Optical readout modules

Abstract

An optical readout module (2) for detecting a position or movement of an object (46) comprises a support (4), a semiconductor photo detector (6) and a light source (8). The semiconductor photo detector comprises a wafer chip (10) having formed thereon one or more photo detector elements (12), and is attached to and spaced from the support (4) by one or more electrical connections (16) which electrically connect the photo detector elements (12) and the support (4). The light source (8) is positioned between the semiconductor photo detector (6) and the support (4), and is arranged to emit light through the support (4) towards the object (46). The semiconductor photo detector (6) is arranged to detect light reflected from the object (46) that has propagated through the support (4).

Description

[0001] 172693 / 01

[0002] Optical readout modules

[0003] 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.

[0004] Various devices are known in the art for performing distance measurements using light over a wide variety of scales. Some examples of optical devices that measure a distance include LIDAR (time-of-flight) sensors for relatively long distances of the order of metres or tens of metres and optical displacement sensors (e.g. optical microphones, optical accelerometers) based on optical interferometric readout over millimetre scales. Other optical devices may also use an optical readout arrangement. 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.

[0005] 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. In general, at least one detector is needed to detect incoming light, but some optical readout arrangements include multiple detectors for detecting the light. An optical readout arrangement may also include a light source to generate the light (e.g. as a beam or pulse). An optical readout arrangement may also include one or more optical components arranged to direct the light towards a target system and / or to direct the light onto the detector(s).

[0006] Optical devices and their readout arrangements may be manufactured on a small length-scale, e.g. they may be MEMS (micro-electromechanical systems) devices or comprises MEMS components. This may be useful for applications requiring very small devices but can present manufacturing challenges, such as difficulty fabricating small-scale electrical connections when assembling an optical readout arrangement from its constituent components, or difficulty in aligning its optical components. 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. There can also be challenges in achieving a high enough detection efficiency of incoming light for some applications.

[0007] Various configurations for optical readout arrangements with associated manufacturing methods are known in the art, but improvements allowing greater ease and efficiency of manufacture and improved device performance are desirable.

[0008] The invention provides an optical readout module for detecting a position or movement of an object, the optical readout module comprising: a support; a semiconductor photo detector comprising a wafer chip having formed thereon one or more photo detector elements, the semiconductor photo detector being attached to and spaced from the support by one or more electrical connections; and a light source positioned between the semiconductor photo detector and the support; wherein: the light source is arranged to emit light through the support towards the object and the semiconductor photo detector is arranged to detect light reflected from the object that has propagated through the support; and the one or more electrical connections electrically connect the photo detector element(s) and the support.

[0009] The invention extends to a method of manufacturing an optical readout module for detecting a position or movement of an object, the method comprising: a providing a support; fabricating a semiconductor photo detector by forming one or more photo detector elements on a wafer; attaching a light source to the support or to the semiconductor photo detector; affixing, via one or more electrical connections electrically connecting the photo detector element(s) and the support, the semiconductor photo detector with respect to the support such that the semiconductor photo detector is attached to and spaced from the support by the electrical connections with the light source having a position between the semiconductor photo detector and the support, said position being such that the light source is arranged to emit light through the support towards the object and the semiconductor photo detector is arranged to detect light reflected from the object that has propagated through the support.

[0010] Thus it can be seen that in accordance with the invention, the electrical connections may provide three functions, namely: providing structural attachment of the semiconductor photo detector to the support; providing physical spacing, which may at least partially accommodate the light source; and electrically connecting the photo detector element(s) to the support.

[0011] Electrically connecting the photo detector element(s) to the support in accordance with the invention may advantageously improve ease of manufacture and robustness of the optical readout module. For example, it may reduce or avoid the need for electrical connections that are complex, expensive and / or challenging to fabricate or which are not very robust, e.g. vias through the wafer chip of the semiconductor photo detector or wire-bonding between the semiconductor photo detector and the support.

[0012] The skilled person will appreciate that the light source being positioned between the semiconductor photo detector and the support may be understood as meaning that the light source is positioned within the area of mutual overlap, i.e. ‘footprint’, of the semiconductor photo detector on the support. The skilled person will also understand from the present disclosure that the light source being positioned between the semiconductor photo detector and the support implies that the light source occupies at least some physical volume between planes of respective surfaces of the semiconductor photo detector and the support that face each other (e.g. including a surface of one of the photo detector elements and / or a surface to which the light source is mounted).

