NSF-Europe: Development and Characterization of Electrically-Active Interfaces for Chemical Sensors

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

This project is a joint collaboration between Prof. Lisa Porter/Carnegie Mellon University (CMU) and Prof. Anita Lloyd Spetz from S-SENCE (Center for Sensor Technology) at Linkoping University, Linkoping, Sweden. The aim is through the combined collaborative expertise to push forward materials science understanding and subsequent development of high-temperature sensors, and to understand mechanisms that limit their performance. Examples of applications for these sensors include monitoring of selective catalytic reduction in automobile combustion engines and of flue gases from power plants. The approach is to develop and characterize ohmic contacts and insulators for SiC based chemical sensors that demonstrate substantial improvements in long-term stability at high temperatures (e.g., 300-800 C) required for optimum detection of certain gas species (e.g., hydrocarbons or NH3). Specifically, test devices (capacitors and Schottky diodes) will be fabricated based on contact and insulator materials, as well as associated processing conditions, developed by the CMU group. The devices will then be tested at S-SENCE for their gas sensor response at high temperatures. Initial research at Carnegie Mellon will consist of materials selection for ohmic contacts (e.g., TaC and PtSi), gate metals (e.g., Pt3Si) and gate insulator (e.g., SiO2 or AlN) followed by device fabrication. The devices will consist of TLM patterns for contact resistance measurements, MIS capacitors and Schottky diodes. The stability of these devices will then be measured using current-voltage (I-V) and/or capacitance-voltage (C-V) measurements as a function of both annealing temperature and measurement temperature. Selected samples will be sent, or brought, to S-SENCE for measurements of their gas response. This will be accomplished by mounting each sample onto a ceramic heater, which is attached to a 16-pin holder. After introducing specified gases into the assembly, the sensor response will be measured as the voltage at a constant current of 0.1 or 1 mA. Promising materials structures will be incorporated in MISiCFET devices. An important part of this research will include investigations of the morphology and interfacial chemistry and their relationship to the electrical properties of the sensors. The morphologies of the contact films will be characterized using scanning electron microscopy. The interfacial chemistry of the metal-insulator, insulator-semiconductor and metal-semiconductor will be characterized by Auger electron spectroscopy (AES), TEM, XRD and SIMS. %%% The project addresses fundamental research issues associated with electronic materials having technological relevance. An important feature of the project is the integration of research and education, and an international collaboration providing both scientific and educational benefits. Broader impacts associated with the project are exemplified by the education of undergraduate and graduate students in a unique technical, cultural and professional context. The approach includes: 1) graduate student exchange through visits to and from Sweden, 2) supervision of an undergraduate research project pertaining to chemical sensors, and 3) introduction of a lunch/speaker series designed to inspire and retain women graduate students and post-docs in materials science. This NSF project is a Cooperative Activity in Materials Research between the NSF and Europe (NSF 02-135).