Sensor and use of a sensor in a 3-D position detection system

Abstract

A sensor and a 3-D position detection system are disclosed. In an embodiment a sensor includes at least one sensor chip configured to detect radiation, at least one carrier on which the sensor chip is mounted and a cast body that is transmissive for the radiation and that completely covers the sensor chip, wherein a centroid shift of the sensor chip amounts to at most 0.04 mrad at an angle of incidence of up to at least 60°, wherein the cast body comprises a light inlet side that faces away from the sensor chip, and the light inlet side comprises side walls bounding it on all sides, wherein the side walls are smooth, planar and transmissive for the radiation, wherein a free field-of-view on the light inlet side has an aperture angle of at least 140°, and wherein the cast body protrudes in a direction away from the sensor chip beyond a bond wire.

Claims

1. A sensor comprising: at least one sensor chip configured to detect radiation; at least one carrier on which the sensor chip is mounted; and a cast body that is transmissive for the radiation and that completely covers the sensor chip, wherein a centroid shift of the sensor chip amounts to at most 0.04 mrad at an angle of incidence of up to at least 60°, wherein the cast body comprises a light inlet side that faces away from the sensor chip, and the light inlet side comprises side walls bounding it on all sides, wherein the side walls are smooth, planar and transmissive for the radiation, wherein a free field-of-view on the light inlet side has an aperture angle of at least 140°, wherein the sensor chip is contacted electrically with at least one bond wire, and wherein the cast body protrudes in a direction away from the sensor chip beyond the bond wire by at most 120 μm so that a thickness of the cast body at the side that faces away from the sensor chip lies at a maximum of 0.2 mm and so that the thickness is smaller than a thickness of the sensor chip.

2. The sensor according to claim 1, wherein the cast body extends beyond the sensor chip equally all around when seen from above, and wherein a ratio of a diagonal length of the cast body and of the sensor chip lies between 1.1 and 1.4 inclusive.

3. The sensor according to claim 1, wherein the light inlet side is smooth and planar, and wherein an angle between the side walls and the light inlet side, seen in cross-section, is between 94° and 106° inclusive.

4. The sensor according to claim 1, wherein the sensor chip is contacted electrically at an upper chip side that faces away from the carrier with the bond wire, and wherein the bond wire is located entirely in the cast body.

5. The sensor according to claim 1, wherein the sensor chip comprises a plurality of electrical contact points at the side that faces away from the carrier, and wherein the electrical contact points are arranged symmetrically around the side of the sensor chip.

6. The sensor according to claim 1, wherein the carrier and the cast body are flush against one another at the sides, and wherein chip side walls of the sensor chip are not transmissive for the radiation and/or do not supply any contribution to a detector signal.

7. The sensor according to claim 1, wherein the centroid shift of the sensor chip amounts to at most 0.15 mrad at angles of incidence of up to at least 40°, wherein the centroid shift depends on the angle of incidence and up to angles of incidence of at least 60° are approximatable by a quadratic function with an error of at most 0.003 mrad, and wherein the centroid shift at small angles of incidence has a different arithmetic sign than at large angles of incidence, and a boundary between small and large angles of incidence lies between 7° and 25° inclusive.

8. The sensor according to claim 1, wherein the side of the cast body that faces away from the sensor chip is roughened so that the sensor chip is configured to receive a Lambertian propagation of the radiation as a result of the roughening, and wherein the cast body is made of a material that is clear for the radiation.

9. The sensor according to claim 1, wherein the carrier is designed to reflect diffusely in regions next to the sensor chip up to a surface proportion of at least 90%.

10. A 3D position detection system comprising: at least one radiation source configured to generate the radiation; and a user device comprising a plurality of sensors, wherein at least one sensor of the plurality of sensors is the sensor according to claim 1, wherein the sensors are configured to determine angles between the user device and the radiation source so that a spatial position and an alignment of the user device is ascertainable based on the angles.

11. The 3D position detection system according to claim 10, wherein each sensor chip is contacted electrically at an upper chip side that faces away from the respective carrier with bond wires, and wherein bond wires are located entirely in the cast body.

12. The 3D position detection system according to claim 10, wherein each sensor chip comprises a plurality of electrical contact points at the sides that face away from the respective carrier, and wherein the electrical contact points are arranged symmetrically around the sides of the sensor chips.

