Display device and electronic device

Abstract

A display device (10) comprises a sensor device (15) comprising a surface-emitting semiconductor laser (102) configured to emit laser radiation (17) in an emission direction, and a metasurface (105) configured to convert a polarization state of the laser radiation (17) into a circularly polarized state. The display device (10) further comprises an array (22) of light emitting elements (23) configured to emit electromagnetic radiation (24) in the emission direction, the array (22) of light emitting elements (23) being arranged on a side of the sensor device (15) along the emission direction.

Description

[0001] DISPLAY DEVICE AND ELECTRONIC DEVICE

[0002] Electronic devices such as smartphones generally comprise a proximity sensor module for detecting the presence of e . g . a face in close proximity to the display .

[0003] Generally, attempts are made in order to provide an improved display device comprising a sensor device .

[0004] SUMMARY

[0005] According to embodiments , a display device comprises a sensor device comprising a surface-emitting semiconductor laser configured to emit laser radiation in an emission direction, and a metasurface configured to convert a polari zation state of the laser radiation into a circularly polari zed state . The display device further comprises an array of light emitting elements configured to emit electromagnetic radiation in the emission direction, the array of light emitting elements being arranged on a side of the sensor device along the emission direction .

[0006] The display device may further comprise a quarter-wave plate and a linear polari zer arranged along the emission direction on a side of the array of light emitting elements along the emission direction . The quarter-wave plate is arranged between the linear polari zer and the array of light emitting elements .

[0007] For example , the surface-emitting semiconductor laser is configured to emit laser radiation having a wavelength larger than 1000 nm .

[0008] According to embodiments , the light emitting elements comprise light emitting elements configured to emit electromagnetic radiation having a wavelength less than 1000 nm . For example , the metasurface may comprise an array of one-dimensional or two-dimensional nanostructures of a first material . According to further examples , the metasurface may further comprise an embedding material arranged between the nanostructures .

[0009] For example , the first material may be selected from a semiconductor material , e . g . a I I I-V compound semiconductor material which is transparent to the emitted electromagnetic radiation . Examples comprise GaAs , AlGaAs or InGaP .

[0010] According to embodiments , the embedding material may be selected from a passivating dielectric material . Examples comprise SiN, A12O3, SiO2or TiO2.

[0011] For example , the surface-emitting semiconductor laser comprises a first semiconductor layer of a first conductivity type , a second semiconductor layer of a second conductivity type , and an active zone arranged between the first semiconductor layer and the second semiconductor layer .

[0012] For example , the active zone comprises AlxGai-xAs .

[0013] According to embodiments , the sensor device is operable as a proximity sensor .

[0014] According to embodiments , an electronic device comprises the display device as described above . For example , the electronic device may be implemented as a smart phone .

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this speci fication . The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles . Other embodiments of the invention and many of the intended advantages will be readily appreciated, as they become better understood by reference to the following detai led description . The elements of the drawings are not necessarily to scale relative to each other . Like reference numbers designate corresponding similar parts .

[0017] Fig . 1A shows a cross-sectional view of a portion of a display device according to embodiments .

[0018] Fig . IB shows elements of a surface-emitting semiconductor laser .

[0019] Fig . 1C illustrates elements of the display device according to embodiments .

[0020] Fig . 2A shows a further configuration of a surface-emitting laser .

[0021] Fig . 2B shows a further example of a surface-emitting laser .

[0022] Fig . 3A shows a hori zontal cross-sectional view of a portion of a metasurface .

[0023] Fig . 3B shows an example of a top view of a metasurface .

[0024] Fig . 3C shows a hori zontal cross-sectional view of a portion of a further example of a metasurface .

[0025] Fig . 3D is a schematic view showing elements of a sensor device .

[0026] Fig . 4A shows an electronic device according to embodiments . Fig. 4B is a perspective view of an electronic device according to embodiments.

[0027] DETAILED DESCRIPTION

[0028] In the following detailed description reference is made to the accompanying drawings, which form a part hereof and in which are illustrated by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "over", "on", "above", "leading", "trailing" etc. is used with reference to the orientation of the Figures being described. Since components of embodiments of the invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope defined by the claims.

