WO2022002730A1

WO2022002730A1 - Method of manufacturing spectral sensors

Info

Publication number: WO2022002730A1
Application number: PCT/EP2021/067240
Authority: WO
Inventors: Francesco Paolo D'ALEO; Kotaro ISHIZAKI; Peter Roentgen; Javier Miguel SÁNCHEZ
Original assignee: Ams International Ag
Priority date: 2020-06-30
Filing date: 2021-06-23
Publication date: 2022-01-06
Also published as: GB202009963D0

Abstract

The present disclosure relates to a method of manufacturing a plurality of spectral sensors. The method comprises providing a first substrate and forming the plurality of spectral sensors on the first substrate. The method further comprises dividing the first substrate to separate the plurality of spectral sensors.

Description

Method of manufacturing spectral sensors

Technical Field of the Disclosure

The disclosure relates to the field of spectral sensors, particularly but not exclusively, to a method of manufacturing a plurality of spectral sensors.

Background of the Disclosure

Spectral sensors are well known and are used in a variety of application areas. Spectroscopy across various wavelength ranges allows non-destructive analysis of substances and/or chemicals. Spectroscopy can be applied to a wide range of applications such as, for example, food, drugs, pharmaceuticals, cosmetics, etc. Known spectral sensors for performing spectroscopy are available as high precision, bulky laboratory equipment. However, a size, complexity and/or cost of known spectral sensors limits their use to laboratory settings.

Typically, a spectral sensor includes a photodetector and an optical element that is used to select the wavelength of light incident upon the photodetector. The optical element may be adjusted gradually over time such that the wavelength of light incident upon the photodetector changes gradually over time. The photodetector thus provides as an output the intensity of light incident upon the photodetector as a function of wavelength. This may be referred to as an intensity spectrum. In known spectral sensors, the optical element that is used to select the wavelength of light incident upon the photodetector is a prism or a diffraction grating.

Known spectral sensors also include electromechanical spectral sensors having an optical element that comprises at least one movable part that is controlled using electronic components. Electromechanical devices are typically understood to involve using an electrical signal to create mechanical movement, and/or or vice versa. Examples of such optical elements include Fourier-transform interferometers and Fabry- Perot interferometers. Fourier-transform interferometers comprise a Michelson interferometer wherein one of the two reflectors is movable. Light from a source is split into two beams by a partial reflector. One of the beams is reflected off a fixed mirror and the other beam is reflected off a movable mirror. In an electromechanical system implementation of a Fourier-transform interferometer an electrical signal may be used to move the movable reflector to introduce a variable delay in the travel time of the reflected light for one of the beams of light. The beams interfere, allowing a temporal coherence of the light to be measured at each different time delay setting (i.e. movable mirror position) effectively converting the time domain into a spatial coordinate. By making measurements of the signal at many discrete positions of the movable mirror, a spectrum can be constructed using a Fourier transform of the temporal coherence of the light.

Fabry-Perot interferometers comprise a pair of reflective plates which are parallel and facing each other. Although reflective, the plates transmit a small amount of light. The wavelength of light which is transmitted by the Fabry-Perot interferometer is determined by the separation of the plates. In a conventional tuneable Fabry-Perot interferometer the separation of the plates is manually adjustable. In an electromechanical system implementation of a Fabry-Perot interferometer the transmission wavelength may be adjusted by using an electronic signal to adjust a voltage applied across the plates of the Fabry-Perot interferometer. Increasing the voltage provides more charge to the plates and causes them to bend towards each other. This reduces the cavity transmission wavelength of the Fabry-Perot interferometer (i.e. reduces the wavelength at which light is transmitted by the Fabry-Perot interferometer).

A spectral sensor with a microelectromechanical system (MEMS) implementation of a Fourier-transform interferometer or a Fabry-Perot interferometer is more compact than a conventional spectral sensor which uses a prism or a diffraction grating.

Progress in the miniaturization of dispersive optical components for spectral sensors has substantially reduced a size and/or cost of known spectral sensors whilst maintaining reasonable performances (e.g. adequate measurement accuracies). Said known spectral sensors are manufactured in a similar way to their laboratory equipment counterparts. The known spectral sensors are individually manufactured in hermetically sealed metallic housings comprising vacuum or an inert gas. The known manufacturing method is limited in the creation of a single known spectral sensor at a time and is therefore unsuitable for high volume manufacture. Known spectral sensors are costly and time-consuming to manufacture, provide limited functionality and are difficult or impossible to reduce in size. As such, known spectral sensors are not suitable for many applications, such as incorporation into consumer electronic devices (e.g. mobile phones and/or tablet computers). It is therefore an aim of the present disclosure to address one or more of the problems above or at least to provide a useful alternative.

Summary

In general, this disclosure proposes to overcome the above problems by providing a method of manufacturing a spectral sensor that involves the use of wafer manufacturing processes, e.g. surface mount device (SMD) technologies. This arrangement advantageously reduces a complexity, time and cost associated with manufacturing spectral sensors, whilst also enabling high volume manufacturing of multiple, compact spectral sensors.

The novel fabrication of spectral sensors on a wafer scale level is disclosed. Wafer manufacturing processes may be used to manufacture multiple spectral sensors in parallel on a single wafer, thereby enabling high volume manufacture and significantly reducing manufacturing complexity and cost compared to known methods. Optionally, additional components not seen in known spectral sensors (e.g. optical components, electronics and/or other sensors to enhance a functionality of the spectral sensors) can be integrated into the spectral sensor with relative ease using wafer manufacturing processes.

According to an aspect of the present disclosure, there is provided a method of manufacturing a plurality of spectral sensors comprising providing a first substrate, forming the plurality of spectral sensors on the first substrate, and dividing the first substrate to separate the plurality of spectral sensors.

Known spectral sensors are formed one at a time in individual hermetically sealed metallic cans (which may be referred to as “TO type packages”) comprising a vacuum environment or an inert gas. Persons skilled in the field of spectral sensors have not considered using manufacturing techniques from other technical fields such as wafer manufacturing processes and/or surface mounting processes (e.g. using pick-and-place machines and operating in non-vacuum, non-inert and/ or non-hermetic environments). This is due to the high sensitivity of the spectral sensors. For example, mechanical changes of the order of l/4 (i.e. a quarter of the wavelength of light being analysed) or less may critically affect a performance and precision of the spectral sensors. The method advantageously provides a substantial reduction of manufacturing costs compared to known methods. This is because multiple units of spectral sensors can be made in parallel on a single substrate or wafer using wafer processing techniques whilst operating in non-vacuum, non-inert and/or non-hermetic environments.

The method advantageously provides a substantial reduction in the size of the spectral sensors compared to known spectral sensors, enabling incorporation into consumer electronic devices such as mobile phones.

The resulting spectral sensors may be surface mountable devices (SMD) that are mountable on any electronic board.

