Semiconductor radiation source

Abstract

Semiconductor radiation source (1) with - several semiconductor chips (2) for radiation generation, - a control unit (4) with several switching elements (41) for pulsed operation of the semiconductor chips (2), and - a capacitor body (3) - the semiconductor chips (2) are arranged together on exactly one capacitor body (3), - the semiconductor chips (2) are each directly electrically connected to the capacitor body (3) over a flat area, - the control unit (4) is electrically connected to a side of the semiconductor chip (2) opposite the capacitor body (3), - the control unit (4), the capacitor body (3) and the semiconductor chips (2) are arranged stacked on top of each other, such that the capacitor body (3) is located between the control unit (4) and the semiconductor chips (2), - the semiconductor chips (2) each lie completely within a base area of ​​the capacitor body (3), viewed from above, - the semiconductor chips (2) are each surface-emitting semiconductor lasers with a vertical resonator structure, and - the capacitor body (3) is designed monolithically as a chip with a capacitance of at least 10 nF.

Description

[0001] A semiconductor radiation source is specified.

[0002] The documents US 2004 / 0 247 005 A1, DE 20 2006 005 148 U1, US 2015 / 0 092 805 A1, US 2003 / 0 086 635 A1 and DE 10 2017 118 349 A1 relate to arrangements with a semiconductor emitter, a capacitor and a submount.

[0003] One problem to be solved is to provide a semiconductor radiation source that can be efficiently operated with high currents in pulsed mode.

[0004] This object is achieved by a semiconductor radiation source having the features of claim 1. Preferred developments are the subject of the dependent claims.

[0005] The semiconductor radiation source comprises several semiconductor chips. The semiconductor chips are configured to generate radiation. This means that the radiation emitted during operation of the semiconductor radiation source is generated by the semiconductor chips. The semiconductor chips are surface-emitting semiconductor lasers with a vertical cavity structure, or VCSELs for short.

[0006] The semiconductor chips are configured to generate near-ultraviolet radiation, visible light, or near-infrared radiation. A wavelength of maximum intensity of the radiation generated by the semiconductor chips is, for example, at least 360 nm, 400 nm, or 700 nm and / or at most 1080 nm, 960 nm, 860 nm, or 485 nm. It is possible for radiation to be emitted from several different spectral ranges. For example, several semiconductor chips with different wavelengths of maximum intensity can be combined in the semiconductor radiation source. Alternatively, only a specific wavelength is generated as intended.

[0007] The semiconductor radiation source comprises one or more capacitor bodies. The semiconductor chips are electrically energized via the at least one capacitor body, particularly in pulsed mode. This means that the capacitor body is configured to electrically operate the semiconductor chips.

[0008] The semiconductor chips and the capacitor body are stacked one above the other. The semiconductor chips lie entirely within the base area of ​​the capacitor body, viewed from above.

[0009] The semiconductor chips and the capacitor body are electrically connected to each other over a large area. The electrical connection between the semiconductor chips and the capacitor body is a direct electrical connection without any intermediate components. This means, in particular, that only a flat electrical connection, such as solder or an electrically conductive adhesive, is located between the semiconductor chips and the capacitor body. Particularly preferably, the electrical connection between the semiconductor chips and the capacitor body is wire-free.

[0010] Thus, the semiconductor radiation source comprises a plurality of semiconductor chips for generating radiation and at least one capacitor body. The semiconductor chips and the associated capacitor body are stacked one above the other. Furthermore, the semiconductor chips are electrically connected directly and flatly to the capacitor body.

[0011] One problem with switching high currents in a short time is reducing inductance, for example, in the current path between a capacitor, a laser, and a switching element such as a field-effect transistor. With the specified semiconductor radiation source, the inductance can be reduced, enabling short pulse rise times and high switching currents.

[0012] Alternative ways to reduce inductance include placing discrete individual components as close as possible to the semiconductor radiation source to minimize the path lengths of electrical leads. In some cases, inductance compensation can be achieved by switching a short-circuit current to a portion of the circuit. However, this compensation for inductance occurs at the expense of electrical power.

[0013] The semiconductor radiation source described here uses capacitor bodies in the form of silicon chips, for example, which have a metal coating, such as gold, on at least one side, so that the capacitor body can serve as a dual component. On the one hand, the capacitor body serves as a mounting platform, also known as a submount, for the semiconductor chips. On the other hand, the capacitor body serves as an energy storage device for the short laser pulses. This combination means that virtually any inductance, otherwise caused by bond wires or electrical lines between the semiconductor chip and the capacitor body, is eliminated. The semiconductor chips are preferably thin-film laser chips from which a growth substrate has been removed, with the capacitor body preferably serving as a carrier substrate for semiconductor layer sequences of the semiconductor chips.

