Molecular Monolayers on CMOS for Nanoscale Chemical Sensors

Arizona State University, Scottsdale AZ

Investigators

Abstract

0097434 Thornton The project outlined in this proposal aims to develop a new type of hybrid molecular-semiconductor chemical sensor that is highly integrated, cheap and versatile. The sensor consists of polarizable molecular monolayers that adhere (i.e. self-assemble) to an underlying CMOS-compatible integrated circuit. The molecular monolayers are designed in such a way that their physical structure changes after exposure to the chemical of interest. The change in physical structure leads to a change in their electrical polarization which is detected by a sensitive transistor immediately below the monolayer. It is possible to design the molecular monolayers to respond to a wide range of individual chemical agents. The device combines the enormous flexibility associated with organic synthesis with the mass production capability of silicon chips. If successful, the research the PIs are proposing will lead to chip-based sensors that are cheap enough to be considered disposable, yet contain multiple sensing elements. The sensing elements will be integrated at the nanoscale and each chip will be capable of detecting a wide range of chemical agents. It will be possible to integrate the sensing elements with peripheral electronic circuitry that will perform both analog and digital signal processing. The information provided by the chip can be fed to a central computer (e.g. a home or office p.c.) to form a complete system for monitoring chemicals that influence our quality of life. The research will concentrate on the science and engineering that underpins a generic chemical sensing technology. Rather than focusing on a sensor that detects a single class of chemicals, they are looking to develop general principles that will allow them to build integrated sensors that can be tailored to a wide range of chemical classes. In this way a standardized processing technology can be used to build sensors for gas-phase or liquid-phase species that could be organic, biological or inorganic in nature. This vision is analogous to the way in which present day CMOS can be used to build analog or digital circuits for different applications including information processing, communications and power electronics. As a demonstrator of this technology the PIs propose to fabricate a chip-based sensor that combines circuitry for basic analog signal processing with molecular monolayers that are individually and selectively sensitive to different chemical agents. For demonstration purposes, they shall focus on three prototype devices for sensing pH, metal ions and biologically important enzymes. However, their principal objective is to complete the basic research that would underpin a generic sensing technology based on hybrid molecular-CMOS integrated circuits. The PIs propose a highly comprehensive and multidisciplinary program to investigate the preparation and properties of chemically active organic molecules, the fundamental factors controlling the interfacing of these species with electronic materials, and the incorporation of the molecules into prototype devices for multi-use sensing applications. The work will combine molecular synthesis with novel device fabrication and advanced scanning probe imaging. The molecular synthesis will initially concentrate on specifically tailored porphyrin-based molecular monolayers that incorporate functional groups that will bind strongly to the surface of the underlying transistor. If this approach shows promise, other sensing molecules for other specific applications will be designed and synthesized. The physical structure and orientation of the molecules on the semiconductor surface will be studied using a combination of scanning tunneling microscopy and atomic force microscopy. The visual, and quantitative data provided by the scanning probe images will be correlated with that provided by electrical measurements, to better understand the physical configuration of the molecular monolayers before and after exposure to the chemical agents of interest. If successful this work will create a revolution in environmental sensing that will have widespread beneficial impact.