The present disclosure is in the field of optical devices comprising a radiationemitting device, in particular wherein the radiation-emitting device is a vertical cavity surface emitting laser (VCSEL).

BACKGROUND

Known optical devices may be vulnerable to moisture ingress when exposed to harsh humidity stress conditions. Transparent epoxide-based compounds commonly used to overmold optical devices are limited in their ability to block diffusion of high moisture concentrations in harsh humidity stress conditions due to the lack of filler particles necessitated by their required optical properties. Such moisture ingress into optical devices may negatively impact reliability and performance of the package.

Proximity sensing devices and time-of-flight sensors comprising oxide-confined VCSEL dice may be particularly prone to degradation in performance as a consequence of moisture ingress. VCSEL dice are increasingly used in optical sensor packages. There are different types of VCSEL dice which may be distinguished by an approach used to define an aperture inside the component. Currently the most dominant and widely used VCSEL-type is based on an oxide-confined aperture. Those components exhibit a competitive performance to cost ratio. However, oxide-confined VCSEL dice may be particularly sensitive to humidity and they can degrade substantially when exposed to harsh humidity stress conditions. This weakness of oxide-confined VCSEL dice translates to a weakness in the optical devices in which they are used.

Furthermore, high thermomechanical stresses between an overmold and active devices in such optical devices are known to cause damage, such as de-lamination, which may in turn result in further hygroscopic deterioration. Thermal expansion of an overmold during manufacture may result in inherent residual stresses in the optical device, which may use may exacerbate such problems, increase hygroscopic deterioration, and thereby impact upon a reliability of such optical devices. It is therefore desirable to provide a highly reliable VCSEL-based optical device that is less susceptible to moisture ingress, without compromising on optical performance and without incurring substantial costs or requiring significant complexity.

It is therefore an aim of at least one embodiment of at least one aspect of the present disclosure to obviate or at least mitigate at least one of the above identified shortcomings of the prior art.

SUMMARY

According to a first aspect of the disclosure, there is provided an optical device comprising a substrate, a radiation-emitting device disposed on the substrate, and a conformal coating layer covering the radiation-emitting device. The conformal coating layer is moisture-resistant and substantially transparent to electromagnetic radiation (EMR) emissions of the radiation-emitting device.

Advantageously, such an optical device may be particularly suitable for use in harsh humidity stress conditions, for example in automotive applications. Beneficially, the conformal coating layer may provide improved moisture resistance, and thereby may improve reliability and longevity of the optical device. The coating being conformal ensures full coverage of the radiation-emitting device, including the sidewall.

The optical device may comprise a stress-decoupling layer.

The stress-decoupling layer may be formed over the conformal coating layer.

In some embodiments, the stress-decoupling layer may be formed between the radiation-emitting device and the conformal coating. In some embodiments, the stressdecoupling layer may be formed between the conformal coating and an overmold. The stress-decoupling layer may be characterised by a lower elastic modulus than the overmold.

Advantageously, the stress-decoupling layer may provide an additional buffer layer covering surface of at least an active device such as the radiation-emitting device. The stress-decoupling layer may work synergistically with the conformal coating layer to minimise moisture ingress into the optical device. For example, while the conformal coating layer may provide a degree of moisture resistance, the conformal coating layer may be subject to high thermomechanical stresses, such as stresses between the conformal coating layer and any overmold, which may result in delamination. Such delamination may further increase a rate of hygroscopic deterioration. Thus, by also implementing a stress-decoupling layer over the conformal coating layer, the optical device may be made highly resistant to moisture ingress.

The stress-decoupling layer may comprise a cross-linked epoxy. The stressdecoupling layer may comprise a re-flow stable polymer, e.g. a silicone.

The stress-decoupling layer may be characterised by coefficients of thermal expansion that are relatively close to those of interfacing layers, e.g. the conformal coating layer and/or any overmold that may be present.

The stress-decoupling layer may be transparent to wavelengths of radiation emitted by the radiation-emitting device.

The stress-decoupling layer may have a refractive index relatively close to that of the conformal coating layer and/or any overmold that may be present. As such, the stress-decoupling layer may exhibit a negligible impact upon optical operation of the optical device.

The stress-decoupling layer may have a thickness in the region of 10 micrometers. The stress-decoupling layer may be formed by a process of dispensing, spraying or jetting in a liquid form. Formation of the stress-decoupling layer may comprise a process of ultraviolet and/or thermal curing.

The radiation-emitting device may be a vertical cavity surface emitting laser (VCSEL). In particular, the conformal coating layer may protect the VCSEL, which may be particularly susceptible to degradation if exposed to a humid environment. Alternatively, the radiation-emitting device may be an edge-emitting laser, a light emitting diode, a laser diode or the like. In the context of the present disclosure, substantially transparent may be defined as absorbing less than 0.1% of EMR emitted by the radiation-emitting device. The conformal coating layer may be configured to absorb less than 0.1% of EMR emitted by the radiation-emitting device. The EMR emitted by the radiation-emitting device may have wavelengths in the range of 200nm to 2500nm, in particular the range 400nm to 2500nm, in particular the range 800nm to 1100nm. The conformal coating layer may be configured to absorb less than 0.1% of near-infrared radiation. Preferably, the conformal coating layer may be configured to absorb less than 0.1% of EMR having wavelengths of 940nm. The transparency and EMR absorption properties of the conformal coating layer ensure that there is negligible impact on the optical operation of the optical device.

