Patent ID: 12259497

DETAILED DESCRIPTION

Optical sensors can include both an emitter and detector in a device package. The device package generally represents a physical device structure of an optical sensor or optical sensing device. The device package defines an internal cavity where the emitter and detector can be positioned. In general, the emitter emits a signal that interacts with a target object outside the package, which reflects a signal detectable by the detector. Each of the emitted signal and the reflected signal can be light waves, such as emitted and reflected rays of IR light, respectively. The emitted light wave signal can cause interference or crosstalk that result from undesired/interfering light waves in the internal cavity of the device package.

The undesired signal may couple with the reflected signal that is detectable by the detector and can degrade the optical device's ability to detect information about a target object accurately and reliably. The undesired signal may be referred to, alternatively, as crosstalk, optical crosstalk, system crosstalk, noise or background (light emitted from environment such as artificial light sources or sun light). Conventional optical devices may include an optical bather (sometimes called an optical isolator) disposed on the detector to reduce undesired or interfering light waves from being detected by the detector. However, these conventional optical bathers can be composed of materials that exhibit weakness when exposed to certain environmental conditions.

This document describes techniques for implementing an improved optical interference filter. The described techniques can be used to improve the physical stability and reliability of an optical interference filter that is comprised of hydrogenated amorphous silicon (a-Si:H). The filter is operable to filter undesired, or interfering, light waves that may degrade a detecting function of an optical sensing device. In particular, techniques are described for effectively leveraging a multiple layer configuration of an interference filter to attenuate or block undesired light waves (or system crosstalk) from degrading the detecting function of a detector. The detector can be a photodiode that is disposed adjacent an emitter in an internal cavity of an optical device.

The interference filter includes an alternating stack of a-Si:H thin films, representing high refractive materials, and silicon dioxide (SiO2) thin films, representing low refractive materials. In some implementations, each thin film of a particular alternating stack corresponds to an additional stack of layers of the interference filter. In one example, the interference filter is deposited on a glass surface of a structure used to enclose a substrate of the detector that detects photons of a light wave (in some cases the interference filter can also cover the emitter substrate). In other implementations, the interference filter is deposited directly on the detecting device, such as the substrate layer of a detector, which is most commonly based on complementary metal-oxide-semiconductor (CMOS) technology.

FIG.1is a block diagram of an example optical sensing system100. System100can represent an integrated circuit (IC) or an optical device, such as one or multiple optical sensors or optical sensing devices. In some examples, the optical sensing device is a color detection sensor, and the reflected signal detected by the detector is used to determine a color of a target object (e.g., a person's head) relative to the optical device. For instance, the optical device may be disposed in a mobile/smartphone device, and the detected reflected signal is processed at the mobile device to determine whether the smartphone is positioned adjacent a person's ear. In some examples, these devices are used for proximity detection, time-of-flight (TOF) applications, or light detection and ranging (LIDAR) applications. In one example the detector is positioned in a camera to detect ambient light relative to an environment in which the camera is located.

In some implementations, an example optical sensing device described in this document is a camera (e.g., a digital camera). The described techniques for implementing the improved optical interference filter can include placing or depositing the alternating stack of layers that form the improved filter directly on (e.g., on top of) an image sensor of the digital camera or on a separate substrate that is in front of, in contact with, or directly adjacent to the image sensor. The improved interference filter described herein can either be a structured filter (a discrete interference filter on respective pixels within a pixel array of the image sensor) or a plain deposition filter (the same interference filter covers all pixels within the pixel array of the image sensor).

System100includes an emitter102, such as a light emitting diode (LED) or vertical-cavity surface-emitting laser (VCSEL), and a detector104, such as a photodetector. In some cases, detector102is alternatively referred to as a sensor and may be a photodiode operable to sense (e.g., detect) light waves at a surface section of detector104. Emitter102can be operable, for example, to generate a signal of a particular wavelength, and the detector104can be a sensor operable to sense the signal produced by the emitter102. The emitter102and detector104may be disposed in, or otherwise located in, an optical device represented by system100.

The emitter102can be configured to produce visible or non-visible light of a desired wavelength. For example, the emitter102can produce light waves that have a wavelength in the near-infrared (NIR) spectrum in the range of 750 nanometers (nm) to 1400 nm. As described in more detail below, in an example implementation, the emitter102produces light, and the detector104incorporates a filter to minimize the detector's response to light other than wavelengths produced by the emitter102.

