WO2025012223A1

WO2025012223A1 - Optical readout module

Info

Publication number: WO2025012223A1
Application number: PCT/EP2024/069227
Authority: WO
Inventors: Matthieu Lacolle; Hallvard ANGELSKÅR
Original assignee: Sensibel As
Priority date: 2023-07-10
Filing date: 2024-07-08
Publication date: 2025-01-16

Abstract

An optical readout module (68) for an optical device comprises a support (70), a light source (74) and a light detector (76) provided in or on a first surface (80) of the support (70), and an optical component (72) formed in or fabricated on the support (70). The support (70) is or comprises a layer of overmolding material. The light source (74) is arranged to emit outbound light through the support (70), and the light detector (76) is arranged to detect inbound light that has propagated to the light detector (76) through the support (70). The optical component (72) is positioned so that in use the outbound light travels via the optical component (72) towards a target object; or so that in use the inbound light travels via the optical component (72) to the light detector (76). A method of manufacturing the optical readout module (68) comprises attaching the light source (74) and the detector to a substrate or wafer; applying the layer of overmolding material to the substrate or wafer; and forming the optical component (72) in the layer of overmolding material or fabricating the optical component (72) on the layer of overmolding material.

Description

Optical readout module

This invention relates to optical readout modules suitable for use in optical devices, in particular but not exclusively in optical distance-measurement devices, and methods of manufacturing such optical readout modules.

Various devices are known in the art for performing measurements, e.g. distance measurements, using light. Some examples of optical devices that measure a distance include LIDAR (time-of-flight) sensors and optical displacement sensors (e.g. optical microphones, optical accelerometers) based on optical interferometric readout. The operation of optical measurement devices typically involves the device causing light to interact with a physical system, and then determining a physical parameter associated with the physical system from a property of the light following the interaction.

To determine the physical parameter using the optical measurement device, an optical readout arrangement is required to convert the light into a signal that can be processed to allow the relevant property of the light to be determined and the physical parameter calculated therefrom. Other optical devices may also use an optical readout arrangement. The optical readout arrangement may include one or more detectors for detecting the light. It may also include a light source to generate the light (e.g. as a beam or pulse), and one or more optical components arranged to direct the light towards a target system and/or to direct the light onto the detector(s).

Optical devices can provide very sensitive output, e.g. very precise measurements, but the components of the optical readout arrangement need to be aligned very precisely. Various configurations for optical readout arrangements with associated manufacturing methods and alignment techniques are known in the art, but improvements allowing greater ease and efficiency of manufacture and alignment are desirable.

When viewed from a first aspect, the invention provides a method of manufacturing an optical readout module for an optical device, wherein the optical readout module comprises: a support comprising a first surface; wherein the support is or comprises a layer of overmolding material; a light source provided in or on the first surface, wherein the light source is arranged to emit outbound light through the support; a light detector provided in or on the first surface, wherein the light detector is arranged to detect inbound light that has propagated to the light detector through the support; and an optical component formed in or fabricated on the support, wherein the optical component is positioned so that in use the outbound light travels via the optical component towards a target object; or wherein the optical component is positioned so that in use the inbound light travels via the optical component to the light detector; the method comprising: attaching the light source and the detector to a substrate or wafer; applying the layer of overmolding material to the substrate or wafer; and forming the optical component in the layer of overmolding material or fabricating the optical component on the layer of overmolding material.

This aspect of the invention extends to an optical readout module for an optical device, the optical readout module comprising: a support comprising a first surface, wherein the support is or comprises a layer of overmolding material; a light source provided in or on the first surface, wherein the light source is arranged to emit outbound light through the support; a light detector provided in or on the first surface, wherein the light detector is arranged to detect inbound light that has propagated to the light detector through the support; an optical component formed in or fabricated on the support, wherein the optical component is positioned so that in use the outbound light travels via the optical component towards a target object; or wherein the optical component is positioned so that in use the inbound light travels via the optical component to the light detector.

This aspect of the invention extends to an optical readout module manufactured according to the method defined above. When viewed from a second aspect, the invention provides an optical readout module for an optical device, the optical readout module comprising: a support comprising a first surface; a light source provided in or on the first surface, wherein the light source is arranged to emit outbound light through the support; a light detector provided in or on the first surface, wherein the light detector is arranged to detect inbound light that has propagated to the light detector through the support; an optical component formed in or fabricated on the support, wherein the optical component is positioned so that in use the outbound light travels via the optical component towards a target object; or wherein the optical component is positioned so that in use the inbound light travels via the optical component to the light detector.

The invention extends to a method of manufacturing an optical readout module in accordance with the second aspect as defined above.

The features set out below are optional features of the invention in accordance with the second aspect. Where applicable (e.g. where technically feasible and consistent with the invention in accordance with the first aspect as defined above), the features below are also optional features of the invention in accordance with the first aspect.

It will be appreciated from the present disclosure that “outbound light” refers to light that is emitted by the light source in use and propagates out of the optical readout module to the target object, and “inbound light” refers light that propagates into the optical readout module and through the support to the light detector. “Inbound light” may refer to the outbound light, or a portion thereof, after it has propagated back to the optical readout module following an interaction with the target object. The target object may comprise one or more target surfaces, e.g. one or more reflecting surfaces, optical elements, etc. The light may interact with one or more of the target surfaces.

Providing an optical component that is formed in or fabricated on the support wherein the light source and light detector are provided in or on a first surface of the same support may provide advantages over the prior art. In particular, it will be appreciated from the present disclosure that the optical readout module of the invention may be manufactured or be suitable for manufacturing using wafer-level packaging techniques. In this context, wafer-level packaging (which may also be referred to as wafer-level assembly) may be understood as referring to an approach for manufacturing in which multiple optical readout modules are manufactured on a single wafer or substrate and a singulation process is subsequently used to separate the optical readout modules into individual units.

The method may comprise manufacturing multiple optical readout modules (e.g. over a thousand) on a single wafer or a single substrate. The method may comprise applying a singulation process to separate the wafer or substrate and/or a layer (e.g. an overmolding layer) applied to the wafer or substrate into multiple individual optical readout modules. The overmolding layer may be singulated after removal of the wafer or substrate. The method may comprise fully removing the wafer or substrate from the overmolding layer, or from a portion of the overmolding layer, e.g. prior to singulation. The method may comprise attaching, e.g. bonding, the wafer or substrate or the overmolding layer to a further wafer or substrate comprising one or more components or circuitry (e.g. such as an ASIC or MEMS component as described below for each optical readout module being manufactured) before the singulation process applied, i.e. so that the further wafer or substrate is singulated together with the wafer or substrate and/or with the overmolding layer in one singulation step.