[0014] With the semiconductor radiation source described here, a low overall inductance can be achieved, which allows for higher currents and / or shorter radiation pulses, combined with increased efficiency. Furthermore, a small component size can be realized. The semiconductor radiation source can be used in the automotive sector, for example, in headlights. Since standardized components can be used for the capacitor body, the costs of the semiconductor radiation source can be reduced. Furthermore, the semiconductor radiation source is preferably suitable for high temperatures, for example, in headlight applications. This can mean that the semiconductor radiation source can be used at operating temperatures of at least 180 °C, 150 °C, or 120 °C.

[0015] The semiconductor chips are semiconductor laser chips. For example, substrateless semiconductor laser chips, also known as thin-film laser chips, are used. This means that the semiconductor chips are preferably free of a growth substrate for a semiconductor layer sequence containing an active zone for generating radiation. The capacitor body can act as a mechanical support for the semiconductor chips, so that the semiconductor chips are not mechanically self-supporting without the capacitor body.

[0016] The semiconductor radiation source comprises one or more control units. The at least one control unit comprises one or more switching elements for pulsed operation of the semiconductor chips. The switching elements are, for example, field-effect transistors. In addition to the at least one switching element, the control unit can contain an integrated circuit, in particular an application-specific integrated circuit (ASIC). The control unit can also comprise a memory unit and / or an identification unit. Each semiconductor chip and / or each emitter unit can be assigned one or more separate switching elements.

[0017] The drive unit is electrically connected to a side of the semiconductor chips opposite the capacitor body. This connection can be made via one or more conductive tracks or one or more bond wires. This means that there is not necessarily a flat electrical connection between the semiconductor chips and the drive unit.

[0018] The control unit, the capacitor, and the semiconductor chip are stacked one above the other. These three components can be stacked directly on top of each other, leaving only connecting materials such as solder or adhesive between them.

[0019] The capacitor body is located between the control unit and the semiconductor chips. These components can be electrically connected to each other directly.

[0020] According to at least one embodiment, the capacitor body is a chip. In particular, the capacitor body is designed as a monolithic body that cannot be divided into subcomponents. In particular, the capacitor body is based on silicon.

[0021] According to at least one embodiment, the direct, planar electrical connection line or connection between the semiconductor chip and the capacitor body and / or between the semiconductor chip and the control unit and / or between the control unit and the capacitor body has only a negligible inductance. For example, this inductance of the connection line or the electrical connection is at most 100 pH, 50 pH, or 10 pH. Thus, the inductance of the connection line or the electrical connection is significantly lower than that of a bond wire.

[0022] The capacitor body has a capacitance of at least 10 nF, 20 nF, or 50 nF. This means the capacitor body has a comparatively large capacitance.

[0023] According to at least one embodiment, the semiconductor radiation source is surface-mountable. This means that electrical connection surfaces for external electrical contacting of the semiconductor radiation source are preferably located in a common plane. Such electrical connection surfaces are attached in particular to the capacitor body or to the control unit or to a carrier of the semiconductor radiation source.

[0024] According to at least one embodiment, a total thickness of the capacitor body together with the semiconductor chip is at least 0.1 mm or 0.2 mm. Alternatively or additionally, this total thickness is at most 1 mm or 0.5 mm. Alternatively or additionally, average lateral dimensions of the capacitor body and / or the semiconductor chip, i.e., in particular their average edge lengths as seen in plan view, are at least 0.2 mm or 0.4 mm and / or at most 2 mm or 1 mm or 0.6 mm. It is possible for the capacitor body to have a greater thickness than the semiconductor chips. For example, the thickness of the capacitor body exceeds that of the semiconductor chips by at least a factor of 2 or 5.

[0025] The semiconductor radiation source comprises a plurality of semiconductor chips. The semiconductor chips are preferably arranged in a regular two-dimensional array, viewed from above. The arrangement can be based on a rectangular or hexagonal pattern.

[0026] The semiconductor chips are arranged together on a single capacitor body. Alternatively, groups of semiconductor chips can each be mounted on a single capacitor body.

[0027] According to at least one embodiment, the semiconductor radiation source is configured to generate laser pulses or radiation pulses with a short average pulse duration. For example, the pulse duration is at least 0.2 ns or 0.5 ns and / or at most 5 ns or 2 ns.

[0028] Especially for time-of-flight applications, so-called TOF applications, increasingly shorter light pulses, even in the sub-nanosecond range, are required. In conventional discrete designs with bond wire contacts, such switching times are not possible or difficult to achieve due to relatively high inductances, for example, correlated with conductor tracks on a printed circuit board or with bond wires. This makes the semiconductor radiation source described here particularly suitable for such applications.

