Electrical component with heat dissipation

Abstract

In order to improve heat dissipation from electrical components with heat-generating component structures, it is proposed to provide a radiation layer with a large surface in the area of the component structures. Preferably, the radiation layer is very heat-conductive or in heat-conductive connection with the component structures.

Claims

1. An electrical component with improved heat dissipation having a chip (CH) comprising a heat-loss generating element with an on-chip heat radiation layer (ASS) applied in thermal contact with the heat-loss generating element, wherein: the heat radiation layer has a roughened surface; the heat radiation layer (ASS) is applied to a first surface area (SA1) of the chip; the heat-loss generating element is arranged on a second surface area (SA2) of the chip; the first and second surface areas are arranged side by side; and a heat conducting layer (WLS) extends over the first and second surface areas (SA1, SA2), forming a heat-dissipation path on the chip (CH) but beneath the heat radiation layer (ASS) and the heat-loss generating element.

2. The electrical component according to claim 1, in which the heat radiation layer (ASS) has a columnar structure and is designed as a polycrystalline or crystalline layer.

3. The electrical component according to claim 2, in which the heat radiation layer (ASS) is an AIN layer, which is further enlarged by crystal-oriented back-etching in the roughened surface.

4. The electrical component according to claim 1, in which a cover layer (CL), on which the heat radiation layer (ASS) is arranged, extends over the heat-loss generating element.

5. The electrical component according to claim 4, in which the cover layer (CL) is part of a thin-film package, which is generated directly on the chip (CH) and forms a cavity for the heat-loss generating element.

6. The electrical component according to claim 5, in which the cover layer (CL) rests over the cavity and terminates adjacent to the cavity with a surface of the chip.

7. The electrical component according to claim 1, in which the chip comprises a BAW or FBAR resonator, and in which the heat radiation layer (ASS) is applied directly to an uppermost layer of the BAW or FBAR resonator.

8. The electrical component according to claim 1, in which the chip comprises a piezoelectric substrate and component structures (BES) arranged thereon, which are designed for generating, converting, propagating or reflecting surface acoustic waves (SAW), and in which the heat radiation layer (ASS) is applied directly to the piezoelectric substrate in the first surface area (SA1) adjacent to the component structures (BES), wherein the first surface area does not extend into an acoustic path of the surface acoustic waves.

9. The electrical component according to claim 1, in which the chip comprises a semiconductor substrate and component structures (BES) arranged thereon and/or integrated therein, and in which the chip is a semiconductor device.

10. The electrical component according to claim 9, in which the chip comprises an integrated circuit.

11. The electrical component according to claim 9, in which the chip is mounted in a flip-chip arrangement on a carrier so that a surface with the component structures (BES) and the heat radiation layer (ASS) faces the carrier (TR), and in which a further heat radiation layer (ASSw) is applied to a surface of the carrier (TR) facing the chip (CH).

12. The electrical component according to claim 1, in which the chip comprises a BAW or FBAR resonator.

Description

(1) The invention will be explained in greater detail below with reference to exemplary embodiments and the associated figures. The figures shown are only schematic and not true to scale. Individual parts may be shown larger or smaller for greater clarity. The figures therefore represent neither absolute nor relative dimensions.

(2) FIG. 1 shows a schematic cross-section through a component according to a first exemplary embodiment,

(3) FIG. 2 shows a photograph of a polycrystalline, roughened layer which is suitable as a radiation layer,

(4) FIG. 3 shows a schematic cross-section through a component according to a second exemplary embodiment,

(5) FIG. 4 shows a schematic cross-section through a component according to a third exemplary embodiment,

(6) FIG. 5 shows the plan view of a component according to an application example,

(7) FIG. 6 shows a component according to a fourth exemplary embodiment,

(8) FIG. 7 shows a component according to a fifth exemplary embodiment,

(9) FIG. 8 shows a sixth exemplary embodiment,

(10) FIG. 9 shows a seventh exemplary embodiment,

(11) FIG. 10 shows a plan view of a component with a structured radiation layer,

(12) FIG. 11 shows the heat distribution in a component according to the invention,

(13) FIG. 12 shows a further exemplary embodiment of the invention with reference to a schematic cross-section.