The plurality of electromechanical spectral sensors may comprise microelectromechanical systems (MEMS).

The plurality of spectral sensors may comprise scanning spectral sensors (e.g. scanning incident light onto a single photodiode). The plurality of spectral sensors may comprise dispersive spectral sensors (e.g. dispersing incident light amongst an array of photodetectors).

The first substrate may be a printed circuit board. The printed circuit board may comprise FR4. The printed circuit board may comprise a plurality of electrical connections and/or electronic components.

Dividing the first substrate to separate the plurality of spectral sensors may comprise dicing the first substrate. Dicing the first substrate may comprise sawing or cutting along scribe lines that run along the first substrate between the plurality of spectral sensors.

Different spectral sensors within the plurality of spectral sensors may be configured to analyse different ranges of wavelengths of light. For example, a first spectral sensor within the plurality of spectral sensor may be configured to analyse light having a wavelength in the range of about 1350nm to about 1650nm. A second spectral sensor within the plurality of spectral sensors may be configured to analyse light having a wavelength in the range of about 1550nm to about 1850nm. Further optical and/or electronic components may be added to the first substrate to enhance a functionality of one or more of the spectral sensors. For example, cameras configured to detect a type of object being analysed by the spectral sensors may be added to the first substrate. As another example, proximity detectors configured to indicate to a user whether an object is close and/or stable enough for analysis may be added to the first substrate. As a further example, a tuneable light source and/or different types of light sources configured to emit different wavelengths of radiation (e.g. ultraviolet, visible and/or infrared radiation) for different spectral analyses may be added to the first substrate. As a yet further example, multiple photodetectors may be added to each spectral sensor to increase a range of spectral information obtainable by the spectral sensor.

Forming the plurality of spectral sensors on the first substrate may comprise forming a plurality of electromechanical spectral sensors having moveable parts that are controllable using an electronic signal. Each electromechanical spectral sensor may comprise at least one moveable part.

Known spectral sensors comprise passive optical elements, such as diffraction gratings and/or prisms, which are less sensitive to manufacturing processes than electromechanical spectral sensors having moveable parts. As such, electromechanical spectral sensors having moveable parts that are controllable using an electronic signal have previously been manufactured individually in hermetically sealed metallic cans, creating a time-consuming and expensive manufacturing process. Contrary to received wisdom in the field of spectral sensors, the inventors of the present invention have realised that it is possible manufacture electromechanical spectral sensors using surface mount technologies (e.g. pick-and-place machines placing separate components on a substrate in non-hermetic and non-vacuum environments).

The method may comprise forming at least some of the plurality of spectral sensors on the first substrate simultaneously. This may advantageously increase a speed with which the plurality of spectral sensors are formed. The at least some of the plurality of spectral sensors may be formed in parallel on the substrate, e.g. using planar robotics.

Forming the plurality of electromechanical spectral sensors on the first substrate may comprise using a pick-and-place machine to simultaneously place a plurality of separate components on the first substrate. Known manufacturing methods comprise forming a plurality of separate wafers, each wafer comprising connected (i.e. non-separated) components, and subsequently joining the wafers together to form a wafer stack. Using a pick-and-place machine to simultaneously place a plurality of separate components on the first substrate advantageously reduces a cost and complexity of the manufacturing process, and increases a speed of the manufacturing process, compared to known manufacturing methods involving wafer stacks. Using a pick-and-place machine to simultaneously place a plurality of separate components on the first substrate advantageously increases a flexibility of the manufacturing process because it is easier to integrate additional components (e.g. cameras, proximity sensors, tuneable light sources, additional photodetectors, etc.) without having to completely redesign one or more wafers in the wafer stack of the known manufacturing methods.

The method may comprise forming the plurality of spectral sensors on the first substrate in a non-hermetic environment.

Forming the spectral sensors on a substrate in a non-hermetic environment allows the use of a wider range of materials. For example, materials such as FR4 and silicon can be used that perform better under thermal and/or mechanical stresses allowing stable optical function even in a non-hermetic package.

The method may comprise forming the plurality of spectral sensors on the first substrate in a non-vacuum environment or a non-inert environment. The non-vacuum environment and/or the non-inert environment may comprise air.

The method may comprise forming a vent hole through the first substrate before forming the plurality of spectral sensors on the first substrate.

During at least some parts of the manufacturing process, a temperature of the spectral sensors may vary, thereby causing thermal expansion and/or contraction of gases within the spectral sensors. Providing a vent hole allows the gases to travel into or out of the vent hole as needed. This advantageously reduces the build-up of pressures acting on the spectral sensors which may otherwise damage the spectral sensors. The method may comprise filling the vent hole to seal the first substrate before dividing the first substrate. This closes the inner components of the spectral sensors off from the external environment to protect the inner components whilst the first substrate is divided.

Forming the plurality of spectral sensors on the first substrate may comprise forming a plurality of thermistors on the first substrate.

Forming the plurality of thermistors may comprise dispensing first portions of thermally activated adhesive on first surface regions of the first substrate. Forming the plurality of thermistors may comprise placing the plurality of thermistors on the first portions of adhesive. Forming the plurality of thermistors may comprise heating the first portions of thermally activated adhesive to attach the plurality of thermistors to the first substrate.

The first portions of thermally activated adhesive may comprise soldering paste and/or solder balls.

Placing the plurality of thermistors on the first portions of thermally activated adhesive may comprise using a pick-and-place machine, advantageously providing highly accurate and fast-paced placing of the thermistors.

A pick-and-place machine may be used to simultaneously place a plurality of separate thermistors on the first substrate.

Forming the plurality of spectral sensors on the first substrate may comprise forming a plurality of photodetectors on the first substrate.

Forming the plurality of photodetectors on the first substrate may comprise dispensing second portions of thermally activated adhesive on second surface regions of the first substrate. Forming the plurality of photodetectors on the first substrate may comprise placing the plurality of photodetectors on the second portions of thermally activated adhesive. Forming the plurality of photodetectors on the first substrate may comprise heating the second portions of thermally activated adhesive to attach the plurality of photodetectors to the first substrate.

The second portions of thermally activated adhesive may comprise soldering paste. Placing the plurality of photodetectors on the second portions of adhesive may comprise using a pick-and-place machine. This advantageously provides highly accurate and fast- paced placing of the photodetectors.

A pick-and-place machine may be used to simultaneously place a plurality of separate photodetectors on the first substrate.

The method may comprise heating the first portions and second portions of thermally activated adhesive simultaneously. This advantageously increases a speed with which the spectral sensors are manufactured.

Forming the plurality of spectral sensors on the first substrate may comprise forming a plurality of spacers on the first substrate. The spacers may be formed from silicon. Each spacer may comprise two elongated pillars. Each thermistor and photodetector pair may be located between the two elongated pillars of each spacer.

