134.

The mesa structure 104 may include an electromagnetic radiation absorber layer 140 and a cathode layer 142. A surface of the electromagnetic radiation (ER) absorber layer 140 (i.e., a bottom surface of the electromagnetic radiation absorber layer 140) may define the first surface 114 of the mesa structure 104 and thus be disposed on the anode layer 130. In particular, an interior portion of the electromagnetic radiation absorber layer 140 may be in contact with the conduction region 134 of the anode layer 130 to form a PN junction, while an outer portion of the electromagnetic radiation absorber layer 140, and in particular a portion of the electromagnetic radiation absorber layer 140 defining the sidewall 118 of the mesa structure 104, is in contact with the dark current isolation region 132 of the anode layer 130. The dark current isolation region 132 limits the PN junction formed between the anode layer 130 and the electromagnetic radiation absorber layer 140 to an interior portion of the mesa structure 104 away from the sidewall 118 thereof. Since the etching process used to create the mesa structure 104 may result in crystallographic defects at the sidewall 118 thereof, the dark current isolation regions 132 may effectively divert a depletion region formed in the device away from these defects and thus reduce dark current in the electromagnetic radiation detector 100. Notably, the electromagnetic radiation absorber layer 140 may have a uniform conductivity type throughout the entire electromagnetic radiation absorber layer 140 (i.e., from sidewall 118 to sidewall 118 in the mesa structure 104) such that the electromagnetic radiation absorber layer 140 defines a portion of the sidewall 118. The cathode layer 142 may be on a surface of the electromagnetic radiation absorber layer 140 opposite the base structure 102 such that a surface of the cathode layer 142 (i.e., a top surface of the cathode layer 142) defines the second surface 116 of the mesa structure 104.

The additional mesa structure 106 may include an additional electromagnetic radiation absorber layer 144 and an additional anode layer 146. A surface of the additional electromagnetic radiation absorber layer 144 (i.e., a bottom surface of the additional electromagnetic radiation absorber layer 144) may define the first surface 120 of the additional mesa structure 106 and thus be disposed on the cathode layer 142. Notably, the additional electromagnetic radiation absorber layer 144 may have a uniform conductivity type throughout the entirety of the additional electromagnetic radiation absorber layer 144 (i.e., from sidewall 124 to sidewall 124 of the additional mesa structure 106) such that the additional electromagnetic radiation absorber layer 144 defines a portion of the sidewall 124. The additional anode layer 146 may be on a surface of the additional electromagnetic radiation absorber layer 144 opposite the mesa structure 104. The additional anode layer 146 may include one or more dark current isolation regions 148 and a conduction region 150. The one or more dark current isolation regions 148 may be in contact with the sidewall of the additional mesa structure 106. While shown in FIG. 1A as being separated by the conduction region 150, the one or more dark current isolation regions 148 may be a single region that is connected in a plane not shown in the cross-sectional view of FIG. 1A. In some embodiments, the one or more dark current isolation regions 148 will contact the entirety of the sidewall 124 of the additional mesa structure 106, which is a three-dimensional structure. Accordingly, the one or more dark current isolation regions 148 may be provided as a rectangular ring, a circular ring, a polygonal ring, or any other suitable shape as viewed looking down from a top of the electromagnetic radiation detector 100. Such a top-down view illustrating the relationship between the sidewall 124 of the additional mesa structure 106 and the one or more dark current isolation regions 148 is shown in FIG. 1B. The conduction region may be in contact with an interior portion of the additional electromagnetic radiation absorber layer 144 to define a PN junction between the additional anode layer 146 and the additional electromagnetic radiation absorber layer 144. The one or more dark current isolation regions 148 may effectively move the PN junction between these layers away from the sidewall 124 of the additional mesa structure where crystallographic defects may be concentrated. This may reduce dark current associated with the electromagnetic radiation detector 100. While referred to herein as an additional anode layer 146, those skilled in the art will appreciate that the entirety of the layer does not comprise an anode. Rather, the additional anode layer 146 contains one or more regions that form an anode, which are defined by the conduction region 150.