(14) A simple exemplary embodiment is shown in FIG. 1 in schematic cross-section. The component comprises a chip CH which essentially consists of a substrate SU and component structures BES applied thereto. The component structures conduct current and generate heat loss during operation of the component. For faster dissipation of the heat loss, a radiation layer ASS is applied to the surface of the substrate, which occupies a first surface area of the chip CH in which no component structures BES are arranged in the exemplary embodiment shown. The radiation layer is a preferably thin layer, which is formed with a large surface area. In particular, the radiation layer comprises a material which has a better thermal conductivity than the substrate SU.

(15) The radiation layer preferably exhibits no interaction with the component structures and is preferably an insulator which accordingly has no electromagnetic interaction with the component structures BES or other current-carrying elements.

(16) FIG. 2 shows a scanning electron micrograph of a polycrystalline surface which can be used as a radiation layer ASS. The exemplary radiation layer ASS is a crystalline material which has grown along the crystal axis and therefore has a columnar structure. The surface of such a crystalline to polycrystalline layer can be etched back in a manner oriented to the crystal surface, exposing different crystal surfaces and crystal facets of the crystallites contained in the layer.

(17) The columnar growth of a polycrystalline layer suitable as ASS is favored by: Provision of a suitable growth layer which is provided under the polycrystalline layer and in particular has a suitable lattice structure, e.g. a lattice structure that fits the lattice structure of AlN. Planar realization of the growth layer. Prevention of contamination on surfaces (e.g. by previous process steps) on and below the growth layer.

(18) During application, e.g. by a sputtering process, columnar growth is promoted by a low growth rate. Firstly, fine separate crystallites grow. As growth continues, the crystallites grow into each other. Overall, the areas crystallographically oriented relative to the surface then grow faster, so that crystal domains oriented in this direction eventually dominate and a layer with a columnar structure is created. The individual domains can then also be skewed relative to each other, but have predominantly parallel-oriented C axes.

(19) A tapering of the crystallites is achieved by etching back oriented to the crystal axis, wherein crystal surfaces of the unit cell are exposed which are in regular alignment and have corresponding angles of inclination to the layer plane. Almost independently of the crystal lattice, pyramid-shaped tips are formed in almost all cases, each corresponding to crystal edges or corners of the unit cell.

(20) Particularly advantageously, a grown-on crystal layer is first etched and then treated in a post-etching step with a wet-chemical or gaseous etchant which etches primarily at crystal defects and selectively etches different crystal facets of the crystal layer.

(21) Particularly suitable for this purpose is the wet-chemical etchant KOH. As a gaseous etchant, for example, a corrosive gas such as H or Cl is suitable. H is preferably used as the etching gas at an elevated temperature, in particular at or above 800° C.

(22) Preferably, wet-chemical etching is used in the pre-etching step. KOH in dilute form is particularly suitable as an etchant. In a particularly preferred embodiment of the invention KOH is used in this etching step at a concentration of 5% at room temperature, wherein the etching time is between 5 min and 15 min.

(23) Alternatively, a dry etching process (RIE process) is also suitable for the pre-etching step, for example. As a rule, a dry etching process is directed so that in this embodiment of the invention surface irregularities are transferred into the crystal layer and thus a roughening of this layer is achieved.

(24) In the pre-etching step, different crystal facets are exposed. After this, in a post-etching step, it is treated with another wet-chemical etchant, which mainly etches at crystal defects and selectively etches different crystal facets at the surface. In the example the further wet-chemical etchant contains KOH. By treating with KOH, the surface can be roughened very effectively. The roughness generated during the pretreatment is significantly improved in terms of efficiency for the heat dissipation of the radiation layer.

(25) In the post-etching step, KOH in concentrated form is preferably used as etchant. In a further preferred embodiment of the invention, etching is done here with KOH at a concentration of 25% at a temperature between 70° C. and 90° C., for example at 80° C., wherein the etching time is between 3 min and 10 min.

