High-k dielectric Al2O3 nanowire and nanoplate field effect sensors for improved pH sensing

Over the last decade, field-effect transistors (FETs) with nanoscale dimensions have emerged as possible label-free biological and chemical sensors capable of highly sensitive detection of various entities and processes. While significant progress has been made towards improving their sensitivity, much is yet to be explored in the study of various critical parameters, such as the choice of a sensing dielectric, the choice of applied front and back gate biases, the design of the device dimensions, and many others. In this work, we present a process to fabricate nanowire and nanoplate FETs with Al2O3 gate dielectrics and we compare these devices with FETs with SiO2 gate dielectrics. The use of a high-k dielectric such as Al2O3 allows for the physical thickness of the gate dielectric to be thicker without losing sensitivity to charge, which then reduces leakage currents and results in devices that are highly robust in fluid. This optimized process results in devices stable for up to 8 h in fluidic environments. Using pH sensing as a benchmark, we show the importance of optimizing the device bias, particularly the back gate bias which modulates the effective channel thickness. We also demonstrate that devices with Al2O3 gate dielectrics exhibit superior sensitivity to pH when compared to devices with SiO2 gate dielectrics. Finally, we show that when the effective electrical silicon channel thickness is on the order of the Debye length, device response to pH is virtually independent of device width. These silicon FET sensors could become integral components of future silicon based Lab on Chip systems. Electronic supplementary material The online version of this article (doi:10.1007/s10544-010-9497-z) contains supplementary material, which is available to authorized users. B. Reddy Jr. : R. Bashir Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA B. Reddy Jr. : B. R. Dorvel : E. K. C. Chow : R. Bashir Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA B. R. Dorvel Department of Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA R. Bashir Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA J. Go : P. R. Nair :M. A. Alam Birck Nanotechnology Center, Purdue University, West Lafayette, IN 47907, USA J. Go : P. R. Nair :M. A. Alam School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN 47907, USA O. H. Elibol :G. M. Credo : J. S. Daniels :X. Su :M. Varma Intel Corporation, 3065 Bowers Avenue, Santa Clara, CA 95054, USA R. Bashir (*) 208 N Wright Street, Urbana, IL 61801, USA e-mail: [email protected] Biomed Microdevices (2011) 13:335–344 DOI 10.1007/s10544-010-9497-z