The conformal coating layer may have a substantially uniform thickness. The conformal coating layer may have a thickness less than 1 pm, preferably less than 100nm. The thickness characteristics of the conformal coating layer ensure that there is negligible impact on the optical operation of the optical device.

The conformal coating layer may have a water vapour transmission rate (otherwise referred to as a moisture vapour transmission rate) less than 10' ² g/m ² /day, preferably less than 10' ⁵ g/m ² /day. Advantageously, the vapour transmission characteristics of the conformal coating layer may prevent ingress of moisture, in particular water vapour, into the optical device.

The conformal coating layer may be formed from an oxide material or multilayer combination of oxide materials. Beneficially, this may ensure that the conformal coating layer has good adhesion to the radiation-emitting device, thereby reducing the risk of disintegration or delamination of the optical device. Preferably, the conformal coating layer may be formed from at least one of aluminium oxide, zinc oxide, titanium dioxide, tantalum oxide, silicone dioxide. Alternatively, the conformal coating layer may be formed from an organic coating, for example parylene.

The substrate may be a printed circuit board (PCB), a laminate substrate, a lead-frame substrate or the like. The substrate may comprise wire bond pads on a first side of the substrate. The substrate may comprise solder pads on a second side of the substrate opposite the first side of the substrate. The radiation-emitting device may be disposed on the first side of the substrate. The radiation-emitting device may be electrically connected to the wire bond pads via wire bonds. The conformal coating layer may cover the first side of the substrate. The conformal coating layer may cover the wire bond pads. The conformal coating layer may cover the wire bonds.

The optical device may further comprise a die mounted on the substrate. The die may be a sensor die, e.g. a die comprising a sensor such as a radiation sensor. The die may be disposed on the first side of the substrate. The die may be electrically connected to the wire bond pads via one or more wire bonds. The conformal coating layer may cover the die.

The optical device may further comprise an overmold. The overmold may be substantially transparent. The overmold may be formed of epoxy or silicone. The overmold may cover the first side of the substrate. The overmold may be formed on the conformal coating layer. Alternatively the conformal coating layer may be formed on the overmold. The overmold may cover the radiation-emitting device. The overmold may cover the die. The overmold may cover the wire bonds. The overmold may cover the first side of the substrate. The overmold may be a structured overmold. The overmold may comprise a shaped lens portion. The shaped lens portion may be adjacent the die. The conformal coating layer may be between the radiation-emitting device and the overmold. Alternatively, the overmold may be between the radiationemitting device and the conformal coating layer. The conformal coating layer may be between the die and the overmold. Alternatively, the overmold may be between the die and the conformal coating layer. Beneficially, the overmold provides the optical device with protection from liquid water, dust and mechanical damage.

The stress-decoupling layer may be formed between the overmold and the radiation-emitting device. As such, the stress-decoupling layer may act as a buffer for thermomechanical stresses that may otherwise exist between the overmold and the radiation-emitting device. The optical device may further comprise one or more caps. The one or more caps may be intransparent. The one or more caps may be formed of a temperaturestable material, for example, fibre reinforced liquid-crystal polymer, polyethersulfone, epoxy or metal. The one or more caps may be disposed over at least a portion of the conformal coating layer. Alternatively, the one or more caps may be disposed over at least a portion of the overmold. A cap may cover the radiation-emitting device. The conformal coating layer may be between the radiation-emitting device and the cap. The cap may comprise an aperture adjacent the radiation-emitting device. A cap may cover the die. The conformal coating layer may be between the die and the cap. The cap may comprise an aperture adjacent the die. The one or more caps may be disposed over at least a portion of the overmold. The overmold may be between the one or more caps and the conformal coating layer.

The optical device may be one of an illuminator, a proximity sensor, or a time of flight sensor.

According to a second aspect of the disclosure there is provided an apparatus comprising an optical device according to the first aspect. The apparatus may be one of a smartphone, a cellular telephone, a tablet, a laptop, a Light Detection and Ranging (LIDAR) system, or a sensing system for an automotive vehicle.

According to a third aspect of the disclosure there is provided a method of manufacturing an optical device comprising the steps of disposing a radiation-emitting device on a substrate and forming a conformal coating layer over the radiation-emitting device. The conformal coating layer is moisture-resistant and substantially transparent to electromagnetic radiation emitted by the radiation-emitting device.

The method may further comprise a step of forming a stress-decoupling layer over the conformal coating layer. The stress-decoupling layer may be formed to have a thickness in the region of 10 micrometers. The stress-decoupling layer may be formed by a process of dispensing, spraying or jetting in a liquid form. Formation of the stressdecoupling layer may comprise a process of ultraviolet and/or thermal curing.

An optical device manufactured according to the present disclosure may be particularly suitable for use in harsh humidity stress conditions, for example in automotive applications. Beneficially the conformal coating layer provides improved moisture resistance, and thereby improves reliability and longevity of the optical device. The coating being conformal ensures full coverage of the radiation-emitting device, including the sidewall.

The radiation-emitting device may be a VCSEL. In particular, the conformal coating layer protects the VCSEL, which can be particularly susceptible to degradation if exposed to a humid environment. Alternatively, the radiation-emitting device may be an edge-emitting laser, a light emitting diode, a laser diode or the like.

