Chemical sensors fabricated in CMOS-MEMS technology

Abstract

This presentation is an overview of standard Integrated Circuits technology that enables the integration of the chemical sensors with the necessary driving and signal conditioning circuitry on the same chip. A variety of Complementary Metal Oxide Semiconductor (CMOS)-based chemical sensors found in the literature and the microprocessing technologic steps necessary for the integration of microelectromechanical systems (MEMS) sensors in CMOS technology are explained in this presentation. CMOS technology has become the mainstream semiconductor technology over the last decade due to its high volume production capability and its circuit advantages. Silicon is a readily available material that is relatively inexpensive. In addition, circuits fabricated in CMOS are low cost. An important advantage of CMOS technology is the possibility of integrating electronic circuitry with the MEMS sensor. Although CMOS processes were originally not intended for MEMS devices, the CMOS technology in combination with additional pre or post fabrication micromachining steps allows for integration of MEMS sensors and CMOS circuitry on the same chip. The monolithic integration of CMOS MEMS chemical sensors is a promising approach that has been motivated by the rapid development in integrated-circuit and MEMS technology. The aim in utilizing CMOS technology for realizing chemical sensors is to create more intelligent, more autonomous, more integrated and more reliable chemical sensor systems at low costs in a generic approach. The integration of electronics with chemical sensors in one single chip improves the sensor signals in terms of robustness and signal-to-noise ratio. On-chip integration also improves the microsystem functionality, interconnection and facilitates a more efficient packaging. At high volumes of production, the monolithic solution presents economical advantages, and it is especially attractive for portable and high sensitivity systems. The main disadvantages of the monolithic CMOS–MEMS integration include the restriction to CMOS-compatible materials and the limited choice of micromachining processes. However, the use of CMOS–MEMS offers, on the other hand, unprecedented advantages over hybrid designs, especially with regard to signal quality, device performance, increased functionality and available standard packaging solutions. These advantages clearly outweigh the drawbacks and limitations. A large number of MEMS gas sensors fabricated in CMOS technology were recently researched and developed. Several important CMOS-MEMS gas sensors will be presented.