[0013] The semiconductor photo detector is attached to the support by the electrical connections. The skilled person will appreciate that this may be understood as meaning that the electrical connections provide at least some structural connection, e.g. rigid mechanical coupling, between the semiconductor photo detector and the support. Additional structural connection may be provided in addition to the electrical connections e.g. glue or structural connection between the semiconductor photo detector and the support may be provided solely by the electrical connections.

[0014] The skilled person will appreciate from the present disclosure that in this context the support provides physical support for the semiconductor photo detector. For example, the support may be attached to a supporting structure of the optical readout module or of an optical device comprising the optical readout module (e.g. comprising or mounted in a housing). The semiconductor photo detector and the light source may thereby be held by the support in a spaced relationship with respect to such a supporting structure, and thus, for example, with respect to other components of the optical readout module and / or the optical device. The skilled person will understand that this implies that the semiconductor photo detector may not be separately physically supported, e.g. by attachment to or integration in a or the supporting structure or housing, other than via the support.

[0015] In a set of embodiments, at least one of the support and the semiconductor photo detector comprises a recess at least partially accommodating the light source. A respective recess may be provided in each of the support and the semiconductor photo detector. In such embodiments, the spacing provided by the electrical connections may be less than a height of the light source (i.e. the dimension of the light source in the direction perpendicular to the surface planes of the support and the semiconductor photo detector). The electrical connections together with the or each recess may thus fully accommodate the light source.

[0016] In a set of embodiments, the spacing provided by the electrical connections is greater than the height of the light source. Accordingly, the semiconductor photo detector may be spaced from the support by the electrical connections by a distance that is sufficient to fully accommodate light source without needing a recess on either the support or the semiconductor photo detector.

[0017] The semiconductor photo detector may be spaced from the support by electrically conductive spacers. For example, each electrical connection may comprise an electrically conductive element (e.g. a bump or pillar such as a solder ball or metal post) formed separately from and attached to electrical contacts (e.g. pads) on the support and semiconductor photo detector. However, this is not essential, and in some embodiments the semiconductor photo detector is spaced from the support by the thickness of electrical contact pads on the support and semiconductor photo detector.

[0018] In a set of embodiments, the support comprises an optical component arranged such that the emitted and / or reflected light passes therethrough.

[0019] The support may comprise more than one optical component. For example, the support may comprise one or more optical components arranged such that the emitted light passes therethrough and one or more further optical components arranged such that the reflected light passes therethrough. The or each optical component may be formed in, fabricated on or attached to the support. As nonlimiting examples, the or each optical component may be a collimating optical element (e.g. a lens), a diffractive optical element (e.g. a grating or diffractive lens), a beam-steering optical component (e.g. a prism) or a beam separating optical element (e.g. a beam-splitter). The optical element(s) may transform the emitted light and / or direct the emitted light onto the object. The optical element(s) may transform the reflected light and / or direct the reflected light onto the photo detector element(s).

[0020] In a set of embodiments, the light source is mounted on the support. This may, for example, facilitate easier alignment of the light source relative to the optical component, where provided. In embodiments comprising a recess in the support, the light source may be attached to a surface of the recess. In embodiments comprising a recess in the semiconductor photo detector, the light source may be attached to a surface of the support opposite the recess. The light source may be electrically connected to the support, e.g. by flip-chip bonding or redistribution lines (RDLs).

[0021] In another set of embodiments, the light source is mounted on the semiconductor photo detector. This may facilitate easier alignment of the light source relative to the photo detector element(s) on the semiconductor photo detector. In embodiments comprising a recess in the semiconductor photo detector, the light source may be attached to a surface of the recess. In embodiments comprising a recess in the support, the light source may be attached to a surface of the semiconductor photo detector opposite the recess. The light source may be electrically connected to one or more contacts on the semiconductor photo detector, e.g. by flip-chip bonding or redistribution lines (RDLs).

[0022] In a subset of embodiments in which the spacing provided by the electrical connections is greater than the height of the light source, the light source is not mounted in a recess in the semiconductor photo detector or in a recess in the support. There may be no recess in the support or in the semiconductor photo detector.