13. The 3D position detection system according to claim 10, wherein the respective carrier and the associated cast body are flush against one another at the sides, and wherein chip side walls of the respective sensor chip are not transmissive for the radiation and/or do not supply any contribution to a detector signal.

14. The 3D position detection system according to claim 10, wherein the centroid shift of the sensor chip amounts to at most 0.15 mrad at angles of incidence of up to at least 40°, wherein the centroid shift depends on the angle of incidence and up to angles of incidence of at least 60° are approximatable by a quadratic function with an error of at most 0.003 mrad, and wherein the centroid shift at small angles of incidence has a different arithmetic sign than at large angles of incidence, and a boundary between small and large angles of incidence lies between 7° and 25° inclusive.

15. The 3D position detection system according to claim 10, wherein the sides of the cast bodies that face away from the sensor chips is roughened so that the sensor chips are configured to receive a Lambertian propagation of the radiation as a result of the roughening, and wherein the cast bodies are made of a material that is clear for the radiation.

16. The 3D position detection system according to claim 10, wherein the carriers are designed to reflect diffusely in regions next to the sensor chips up to a surface proportion of at least 90%.

17. The 3D position detection system according to claim 10, wherein the user device is a pair of glasses for virtual reality with at least one display, and wherein the display is configured to display three-dimensional images.

18. A method for using the 3D position detection system according to claim 10, wherein the 3D position detection system comprises at least five of the sensor chips, the method comprising: providing pulsed, laminar and near infra-red laser radiation; moving the radiation over a spatial region in which the user device is located so that multiple sequentially following pulses of the laser radiation impinge on a relevant sensor chip; detecting a temporal curve of intensity of impinging pulses by the relevant sensor chip; and ascertaining an angle to an associated radiation source based on detecting the temporal curve of intensity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A sensor and a 3-D position detection system are described in more detail below with reference to the drawing and on the basis of exemplary embodiments. The same reference signs here indicate the same elements in the individual figures. No true-to-scale references are, however, illustrated, but the individual elements may rather be illustrated with exaggerated size for the sake of better understanding.

(2) FIGS. 1,2A-2C, and 15A-15D show schematic illustrations of exemplary embodiments of sensors;

(3) FIGS. 3A, 3B, 4A, and 4B show schematic illustrations of 3D position detection systems with sensors;

(4) FIG. 5 shows a schematic illustration of a scanning of a sensor;

(5) FIGS. 6, 7A-7C, 8A-8F, 9A, and 9B show schematic illustrations of the optical properties of conventional sensors;

(6) FIGS. 10, 11, and 12A-12E show schematic illustrations for the optimization of sensors; and

(7) FIGS. 13A-13C and 14A-14E show schematic illustrations of optical properties of sensors.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(8) A sectional view of an exemplary embodiment of a sensor 1 is shown in FIG. 1. The sensor 1 comprises a carrier 3, such as a printed circuit board. A sensor chip 2 with an upper chip side 21 that faces away from the carrier 3, which is a detection face, is located on the carrier 3. Preferably, no signal is detected via chip side walls 22. The sensor chip 2 is preferably a PIN silicon photodiode.

(9) The sensor 1 further comprises a cast body 4. According to FIG. 1, a light inlet side 41 that faces away from the carrier 3 is smooth, flat and planar. An angle φ between the light inlet side and the side walls 42 of the cast body 4, wherein the walls are also designed to be smooth, flat and not transmissive to the radiation, lies, for example, at 100°.

(10) The sensor 1 can comprise additional components, not illustrated, such as spectral filters, so that only the radiation that is to be detected reaches the sensor chip 2, and other wavelengths are absorbed or reflected. The cast body 4 is, for example, absorbent for visible light.

(11) FIG. 2A illustrates a plan view, FIG. 2B a side view and FIG. 2C a view from underneath of a further exemplary embodiment of the sensor 1. The dimensions given in FIG. 2 preferably apply individually or jointly, each having a tolerance of at most 50% or 25% or 5%.

(12) On a lower side that faces away from the sensor chip 2 and also on the upper side that faces the sensor chip 2, the carrier 3 comprises a plurality of electrical carrier contact surfaces 31, via which the carrier 3 can be electrically and mechanically attached. The electrical contact points 45 at the upper chip side 21 are formed through metallizations, and each is connected via bond wires 5 to associated carrier contact surfaces 31. Of the total of five electrical contact points 45, four are arranged point-symmetrically to one another with reference to a geometrical center point of the upper chip side 21.