The emitter102can be fabricated directly onto an IC of system100or may include an IC chip or other modular component that is added to the IC of system100during or after fabrication of the IC. The emitter102may be a single emitter or may represent multiple emitters (e.g., an array of emitters). The detector104is configured to detect light of the wavelength produced by the emitter102(e.g., in the range of 850 nm to 940 nm). The detector104also may be fabricated directly onto an IC of system100or may include an IC chip or other modular component that is added to the IC of system100during or after fabrication of the IC. The detector104may be a single detector or may represent multiple detectors (e.g., an array of detectors).

A projection portion106can include circuitry of the emitter102that enables the emitter to generate an example light wave or related optical signal. Similarly, a detection portion108can include circuitry of the detector104that enables the detector to detect an example light wave or optical signal. In some implementations, system100is an optical sensor that includes both an emitter102and a detector104in a single device package120. The device package120generally represents a physical device structure of an optical sensor or optical sensing device.

FIG.2Ais a block diagram of an example optical device(s) represented by system100. For purposes of example, emitter102and detector104may be used for a variety of applications, including presence detection, motion detection, color detection, and other related applications in which an emitted signal is later detected and processed or analyzed. In the implementation ofFIG.2A, the system100is an optical device that emits a signal for sensing a target object. The signal can correspond to an example light wave202that is associated with a reflected light wave204.

As noted above, the optical device can include both the emitter102and detector104in a device package that defines an internal cavity210. The light wave202emitted by emitter102interacts with a target object215to cause the reflected light wave204. The target object215is external to the device package120. In this manner, the emitted light wave202exits the internal cavity210of the optical device after being emitted for sensing the target object215, and the reflected light wave204enters the internal cavity210of the optical device in response to the emitted light wave202interacting with the target object215.

Referring now toFIG.2B, in this implementation an optical device(s) represented by system100emits a signal corresponding to a light wave220. The light wave220is emitted for sensing target object215, and causes one or more light waves225to be reflected by the optical device. As described herein, the light wave220may have signal characteristics or attributes230that may result in cross-talk, interference, or undesired light waves at the optical device of system100. For example, the emitted light wave220may have certain power and/or spectral attributes230that cause undesired light waves235to occur in the internal cavity210of the device package120.

The undesired light waves are based on the emitted light wave220and can result in cross-talk or interference at the optical device. In some implementations, the undesired light waves235occur when one or more light waves220reflect off a portion of the device package120that forms the optical device. For example, undesired light waves235can occur when light wave220reflects off an inner wall associated with the internal cavity210of the device package120. In other examples, undesired light waves235can occur when light wave220reflects off a glass surface of the device package120.

FIG.3is a block diagram of an example optical sensing system300. System300can represent one or more optical devices306that leverage the spectral transmission's angular dependency property of an interference filter310to reduce optical cross-talk caused by undesired light waves235. In some cases, the spectral transmission's angular dependency property corresponds to a filter property of the interference filter. Interference filter310can be disposed on detector104. In some implementations, interference filter310is placed on a glass portion of detector104or directly on a silicon substrate that forms an IC of detector104, such as an IC of a photodiode or other photodetector.

In some implementations, interference filter310can be formed using at least two different materials that are particularly suited for attenuating signals that correspond to light waves having a certain angle of reflection. For example, each of the respective materials can have a different index of refraction that cooperates to define a filter property of the interference filter310. The filter property is operable to cause the interference filter310to attenuate the undesired light waves235based on an angle of reflection of the undesired light waves235. The filter property of the interference filter310can be based on a composition of layers315that form the interference filter.

The different materials of the interference filter310can be associated with respective layers315of the interference filter. Each of the respective layers315can have a particular thickness, a particular material composition, or both, and the layers may be arranged in a stacked configuration. In some implementations, a thickness of the materials at each layer can be varied or adjusted so as to control an amount of light that is received or detected by the detector104and to control an amount of undesired light that is blocked from detection by the detector104. In some cases, the interference filter310can have up to one hundred fifty layers315of the light refracting material. In other cases, the interference filter310can have more than one hundred fifty layers315of the light refracting material.

FIG.4shows example layers of an interference filter400exhibiting instability due to environmental effects. The interference filter400ofFIG.4can include multiple alternating layers. For example, the interference filter400can include a top layer402and a layer404that is adjacent the top layer402. In some cases, the top layer402is composed of a silicon dioxide (SiO2) material and adjacent layer404is composed of a a-Si:H material. The interference filter400can further include multiple alternating layers406,408. In some implementations, each layer of the alternating layers is formed from a different material than a material used to form an adjacent alternating layer. For example, layer406can be composed of a material such as SiO2, whereas layer408is composed of a different material such as a-Si:H.

