OPTICAL INTEGRATED CIRCUIT SENSOR PACKAGE USING A STACKED CONFIGURATION FOR THE SENSOR DIE AND THE EMITTER DIE

An optical sensor package includes an emitter die mounted to an upper surface of a package substrate. A sensor die is mounted to the upper surface of the package substrate using a film on die (FOD) adhesive layer that extends over the upper surface and encapsulates the emitter die. The sensor die is positioned in a stacked relationship with respect to the emitter die such that a light channel region which extends through the sensor die is optically aligned with the emitter die. Light emitted by the emitter die passes through the light channel region of the sensor die. The emitter die and the sensor die are each electrically coupled to the package substrate.

TECHNICAL FIELD

Embodiments relate to an optical integrated circuit sensor package which includes both a sensor die and an emitter die.

BACKGROUND

Reference is made toFIG. 1which shows a cross-section of an optical integrated circuit sensor package10. The package includes a package substrate12, for example in the form of a leadframe, having an upper surface to which a sensor die14and an emitter die16are mounted. Any suitable die attachment mechanism as known by those skilled in the art may be employed to mount the sensor die14and emitter die16to the package substrate12. Bonding wires18are used to electrically connect pads (not explicitly shown) at a front face of the die to conductor portions of the package substrate12(for example, leads of the leadframe). The sensor die14includes a first photosensitive region20and a second photosensitive region22at a front face of the die. The photosensitive regions20and22may, for example, each be formed by one or more single photon avalanche diode (SPAD) devices. The emitter die16includes a light emission region24at a front face of the die. The emitter die16may, for example, comprise a vertical cavity surface emitting laser (VCSEL) diode which is configured to emit light perpendicularly from the front face of the die. In an embodiment, this light may have any suitable wavelength for a desired sensing application but is preferably emitted in the infrared or near infrared range.

A cap30is mounted to the package substrate12. The cap30includes a peripheral outer wall32and a front wall (or ceiling)34, which define a cavity, and an interior wall36extending between opposite sides of the peripheral outer wall32which splits the cavity into a first cavity region38and a second cavity region40. Distal end edges of the peripheral outer wall32are mounted to the upper surface of the package substrate12using a suitable adhesive material so as to enclose the sensor die14and emitter die16within the cavity of the cap30(more specifically with the sensor die14partially within each of the first and second cavity regions and the emitter die16solely within the first cavity region). The interior wall36is positioned between the first photosensitive region20and the second photosensitive region22, and sealed by an adhesive to the front face of the sensor die14, to form a light barrier that prevents light emitted by the light emission region24of the emitter die16within the first cavity region38from reaching the second photosensitive region22within the second region40by passing within the cavity of the cap30. This light barrier, however, does not prohibit such emitted light within the first cavity region38from reaching the first photosensitive region20.

The front wall (or ceiling)34of the cap30includes a first opening42optically aligned with the location of the light emission region24for the emitter die16. An optical element44is mounted at (or perhaps in) the first opening42. The front wall (or ceiling)34of the cap30further includes a second opening46optically aligned with the location of the second photosensitive region22for the sensor die14. An optical element48is mounted at (or perhaps in) the second opening44. The optical elements44and48may be designed to include lens and/or filter structures as desired for the optical sensing application.

The optical integrated circuit sensor package10is particularly well-suited for use in proximity sensing or distance measuring applications using time-of-flight (ToF) techniques. A pulse of light4is emitted from the light emission region24of the emitter die16, and this light emission event is detected (using reflected light path6) by the first photosensitive region20of the sensor die14to provide an emission pulse time reference. The emitted light pulse4exits the package10through the optical element44and first opening42and is reflected from a target object (not explicitly shown) back towards the package. The reflected light pulse8passes through the optical element48and second opening46and is detected by the second photosensitive region22of the sensor die14to provide a reflected pulse time reference. The time taken for the light pulse to travel to the object and be reflected back and sensed (i.e., the difference between the reflected pulse time reference and the emission pulse time reference) may be used to determine the distance between the object and the package10based on the known speed of light.

A concern with optical integrated circuit sensor packages, like the package10ofFIG. 1, which include multiple integrated circuit die and which must be designed in accordance with certain design spacing rules, and which must further include optical elements, is the overall size of the package (both in terms of occupied area in the X-Y plane and overall volume taking into consideration the thickness in the Z direction). It would particularly be an advantage if a reduction in occupied area and a simpler construction could be supported for an optical integrated circuit sensor package.