[0023] Where the light source is mounted on the semiconductor photo detector, it may be electrically connected to the support by one or more of the electrical connections spacing the semiconductor photo detector from the support.

[0024] In a set of embodiments, the semiconductor photo detector comprises a plurality of photo detector elements formed on the wafer chip. Fabricating the semiconductor photo detector may comprise forming a plurality of photo detector elements on the wafer.

[0025] The Applicant has appreciated that in some applications using multiple photo detector elements (e.g. to detect different portions of incoming light), it can be beneficial to position the light source between the photo detector elements - for example, instead of having all of the photo detector elements on one side of the light source, such as in the case of a photo detector comprising multiple photo detector elements mounted to the side of a laser die. Positioning the light source between the photo detector elements may improve the detection efficiency of the semiconductor photo detector (e.g. by making it easier to direct incoming light onto the photo detector elements which may allow a greater fraction of the light to be detected and converted to a detector signal).

[0026] In a set of embodiments therefore, the light source is positioned on or relative to the semiconductor photo detector such that the photo detector elements are arranged around an optical axis of the light source, e.g. on opposite sides of the optical axis or surrounding the optical axis. For example, the light source may be mounted on the semiconductor photo detector with the photo detector elements arranged around the light source. The light source may be mounted on the support opposite the semiconductor photo detector with the photo detector elements arranged around a footprint of the light source (i.e. a corresponding area opposite the light source) on the semiconductor photo detector.

[0027] It will be appreciated that such arrangements are facilitated in accordance with the invention by a single semiconductor photo detector bearing multiple photo detector elements being spaced from the support by the electrical connections. This is beneficial compared with using multiple separate semiconductor photo detectors, each comprising a wafer chip having a single photo detector element formed thereon, where the additional space and packaging between each semiconductor photo detector may increase the overall size of the device and / or reduce the amount of the incoming light that can be directed onto a photo detector element.

[0028] In a set of embodiments, the footprint of the semiconductor photo detector on the support is smaller than the support. This may allow space for one or more electrical contacts (e.g. pads) on the same side of the support as the semiconductor photo detector. The support may comprise one or more electrical contacts that are positioned outside of the footprint of the semiconductor photo detector on the support. This may allow the support (and thereby photo detector element(s) and the light source) to be electrically connected to an external component or circuit, e.g. an application-specific integrated circuit (ASIC), without creating vias through the support, which may improve ease of manufacture.

[0029] In general, there may be no vias through the support. However, this is not essential and, in some embodiments, vias may be provided through the support, e.g. to electrically connect the light source and / or photo detector element(s) to an electrical contact on the opposite side of the support from the semiconductor photo detector.

[0030] 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).

[0031] In a set of embodiments, the optical device comprises an optical distancemeasurement 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.

[0032] In a set of embodiments, the optical device comprises a moveable object, wherein the optical readout module is arranged to detect movement thereof. The optical device may comprise an optical displacement sensor, e.g. an optical microphone or an optical accelerometer. The optical device may use optical interferometric readout to detect movement of the moveable object, for example as described in WO 2022 / 129893.

[0033] In a set of embodiments, the moveable object comprises a membrane.

[0034] The optical device may comprise a MEMS (microelectromechanical systems) component comprising the moveable object, e.g. a MEMS component comprising a membrane spaced from an optical element to form an interferometric arrangement. The optical readout module may be mounted on the MEMS component.

[0035] The optical device may comprise a LIDAR (time-of-flight) sensor. The object may comprise a surface, external to the optical device, whose distance from the optical device is to be measured.

[0036] It is to be understood that in the present context, “light” is not limited to light in the visible range. The light may be or comprise light in the infrared, visible and / or ultraviolet ranges. The optical device may comprise electronics and / or circuitry (e.g. an ASIC) that processes the signal to determine the property of the light and which may determine a physical parameter therefrom. The electronics and / or circuitry may be provided remotely or otherwise separately from the optical readout module, e.g. integrated in the optical device. The electronics and / or circuitry may be electrically connected to the optical readout module, e.g. to the electrical contact(s) on the support.