It will thus be understood from this disclosure that the layer of overmolding material corresponding to the support in each optical readout module may be applied as a single overmolding layer over the single wafer or single substrate, and then singulated so that each module comprises a layer of overmolding material that is a singulated piece of the overmolding layer.

The possibility of using wafer-level packaging techniques to manufacture the optical readout module may provide advantages over prior art optical readout arrangements in particular in the ease and efficiency of manufacture of the optical readout module and alignment of its components. For example, using wafer-level packaging techniques, multiple dies (e.g. for the light source and/or the light detector) may be simultaneously bonded to a wafer or substrate with high precision. Multiple optical components may be simultaneously formed or fabricated with high precision. For each module, the light source and detector may be precisely aligned with respect to the optical component, or vice versa, during the bonding or formation/fabrication process. The possibility of precise alignment may be advantageous for light sources suitable such as vertical-cavity surface-emitting lasers (VCSELs), which are typically divergent and therefore in general are not suitable for measurements that are carried out at a distance unless the light source is suitably collimated. The collimation of light beams from such light sources to sufficiently control the light direction typically requires an optical component aligned with high precision. Manufacturing multiple modules on a single wafer or substrate before singulation may advantageously allow mass manufacture of the optical readout module.

The optical component may be formed in or fabricated on a second surface of the support. It will be understood that the optical component being formed in or fabricated on the second surface is distinguished from arrangements in which an optical component is manufactured separately and then mounted on (e.g. bonded to) the second surface. It is also distinguished from arrangements in which an optical component is formed in or fabricated on a separate support that is then bonded on or otherwise attached to the second surface of the support.

The layer of overmolding material may comprise a planarized surface. The method may comprise planarizing a surface of the layer of overmolding material, e.g. by polishing. The planarized surface may comprise the second surface of the support. The surface may be planarized before the wafer or substrate is removed from the layer of overmolding material.

Planarizing the surface of the layer of overmolding material may facilitate easier formation or fabrication of the optical component. Planarizing the surface of the layer of overmolding material may render the surface more suitable for attaching to another surface, e.g. to a housing, to a support, or to a component of a optical device, e.g. facilitating easier positioning or alignment of the optical readout module relative to another component. The optical module may be attached (e.g. mounted) via the planarized surface to a housing, a support, or a component of an optical device.

The first and second surfaces may be on respective first and second opposing sides of the support. For example, the support may be a planar piece of material with first and second parallel surfaces, corresponding to the first and second surfaces defined above.

The outbound light may propagate through the support and exit the support via the second surface. The inbound light may enter the support via the second surface and propagate to the light detector.

The second surface may be a surface of a recess formed in the support. For example, the first surface may have the recess formed therein, a surface (e.g. a floor or bottom surface) of the recess defining the second surface, e.g. such that the first and second surfaces are parallel and offset from each other in a direction perpendicular to the first surface.

The outbound light may propagate into the recess and enter the support via the optical component that is in or on the second surface. The outbound light may exit the support via a further surface on an opposing side of the support from the first surface.

The inbound light may enter the support via the further surface. The inbound light may exit the support via the optical component that is in or on the second surface and propagate via the recess to the light detector.

The optical component may be formed in an interior of the support, e.g. such that the optical component is encapsulated by the support, or such that the optical component extends to the second surface of the support.

In accordance with the first aspect and in a set of embodiments in accordance with the second aspect, the method comprises attaching (e.g. bonding) the light source and the detector to a substrate or wafer, e.g. glass substrate or a semiconductor wafer. The support may be or may comprise a substrate die or a wafer die (e.g. formed through a singulation process of the wafer or substrate). The light source and the light detector may be attached (e.g. bonded) to a substrate die or a wafer die. The optical component may be formed in or fabricated on the substrate die or wafer die, e.g. on a surface of the substrate die or wafer die.

It is to be understood that when it is said that a component or feature (e.g. the light source, light detector, optical component, recess, etc.) “is formed in”, “is fabricated on”, “is bonded to”, etc. the support, a surface, etc. in the context of the optical readout module of the invention, this is to be understood to refer to a state and not a process, e.g. it refers to a component for feature that has been formed in, fabricated on, or bonded to, etc., the support, the surface, etc. The method may comprise method steps corresponding to any statements in this disclosure describing the state of a feature, e.g. a feature that “is formed in” a surface, a die, etc. may have a corresponding method step of forming the component in the surface, the die, etc. However, for components and other features whose state is described in relation to the substrate die or the wafer die (e.g. is formed in, is fabricated on, is bonded to, etc. the substrate die or the wafer die or a surface thereof), the corresponding method step may instead be performed on the substrate or wafer, instead of the substrate die or wafer die respectively. This is because the method step may be carried out for multiple optical readout module manufacture on a single substrate or a single wafer which is subsequently singulated into multiple optical readout modules, each comprising a respective die.

The method may comprise forming the optical component in the substrate or wafer or fabricating the optical component on the substrate or wafer, and subsequently attaching (e.g. bonding) the light source and the light detector to a surface of the substrate or wafer. Such a surface may correspond to the first surface of the support of the optical readout module. The method may comprise aligning the light source or the light detector relative to the optical component. The light source or the light detector may be aligned relative to the optical component directly or indirectly - e.g. alignment may be relative to a secondary element, e.g. a metal contact pad, that itself has been aligned relative to the optical component e.g. during fabrication of the secondary element. In embodiments that comprise manufacturing multiple optical readout modules on a single wafer or a single substrate, the method may comprise forming or fabricating a plurality of optical components, wherein the method comprises collectively aligning the plurality of optical components (directly or indirectly) with a corresponding plurality of light sources or a corresponding plurality of light detectors.

In accordance with the first aspect and in a set of embodiments in accordance with the second aspect, the optical readout module comprises a layer of overmolding material. For example, the overmolding material may be an epoxy mould compound. Similarly, in accordance with the first aspect and in a set of embodiments in accordance with the second aspect, the method of manufacture comprises applying a layer of overmolding material to the substrate or wafer. The overmolding material may encapsulate or substantially encapsulate the light source and the light detector.

