The present invention relates to a semiconductor package, more precisely to a semiconductor package comprising a surface-emitting laser, at least one driver circuit for the surface-emitting laser and at least one interposer as well as to a LIDAR transmitting unit comprising such a semiconductor package.
In laser array arrangements, such as for LIDAR applications (Light Detection and Ranging, light-based detection and distance measurement), surface-emitting lasers, so-called VCSEL (Vertical-Cavity Surface-Emitting Laser, surface-emitting laser with a vertical resonator) are frequently used. These surface-emitting lasers, together with corresponding driver circuits, are arranged on a semiconductor package. In this case, it is usual that the electrical contacting between the driver circuits and the surface-emitting laser is made by means of bond wires.
In some applications such as in the automobile area, such bond wires have a distance, also called “pitch”, which is limited by a minimum distance in order to eliminate contacts which can result in short circuits. As a result, the arrays of the laser diodes in the surface-emitting laser have a minimum distance which is based on the minimum distance of the bond wires. In the case of an at least required resolution of the surface-emitting laser, a minimum size of the laser is thus predefined which can result in high costs in the semiconductor fabrication since both the semiconductor surface per se and also the error rate, which increases the rejects in the case of larger semiconductor components results in higher costs.
The object according to the invention is therefore to provide a more inexpensive laser array which can be used in the automobile area, such as in LIDAR applications.
The invention is based on the idea of using, instead of contacting by bond wires, contacting via a so-called interposer, wherein the interposer makes contact with the surface-emitting laser and the corresponding driver circuits via so-called solder bumps. Since such interposers can also be fabricated in a semiconductor fabrication process, these can have a very small pitch of the contacts which makes it possible to use surface-emitting lasers with a narrow array spacing. As a result, whilst the resolution of the surface-emitting laser remains the same, the laser can be reduced in size so that inexpensive laser arrays are possible.
Exemplary embodiments thus create a semiconductor package comprising a surface-emitting laser, at least one driver circuit for the surface-emitting laser, a connecting structure and at least one interposer. The connecting structure comprises a plurality of solder bumps. The surface-emitting laser is electrically connected to the at least one driver circuit via the at least one interposer and the connecting structure. As has already been stated above, the object according to the invention is achieved by such a semiconductor package.
In some variants, the semiconductor package further comprises a potting structure. This potting structure can be designed to shield the connecting structure with respect to external effects. This makes it possible to achieve a greater robustness of the semiconductor package, specifically in the raw automobile area.
In this case, the potting structure can be arranged at least partially between the surface-emitting laser and a package substrate of the semiconductor package Thus, the potting structure can be part of the so-called underfill of the semiconductor package.
Nevertheless, a part of the surface-emitting laser can be in direct contact with the package substrate. This allows a stable fastening of the surface-emitting laser to the package substrate.
The at least one interposer can, for example, be arranged at least partially vertically between the surface-emitting laser and the package substrate. Alternatively, the at least one interposer can be formed by the package substrate. This enables a flat construction.
Alternatively the at least one surface-emitting laser can be arranged at least partially vertically between the at least one interposer and the package substrate. This optionally enables a more stable fastening of the surface-emitting laser and the at least one driver circuit on the package substrate.
In exemplary embodiments, the plurality of solder bumps corresponds to a plurality of micro-bumps. This makes it possible to achieve a particularly narrow pitch.
In at least some exemplary embodiments, the semiconductor package comprises a further connecting structure. A connection structure of the package substrate can be electrically connected to the at least one driver circuit via the further connecting structure. This enables electrical contacting of the at least one driver circuit via the package substrate.
Accordingly, the semiconductor package can also comprise a further potting structure. The further potting structure can be designed to shield the further connecting structure with respect to external effects. This enables a greater robustness of the semiconductor package, specifically in the harsh automobile environment.