[0037] The method of manufacture may comprise manufacturing multiple optical readout modules on a single support substrate.

[0038] The method may comprise fabricating multiple semiconductor photo detectors on a single wafer (e.g. multiple sets of photo detector elements each corresponding to one optical readout module), attaching the single wafer to the single support substrate by forming sets of one or more electrical connections therebetween.

[0039] The method may comprise removing part of the single wafer (e.g. by etching) to leave multiple individual semiconductor photo detectors on the single support substrate.

[0040] The method may comprise individual placement of multiple individual semiconductor photo detectors on the single support substrate.

[0041] The method may comprise applying a dicing process to separate the single support substrate (and, where applicable, the single wafer) into multiple individual optical readout modules.

[0042] In a set of embodiments, the support is made from a material that 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). The support may be made from glass. 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 detected light or encode a time of arrival of the detected light.

[0043] The light source may be a laser, e.g. a vertical-cavity surface-emitting laser (VCSEL). The light source may comprise a die, e.g. a VCSEL fabricated on a 11 l-V semiconductor die. The light source may be a top-emitting laser or a bottomemitting laser.

[0044] The optical readout module may be a micro-electromechanical systems device, e.g. manufacturing using MEMS techniques. The meaning of the term microelectromechanical system (MEMS) is well understood by a person skilled in the art, so it will be understood that when a device or component is described as being a “MEMS” device or component, this means that the device or component comprises miniaturized mechanical and / or electro-mechanical elements (i.e. devices and structures), for example, which may have been made using microfabrication techniques, where miniaturized means that the physical dimensions of the miniaturized elements are on the scale of micrometres, e.g. up to length-scales on the order of a millimetre.

[0045] Certain preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0046] Figure 1 shows a first embodiment of an optical readout module in accordance with the present invention;

[0047] Figure 2 shows a second embodiment of an optical readout module in accordance with the present invention;

[0048] Figure 3 shows a plan view of the semiconductor photo detector of the optical readout module of Figure 2; Figure 4 shows the optical readout module of the first embodiment installed in an optical microphone;

[0049] Figure 5 shows a further embodiment of an optical readout module in accordance with the invention, comprising a recess to partially accommodate the VCSEL;

[0050] Figure 6 shows multiple optical readout modules manufactured on a single support substrate in accordance with an embodiment of the manufacturing method of the present invention, prior to application of a dicing process;

[0051] Figures 7A and 7B illustrate method steps which represent a variation on the embodiment of Figure 6; and

[0052] Figure 8 shows multiple optical readout modules manufactured on a single support substrate in accordance with a further embodiment of the method, prior to application of a dicing process.

[0053] Figure 1 shows an optical readout module 2 comprising a support 4, a semiconductor photo detector 6, and a vertical-cavity surface-emitting laser (VCSEL) 8.

[0054] The semiconductor photo detector 6 comprises a semiconductor wafer chip 10 with a plurality of photo detector elements 12 formed therein. Each photo detector element 12 acts as an individual light-detecting pixel that detects the total intensity of incident light across its surface. In Figure 1, only two photo detector elements 12 are visible, but in this embodiment, there are nine photo detector elements 12 in total, and in general there may typically be more than two.

[0055] The semiconductor photo detector 6 is attached to and spaced from a first surface 14 of the support 4 by electrical connections 16. The electrical connections 16 are formed from solder bumps 18 that are bonded between electrical contact pads 20 on the semiconductor photo detector 6 and corresponding electrical contact pads 22 on the support 4. In this embodiment, gold-tin alloy solder bumps are used, but other types of electrical connection could be used instead, e.g. gold bumps or copper pillars. The electrical contact pads 20 on the semiconductor photo detector 6 are electrically connected to the photo detector elements 12 by circuitry on the semiconductor photo detector 6, so that the electrical connections 16 electrically connect the photo detector elements 12 and the support 4.

[0056] Redistribution lines (RDLs) 24 on the support 4 connect the electrical contact pads 22 to electrical contact pads 26 at the edge of the support 4, which are provided for connecting to readout electronics and circuitry (e.g. in an ASIC provided separately from the optical readout module 2). The semiconductor photo detector 6 is smaller than the support. This allows the contact pads 26 to be positioned on the support outside of the footprint of the semiconductor photo detector 6, so that they are accessible for bonding to readout electronics and circuitry, e.g. by wire-bonding.