The interference filter400can be disposed on a detector104. In general, signal characteristics of a reflected light wave are detected, measured, and processed based on detection functions of detector104. However, detectors are often placed in certain locations where environmental conditions at those locations can degrade accurate detection capabilities of a detector. The degraded detection functions cause distorted measurement readings of the reflected light. In general, the degraded detection function occurs in response to instability of the a-Si:H layers when the a-Si:H layers are exposed to certain environmental conditions.

One physical problem that can occur due to the instability is the formation of blisters at the a-Si:H layers which can cause delamination of the layers. For example, adjacent layer404of interference filter400can exhibit instability such as voids and blisters due to environmental effects. In some cases, the cause of the blistering can be attributed to hydrogen dose or ion energy during implantation, annealing after deposition, or reaction of the a-Si:H layers to water or water vapour in the environment. Further, the hydrogen content that occurs during layer deposition, e.g., plasma enhanced chemical vapor deposition (PECVD) or magnetron sputtering, may also have an influence on the blister formation.

FIG.5is a diagram of an example interference filter500that includes an example protective layer stack. In some implementations, an optical device includes interference filter500disposed on detector104of the optical device. The interference filter500includes a first filter portion502and a second filter portion504. As described here, the first filter portion502corresponds to the protective layer stack.

Filter portion502has a first set of alternating layers, e.g., that includes layers506,508. One layer506in the first set of alternating layers is formed from a first material, whereas another layer508in the first set of alternating layers is formed from a second, different material. For example, layer506can be composed of a material such as SiO2, whereas layer508can be composed of a different material. In some implementations, layer508can be composed of a variety of different respective materials, such as silicon nitride (Si3N4), niobium oxide (Nb2O5), Hafnium(IV) oxide (HfO2), or aluminum oxide (Al2O3).

Filter portion504has a second set of alternating layers, e.g., that includes layers406,408described above. Filter portion504can correspond to interference filter400or at least to the multiple alternating layers406,408of interference filter400, where layer406is formed from an example material such as SiO2, while layer408is formed from a different example material such as a-Si:H. In the implementation ofFIG.5, interference filter500is disposed on a substrate510which represents a substrate of detector104, which can be based on CMOS technology. In some cases, the substrate510is a glass substrate.

As described herein, the interference filter500is operable to attenuate undesired light waves in multiple distinct environments based at least on the multiple alternating layers in the first filter portion502. The filter portion502represents an additional protective layer stack of the interference filter500. In some implementations, filter portion502is an additional layer stack composed of dielectric layers, e.g., alternating dielectric layers. The additional layer stack can be disposed on (or on top of) an example a-Si:H based optical interference filter, such as filter400described above. The additional protective layer stack of dielectric layers is operable to improve the overall stability of the interference filter500such that the interference filter is resistant to, or has immunity against, certain environmental influences that would otherwise cause physical deformation, including voids and blisters, of the interference filter.

In some implementations, the additional layer stack corresponds to a filter property of the interference filter500. For example, the filter property is operable to cause the interference filter500to have immunity to one or more environmental conditions that would otherwise cause physical deformation of one or more layers included in the multiple alternating layers of the second filter portion504. For example, the filter property corresponding to the additional layer stack is operable to cause the interference filter500to have immunity to certain humidity driven defects.

The additional protective layers are operable to prevent water, water vapour, liquids, fluids, and/or other gaseous or fluid-based elements from reaching a top-most a-Si:H layer or SiO2layer of the second filter portion504. In some cases, incorporating additional dense dielectric layers of filter portion502on top of interference filter400can reduce, substantially reduce, or eliminate possible paths used by gaseous or fluid-based elements that degrade stability of the one or more layers in the filter portion504. The additional protective layer stack of filter portion502can be operable to attenuate undesired light waves and provide immunity to certain environmental effects, while still maintaining high transparency in the near infrared region.

In some implementations, the interference filter is configured for optical applications that focus on light waves near the infrared (IR) spectrum. However, applications of the interference filter using a-Si:H can be further extended into the IR region, for example, if a different detector technology is used. Examples of detector technology that can be used to extend the interference filter into the IR region include silicon-germanium (SiGe) or indium gallium arsenide (InGaAs). For certain sensing applications, an infrared (IR) light source may be used to emit photons that reflect off of an object and are detected by an IR detector of an optical sensing device.