The support may consist of a single material or a homogeneous mix of materials. In a set of embodiments, the support consists of the layer of overmolding material, wherein the overmolding material consists of a single material or a homogeneous mix of materials. This may improve ease of manufacture (e.g. mass manufacture via wafer-level packaging and singulation). It may also help to improve the structural integrity of the support, e.g. in embodiments in which the wafer or substrate is fully removed from the layer of overmolding material. The layer of overmolding material may comprise a homogeneous volume of material applied over at least the light source and the light detector. Applying the layer of overmolding material may comprise applying a homogeneous volume of material over at least the light source and the light detector. The homogeneous volume of material may encapsulate the light source and the light detector. The optical component may be formed in or fabricated on the homogeneous volume of material.

The layer of overmolding material may extend over the support, e.g. over the first surface thereof. For example, the optical readout module may comprise a substrate die or wafer die as described above with the light source and the photo detector attached to a first side thereof, wherein the optical readout module further comprises a layer of overmolding material extending over the first side of the substrate die or wafer die, e.g. fully encapsulating the light source and light detector.

The method may comprise removing the wafer or substrate from the layer of overmolding material, e.g. fully or partially removing it, e.g. thinning the substrate or wafer. In some preferred embodiments, the method comprises fully removing the wafer or substrate from the layer of overmolding material e.g. to expose a surface of the layer of overmolding material. This may allow access to the exposed surface, e.g. to provide access to electrical contracts on the exposed surface, or for mounting the support or attaching it to another component via the exposed surface.

It will be understood from the present disclosure that the “layer” of overmolding material may refer to overmolding material that was applied as a layer over the wafer or substrate (i.e. to form a structure comprising at least two layers), but which has had the other layer(s) removed, e.g. so that it is a free-standing or standalone piece. In the context of the optical readout module of the present invention, the layer of overmolding material may be referred to as a planar piece of overmolding material.

The method may comprise removing the wafer or substrate using back-grinding, e.g. wafer back-grinding. The method may comprise applying a temporary adhesion layer to the wafer or substrate before applying the overmolding material, and subsequently releasing the overmolding material from the wafer or substrate, e.g. by applying heat or light to de-laminate it from the wafer or substrate. Other methods of removing the wafer or substrate from the overmolding material may be used in accordance with the invention.

The surface of the overmolding material that may be exposed by removing the wafer or substrate may be the first surface of the support, e.g. wherein the light source and the light detector are embedded in the first surface of the support.

In some embodiments, the optical readout module does not comprise an overmolding substrate (e.g. a wafer or wafer die, or a substrate or substrate die) to which the layer of overmolding material was applied during an overmolding process. For example, the support may comprise a free-standing layer of overmolding material. In some embodiments, the first surface of the support comprises an at least partially exposed surface of the layer of overmolding material. The surface may be fully exposed or fully exposed except for electrical contacts.

The method may comprise providing electrical contacts for the light source and/or light detector between the wafer or substrate and the layer of overmolding material. The method may comprise fabricating electrical contacts on the wafer or substrate prior to applying the layer of overmolding material. The method may comprise fabricating electrical connections, e.g. as part of the electrical contacts or between the electrical contacts and the light source and/or light detector, prior to applying the layer of overmolding material. The electrical contacts and/or the electrical connections may comprise redistribution layers (RDLs). The electrical contacts and/or the electrical connections may be formed by bump bonding the light source and/or the light detector to the wafer or substrate. The method may comprise fully removing the wafer or substrate from the layer of overmolding material to expose the electrical contacts.

The optical readout module may comprise electrical contacts at the first surface for providing an electrical connection to the light source and/or an electrical connection to the light detector.

In accordance with the first aspect and in a set of embodiments in accordance with the second aspect, the support is or comprises the layer of overmolding material, e.g. wherein the light source and the light detector are embedded in the first surface of the support. The method of manufacture may correspondingly comprise removing the substrate or wafer from the overmolding material. For example, the wafer or substrate may be removed by wafer back-grinding or similar techniques. As another example, the wafer or substrate may have a temporary adhesion layer applied before the overmolding material is applied, and the overmolding material may subsequently be released e.g. by applying heat or light to de-laminate it from the wafer or substrate. The first surface of the support may be a surface of the overmolding material that is left exposed after the substrate or wafer has been removed, i.e. a surface that was facing the substrate or wafer before the substrate or wafer was removed. The overmolding material may fully encapsulate the light source and the light detector except for electrical contacts, e.g. electrical contacts left exposed by the removal of the substrate or wafer.

In accordance with the first aspect and in a set of embodiments in accordance with the second aspect, the method of manufacturing the optical readout module comprises forming the optical component in the layer of overmolding material or fabricating the optical component on the layer of overmolding material, e.g. during application of the overmolding layer. The method of manufacturing the optical readout component may comprise forming the optical component in a surface of the layer of overmolding material or fabricating the optical component on a surface of the layer of overmolding material (e.g. such that said surface is the second surface of the support). The step of forming or fabricating the optical component may comprise aligning the optical component with respect to the light source or the light detector. The step of forming or fabricating the optical component is preferably carried out before removal of the substrate or wafer.

The optical readout module may comprise redistribution layers (RDLs) in the overmolding material, e.g. to provide electrical contacts on a top surface of the layer of overmolding material, or to provide electrical contacts on the first or second surface of the support. The method may comprise fabricating RDLs in the overmolding material.

The optical readout module may comprise more than one light detector. For example, in embodiments in which the optical readout module is configured for use in an optical displacement sensor that uses optical interferometric readout, a plurality of light detectors may be provided, wherein each light detector is positioned to detect a respective diffraction order of the inbound light. As another example, the optical component may separate the outbound light into a plurality of beams, and a respective light detector may detect each beam or a portion thereof. Each beam may be diffracted to produce a respective plurality of diffraction orders, and a respective light detector may detect each diffraction order for each beam, e.g. the light may be split into three beams, each producing three diffraction orders, with a total of nine light detectors each detecting a respective diffraction order. The light detector(s) may comprise any suitable light detector, e.g. a photo detector such as a photo diode, CCD, bolometer, etc. The type of light detector may be selected based on the application of the optical device in which the optical readout module is to be incorporated.