The step of disposing the radiation-emitting device on the substrate may comprise mounting the radiation-emitting device on the substrate. The step of disposing the radiation-emitting device on the substrate may comprise forming the radiation-emitting device on the substrate.

The step of forming a conformal coating layer over the radiation-emitting device may be performed by atomic layer deposition. Beneficially, this ensures high material density which allows for a thin coating without a reduction in mechanical integrity.

Alternatively, the conformal coating layer may be formed by Chemical Vapor Deposition or Physical Vapor Deposition, with or without plasma enhancement.

The radiation-emitting device and the conformal coating layer may be applied to a first side of the substrate. The first side of the substrate may be covered by the conformal coating layer. The conformal coating layer may be formed directly on to the radiation-emitting device. The conformal coating layer may be formed directly on to the first side of the substrate.

A removable coating may be applied to a second side of the substrate opposite the first side prior to forming the conformal coating layer. The removable coating may be removed after forming the conformal coating layer. Beneficially, any solder pads on the second side of the substrate may be protected by the removable coating from the conformal coating layer during formation. The radiation-emitting device may be bonded to the substrate. The radiationemitting device may be bonded with conductive glue. Alternatively, the radiationemitting device may be soldered to the substrate. The radiation-emitting device may be electrically connected to wire bond pads on the substrate, via wire bonds, prior to forming the conformal coating layer.

A die may be mounted on the substrate prior to forming the conformal coating layer. The die may be a sensor die. The die may be bonded to the substrate. The die may be bonded via die attach film or die attach adhesive to the first side of the substrate. The conformal coating layer may be formed over the die. The conformal coating layer may be formed on the die.

An overmold may be formed over the radiation-emitting device. The overmold may be formed over the die. The overmold may be formed on the conformal coating layer.

Alternatively, the overmold may be formed on the radiation-emitting device. The overmold may be formed on the die. The overmold may be formed on the first side of the substrate. The conformal coating layer may be formed on the overmold.

A slit or aperture may be formed, e.g. cut or etched, into the overmold between the die and the radiation-emitting device. A portion of the conformal coating layer may be removed adjacent the slit or aperture in the overmold. Beneficially, the overmold provides the optical device with protection from liquid water, dust and mechanical damage.

One or more caps may be disposed over at least a portion of the conformal coating layer. Alternatively, the one or more caps may be disposed over at least a portion of the overmold. The one or more caps may be glued or soldered to the first side of the substrate.

According to a fourth aspect of the disclosure there is provided a method of wafer-level manufacturing of optical devices. The method comprises the step of disposing a plurality of radiation-emitting devices on a substrate. The method comprises the step of forming a conformal coating layer over the plurality of radiation- emitting devices. The conformal coating layer is moisture-resistant and substantially transparent to electromagnetic radiation emitted by the radiation-emitting devices. The method comprises the step of dicing the substrate into a plurality of optical devices. Each optical device comprises at least one of the plurality of radiation-emitting devices.

According to a fifth aspect of the disclosure there is provided an optical device comprising: a substrate; a radiation-emitting device disposed on the substrate; a stress-decoupling layer formed over the radiation-emitting device; and an overmold formed over the stress-decoupling layer; wherein the stress-decoupling layer has a lower elastic modulus than the overmold.

The stress-decoupling layer may be substantially transparent to electromagnetic radiation emissions of the radiation-emitting device.

The optical device may comprise a conformal coating layer, wherein the conformal coating layer is moisture-resistant and substantially transparent to electromagnetic radiation emitted by the radiation-emitting device.

The conformal coating layer may be formed over the radiation-emitting device, such that the stress-decoupling layer is between the conformal coating layer and the overmold.

The radiation-emitting device may be a VCSEL.

The conformal coating layer may be formed from aluminium oxide, zinc oxide, titanium dioxide, tantalum oxide, silicone dioxide or parylene.

The stress-decoupling layer may comprise a cross-linked epoxy. The stressdecoupling layer may comprise a re-flow stable polymer.

The optical device may be one of: an illuminator; a proximity sensor; or a time- of-flight sensor.

According to a sixth aspect of the disclosure there is provided an apparatus comprising an optical device according to the fourth aspect, wherein the apparatus is one of: a smartphone; a cellular telephone; a tablet; a laptop; a Light Detection and Ranging (LIDAR) system; or a sensing system for an automotive vehicle.

According to a seventh aspect of the disclosure, there is provided a method of manufacturing an optical device comprising the steps of: disposing a radiation-emitting device on a substrate; forming a stress-decoupling layer over the radiation-emitting device; and forming an overmold over the stress-decoupling layer, wherein the stressdecoupling layer has a lower elastic modulus than the overmold.

The method may comprise an intermediate step of forming a conformal coating layer over the radiation-emitting device, wherein the conformal coating layer is moisture-resistant and substantially transparent to electromagnetic radiation emitted by the radiation-emitting device. As such, the conformal coating layer may be formed over the radiation-emitting device such that the stress-decoupling layer is between the conformal coating layer and the overmold.