An anode contact 152 may be provided on a surface of the anode layer 130 opposite the buffer layer 128 between the sidewall 112 of the base structure 102 and the sidewall 118 of the mesa structure 104. In particular, the anode contact 152 may be provided over the contact region 136 in the anode layer 130 such that it is in electrical contact with the contact region 136. An additional anode contact 154 may be provided on a surface of the additional anode layer 146 opposite the additional electromagnetic radiation absorber layer 144. In particular, the additional anode contact 154 may be provided over the conduction region 150 in the additional anode layer 146 such that it is in electrical contact with the conduction region 150. The anode contact 152 and the additional anode contact 154 may comprise a metal alloy. In some embodiments, a passivation coating 156, which may include an antireflective component, may be provided on the exposed portions of the sidewall 118 of the mesa structure and the sidewall 124 of the additional mesa structure 106, as well as other exposed portions of the electromagnetic radiation detector 100. The passivation coating 156 may reduce the impact of crystallographic defects near the sidewall 118 of the mesa structure 104 and the sidewall 124 of the additional mesa structure 106 on the operation of the electromagnetic radiation detector 100.

The electromagnetic radiation detector 100 essentially provides two photodiodes coupled at the cathode. In operation, a biasing signal (i.e., voltage and/or current) may be applied between the anode contact 152 and the additional anode contact 154. As the electromagnetic radiation detector 100 is exposed to electromagnetic radiation (e.g., photons), the radiation enters the electromagnetic radiation absorber layer 140 and the additional electromagnetic radiation absorber layer 144 and generates electron-hole pairs that cause a photocurrent to flow in the device. The electromagnetic radiation absorber layer 140 and the additional electromagnetic radiation absorber layer 144 may be designed (e.g., by choosing the material, lattice constant, bandgap, thickness, etc.) to absorb certain wavelengths of light at a higher efficiency than others. In some embodiments, the electromagnetic radiation absorber layer 140 is designed to absorb electromagnetic radiation within a first frequency band and the additional electromagnetic radiation absorber layer 144 is designed to absorb electromagnetic radiation within a second frequency band. The first frequency band and the second frequency band may be overlapping or non-overlapping. Including the electromagnetic radiation absorber layer 140 and the additional electromagnetic radiation absorber layer 144 in this manner may allow for the electromagnetic radiation detector 100 to detect electromagnetic radiation within a wide frequency band.

The one or more dark current isolation regions 132 and the one or more additional dark current isolation regions 138 in the anode layer 130 may have a first conductivity type, while the conduction region 134 and the contact region 136 in the anode layer 130 may have a second conductivity type opposite the first conductivity type. In various embodiments the anode layer 130 may be provided (e.g., grown and in-situ doped) having the first conductivity type, and the conduction region 134 and the contact region 136 may be created by inverting the conductivity in these regions (e.g., via diffusion or ion implantation). However, the opposite may also be true. Similarly, the one or more dark current isolation regions 148 in the additional anode layer 146 may have the first conductivity type and the conduction region 150 in the additional anode layer 146 may have the second conductivity type. In various embodiments the additional anode layer 146 may be provided (e.g., grown and in-situ doped) having the first conductivity type, and the conduction region 150 may be created by inverting the conductivity type in this region (e.g., via diffusion or ion implantation). However, the opposite may also be true. The electromagnetic radiation absorber layer 140, the cathode layer 142, and the additional electromagnetic radiation absorber layer 144 may have the first conductivity type. The buffer layer 128 may have the second conductivity type. The substrate 126 may have the second conductivity type, or may be an undoped, intrinsic, or semi-insulting layer. While FIG. 1A shows the first conductivity type as n-type and the second conductivity type as p-type for purposes of illustration, those skilled in the art will readily appreciate that the principles of the present disclosure apply equally to devices having inverted conductivity types to the ones shown.

In one embodiment, the substrate 126 comprises InP, the buffer layer 128, the anode layer 130, the cathode layer 142, and the additional anode layer 146 comprise InAsP, and the electromagnetic radiation absorber layer 140 and the additional electromagnetic radiation absorber layer 144 comprise InGaAs. However, these materials are merely exemplary. Those skilled in the art will readily appreciate that the principles of the present disclosure apply equally to electromagnetic radiation detectors including any number of material systems.