[0057] As the photo detector elements 12 are electrically connected to the support 4 by the electrical connections 16 comprising the solder bumps 18, it is not necessary to use other electrical connections such as vias through the wafer chip 10, or wire-bonding to a contact pad on the wafer chip 10. This simplifies the manufacture of the optical readout module 2.

[0058] In addition to physically attaching the semiconductor photo detector 6 to the support 4 and electrically connecting the photo detector elements 12 to the support 4, the electrical connections 16 also act as spacers. The solder bumps 18 are formed with a larger size than would otherwise have been necessary to give the electrical connections 16 a height h, spacing the semiconductor photo detector 6 from the support 4 to create a gap 28 sufficient to accommodate the VCSEL 8.

[0059] The VCSEL 8 is positioned in the gap 28 and mounted to the support 4. In this embodiment, the VCSEL 8 is electrically connected to contact pads 32 at the edge of the support 4 (for connection to readout electronics and circuitry) by a RDL 30 fabricated over the VCSEL 8 and RDLs 34 over the support 4. The VCSEL 8 could be mounted and electrically connected in other ways, e.g. mounted to the support 4 by flip chip bonding. The VCSEL 8 is arranged to emit light 36 to propagate into and through the support 4. The support 4 is made from a material such as glass which is transparent at the wavelength of the VCSEL 8 and comprises a microlens 38 on the opposite surface 40 from the VCSEL 8. The VCSEL 8 is aligned relative to the microlens 38 so that the light 36 from the VCSEL 8 passes through microlens 38 which collimates the light 36 as it propagates towards a target object.

[0060] The semiconductor photo detector 6 is positioned so that the photo detector elements 12 each detect a portion of light 44 that has propagated through the support 4 after being reflected back from the target object.

[0061] In this embodiment, the target object is a micro-electromechanical systems (MEMS) component 46. In Figure 1 , for clarity the positional relationship between the optical readout module 2 and the MEMS component 46 is illustrated schematically without showing supporting structure such as packaging. An example of suitable packaging is described below with reference to Figure 4.

[0062] The MEMS component 46 comprises a moveable membrane 48 suspended over a substrate 50. The substrate 50 comprises three diffraction gratings 52 with a relative height offset, although only two are visible in Figure 1. Each diffraction grating 52 together with the membrane 48 defines an interferometric arrangement which is used to measure the displacement of the membrane 48 relative to a respective working point as the membrane 48 vibrates.

[0063] When the light 36 impinges on each interferometric arrangement, the membrane 48 and the diffraction grating 52 each reflect a respective portion of the light 44. The portions of light 44 propagate back to one of the photo detector elements 12 where they generate an interference pattern that is dependent on the membrane displacement.

[0064] The configuration of the interferometric arrangements separates the reflected light 44 into three sets of three beams, where each beam is directed onto a respective one of the nine photo detector elements and includes two interfering portions of light. Each set of three beams is produced by a respective one of the interferometric arrangements, and the three beams in each set correspond to the -1st, 0th, and 1storders diffracted from the diffraction grating 52 of the respective interferometric arrangement.

[0065] The VCSEL 8 is positioned relative to the semiconductor photo detector 6 so that the photo detector elements 12 are arranged around the optical axis 54 of the VCSEL 8. This makes it easier to direct the beams of light onto the corresponding photo detector elements 12, which helps to increase the amount of light captured by the photo detector elements 12 compared with, for example, a semiconductor photo detector positioned to one side of the VCSEL.

[0066] In this embodiment, there are three interferometric arrangements each generating three diffraction orders that are detected, but different numbers of interferometric arrangements may be used and different numbers of diffraction orders may be detected.

[0067] Figure 2 shows a second embodiment of an optical readout module 56 in accordance with the present invention, which is a variation on the embodiment of Figure 1 . Where features are the same as in Figure 1 , the same reference numerals are used and the description thereof is not repeated.

[0068] The optical readout module 56 differs from the optical readout module 2 of Figure 1 in that it comprises a VCSEL 58 which is mounted on the semiconductor photo detector 6 instead of on the support 4. The VCSEL 58 is positioned on the semiconductor photo detector 6 between the photo detector elements 12, which are arranged around the VCSEL 58.

