Abstract
A miniature pressure sensor for biomedical application has been fabricated. By means of integrated-circuit (IC) fabrication techniques, these sensors can be produced in batches.
The sensor, of dimentions 3×1mm2 and 0.4mm thick, consists of eutectic-sealed two silicontips and a silicon diaphragm of 560μm diameter and 10μm thickness is formed on one side. This structure allows easy bonding of lead wires and mounting to a catheter-tip, and it is effective to reduce hysteresis and temperature drift caused by the thermal expansion mismatch of different materials.
A thin circular diaphragm has been fabricated from 130μm thick silicon wafer which has 10μm thick n-epitaxial layer on n+substrate by etching n+substrate electrochemically. Four p-type piezoresistors on the edge of the diaphragm are aligned to the direction of maximum sensitivity, and p+-type diffused conductors are formed for the connection to each contact pads. Lead wires are bonded to the contact pads with soldering. After mounting to a catheter, the sensor is coated with Parylene-C (Union Carbide Corporation, U.S.A.) to ensure the insulation and the passivation for the long-term operation.
The pressure sensitivity of the sensor is 27μV/Vsupply/mmHg, hysteresis and nonlinearity have not been observed over the pressure range from 0 to 300mmHg, and the diaphragm has not been broken even by a pressure over 9, 000mmHg.
The zero-pressure shift with a temperature change is less than 0.3mmHg/°C and the sensitivity change -0.27%/°C.
Satisfactory results have been obtained using the sensor for blood pressure measurement of a dog.