FIG. 1B shows a top-down view of some parts the electromagnetic radiation detector 100 according to one embodiment of the present disclosure. In particular, FIG. 1B shows an exemplary spatial relationship between the one or more dark current isolation regions 132 in the anode layer 130 and the sidewall 118 of the mesa structure 104. As shown, the dark current isolation regions 132 follow a perimeter of the sidewall 118 of the mesa structure 104 with a margin on either side. FIG. 1B also shows an exemplary spatial relationship between the one or more dark current isolation regions 148 in the additional anode layer 146 and the sidewall 124 of the additional mesa structure 106. As shown, the one or more dark current isolation regions 148 follow a perimeter of the sidewall 124 of the additional mesa structure 106, extending all the way to the sidewall 124. Notably, the particular shapes of the mesa structures and dark current isolation regions shown in FIG. 1B are merely exemplary. The mesa structures and corresponding dark current isolation regions may be provided in circular rings, polygonal rings, or any other suitable shape. Further, while the dark current isolation regions are shown as a single region, these may also be provided as multiple discrete regions that contact a substantial portion of the respective sidewall, rather than encompassing the entirety of the sidewall.

FIG. 1C shows the electromagnetic radiation detector 100 according to an additional embodiment of the present disclosure. The electromagnetic radiation detector 100 shown in FIG. 1C is substantially similar to that in FIG. 1A, except that a cathode contact 158 is provided. The cathode contact 158 is disposed on a surface of the cathode layer 142 opposite the electromagnetic radiation absorber layer 140 between the sidewall 118 of the mesa structure 104 and the sidewall 124 of the additional mesa structure 106. The cathode contact 158 may allow for additional control over the operation of the electromagnetic radiation detector 100, including an additional contact point for biasing and/or separate control over the photodiodes therein.

FIGS. 1A through 1C show an isolated electromagnetic radiation detector 100. In some cases, however, two or more electromagnetic radiation detectors 100 may be monolithically integrated, as illustrated in FIG. 1D. As shown, two electromagnetic radiation detectors 100, which are the same as described with respect to FIG. 1A, may share the substrate 126, the buffer layer 128, and the anode layer 130. Further, the electromagnetic radiation detectors 100 may share a common dark current isolation region 132 where they meet. One or more additional regions having an opposite conductivity type may also be provided between the electromagnetic radiation detectors 100. The mesa structures 104 of the electromagnetic radiation detectors 100 may be isolated from one another. The electromagnetic radiation detectors 100 may operate individually as discussed with respect to FIG. 1A, and in various embodiments may be electrically connected in different configurations (i.e., series, parallel) for different applications. While two electromagnetic radiation detectors 100 are shown in FIG. 1D for purposes of illustration, any number of electromagnetic radiation detectors 100 may be monolithically integrated with one another in a similar manner, and may tile in two or three dimensions in any desired pattern.

FIGS. 1A through 1D show an electromagnetic radiation detector having a mesa structure. However, electromagnetic radiation detectors may also be provided having planar structures. FIG. 2 shows a cross-sectional view of an electromagnetic radiation detector 200 having a planar structure. The electromagnetic radiation detector 200 may define a first surface 202, a second surface 204 opposite the first surface 202, and a sidewall 206 between the first surface 202 and the second surface 204. A surface of a substrate 208 (i.e., a bottom surface of the substrate 208) may define the first surface 202. An optional buffer layer 210 may be disposed on a surface of the substrate 208 opposite the first surface 202. An anode layer 212 may be disposed on a surface of the buffer layer 210 opposite the substrate 208. The buffer layer 210 may provide a transition between a lattice constant of the substrate 208 and a lattice constant of the anode layer 212. In some embodiments, the buffer layer 210 may be omitted. The anode layer 212 may include one or more dark current isolation regions 214 and a conduction region 216. The one or more dark current isolation regions 214 may be provided along the sidewall 206, and the conduction region 216 may be located in an interior portion of the anode layer 212. An electromagnetic radiation absorber layer 218 may be disposed on a surface of the anode layer 212 opposite the buffer layer 210. In particular, an interior portion of the electromagnetic radiation absorber layer 218 may be in contact with the conduction region 216 of the anode layer 212 to form a PN junction, while an outer portion of the electromagnetic radiation absorber layer 218, and in particular a portion of the electromagnetic radiation absorber layer 218 defining a portion of the sidewall 206, is in contact with the dark current isolation region 214 of the anode layer 212. The electromagnetic radiation detector 200 may be cut/singulated at the sidewall 206. This process may result in crystallographic defects at the sidewall 206, which are prone to generating dark current. The one or more dark current isolation regions 214 move the PN junction formed between the anode layer 212 and the electromagnetic radiation absorber layer 218 to an interior portion of the device away from the sidewall 206, which may reduce dark current in the device that may otherwise be caused if a depletion region were provided in this area.