In this case, the at least one driver circuit can be electrically connected to the connection structure of the package substrate via various contacting technologies. Thus, the at least one driver circuit can be electrically connected to the connection structure of the package substrate via one or more bond wires of the further connecting structure in each case. Alternatively or additionally the at least one driver circuit can be electrically connected to the connection structure of the package substrate via one or more solder bumps of the further connecting structure in each case. Both contacting technologies have advantages and disadvantages in relation to fabrication, costs and robustness.
The at least one driver circuit can, for example, be electrically connected to the connection structure of the package substrate via one or more solder bumps of the further connecting structure in each case via the at least one interposer. Thus, the interposer can serve as a support on which the remaining components are arranged.
In at least some exemplary embodiments, the at least one interposer is at least one semiconductor component. This makes it possible to fabricate particularly fine structures and therefore also a particularly small pitch.
A horizontal surface of the at least one interposer can project at least partially laterally beyond a horizontal surface of the surface-emitting laser and the at least one driver circuit. This enables a contacting of the interposer via bond wires, e.g. in order to electrically contact the interposer with the package substrate.
Exemplary embodiments thus create a robust and/or miniaturized structure of electronic components for laser array and lidar applications. In this case, by using new micro-electronic structure and connection techniques, such as the use of bumps, a further miniaturization of the laser diode distances can be achieved. Since the special semiconductor materials are extremely expensive, by this means chip area and therefore costs can be saved. In addition, such a connection is more robust than that made by bond wires.
Further advantageous configurations are described in detail hereinafter with reference to the exemplary embodiments shown in the drawings, to which exemplary embodiments however the invention is not generally restricted overall.
Exemplary embodiments are now described in detail with reference to the appended drawings which show some exemplary embodiments. In the following description of the appended figures which merely show some exemplary embodiments, the same reference numbers can designate the same or comparable components. Furthermore, summarizing reference numbers can be used for components and objects which occur multiple times in one exemplary embodiment or in one drawing but are described jointly with regard to one or several features. In this case, a vertical extension or a vertical arrangement is defined orthogonally to a front side of the package substrate and a lateral extension or a lateral arrangement is defined parallel to the front side of the package substrate.
The semiconductor package shown in
The semiconductor package can in this case be a multi-chip module, i.e. it can accommodate more than only one chip, such as the surface-emitting laser and the at least one driver circuit. In this case, in the semiconductor package of
In the exemplary embodiment of
In the exemplary embodiments of
In order to be able to bring the interposer and the surface-emitting laser or the two driver circuits electrically in contact with one another, so-called re-flow techniques can be used in which the material of the bumps is partially liquefied before the interposer is placed on the laser and a driver circuit (or conversely if the interposer or interposers are arranged between package substrate and laser/driver circuit) and the interposer with the partially liquefied bumps is placed on corresponding contacts of the surface-emitting laser and a driver circuit. In this case, the partially liquefied bumps form a self-aligning structure when solidifying so that the interposer is aligned in a precisely fitting manner to the contacts of the surface-emitting laser and the respective driver circuit. The liquefying can be brought about, for example, by hot air.
In at least some of the exemplary embodiments, the interposer is a semiconductor component, i.e. the interposer can be fabricated from a semiconductor material such as silicon, silicon carbide or gallium arsenide. In other words the interposer can be fabricated from or on a semiconductor wafer. Alternatively the interposer itself can comprise a package substrate which allows fine granular conductor tracks and contacts, i.e. the interposer can be formed by a further package substrate. In this case, the interposer can comprise a first plurality of contacts for the contacting of the surface-emitting laser, a second plurality of contacts for the contacting of a driver circuit and a plurality of conductor tracks which produce an electrical connection between the first plurality of contacts and the second plurality of contacts. In this case, the first plurality of contacts and the second plurality of contacts can be arranged on the same side of the interposer.
In at least some exemplary embodiment, the surface-emitting laser is a VCSEL array, i.e. the surface-emitting laser comprises a plurality of emitter elements in a first lateral extension of the surface-emitting laser and a plurality of emitter elements in a second lateral extension of the surface-emitting laser arranged orthogonally to the first. For example, the surface-emitting laser can comprise a plurality of emitter elements which are arranged in a matrix arrangement. Alternatively a different arrangement can be selected, such as an arrangement based on hexagons.