(13) Differing from FIG. 1, the side walls 42 of the cast body 4 are configured perpendicular to the light inlet side 41. In other respects the explanations to FIG. 1 preferably also apply to FIG. 2, and vice versa.

(14) A 3D position detection system 10 is illustrated in a perspective view in FIG. 3A; see also the document US 2016/0131761 A1. The system 10 comprises a plurality of radiation sources 11 which emit a laminar laser radiation R horizontally and vertically in the near-infra-red spectral region, and which scan in vertical and horizontal lines, also referred to as a SWEEP. A user 14 wears a user device 12 that comprises a plurality of the sensors. This system 10 enables a high temporal resolution, so that a time difference between a movement of the user 14 and a new acquisition of the position of the user 14 is relatively small, in order to minimize or prevent the occurrence of motion sickness.

(15) Each radiation source 11, also referred to as a lighthouse, here emits an infra-red flash with a duration T in order to specify a starting time point to. The infra-red flash follows the vertical and horizontal laser scanning. The infra-red flash is also referred to as a SYNC. A time difference between this SYNC and a detection time of the SWEEP allows for the calculation of the angle of the sensor concerned relative to the radiation source 11; see FIG. 3B.

(16) In the exemplary embodiment of the system 10 as is shown in FIG. 4A each radiation source 11 emits a laser sweep with a repetition rate of 50 Hz or 60 Hz.

(17) In particular, the angular position is found from a position of a centroid C of a signal intensity I; see FIG. 4B.

(18) The emergence of the signal is illustrated in connection with FIG. 5. During the laser sweep, the laser intensity, leaving aside the modulation, is constant, and the radiation R is moved over the sensitive surface of the sensor chip 2. A detector signal here is a convolution of the sensor geometry and the beam profile of the laser radiation. The centroid C of the detected signal corresponds in the ideal case to a center of the detector. An incorrect determination of the position of the centroid C thus yields incorrect time information and an incorrect angular position relative to the radiation source 11. Since a positional accuracy in the sub-millimeter range is required, even small centroid shifts can lead to an impairment in the 3D positional accuracy.

(19) A perspective view of a conventional sensor 1′ is illustrated in FIG. 6. The sensor 1′ is, for example, the BPW34S sensor manufactured by Osram.

(20) Various center lines H relative to the sensor 1′ of FIG. 6 are shown in FIG. 7. While the laser beam R is scanned over the detector surface, the left-hand and right-hand halves of the detector surface, separated by the line H, must, in the ideal case, receive the same optical power. The line H can have any orientation to the sensor 1′, illustrated in FIGS. 7A, 7B and 7C.

(21) Various cases, through which a shift between the centroid C as the geometrical center point and the detected centroid C* can arise at larger angles of incidence, are illustrated in FIG. 8.

(22) An asymmetrically applied electrical contact point 45 is present according to FIG. 8A. As a result, the radiation sensitive area is reduced on one side, and the centroid C* shifts in the direction away from this contact point 45, so that a centroid shift Δ results.

(23) In FIG. 8B it is shown that a reflective element, in particular a carrier contact surface 31, is present. The laser radiation R is reflected at this reflective element, and this region appears brighter, in part due to multiple reflections. The centroid C* thus shifts toward this carrier contact surface 31.

(24) According to FIG. 8C, partial shading results from the side walls 42. The centroid shift Δ of the detected centroid C* with respect to the ideal centroid C thus occurs in a direction away from this side wall 42.

(25) FIG. 8D illustrates that a part of the radiation R enters through the side wall 42, is reflected at the carrier 3, and contributes to the signal by way of multiple reflections or diffuse scatter. The centroid C* thus shifts in a direction toward the relevant side wall 42.

(26) FIG. 8E illustrates the case in which the radiation R arrives obliquely. The carrier 3 is thereby partially shaded, and reflections of different strengths occur at different locations of the carrier 3. The centroid C* thus moves in the direction toward the unshaded region.

(27) FIG. 8F finally shows that a centroid shift Δ occurs as a result of refraction of the radiation R at the light inlet side 41. The centroid C* thus moves in the radiation direction away from the geometric centroid C.

(28) The centroid shift Δ depends here on the angle of incidence α. This is illustrated in connection with FIG. 9. FIG. 9A here refers to the sensor 1′ illustrated in FIGS. 6 and 7. FIG. 9B relates to the SFH 2200 sensor manufactured by Osram.