A cathode layer 220 may be disposed on a surface of the electromagnetic radiation absorber layer 218 opposite the anode layer 212. An additional electromagnetic radiation absorber layer 222 may be disposed on a surface of the cathode layer 220 opposite the electromagnetic radiation absorber layer 218. An additional anode layer 224 may be disposed on a surface of the additional electromagnetic radiation absorber layer 222 opposite the cathode layer 220. The additional anode layer 224 may include one or more dark current isolation regions 226 and a conduction region 228. The one or more dark current isolation regions 226 may be provided along the sidewall 206, and the conduction region 228 may be located in an interior portion of the additional anode layer 224. An interior portion of the additional electromagnetic radiation absorber layer 222 may be in contact with the conduction region 228 of the additional anode layer 224 to form a PN junction. An outer portion of the additional electromagnetic radiation absorber layer 222, and in particular a portion of the additional electromagnetic radiation absorber layer 222 that defines a portion of the sidewall 206, is in contact with the dark current isolation region 226. As previously discussed, the dark current isolation region 226 may effectively move the PN junction between the additional anode layer 224 and the additional electromagnetic radiation absorber layer 222 to an interior portion of the device away from the sidewall 206, and thereby may reduce dark current.

Notably, the electromagnetic radiation absorber layer 218 and the additional electromagnetic radiation absorber layer 222 may have a uniform conductivity type throughout the respective layers (i.e., from sidewall 206 to sidewall 206 in the electromagnetic radiation detector 200) such that each of these layers defines a portion of the sidewall 206. While the one or more dark current isolation regions 214 in the anode layer 212 and the one or more dark current isolation regions 226 in the additional anode layer 224 are shown separated by a conduction region, each of these, respectively, may be a single region that is connected in a plane not shown in the cross-sectional view of FIG. 2. In some embodiments, the one or more dark current isolation regions 214 in the anode layer 212 and the one or more dark current isolation regions 226 in the additional anode layer 224, respectively, will contact the entirety of the sidewall 206, which is a three-dimensional structure. Accordingly, the one or more dark current isolation regions 214 in the anode layer 212 and the one or more dark current isolation regions 226 in the additional anode layer 224, respectively, may be provided as a rectangular ring, a circular ring, a polygonal ring, or any other suitable shape as viewed looking down from a top of the electromagnetic radiation detector 200.

An anode contact 230 may be disposed on a surface of the additional anode layer 224 over the conduction region 228. A passivation coating 232, which may include an anti-reflective component, may be provided on the surface of the additional anode layer 224 over the one or more dark current isolation regions 226. An additional contact 234 may be disposed on a portion of a surface of the substrate 208. The anode contact 230 and the additional contact 234 may comprise a metal alloy. The remainder of the surface of the substrate 208 may be covered in the passivation coating 232.

