FIELD OF THE INVENTION

The present invention relates to an optical assembly, e.g. an implantable optical sensor, comprising a substrate and an optical microstructure integrated with the substrate, the optical microstructure being positioned to form an optical interaction area on a part of a surface of the substrate. In a further aspect, the present invention relates to a method of manufacturing an optical assembly, the method comprising providing a substrate with an integrated optical microstructure forming an optical interaction area.

BACKGROUND ART

International Patent publication WO2016/137444 discloses a sensor and a method for measuring an analyte in a medium within a living animal. The sensor includes an inductive element, a charge storage device and a memory. The sensor performs analyte measurements initiated by an external device using power received from the external device and conveys analyte measurements to the external device using the inductive element. The sensor is entirely sealed in a glass capsule

US patent publication U.S. Pat. No. 6,981,806 B2 discloses a method for micro-hermetic packaging an optical device. The method comprises forming a micro-hermetic cavity on a substrate, providing a transmission optical waveguide on the substrate and sealing an optical device within the micro-hermetic cavity. A lid separate from the first substrate is employed for the sealing process or the micro-hermetic cavity is provided on the lid and sealed on to the first surface. The optical device may be positioned within the cavity for optical power transfer with the optical waveguide.

US 2004/0245425 A1 discloses a hybrid electro-optical device which has a portion defining a mounting location for optoelectronic components such as laser sources, photodetector diodes, LEDs, requiring local hermetic protection of the bare chips. A planar lightwave circuit (PLC) waveguide structure formed on the substrate extends to the mounting location to define an optical signal feed-through for the device. At least one electrode is associated with the planar lightwave circuit waveguide structure and extends said mounting location to define an electrical signal feed-through for the device. A ring-like structure continuously surrounds said mounting location and a continuous cover member is soldered thereon to cover and hermetically seal the mounting location. As a result of this ring-like structure, which is a metal rim, the device is not suitable for wafer scale production.

A well-known approach in art used to protect optical assemblies is by using e.g. a titanium box. However this approach has the drawbacks of not being a wafer scale process and each device needs to be processed separately, thereby making the approach costly. If an optical measurement needs to be carried out in an optical assembly, a feedthrough needs to be foreseen; which is not standard. A further approach is using parylene-c coating, but then it is not possible to test a device for a successful hermetic packaging. Another approach used, e.g. in telecommunications, and data communications applications, is by using a wafer scale capping in which the feedthroughs are made through the wafer scale cap. These feedthroughs are weak points especially when regarded in relation to a desired long life time.

SUMMARY OF THE INVENTION

The present invention seeks to provide an optical assembly, e.g. an implantable optical sensor, which is particularly suited to interact optically with harsh environments. More in particular, the present invention seeks to provide an optical assembly having an optical interaction area to provide exposure to a fluid, such as body fluids, as well as associated further active components which are sealed from the fluid, in order to have a reliable and safely working optical assembly. Further, the present invention seeks to provide an optical assembly which can be produced by wafer scale processes.

According to the present invention, an optical assembly as defined above is provided, further comprising a cover cap on a part of the substrate adjacent to the optical interaction area. At least one active component is positioned in a sealed cavity which is formed between the surface and the cover cap. The substrate comprises at least one optical feedthrough extending from the sealed cavity to the optical interaction area. As a result, there is no need to protrude the cover cap for reasons of communicating or interfacing with electronic components within the sealed cavity. This effectively shields the electronic component, and more specifically the electrical components of the optical assembly from contact with the fluid during use, without influencing the optical properties and measurement capabilities of the optical assembly. Furthermore, optical communication is possible from the active component(s) in the sealed cavity to an optical microstructure (which is present on the substrate) and back.

The cover cap is hermetically sealed to said substrate part by wafer-to-wafer bonding technology or another wafer-level hermetic packaging technique. The resulting device may be characterized by absence of any metal rim or ring-like structure as described in US 2004/0245425 A1 to prepare the substrate for sealing the cover cap thereto, absence of soldering material between the cover cap and the substrate, i.e. the bottom edge of the cap may be in direct contact with the surface of the substrate. Furthermore, the resulting device may be characterized by absence of a flange at the bottom edge of the cover cap, i.e. the techniques used for sealing the cap onto the substrate do not require such a flange.

A further aspect the present invention relates to a method of manufacturing an optical assembly as defined above, wherein the method further comprises providing at least one active component on the surface adjacent to the optical interaction area, and providing a cover cap on a part of the substrate to form a sealed cavity where the at least one active component is positioned. Furthermore, the method comprises sealing the cover cap to the substrate by wafer-to-wafer bonding technology or another wafer-level hermetic packaging technique, and providing at least one optical feedthrough extending from the sealed cavity to the optical interaction area (i.e. without protruding the cap). As the method uses techniques which are compatible with the manufacturing steps for other elements of the optical assembly, the method can be implemented as an efficient and cost-effective manufacturing method.

