacked laser arrangements are listed in the following non-exhaustive list:
The individual laser devices of the stacked laser arrangements described here can of course be combined with each other. In this respect, it is possible to form a stacked laser arrangement that has laser devices with contacts on the side surfaces as well as on the main surfaces.
Further aspects and embodiments according to the proposed principle will become apparent with reference to the various embodiments and examples described in detail in connection with the accompanying drawings.
The following embodiments and examples show various aspects and their combinations according to the proposed principle. The embodiments and examples are not always to scale. Likewise, various elements may be shown enlarged or reduced in size in order to emphasize individual aspects. It is understood that the individual aspects and features of the embodiments and examples shown in the figures can be readily combined with each other without affecting the principle of the invention. Some aspects have a regular structure or shape. It should be noted that slight deviations from the ideal shape may occur in practice without, however, contradicting the inventive concept.
In addition, the individual figures, features and aspects are not necessarily shown in the correct size, and the proportions between the individual elements are not necessarily correct. Some aspects and features are emphasized by enlarging them. However, terms such as “above”, “above”, “below”, “below”, “larger”, “smaller” and the like are shown correctly in relation to the elements in the figures. It is thus possible to deduce such relationships between the elements on the basis of the figures.
The area 251 is arranged above the laser comb 25′, the area 252 below the active zone 25. The electrical areas are covered by a further dielectric layer 22 or 23, which form the first and second main sides. The thickness of the layers can be chosen differently or, in some embodiments, can be partially omitted. Similarly, the side surfaces 24 and 24′ are formed by an insulating material. In other words, the semiconductor body is substantially surrounded by a dielectric material which is at least partially located on the side surfaces.
Openings 241 are provided in this insulating material, which lead the electrical areas 251 and 252 to the outside and connect them to an electrical contact 220 and 220′ in the form of a metallic layer on the dielectric material of the side surfaces 24 and 24′. Thus, contacting of the laser device according to the invention does not take place along the main sides, i.e. against or in the direction of growth of the laser device, but along the side surfaces. This makes it possible to arrange contacting along the entire length of the resonator and at the same time to stack the laser devices on top of each other. The metallic layer can have different thicknesses or even different materials (e.g. a layer sequence or similar) and thus be particularly suitable for applying a batch or for bonding.
The laser arrangement shown in
The design with the contacts along the side surfaces now makes it possible to attach the stacked laser arrangement to a carrier in different and therefore flexible ways.
The stacked laser arrangement 1 comprises 3 laser devices, 2, 3 and 4, which are each designed as so-called edge-emitting lasers with a laser bar. The light-emitting surface lies on the edges 21, 31 and 41 facing the observer. The laser devices 2, 3 and 4 shown here are designed to generate and emit light of different wavelengths. Specifically, the laser device 2 is designed to generate and emit red laser light on the light-emitting surface 21, the laser arrangement 3 is designed to generate blue laser light and the laser arrangement 4 is designed to generate green laser light.
The individual laser devices 2, 3 and 4 are stacked on top of each other as shown. In particular, the device 4 is mounted with a first main side on a contact surface of a carrier 5. Its second main side is in turn arranged adjacent to the second laser device 3 and mechanically connected to it. The laser device 2 is attached to the second main side of the laser device 3 facing away from it. This results in the stacked arrangement of several laser devices shown in this and the further embodiments.
All 3 laser devices are designed in such a way that they have the same width so that the side surfaces of the respective laser devices are flush with each other. An end layer 210 is applied to the main side of the uppermost laser device 2 facing away from the carrier 5. In the present embodiment example, the width of the light-emitting surface 21, 31, 41 is significantly smaller than the length of the respective laser devices. Accordingly, the height of each laser device is also significantly smaller than the width of the light-emitting side or the length of the corresponding laser device. The resonance length of the respective device is also essentially determined by the length of the laser device.