The electromagnetic radiation detector 200 essentially provides two photodiodes coupled at the cathode. In operation, a biasing signal (i.e., voltage and/or current) may be applied between the anode contact 230 and the additional contact 234. As the electromagnetic radiation detector 200 is exposed to electromagnetic radiation (e.g., photons), the radiation enters the electromagnetic radiation absorber layer 218 and the additional electromagnetic radiation absorber layer 222 and generates electron-hole pairs that cause a photocurrent to flow in the device. The electromagnetic radiation absorber layer 218 and the additional electromagnetic radiation absorber layer 222 may be designed (e.g., by choosing the material, lattice constant, bandgap, thickness, etc.) to absorb certain wavelengths of light at higher efficiency than others. In some embodiments, the electromagnetic radiation absorber layer 218 is designed to absorb electromagnetic radiation within a first frequency band and the additional electromagnetic radiation absorber layer 222 is designed to absorb electromagnetic radiation in a second frequency band. The first frequency band and the second frequency band may be overlapping or non-overlapping. Including the electromagnetic radiation absorber layer 218 and the additional electromagnetic radiation absorber layer 222 in this manner may allow for the electromagnetic radiation detector to detect electromagnetic radiation in a wide frequency band.

The one or more dark current isolation regions 214 in the anode layer 212 may have a first conductivity type, while the conduction region 216 in the anode layer 212 may have a second conductivity type opposite the first conductivity type. In various embodiments the anode layer 212 may be provided (e.g., grown and in-situ doped) having the first conductivity type, and the conduction region 216 may be created by inverting the conductivity type in this region (e.g., via diffusion or ion implantation). However, the opposite may also be true. Similarly, the one or more dark current isolation regions 226 in the additional anode layer 224 may have the first conductivity type, while the conduction region 228 in the additional anode layer 224 may have the second conductivity type. In various embodiments the additional anode layer 224 may be provided (e.g., grown and in-situ doped) having the first conductivity type, and the conduction region 228 may be created by inverting the conductivity type in this region (e.g., via diffusion or ion implantation). However, the opposite may also be true. The electromagnetic radiation absorber layer 218, the cathode layer 220, and the additional electromagnetic radiation absorber layer 222 may have the first conductivity type. The buffer layer 210 may have the second conductivity type. The substrate 208 may have the second conductivity type, or may be an undoped, intrinsic, or semi-insulating layer. While FIG. 2 shows the first conductivity type as n-type and the second conductivity type as p-type for purposes of illustration, those skilled in the art will readily appreciate that the principles of the present disclosure apply equally to devices having inverted conductivity types to the ones shown.

In one embodiment, the substrate 208 comprises InP, the buffer layer 210, the anode layer 212, the cathode layer 220, and the additional anode layer 224 comprise InAsP, and the electromagnetic radiation absorber layer 218 and the additional electromagnetic radiation absorber layer 222 comprise InGaAs. However, these materials are merely exemplary. Those skilled in the art will readily appreciate that that principles of the present disclosure apply equally to electromagnetic radiation detectors including any number of material systems.

FIG. 3 is a flow diagram illustrating a method 300 for manufacturing an electromagnetic radiation detector according to one embodiment of the present disclosure. For purposes of illustration, FIG. 3 illustrates a method for manufacturing the electromagnetic radiation detector 100 discussed with respect to FIG. 1A, however, those skilled in the art will readily appreciate the applicability of the method to other embodiments discussed herein. FIGS. 4A through 4L illustrate each of the steps of the method 300. A base structure 102 may be provided. Providing the base structure 102 may include providing the substrate 126 (step 302 and FIG. 4A), optionally providing the buffer layer 128 on the substrate 126 (step 304 and FIG. 4B), and providing the anode layer 130 on the buffer layer 128 (step 306 and FIG. 4C). The substrate 126, the buffer layer 128, and the anode layer 130 may be provided by any suitable processes, such as, for example, a growth process or a deposition process.