[0029] The description of the embodiments is not limiting. In particular, elements of the embodiments described hereinafter may be combined with elements of different embodiments.

[0030] The terms "wafer" or "semiconductor substrate" used in the following description may include any semiconductor-based structure that has a semiconductor surface. Wafer and structure are to be understood to include doped and undoped semiconductors, epitaxial semiconductor layers, e.g. supported by a base semiconductor foundation, and other semiconductor structures. For example, a layer of a first semiconductor material may be grown on a growth substrate of a second semiconductor material. According to further embodiments, the growth substrate may be an insulating substrate such as a sapphire substrate. Depending on the purpose of use , the semiconductor may be based on a direct or an indirect semiconductor material . Examples of semiconductor materials particularly suitable for generation of electromagnetic radiation comprise nitride-compound semiconductors , by which e . g . ultraviolet or blue light or longer wavelength light may be generated, such as GaN, InGaN, AIN, AlGaN, AlGalnN, phosphide-compound semiconductors , by which e . g . green or longer wavelength light may be generated such as GaAsP, AlGalnP, GaP, AlGaP, as well as further semiconductor materials including AlGaAs , SiC, ZnSe , GaAs , ZnO, Ga2Os, diamond, hexagonal BN und combinations of these materials . Further examples of semiconductor materials may as well be silicon, silicon-germanium and germanium . The stoichiometric ratio of the compound semiconductor materials may vary . In the context of the present speci fication, the term " semiconductor" further encompasses organic semiconductor materials .

[0031] The term " substrate" generally refers to semiconductor substrates , conductive or insulating substrates .

[0032] The terms " lateral" and "hori zontal" as used in this speci fication intends to describe an orientation parallel to a first surface of a substrate or semiconductor body . This can be for instance the surface of a wafer or a die .

[0033] The term "vertical" as used in this speci fication intends to describe an orientation which is arranged perpendicular to the first surface of a substrate or semiconductor body .

[0034] The present disclosure relates to metasurfaces configured to convert a polari zation state of incident electromagnetic radiation . Generally, the term "metasurface" or "metaoptic structure" refers to an optical element that imparts a phase shi ft using an array of nanostructures that are formed on a ( ideally flat ) surface of a substrate , instead of via e . g . birefringence . More speci fically, a metasurface may include an array of nanostructures , wherein the nanostructure array is configured to convert a polari zation state of incident electromagnetic radiation by altering its phase . For example , a metasurface consistent with the present disclosure can include an array of nanostructures that can impart a phase change to incident light .

[0035] The change of the polari zation state may be accomplished due to phase shi fts and interference ef fects of geometrical structures having si zes below the wavelength of the electromagnetic radiation . According to an approximation, the phase shi fts may be interpreted as waveguide modes propagating in the pillars , generating a phase shi ft dependent on the height of the pillar of a given geometry and si ze .

[0036] For example , nanostructures that may be a component of metasurfaces are generally configured to function as resonators or waveguides that impart a phase change to light incident thereon . As will be described hereinafter, the metasurfaces may comprise pillars or ridges . For example , the metasurfaces may further comprise a layer of an embedding material filling the spaces between adj acent pillars or ridges . In this context , the pil- lars / ridges or the embedding material in between may constitute the nanostructures mentioned above . According to further embodiments , the spaces between adj acent pillars or ridges may be filled with air .

[0037] According to further examples , the metasurface may be implemented as an ordered photonic structure . In the context of the present disclosure , the term "ordered photonic structure" means a structure the structural elements of which are arranged at predetermined locations . The arrangement pattern of the structural elements is subj ect to a specific order . The functionality of the ordered photonic structure results from the arrangement of the structural elements. The structural elements are, for example, arranged such that diffraction effects occur. The structural elements may be implemented in the form of a nanotexture. The structural elements may be in a submicron size range. For example, a dimension of the structural elements, e.g. a horizontal dimension may be smaller than 10 pm. The structural elements may be arranged periodically, for example, so that a photonic crystal is realized. According to further embodiments, the structural elements may be arranged such that they represent deterministic aperiodic structures, for example bird spirals. According to further embodiments, the structural elements may be arranged such that they realize a quasi-periodic crystal, for example an Archimedean lattice.