The optical readout module may comprise more than one light source. The light source(s) may comprise any suitable light source, e.g. a laser, a laser diode, a vertical-cavity surface-emitting laser (VCSEL) or an LED. The type of light source may be selected based on the application of an optical device in which the optical readout module is to be incorporated.

The inbound light and/or the outbound light may propagate via the optical component. The optical readout module may comprise two or more optical components. For example, one or more optical components may be positioned in or on the support or the second surface such that the outbound light propagates via the one or more optical components, and one or more further optical components may be positioned in or on the support or the second surface such that the inbound light propagates to the light detector(s) via the one or more further optical components. One or more of the optical component(s) may be arranged to direct the outbound light towards or onto the target surface. One or more of the optical component(s) may be arranged to direct the inbound light towards or onto the light detector(s).

In general, when it is said that the outbound light or the inbound light propagates via an optical component, this may mean that all or a portion of the light propagates via the optical component.

The optical component(s) may comprise a lens or microlens, e.g. a diffractive lens, a Fresnel lens, a refractive lens (e.g. a moulded polymer) or a gradient-index (GRIN) lens. The optical component(s) may comprise a beam-steering component, e.g. a prism. The optical component(s) may comprise a meta-surface. The optical component(s) may comprise freeform optics. The optical component(s) may diffract, focus, or steer (e.g. refract) the outbound and/or inbound light. The optical component(s) may be formed or fabricated by surface patterning, etching, photolithography, nano-imprinting, or any other suitable technique.

The optical component(s) may be formed directly in or fabricated directly on the second surface of the support, e.g. directly in or on the substrate material, the wafer material, or the overmolding material. However, the formation or fabrication of the optical component(s) may involve the addition (e.g. deposition) of one or more layers onto the second surface of the support, e.g. as part of the formation or fabrication process, such that the optical component is formed in or fabricated on such one or more layers. It will be understood that forming the optical component in or fabricating the optical component on the second surface of the support as defined herein in accordance with the invention is distinct from forming or fabricating the optical component in/on a separate piece and attaching that piece to a support.

The light source(s) and the light detector(s) may be attached to the substrate die or wafer die via metal contact pads on the substrate or wafer. The light source may comprise a die, e.g. a VCSEL fabricated on a lll-V semiconductor die, which may be bonded to the wafer die or substrate die. The light detector may comprise a die, e.g. a photo detector fabricated on a silicon, lll-V or other semiconductor die, which may be bonded to the substrate die or wafer die.

The support may be formed from a single (i.e. integrally formed) piece of material. For example, in embodiments comprising a substrate die or in which a substrate is used during manufacture, the substrate or substrate die may be made from glass. In embodiments comprising a wafer die or in which a wafer is used during manufacture, the wafer or wafer die may be made from a semiconductor, e.g. a silicon wafer or wafer die.

In a set of embodiments, the support is at least partially transparent, e.g. transparent or substantially transparent, at a wavelength of the light source. The wavelength of the light source may refer to a central wavelength of the light source or a range of wavelengths of the light source (e.g. full-width half-maximum). Similarly, one or more of the wafer or wafer die, the substrate or substrate die, or the overmolding material may be at least partially transparent at a wavelength of the light source.

It will be understood that “optical readout” as used in the context of an “optical readout module” in accordance with the present invention refers to the process of converting light into a signal that can be processed, e.g. in order to determine one or more properties of the light and to calculate a physical parameter therefrom. The signal may be an electrical signal which may, for example, correspond to an intensity of the inbound light or encode a time of arrival of the inbound light.

The optical readout module may comprise electronics and/or circuitry that processes the signal to determine the property of the inbound light and which may determine a physical parameter therefrom. However, this is not essential. For example, readout electronics and/or circuitry (e.g. an ASIC) may be provided remotely or otherwise separately from the optical readout module, e.g. integrated in the optical device.

The invention extends to an optical device comprising an optical readout module in accordance with the present invention as defined herein.

The optical device may comprise an optical measurement device. The optical measurement device may be configured to measure any parameter that can be determined using a measurement process that uses light, e.g. a distance, a rotation, a speed, an optical path difference (e.g. due to a refractive index change or a change in light path distance).

The optical device may comprise an optical distance-measurement device. The optical distance-measurement device may be configured to measure any distance, e.g. the distance to a surface, the position or displacement of an object, etc. It is to be understood that in the context of an optical distance-measurement device, the measurement of a “distance” may refer to the measurement of any spatial parameter (i.e. having dimensions of length), e.g. position, separation, displacement, etc. The optical device may comprise an optical displacement sensor, e.g. that uses optical interferometric readout, e.g. an optical microphone or an optical accelerometer. The optical device may comprise a movable element, e.g. a membrane or proof mass, wherein the moveable element is moveable relative to an optical element (e.g. a diffractive optical element). The outbound light may impinge on the optical element and the moveable element, such that each reflects a respective portion of the outbound light back towards the optical readout module. The reflected light (which corresponds to the inbound light) propagates back to the optical readout module, where it forms an interference pattern that is detected by the light detector and converted into a processable signal. The interference pattern, and thus the signal, is dependent on the separation between the optical element and the moveable element. The separation between the optical element and the moveable element can thus be determined from the signal.

The optical device may comprise a MEMS (microelectromechanical systems) component comprising the moveable element. The optical device may comprise an ASIC. The optical readout module may be mounted on the MEMS component. The optical readout module may be electrically connected to the ASIC, e.g. via wire-bonding or bump-bonding.

The optical device may comprise a LIDAR (time-of-flight) sensor. The target object may comprise a surface whose distance from the optical device is to be measured.

It is to be understood that in the present context, “light” refers to electromagnetic radiation. The light may be or comprise light in the visible range. The light may be or comprise light in the infrared, visible and ultraviolet ranges.