A conductivity type of one or more regions in the anode layer 130 may be inverted (step 308 and FIG. 4D). In particular, the conductivity type of the one or more regions in the anode layer 130 may be inverted such that the anode layer 130 includes and defines the one or more dark current isolation regions 132, the conduction region 134, the contact region 136, and the one or more additional dark current isolation regions 138. As discussed with respect to FIG. 1A, the one or more dark current isolation regions 132 and the one or more additional dark current isolation regions 138 may have a first conductivity type, while the conduction region 134 and the contact region 136 may have a second conductivity type opposite the first conductivity type. In some embodiments the anode layer 130 may be provided having the first conductivity type, and the conductivity type of the conduction region 134 and the contact region 136 may be inverted. However, the opposite may also be true, wherein the anode layer 130 may be provided having the second conductivity type and the conductivity type of the one or more dark current isolation regions 132 and the one or more additional dark current isolation regions 138 may be inverted. The conductivity type of the one or more regions in the anode layer 130 may be inverted by any suitable process, such as via a diffusion doping process or an ion implantation process. In various embodiments, inverting the conductivity type of the one or more regions in the anode layer 130 may include providing a patterned mask on a surface of the anode layer 130 opposite the buffer layer 128, introducing a dopant into the anode layer 130 via one or more openings in the patterned mask to invert the conductivity type of the regions below the one or more openings (e.g., via diffusion or ion implantation), and subsequently removing the patterned mask. Details of such a process will be readily appreciated by those skilled in the art and thus are not discussed in detail herein. Notably, the conductivity type of the one or more regions in the anode layer 130 may be inverted before the electromagnetic radiation absorber layer 140 is provided on the anode layer 130. The result is that the electromagnetic radiation absorber layer 140 maintains a consistent conductivity type throughout, from sidewall 118 to sidewall 118 of the mesa structure 104.

A mesa layer stack may be provided on the base structure. Providing the mesa layer stack may include providing the electromagnetic radiation absorber layer 140 on the anode layer 130 (step 310 and FIG. 4E), and providing the cathode layer 142 on the electromagnetic radiation absorber layer 140 (step 312 and FIG. 4F). In instances where the electromagnetic radiation detector includes multiple mesa layer stacks, an additional mesa layer stack may be provided on the mesa layer stack. Providing the additional mesa layer stack may include providing the additional electromagnetic radiation absorber layer 144 on the cathode layer 142 (step 314 and FIG. 4G), and providing the additional anode layer 146 on the additional electromagnetic radiation absorber layer 144 (step 316 and FIG. 4H).

A conductivity type of one or more regions in the additional anode layer 146 may be inverted (step 318 and FIG. 4I). In particular, the conductivity type of the one or more regions in the additional anode layer 146 may be inverted such that the additional anode layer includes the one or more dark current isolation regions 148 and the conduction region 150. As discussed with respect to FIG. 1A, the one or more dark current isolation regions 148 may have the first conductivity type and the conduction region 150 may have the second conductivity type. In some embodiments the additional anode layer 146 may be provided having the first conductivity type and the conductivity type of the conduction region 150 may be inverted. However, the opposite may also be true, wherein the additional anode layer 146 may be provided having the second conductivity type and the conductivity type of the one or more dark current isolation regions 148 may be inverted. The conductivity type of the one or more regions in the additional anode layer 146 may be inverted by any suitable process, such as a diffusion doping process or an ion implantation process. In various embodiments, inverting the conductivity type of the one or more regions in the additional anode layer 146 may include providing a patterned mask on a surface of the additional anode layer 146, introducing a dopant into the additional anode layer 146 via one or more openings in the patterned mask layer to invert a conductivity type of the regions below the one or more openings (e.g., via diffusion or ion implantation), and subsequently removing the patterned mask. Details of such a process will be readily apparent to those skilled in the art and thus are not discussed in detail herein. Notably, inverting the conductivity type of the one or more regions in the additional anode layer 146 may be done so that it does not affect the conductivity type of the additional electromagnetic radiation absorber layer 144. The result is that the additional electromagnetic radiation absorber layer 144 maintains a consistent conductivity type throughout, from sidewall 124 to sidewall 124 of the additional mesa structure 106.