Forming the plurality of spacers on the first substrate may comprise dispensing third portions of thermally activated adhesive on third surface regions of the first substrate. Forming the plurality of spacers on the first substrate may comprise placing the plurality of spacers on the third portions of thermally activated adhesive. Forming the plurality of spacers on the first substrate may comprise heating the third portions of thermally activated adhesive to attach the plurality of spacers to the first substrate.

The third portions of thermally activated adhesive may comprise a thermally activated glue. The third portions of thermally activated adhesive may be softer and/or have a greater elasticity than the first and second portions of thermally activated adhesive.

Placing the plurality of spacers on the third portions of adhesive may comprise using a pick-and-place machine. This advantageously provides highly accurate and fast-paced placing of the photodetectors.

A pick-and-place machine may be used to simultaneously place a plurality of separate spacers on the first substrate.

Forming the plurality of spectral sensors on the first substrate may comprise forming a plurality of interferometers on the first substrate. The interferometers may be tuneable interferometers. The interferometers may be tuneable MEMS interferometers. Forming the plurality of interferometers on the first substrate may comprise dispensing fourth portions of thermally activated adhesive on fourth surface regions of the plurality of spacers. Forming the plurality of interferometers on the first substrate may comprise placing the plurality of interferometers on the fourth portions of thermally activated adhesive. Forming the plurality of interferometers on the first substrate may comprise heating the fourth portions of thermally activated adhesive to attach the plurality of interferometers to the first substrate.

The fourth portions of thermally activated adhesive may comprise a thermally activated glue. The fourth portions of thermally activated adhesive may be softer and/or have a greater elasticity than the first and second portions of thermally activated adhesive.

Forming the plurality of interferometers on the first substrate may comprise forming a plurality of Fabry-Perot interferometers on the first substrate. Forming the plurality of interferometers on the first substrate may comprise forming a plurality of Fourier- transform interferometers on the first substrate. Forming the plurality of interferometers on the first substrate may comprise forming a plurality of Fabry-Perot interferometers on the first substrate and forming a plurality of Fourier-transform interferometers on the first substrate.

Forming the plurality of Fabry-Perot interferometers on the first substrate may comprise forming a plurality of MEMS Fabry-Perot interferometers on the first substrate. Forming the plurality of Fourier-transform interferometers on the first substrate may comprise forming a plurality MEMS Fourier-transform interferometers on the first substrate.

Placing the plurality of interferometers on the fourth portions of adhesive may comprise using a pick-and-place machine. This advantageously provides highly accurate and fast- paced placing of the interferometers.

A pick-and-place machine may be used to simultaneously place a plurality of separate interferometers on the first substrate.

The method may comprise heating the third portions and fourth portions of thermally activated adhesive simultaneously. This advantageously increases a speed with which the spectral sensors are manufactured. The method may comprise forming a multi-housing structure. The multi-housing structure may comprise a plurality of housing units configured to house the plurality of spectral sensors. The multi-housing structure may comprise a plurality of openings for allowing light into the plurality of spectral sensors.

Forming the multi-housing structure may comprise moulding a plastic material.

Moulding the plastic material may comprise moulding a fiber metal filled liquid crystal polymer.

The method may comprise forming a plurality of windows over the plurality of openings.

The method may comprise attaching the multi-housing structure to the first substrate.

Attaching the multi-housing structure to the first substrate may comprise dispensing fifth portions of thermally activated adhesive on fifth surface regions of the first substrate. Attaching the multi-housing structure to the first substrate may comprise placing the multi-housing structure on the fifth portions of thermally activated adhesive. Attaching the multi-housing structure to the first substrate may comprise heating the fifth portions of thermally activated adhesive to attach the multi-housing structure to the first substrate.

Placing the multi-housing structure on the fifth portions of thermally activated adhesive may comprise using a pick-and-place machine.

Dispensing the fifth portions of thermally activated adhesive may comprise dispensing an electrically conductive material. The electrically conductive material may comprise silver.

According to another aspect of the present disclosure, there is provided a spectral sensor manufactured according to the method of any previous aspect.

According to another aspect of the present disclosure, there is provided an electronic device comprising the spectral sensor of any previous aspect. According to another aspect of the present disclosure, there is provided a computer program comprising computer readable instructions configured to cause a computer to carry out a method according to any previous aspect.

According to another aspect of the present disclosure, there is provided a computer readable medium carrying a computer program according to any previous aspect.

Features of different aspects of the invention may be combined together.

Brief Description of the Preferred Embodiments

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

Fig. 1 schematically depicts a cross-sectional view of an example of a spectral sensor manufactured according to an aspect of the present disclosure;

Fig. 2 shows an example of a spectral sensor manufactured according to an aspect of the present disclosure relative to a known spectral sensor manufactured according to known methods;

Fig. 3 schematically depicts a cross-sectional view of components of a spectral sensor at an early stage of a method of manufacture according to an aspect of the present disclosure;

Fig. 4 schematically depicts a cross-sectional view of further components of the spectral sensor at a further stage of the method of manufacture according to an aspect of the present disclosure;

Fig. 5 schematically depicts a cross-sectional view of yet further components of the spectral sensor at a yet further stage of the method of manufacture according to an aspect of the present disclosure;

Fig. 6 schematically depicts a view from above an array of one hundred spectral sensors formed on a wafer according to an aspect of the present disclosure;

Fig. 7 schematically depicts an electronic device incorporating a spectral sensor manufactured according to an aspect of the present disclosure; and,

Fig. 8 shows a flowchart of a method of manufacturing a spectral sensor according to an aspect of the present disclosure.

Detailed Description of the Preferred Embodiments Fig. 1 schematically depicts a cross-sectional view of an example of a spectral sensor 100 manufactured according to an aspect of the present disclosure. The spectral sensor 100 comprises a photodetector 102 located beneath a Fabry-Perot interferometer 104. The photodetector 102 may for example be a photodiode. The photodetector 102 may be connected to an amplifier (not shown) and/or a microcontroller (not shown). The amplifier and/or microcontroller may be located within a first substrate 112. The substrate 112 may for example be a printed circuit board (e.g. formed from FR4). The photodetector 102 may provide an output that is proportional to an intensity of incident light. The output of the photodetector 102 may be amplified by the amplifier before passing to the microcontroller.

The Fabry-Perot interferometer 104 comprises a substrate 103 (e.g. formed from silicon) provided with a recess having a planar bottom. A layer 107 (e.g. formed from silicon, e.g. a silicon wafer) is supported either side of the substrate 103 and extends across the recess to form a gap 105. A lowermost surface of the silicon layer 107 is provided with a multilayer reflective structure 104a (e.g. formed from SiO and/or SiN layers). The planar surface of the recess is also provided with a multilayer reflective structure 104b (e.g. formed from SiO and/or SiN layers). Thus, two reflectors 104a, 104b are provided which face each other. These reflectors 104a, 104b act as a pair of reflective plates 104a, 104b of the Fabry-Perot interferometer 104. The substrate 103 and reflectors 104a, 104b may be square (or rectangular) when viewed from above.