According to an eighth aspect of the disclosure, there is provided a method of wafer-level manufacturing of optical devices. The method comprises the steps of: disposing a plurality of radiation-emitting devices on a substrate; forming a stressdecoupling layer over the plurality of radiation-emitting device; forming an overmold over the stress-decoupling layer, wherein the stress-decoupling layer has a lower elastic modulus than the overmold; and dicing the substrate into a plurality of optical devices, each optical device comprising at least one of the plurality of radiation-emitting devices

The above summary is intended to be merely exemplary and non-limiting. The disclosure includes one or more corresponding aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. It should be understood that features defined above in accordance with any aspect of the present disclosure or below relating to any specific embodiment of the disclosure may be utilized, either alone or in combination with any other defined feature, in any other aspect or embodiment or to form a further aspect or embodiment of the disclosure. BRIEF DESCRIPTION OF DRAWINGS

These and other aspects of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 depicts a cross-sectional view of an optical device according to an embodiment of the disclosure;

Figure 2 depicts a first stage of manufacture of the optical device of Figure 1;

Figure 3 depicts a second stage of manufacture of the optical device of Figure 1;

Figure 4 depicts a third stage of manufacture of the optical device of Figure 1;

Figure 5 depicts a fourth stage of manufacture of the optical device of Figure 1;

Figure 6 depicts a fifth stage of manufacture of the optical device of Figure 1 ;

Figure 7 depicts an optical device according to a further embodiment of the disclosure;

Figure 8 depicts an optical device according to a further embodiment of the disclosure;

Figure 9 depicts an optical device according to a further embodiment of the disclosure;

Figure 10 depicts an optical device according to a further embodiment of the disclosure;.

Figure 11 depicts a cross-sectional view of an optical device comprising a stressdecoupling layer, according to a further embodiment of the disclosure;

Figure 12 depicts a cross-sectional view of an optical device comprising a stressdecoupling layer according to a further embodiment of the disclosure.

Figure 13 depicts a cross-sectional view of an optical device comprising a stressdecoupling layer and a moisture-resistant layer, according to an embodiment of the disclosure; and

Figure 14 depicts a cross-sectional view of an optical device comprising a stressdecoupling layer and a moisture-resistant layer, according to a further embodiment of the disclosure.

DETAILED DESCRIPTION

In reference to Figure 1, there is provided an example optical device 10 according to an embodiment of the disclosure, suitable for use as a proximity sensor, a time-of-flight sensor or an illuminator. The optical device 10 comprises a substrate 12 having a first side 12a (a top side as shown) and a second side 12b (a bottom side as shown). In some embodiments the second side 12b comprises solder pads 14 suitable for coupling the optical device 10 to a further component, a further substrate, a printed circuit board, or the like. The first side 12a comprises wire bond pads 16. Disposed on the first side 12a of the substrate 12 is a radiation-emitting device. In the present exemplary embodiment the radiation-emitting device is a vertical cavity surface emitting laser (VCSEL) 18. In alternative embodiments, the radiation-emitting device may be an edge-emitting laser, a light emitting diode, a laser diode or the like. Also disposed on the first side 12a of the substrate 12 is a sensor die 20 comprising an integrated sensor array 22. Both the VCSEL 18 and the sensor die 20 are in electrical connection with the wire bond pads 16 via wire bonds 24.

In some embodiments the sensor die 20 may comprise control circuitry and/or driver circuitry. As such, in some embodiments the sensor die 20 may be electrically coupled to the VCSEL 18, such as to control and/or drive the VCSEL 18. In some embodiments, the VCSEL 18 may comprise an integrated driver. In yet further embodiments, a VCSEL driver may be provided on another die of component (not shown) that is electrically coupled to the VCSEL 18.

With continued reference to Figure 1, the optical device 10 comprises a conformal coating layer 26. In some embodiments, the conformal coating layer 26 may be formed of aluminium oxide. In other examples, the conformal coating layer may be formed of one or more other oxide materials such as zinc oxide, titanium dioxide, tantalum oxide and/or silicone dioxide. The conformal coating layer 26 covers the top and sidewalls of the VCSEL 18, the top and sidewalls of the sensor die 20, and the exposed areas of the first side 12a of the substrate 12. Although not shown in Figure 1 , some of the conformal coating layer 26 may cover the wire bonds 24 as a result of the formation process of the conformal coating layer 26 which will be later described. The conformal coating layer 26 has a uniform thickness of less than 1 m, preferably less than 100nm. The conformal coating layer 26 is moisture resistant, having a water vapour transmission rate less than 10' ² g/m ² /day, preferably less than 10' ⁵ g/m ² /day, thus the conformal coating layer protects the VCSEL 18 and the sensor die 20 from ingress of water vapour which could be potentially damaging to the aforementioned components, the VCSEL 18 in particular. The conformal coating layer 26 is substantially transparent to near-infrared electromagnetic radiation, i.e. it absorbs less than 0.1% of electromagnetic radiation having wavelengths in the range of 200nm to 2500nm, preferably electromagnetic radiation having wavelengths in the range of 400nm to 2500nm, more preferably electromagnetic radiation having a wavelength of 940nm. The transparency of the conformal coating layer 26 ensures that the conformal coating layer 26 does not substantially interfere with the operation of the VCSEL 18 and the sensor die 20.

