In this paper, a novel 3D packaging technique for miniature implantable wireless biomedical sensors for intraocular pressure (IOP) sensing in mice is introduced. Due to the limited size of a mouse eye, the packaging of the sensor and control integrated circuit (IC) is very challenging. The overall size of the packaged sensor must be less than 12 mils cubed. In order to achieve the desired thickness, a magnetically aligned Z-axis anisotropic conductive adhesive (ACA) is used to create the vertical interconnects and micro-vias in the packaging material to distribute signals vertically to limit the eventual area of the device. The first step is to demonstrate the layer-to-layer interconnection between a silicon IC and a liquid crystal polymer (LCP) layer using the Z-axis ACA. The total thickness of the IC and the packaging layer is less than 6 mils. The measured resistance through vertical interconnection is 1.15 ohms on average for 3 mil × 3 mil pads. The second step is to demonstrate 3D transitions through 0.8 mil via holes in a LCP layer. A transition from an antenna layer through the LCP to a rectifier circuit on the above layer is demonstrated. RF power received by a loop antenna on the bottom LCP layer is rectified and generates 5 volts of DC voltage. This miniature 3D packaging technique enables extremely tight integration of all the sensor's components in a small form factor package, which can be implanted into mice eyes for wireless monitoring of the intraocular pressure.

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