[0069] The VCSEL 58 is electrically connected via an RDL 60 to circuitry provided on the wafer chip 10 of the semiconductor photo detector 6. This allows the electrical connections 16 to electrically connect the VCSEL 58 to the support 4, as well as electrically connecting the photo detector elements 12 to the support 4. RDLs 24 on the support 4 electrically connect the VCSEL 58 and the photo detector elements 12 to the electrical contact pads 26, 32 at the edge of the support 4. As with the previous embodiment, there is no need for any vias to pass through the semiconductor wafer 10. Figure 3 shows a plan view of the semiconductor photo detector 6 of the optical readout module 56 of Figure 2, which comprises the semiconductor wafer chip 10 with the nine photo detector elements 12 formed thereon. The photo detector elements 12 are arranged in three sets 12A, 12B, 12C of three, and are arranged around the VCSEL 58, which is mounted on the wafer chip. Each set of photo detector elements 12 is positioned to detect one of the sets of beams of lights, where each photo detector element in the set detects a respective one of the -1st, 0thand 1stdiffraction orders.

[0070] The photo detector elements 12 and the VCSEL 58 are connected to the contact pads 20 by circuitry (not shown). A contact pad 62 is provided for connecting the VCSEL to the circuitry.

[0071] The semiconductor photo detector shown in Figure 3 and variations thereon may be used in other embodiments, e.g. in the embodiment of Figure 1. In embodiments in which the VCSEL is attached to the support instead of to semiconductor photo detector, the position of the VCSEL 58 shown in Figure 3 would instead indicate a footprint of the VCSEL mounted opposite the semiconductor photo detector on the support.

[0072] Figure 4 shows the optical readout module 2 together with the MEMS component 46 of Figure 1 installed in an optical microphone 64. The optical microphone 64 is packaged within an enclosure 66 mounted over a base 68 which comprises an acoustic port 70. The MEMS component 46 is mounted on the base 68 over the acoustic port 70 so that the membrane 48 closes the acoustic port 70. The enclosure 66 is sealed to the base 68 to create an acoustic cavity 72 which functions as a back volume for the optical microphone 64. Apertures 74 in the substrate 50 of the MEMS component 46 provide fluid communication between the inward-facing surface of the membrane 48 and the acoustic cavity 72. When an incoming acoustic wave impinges on the membrane 48, the membrane 48 moves in response to the resulting pressure differential between the acoustic cavity 72 and the exterior 76 of the optical microphone 64.

[0073] The optical readout module 2 is mounted on and aligned relative to the MEMS component 46 for readout of the membrane displacement as described with reference to Figure 1. An ASIC 78 is mounted to the base 68 adjacent to the MEMS component 46 and the optical readout module 2. Wire-bonding 79 between the contact pads 26, 32 on the optical readout module 2 and the ASIC 78 allow the ASIC 78 to control the function of the VCSEL 8 and to receive detector signals from the photo detector elements 12. The ASIC 78 processes the detector signals to determine a time-varying position of the membrane 48 and thereby generate an output electronic audio signal corresponding to the detected acoustic wave.

[0074] Figure 5 shows a further embodiment of an optical readout module 80 in accordance with the invention, which is a variation on the embodiment of Figure 1. Where features are the same as in Figure 1 , the same reference numerals are used and the description thereof is not repeated.

[0075] The optical readout module 80 differs from the optical readout module 2 of Figure 1 in that the support comprises a recess 82 which partially accommodates the VCSEL 8, which is mounted on a floor 84 of the recess 82. The electrical connections 16 still act as spacers, however the height h2 of the electrical connections 16 is smaller than the height of the VCSEL 8 plus a suitable gap to avoid contact with the detector wafer chip 6. The height of the electrical connections 16 and the depth of the recess 82 together accommodate the VCSEL 8.

[0076] In variations on this embodiment, the VCSEL may be mounted on the semiconductor photo detector 6, opposite the recess 82 in the support 4 which accommodates the VCSEL. In other variations, a recess may additionally or alternatively be provided in the semiconductor photo detector 6, e.g. with the photo detector elements 12 in the recess. The VCSEL may be mounted on the semiconductor photo detector 6 in the recess, or it may be mounted on the support 4, opposite the recess in the semiconductor photo detector 6.