With continued reference to Figure 1, the example optical device 10 further comprises an overmold 28 formed of transparent epoxy resin. The overmold 28 covers the conformal coating layer 26. The overmold 28 protects the VCSEL and the sensor die from liquid water, dust and mechanical damage. The overmold 28 is structured to comprise a shaped portion that functions as an optical lens 30. The optical lens 30 is positioned over the integrated sensor array 22 of the sensor die 20. The overmold 28 comprises a slit 32. The conformal coating layer 26 is interrupted adjacent the slit 32. The optical device 10 further comprises a cap 34 formed of a plurality of cap portions 34a, 34b, 34c. The cap 34 may be unitary, or one or more of the cap portions 34a, 34b, 34c may be formed separately. The cap 34 covers the sensor die 20 and the VCSEL 18. The cap 34 is intransparent to near-infrared electromagnetic radiation. Furthermore, the cap 34 is formed of a temperature-stable material. An aperture 36a is formed between cap portion 34a and cap portion 34b. The aperture 36a is aligned with the optical lens 30 and the integrated sensor array 22, and light can pass through the aperture. Cap portions 34a and 34c are mounted on the substrate 12 either side of the overmold 28. Cap portion 34b is mounted on the substrate 12 in the slit 32. An aperture 36b is formed between cap portion 34b and 34c. The aperture 36b is aligned with the VCSEL 18, and light can pass through the aperture.

A method of manufacturing the optical device 10 of Figure 1 will now be described in reference to Figures 2 to 6. The described manufacturing method is a wafer-level manufacturing, therefore a plurality of optical devices are formed on the substrate 12. As such, the method of manufacture is the same for each optical device 10. It will be appreciated that in other embodiments of the invention, one or more optical devices 10 may be manufactured in isolation. As shown in Figure 2, the sensor dice 20 are bonded on the substrate 12 with die attach film 38. The sensor dice 20 are mounted such that the integrated sensor array 22 of each sensor die 20 is distal the substrate 12. The VCSELs 18 are bonded on the substrate 12 with conductive glue 40. In an alternative method the VCSELs may be formed on, i.e. grown from, the substrate. As shown in Figure 3, the wire bonds 24 are connected between the VCSELs 18 and the wire bond pads 16, and between the sensor dice 20 and the wire bond pads 16, to provide electrical connectivity. As shown in Figure 4, the conformal coating layer 26 is formed over the first side 12a of the substrate 12, the VCSELs 18 and the sensor dice 20. In some embodiments, the conformal coating layer 26 is formed by atomic layer deposition. This forming process ensures a high material density, which allows for a thin layer without a reduction in mechanical integrity. Other forms of deposition, i.e Chemical Vapor Deposition or Physical Vapor Deposition, with or without plasma enhancement, may also be suitable because the deposition process provides good conformity of the coating to the contours of the components. A removable coating layer (not shown) may be applied to the second side 12b of the substrate 12, covering the solder pads 14, prior to formation of the conformal coating layer 26. After formation of the conformal coating layer 26, the removable coating layer may be removed, thus ensuring that no conformal coating layer 26 is formed on the second side 12b of the substrate, in particular the solder pads 14. As shown in Figure 5, the overmold 28 is formed over the conformal coating layer 26. The optical lens 30 is shaped during the application of the overmold 28 using a mold tool. In the example embodiment of Figure 5, the optical lens 30 is formed as a convex lens. It will be appreciate that this is for purposes of example only, and other lens or optical components may be formed in other embodiments of the disclosure. For example, in some embodiments the overmold 28 may be formed with a microlens array, a Fresnel lens, a grating or the like. In some embodiments, overmold 28 may be configured to focus and/or diffuse and/or alter a phase of radiation propagating through the overmold 28. Furthermore, although the example embodiment of Figure 5 depicts an optical lens 30 formed over each of the sensor dice 20, in other embodiments of the disclosure an optical lens or other optical component may be additionally or alternatively formed over each of the VCSELs 18. In the example of Figure 5, the overmold 28 is then cut between the VCSELs 18 and the sensor dice 20 to form the slits 32, and portions of the conformal coating layer 26 are removed to expose the substrate 12 adjacent each slit 32. As shown in Figure 6, the caps 34 are then mounted on the substrate 12, over the overmold 28, to cover the VCSEL 18 and the sensor die 20 of each optical device 10. The caps are positioned such that apertures 36 are formed over the optical lenses 30 and the VCSELs 18. The caps 34 are fixed to the substrate 12 using a glue 42. In alternative methods, the caps may be soldered to the substrate. Upon completion of these manufacturing steps, the substrate is diced to separate each of the optical devices 10.