(26) Alternatively, a corrosive gas, for example H or Cl, can be used as an etchant for the post-etching step.

(27) The figure shows the surface of the radiation layer ASS, which has a plurality of precisely these pointed pyramids whose side surfaces are crystal facets aligned in parallel to different crystal planes of the unit crystal. Aluminum nitride is an example of a material that can be provided with such a structure. However, other materials which grow in a crystalline or polycrystalline manner are known which can be provided in the same way with a rough pyramidal structure. By way of example, only gallium nitrides, aluminum oxide, silicon oxide, silicon carbide and amorphous carbon may be mentioned as substances which can be used in the same way to form a radiation layer with an increased surface area.

(28) FIG. 3 shows, on the basis of a schematic cross-section, another chip CH, in which a large-area component structure BES is arranged on a substrate SU, for example a plate-shaped electrode. To improve the heat dissipation from the component comprising a chip CH, a radiation layer ASS is applied to the component structure BES, which is likewise characterized by its rough and thus enlarged surface. This embodiment is suitable for components that are not hindered in their function by an additional layer being applied or in which the interaction between the radiation layer ASS and the component can be monitored, so that the component properties are reproducibly adjustable despite the additional layer.

(29) As an example of such an embodiment, capacitors, ceramic resistors, varistors or thermistors may be mentioned, all of which represent a component that generates sufficient heat loss during the normal operation of the component and lead to a heating of the component, which usefully is to be dissipated in an easy and quick manner.

(30) With the radiation layer according to the invention, heat output from the component to the environment is improved.

(31) If the environment comprises air as in the example shown, radiation will be improved, in particular in the infrared range, that is to say precisely in the area of heat radiation.

(32) A further component that leads to improved heat dissipation with the illustrated design is a BAW resonator, which has a layered structure and whose uppermost electrode layer represents the illustrated component structure BES. With sufficiently high layer thickness uniformity of the radiation layer ASS, the acoustic properties of the BAW resonator are not unduly influenced.

(33) FIG. 4 shows a component chip CH according to a third exemplary embodiment in schematic cross-section. The chip CH comprises a substrate SU onto which component structures BES are applied. However, in contrast to the first exemplary embodiment according to FIG. 1, a heat-conducting layer WLS is arranged between the substrate SU and the component structure BES. The heat-conducting layer extends over a first surface area SA1 with the radiation layer ASS and a second surface area SA2 with the component structures BES and thus represents a heat-conducting path between the heat-generating component structures BES and the radiation layer ASS. In this way heat transfer from the component structures to the radiation layer is improved.

(34) For this embodiment, it is advantageous if the heat-conducting layer WLS is an insulator or is at least electrically insulated from the component structures, e.g. by means of an insulator layer (not shown in the figure). In one embodiment, heat-conducting layer WLS and radiation layer ASS may comprise the same material as e.g. aluminum nitride, which is an electrical insulator with high thermal conductivity.

(35) In a modification of this embodiment, not shown, it is possible to use as heat-conducting layer WLS a material which can be provided with a large surface area by an appropriate application or post-treatment processes. In the first surface area SA1, the heat-conducting layer can then undergo the said post-treatment, whereby the surface is correspondingly roughened or enlarged. It is therefore not necessary to apply an additional radiation layer to such a heat-conducting layer WLS, but rather to transform only the first surface area of the heat-conducting layer into a radiation layer by roughening it.

(36) FIG. 5 shows a plan view of a SAW component, which can advantageously be provided with a radiation layer ASS in a first surface area SA1. The component structures BES are applied to a piezoelectric substrate SU in the form of strip-shaped metallizations. The component structures form an acoustic track, in which at least one interdigital transducer is arranged between two reflectors. The surface acoustic wave is propagatable between the two reflectors so that the two reflectors bound the acoustic path.