The substrate 103 is supported by two elongated pillars 106 (e.g. formed from silicon). The elongated pillars 106 run along two sides of the substrate 103. Other forms of support may be used to support the substrate 103. The support and the substrate 103 may be formed from the same material.

A thermistor 108 is located adjacent to the photodetector 102 and beneath the Fabry- Perot interferometer 104. The photodetector 102, thermistor 108 and elongate pillars 106 are all fixed to the first substrate 112. Control electronics 114 are also provided. The control electronics 114 may comprise a processor, a memory and other components. The control electronics 114 may be provided adjacent to the photodetector 102 and beneath the Fabry-Perot interferometer 104. The control electronics 114 may have some other position, such as beneath the first substrate 112 or within the first substrate 112. The thermistor 108 may be connected to an amplifier (not shown) and/or a microcontroller (not shown). The thermistor 108 may be configured to provide a resistance value that is indicative of a temperature of the spectral sensor 100. The resistance value may be passed via the amplifier to the microcontroller. This is beneficial because electromechanical spectral sensors are sensitive to temperature changes, and these can be at least partially accounted for using the information gathered by the thermistor.

A housing 116 extends over the photodetector 102, Fabry-Perot interferometer 104 and thermistor 108. The housing 116 may be formed from a fiber metal filled liquid crystal polymer. An opening 118 is provided in the housing 116. The opening 118 is positioned above the Fabry-Perot interferometer 104. The photodetector 102 may be positioned directly below the opening 118. Advantageously this may provide a symmetric distribution of light onto the photodetector 102.

A window 120 is provided to close the opening 118 whilst allowing the transmission of light. The window 120 is provided beneath the opening 118. This minimizes the possibility of the window 120 being damaged. The window 120 could however be provided above the opening 118. The window 120 seals shut a volume within which the Fabry-Perot interferometer 104 is provided. This controls the environment around the Fabry-Perot interferometer 104 (usually air). The window 120 may be provided with a band-pass filter (not shown) that limits the range of wavelengths of light that are incident upon the Fabry-Perot interferometer 104.

As noted above, the Fabry-Perot interferometer 104 comprises a pair of reflectors 104a, 104b. The reflectors 104a, 104b may have a reflectivity of more than 80%. The reflectivity of the reflectors 104a, 104b may for example be 85% or more. The reflectivity of the reflectors 104a, 104b may be 99% or more (e.g. 99.9% or more). The Fabry-Perot interferometer 104 acts as a wavelength filter. The higher the reflectivity of reflectors 104a, 104b the narrower the wavelength band which is transmitted by the Fabry-Perot interferometer 104.

Operation of the Fabry-Perot interferometer 104 may be understood as follows. Some of the light incident upon the first reflector 104a of the Fabry-Perot interferometer 104 will pass through the first reflector 104a. The light will propagate to and be incident upon the second reflector 104b. Some of this light will be transmitted by the second reflector 104b and some will be reflected. The reflected light is then incident upon the first reflector 104a, and part of that light is again reflected. Multiple more partial transmissions and reflections of the light will occur. Consequently, light which has undergone different numbers of reflections is transmitted by the second reflector 104b.

For most wavelengths of light, destructive interference occurs when the light leaves the second reflector 104b, and light at those wavelengths is not seen by the photodetector 102. However, if the optical path length of the light in the Fabry-Perot interferometer 104 (i.e. passage across a gap 105 between the reflectors 104a, 104b and back again) is an integer multiple of a wavelength of the light, then constructive interference of light at that wavelength occurs. That wavelength is transmitted by the Fabry-Perot interferometer and is seen by the photodetector 102. Thus, when light with a broad wavelength range is incident upon the Fabry-Perot interferometer 104, only light with a specific wavelength which is an integer multiple of the plate separation (or “cavity length”) will be transmitted to the photodetector 102. A phase shift experienced by the light after one round trip through the cavity may be given by the following equation:

Where k is a wave vector (or propagation constant) of the light, L is a length of the cavity, n is a refractive index of the cavity and A₀ is a wavelength of the light. Resonance occurs when the phase shift is an integer multiple of 2TT, orwhen 0 = 2m7r where m is an integer.

The wavelength of light which is transmitted by the Fabry-Perot interferometer 104 may be adjusted by applying a voltage across the reflectors 104a, 104b (the reflectors may be conductive). Electrical connection to the reflectors 104a, 104b may be provided by wires (not shown). The control electronics 114 may be used to control the voltage applied across the reflectors 104a, 104b via the wires. Increasing the voltage that is applied across the reflectors 104a, 104b attracts the reflectors 104a, 104b to each other and as a result the upper reflector 104a moves towards the lower reflector 104b. This reduces a gap 105 between the reflectors 104a, 104b and reduces the wavelength of light that is transmitted by the Fabry-Perot interferometer 104. Reducing the voltage applied across the reflectors 104a, 104b reduces the attraction of the reflectors to each other, and allows the upper reflector 104a to move away from the lower reflector 104b. This increases the wavelength of light that is transmitted by the Fabry-Perot interferometer 104. Movements of the upper reflector 104a by as little as 1nm may be achieved.

Thus, the control electronics 114 can (by selecting a voltage applied across the reflectors 104a, 104b of the Fabry-Perot interferometer 104) select a wavelength to be transmitted by the Fabry-Perot interferometer 104. As will be appreciated, in order to be able to select the wavelength with accuracy, accurate control of the gap 105 between the reflectors 104a, 104b is desirable. However, the temperature of the spectral sensor 100 will have an effect upon the gap 105 (a higher temperature may increase the separation between reflectors 104a, 104b due to thermal expansion).

The wavelength of light transmitted by the Fabry-Perot interferometer 104 may be selected by measuring the capacitance of the Fabry-Perot interferometer, and then using the measured capacitance to determine the voltage needed in order to achieve transmission of that wavelength. The method may take into account constant properties of the Fabry-Perot interferometer (i.e. properties which do not vary with temperature). The method may be based on use of the following equation:

V=BXm/C where V is the voltage applied across the reflectors 104a, 104b of the Fabry-Perot interferometer 104, B is a temperature-independent constant of a capacitor formed by the reflectors 104a, 104b, l is the wavelength of light to be transmitted, and C is the capacitance of the capacitor formed by the reflectors 104a, 104b.

