A Subcubic Millimeter Wireless Implantable Intraocular Pressure Monitor Microsystem

We present a sub-mm ³ , fully wireless, implantable intraocular pressure monitor microsystem (IMM) that comprises a powering coil, an antenna, a piezoresistive micro-electro-mechanical system pressure sensor, and a pressure sensing IC. The system provides a 24-h intraocular pressure monitoring, which is not possible with currently used tonometric measurements. The IMM volume is limited to 0.38 mm ³ (4 × smaller than previous state-of-the-art) for the studies on laboratory rodents prior to human use. A cavity resonator magnetic coupling delivers the wireless power to the chip with 4.89% efficiency. The chip senses a change in a differential sensor resistance by providing a low-power differential resistance to frequency conversion with the measured standard deviation in differential resistance sensing of 133 mΩ. The data packets are wirelessly transmitted by an ultralow power 2.4-GHz ISM band OOK transmitter. The IMM is integrated on a 5-μm-thick biocompatible Parylene C substrate. Implemented in a 0.18-μm CMOS process, the system achieves 0.67-mmHg pressure sensitivity with differential resistance sensing and dissipates only 6.3 nW with 30 min of measurement intervals. We verify the IMM functionality in the in vivo biological experiment.