(37) The second surface area SA2 therefore comprises at least the acoustic path. On the other hand, the first surface area SA1 onto which the radiation layer ASS is applied or generated spares the second surface area, so that the radiation layer ASS does not interact acoustically with the surface acoustic wave. Also in this embodiment, it is possible to apply the radiation layer ASS as an additional layer onto the substrate in the first surface area SA1. However, it is also possible to structure the substrate in the first surface area SA1 accordingly and thus to provide it with an enlarged surface.

(38) FIG. 6 shows a component according to a fourth exemplary embodiment with the aid of a schematic cross-section. The device is encapsulated in a thin-film package. The component comprises a substrate SU onto which component structures BES are applied. The device structures are mechanically sensitive and must be encapsulated such that a cavity forms over the device structures.

(39) The thin-film package used for this purpose comprises a cover layer CL applied in a large area over the component structures, under which cavities for receiving the component structures are formed by means of a sacrificial layer which is later removed. A radiation layer ASS can now be applied to this cover layer CL. In this case, heat dissipation takes place from the component structures, in part via the air gap enclosed in the cavity, through the cover layer CL and into the radiation layer ASS, from which it can be dissipated more quickly due to the increased surface area.

(40) A second part of the heat loss, which is generated in the component structures, is conducted via the substrate surface directly into the cover layer CL and from there into the radiation layer ASS. For this purpose, the cover layer CL in the area between different component structures is brought up as far as the surface of the substrate SU or at least up to its vicinity.

(41) Alternatively, the cover layer is in a good heat-conducting connection with the surface of the substrate, for example via thermally highly conductive structures, such as via metallic structures. The cover layer CL may be an organic layer. Preferably, however, it comprises a ceramic layer etchable selectively against the sacrificial layer.

(42) FIG. 7 shows, on the basis of a schematic cross-section, a fifth exemplary embodiment of a component with improved heat dissipation. The component comprises a component chip with a substrate SU, on the surface of which component structures BES are arranged. In the surface area of the substrate not occupied by the component structures BES, i.e., in the first surface area SA1, a radiation layer ASS is applied or generated. Also left out of the first surface area SA1 are electrical contact surfaces via which the chip is mounted on a carrier TR.

(43) Bumps BU, taking the form of solder bumps or stud bumps, serve for electrical and mechanical connection. The component chip comprising the substrate SU is mounted on the carrier TR in such a way that the component structures BES face the carrier TR. On the substrate-facing surface of the carrier TR, a further radiation layer ASS.sub.w is arranged, which facilitates the transport of heat in the opposite direction, i.e., from the air gap between substrate and carrier into the carrier.

(44) Beneath the further radiation layer ASSw, a heat-conducting layer WLS can be provided on the surface of the carrier TR, for example a metallic layer.

(45) At least one metallization plane is provided in the carrier itself, via which an interconnection of different component structures that are electrically connected via the bumps, different chips or passive elements, not shown, is made possible.

(46) Furthermore, vias may be routed to the upward-facing surface in the figure, on which contacts are provided for connection to a circuit environment (not shown in the figure). It is possible, on the one hand to use the metallic structures provided for electrical conduction within the support for heat dissipation. In addition, metallic heat guidance paths serving heat dissipation alone are possible, which lead to an outer surface of the arrangement.

(47) FIG. 8 shows a sixth exemplary embodiment with the aid of a schematic cross-section. Here too, the chip once again comprises a substrate SU with component structures BES. However, the component structures are covered with a compensation layer KS, for example a silicon oxide layer, which serves to compensate for the temperature coefficient TCF of the frequency.

(48) On the surface of the compensation layer KS, a radiation layer ASS is applied whose thickness is preferably small in relation to the thickness of the compensation layer KS. It is also possible to correspondingly roughen the compensation layer KS at the surface and thus to convert it into a radiation layer ASS, so that the additional application of a radiation layer is unnecessary.

(49) The component may be embodied as a SAW component, wherein the component structures represent interdigital transducers and/or reflectors.