A capacitance measurement circuit (not shown) is connected to the Fabry-Perot interferometer 104 and also connected to a microcontroller (not shown). The capacitance measurement circuit may for example comprise an oscillator which applies a modulation to the capacitor and measures the effect of the capacitor on the modulation. The capacitance measurement circuit may be configured to measure the capacitance of the Fabry-Perot interferometer 104 and provide the measured capacitance to the microcontroller. The capacitance measurement circuit may be located within the first substrate 112. The capacitance measurement circuit may be referred to as a capacitance readout. Fig. 2 shows an example of a spectral sensor 200 manufactured according to an aspect of the present disclosure compared to a known spectral sensor 210. The spectral sensor 200 according to an aspect of the disclosure is more compact than the known spectral sensor 210. For example, the spectral sensor 200 according to an aspect of the disclosure may be between about five and ten times smaller than the known spectral sensor 210. The known spectral sensor 210 is too large to incorporate into certain electronic devices such as mobile phones or tablet computers. In contrast, the spectral sensor 200 according to an aspect of the disclosure is compact enough and suitable for incorporating into such electronic devices. The spectral sensor 200 according to an aspect of the disclosure is less expensive to manufacture than the known spectral sensor 210. For example, the cost of manufacturing the spectral sensor 200 according to an aspect of the disclosure may be between about five and ten times lower than the cost of manufacturing the known spectral sensor 210. This may be at least partially because the components of the known spectral sensor 210 are manufactured in a controlled environment comprising a vacuum or an inert gas. Components of the known spectral sensor 210 are hermetically sealed within a metallic housing 220 having a controlled environment. A vacuum or an inert gas exists within the hermetically sealed metallic housing 220 to provide a stable environment for the sensitive optical components therein. In contrast, the components of the spectral sensor 200 according to an aspect of the disclosure may be manufactured in a non-vacuum and/or non-inert environment. The spectral sensor 200 according to an aspect of the disclosure my not be hermetically sealed, and may be fully operational when exposed to a non-vacuum and/or non-inert environment (e.g. ambient air). The known spectral sensor 210 comprises a fixed number of pins 230 for connecting the known spectral sensor 210 to a device. The fixed number of pins 230 limits a compatibility of the known sensor 210 to specific devices comprising inputs having the appropriate number of pin receivers. The spectral sensor 200 according to an aspect of the disclosure does not suffer from this drawback, and may be referred to as a surface mount spectral sensor.

Fig. 3 schematically depicts a cross-sectional view of components of a spectral sensor at an early stage of a method of manufacture according to an aspect of the present disclosure. A first substrate 312 is provided. Only a portion of the first substrate 312 is shown in Figs. 3-5. The entirety of the first substrate 312 is shown in Fig. 6. The first substrate 312 may be a printed circuit board (e.g. comprising FR4). The first substrate 312 may comprise a plurality of electrical connections (not shown) such as a plurality of electrically conductive layers and/or vias for connecting different electronic components (e.g. one or more amplifiers, one or more microprocessors, one or more controllers, a capacitance measurement circuit, etc.) of the spectral sensor. The electronic connections may, for example, comprise Copper. Solder paste or a solder balls 307 may be provided on the bottom of the first substrate 312 for mounting the first substrate 312 to an electronics board of an electronic device (e.g. a mobile phone). The solder paste or solder balls 307 may be added to the bottom of the first substrate 312 after the spectral sensor has been manufactured (e.g. before the spectral sensor is to be mounted to an electronics board of electronic device).

A thickness of the first substrate 312 may be selected to house a desired number of electrical connections. The first substrate 312 may have a thickness of about 100pm or more. The first substrate 312 may have a thickness of about 2mm or less. A length and width of the first substrate 312 may be selected to support a desired number of spectral sensors (themselves having a desired size). For example, an entirety of the first substrate 312 may have a length and/or width of about 50mm or more. For example, an entirety of the first substrate 312 may have a length and/or width of about 510 mm or less. Each spectral sensor may have a length and/or a height and/or a width of about 1mm or more. Each spectral sensor may have a length and/or a height and/or a width of about 5mm or less. For example, each spectral sensor may have a length and/or a height and/or a width of about 3mm. The first substrate 312 may be large enough to support an array of between two spectral sensors or more. The first substrate 312 may be large enough to support an array of about one hundred spectral sensors or less.

In the examples of Figs 3-5, only a portion of the first substrate 312 is shown. In the examples of Figs 3-5, the construction of a single spectral sensor on the portion of the first substrate 312 is shown in order to clearly convey the manufacturing process. Fig. 6 shows an example of an array 600 of one hundred spectral sensors 100 manufactured on the entirety of the first substrate 312 according to the stages of manufacture shown in Figs 3-5.

A thermistor 308 is formed on the first substrate 312. The first substrate 312 may comprise a first portion of adhesive 330 on a first surface region arranged to receive the thermistor 308. The first portion of adhesive 330 may be dispensed on the first surface region in a line pattern and/or a dot pattern. The first portion of adhesive 330 may comprise a thermally activated adhesive. The first portion of adhesive 330 may comprise solder paste or solder balls. The first portion of adhesive 330 may be electrically conductive to pass electronic signals between the thermistor 308 and a circuitry of the first substrate 312. The thermistor 308 may be aligned with and placed on the first portion of adhesive 330 using a pick-and-place machine (not shown). The pick-and-place machine may comprise a robotic arm (e.g. planar robotics typically used in wafer manufacturing processes).

A photodetector 302 is formed on the first substrate 312. The photodetector 302 may comprise a photodiode. The photodetector 302 may comprise an array of photodiodes. The first substrate 312 may comprise a second portion of adhesive 335 on a surface region arranged to receive the photodetector 302. The second portion of adhesive 335 may be dispensed on the second surface region in a line pattern and/or a dot pattern. The second portion of adhesive 335 may comprise a thermally activated adhesive. The second portion of adhesive 335 may comprise solder paste or solder balls. The second portion of adhesive 335 may be electrically conductive to pass electronic signals between the photodetector 302 and a circuitry of the first substrate 312. The photodetector 302 may be aligned with and placed on the second portion of adhesive 335 using a pick-and- place machine (not shown). The pick-and-place machine may comprise a robotic arm (e.g. planar robotics typically used in wafer manufacturing processes).

The thermistor 308 may be formed on the first substrate 312 before the photodetector 302 is formed on the first substrate 312. Alternatively, the photodetector 302 may be formed on the first substrate 312 before the thermistor 308 is formed on the first substrate 312.

A vent hole 315 is formed through the first substrate 312. During at least some parts of the manufacturing process, a temperature of the spectral sensor may vary, thereby causing thermal expansion and/or contraction of gases within the spectral sensor. Providing a vent hole 315 allows the gases to travel into or out of the vent hole 315 as needed. This advantageously reduces the build-up of pressures acting on the spectral sensor which may otherwise damage the spectral sensor. The vent hole 315 may be filled to seal the first substrate 312 before a later manufacturing stage takes place that involves dividing the first substrate 312.