In his case, the plurality of laser emitters can be controlled line-by-line, i.e. each driver circuit can comprise a plurality of driver cells, wherein each cell is configured to control one line of the surface-emitting laser. Each line of the surface-emitting laser can in turn comprise a plurality of emitter elements. In this case, as shown in
For example, the surface-emitting laser can be a surface-emitting laser for a LIDAR transmitting unit. This LIDAR transmitting unit can correspond to the semiconductor package or the LIDAR transmitting unit can comprise the semiconductor package. The surface-emitting laser can be configured to produce a plurality of laser beams through the plurality of emitter elements which are provided to be transmitted via a transmission optics, in this case, preferably laser pulses are used.
The at least one driver circuit is configured to control at least a part of the surface-emitting laser. In this case, the at least one driver circuit can be configured to generate a plurality of power supply signals based on a control signal in order to control the plurality of emitter elements. In other words, each driver circuit can be configured to control the power supply of a plurality of emitter elements of the surface-emitting laser (based on the control signal). In this case, each driver circuit can be configured to receive the control signal via a further connecting structure. The semiconductor package can comprise the further connecting structure. A connection structure of the package substrate 10 can be electrically connected to the at least one driver circuit 30 via the further connecting structure. The control signal can be transmitted via the further connecting structure. In this case, the further connecting structure is formed as bond wires 72 in
As has already been described above, the semiconductor package can be part of a LIDAR transmitting unit or correspond to a LIDAR transmitting unit. A LIDAR transmitting unit is usually a component of a LIDAR measuring system. Exemplary embodiments thus also create a LIDAR measuring system comprising a LIDAR transmitting unit with the semiconductor package and a LIDAR receiving unit. The LIDAR measuring system is configured in its basic structure according to the explanations for the prior art (WO 2017/081294 A1).
The LIDAR receiving unit and/or the LIDAR transmitting unit are favourably configured in a focal plane array configuration. The elements of the respective unit are substantially arranged in one plane, favourably on a chip. The respective unit is preferably arranged on the LIDAR measuring system at a focal point of a corresponding optics, transmission optics or receiving optics. In particular, the sensor elements or the emitter elements are arranged at the focal point of the receiving optics. Such optics can, for example, be formed by an optical lens system.
The LIDAR receiving unit comprises a plurality of sensor elements which are preferably formed as SPADs, single photon avalanche diodes. The LIDAR transmitting unit comprises a plurality of emitter elements for emitting laser lights, favourably laser pulses. The emitter elements are favourably configured as VCSEL, vertical cavity surface emitting laser.
The transmitting unit comprises emitter elements which are distributed over the surface of the transmitting chip, of the surface-emitting laser. The receiving unit comprises sensor elements which are distributed over a surface of the receiving chip. Transmission optics are assigned to the transmitting chip and receiving optics are assigned to the receiving chip. The optics image light from a spatial region on the respective chip. The spatial region corresponds to the viewing range of the measurement system which is investigated or sensed on objects. The spatial region of the transmitting unit and the receiving unit are substantially identical. The transmission optics image an emitter element onto a solid angle which forms a partial region of the spatial region. The emitter element accordingly emits laser light in this solid angle. The emitter elements together cover the entire spatial region.
The receiving optics image a sensor element onto a solid angle which forms a partial region of the spatial region. The number of all the sensor elements covers the entire spatial region. Emitter elements and sensor elements which observe the same solid angle image onto one another and are accordingly assigned to one another. Laser light of an emitter element always images onto the relevant sensor element in the normal case. Optionally a plurality of sensor elements are arranged within the solid angle of an emitter element.
In order to determine objects within the spatial region, the measurement system performs a measurement process. Such a measurement process comprises one or more measurement cycles according to the constructive structure of the measurement system and its electronics.
Preferably the time correlated single photon counting method, TCSPC is used. In this case, individual incident photons are detected, in particular by SPAD and the time of triggering of the sensor element, also detection time, is stored in a storage element. The detection time is related to a reference time at which the laser light is emitted. The transit time of the laser light can be determined from the difference, from which the distance of the object can be determined.