[0038] Fig. 1A shows a portion of a display device, e.g. a display device 10 of an electronic device 20 such as a smartphone. The display device 10 comprises a sensor device 15. As will be explained hereinbelow, the sensor device 15 may comprise a surfaceemitting semiconductor laser 102 which is configured to emit laser radiation 17 in an emission direction, e.g. the z-direc- tion. The display device 10 further comprises an array 22 of light emitting elements 23 which are arranged in the emission direction of the sensor device 15. The light emitting elements 23 may be arranged in a plane perpendicular to the emission direction, e.g. in the y-z plane. The light emitting elements 23 are configured to emit electromagnetic radiation 24 in the emission direction. For example, a wavelength range of the electromagnetic radiation 24 may be different from the wavelength region of the laser radiation 17 emitted by the surface-emitting semiconductor laser which is a component of the sensor device 15.

[0039] For example, the display device 10 may further comprise a quarter-wave plate 121 and a linear polarizer 120. The quarter-wave plate 121 may be arranged between the linear polarizer 120 and the array 22 of light emitting elements along the emission direction of the surface-emitting laser. For example, laser radiation 17 emitted by the sensor device 15 may be reflected by an object 16 and may be detected by the sensor device 15. Accordingly, the presence of an object, e.g. a face, may be easily detected .

[0040] Fig. IB shows an example of a surface-emitting semiconductor laser 102 and a metasurface 105 that may be a component of the sensor device 15 illustrated in Fig. 1A. For example, the surface-emitting laser 102 may be implemented as a VCSEL ("vertical cavity surface-emitting laser") comprising a vertical resonator. In more detail, the surface-emitting laser 102 may comprise a first semiconductor layer 110 of a first conductivity type, e.g. n-type. The first semiconductor layer 110 may be implemented as a doped distributed Bragg reflector.

[0041] In more detail, the first semiconductor layer 110 may comprise an alternating sequence of n doped layers having comparably high and low refractive indices, respectively.

[0042] According to further embodiments, a reflector may be implemented by a dielectric layer stack (not illustrated in Fig. IB) adjacent to the first semiconductor layer 110. The dielectric layers may comprise an alternating sequence of layers having comparably high and low refractive indices, respectively, thus implementing a dielectric distributed Bragg reflector.

[0043] The surface-emitting laser 102 further comprises a second semiconductor layer 118 of a second conductivity type, e.g. p-type. For example, the second semiconductor layer 118 may implement a distributed Bragg reflector. According to further embodiments, it is possible that the second semiconductor layer 118 does not implement a distributed Bragg reflector, and the surface- emitting semiconductor laser 102 further comprises a dielectric layer stack acting as a reflector . The surface-emitting semiconductor laser 102 further comprises an active zone 115 which is arranged between the first semiconductor layer 110 and the second semiconductor layer 118 .

[0044] The active zone may, for example , comprise a pn j unction, a double heterostructure , a single quantum well structure ( SQW, single quantum well ) or a multiple quantum well structure (MQW, multi quantum well ) for generating radiation . The term "quantum well structure" does not imply any particular meaning here with regard to the dimensionality of the quanti zation . Therefore it includes , among other things , quantum wells , quantum wires and quantum dots as well as any combination of these layers .

[0045] The surface-emitting semiconductor laser 102 may further comprise an aperture , e . g . an oxide layer for confining a current across the semiconductor layer stack .

[0046] The surface-emitting semiconductor laser 102 may further comprise a first contact element 101 and a second contact element 119 for applying a voltage between the first semiconductor layer 110 and the second semiconductor layer 118 . For example , the first semiconductor layer 110 may be attached to a substrate 100 .