Certain preferred embodiments will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 shows an optical readout module in accordance with a first embodiment of the invention; Figure 2 shows the optical readout module of Figure 1 installed in an optical microphone;

Figure 3 shows a schematic diagram illustrating the optical aspects of the operation of the optical readout module of Figure 1 ;

Figures 4 to 7 show a series of steps in a method of manufacturing the optical readout module of Figure 1 using wafer-level packaging;

Figure 8 shows a second embodiment of an optical readout module in accordance with the invention;

Figure 9 shows the optical readout module of Figure 8 installed in an optical microphone;

Figures 10 to 11 show two steps in a method of manufacturing the optical readout module of Figure 8 using wafer-level packaging;

Figure 12 shows an optical readout module in accordance with a third embodiment of the invention;

Figure 13 shows the optical readout module of Figure 12 installed in an optical microphone;

Figures 14 to 19 show a series of steps in a method of manufacturing the optical readout module of Figure 12 using wafer-level packaging;

Figure 20-23 show schematic diagrams illustrating the optical aspects of the operation of some further embodiments of optical readout modules in accordance with the invention;

Figures 24 and 25 show further embodiments of optical readout modules which are variations on the embodiment of Figure 12; Figures 26 to 33 show a series of steps in a method of manufacturing the optical readout module of Figure 25 using wafer-level packaging; and

Figure 34 shows a further embodiment of an optical readout module which is a variation on the embodiment of Figure 8.

Figure 1 shows an optical readout module 2 in accordance with a first embodiment of the invention. The optical readout module 2 comprises a support 4, a microlens 6, a vertical-cavity surface-emitting laser (VCSEL) 8 and two photo detectors 10.

The support 4 is made from a glass substrate die, which is a singulated portion of a glass substrate on which multiple optical readout modules were fabricated using a method as described below with reference to Figures 4 to 7. The photo detectors 10 each comprise a silicon die bonded to a first side 12 of the support 4. The VCSEL 8 comprises a semiconductor die bonded to the first side 12 of the support 4, between the photo detectors 10. The microlens 6 is formed by lithography in a second side 14 of the support 4. The microlens 6 is positioned such that when light emitted by the VCSEL 8 is use, the light passes through the microlens 6 as it propagates towards a target surface.

Figure 2 shows the optical readout module 2 of Figure 1 installed in an optical microphone 16. This is just one example application for the optical readout module 2 and other applications are possible.

The optical microphone includes a base 18 with an acoustic port 20 and an enclosure 22 sealed over the base 18 to form an acoustic cavity 24. The optical microphone 16 also comprises an application-specific integrated circuit (ASIC) 26 mounted on the base 18, a microelectromechical systems (MEMS) 28 mounted on the base 18 over the acoustic port 20, and the optical readout module 2 mounted on the MEMS component 28 via a spacer 30.

The MEMS component 28 comprises a diffractive optical element 32 and a membrane 34 that is spaced from and moveable relative to the diffractive optical element 32. The MEMS component 28 is attached to the base 18 to seal the acoustic port 20, such that acoustic waves entering the acoustic port 20 cause the membrane 34 to vibrate.

The optical readout module 2 is positioned over the MEMS component 28 so light from the VCSEL 8 passes through the microlens 6 onto the membrane 34 and the diffractive optical element 32, which reflect and diffract portions of the light back towards the photo detectors 10, as illustrated in Figure 3.

Figure 3 shows a schematic diagram illustrating the propagation of light from the optical readout module 2 to the MEMS component 28 and back to the optical readout module 2. For clarity, only the optical readout module 2, the membrane 34 and the diffractive optical 32 are shown in Figure 3.

The VCSEL generates a beam of light 36 which propagates through the support 4 to the microlens 6. The microlens 6 collimates the light 36 and directs it onto the diffractive optical element 32. A first portion 38 of the light is reflected and diffracted back from the diffractive optical element 32. A second portion 40 of the light passes though the diffractive optical element 32 and is reflected from the membrane 34 back through the diffractive optical element 32. The second portion 40 of the light is also diffracted by the diffractive optical element 32 as it passes through it.

The first and second portions 38, 40 of the light propagate back to the optical readout module 2, where they enter the support 4 and propagate through it to the photo detectors 10. The diffraction of the light by the diffractive optical element 32 separates each of the first and second portions 38, 40 into diffractive orders, such that each order comprises light from each of the first and second portions 38, 40. In this embodiment, each one of the photo detectors 10 detects a respective one of the +1^st and -1^st diffractive orders. The photo detectors 10 detect an intensity of the light corresponding to the interference pattern, generating a corresponding electrical signal.

Referring again to Figure 2, the ASIC 26 is connected to the support 4 with wirebonding 42 to form electrical connections with the VCSEL 8 and photo detectors 10. The ASIC 26 controls the operation of the VCSEL 8 via the electrical connections. The ASIC 26 also receives the electrical signals generated by the photo detectors 10. The ASIC 26 converts the electrical signals corresponding to the light intensity into a signal that represents the time-varying position of the membrane 34, and thus also represents the acoustic wave.

Figures 4 to 7 show a series of steps in a method of manufacturing the optical readout module 2 of Figure 1 using wafer-level packaging.

The method uses a glass substrate 44, as shown in Figure 4. The substrate 44 is planar and has a first surface 46 that is depicted facing upwards in Figure 4, and a second surface 48 that is depicted facing downwards.

The substrate 44 is large enough to manufacture many optical readout modules (e.g. thousands or tens of thousands), which may be arranged in a two-dimensional pattern, e.g. a grid, on the substrate 44. For clarity, Figure 7 only shows three optical readout modules 2 in a one-dimensional arrangement, but it is to be understood that much larger numbers are possible in practice.

Figure 5 shows three microlenses 6 that have been fabricated on the second surface 48 of the glass substrate 44 using nanoimprint photolithography. All of the microlenses 6 are fabricated simultaneously on the glass substrate 44 in this step. Each microlens 6 will form part of a respective optical readout module 2.

In another step shown in Figure 6, metal contact pads with routing metal lines (not shown) for wire-bonding are deposited on the first surface 46 of the glass substrate. This step could be performed before the fabrication of the microlenses 6, but in this example is it performed afterwards.

In a further step, for each microlens 6, one VCSEL 8 and two photo detectors 10 are bonded to the metal contact pads on the first surface 46 of the glass substrate 44, i.e. three VCSELs 8 and six photo detectors 10 in total for the example shown in Figure 6. The VCSELs 8 and photo detectors 10 are aligned with high precision relative to the microlenses 6. Then in a further step, the glass substrate 44 is diced to separate the optical readout modules 2 into individual units, as indicated by the dotted lines 50 in Figure 7. Each unit is an optical readout module 2 as shown in Figure 1.

Figure 8 shows a second embodiment of an optical readout module 52 in accordance with the invention. The optical readout module 52 of Figure 8 is a variation on the optical readout module 2 of Figure 1 where the same reference numerals are used for common features.