The first substrate 312 comprising the thermistor 308 and the photodetector 302 may be heated to thermally activate (e.g. melt) the first and second portions of adhesive 330, 335. For example, the first substrate 312 may be placed in an oven configured to heat the first substrate 312 to a temperature of about 200°C or more, e.g. about 240°C. After melting the first and second portions of adhesive 330, 335, the first substrate 312 may be cooled to solidify the first and second portions of adhesive 330, 335. Upon solidification, the thermistor 308 and the photodetector 302 may be considered to be attached to the first substrate 312.

Further attachment processes (which may be referred to as die attachment processes) may be performed between the thermistor 308 and/or the photodetector 302 and the first substrate 312 (e.g. epoxy bonding, soldering, wire bonding, etc.). For example, a first electrical connector 340 may be provided between an electrical contact (not shown) of the thermistor 308 and an electrical contact (not shown) of the first substrate 312. The first electrical connector 340 may be configured to transmit one or more electrical signals between the thermistor 308 and the first substrate 312. The electrical contact of the first substrate 312 may be electrically connected to one or more other electronic components (e.g. one or more amplifiers, one or more microprocessors, one or more controllers, a capacitance measurement circuit, etc.) of the spectral sensor. The first electrical connector 340 may comprise metallic wiring (e.g. gold or aluminium wiring). There may be no wiring provided between the thermistor 308 and the first substrate 312 and/or the photodetector 302 and the first substrate 312. The thermistor 308 may be a surface mount thermistor. The photodetector 302 may be a surface mount photodetector. The photodetector 302 may be a back-side illuminated photodetector.

Fig. 4 schematically depicts a cross-sectional view of further components of the spectral sensor at a further stage of the method of manufacture according to an aspect of the present disclosure. A spacer 345 is formed on the first substrate 312. The spacer 345 may be formed from silicon. The spacer 345 may comprise two elongated pillars 306. The thermistor 308 and the photodetector 302 may be located between the two elongated pillars 306. The first substrate 312 may comprise a third portion of adhesive (not shown) on a third surface region arranged to receive the spacer 345. The third portion of adhesive may comprise a thermally activated glue. The third portion of adhesive may be dispensed on the third surface region in a line pattern and/or a dot pattern. For example, the third portion of adhesive may be dispensed along a perimeter (e.g. either side of) of both the photodetector 302 and thermistor 308. The spacer 345 may be aligned with and placed on the third portion of adhesive using a pick-and-place machine (not shown). The pick-and-place machine may comprise a robotic arm (e.g. planar robotics typically used in wafer manufacturing processes). The spacer 345 may be a surface mount spacer.

An interferometer 304 is formed on the spacer 345. The interferometer 304 may be an electromechanical interferometer, e.g. a MEMS interferometer. In the example of Figs 4-5, the interferometer 304 is a Fabry-Perot interferometer. The interferometer 304 may be substantially the same as (e.g. comprise substantially the same arrangement of substantially the same components formed from substantially the same materials) the Fabry-Perot interferometer 104 shown and described above with respect to Fig. 1. Alternatively, the interferometer 304 may be a Fourier-transform interferometer.

The spacer 345 may comprise a fourth portion of adhesive (not shown) on a fourth surface region arranged to receive the interferometer 304. The fourth portion of adhesive may be dispensed on the fourth surface region in a line pattern and/or a dot pattern. For example, the fourth portion of adhesive may be dispensed on an upper surface of each of the two elongated pillars 306 of the spacer 345. The fourth portion of adhesive may comprise a thermally activated glue. The interferometer 304 may be aligned with and placed on the fourth portion of adhesive using a pick-and-place machine (not shown). The pick-and-place machine may comprise a robotic arm (e.g. planar robotics typically used in wafer manufacturing processes).

The first substrate 312 comprising the thermistor 308, the photodetector 302, the spacer 345 and the interferometer 304 may be heated to thermally activate (e.g. melt) the third and fourth portions of adhesive. For example, the first substrate 312 may be placed in an oven configured to heat the third and fourth portions of adhesive to a temperature of about 200°C or more, e.g. 240°C. After melting the third and fourth portions of adhesive, the first substrate 312 may be cooled to solidify the third and fourth portions of adhesive. Upon solidification, the spacer 345 may be considered to be attached to the first substrate 312 and the interferometer 304 may be considered to be attached to the spacer 345.

Further attachment processes (which may be referred to as die attachment processes) may be performed between the spacer 345 and/or the interferometer 304 and the first substrate 312 (e.g. epoxy bonding, soldering, wire bonding, etc.). For example, second and third electrical connectors 350, 355 may be provided between an electrical contact (not shown) of the interferometer 304 and an electrical contact (not shown) of the first substrate 312. The second and third electrical connectors 350, 355 may be configured to transmit one or more electrical signals between the interferometer 304 and the first substrate 312. The electrical contact of the first substrate 312 may be electrically connected to one or more other electronic components (e.g. one or more amplifiers, one or more microprocessors, one or more controllers, a capacitance measurement circuit, etc.) of the spectral sensor. The second and third electrical connectors 350, 355 may comprise metallic wiring (e.g. gold or aluminium wiring).

Fig. 5 schematically depicts a cross-sectional view of yet further components of the spectral sensor at a yet further stage of the method of manufacture according to an aspect of the present disclosure. The spectral sensor of Fig. 5 may be substantially the same (i.e. comprise substantially the same arrangements of substantially the same components formed from substantially the same materials) as the spectral sensor 100 of Fig. 1. Control and/or processing electronics (not shown) of the spectral sensor of Fig. 5 (e.g. one or more amplifiers, one or more microprocessors, a capacitance measurement circuit, etc.) may be located within the first substrate 312.

Optionally, additional components not seen in known spectral sensors (e.g. optical components, electronics and/or other sensors to enhance a functionality of the spectral sensors) can be formed on the first substrate 312 using wafer manufacturing processes such as those shown and described with respect to Figs 3-4. For example, further optical and/or electronic components may be added to the first substrate 312 to enhance a functionality of one or more of the spectral sensors on the first substrate 312. For example, cameras configured to detect a type of object being analysed by the spectral sensors may be formed on the first substrate 312. As another example, proximity detectors configured to indicate to a user whether an object is close and/or stable enough for analysis may be formed on the first substrate 312. As a further example, a tuneable light source and/or different types of light sources configured to emit different wavelengths of radiation (e.g. ultraviolet, visible and/or infrared radiation) for different spectral analyses may be formed on the first substrate 312. As a yet further example, multiple photodetectors may be formed on one or more spectral sensors on the first substrate 312 to increase a range of spectral information obtainable by the spectral sensor(s).