[0047] The surface-emitting laser 102 further comprises a metasurface 105 that is configured to convert the emitted laser radiation into circularly polari zed laser radiation . This will be explained in more detail with re ference to Figs . 3A and 3B . As a result , the emitted laser radiation 17 is circularly polari zed . For example , the surface-emitting semiconductor laser 102 may be configured to emit laser radiation at a wavelength larger than 1000 nm, e . g . larger 1100 nm, for example , approximately 1130 nm . As a result , the array of light emitting elements 23 may be transparent to the emitted laser radiation . Accordingly, it is possible to arrange the surface-emitting laser 102 behind the array 22 of light emitting elements . In more detail , there is no need to assign a dedicated space of the display device for the sensor device 15 . Moreover, an emission wavelength of more than 1100 nm, e . g . approximately 1130 nm has minimal interference with the solar spectrum thus enhancing the signal-to-noise ratio and detecting the back-reflected light . For example , a material system of the surface-emitting laser 102 , e . g . the material of the active zone 115 , may comprise AlxGai-xAs .

[0048] Fig . 1C shows elements of the display device 10 comprising a sensor device which comprises a surface-emitting semiconductor laser and a metasurface 105 in the manner as has been discussed with reference to Fig . IB .

[0049] As is shown in Fig . 1C, the laser radiation 17 emitted by the surface-emitting semiconductor laser 102 which is a component o f the sensor device 15 passes the array 22 of light emitting elements 23 . The emitted laser radiation 17 passes the quarter-wave plate 121 resulting in linearly polari zed radiation . The linearly polari zed radiation then is transmitted by the linear polari zer 120 . When the axes of the linear polari zer 120 are correctly adj usted, the linearly polari zed radiation transmitted by the quarter-wave plate 121 is completely transmitted or transmitted to a large degree by the linear polari zer 120 . Thereafter, the laser radiation transmitted by the linear polari zer 120 is incident on an obj ect and may be re flected by the obj ect to be detected by the sensor device 15 after passing through the layer stack .

[0050] Accordingly, due to the combination of a surface-emitting semiconductor laser 102 and the polari zation-converting metasurface 105 , emitted laser radiation 17 is a circularly polari zed . As a result , the laser radiation 17 may pass the components of the display device 10 without a substantial amount of losses due to the quarter-wave plate 121 and the linear polari zer 120 . Therefore , an amount of available power for sensing purposes is higher in comparison to devices without a polari zation state converting metasurface . As a result , the detection accuracy may be increased due to an increased signal-to-noise ratio .

[0051] Fig . 2A shows a further example of a surface-emitting semiconductor laser 102 which may be a component of the sensor device 15 . The surface-emitting semiconductor laser 102 illustrated in Fig . 2A is a PCSEL ("photonic crystal surface-emitting laser" ) . The surface-emitting semiconductor laser 102 comprises a first semiconductor layer 131 of the first conductivity type , a second semiconductor layer 132 of a second conductivity type , and an active zone 115 arranged between the first semiconductor layer 131 and the second semiconductor layer 132 . An aperture 116 may be arranged between the active zone and the second semiconductor layer 132 . The first semiconductor layer 131 may be arranged over a semiconductor substrate 100 . Moreover, a first contact element 101 may be electrically connected to the first semiconductor layer 131 , and the second contact element 119 may be electrically connected to the second semiconductor layer 132 . The surface-emitting semiconductor laser 102 further comprises an ordered photonic structure 107 , e . g . within the epitaxially grown semiconductor layers , e . g . in a position close to the active zone 115 . For example , the ordered photonic structure 107 may be arranged within the second semiconductor layer 132 .

[0052] According to further embodiments , the ordered photonic structure 107 may be arranged at any other suitable position within the semiconductor layer stack, as is generally known . Moreover, a metasurface 105 which is configured to convert a polari zation state of the laser radiation 17 into a circularly polari zed state is arranged over an emission surface of the surface-emitting semiconductor laser 102 .