An alternative optical device 110 is shown in Figure 7. The optical device 110 substantially corresponds to the optical device 10, therefore like features are provided with like reference numerals, augmented by 100. The optical device 110 comprises a substrate 112 having a first side 112a (a top side as shown) and a second side 112b (a bottom side as shown). The second side 112b comprises solder pads 114. The first side 112a comprises wire bond pads 116. Disposed on the first side 112a of the substrate 112 is a radiation-emitting device. In the present exemplary embodiment the radiation-emitting device is a vertical cavity surface emitting laser (VCSEL) 118. In other embodiments, the radiation-emitting device may be an edge-emitting laser, a light emitting diode, a laser diode or the like. Also disposed on the first side 112a of the substrate 112 is a sensor die 120 comprising an integrated sensor array 122. Both the VCSEL 118 and the sensor die 120 are in electrical connection with the wire bond pads 116 via wire bonds 124. The optical device 110 further comprises a conformal coating layer 126. The conformal coating layer 126 is formed of aluminium oxide. In other examples, the conformal coating layer may be formed of other oxide materials such as zinc oxide, titanium dioxide, tantalum oxide, silicone dioxide. The conformal coating layer 126 covers the VCSEL 118, the sensor die 120 and the exposed areas of the first side 112a of the substrate between and adjacent the VCSEL 118 and the sensor die 120. Although not shown in Figure 7, some of the conformal coating layer 126 may cover the wire bonds 124 as a result of the formation process of the conformal coating layer 126. The conformal coating layer 126 has a uniform thickness of less than 1 m, preferably less than 100nm. The conformal coating layer 126 is moisture resistant, having a water vapour transmission rate less than 10' ² g/m ² /day, preferably less than 10' ⁵ g/m ² /day, thus the conformal coating layer 126 protects the VCSEL 118 and the sensor die 120 from ingress of water vapour which could be potentially damaging to the aforementioned components, the VCSEL 118 in particular. The conformal coating layer 126 is substantially transparent to near-infrared electromagnetic radiation, thus the conformal coating layer 126 does not interfere with the operation of the VCSEL 118 and the sensor die 120. The optical device 110 further comprises an overmold 128 formed of transparent epoxy resin. The overmold 128 covers the conformal coating layer 126. The optical device 110 is manufactured in a similar manner to the steps described above in reference to Figures 2 to 6, with the omission of mounting a cap over the overmold. Furthermore, for purposes of example, the overmold 128 does not comprise a lens, e.g. optical lens 30.

An alternative optical device 210 is shown in Figure 8. The optical device 210 substantially corresponds to the optical device 10, therefore like features are provided with like reference numerals, augmented by 200. The optical device 210 comprises a substrate 212 having a first side 212a (a top side as shown) and a second side 212b (a bottom side as shown). The second side 212b comprises solder pads 214. The first side 212a comprises wire bond pads 216. Disposed on the first side 212a of the substrate 212 is a radiation-emitting device. In the present exemplary embodiment the radiation-emitting device is a vertical cavity surface emitting laser (VCSEL) 218. In other embodiments, the radiation-emitting device may be an edge-emitting laser, a light emitting diode, a laser diode or the like. Also disposed on the first side 212a of the substrate 212 is a sensor die 220 comprising an integrated sensor array 222. Both the VCSEL 218 and the sensor die 220 are in electrical connection with the wire bond pads 216 via wire bonds 224. The optical device 210 comprises a conformal coating layer 226. The conformal coating layer 226 is formed parylene. The conformal coating layer 226 covers the VCSEL 218, the sensor die 220 and the exposed areas of the first side 212a of the substrate between and adjacent the VCSEL 218 and the sensor die 220. Although not shown in Figure 8, some of the conformal coating layer 226 may cover the wire bonds 224 as a result of the formation process of the conformal coating layer 226. The conformal coating layer 226 has a uniform thickness of less than 1 m. The conformal coating layer 226 is moisture resistant, having a water vapour transmission rate less than 10' ² g/m ² /day, preferably less than 10' ⁵ g/m ² /day, thus the conformal coating layer 226 protects the VCSEL 218 and the sensor die 220 from ingress of water vapour which could be potentially damaging to the aforementioned components, the VCSEL 218 in particular. The conformal coating layer 226 is substantially transparent to near-infrared electromagnetic radiation, thus the conformal coating layer 226 does not interfere with the operation of the VCSEL 218 and the sensor die 220. The optical device 210 further comprises a cap 234 formed of a plurality of cap portions 234a, 234b, 234c mounted on the first side 12a of the substrate 12. The cap 234 may be unitary, or one or more of the cap portions 234a, 234b, 234c may be formed separately. The cap 234 covers the sensor die 220 and the VCSEL 218. An aperture 236a is formed between cap portion 234a and cap portion 234b. The aperture 236a is aligned with the integrated sensor array 222. An aperture 236b is formed between cap portion 234b and 234c. The aperture 236b is aligned with the VCSEL 218. The optical device 210 is manufactured in a similar manner to the steps described above in reference to Figures 2 to 6, with the omission of formation of an overmold over the conformal coating layer.