As described above with respect to Fig. 1 , a housing 316 extends over the photodetector 302, the interferometer 304 and the thermistor 308. The opening 318 is positioned above the interferometer 304. A window 320 is provided to close the opening 318 whilst allowing the transmission of light. The window 320 is provided beneath the opening 318. This minimizes the possibility of the window 320 being damaged. The window 320 could however be provided above the opening 318. The window 320 may be provided with a band-pass filter (not shown) that limits the range of wavelengths of light that are incident upon the interferometer 304.

As mentioned above, only a portion of the first substrate 312 is shown in Figs 3-5. The housing 316 forms part of a multi-housing structure. The multi-housing structure comprises a plurality of housing units configured to house the plurality of spectral sensors on the first substrate 312. The number, shape and/or size of the housing units may correspond to the number, shape and/or size of spectral sensors that are to be formed on the first substrate 312. The multi-housing structure also comprises a plurality of openings for allowing light into the plurality of spectral sensors on the first substrate 312. A plurality of windows 320 are formed over the plurality of openings.

The housing 316 may be substantially opaque. The housing 316 may be formed from a plastic material. The plastic material may comprise an electrically conductive material. For example, the plastic material may comprise a fiber metal filled liquid crystal polymer. The housing 316 may be moulded. For example, a fiber metal filled liquid crystal polymer may be melted within a mould having a desired shape and subsequently solidified. The housing 316 may be separately formed whilst the previously discussed manufacturing steps take place (i.e. in a separate process whilst the thermistor 308, the photodetector 302, the spacer 345 and the interferometer 304 are attached to the first substrate 312).

The window 320 is formed on the housing 316. The housing 316 may comprise a portion of adhesive (not shown) on a surface region proximate the opening 318 arranged to receive the window 320. The portion of adhesive may be dispensed on the surface region proximate the opening 318 in a line pattern (e.g. corresponding to edges of the window 320) and/or a dot pattern (e.g. four dots corresponding to four corners of the window 320). The portion of adhesive proximate the opening 318 may comprise a thermally activated glue. The window 320 may be aligned with and on the proximate the opening 318 using a pick-and-place machine (not shown). The pick-and-place machine may comprise a robotic arm (e.g. planar robotics typically used in wafer manufacturing processes). Once formed, the multi-housing structure comprising the housing 316 may be placed on the first substrate 312. The first substrate 312 may comprise a fifth portion of adhesive (not shown) on a fifth surface region arranged to receive the housing 316. The fifth portion of adhesive may be dispensed in a line pattern and/or a dot pattern on the fifth surface region. For example, the fifth portion of adhesive may be dispensed along a perimeter (e.g. either side of) of the two elongated pillars 306 of the spacer 345. The fifth portion of adhesive may comprise thermally activated electrically conductive paste. The thermally activated electrically conductive paste may comprise silver. The housing 316 may be aligned with and placed on the fifth portion of adhesive using a pick-and- place machine (not shown). The pick-and-place machine may comprise a robotic arm (e.g. planar robotics typically used in wafer manufacturing processes).

The fiber metal filled liquid crystal polymer of the housing 316 may be configured to reduce external electromagnetic interference from negatively affecting the spectral sensor. The fifth portion of thermally activated electrically conductive paste may be configured to ground the housing 316 to assist with the reduction of external electromagnetic interference.

The first substrate 312 comprising the thermistor 308, the photodetector 302, the spacer 345, the interferometer 304 and the housing 316 may be heated to thermally activate (e.g. melt) the fifth portion of adhesive. For example, the first substrate 312 may be placed in an oven configured to heat the first substrate 312 to a temperature of about 200°C or more, e.g. 240°C. After melting the fifth portion of adhesive, the first substrate 312 may be cooled to solidify the fifth portion of adhesive. Upon solidification of the fifth portion of adhesive, the housing 316 may be considered to be attached to the first substrate 312. Further attachment processes (which may be referred to as die attachment processes) may be performed between the housing 316 and the first substrate 312 (e.g. epoxy bonding, soldering, wire bonding, etc.).

Fig. 6 schematically depicts a view from above an array 600 of one hundred spectral sensors 100 manufactured according to an aspect of the present disclosure. An entirety of the first substrate 312 is visible in Fig. 6. Each spectral sensor 100 comprises a window 120 for allowing light into the spectral sensor 100. The array 600 may have been manufactured according to the stages of manufacture shown in Figs 3-5. The stages of manufacture shown in Figs 3-5 have taken place across different areas of the first substrate 312 to form a plurality of spectral sensors 100 on the first substrate 312. The creation of the array 600 may be referred to as a batch manufacturing process, whereby each first substrate 312 comprises a batch of unit areas upon which a batch of spectral sensors may be formed. For example, a plurality of thermistors may have been attached to first surface regions of the first substrate, a plurality of photodetectors may have been attached to second surface regions of the first substrate, a plurality of spacers may have been attached to third surface regions of the first substrate, and a plurality of interferometers may have been attached to fourth surface regions of the plurality of spacers. Some or all of these attachments may have been performed in parallel (e.g. in rows or columns using a pick-and-place machine capable of simultaneously carrying ten components in a straight line).

At least some of the plurality of spectral sensors may be formed on the first substrate simultaneously. For example, each row or column of spectral sensors may have been formed on the first substrate 312 simultaneously, e.g. using planar robotics typically used in wafer manufacturing processes. The array 600 may have been formed in a non- hermetic environment. That is, the spectral sensors 100 and/or their surroundings may not have been hermetically sealed during manufacture. The array 600 may have been formed in a non-vacuum environment or a non-inert environment (e.g. in air).

The array 600 may be divided to form one hundred individual spectral sensors 100. Dividing the array 600 may involve dicing the array 600 (e.g. using wafer manufacturing processes). The dicing process may include mounting the first substrate 312 to a dicing tape (not shown). The dicing tape may comprise a photosensitive adhesive structure configured to support the first substrate 312 on a sheet metal frame. The dicing process may include scribing along scribe lines 610 of the first substrate 312 and separating individual spectral sensors 100 from the array 600. This process may include using mechanical sawing (e.g. a dicing saw) and/or laser cutting. The sawing and/or cutting may not reach or affect the dicing tape. Walls of the multi-housing structure that separate different spectral sensors from one another may run along the scribe lines 610. Once the scribe lines 610 have been sawn or cut, the photosensitive adhesive structure of the dicing tape may be exposed to electromagnetic radiation (e.g. ultraviolet light) to remove the dicing tape from the individual spectral sensors 100.

Fig. 7 schematically depicts an electronic device 700 incorporating a spectral sensor 100 manufactured according to an aspect of the present disclosure. In the example of Fig. 7, the electronic device 700 is a mobile phone. The spectral sensor 100 enables the mobile phone 700 to perform non-destructive spectroscopic analysis of materials (substances and/or chemicals) across various wavelengths. For example, the mobile phone 700 incorporating the spectral sensor 700 may be used to analyse a chemical composition of food, drink, cosmetics, etc.