[0029] A semiconductor radiation source described herein is explained in more detail below with reference to the drawings using exemplary embodiments. Like reference numerals indicate like elements in the individual figures. However, they are not drawn to scale; rather, individual elements may be exaggerated for clarity.

[0030] They show: Fig. 1A, Fig. 2A, Fig. 3, Fig. 4A, Fig. 5A, Fig. 6A, Fig. 7A and Fig. 8B schematic sectional views of modifications of semiconductor radiation sources not according to the invention for a better understanding of the invention, Fig. 8B is a schematic sectional view of an embodiment of a semiconductor radiation source described here, Fig. 5B, Fig. 6B and Fig. 7B schematic plan views of non-inventive modifications of semiconductor radiation sources for a better understanding of the invention, Fig. 1B, Fig. 2B, Fig. 4B and Fig. 9 schematic circuit diagrams of non-inventive modifications of semiconductor radiation sources described here for a better understanding of the invention, Fig. 10 is a perspective view of an example of a capacitor body for semiconductor radiation sources described here, and Fig. 11 is a schematic sectional view of a modification of a semiconductor radiation source not according to the invention.

[0031] In Fig. Figure 1 illustrates a modification of a semiconductor radiation source 1. For example, the semiconductor radiation source 1 is configured to emit near-infrared radiation.

[0032] The semiconductor radiation source 1 comprises a semiconductor chip 2. For example, the semiconductor chip 2 is an edge-emitting laser. The semiconductor radiation source 1 further includes a control unit 4 and a capacitor body 3. The semiconductor chip 2, the capacitor body 3, and the control unit 4 are mounted on a common carrier 5. The carrier 5 represents the component that carries and mechanically supports the semiconductor radiation source 1.

[0033] The semiconductor chip 2 for generating radiation and the capacitor body 3 are stacked one above the other on the carrier 5. The control unit 4 is located laterally next to this stack. The capacitor body 3 and the control unit 4 are electrically connected to one another via a planar conductor track 55 or a continuous electrical contact surface. The capacitor body 3 and the semiconductor chip 2 are connected to one another via a direct, planar electrical connection D, in Fig. 1B is illustrated by a bold line. Other electrical connections can be realized by bond wires 6.

[0034] The capacitor body 3 and the semiconductor chip 2 are connected to a supply voltage V and to a ground line GND. A switching element 41, such as a field-effect transistor, of the control unit 4 is also connected to a signal line S. The control unit 4 is composed, for example, of the at least one switching element 41 and an application-specific integrated circuit.

[0035] Due to the planar electrical connection D, the semiconductor chip 2 and the capacitor body 3 are electrically connected to each other with virtually no inductance. This enables fast pulse rise times and high currents to operate the semiconductor chip 2. The current intensity is, for example, between 5 A and 35 A. For automotive applications, particularly LIDAR (Light Detection and Ranging), the current intensity is typically in the range of 20 A to 35 A, for example, approximately 30 A. For other time-of-flight applications, the current intensity is typically between 5 A and 15 A, for example, approximately 10 A.

[0036] Deviating from the representation in Fig. 1A, it is possible for the semiconductor chip 2 and the capacitor body 3 to be housed in a common housing (not shown), also referred to as a package. As an alternative to the bonding wires 6, as in all embodiments, electrical conductor tracks can be used, which are routed, for example, on the side surfaces of the respective components or along such side surfaces.

[0037] When modifying the Fig. 1, an anode-side contact of the semiconductor chip is located on a side facing away from the carrier 5. This side facing away from the carrier 5 is electrically connected to the control unit 4 via one or more bonding wires 6 or via at least one electrical conductor track. In contrast, according to Fig. 2, the polarity is reversed so that the anode side of the semiconductor chip 2 faces the carrier 5. Otherwise, the modification of the Fig. 2 with the Fig. 1 agree.

[0038] When modifying the Fig. 3, both the semiconductor chip 2 and the control unit 4 are mounted on the common capacitor body 3. Thus, the capacitor body 3 can serve as a mounting platform for the semiconductor chip 2 and the control unit 4. The carrier 5 is therefore optional. An anode side of the semiconductor chip 2 can face the capacitor body 3 or face away from it. This means that Fig. 3, the electrical connections can be made according to Fig. 1B or according to Fig. 2B are present.

