Piezoresistive CMOS-MEMS pressure sensor with ring oscillator readout including Δ-Σ analog-to-digital converter on-chip

The application of microelectromechanical systems (MEMS) is currently growing, increasing the demands for efficient interfacing between the MEMS sensor and CMOS interfacing circuitry. This paper presents a fully integrated CMOS-MEMS pressure sensor, including a frequency-to-digital converter on the same CMOS die. The main purpose of this work is to explore the properties of monolithically integrated MEMS-sensors and CMOS circuitry. The expected features are reduced production cost and reduced noise sensitivity. The fully integrated sensor has been fabricated in a standard 0.6μm CMOS process from Austria Micro Systems (AMS). Only one single post-processing step is required to form the pressure sensitive diaphragm. Theoretical discussions are presented along with measured results. The measured results confirm the theoretical discussions. The chip size is 13mm² and the power consumption is 30mW@3.0V.