For contacting the individual laser devices, metallic contact bars 62, 63 and 64 are now provided, which are electrically connected to contact surfaces 52, 53 and 54 on the upper side of the carrier 5. The contact bars 62, 63 and 64 lead along the side surfaces of the laser devices up to the respective contacting (not visible as they are covered by the bars). For this purpose, the side surface made of an insulating material is perforated at the corresponding point so that an electrical connection is created between the respective contact web and the active zone within the laser device. In detail, the contact web 62 running along the side surface thus contacts the laser device 2, the contact web 63 contacts the laser device 3 and the contact web 64 contacts the laser device 4. The respective contact web runs over the insulating material of the side surfaces of the respective other laser devices, so that a short circuit or undesired electrical contact with the other laser devices is avoided. The individual contact bars also end in the upper quarter of the respective side surface of the laser devices, as this is where the opening through the insulating material is located.
In this way, stacked laser arrangements with the same resonator length can be realized in a space-saving manner, with contact being made via contact bars along the side surfaces. This approach makes it possible to produce stacked laser arrangements as such in a separate manufacturing process and then to arrange and attach them to an appropriately prepared carrier.
The web contacts 221′ for feeding charge carriers to the contact area 251 of the respective laser device, on the other hand, extend only over the side surface and a part of the adhesive layer 8. The web contacts 221 and 221′ are designed as elongate contact webs 62, 63 and 64, which extend over the side surfaces of the respective other laser devices as far as a lower area, where they are attached to the contact surfaces 52, 53 and 54.
A corresponding side view to explain this structure is shown in
A top view of the structure shown in
In an alternative embodiment, shown in
For contacting the inner metallic layer to the active zone, a breakthrough through the insulating electrical material, as for example in
Alternatively, as can be seen in some other embodiments with reference to the figures, the laser arrangement can be placed rotated by 90° on the carrier 5 and on a common contacting plane 51. The conductive metallic layers on the side surfaces are electrically conductively connected to the apertures 252, so that the contact surface 51 on the upper side of the carrier forms a common contact for the individual laser devices of the laser arrangement. The averted side surfaces are guided to separately arranged contact areas on the surface via bonding wires 520, 530 and 540. In this respect, this design is also similar to the illustration in
In
In
It comprises a substrate, an n-contact on the rear side and a p-contact on the top side. An additional laser comb is provided by a corresponding structure, simultaneously forming the active zone 25 and serving as a resonator for the laser device. In the left-hand section of the figure, the n-contact and p-contact are schematically represented by the metallic areas 251 and 252 respectively. This simplified representation serves to illustrate the essential aspects of the laser device, but is not to be understood as a geometrically or structurally precise design of the laser device. Alternative designs and manufacturing possibilities are known to the skilled person. However, it is essential that the electrically conductive areas 251 and 252 are designed up to the side surface of the semiconductor body 20, as shown in the left partial figure, so that the active zone can be contacted from above or below as well as from the side. In a subsequent step, the top or bottom side, i.e. the respective metallic contacting, is provided with a dielectric material. These form the two main sides of the laser device. In the right-hand embodiment of the manufacturing process, only the side facing the laser comb is covered with a dielectric material, while the lower side with the n-contact 252 remains free.
In a further process step in
In a further process step in
In the right-hand partial figure of
The method of this final manufacturing step, in particular the creation of dielectric side surfaces with corresponding contacting and openings at the level of the electrical areas, is flexible and can be carried out in various ways.
In an alternative embodiment, shown in
The advantage of this design is the separate and thus distinct production of the later side surfaces from the stacked laser arrangement, whereby an independent process optimization of both manufacturing processes is achieved. Suitable epitaxial measures can be used to increase the surface area of the electrically conductive areas in the area of the side edges of the laser devices, thus enabling a greater tolerance for the alignment of the side surfaces to the side edge of the laser devices.
In this case, the stacked laser arrangements are surrounded by a dielectric material. In particular, the side edges are coated with a dielectric material. The dielectric material can then be structured and several openings created in it. The position of the openings is selected in such a way that the edges of the areas 251 and 252 are exposed on the different side surfaces. In the present embodiment example, the areas 251 are exposed through apertures in the right-hand side surface, while the electrical areas 252 of the laser devices are exposed through apertures in the left-hand side surface. Of course, it is also possible in this context to provide both contacts on one side surface or alternately depending on the requirements and application. The apertures can be made larger than the thickness of the contacting areas 251, 252 within the laser device in order to ensure reliable contact with a conductive material that is subsequently filled. In a further final step, a material is filled into the apertures and an electrically conductive layer is applied to the outside of the side surfaces.