[0039] In the modification of the Fig. Figure 4 illustrates that both the control unit 4 and the capacitor body 3 and the semiconductor chip 2 are arranged stacked one above the other in the specified order. Thus, flat, direct electrical connections D are present on both sides of the capacitor body 3. Remaining electrical connections are formed by the bonding wires 6 or, alternatively, by metallizations or conductor tracks, in particular along side surfaces.

[0040] Deviating from Fig. 4A, the control unit 4 can serve as a mounting level, so that the carrier 5 can then be omitted.

[0041] The corresponding electrical wiring is in Fig. 4B. On both sides of the capacitor body 3, the electrical connections D are designed to be virtually inductance-free. The electrical connection of the Fig. 4B corresponds to the Fig. 1B. Alternatively, the connection can be made as in connection with Fig. 2B illustrated.

[0042] According to Fig. 5A again shows a stacked arrangement of the control unit 4, the semiconductor chip 2, and the capacitor body 3. The semiconductor chip 2 is located directly between the capacitor body 3 and the control unit 4 and is connected to them via the flat electrical connections D. Viewed from above, the semiconductor chip 2, the capacitor body 3, and the control unit 4 can be arranged congruently.

[0043] When modifying the Fig. 6, the semiconductor chip 2 is a ridge waveguide semiconductor laser with a ridge waveguide 22. The ridge waveguide 22 is located on a side of the semiconductor chip 2 facing away from the capacitor body 3. It is possible that the capacitor body 3 acts as a support carrier for the semiconductor chip 2.

[0044] Optionally, the capacitor body 3 can surround the semiconductor chip 2 in a narrow strip, as seen in plan view. Thus, the semiconductor chip 2 rests completely on the capacitor body 3. A main emission direction of the semiconductor chip 2 is along the ridge waveguide 22 and thus parallel to the main sides of the capacitor body 3.

[0045] In Fig. Figure 7 shows that the semiconductor chip 2 has a plurality of emitter units 21. The emitter units 21 are arranged, in particular, in the form of a regular, for example, square, grid when viewed from above. The emitter units 21 can be electrically controlled independently of one another or connected electrically in parallel. The semiconductor chip 2 is, for example, a surface-emitting semiconductor laser with an emission direction perpendicular to the main sides of the capacitor body 3. All emitter units 21 are electrically assigned to the common capacitor body 3.

[0046] According to Fig. 8, several of the semiconductor chips 2 are present for generating radiation. In this case, see the modification in Fig. 8A, there may be a separate capacitor body 3 per semiconductor chip 2 or, see the embodiment in Fig. 8B, all semiconductor chips 2 are mounted on a common capacitor body 3.

[0047] One of the Fig. 8A can also be used with respect to the emitter units 21 from Fig. 7 are present.

[0048] Furthermore, Fig. Figure 8B illustrates that the control unit 4 can be integrated into the carrier 5. In this example, the carrier 5 is based on silicon. The same can apply to all other embodiments or modifications.

[0049] In Fig. 8A, a common control unit 4 is provided for all semiconductor chips 2. Alternatively, each stack of semiconductor chip 2 and associated capacitor body 3 may have its own control unit 4.

[0050] In Fig. 9 shows an electrical circuit which can equally be present in all other embodiments or modifications. The circuit of the Fig. 9 is analogous to the circuit of the Fig. 2B, but can also be used in the same way as in Fig. 1B should be constructed.

[0051] In Fig. 9, several switching elements 41 are provided, which are electrically connected in parallel. Alternatively or additionally, several individual capacitors 33 are provided, which together form the capacitor body 3. The individual capacitors 33 are also electrically connected in parallel.

[0052] These multiple switching elements 41 and / or individual capacitors 33 reduce the current in the respective electrical supply lines. This allows the inductance to be further reduced, especially at the electrical connections that are not realized by the direct, flat connection D.

[0053] In Fig. 10 shows an example of a capacitor body 3. The capacitor body 3 is based on silicon. A thickness T of the capacitor body 3 is, for example, approximately 0.25 mm. A length L and a width W are in particular in the range from 0.4 mm to 0.8 mm. Electrical contact surfaces 31a, 31b are located on both main sides of the capacitor body 3. On a bottom side, the electrical contact surface 31b can extend completely over the capacitor body 3. On a top side, the contact surface 31a has smaller lateral dimensions a, b than the capacitor body 3 itself. The contact surface 31a can be located centrally on the top side of the capacitor body 3. Lengths and widths a, b of the contact surface 31a are, for example, each at least 50 µm or 100 µm and / or at most 200 µm or 100 µm smaller than the corresponding length L and width W of the capacitor body 3.