The optical readout module 52 of Figure 8 differs from the optical readout module 2 of Figure 1 in that it further comprises a layer of overmolding material 54 that encapsulates the VCSEL 8 and the photo detectors 10. In addition, redistribution layers (RDLs) 56 are provided through the layer of overmolding material 54 to electrically connect the VCSEL 8 and the photo detectors 10 via the metal contact pads on the first surface 12 of the support 4 to metal contact pads 58 on an upper surface 60 of the layer of overmolding material 54.

The optical readout module 52 functions in a similar manner to the optical readout module 2 as described with reference to Figure 3.

Figure 9 shows the optical readout module 52 of Figure 8 installed in an optical microphone 62. Except for the optical readout module 52, the optical microphone 62 is the same as the optical microphone 16 of Figure 2, and the same reference numerals are used for corresponding features. The optical microphone 52 is mounted in a similar manner, except that wirebonding 64 from the ASIC 26 is connected to the metal contact pads 58 on the upper surface of the layer of overmolding material 54.

The optical readout module 52 of Figure 8 can be manufactured starting with the steps described above with references to Figure 4 to 6. However, following the bonding of the VCSEL 8 and the photo detectors 10 to the glass substrate 44, the layer of overmolding material 54 is applied to the first surface 46 of the glass substrate 44 to encapsulate the VCSEL 8 and photo detectors 10, as shown in Figure 10. In this example, the overmolding material 54 is an epoxy moulding compound. After the application of the layer of overmolding material 54, the RDLs 56 are formed.

After the layer of overmolding material 54 has been applied, the glass substrate 44, including the overmolding material 54, is diced (i.e. singulated) to separate the optical readout modules 52 into individual units, as indicated by the dotted lines 66 in Figure 11. Each unit is an optical readout module 52 as shown in Figure 8.

Figure 12 shows an optical readout module 68 in accordance with a third embodiment of the invention. The optical readout module comprises a support 70, a microlens 72, a vertical-cavity surface-emitting laser (VCSEL) 74 and two photo detectors 76. However, in contrast with the optical readout modules 2, 52 of Figures 1 and 8, the support 70 is made from overmolding material, and the VCSEL 74 and the photo detectors 76 are embedded in the support 70, rather than mounted on it, with electrical contacts 78 exposed at a first surface 80 of the support 70.

The optical readout module 68 can be fabricated using a method as described below with reference to Figures 14 to 19. The photo detectors 76 each comprise a silicon die embedded in the first side 80 of the support 70. The VCSEL 74 comprises a semiconductor die embedded in the first side 80 of the support 70, between the photo detectors 76. The microlens 72 is formed in a second side 82 of the support 70. The microlens 72 is positioned such that when light emitted by the VCSEL 74 is use, the light passes through the microlens 72 as it propagates towards a target surface.

Figure 13 shows the optical readout module of Figure 12 installed in an optical microphone 84. Except for the optical readout module 68, the optical microphone 84 is the same as the optical microphone 16 of Figure 2, and the same reference numerals are used for corresponding features. The optical microphone 84 is mounted in a similar manner, except wirebonding 86 from the ASIC 26 is connected to the metal contact pads 78 exposed at the first surface 80 of the support 70 where the VCSEL 74 and photo detectors 76 are embedded. Figures 14 to 19 show a series of steps in a method of manufacturing the optical readout module 68 of Figure 12 using wafer-level packaging. For clarity, Figures 14 to 19 only show the manufacture of three optical readout modules 68, but it is to be understood that much larger numbers are possible in practice.

The method uses a wafer 88, as shown in Figure 14. The wafer 88 is a semiconductor wafer, although other materials (e.g. glass, plastic) could be used instead. The wafer 88 is planar and is shown in Figure 14 with an upper surface 90 and a lower surface 92.

In a step of the method, for each optical readout module 68 to be manufactured, one VCSEL 74 and two photo detectors 76 are bonded to the upper surface 90 of the semiconductor wafer 88, i.e. for this example, three VCSELs 74 and six photo detectors 76 in total are shown in Figure 15, although as mentioned above in practice there would typically be many more, e.g. thousands. The VCSEL 74 and photo detectors 76 each comprise a die, which may all be placed on the wafer 88 using a fan-out die placement process.

Following the bonding of the VCSEL 74 and the photo detectors 76 to the wafer 88, a layer of overmolding material 94 is applied to the upper surface 90 of the wafer 88 to encapsulate the VCSELs 74 and photo detectors 76, as shown in Figure 16. In this example, the overmolding material 94 is an epoxy moulding compound that is transparent to light at the VCSEL’s wavelength. The overmolding material 94 forms a layer having a first surface 96 and a second surface 98. The VCSEL and photo detectors are embedded in the first surface. Each VCSEL 74 is oriented to emit light in the direction of the second surface 98, i.e. through the transparent overmolding material 94. The photo detectors 76 are oriented to detect light arriving from the direction of the second surface 98, i.e. through the transparent overmolding material 94.

After the application of the layer of overmolding material 94, three microlenses 72 are simultaneously fabricated in the second surface 98 of the layer of overmolding material 94 using nanoimprint photolithography (although other processes such as photolithography with subsequent etching could be used). The fabricated microlenses 72 are shown in Figure 17. As part of the fabrication process, the microlenses 72 are collectively aligned with high precision with respect to the VCSELs 74. Consequently, after fabrication each microlens 72 is in a precisely aligned position relative to a respective one of the VCSELs 74 so that when the corresponding VCSEL 74 emits light during use, the light impinges on the microlens 72, which directs the light towards a target surface. Each microlens 72 corresponds to a respective one of the optical readout modules 68 being manufactured. As mentioned above, in practice typically thousands of optical readout modules or more may be manufactured on a single wafer. Aligning the microlenses 72 collectively as part of the microlens fabrication process therefore significantly increases the efficiency of manufacture. In some other examples, a subset of the microlenses 72 may be collectively aligned with a subset of VCSELs 74, which also provides improved efficiency over individual alignment.

In a further step, the semiconductor wafer 88 is removed using back-grinding, leaving electrical contacts 78 exposed at the first surface for each VCSEL 74 and each photo detector 76, as shown in Figure 18.