[0077] Figure 6 shows multiple optical readout modules 2 that have been manufactured on a single support substrate 86 in accordance with an embodiment of the manufacturing method of the present invention, prior to application of a dicing process to separate the single support substrate 86 into multiple individual optical readout modules 2 according to the embodiment of Figure 1. The step of this embodiment of the method are set out below.

[0078] Multiple microlenses 38 are fabricated (e.g. etched) on the surface of a glass substrate 86. Each microlens 38 is part of a respective one of the optical readout modules 2 being manufactured.

[0079] Multiple sets of electrical contact pads 22, 26, 32 and connecting RDLs (omitted from Figure 6 for clarity) are fabricated on the glass substrate 86. The electrical contact pads 22, 26, 32 include contact pads 22 for attaching semiconductor photo detectors 6 via solder bumps 18 and contact pads 26, 32 for connecting the optical readout module 2 to readout electronics and circuitry.

[0080] For each optical readout module 2 being manufactured, a respective VCSEL 8 is attached to the glass substrate 86 (e.g. using micro transfer printing), including aligning each VCSEL 8 with respect to the corresponding microlens 38. An RDL 30 is fabricated over each VCSEL 8 to electrically connect it to the connecting RDLs and contact pads 32 on the glass substrate 86.

[0081] For each optical readout module 2 being manufactured, a respective semiconductor photo detector 6 is attached to the glass substrate 86 using solder bumps 18, forming electrical connections 16. The semiconductor photo detectors 6 are manufactured as chips by fabricating respective sets of photo detector elements 12 in a silicon wafer and dicing the wafer into chips. The photo detector elements 12 are PIN photodiodes fabricated in the silicon wafer using known semiconductor wafer processing techniques, e.g. photolithography, etching, doping and thin film deposition.

[0082] A dicing process is used to separate the glass substrate 86, as shown by the dotted lines 88 in Figure 6, into multiple support dies 90. Each support die 90 is a support 4 for a respective optical readout module 2 as shown in Figure 1.

[0083] In variations and other embodiments of the method, instead of attaching the VCSELs to the glass substrate, a respective VCSEL may be attached to a respective semiconductor photo detector (with suitable adjustments to the contact pads, RDLs and other circuitry) prior to attaching each semiconductor photo detector to the glass substrate.

[0084] In variations and other embodiments of the method, a respective recess may be formed in the glass substrate, e.g. prior to fabrication of the contact pads and RDLs and attaching of the VCSELs, and / or the semiconductor photo detector may be provided with a recess, e.g. with the photo detector elements formed in a floor of the recess.

[0085] In variations and other embodiments of the method, each optical readout module 2 may be manufactured individually on an individual support 4, following the steps above applied to a single optical module 2, and omitting the dicing step.

[0086] Figures 7A and 7B illustrate an alternative to individually placing each semiconductor photo detector 6 on the glass substrate 86.

[0087] In this variation on the method, multiple semiconductor photo detectors 92 are provided on a single wafer 94 (i.e. multiple sets of photo detector elements 12 with corresponding sets of circuitry and contact pads 20).

[0088] The single wafer 94 is attached to the glass substrate 86, as shown in Figure 7A.

[0089] An etching process is used to separate and remove part 96 of the single wafer 94 to leave individual semiconductor photo detectors 6, as shown in Figure 7B.

[0090] Figure 8 shows multiple optical readout modules 98 that have been manufactured on a glass substrate 86 in accordance with a further embodiment of the method, prior to application of a dicing process.

[0091] In this embodiment, prior to or as part of fabrication of the contact pads 26, 32, vias 100 are formed through the glass substrate 86 to electrically connect the contact pads 26, 32 to corresponding contact pads 102, 104 on the bottom of the glass substrate 86. A single wafer 106 comprising multiple semiconductor photo detectors is attached to the glass substrate 86, similar to the embodiment of Figure 7A. However, in this embodiment, the single wafer 106 is not etched to create individual semiconductor photo detectors.

