Low power integrated pressure sensor system for medical applications

A new low power integrated pressure sensor system with digital output (1 bit PDM signal) for medical applications is presented. The absolute pressure sensor comprising 400 nm thick surface micromachined polysilicon membranes for capacitive pressure detection and a monolithic integrated Znd order sigma-delta-modulator including voltage reference and timing generator is extremely miniaturized on an area of approximately 3 mm(2). For protection and biocompatibility reasons the sensor is coated with a silicone elastomer of up to 100 mu m thickness, which does not influence the sensor's performance. The sensor system was tested in vitro in physiological NaCl solution, showing excellent results compared to a commercial available reference sensor. The sensor system is working well down to a supply voltage of 2.2 V with a power consumption of 0.5 mW. The resolution is better than 12 bit. Due to the small chip area, low power consumption and cost effective production process, the sensor is ideal for medical applications, e.g., in combination with telemetric power and data transmission [J. Zacheja, B. Clasbrummel, J. Binder, U. Steinau, Implantable Telemetric Endosystem for Minimal Invasive Pressure Measurements, MedTech95, Berlin, Germany, (1995)] as an implantable sensor to reduce the mortality risk of intensive care patients. (C) 1999 Elsevier Science S.A. All rights reserved.