Fig. 8 schematically depicts a flowchart of a method of manufacturing a spectral sensor according to an aspect of the present disclosure. A first step 810 of the method comprises providing a first substrate. A second step 820 of the method comprises forming a plurality of spectral sensors on the first substrate. A third step 830 of the method comprises dividing the first substrate to separate the plurality of spectral sensors.

Spectral sensors according to aspects of the present disclosure can be employed in many different applications including, for example, food and drink analysis, colour sensing, infrared sensing, biomedical sensors, anti-counterfeiting, make-up analysis, medicine analysis, process control, thickness measurements, high temperature thermometry, LED measurements, etc.

List of reference numerals:

100 spectral sensor

102 photodetector

103 substrate

104 Fabry-Perot interferometer 104a reflector

104b reflector

105 gap

106 elongated pillars

107 layer

108 thermistor 112 first substrate 114 control electronics 116 housing

118 opening 120 window

200 spectral sensor

210 known spectral sensor 220 metallic housing 230 pins

302 photodetector

307 solder balls

308 thermistor 312 first substrate

315 vent hole

330 first portion of adhesive 335 second portion of adhesive 340 first electrical connector

304 interferometer 306 elongated pillars 345 spacer

350 second electrical connector 355 third electrical connector

316 housing 318 opening 320 window

600 array of one hundred spectral sensors 610 scribe lines

700 electronic device

810 first step of method 820 second step of method

830 third step of method

The skilled person will understand that in the preceding description and appended claims, positional terms such as ‘above’, ‘along’, ‘side’, etc. are made with reference to conceptual illustrations, such as those shown in the appended drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to an object when in an orientation as shown in the accompanying drawings. The terms “first”, “second,” “third” etc., may be used merely as titles to differentiate different components, and may not necessarily indicate a temporal sequence. Although the disclosure has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in any embodiments, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS:

1. A method of manufacturing a plurality of spectral sensors comprising: providing a first substrate; forming the plurality of spectral sensors on the first substrate; and, dividing the first substrate to separate the plurality of spectral sensors.

2. The method of claim 1 , wherein forming the plurality of spectral sensors on the first substrate comprises forming a plurality of electromechanical spectral sensors having moveable parts that are controllable using an electronic signal.

3. The method of claim 2, wherein forming the plurality of electromechanical spectral sensors on the first substrate comprises using a pick-and-place machine to simultaneously place a plurality of separate components on the first substrate.

4. The method of any preceding claim, comprising adding to the first substrate a plurality of cameras configured to detect a type of object being analysed by the plurality of spectral sensors.

5. The method of any preceding claim, comprising adding to the first substrate a plurality of proximity detectors configured to indicate to a user whether an object is close and/or stable enough for analysis.

6. The method of any preceding claim, comprising adding to the first substrate a tuneable light source and/or different types of light sources configured to emit different wavelengths of radiation for different spectral analyses.

7. The method of any preceding claim, comprising forming a vent hole through the first substrate before forming the plurality of spectral sensors on the first substrate.

8. The method of claim 7, comprising filling the vent hole to seal the first substrate before dividing the first substrate.

9. The method of any preceding claim, wherein forming the plurality of spectral sensors on the first substrate comprises forming a plurality of thermistors on the first substrate by: dispensing first portions of thermally activated adhesive on first surface regions of the first substrate; placing the plurality of thermistors on the first portions of adhesive; and, heating the first portions of thermally activated adhesive to attach the plurality of thermistors to the first substrate.

10. The method of any preceding claim, wherein forming the plurality of spectral sensors on the first substrate comprises forming a plurality of photodetectors on the first substrate by: dispensing second portions of thermally activated adhesive on second surface regions of the first substrate; placing the plurality of photodetectors on the second portions of thermally activated adhesive; and, heating the second portions of thermally activated adhesive to attach the plurality of photodetectors to the first substrate.

11. The method of claim 9 and claim 10, comprising heating the first portions and second portions of thermally activated adhesive simultaneously.

12. The method of claim 3 or any claim dependent thereon, wherein using the pick- and-place machine to simultaneously place a plurality of separate components on the first substrate comprises placing a plurality of spacers on the first substrate.

13. The method of claim 12, wherein placing the plurality of spacers on the first substrate comprises: dispensing third portions of thermally activated adhesive on third surface regions of the first substrate; placing the plurality of spacers on the third portions of thermally activated adhesive; and, heating the third portions of thermally activated adhesive to attach the plurality of spacers to the first substrate.

14. The method of claim 12 or claim 13, wherein each spacer comprises two elongated pillars.

15. The method of claim 3 or any claim dependent thereon, wherein using the pick- and-place machine to simultaneously place a plurality of separate components on the first substrate comprises placing a plurality of tuneable interferometers on the first substrate.

16. The method of claim 15, wherein placing the plurality of tuneable interferometers on the first substrate comprises: dispensing fourth portions of thermally activated adhesive on fourth surface regions of the plurality of spacers; placing the plurality of tuneable interferometers on the fourth portions of thermally activated adhesive; and, heating the fourth portions of thermally activated adhesive to attach the plurality of tuneable interferometers to the first substrate.

17. The method of claim 15 or claim 16, wherein placing the plurality of tuneable interferometers on the first substrate comprises placing a plurality of Fabry-Perot interferometers on the first substrate and/or placing a plurality of Fourier-transform interferometers on the first substrate.

18. The method of claim 13 and claim 16, comprising heating the third portions and fourth portions of thermally activated adhesive simultaneously.

19. The method of any preceding claim, comprising forming a multi-housing structure comprising: a plurality of housing units configured to house the plurality of spectral sensors; and, a plurality of openings for allowing light into the plurality of spectral sensors.

20. The method of claim 19, wherein forming the multi-housing structure comprises moulding a plastic material.

21. The method of claim 20, wherein moulding the plastic material comprises moulding a fiber metal filled liquid crystal polymer.

22. The method of any of claims 19 to 21, comprising forming a plurality of windows over the plurality of openings.

23. The method of claim 22, comprising attaching the multi-housing structure to the first substrate.

24. The method of claim 23, wherein attaching the multi-housing structure to the first substrate comprises: dispensing fifth portions of thermally activated adhesive on fifth surface regions of the first substrate; placing the multi-housing structure on the fifth portions of thermally activated adhesive; and, heating the fifth portions of thermally activated adhesive to attach the multi housing structure to the first substrate.

25. The method of claim 24, wherein dispensing the fifth portions of thermally activated adhesive comprises dispensing an electrically conductive material.

26. A spectral sensor manufactured according to the method of any of claims 1 to 25.

27. An electronic device comprising the spectral sensor of claim 26.

28. A computer program comprising computer readable instructions configured to cause a computer to carry out a method according to any of claims 1 to 25.

29. A computer readable medium carrying a computer program according to claim 28.