Microhotplate platforms for chemical sensor research
Introduction
The temperature of a sensing film can affect a variety of factors, including the film’s base conductance, the quantity of gases it will adsorb, and the rates of reactions between adsorbates on its surface. As these effects can be important in producing response signals, temperature-controlled platforms have been used in developing gas sensors for many years. Increasingly, smaller device platforms have been fabricated recently in an attempt to achieve low power consumption when employing temperature control. The evolution of micromachining as a fabrication technology for chemical sensing has allowed miniaturization to progress toward a smaller scale with more convenient fabrication methods [1]. Micromachining of silicon to produce sensor platforms also provides the possibility for including on-chip circuitry, and replication of device structures into integrated arrays is straightforward.
Beginning in the early 1990s, the opportunities of silicon micromachining led to the fabrication of new types of microhotplate devices and arrays for gas sensing. These devices have been produced both by surface [2] and bulk etching of silicon [3], [4], and have been employed for developing gas microsensor prototypes [5]. The ability to locally heat miniature elements has been utilized both in fabricating gas microsensor films and in operating devices in rapid temperature-programmed modes [6]. For example, thermally-activated chemical vapor deposition (CVD) has been employed for depositing oxides and metals from gas phase precursors and reactants [7], [8], [9]. Such processes offer the benefit of self-lithography for incorporating sensing materials onto microdevice structures. Rapid thermal characteristics (τ∼5 ms for the surface micromachined NIST microhotplates) also permit control of heating pulses in thermal programs that are capable of producing response signatures [6], [10]. This approach has been demonstrated to increase signal information content and enable rapid analyte recognition [11]. Recently, the advantages of microhotplates as gas sensor platforms have been more broadly demonstrated [12], [13], [14], [15].
While development efforts on microhotplate platforms for gas microsensor prototypes continue at NIST, we have also recognized that the characteristic features of these temperature-controllable platforms can be used to great advantage in conducting focused types of sensor research on temperature-dependent phenomena. In this paper we emphasize the adaptability of microhotplate fabrication methods for producing array configurations with functionalities that facilitate investigations of sensing materials, detection principles and mechanisms. Several examples are used to illustrate the value of such micro-platform studies for developing improved sensing films and operating modes.
Section snippets
Microhotplate fabrication
The basic element we have used in fabricating gas microsensor prototypes and micro-scale research platforms is a multi-level, CMOS-compatible structure called a microhotplate, which has been described elsewhere [2]. The mask set originally used to create the microhotplates at silicon foundries was designed using the MAGIC CAD tool
Processing of sensing materials on micro-scale platforms
To study sensing materials and mechanistic phenomena of sensing using micro-scale devices and arrays, methods must be developed for compatibly incorporating the sensing materials of interest onto the miniature elements. As a variety of material types, and microstructures are used in gas sensing research and development, micro-scale processing onto microhotplates can present a considerable challenge. The sensing films of interest include oxides, metals and polymers that can be produced and
Temperature-dependent studies
The ability to control the temperatures of microarray elements allows efficient studies of temperature-dependent processing, temperature-dependent film properties, and temperature-dependent interfacial phenomena [29] critical to sensing. Some of the factors and effects that can be investigated are listed in Table 1.
Arrays of thermally-isolated and individually addressable microhotplate devices can provide matrices of temperature for highly efficient, parallel studies of processing/performance
Multielement materials study
Although, there have been sensor arrays developed with tens of elements [31], [32], much of the current developmental work on microsensor arrays involves configurations with less than 10-elements. Often recognition of analytes can be performed using just a few different materials within an array format, along with chemometric analysis. More recently, the use of thermal programming of individual (microhotplate) elements has elevated the level of information content, so that selectivity is
Prototype devices for sensing
While this paper and the examples just discussed have focused on the use of micromachined structures in sensor research, it is important to remember that similar platforms were initially used in developing microsensor prototypes. Four-element arrays like that in Fig. 2 have been our primary devices for developing micro-deposition methods, post-deposition film modification, and temperature programmed sensing.
The adaptation of the microhotplate structure into array research platforms has allowed
Summary
Micromachined silicon structures called microhotplates have been adapted to develop sensing device prototypes and micro-scale research platforms. The same features critical to temperature-controlled conductometric gas microsensor development and operation have been applied to advantage in producing arrays of elements designed as research tools. We have illustrated the use of such arrays in statistically-designed studies of conductometric sensing film process/performance correlations, for
Acknowledgements
The authors wish to acknowledge the technical support provided by J. Allen, M. Aquino-Class, M. Carrier, J. Melvin, and C. Ellenwood, and thank M. Widmaier of Hitachi Instruments, Inc. for providing assistance with SEM imaging. M. C. Wheeler would like to acknowledge the support of the National Research Council-National Institute of Standards and Technology Post-doctoral Research Program. We also gratefully acknowledge the partial support of this work by the US Department of Energy — Grant No.
Steve Semancik received his BS degree in Physics in 1974 from Rensselaer Polytechnic Institute, and his MSc and PhD degrees in Physics from Brown University during 1976 and 1980, respectively. He was then awarded a National Research Council Post-doctoral Associateship to do experimental studies in the Surface Science Division at the National Institute of Standards and Technology (NIST). In late 1982, he joined the Process Measurements Division at NIST as a Research Physicist and became Project
References (40)
- et al.
Selected-area deposition of multiple active films for conductometric microsensor arrays
Sens. Actuators B
(1996) - et al.
Optimization of temperature programmed sensing for gas identification using micro-hotplate sensors
Sens. Actuators B
(1998) - et al.
