Micromachined CMOS in vivo pressure sensor

A novel integrated microsystem for pressure sensing fabricated on a silicon chip in CMOS technology is reported. The microsystem uses capacitance change for sensing pressure. The readout uses the variable capacitor as the timing element in an oscillator so that the output frequency is a function of the capacitance and, hence, the pressure. The mechanically displaced plate of the capacitive pressure sensor is provided by crystalline silicon membranes fabricated in an anisotropic electrochemical bulk micromachining etch stop process. The surface and bulk micromachining steps required to complete the integrated CMOS pressure sensing microsystem are performed after the formation of the VLSI circuitry in a standard CMOS process and can be batch fabricated. The novel integrated pressure sensing microsystem is characterized by small dimensions, high sensitivity, high signal to noise ratio, improved long-term mechanical as well as electrical stability, and very low power consumption. These properties are essential for totally implantable biomedical applications. The microsystem is designed to monitor, in vivo, the cerebrospinal fluid (CSF) pressure after injury or stroke.