SUMMARY

In an embodiment, an optical sensor package comprises: a package substrate; an emitter die mounted to an upper surface of the package substrate; an adhesive layer extending over the upper surface and encapsulating the emitter die; a sensor die mounted to an upper surface of the adhesive layer in a stacked relationship where the sensor die is positioned to cover over the emitter die; said sensor die including a light channel region that extends through the sensor die and which is optically aligned with the emitter die such that light emitted by the emitter die passes through the light channel region of the sensor die; and electrical connections between the package substrate and each of the emitter die and the sensor die.

The sensor die may further include, for the light channel region, an integrated diffractive optical element configured to diffract said light passing through the light channel. This integrated diffractive optical element may comprise a passive element formed, for example, by a plurality of metal structures associated with one or more metallization layers of the sensor die. The integrated diffractive optical element may alternatively comprise an active element formed, for example, by a plasmonic device or a liquid crystal on silicon (LCOS) device.

In an embodiment of the active element, one of or more of: a selectively configurable diffractive effect, a selectively configurable shutter, a selectively controllable diffraction pattern, a selectively controllable polarization filter, and a selectively controllable lens, may be provided.

In an embodiment, the adhesive layer may be provided by a film on die (FOD) structure.

In an embodiment, an apparatus comprises: a substrate; a first integrated circuit die mounted to an upper surface of the substrate; an adhesive film layer extending over the upper surface and encapsulating the first integrated circuit die; a second integrated circuit die mounted to an upper surface of the adhesive film layer in a stacked relationship where the second integrated circuit die is positioned to cover over the first integrated circuit die; and electrical connections between the substrate and each of the first and second integrated circuit dies.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is made toFIG. 2which shows a cross-section of an optical integrated circuit sensor package50. The package includes a package substrate52, for example in the form of a leadframe, having an upper surface to which an emitter die56is mounted. Any suitable die attachment mechanism as known by those skilled in the art may be employed to mount the emitter die56to the package substrate52. The emitter die56includes a light emission region64at a front face of the die. The emitter die56may, for example, comprise a vertical cavity surface emitting laser (VCSEL) diode which is configured to emit light perpendicularly from the front face of the die. In an embodiment, this light may have any suitable wavelength, but is preferably emitted in the infrared or near infrared range. One or more bonding wires58are used to electrically connect pads (not explicitly shown) at a front face of the emitter die56to conductor portions of the package substrate52(for example, leads of the leadframe). A thick die attach film layer53extends in contact with the upper surface of the package substrate52and further encapsulates the emitter die56and its bonding wire(s)58. This is referred to in the art as a “film on die” (FOD) structure. A sensor die54is mounted to the upper surface of the package substrate52using the thick die attach film layer53. The sensor die54is positioned in a stacked relationship in the Z direction with respect to the emitter die56such that in the X-Y plane the sensor die54overlies (i.e., completely covers over) the emitter die56. With this stacked die arrangement, light emitted by the light emission region64of the emitter die56(in the Z direction perpendicular to upper surface of the package substrate52) will pass through an overlying portion of the film layer53and completely through the thickness of the sensor die54in a light channel region55that extends through the sensor die from its back surface to its front surface. This is possible because many of the materials (silicon, oxides, etc.) used in the manufacture of sensor die are transparent to the preferred infrared or near infrared light emitted by the emitter die56. The light channel region55is optically aligned with the light emission region64of the emitter die56. In an embodiment, the light channel region55may be partially delimited by a region of the semiconductor substrate of the sensor die54with a different, for example lower, native doping concentration than a remainder of the semiconductor substrate within which active semiconductor devices (such as analog and or digital circuits) are fabricated. In an embodiment, the light channel region55may be further partially delimited by a region of an overlying interconnect layer which is devoid of metal electrical connection lines and vias for electrically interconnecting integrated circuits of the sensor die. Bonding wires59are used to electrically connect pads (not explicitly shown) at a front face of the die54to conductor portions of the package substrate52(for example, leads of the leadframe). The integrated circuits of the sensor die54include a first photosensitive region60and a second photosensitive region62at a front face of the die. The photosensitive regions60and62may, for example, each be formed by one or more single photon avalanche diode (SPAD) devices integrated at and/or within the semiconductor substrate.