[0054] Deviating from the representation in Fig. 10, the contact surface 31b on the underside can also be designed like the contact surface 31a, as in Fig. 10, so that the underside is then only partially covered by the contact surface 31b. Furthermore, it is possible for both contact surfaces 31a, 31b to completely cover the corresponding main sides of the capacitor body 3.

[0055] For example, capacitor body 3 is a silicon chip capacitor from IPDiA, specifically from the WTSC series. The capacitance of capacitor body 3 is, for example, in the range of a few tens of nF.

[0056] In Fig. Figure 11 shows a modification 10 of the semiconductor radiation source. Here, the semiconductor chip 2, the capacitor body 3, and the control unit 3 are located side by side on the carrier 5. Thus, there are no flat, direct electrical connections between the aforementioned components. This increases the inductance of the electrical supply lines.

[0057] When comparing components such as the Fig. 2 and Fig. 11 can be combined with the Fig. 2, a lower total inductance can be achieved. This allows for higher maximum optical powers, smaller pulse widths in the time domain, and faster pulse rise times, as well as overall higher efficiency.

[0058] For example, in the Fig. 2 and Fig. 11, the inductance of the semiconductor chip 2 is always at 100 pH or less. The inductance of the switching element 41, in particular a field-effect transistor, is also, for example, at most 100 pH or at approximately 100 pH. The bonding wires 6 result in an inductance of approximately 0.25 nH. In the modification 10 in Fig. 11, the capacitor body 3 results in an inductance in the range of 200 pH to 700 pH and for the electrical leads across the carrier 5 of approximately 0.2 nH or more.

[0059] In contrast, designs such as those in connection with Fig. 2, an inductance of the capacitor body 3 of approximately 50 pH and of leads via the carrier 5 of less than 0.1 nH can be achieved.

[0060] Thus, variation 10 of the Fig. 11 has a total inductance of approximately 1.2 nH, whereas in the semiconductor radiation source 1 according to in particular Fig.2, a total inductance of only approximately 0.5 nH can be achieved. The semiconductor radiation source described here allows the inductance to be significantly reduced.

[0061] Unless otherwise indicated, the components shown in the figures preferably follow one another directly in the specified order. Layers that do not touch in the figures are spaced apart. Where lines are drawn parallel to each other, the corresponding surfaces are also aligned parallel to each other. Likewise, unless otherwise indicated, the relative thickness ratios, length ratios, and positions of the drawn components are correctly reproduced in the figures. List of reference symbols 1 semiconductor radiation source 2 semiconductor chips 21 Emitter unit 22 ridge waveguides 3 capacitor bodies 31 electrical contact surface of the capacitor body 33 single capacitor 4 Control unit 41 Switching element 5 carriers 55 flat conductor tracks 6 bonding wire 10 Variation D direct, flat electrical connection line GND Ground contact S signal line V supply voltage a, b, L, T, W Dimensions of the capacitor body

Claims

[1] Semiconductor radiation source (1) with - several semiconductor chips (2) for generating radiation, - a control unit (4) with several switching elements (41) for pulsed operation of the semiconductor chips (2), and - a capacitor body (3), wherein - the semiconductor chips (2) are arranged together on exactly one capacitor body (3), - the semiconductor chips (2) are each directly electrically connected to the capacitor body (3), - the control unit (4) is electrically connected to a side of the respective semiconductor chip (2) opposite the capacitor body (3), - the control unit (4), the capacitor body (3) and the semiconductor chips (2) are arranged stacked one above the other, so that the capacitor body (3) is located between the control unit (4) and the semiconductor chips (2), - the semiconductor chips (2) are each located completely within a base area of ​​the capacitor body (3), seen in plan view, - the semiconductor chips (2) are each surface-emitting semiconductor lasers with a vertical resonator structure, and - the capacitor body (3) is designed monolithically as a chip with a capacitance of at least 10 nF. [2] Semiconductor radiation source (1) according to the preceding claim, wherein the capacitor body (3) is based on silicon. [3] Semiconductor radiation source (1) according to one of the preceding claims, in which a direct, planar electrical connection line (D) between at least one of the semiconductor chips (2) and the capacitor body (3) has an inductance of at most 50 pH. [4] Semiconductor radiation source (1) according to one of the preceding claims, in which the capacitor body (3) has a capacitance of at least 20 nF, wherein a total thickness of the capacitor body (3) together with the semiconductor chip (2) is at least 0.1 mm and at most 0.5 mm. [5] Semiconductor radiation source (1) according to one of the preceding claims, in which the semiconductor chips (2) are arranged regularly in a field two-dimensionally and jointly on the single capacitor body (3) when viewed in plan view. [6] Use of the semiconductor light source (1) according to one of the preceding claims in an automobile as a radiation source for LiDAR.