The sensor measures the reflected signal when an object is within a detectable distance from a sensor that includes the IR light source and the IR detector. The sensor uses the reflected signal to determine a color, light range, or motion readout that may be proportional to the measured light signal intensity of the reflected signal. The signal characteristics of the reflected light are detected, measured, and processed based on detection functions of the detector. However, as described above, detectors are often placed in certain locations where environmental conditions at those locations can degrade accurate detection capabilities of a detector.

Other approaches that seek to improve stability of certain layers of an interference filter use solutions that focus on optimizing process conditions during deposition of the a-Si:H layers or direct encapsulation of the layers. However, techniques that include integrating an optically suitable dielectric multilayer protective stack with a fully functional a-Si:H/SiO2layer stack of an optical interference filter (as described herein) provide a more robust approach to improving stability of the filter's layers. Rather than focus solely on improving intrinsic properties of a-Si:H layers, which can be tedious and strongly dependent on the deposition technique used, the described approach uses protective layer stack deposition that is substantially independent of the hydrogenated amorphous silicon deposition.

The proposed techniques can improve the reliability of interference filters that use a-Si:H as a layer material without having a negative impact on the optical performance of the interference filters. In some cases, the described approach can be implemented easily as an example add-on feature to other existing interference filter solutions.

To construct an example interference filter500, an alternating stack of a-Si:H and SiO2thin films can be deposited onto a substrate510. In some implementations, the substrate510is a glass substrate. In other implementations, the substrate510is a CMOS-wafer that can represent an example integrated circuit die. For an interference filter that includes filter portion502, SiO2can be the material used as a first layer of the interference filter as well as the material used as a last layer material of the interference filter. However, the described techniques are not limited or restricted to this layer scheme. Other layer materials as well as other alternating and non-alternating layer configurations are within the scope of this disclosure. For example, a-Si:H can be the material used as a first layer of the interference filter as well as the material used as a last layer material of the interference filter.

In some implementations, the protective layer stack represented by first filter portion502is disposed on the second filter portion504by way of deposition. The deposition of the protective layer either can be done during the same deposition run for depositing filter portion504on substrate510, in a different deposition run, or using a different coating equipment. In some implementations, the deposition process results in the optical interference filter being exposed to ambient air prior to deposition of deposition of the protective layer stack represented by filter portion502.

FIG.6is a diagram of example interference filters600each of which includes a distinct example protective layer stack602A,602B, and602C. Protective layer stack602A can include fewer protective layers than layer stack602B, while protective layer stack602B can include fewer protective layers than layer stack602C. As described above, in some cases, one or more of the interference filters600can each have up to one hundred fifty protective layers602of light refracting material. In other cases, each of one or more of the interference filters600can have more than one hundred fifty protective layers315of the light refracting material.

In some implementations, each of the protective layer stacks602A/B/C uses light refracting materials such as SiO2, Si3N4, Nb2O5, HfO2, or Al2O3. In other implementations, each of the protective layer stacks602A/B/C uses light refracting materials such as silicon monoxide (SiO), titanium dioxide (TiO2), zirconium dioxide (ZrO2), or tantalum pentoxide (Ta2O5). In these implementations, SiO2can be used as a low refractive index material (L), while any of the other remaining materials can be used as a high refractive index material (H).

The additional protective layer stack corresponding to filter portion502on top of the a-Si:H/SiO2 filter stack (filter portion504) is part of a final fully assembled optical interference filter500or600. Design options should account for refractive capabilities of the protective layer stack during the filter design phase in order to not degrade optical performance of a final fully assembled optical interference filter. In some implementations, the filter portion504that represents the a-Si:H/SiO2 part of the layer stack provides the basic functionality of the optical interference filter. For example, this portion of the interference filter may be required to form a long-pass, a band-pass, a short-pass, or a peak-shaped transmission curve with reference to light waves that interact with these layers of the optical interference filter.

In some implementations, protective stack602A can include two layers, protective stack602B can include six layers, and protective stack602C can include twelve layers. Each stack of protective layers602A/B/C is comprised of SiO2layers and layers formed from one of the following materials: Si3N4, Nb2O5, HfO2, Al2O3. Each of protective layers602demonstrates a clear improvement to layer stability when compared to interference filter layers that are simultaneously stressed without any protective layers. In some examples, increasing a number of protective layers in a stack, or total thickness of an example protective layer stack, further improves the effectiveness and stability of the protective layer stack and the overall interference filter. In some cases, improvements such as defect-free samples can be achieved depending on the particular type of environment to which the samples were exposed.