The mesa layer stack and the additional mesa layer stack may be patterned to form the mesa structure 104 and the additional mesa structure 106 (step 320 and FIG. 4J). The patterning may be accomplished in any suitable manner including any number of steps. For example, a first etching step may be used to provide the additional mesa structure 106 and a second etching step may be used to provide the mesa structure 104. As discussed above, the dark current isolation regions 132 and the additional dark current isolation regions 138 in the anode layer 130, as well as the dark current isolation regions 148 in the additional anode layer 146 may reduce dark current that would otherwise result from crystalline defects introduced by such an etching process by moving the PN junction between the anode layer 130 and the electromagnetic radiation absorber layer 140 and the PN junction between the additional anode layer 146 and the additional electromagnetic radiation absorber layer 144, respectively, away from the etched sidewalls. The passivation coating 156, which may include an antireflective component, may be provided on exposed portions of the electromagnetic radiation detector 100, including the sidewall 118 of the mesa structure 104 and the sidewall 124 of the additional mesa structure 106 (step 322 and FIG. 4K). The passivation coating 156 may be provided using any suitable process, such as a deposition process. The anode contact 152 and the additional anode contact 154 may be provided (step 324 and FIG. 4L). The anode contact 152 and the additional anode contact 154 may be provided using any suitable process, such as a deposition process.

FIGS. 5A and 5B show an example of a wearable device 400 that may incorporate one or more sensors, including one or more electromagnetic radiation sensors as discussed herein. Specifically, FIG. 5A shows a front isometric view of the wearable device 400, while FIG. 5B shows a back isometric view of the wearable device 400. The sensors of the wearable device 400 may be used, for example, to acquire biometric data from a user (e.g., heart rate, respiration rate, blood pressure, blood flow rate, blood oxygenation), or to determine a status of the wearable device 400 (e.g., whether the wearable device is being worn, one or more ambient environmental conditions). While the wearable device 400 is shown having the form factor of a watch, the wearable device 400 could by any suitable type of wearable device having any form factor. Further, the principles of the present disclosure apply equally to non-wearable devices such as smartphones, tablets, laptop computers, desktop computers, and the like.

The wearable device 400 includes a body 402 (e.g., a watch body) and a band 404. The body 402 may include an input or selection device, such as a crown 406 or a button 408. The band 404 may be attached to a housing 410 of the body 402, and may be used to attach the body 402 to a body part of a user (e.g., an arm, wrist, leg, ankle, or waist). The housing 410 may at least partially surround a display 412. In some embodiments, the housing 410 may include a sidewall 414, which may support a front cover 416 (shown in FIG. 5A) and/or a back cover 418 (shown in FIG. 5B). The front cover 416 may be positioned over the display 412, and may provide a window through which the display 412 is viewed. In some embodiments, the display 412 may be attached to (or about) the sidewall 414 and/or the front cover 416. In other embodiments, the display 412 may not be included and/or the housing 410 may have an alternative configuration.

The display 412 may include one or more light emitting elements including, for example, light-emitting elements that define a light-emitting diode (LED) display, an organic LED (OLED) display, a liquid crystal display (LCD), an electroluminescent (EL) display, or any other type of display. In some embodiments, the display 412 may include, or be associated with, one or more touch and/or force sensors that are configured to detect touch and/or force applied to the front cover 416.

In some embodiments, the sidewall 414 of the housing 410 may be formed using one or more metals (e.g., aluminum or stainless steel), polymers (e.g., plastics), ceramics, or composites (e.g., carbon fiber). The front cover 416 may be formed, for example, using one or more of glass, a crystal (e.g., sapphire), or a transparent polymer (e.g., plastic) that enables a user to view the display 412 through the front cover 416. In some cases, a portion of the front cover 416 (e.g., a perimeter portion of the front cover 416) may be coated in an opaque ink to obscure components included within the housing 410. In some cases, all of the exterior components may be formed of a transparent material, and the components of the wearable device 400 may or may not be obscured by an opaque ink or opaque structure within the housing 410.

The back cover 418 may be formed using the same material or materials used to form the sidewall 414 and/or the front cover 416. In some cases, the back cover 418 may be part of a monolithic element that also forms the sidewall 414. In other cases, and as shown, the back cover 418 may be a multi-part back cover, such as a back cover having a first back cover portion 418-1 attached to the sidewall 414 and a second back cover portion 418-2 attached to the first back cover portion 418-1. The second back cover portion