(29) It can be seen from FIGS. 9A and 9B that, in particular toward larger angles of incidence α, there is a significant increase in the centroid shift Δ, which lies in the region significantly above 0.05 mrad. Here, S indicates a scan angle around the respective angle of incidence α.

(30) A centroid shift Δ of, for example, 0.1 mrad corresponds to a shift in the apparent position of the sensor 1 of 0.5 mm if there is a distance of 5 m to the respective radiation source 11.

(31) The effects illustrated in FIG. 8 can be partially or completely compensated for through various design measures. For example, the effects illustrated in FIGS. 8A and 8B depend entirely on the geometry, and have no significant angular dependency and an approximately constant amplitude.

(32) In the effects of FIGS. 8C and 8F, the direction of the centroid shift Δ and its magnitude depend on the angle of incidence α, and run in the opposite direction to the angle of incidence α, meaning that if the radiation R comes, for example, from the left, the centroid C* shifts to the right.

(33) In contrast, the shifts A of FIGS. 8D and 8E shift in the same direction as the angle of incidence α, so that if radiation R comes from the left, a centroid shift Δ also occurs to the left, while the magnitude of the centroid shift Δ also depends on the angle of incidence α.

(34) The effects of FIGS. 8C and 8F can thus partially or fully compensate for the effects of FIGS. 8D and 8E. The considerations in this respect are explained in more detail, in particular in connection with the following FIGS. 10 to 12.

(35) A sectional view is shown in this connection in FIG. 10, wherein the plurality of parameters are illustrated. n represents the refractive index of the cast body 4 at the wavelength of the radiation R that is to be detected. h indicates the thickness of the cast body 4 between the light inlet side 41 and the upper chip side 21. The parameter w indicates the thickness of the sensor chip 2, det identifies the edge length of the sensor chip 2, and pck refers to the edge length of the light inlet side 41. γ represents an angle of the side walls 42 to a perpendicular to the light inlet side 41. The magnitude η.sub.pcb is an empirical factor, and relates to the influence of the reflectivity of the carrier 3. η°.sub.sw is, correspondingly, an empirical parameter for the influence of the reflectivity of the side walls 42.

(36) The geometrical aspects are illustrated in more detail in FIG. 11 on the basis of the sectional illustration of FIG. 10. The angle α stands for the angle of incidence that is the angle to the light source 11. The angle δ is the scanning angle about the angle α. The angle β results from light refraction at the light inlet side 41. The centroid shift Δ between the ideal centroid position C and the apparent centroid position C* results from this effect in particular.

(37) Various distances d, L are furthermore drawn. The distance L between the sensor 1 and the radiation source 11 is, for example, 1 m. Relationships accordingly resulting from this are illustrated in the formulas in FIG. 12A, and are illustrated again in more detail in connection with FIG. 12B. The signal S resulting from this at the detector, depending on the scan angle δ, can be seen for various cases in FIG. 12C. A contribution from Fresnel transmissions results from FIG. 12D, while contributions of the side walls can be found in FIG. 12E.

(38) Depending on the desired application case, the geometry can be varied accordingly with reference to the illustrations of FIGS. 10 to 12, in order to achieve the desired result. Exemplary results derived from this are shown in FIGS. 13 and 14.

(39) The data in particular show that the cast body 4 is particularly preferably clear and transparent for the radiation to be detected, and comprises a smooth, transmissive light inlet side 41 as well as smooth side walls 42 that are transmissive for the radiation. As is also the case in all the other exemplary embodiments, additional components can be present which do not impair or do not significantly impair the radiation R that is to be detected, for example, daylight filters which to a large extent only allow the radiation R that is to be detected to pass through.

(40) The sensor chip 2, the electrical contact points 45, and the carrier contact surfaces 31 on the side of the carrier 3 that faces toward the sensor chip 2 are, moreover, to be arranged as point-symmetrically as possible. This eliminates or reduces in particular the effects that are illustrated in FIGS. 8A and 8B. For example, at least 80% or 90% or 95% of the relevant surfaces of the sensor chip 2, of the carrier 3, of the light inlet side 41, of the carrier contact surfaces 31 and/or of the electrical contact points 45 are arranged point-symmetrically.