(50) The device may be a semiconductor device and the chip may include a semiconductor substrate and component structures disposed thereon and/or integrated therein. In particular, the chip may include an integrated circuit.

(51) FIG. 9 shows a seventh exemplary embodiment in a schematic cross-section through a chip CH, which has already been explained in connection with the previous figures as an alternative, not shown. In this exemplary embodiment, in the first surface areas SA1, the surface of the substrate SU is roughened and thus represents a radiation layer ASS, which therefore does not have to be applied separately. The area of the component structures BES corresponding to the second surface area SA2 is omitted from the roughening treatment in order to avoid an interaction with the component function.

(52) FIG. 10 shows a plan view of a SAW component, in which the first surface area SA1, on which a radiation layer ASS is generated or applied to, extends over part of the component structures BES. Shown in FIG. 10 is an overlap of the radiation layer ASS with the bus bars of the interdigital transducers, which on the one hand ensures good thermal contact with the component structures and, on the other hand, does not impair the acoustic track, which does not reach all the way to the bus bars of the interdigital transducer.

(53) FIG. 11 shows an exemplary temperature distribution, based on isotherms, within a component chip CH with an applied radiation layer ASS. The component structures BES, which represent the heat-loss generating element, also have the highest temperature range during operation of the component.

(54) The isotherms extend through the substrate SU and represent lines that are at the same temperature. Arrows indicate the temperature gradient which points radially away from the component structures BES.

(55) Since an improved heat dissipation to the environment takes place via the radiation layer ASS, represented by serpentine lines, a stronger temperature gradient arises in the lateral direction away from the component structures, which likewise improves heat radiation via the radiation layer ASS.

(56) FIG. 12 shows a further embodiment variant of a component according to the invention. Here, similarly to the third exemplary embodiment according to FIG. 4, a heat-conducting layer WLS is applied over the entire surface of the substrate SU, which here may comprise a metal or another electrically conductive material. In order to prevent a short circuit of the component structures here, an insulation layer IS is arranged between component structures BES and heat-conducting layer WLS. This can extend over the entire heat-conducting layer WLS, but is advantageously arranged only in the second surface area SA2, i.e., below the component structures BES. In the first surface area SA1, the radiation layer ASS is applied.

(57) Alternatively, the surface of the heat-conducting layer WLS is correspondingly roughened and no separate radiation layer ASS is applied.

(58) Although not shown separately in the figures, the improved heat dissipation from the component may be combined with additional measures known in the prior art. For example, additional heat dissipation can take place via very heat-conductive structures, in particular via contact pads, bumps and other electrically conductive structures, something which does not hinder the improved heat radiation through the radiation layer ASS and can be easily combined with this. However, it is then advantageous to bring the radiation layer close to these heat-conducting structures, in order to also improve this heat contact flow and to improve the overall heat dissipation.

(59) It was only possible to describe the invention within reference to a few exemplary embodiments and it is therefore not limited to these. The invention can be implemented on a variety of different components, can be realized using different materials for radiation layer and substrate.

(60) The roughened surface of the radiation layer may be generated as described by a special treatment or alternatively may be a material-inherent layer property.

(61) In particular, particles comprising layers having particle segments projecting above the layer plane also have a rough and thus an increased surface area.

(62) The radiation layers can be mechanically strong or more loosely placed layers, since they are not exposed to mechanical stress. The radiation layers can be electrically insulating or electrically conductive, wherein in the latter case, an electrical contact with the component structures can be excluded.

(63) Alternatively, planar component structures BES with a roughened surface can also function as a radiation layer, or radiation layers can assume component function.

LIST OF REFERENCE SIGNS

(64) CH chip, comprising SU substrate and on top of it BES component structures (heat-loss generating element) ASS radiation layer (=heat-radiating layer) SA1 first surface area (with ASS) SA2 second surface area (without ASS) WLS additional heat-conducting layer, forming CL cover layer TR carrier ASS.sub.w further radiation layer (heat-radiating layer) on carrier BU bump KS auxiliary layer, e.g. TCF compensation layer IS insulating layer (FIG. 12)