[0092] A dicing processing is used to separate the single wafer 106 and the glass substrate 86, as shown by the dotted lines 108 in Figure 7B, into multiple individual optical readout modules 98 with individual semiconductor photo detectors 110. In each individual optical readout module 98, the semiconductor photo detector 110 extends over the contact pads 26, 32. This may make it more difficult to attach wire bonds or similar connections to the contact pads 26, 32. The vias 100 allow electrical connection via the contact pads 102, 104 instead. It will be appreciated that the above-described embodiments are exemplary only, and that other embodiments and variations are possible within the scope of the invention, which is defined by the appended claims.

Claims

Claims:

1. An optical readout module for detecting a position or movement of an object, the optical readout module comprising: a support; a semiconductor photo detector comprising a wafer chip having formed thereon one or more photo detector elements, the semiconductor photo detector being attached to and spaced from the support by one or more electrical connections; and a light source positioned between the semiconductor photo detector and the support; wherein: the light source is arranged to emit light through the support towards the object and the semiconductor photo detector is arranged to detect light reflected from the object that has propagated through the support; and the one or more electrical connections electrically connect the photo detector element(s) and the support.

2. The optical readout module of claim 1, wherein the spacing provided by the electrical connections is greater than a height of the light source.

3. The optical readout module of claim 1 or 2, wherein at least one of the support and the semiconductor photo detector comprises a recess at least partially accommodating the light source.

4. The optical readout module of any preceding claim, wherein the semiconductor photo detector is spaced from the support by electrically conductive spacers.

5. The optical readout module of any preceding claim, wherein the support comprises an optical component arranged such that the emitted and / or reflected light passes therethrough.

6. The optical readout module of any preceding claim, wherein the light source is mounted on the support.

7. The optical readout module of any of claims 1 to 5, wherein the light source is mounted on the semiconductor photo detector.

8. The optical readout module of claim 7, wherein the light source is electrically connected to the support by one or more of the electrical connections spacing the semiconductor photo detector from the support.

9. The optical readout module of any preceding claim, wherein the semiconductor photo detector comprises a plurality of photo detector elements formed on the wafer chip.

10. The optical readout module of claim 9, wherein the light source is positioned on or relative to the semiconductor photo detector such that the photo detector elements are arranged around an optical axis of the light source.

11. The optical readout module of any preceding claim, wherein a footprint of the semiconductor photo detector on the support is smaller than the support.

12. The optical readout module of any preceding claim, wherein the support comprises one or more electrical contacts that are positioned outside of a footprint of the semiconductor photo detector on the support.

13. The optical readout module of any preceding claim, wherein there are no vias through the support.

14. The optical readout module of any preceding claim, wherein the support is made from a material that is at least partially transparent at a wavelength of the light source.

15. The optical readout module of any preceding claim, wherein the optical readout module is a micro-electromechanical systems device.

16. An optical device comprising an optical readout module as claimed in any preceding claim.

17. The optical device of claim 16, wherein the optical device comprises an optical distance-measurement device.

18. The optical device of claim 16 or 17, comprising a moveable object wherein the optical readout module is arranged to detect movement of the moveable object.

19. The optical device of claim 18, wherein the moveable object comprises a membrane.

20. The optical device of claim 18 or 19, arranged to use optical interferometric readout to detect movement of the moveable object.21 . A method of manufacturing an optical readout module for detecting a position or movement of an object, the method comprising: providing a support; fabricating a semiconductor photo detector by forming one or more photo detector elements on a wafer; attaching a light source to the support or to the semiconductor photo detector; affixing, via one or more electrical connections electrically connecting the photo detector element(s) and the support, the semiconductor photo detector with respect to the support such that the semiconductor photo detector is attached to and spaced from the support by the electrical connections with the light source having a position between the semiconductor photo detector and the support, said position being such that the light source is arranged to emit light through the support towards the object and the semiconductor photo detector is arranged to detect light reflected from the object that has propagated through the support.

22. The method of claim 21 , wherein fabricating the semiconductor photo detector comprises forming a plurality of photo detector elements on the wafer.

23. The method of claim 21 or 22, comprising manufacturing multiple optical readout modules on a single support substrate.

24. The method of claim 23, comprising applying a dicing process to separate the single support substrate into multiple individual optical readout modules.

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