(41) The height of the cast body 4 and the width of the cast body 4 are set such that the sensitive surface of the sensor chip 2 has an angle of view of at least 60°, preferably of at least 70° or 80° with respect to an optical axis of the sensor chip 2. Shadowing effects are thereby reduced. In addition, an optical thickness of the cast body 4, in particular above the upper chip side 21, is to be minimized, and the light inlet side 41 is to be designed to be as flat as possible. This reduces or overcomes the effects of FIGS. 8C and 8F. The effects of FIGS. 8C and 8F here usually make the biggest contributions.

(42) The contributions that are caused by the effects of FIGS. 8C and 8F and that cannot be eliminated can be partially or fully compensated for by the opposing effects of FIGS. 8D and 8E, in particular through adjusting the diffuse or specular reflectivity of the side walls 42 and of the upper side of the carrier 31 that faces toward the sensor chip 2, for example, through a deliberate enlargement of a surface of the carrier contact faces 31 or through the angle γ of the side walls 42.

(43) A quotient of the edge length pck of the cast body 4 and of the edge length det of the sensor chip 2 is plotted for this purpose in FIG. 13 against the centroid shift Δ for various thicknesses h of the cast body 4 over the upper chip side 21. In FIG. 13A, det is here 1 mm, in FIG. 13B it is 2 mm and in FIG. 13C it is 3 mm.

(44) It can be seen that the centroid shift Δ has a minimum value for a pck/det quotient of 1.3. The pck/det quotient is accordingly to be set to about 1.3.

(45) The geometrical parameters are illustrated in FIG. 14A for a further exemplary embodiment of the sensor 1. In contrast to the BPW34S manufactured by Osram of FIG. 6, with the sensor 1 described here a significant reduction in the centroid shift Δ results; see the left-hand side of FIG. 14B. The corresponding signal intensities I depending on the respective scan angle δ are illustrated here for various angles of incidence α in the right-hand side of FIG. 14B. The solid line here is related to the BPW34S sensor, and the dotted line to the sensor 1 described here. As a result of the geometric optimization, there is no significant effect on the signal intensity I.

(46) In a manner similar to that of FIG. 14B, the influence of a diffuse reflectivity of the carrier 3 at the side that faces the sensor chip is plotted in FIG. 14C. The empirical parameter η.sub.pcb here has a value of 1.0, corresponding to a diffusely reflecting surface. The centroid shift Δ can be reduced through the diffuse reflectivity.

(47) The case of diffusely reflecting side walls 42 is illustrated in FIG. 14D for a η°.sub.sw of 10.0 and for an absorptive upper side of the carrier 3, i.e., η.sub.pcb=0. A negative centroid shift Δ can be achieved through such side walls 42, with which other effects can be compensated for.

(48) The effect of the tilt angle γ of the side walls 42 is shown in FIG. 14E. An angle of incidence Δ of 60° is assumed here, and a parameter η°.sub.sw of 0.5, and a contribution of the carrier of η.sub.pcb of 0.1. The pck/det quotient lies in the present case at 2.8. The centroid shift Δ can be further adjusted through the angle γ.

(49) A further exemplary embodiment of the sensor 1 is shown in a sectional view in FIG. 15A. The light inlet side 41 is here roughened 44 over the whole area. The explanations relating to the other exemplary embodiments otherwise apply here correspondingly. The associated geometric parameters can be found in FIG. 15C.

(50) A Lambertian scatter of the radiation R at an inner side of the light inlet side 41 through to the sensor chip 2 is achieved through the roughening 44; see FIG. 15B.

(51) It is shown in FIG. 15D that the centroid shift Δ can be practically eliminated through the roughening 44. In contrast to the comparable example of the BPW34S detector, however, the signal strength I is relatively strongly reduced; see the right-hand side of FIG. 15D.

(52) The components shown in the figures each follow, unless otherwise made known, preferably in the given sequence each after one another. The layers that are not in contact in the figures are preferably spaced apart from one another. Wherever lines are drawn parallel to one another, the corresponding surfaces are preferably also aligned parallel to one another. Equally, unless otherwise made known, the positions of the illustrated components relative to one another are correctly reproduced in the figures.

(53) The invention described here is not restricted to the description based on the exemplary embodiments. The invention rather comprises any new feature or any combination of features that in particular contains any combination of features in the patent claims, even when this feature or this combination is not itself explicitly stated in the patent claims or exemplary embodiments.