In this context, it is also conceivable that the individual contact via or apertures not only contact a layer in an individual laser device, but also serve as a common contact for a laser device and the laser device stacked on top of it. For example, the contact aperture 64′ can contact both an electrically conductive area to the active zone of the laser device 4 and a further electrically conductive area to the active zone of the laser device 3 as a common contact. Contact is also made between the electrically conductive areas to the respective active zone of the laser devices 3 and 2 with the contact via 63′. The laser device 4 also lies on a contact surface 51 of the carrier 5. Electrical activation is achieved, for example, by a current via the contact surface 51 and the common contact aperture 64′. In the same way, the laser devices 2 and 3 can also be controlled individually, i.e. separately or together.
The vias 82, 83 and 84, on the other hand, are designed in such a way that they only contact an upper main side of each individual laser device. Specifically, the through-holes 82 lead from the carrier 5 through the first and second laser devices 4 and 3 and the third laser device 2. On the upper main side, the laser device 2 now comprises a contact lug 82′, which forms the contact for the laser device on the upper main side. In the same way, the through-hole plating 83 is designed so that it makes electrical contact with the contact area 83′ on the main side of the laser device 3. This contact area is also separated from the lower main side of the laser device 2 by an electrical insulation 8. The third aperture 84 leads from the carrier 5 through the material of the laser device 4 to the contact area 34′, which contacts the upper side of the laser device 4.
In the embodiment example shown here in
The current distribution layer on the uppermost laser device 2 is connected to the through-hole plating 81. In this way, different lasers of different colors can be stacked on top of each other and controlled separately. Laser devices of the same color can have the same design so that they can be controlled together through corresponding feedthroughs.
The openings are shown again in detail in
Another, slightly simpler embodiment is shown in
The bonding wire 530 leads from the contact surface 53 on the carrier 5 to a contact area 210 of the laser device 3 at the end facing away from the light exit side. Accordingly, the bonding wire 540 contacts the contact surface 54 on the carrier with a contact area of the laser device 4, also at the end facing away from the light exit side.
Referring again to
Due to the different resonator lengths of the laser devices 2 and 3, an area of the metallic layer 310 of the respective insulation layers 300 is exposed. This is connected to the contact surface 51 on the carrier via a bonding wire. The metallization layers 310 of the individual insulation layers 300 are thus at the same potential as the electrically conductive contact surface 51 of the carrier. In this respect, each contact on the lower main side of the laser devices is at the same potential.
With this design, laser devices can also be stacked on top of each other which, on the one hand, have a different resonance length and, on the other hand, whose contacts are arranged on the opposite main sides. The additional insulating layer 300 thus enables the contact of the lower main side to make contact with the metallization applied to the surface while at the same time providing insulation between the individual laser devices. Depending on the embodiment, it is also possible that the insulation layers allow a certain amount of heat transport and can be used to cool the laser devices.
In a further embodiment not shown here, the metallic contact webs also shown in the preceding embodiment examples can be formed along the side surfaces, which are in contact with the exposed contact areas on the upper main side of the respective laser device or with the metallization layer 310 of the individual insulation layers. This makes it possible to stack laser devices whose contacts are located on the opposite main sides on top of each other and still contact them via the webs running across the side surface shown in the previous embodiment examples.
The embodiments shown here in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2022 106 937.0 | Mar 2022 | DE | national |
The present application is a national stage entry from International Application No. PCT/EP2023/057694, filed on Mar. 24, 2023, published as International Publication No. WO 2023/180550 A1 on Sep. 28, 2023, and claims the priority of the German first application DE 10 2022 106 937.0 filed Mar. 24, 2022, the disclosures of all of which are hereby incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/057694 | 3/24/2023 | WO |