Then in a further step, the layer of overmolding material 94 is diced to separate the optical readout modules 68 into individual units, as indicated by the dotted lines 100 in Figure 19. Each unit is an optical readout module 68 as shown in Figure 12.

Figure 20-23 show schematic diagrams illustrating the optical aspects of the operation of some further embodiments of optical readout modules in accordance with the invention. These further embodiments are shown by way of example as variations on the embodiment of Figure 1 and the operation thereof as illustrated in Figure 3. Features that are the same as corresponding features in Figures 1 and 3 are labelled with the same reference numerals.

The optical readout module 102 of Figure 20 is the same as the optical readout module 2 depicted in Figures 1 and 3 and operates in the same manner, except that two additional microlenses 104 have been fabricated on the second surface 14 of the support 4. The additional microlenses 104 are positioned so that the light propagating back from the diffractive optical element 34 and the membrane 34 impinges on them. The additional microlenses 104 direct and focus the light onto the photo detectors 10. In the embodiment of Figure 21 , the optical readout module 106 comprises a support 108 with a VCSEL 8 and two photo detectors 10 bonded to a first surface 110 thereof. However, in contrast with the embodiments of Figures 3 and 20, the second surface of the support 108 is not defined by the opposing surface 112 of the opposite side of the support 108 from the first surface 110. Instead, a recess 114 is formed in the first surface 110, and the second surface 116 is defined by the floor of the recess 114.

A microlens 6 is formed in the second surface 116 at the floor of the recess 114. In use, light 118 from the VCSEL 8 propagates into the recess 114, and impinges on the microlens 6. The microlens 6 collimates and directs this light onto a target surface 120, which reflects the light back towards the photo detectors 10 where it is detected.

Figures 22 and 23 show optical readout modules 122, 124 that have the same features as the optical readout module 106 of Figure 21, except that instead of a microlens fabricated in a recess in the support, the optical readout modules 122, 124 each comprise a gradient-index (GRIN) lens 126, 128, which collimates and directs the light towards the target surface 120.

In the embodiment of Figure 22, the GRIN lens 126 is formed in the support 130 at the second surface 132. In the embodiment of Figure 23, the GRIN lens 128 is formed in the support 134 close to but not at the second surface 136, i.e. so that the GRIN lens 128 is contained entirely inside the support 132.

In the embodiments of Figures 21 to 23, the optical readout module is configured for use in a LIDAR device and the target surface is part of a physical object whose distance from the LIDAR device is to be measured. However, this is just an example and other applications are possible for these and other embodiments of the invention.

The embodiments of Figures 21 to 23 only include an optical component ( the recessed microlens 6 and the GRIN lenses 126, 128) in the path of the outbound light travelled from the VCSEL 8 to the target surface 120. Additionally or alternatively, optical components could be provided in the path of the inbound light travelling from the target surface 120 to the photo detectors 10 (in a similar manner to Figure 20).

Figures 24 and 25 each show an optical readout module 138, 140 in accordance with two further embodiments of the invention which are variations on the third embodiment shown in Figure 12. Where features shown in Figures 24 and 25 are the same as corresponding features in Figure 12, or where Figures 24 and 25 have features in common with each other, the same reference numerals are used for those features.

The optical readout module 138 of Figure 24 differs from the optical readout module 68 of Figure 12 in it comprises a top-emitting VCSEL 142 with electrical contacts on its top (emitting) side 144, and in the type of electrical contacts and connections provided to the VCSEL 142. In this embodiment, redistribution layers (RDLs) 146 provide contacts 148 at the first surface 80 of the support 70 with corresponding connections to the electrical contacts on the top side of the VCSEL 142. In a further variation, the photo detectors could be provided with RDLs and the VCSEL could be provided with contacts of the type shown in Figure 12, with the method of manufacture modified accordingly.

The optical readout module 140 of Figure 25 also comprises a top-emitting VCSEL 142 and RDLs 146, like the optical readout module 138 of Figure 24. The optical readout module 140 also comprises photo detectors 150 whose electrical contacts are on their top (receiving) surfaces 152, and corresponding RDLs 154 to provide electrical connections from the photo detectors 150 to contacts 156 at the first surface 80 of the support 70.

Each optical readout module 138, 140 of Figures 24 and 25 may be installed in an optical microphone in a similar manner to that shown in Figure 13, with wirebonding from an ASIC to the RDL contacts 148, 156 exposed at the first surface 80 of the support 70 where the VCSEL 142 and/or photo detectors 150 are embedded.

The optical readout module 140 can be manufactured using a method as described below with reference to Figures 26 to 33. The optical readout module 138 can be manufactured using the method of Figures 14-19, with a modification to provide the RDLs 146 for the VCSELs 142 based on the corresponding steps of the method of Figures 26 to 33.

Figures 26 to 33 show a series of steps in a method of manufacturing the optical readout module 140 of Figure 25 using wafer-level packaging. For clarity, Figures 24 to 33 only show the manufacture of three optical readout modules 140, but it is to be understood that much larger numbers are possible in practice.

The method described with reference to Figures 26 to 33 differs from the method of Figure 14-19 in the way electrical contacts are provided for the VCSELS 142 and photo detectors 150. In addition, a planarizing step is described, which may also be used in other methods in accordance with the invention, e.g. the method of Figures 14-19. In other respects, the method and the manufactured optical readout module 140 may be the same as or similar to the method and optical readout module 68 of Figure 14-19.

The method of manufacturing the optical readout module 140 uses a wafer 88 with an upper surface 90 and a lower surface 92, as shown in Figure 26.

In a step of the method, for each optical readout module 140 to be manufactured, one VCSEL 142 and two photo detectors 150 are bonded to the upper surface 90 of the semiconductor wafer 88. In this embodiment, in contrast with the embodiment of Figures 14-19, the VCSELs 142 and two photo detectors 150 are not bonded to the wafer 88 via electrical contacts.

Following the bonding of the VCSEL 142 and the photo detectors 150 to the wafer 88, redistribution layers (RDLs) 146, 154 are fabricated on the wafer 88 and over the VCSELs 142 and photo detectors 150, providing a contact 148, 156 on the surface of the wafer 88 for each VCSEL 142 and photo detector 150 with an electrical connection between each contact 148, 156 and the respective VCSEL 142 or photo detector 150. The RDLs 146, 154 are shown in Figure 28.