An alternative optical device 310 is shown in Figure 9. The optical device 310 substantially corresponds to the optical device 10, therefore like features are provided with like reference numerals, augmented by 300. The optical device 310 comprises a substrate 312 having a first side 312a (a top side as shown) and a second side 312b (a bottom side as shown). In some embodiments the second side 312b comprises solder pads 314 suitable for coupling the optical device 310 to a further component, a further substrate, a printed circuit board, or the like. The first side 312a comprises wire bond pads 316. Disposed on the first side 312a of the substrate 312 is a radiation-emitting device. In the present exemplary embodiment the radiation-emitting device is a vertical cavity surface emitting laser (VCSEL) 318. In other embodiments, the radiationemitting device may be an edge-emitting laser, a light emitting diode, a laser diode or the like. Also disposed on the first side 312a of the substrate 312 is a sensor die 320 comprising an integrated sensor array 322. Both the VCSEL 318 and the sensor die 320 are in electrical connection with the wire bond pads 316 via wire bonds 324. The optical device 310 further comprises an overmold 328 formed of transparent epoxy resin. The overmold covers the VCSEL 318, sensor die 320, the exposed areas of the first side 312a of the substrate 312, and the wire bonds 24. The overmold 328 protects the VCSEL 318 and the sensor die 320 from liquid water, dust and mechanical damage. The overmold 328 is structured to comprise a shaped portion that functions as an optical lens 330. The optical lens 330 is positioned over the integrated sensor array 322 of the sensor die 320. The overmold 328 further comprises a slit 332 between the VCSEL 318 and the sensor die 318. The optical device 310 further comprises a conformal coating layer 326. In some embodiments, the conformal coating layer 326 may be formed of aluminium oxide. In other examples, the conformal coating layer may be formed of one or more other oxide materials such as zinc oxide, titanium dioxide, tantalum oxide and/or silicone dioxide. The conformal coating layer 326 covers and is formed on the overmold 328. The conformal coating layer 326 has a uniform thickness of less than 1 pm, preferably less than 100nm. The conformal coating layer 326 is moisture resistant, having a water vapour transmission rate less than 10' ² g/m ² /day, preferably less than 10' ⁵ g/m ² /day, thus the conformal coating layer protects the VCSEL 318 and the sensor die 320 from ingress of water vapour which could be potentially damaging to the aforementioned components, the VCSEL 318 in particular. The conformal coating layer 326 is substantially transparent to near-infrared electromagnetic radiation, thus the conformal coating layer 326 does not substantially interfere with the operation of the VCSEL 318 and the sensor die 320. The conformal coating layer 26 is interrupted adjacent the slit 332 in the overmold 328. The optical device 310 further comprises a cap 334 formed of a plurality of cap portions 334a, 334b, 334c. The cap 334 may be unitary; alternatively one or more of the cap portions 334a, 334b, 334c may be formed separately. The cap 334 covers the sensor die 320 and the VCSEL 318. The cap 334 is intransparent to near-infrared electromagnetic radiation. Furthermore, the cap 334 is formed of a temperature-stable material. An aperture 336a is formed between cap portion 334a and cap portion 334b. The aperture 336a is aligned with the optical lens 330 and the integrated sensor array 322, and light can pass through the aperture. Cap portions 334a and 334c are mounted on the substrate 312 either side of the coated overmold 328. Cap portion 334b is mounted on the substrate 312 in the slit 332. An aperture 336b is formed between cap portion 334b and 334c. The aperture 336b is aligned with the VCSEL 18, and light can pass through the aperture 336b.

An alternative optical device 410 is shown in Figure 10. The optical device 410 substantially corresponds to the optical device 10, therefore like features are provided with like reference numerals, augmented by 400. The optical device 410 comprises a substrate 412 having a first side 412a (a top side as shown) and a second side 412b (a bottom side as shown). In some embodiments the second side 412b comprises solder pads 414 suitable for coupling the optical device 410 to a further component, a further substrate, a printed circuit board, or the like. The first side 412a comprises wire bond pads 416. Disposed on the first side 412a of the substrate 412 is a radiation-emitting device. In the present exemplary embodiment the radiation-emitting device is a vertical cavity surface emitting laser (VCSEL) 418. In other embodiments, the radiationemitting device may be an edge-emitting laser, a light emitting diode, a laser diode or the like. Also disposed on the first side 412a of the substrate 412 is a sensor die 420 comprising an integrated sensor array 422. Both the VCSEL 418 and the sensor die 420 are in electrical connection with the wire bond pads 416 via wire bonds 424. The optical device 410 further comprises an overmold 428 formed of transparent epoxy resin. The overmold covers the VCSEL 418, sensor die 420, the exposed areas of the first side 412a of the substrate 412, and the wire bonds 424. The overmold 428 protects the VCSEL 418 and the sensor die 420 from liquid water, dust and mechanical damage. The optical device 410 further comprises a conformal coating layer 426. In some embodiments, the conformal coating layer 426 may be formed of aluminium oxide. In other examples, the conformal coating layer may be formed of one or more other oxide materials such as zinc oxide, titanium dioxide, tantalum oxide and/or silicone dioxide. The conformal coating layer 426 covers and is formed on the overmold 428. The conformal coating layer 426 has a uniform thickness of less than 1 pm, preferably less than 100nm. The conformal coating layer 426 is moisture resistant, having a water vapour transmission rate less than 10' ² g/m ² /day, preferably less than 10' ⁵ g/m ² /day, thus the conformal coating layer protects the VCSEL 418 and the sensor die 420 from ingress of water vapour which could be potentially damaging to the aforementioned components, the VCSEL 418 in particular. The conformal coating layer 426 is substantially transparent to near-infrared electromagnetic radiation, thus the conformal coating layer 426 does not substantially interfere with the operation of the VCSEL 418 and the sensor die 420.

Figure 11 depicts a cross-sectional view of an optical device 510 comprising a stress-decoupling layer, according to a further embodiment of the disclosure.

The optical device 510 comprises a substrate 512 having a first side 512a (a top side as shown) and a second side 512b (a bottom side as shown). In some embodiments the second side 512b comprises solder pads 514 suitable for coupling the optical device 510 to a further component, a further substrate, a printed circuit board, or the like. The first side 512a comprises wire bond pads 516. Disposed on the first side 512a of the substrate 512 is a radiation-emitting device 518. In the present example, the radiation-emitting device 518 is a VCSEL. In alternative embodiments, the radiation-emitting device 518 may be an edge-emitting laser, a light emitting diode, a laser diode or the like. For purposes of example only, also disposed on the first side 512a of the substrate 512 is a sensor die 520 comprising an integrated sensor array 522. Both the radiation-emitting device 518 and the sensor die 520 are in electrical connection with the wire bond pads 516 via wire bonds 524. In some embodiments the sensor die 520 may comprise control circuitry and/or driver circuitry. As such, in some embodiments the sensor die 520 may be electrically coupled to the radiation-emitting device 518, such as to control and/or drive the radiation-emitting device 518. In some embodiments, the radiation-emitting device 518 may comprise an integrated driver. In yet further embodiments, a driver may be provided on another die of component (not shown) that is electrically coupled to the radiation-emitting device 518.