[0053] Fig . 2B shows a cross-sectional view of a further example of a surface-emitting semiconductor laser 102 that may be a component of the sensor device 15 . The surface-emitting semiconductor laser 102 illustrated in Fig . 2B implements a HCSEL ("hori zontal cavity surface-emitting laser" ) . The surface-emitting semiconductor laser 102 comprises a first semiconductor layer 131 of a first conductivity type , a second semiconductor layer 132 of a second conductivity type and an active zone 115 arranged between the first semiconductor layer 131 and the second semiconductor layer 132 . Side faces of the resulting semiconductor layer stack are oblique e . g . at an angle of approximately 40 to 50 ° , for example approximately 45 ° . A first reflector 133 may be arranged adj acent to a first sidewall of the semiconductor layer stack . A second reflector 134 may be arranged adj acent to a second sidewall of the semiconductor layer stack . A first contact element 101 is arranged in electrical contact with the first semiconductor layer 131 . A second contact element 119 is arranged in electrical contact with the second semiconductor layer 132 . An optical resonator 135 may extend in a hori zontal direction . Laser radiation 17 may be emitted via a main surface of the second semiconductor layer 132 .

[0054] According to further modi fications , a further reflector may be arranged on a portion of a main surface of the second semiconductor layer 132 so that electromagnetic radiation is only emitted via one emission surface . The metasurface 105 for converting the polari zation state of the laser radiation may be arranged over the emission surface of the second semiconductor layer 132 . Fig. 3A shows an example of nanostructures, e.g. pillars 112 that may be arranged in a regular pattern to form a metasurface 105. For example, the pillars 112 may be arranged in rows and columns. According to further examples, as is also shown in Fig. 3C, the nanostructures may have a shape of ridges 114. For example, the ridges may be arranged at a constant pitch.

[0055] A space between adjacent nanostructures may be filled with a suitable embedding material 113, e.g. having a dielectric constant that is different from the material of the pillars 112. According to further embodiments, the space between adjacent nanostructures is not filled with an embedding material.

[0056] For example, a material of the pillars or ridges may be selected from a semiconductor material, e.g. a III-V compound semiconductor which is transparent to the emitted electromagnetic radiation. Examples comprise GaAs, AlGaAs or InGaP.

[0057] According to embodiments, the embedding material may be selected from a passivating dielectric material. Examples comprise SiN, AI2O3, SiCh or TiCy.

[0058] Fig. 3B shows a horizontal cross-sectional view of a metasurface 105 according to examples. In particular, Fig. 3B shows an example of an arrangement of pillars 112. According to examples illustrated in Fig. 3B, the single pillars 112 may be arranged in rows and in columns to form a cubic lattice. As is indicated in Fig. 3B, the positions of the pillars 112 may form a lattice and the size of the individual pillars 112 may vary. For example, pillars 112 of identical size may be arranged in a circular pattern .

[0059] Generally, as has been described with reference to Figs. 3A to 3B, the metasurface 105 may be implemented as a ID or 2D metasurface and may comprise nanostructures such as etched surface gratings, high contrast gratings, etc. For example, these metasurfaces may be formed at the top surface of the surfaceemitting semiconductor laser 102 using lithographic methods. For example, the grating may also implement a dielectric grating or an ordered photonic structure. A grating period, e.g. the sum of the grating width and the grating spacing (one-dimensional or two-dimensional) may be 250 nm or more, e.g. less than 500 nm. A duty cycle of the grating, e.g. a ratio of grating width / grat- ing period may be larger than 45 % and may be less than 55 %. For example, a grating thickness, e.g. a thickness of the nanostructures in a vertical direction, may be more than 80 nm, e.g. less than 160 nm.

[0060] Fig. 3D shows further elements of a sensor device 15. For example, the sensor device 15 may comprise an emitter 125, a photodetector 126 and electrical circuitry 127 which may be arranged on an electronic board 128. The emitter 125 may be configured to emit circularly polarized laser radiation. The emitter 125 may comprise the surface-emitting semiconductor laser 102 which has been described herein above. The emitter 125 further comprises the metasurface 105 that has been described above and which is configured to convert the laser radiation into circularly polarized laser radiation 17.

[0061] The photodetector 126 may be configured to detect laser radiation that has been reflected by an object 16. The electrical circuitry 127 may be configured to process the received signals to detect e.g. the presence of a person or a face in proximity to the sensor device 15.