A sensor element can be triggered on the one hand by the laser light and on the other hand by the ambient radiation. Laser light is always incident at the same time in the case of a specific distance of the object whereas the ambient light provides the same probability to trigger a sensor element at any time. When a measurement is carried out multiple times, in particular a plurality of measurement cycles, the triggerings of the sensor element are summed at the detection time which corresponds to the transit time of the laser light in relation to the distance of the object, whereas the triggerings by the ambient radiation are distributed uniformly over the measurement time of a measurement cycle. A measurement corresponds to the emission and subsequent detection of the laser light. The data of the individual measurement cycles of a measurement process stored in the storage element make it possible to evaluate the multiply determined detection times in order to determine the distance of the object.
A sensor element is favourably connected to a time to digital converter, TDC which stores the time of the triggering of the sensor unit in the storage element. Such a storage element can be configured, for example, as a short-term storage device or as a long-term storage device. The TDC fills a storage unit for a measurement process with the times at which the sensor elements detected an incident photon. This can be represented graphically by a histogram which is based on the data of the storage element. In a histogram the duration of a measurement cycle is divided into short time periods, so-called bins. If a sensor element is triggered, the TDC increases the value of a bin by one. The bin which corresponds to the transit time of the laser pulse, i.e. the difference between detection time and reference time, is filled.
In addition to the semiconductor package of
As is further shown in
More details and aspects of the semiconductor package 200 are mentioned in connection with the concept or examples which were described previously (e.g.
In contrast to the exemplary embodiments of
Accordingly, the potting structure 60 is also arranged at least partially between the surface-emitting laser 20 and the package substrate 10 and at least partially between the two driver circuits and the package substrate. In this case, the potting structure can be used as so-called underfill. The potting structure can be further configured to shield the further connecting structure, here formed by solder bumps 74 with respect to external effects. As can be further seen in
As has already been described above, the semiconductor package 300 further comprises the further connecting structure. A connection structure of the package substrate 10 (contact pads, not shown) is electrically connected to the at least one driver circuit 30 via the further connecting structure. In this case, the further connecting structure comprises one or more solder bumps or solder balls 74 which are arranged between the driver circuits and the package substrate. In other words, the at least one driver circuit 30 is electrically connected to the connection structure of the package substrate 10 in each case via one or more solder bumps 74 or solder balls of the further connecting structure. In addition, the further connecting structure comprises conductor tracks which electrically connect the solder bumps 74 to the contacts of the package substrate (not shown) which are suitable for connection of the semiconductor package.
More details and aspects of the semiconductor package 300 are mentioned in connection with the concept or examples which were described previously (e.g.
As also in
More details and aspects of the semiconductor package 400 are mentioned in connection with the concept or examples which were described previously (e.g.
In the case of the semiconductor package 500, the interposer 50 is also arranged vertically between the surface-emitting laser 20 and the package substrate 10. In this case, the interposer even forms a platform for the surface-emitting laser 20 and the two driver circuits 30, i.e. in this case the combination of interposer, laser, driver circuits and connecting structure can be mounted as a cohesive unit on the package substrate 40. For this purpose the interposer 50 can be coupled non-positively to the surface-emitting laser 20 and the driver circuits 30 via the connecting structure 40. In this case, the interposer 50 and the package substrate 10 are two separate components. Alternatively the at least one interposer 50 can be formed by the package substrate 50 or rather the interposer 50 can form the package substrate. In this case, the package substrate which also forms the interposer 50 can be a semiconductor component. As in other exemplary embodiments, the potting structure 60 is arranged at least partially between the surface-emitting laser 20 and/or the driver circuits 30 and the package substrate 10.
As shown in
More details and aspects of the semiconductor package 500 are mentioned in connection with the concept or examples which were described previously (e.g.
Number | Date | Country | Kind |
---|---|---|---|
102019206508.2 | May 2019 | DE | national |