Following the fabrication of the RDLs 146, 154, a layer of overmolding material 94 is applied to the upper surface 90 of the wafer 88 to encapsulate the VCSELs 142, the photo detectors 150 and the RDLs 146, 154, as shown in Figure 29. The overmolding material 94 forms a layer having a first surface 96 and a second surface 98. The VCSEL and photo detectors are embedded in the first surface 96 and the contacts 148, 156 of the RDLs 146, 154 are positioned between the layer of overmolding material 94 and the wafer 88, at the first surface 96.

As shown in Figure 29, after the overmolding layer 94 has been applied, its second surface 98 is uneven. After the application of the layer of overmolding material 94, the second surface 98 of the overmolding material 64 is planarized, e.g. by polishing. Figure 30 shows the second surface 98 after planarization.

After the planarization step, three microlenses 72 are simultaneously fabricated on the planarized second surface 98 of the layer of overmolding material 94 using nanoimprint photolithography (although other processes could be used). The fabricated microlenses 72 are shown in Figure 31. As part of the fabrication process, the microlenses 72 are collectively aligned with high precision with respect to the VCSELs 142.

In a further step, the semiconductor wafer 88 is fully removed using back-grinding, leaving the contacts 148, 156 of the RDLs 146, 154 exposed at the first surface 96, as shown in Figure 32.

In a further step, the layer of overmolding material 94 is diced to separate the optical readout modules 140 into individual units, as indicated by the dotted lines 158 in Figure 33. Each unit is an optical readout module 140 as shown in Figure 25.

Redistribution layers (RDLs) may be used for providing electrical contacts and connections for the VCSEL and/or photo detectors in other embodiments, e.g. in variations on the embodiments of Figure 1 or Figure 8. Figure 34 shows an optical readout module 160 which is a variation on the embodiment of Figure 8 in which RDLs 162 are used to provide electrical contacts and connections for the VCSEL 8 and photo detectors 10. In will be appreciated that the above embodiments are only examples and that other embodiments and variations on these embodiments are possible within the scope of the invention, which is defined by the appended claims.

Claims

Claims:

1. A method of manufacturing an optical readout module for an optical device, wherein the optical readout module comprises: a support comprising a first surface; wherein the support is or comprises a layer of overmolding material; a light source provided in or on the first surface, wherein the light source is arranged to emit outbound light through the support; a light detector provided in or on the first surface, wherein the light detector is arranged to detect inbound light that has propagated to the light detector through the support; and an optical component formed in or fabricated on the support, wherein the optical component is positioned so that in use the outbound light travels via the optical component towards a target object; or wherein the optical component is positioned so that in use the inbound light travels via the optical component to the light detector; the method comprising: attaching the light source and the detector to a substrate or wafer; applying the layer of overmolding material to the substrate or wafer; and forming the optical component in the layer of overmolding material or fabricating the optical component on the layer of overmolding material.

2. The method of claim 1 , comprising fully removing the wafer or substrate from the layer of overmolding material.

3. The method of claim 1 or 2, wherein the overmolding material encapsulates or substantially encapsulates the light source and the light detector.

4. The method of claim 1 , 2 or 3, comprising providing electrical contacts for the light source and/or light detector between the wafer or substrate and the layer of overmolding material.

5. The method of claim 4, comprising fully removing the wafer or substrate from the layer of overmolding material to expose the electrical contacts.

6. The method of any preceding claim, comprising planarizing a surface of the layer of overmolding material.

7. The method of any preceding claim, comprising forming the optical component in a second surface of the support or fabricating the optical component on a second surface of the support.

8. The method of claim 7, wherein the first and second surfaces are on respective first and second opposing sides of the support.

9. The method of any preceding claim, wherein the support consists of the layer of overmolding material, wherein the overmolding material consists of a single material or a homogeneous mix of materials.

10. The method of any preceding claim, wherein forming or fabricating the optical component comprises aligning the optical component with respect to the light source or the light detector.

11. The method of any preceding claim, comprising forming the optical component in an interior of the layer of overmolding material.

12. The method of any preceding claim, comprising manufacturing multiple optical readout modules on a single wafer or a single substrate.

13. The method of claim 12, comprising applying a singulation process to separate an overmolding layer applied to the single wafer or single substrate into multiple individual optical readout modules.

14. The method of claim 12 or 13, comprising forming or fabricating a plurality of optical components, wherein the method comprises collectively aligning the plurality of optical components with a corresponding plurality of light sources or a corresponding plurality of light detectors.

15. An optical readout module manufactured according to the method of any of claims 1 to 14.

16. An optical readout module for an optical device, the optical readout module comprising: a support comprising a first surface, wherein the support is or comprises a layer of overmolding material; a light source provided in or on the first surface, wherein the light source is arranged to emit outbound light through the support; a light detector provided in or on the first surface, wherein the light detector is arranged to detect inbound light that has propagated to the light detector through the support; an optical component formed in or fabricated on the support, wherein the optical component is positioned so that in use the outbound light travels via the optical component towards a target object; or wherein the optical component is positioned so that in use the inbound light travels via the optical component to the light detector.

17. The optical readout module of claim 16, wherein the first surface of the support comprises an at least partially exposed surface of the layer of overmolding material.

18. The optical readout module of claim 16 or 17, wherein the overmolding material encapsulates or substantially encapsulates the light source and the light detector.

19. The optical readout module of claim 16, 17 or 18, comprising electrical contacts at the first surface for providing an electrical connection to the light source and/or an electrical connection to the light detector.

20. The optical readout module of any of claims 16 to 19, wherein the layer of overmolding material comprises a planarized surface.

21. The optical readout module of any of claims 16 to 20, wherein the optical component is formed in or fabricated on a second surface of the support.

22. The optical readout module of any of claims 16 to 21 , wherein the first and second surfaces are on respective first and second opposing sides of the support.

23. The optical readout module of of any of claims 16 to 22, wherein the support consists of the layer of overmolding material, wherein the overmolding material consists of a single material or a homogeneous mix of materials.

24. The optical readout module of any of claims 16 to 23, wherein the optical component is formed in an interior of the support.

25. The optical readout module of of any of claims 16 to 24, comprising more than one light detector and/or more than one light source.

26. An optical device comprising the optical readout module as claimed in of any of claims 16 to 25.

27. The optical device of claim 26, wherein the optical device is an optical displacement sensor that uses optical interferometric readout.