[0062] Fig. 4A shows an example of an electronic device 20 which comprises the display device 10 which has been described herein above. The electronic device 20 may e.g. be a smartphone, a laptop, AR / VR glasses or any other electronic device comprising a display including a sensor device .

[0063] Fig . 4B shows a perspective view of an electronic device 20 according to embodiments . For example , the electronic device 20 may be a smartphone . Due to the feature that the emitter 125 is arranged behind the array 22 of light emitting elements 23 , there is no need to provide an extra space of the display device 10 for the sensor device 15 . As a result , the entire surface of the electronic device 20 may represent a surface of the display device 10 . As has been described, the polari zation behavior of a surface-emitting laser device 102 may be stabili zed by using ID or 2D metasurfaces 105 as has been explained above .

[0064] While embodiments of the invention have been described above , it is obvious that further embodiments may be implemented . For example , further embodiments may comprise any subcombination of features recited in the claims or any subcombination of elements described in the examples given above . Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein .

[0065] LIST OF REFERENCES display device sensor device obj ect laser radiation reflected radiation electronic device array of light emitting elements light emitting element electromagnetic radiation substrate first contact element surface-emitting semiconductor laser metasurface ordered photonic structure first semiconductor layer / DBR layer pillar embedding material ridge active zone aperture second semiconductor layer / DBR layer second contact element linear polari zer quarter-wave plate emitter photodetector electrical circuitry electronic board first semiconductor layer second semiconductor layer first reflector second reflector optical resonator

Claims

CLAIMS1. A display device (10) comprising: a sensor device (15) comprising: a surface-emitting semiconductor laser (102) configured to emit laser radiation (17) in an emission direction; and a metasurface (105) configured to convert a polarization state of the laser radiation (17) into a circularly polarized state, the display device (10) further comprising an array (22) of light emitting elements (23) configured to emit electromagnetic radiation (24) in the emission direction, the array (22) of light emitting elements (23) being arranged on a side of the sensor device (15) along the emission direction.

2. The display device (10) according to claim 1, further comprising a quarter-wave plate (121) and a linear polarizer (120) arranged along the emission direction on a side of the array (22) of light emitting elements (23) along the emission direction, the quarter-wave plate (121) being arranged between the linear polarizer (120) and the array (22) of light emitting elements (23) .

3. The display device (10) according to claim 1 or 2, wherein the surface-emitting semiconductor laser (102) is configured to emit laser radiation (17) having a wavelength larger than 1000 nm.

4. The display device (10) according to any of the preceding claims, wherein the light emitting elements (23) comprise light emitting elements configured to emit electromagnetic radiation (24) having a wavelength less than 1000 nm.

5. The display device (10) according to any of the preceding claims, wherein the metasurface (105) comprises an array of one-dimensional nanostructures (112) of a first material.

6. The display device (10) according to any of claims 1 to 4, wherein the metasurface (105) comprises an array of two-dimensional nanostructures (114) of a first material.

7. The display device (10) according to claim 5 or 6, wherein the first material comprises a III-V compound semiconductor material.

8. The display device (10) according to any of claims 5 to 7, further comprising an embedding material (113) arranged between the nanostructures (114) .

9. The display device (10) according to claim 8, wherein the embedding material (131) is selected from SiN, AI2O3, SiCy or TiO2.

10. The display device (10) according to any of the preceding claims, wherein the surface-emitting semiconductor laser (102) comprises a first semiconductor layer (110, 131) of a first conductivity type, a second semiconductor layer (118, 132) of a second conductivity type, and an active zone (115) arranged between the first semiconductor layer (110, 131) and the second semiconductor layer (118, 132) .

11. The display device (10) according to claim 10, wherein the active zone (115) comprises AlxGai-xAs .

12. The display device (10) according to any of the preceding claims, wherein the sensor device (15) is operable as a proximity sensor.

13. An electronic device (20) comprising the display device(10) according to any of the preceding claims.

14. The electronic device (20) according to claim 13, being implemented as a smart phone.

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