With continued reference to Figure 11 , the optical device 510 comprises a stress-decoupling layer 544. In some embodiments, the stress-decoupling layer 544 comprise a cross-linked epoxy. The stress-decoupling layer may comprise a re-flow stable polymer.

In the example embodiment of Figure 11, the stress-decoupling layer 544 covers the top and sidewalls of the radiation-emitting device 518. Although not shown in Figure 11 , some of the stress-decoupling layer 544 may cover the wire bonds 524 as a result of the formation process of the stress-decoupling layer 544 which will be later described. In some embodiments, the stress-decoupling layer 544 may have a uniform thickness of approximately 10 micrometres.

With continued reference to Figure 11, the example optical device 510 further comprises an overmold 528 formed of transparent epoxy resin. The overmold 528 covers the stress-decoupling layer 544.

The stress-decoupling layer 544 has a lower elastic modulus than the overmold 528.

The overmold 528 protects the radiation-emitting device 518 and the sensor die 520 from moisture, dust and mechanical damage. In some example embodiment, the overmold 528 may be structured to comprise a shaped portion that functions as an optical lens, such as the optical lens 30 depicted in Figure 1. Figure 12 depicts a cross-sectional view of a further optical device 610 comprising a stress-decoupling layer 644, according to a further embodiment of the disclosure.

The features of the optical device 610 of Figure 12 generally correspond to the features of the optical device 510 of Figure 11 , and therefore are not described in further detail for purposes of brevity.

It can be seen that in the embodiment of Figure 12, the stress-decoupling layer 644 covers the top and sidewalls of a radiation-emitting device 618, the top and sidewalls of a sensor die 620. In some embodiments, the stress-decoupling layer 644 may also cover exposed areas of an upper side of the substrate 612.

Figure 13 depicts a cross-sectional view of an optical device 710 comprising a stress decoupling layer 744 and a conformal coating layer 726. The conformal coating layer 726 is a moisture resistant layer.

The features of the optical device 710 of Figure 13 generally correspond to the features of the optical device 510 of Figure 11 , and therefore are not described in further detail for purposes of brevity.

In the embodiments of Figure 13, the stress-decoupling layer 744 is formed between the moisture-resistant conformal coating layer 744 and an overmold 728. The stress-decoupling layer 744 has a lower elastic modulus than the overmold 728.

The stress-decoupling layer 744 works synergistically with the conformal coating layer 728 to minimise moisture ingress into the optical device 710. For example, while the conformal coating layer 728 may provide a degree of moisture resistance, for embodiments not comprising the stress-decoupling layer 744 the conformal coating layer 728 may be subject to delamination due to thermomechanical stresses. Such delamination may further increase a rate of hygroscopic deterioration. Thus, the embodiment of Figure 13, which also implements the stress-decoupling layer 744 over the conformal coating layer 728, is highly resistant to moisture ingress. Figure 14 depicts a cross-sectional view of an optical device 810 comprising a stress-decoupling layer 844 and a moisture-resistant layer 826, according to a further embodiment of the disclosure. For purposes of example only, it can be seen that only a radiation-emitting device 818 is covered by the stress-decoupling layer 844 and the moisture-resistant layer 826. It will be understood that in other embodiments, other features of the optical device 810, such as sensor die 820, may also be covered, as is depicted in Figure 13.

Furthermore, for purposes of example, the optical device 810 also comprises a cap 834. The cap 834 generally corresponds to the cap 34 of the optical device 10 of Figure 1, and therefore is not described in further detail.

Although the disclosure has been described in terms of particular embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure, which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in any embodiments, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

LIST OF REFERENCE NUMERALS

10, 110, 210, 310, 410, 510, 610, 710, 810 Optical device

12, 112, 212, 312, 412, 512, 612 Substrate

12a, 112a, 212a, 312a, 412a, 512a, 612a First side of substrate

12b, 112b, 212b, 312b, 412b, 512b Second side of substrate

14, 114, 214, 314, 414, 514 Solder pads

16, 116, 216, 316, 416, 516 Wire bond pads

18, 118, 218, 318, 418, 518, 618, 718, 818 VCSEL

20, 120, 220, 320, 420, 520, 620, 820 Sensor die

22, 122, 222, 322, 422, 522 Integrated sensor array

24, 124, 224, 324, 424, 524 Wire bonds

26, 126, 226, 326, 426, 526, 726, 826 Conformal coating layer

28, 128, 328, 428, 528, 728 Overmold 30, 330 Optical lens

32, 332 Slit

34, 234, 334, 834 Cap

34a, 34b, 34c, 234a, 234b, 234c, 334a, 334b, 334c Cap portion 36a, 36b, 236a, 236b, 336a, 336b Aperture

38 Die attach film

40 Conductive glue

42 Glue

544, 644, 744, 844 stress-decoupling layer