Catheter‐tip capacitive pressure sensor

As a pressure sensor to be used at the tip of a catheter, a capacitive relative pressure sensor was fabricated. This paper describes the fabrication process and the characteristics of this pressure sensor. The size of the sensor fabricated is 0.7 × 3.5 × 0.8 mm³ and the spacing between the capacitor electrodes is either 1.0 μm or 1.5 μm. The principal features are as follows: (1) In the fabrication of the diaphragm, high‐concentration boron was diffused into an Si wafer. The diaphragm thickness was controlled accurately by etch stop; (2) to reduce the effect of the stray capacitance and to increase the S/N ratio of the sensor, the capacitance detection IC was placed near the diaphragm; (3) since the consumption current flows at the oscillation frequency, it is possible to use two lead wires from the sensor; and (4) this IC has a size of 1.2 × 0.5 mm² and the temperature dependence of the oscillation frequency can be made zero by letting the power supply voltage be 2.24 V. The pressure sensitivity of the obtained sensor is 3.45 × 10⁻⁵/mmHg and the temperature coefficient at the zero pressure was 0.17 mmHg/°C. The output of the IC placed by the sensor had a frequency change of about 7 kHz for 1000 mmHg.