A cap70is mounted to the package substrate52. The cap70includes a peripheral outer wall72and a front wall (or ceiling)74, which define a cavity, and an interior wall76extending between opposite sides of the peripheral outer wall72which splits the cavity into a first cavity region78and a second cavity region80. Distal end edges of the peripheral outer wall72are mounted to the upper surface of the package substrate52using a suitable adhesive material so as to enclose the sensor die54and emitter die56within the cavity of the cap70(more specifically with the sensor die54partially within each of the first and second cavity regions and the emitter die56solely within the first cavity region). The interior wall76is positioned between the first photosensitive region60and the second photosensitive region62, and sealed by an adhesive to the front face of the sensor die54, to form a light barrier that prevents light emitted by the light emission region64of the emitter die56(which passes through the channel region55and into the first cavity region78) from reaching the second photosensitive region62within the second region80by passing within the cavity of the cap70. This light barrier, however, does not prohibit such emitted light within the first cavity region78from reaching the first photosensitive region60.

The front wall (or ceiling)74of the cap70includes a first opening82optically aligned with the location of both the channel region55and the light emission region64for the emitter die56. An optical element84is mounted within the first opening82. The front wall (or ceiling)74of the cap70further includes a second opening86optically aligned with the location of the second photosensitive region62for the sensor die54. An optical element88is mounted within the second opening84. The optical elements84and88are typically transparent glass structures but may also be designed to include lens and/or filter structures as desired for the optical sensing application.

In addition to the first photosensitive region60and the second photosensitive region62which are integrated into the sensor die54at the front face, the sensor die further includes an integrated diffractive optical element (DOE)90, for example located at or near the front face of the die and provided in connection with (e.g., as an integral part of) the light channel region55. This integrated diffractive optical element90is optically aligned within the channel region55in the Z direction to the light emission region64of the emitter die56, and is configured to diffract the light emitted from the light emission region64of the emitter die56and which passes through the channel region55. In one embodiment, the integrated diffractive optical element90is a passive element provided in the form of a pattern of metal structures92(forming, for example, an optical grating). The metal structures92are formed by and in one or more of the metallization layers94of the interconnect layer96which extends over the top surface of the semiconductor substrate98of the sensor die54(see,FIG. 3)—it being understood by those skilled in the art that this interconnect layer further includes, in areas other than in the channel region55, metal lines and vias (generally, reference9) in the metallization layers94for electrically connecting integrated circuit devices. In another embodiment, the integrated diffractive optical element90is a passive element provided in the form of a pattern of transparent structures100,102within the interconnect96that have different indices of refraction (see,FIG. 4). In yet another embodiment, the integrated diffractive optical element90is an active element provided in the form a plasmonic diffraction element or a liquid crystal on silicon (LCOS) diffraction element (see,FIG. 5). The active integrated diffractive optical element can be controlled by a control circuit located on the sensor die54(or provided externally and electrically coupled to the sensor die54) to actively control the type of diffractive effect to be provided. For example, the active integrated diffractive optical element may be configured to provide a controllable shutter function to selectively block/pass the light emitted by the emitter die56. As another example, the active integrated diffractive optical element may be configured to provide a controllable diffraction pattern (for example, through an adaptive control over one or more of: the number of openings, size of the openings, and separation between openings). In a further example, the active integrated diffractive optical element may be configured to provide a controllable polarization filter (for example, switching between polarization modes). In still another example, the active integrated diffractive optical element may be configured to provide a controllable lens (for example, for the purpose of controlling beam shape, focal point, field of view, etc., for the emitted pulse of light4).

The optical integrated circuit sensor package50is particularly well-suited for use in proximity sensing or distance measuring applications using time-of-flight (ToF) techniques. A pulse of light4is emitted from the light emission region64of the emitter die56to pass through the channel region55and into the first cavity region78. The emitted light pulse4is further (actively or passively) diffracted by the integrated diffractive optical element90. This light emission event is detected (using reflected light path6) by the first photosensitive region60of the sensor die54to provide an emission pulse time reference. The emitted and diffracted light pulse4exits the package50through the optical element84and first opening82and is reflected from a target object (not explicitly shown) back towards the package. The reflected light pulse8passes through the optical element88and second opening86and is detected by the second photosensitive region62of the sensor die54to provide a reflected pulse time reference. The time taken for the light pulse to travel to the object and be reflected back and sensed (i.e., the difference between the reflected pulse time reference and the emission pulse time reference) may be used to determine the distance between the object and the package50based on the known speed of light.

An advantage of the package50ofFIG. 2over the package10ofFIG. 1is a reduction of occupied area in the X-Y plane at the expense of a relatively small thickness increase in Z-direction. A further advantage is that the functionality of the optical diffraction element90, whether passive or active, is provided through the sensor die54. This simplifies the construction and further reduces part count for the overall device.