Implantable Pressure Measurement System

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An implantable pressure measurement system was studied. The results of the research are as follows; 1. A new electrical feedthrough structure for an implantable pressure sensors has been developed. This structure is indispensable for the absolute pressure sensor. It enables air-tight seal at the output read part and makes the packaging easy. The Pyrex glass-to-silicon anodic bonding, free from residual stress, and electrochemical discharge drilling which is useful to engrave narrow through-hole were developed. 2. A piezoresistive pressure sensor, using the new feedthrough structure was fabricated. The size of the sensor is 1.8mmxl.8mm and 580um in thickness. The diaphragm size is 0.8mmxO.8mm, and the depth of reference cavity is 3um.The sensitivity was 13uV/mmHg/Vs when the diaphragm thickness was 9um. 3. A capacitive relative pressure sensor for a catheter was fabricated. The size was 0.7x3.5xO.4mm. The normalized pressure sensitivity was 3.45xlO-4/mmHg and the temperature coefficient was 0.17mmHg/ C. 4. An integrated silicon capacitive pressure sensor has been fabricated. The size is 2.2mmxl.7mm and 500um in thickness. The CMOS capacitance to frequency converter circuit is integrated on the same silicon chip. output of the circuit is taken through glass holes which are at the opposite side of the silicon diaphragm. Output frequency is detected by monitoring the supply current in the power line, so that only two lead wires are necessary for the sensor. The thermal zero shift is less than 0.1%F.S./ C. The sensitivity is -31.3Hz/mmHg (0.048%F.S./mmHg). The power dissipation is 86.5uW. The sensor is suitable for implantable telemetry system because of its good stability, low power deception, and simple output signal detection.Design and fabrication principle of implantable pressure sensing system was established.