FIG.7shows an example process700for reducing optical interference using an interference filter, such as interference filter310,500, or600described above. In some implementations, process700is performed using optical device306of system300described above. In these implementations, optical device306can include one or more of interference filters310,500, or600described above.

Referring now to the process700, an emitter disposed in an optical device emits a first light wave (702). The first light wave causes an undesired light wave in the optical device. For example, emitter102of optical device306generates a signal that corresponds to light wave220. The emitter102can be, for example, an IR LED that has a narrow spectral power density (SPD).

A detector disposed in the optical device detects a second light wave that is based on the first light wave (704). The second light wave is detectable by the detector and is susceptible to being coupled with an undesired light wave that results from the first light wave. For example, detector104detects reflected light wave225in response to the IR light wave emitted by emitter102reflecting off target object215. In this implementation, reflected light wave225is susceptible to being coupled with undesired light waves235. For example, the SPD of emitter102causes light wave220to have certain power and/or spectral attributes230that cause undesired light waves235to occur at optical device306.

An interference filter500disposed on the detector104is used to filter the undesired light wave caused by the first light wave (706). Filtering the undesired light wave includes attenuating the undesired light wave based on a filter property of the interference filter. For example, the interference filter can include a first set of alternating layers that are composed of a first set of materials and a second set of alternating layers that are composed of a second set of materials. The filter property corresponds to an additional protective layer stack that is represented by one set of the alternating layers, e.g., the second set of alternating layers.

The filter property is operable to cause the interference filter to attenuate the undesired light wave while being resistant to an environmental condition that would otherwise cause physical deformation of the interference filter. The environmental condition can be based on a temperature of the environment exceeding a threshold temperature, based on water or water vapor that causes humidity in the environment, or based on a process by which the detector104was enclosed in a device package.

In some implementations, the additional protective layer stack is comprised of multiple dielectric layers arranged in a stacked configuration and that are disposed on a surface of the detector. The dense dielectric layers that are disposed on the surface of the detector104are operable to reduce a number of potential paths through which gaseous or fluid-based elements that degrade stability of the filter layers travel to one or more portions of the interference filter. In some implementations, the dense dielectric layers are disposed on a glass substrate that encloses the detector. The glass substrate may be parallel to a surface of the detector.

In some implementations, optical device306is part of a sensing system300installed in a host device, such as a mobile smartphone, tablet, in-ear headphones, a wearable device, camera, or other electronic device. In such implementations, the advantages of optical device306that pertain to reducing, attenuating, or blocking cross-talk can translate to improved sensing features as well as other detection features at the host device. For example, the optical device306may be integrated in a host device, and the reflected light wave signal225is processed at the host device to more accurately determine whether the host device is positioned adjacent an ear of a person's head.

In some implementations, the host device receives signals from the detector and uses one or more processing devices to adjust a feature of the host device in response to receiving the signals from the detector. For example, the host device can adjust a brightness of a display screen integrated at the host device, turn off the display screen, or cause the host device to transition from a locked operating state to an unlocked operating state. In some examples, the host device, or circuitry associated with the detector104, includes one or more processors that are configured to execute instructions to cause performance of operations for adjusting features of the host device in response to receiving the signals from the detector104.

Various implementations of the systems and techniques described here can be realized in digital electronic circuitry, integrated circuitry, specially designed ASICs, computer hardware, firmware, software, and/or combinations thereof. These various implementations can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which may be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device.

These computer programs, also known as programs, software, software applications or code, include machine instructions for a programmable processor, and can be implemented in a high-level procedural and/or object-oriented programming language, and/or in assembly/machine language. In some implementations, the computer programs are used by a controller of a host device (e.g., a smartphone or tablet). For example, the controller uses the programs to control operation of an emitter disposed in the host device and to process signals generated by a detector disposed in the host device. The signals generated by the detector are processed in response to the detector receiving reflected light corresponding to light waves emitted by the emitter.

As used herein, the terms “machine-readable medium” “computer-readable medium” refers to any computer program product, apparatus and/or device, e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs) used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term “machine-readable signal” refers to any signal used to provide machine instructions and/or data to a programmable processor.

To provide for interaction with a user, the systems and techniques described here can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

The systems and techniques described here can be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component such as an application server, or that includes a front-end component such as a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the systems and techniques described here, or any combination of such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication such as, a communication network. Examples of communication networks include a local area network (“LAN”), a wide area network (“WAN”), and the Internet.

The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Further, while this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment.

Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system modules and components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Accordingly, other implementations are within the scope of the following claims.