Thin-film gas sensor implemented on a low-power-consumption micromachined silicon structure
Sens. Actuators B
(1998) - et al.
Very low power consumption micromachined CO sensors
Sens. Actuators B
(1999) - et al.
Pulsed mode of operation and artificial neural network evaluation for improving the CO selectivity of SnO2 gas sensors
Sens. Actuators B
(2000) - et al.
The use of surface and thin film science in the development of advanced gas sensors
Appl. Surf. Sci.
(1993) - et al.
Surf. Sci.
(1979) - M. Madou, Fundamentals of Microfabrication, CRC Press, Boca Raton, FL,...
- et al.
Tin oxide gas sensor fabricated using CMOS micro-hotplates and in situ processing
IEEE Electron Device Lett.
(1993) - N. Najafi, K.D. Wise, R. Merchange, J.W. Schwank, An integrated multi-element ultrathin film gas analyzer, in:...
A micromachined ultra-thin-film gas detector
IEEE Trans. Electron Devices
Kinetically-controlled chemical sensing using micromachined structures
Accounts Chem. Res.
Growth of SnO2 films on micromachined hotplates
Appl. Phys. Lett.
A selected-area CVD method for deposition of sensing films on monolithically integrated gas detectors
IEEE Electron Device Lett.
Fast temperature sensing for micro-hotplate gas sensors
IEEE Electron Device Lett.
The user interface and implementation of an IC layout editor
IEEE Trans. Computer-Aided Design
Cited by (281)
Picoliter drop deposition of SnO<inf>2</inf> nanoparticles onto microsensor platforms
2024, Sensors and Actuators B: ChemicalExplosive sensing with insect-based biorobots
2020, Biosensors and Bioelectronics: XPlasma assisted formation of 3D highly porous nanostructured metal oxide network on microheater platform for Low power gas sensing
2019, Sensors and Actuators, B: ChemicalSelective H<inf>2</inf>S sensing without external heat by a synergy effect in self-heated CuO-functionalized SnO<inf>2</inf>-ZnO core-shell nanowires
2019, Sensors and Actuators, B: ChemicalCitation Excerpt :The internet of things paradigm in big cities [4], needs low-cost and low-power consumption electronic devices to apply to different places [5]. It has been known that MEMS technology can decrease the power consumption to levels that make possibility of use of resistive-based gas sensors for mobile applications [6]. In this context, further minimization of power consumption is expected to have several advantages.
CMOS-based sensors and actuators for life science applications
2024, CMOS-Based Sensors and Actuators for Life Science Applications
Steve Semancik received his BS degree in Physics in 1974 from Rensselaer Polytechnic Institute, and his MSc and PhD degrees in Physics from Brown University during 1976 and 1980, respectively. He was then awarded a National Research Council Post-doctoral Associateship to do experimental studies in the Surface Science Division at the National Institute of Standards and Technology (NIST). In late 1982, he joined the Process Measurements Division at NIST as a Research Physicist and became Project Leader of NISTs program in solid state chemical sensing. Dr. Semancik’s work has included research on oxide surfaces, thin film growth, model catalytic systems, surface structural transitions, and the kinetics of fundamental surface reactions. His recent activities have been focused on developing improved materials for chemical sensing and combining active films with micromachined structures to realize advanced microsensor devices and operating modes. Dr. Semancik is a Fellow of the American Vacuum Society.
Richard E. Cavicchi is a physicist and co-project leader in chemical sensors at the National Institute of Standards and Technology. He received a BS in physics at MIT (1980) with a thesis on laser light scattering from colloidal crystals. At Cornell University he received a PhD in physics (1987) with a thesis on electron tunneling in small metal particles at low temperatures. While a post-doc at AT&T Bell Laboratories (1986–1988), he investigated carrier transport in quantum well devices. He joined NIST in 1989 where he has worked in the area of chemical sensors. This work includes the surface characterization of sensor interfaces, studies of sensor materials, micromachined device design, and novel sensing strategies.
M. Clayton Wheeler is a National Research Council Post-doctoral Research Associate at the National Institute of Standards and Technology in Gaithersburg, MD. He received his PhD in Chemical Engineering from The University of Texas at Austin in 1997. After graduation, he worked for two years as a Research Engineer for Texaco Inc., a global energy company, in Houston, Texas. He has been at his present position since 1999. His research interests include gas sensing mechanisms on oxide sensors, heterogeneous catalysis and microscale reaction phenomena.
Jason E. Tiffany received an MS in Chemical Engineering from Arizona State University in 1998. He has since worked in semiconductor manufacturing for Motorola and is currently investigating surface catalyst modifications for increased selectivity of tin oxide gas sensing arrays at the National Institute of Standards and Technology in Gaithersburg, MD.
Gregory E. Poirier completed his bachelor work at Indiana University, Bloomington, in 1986. His undergraduate research focused on time resolved fluorescence measurements of dyes in matrices. His graduate work, on ultra-high vacuum surface science and scanning tunneling microscopy studies of single crystal transition metal oxides, was conducted at the University of Texas, Austin, where he received his PhD in Physical Chemistry in 1991. The last summer of his PhD career was spent at Sandia National Laboratories where he investigated charge carrier dynamics in highly-excited semiconductor superlattices and quantum wells under the Outstanding Summer Student Program. Following his PhD, he spent two years at NIST as a National Research Council Post-doctoral Associate exploring oxygen depletion phenomena in nanothin metal-oxide films using ultra high vacuum surface analytical tools. On completion of his post-doctoral tenure, he joined the NIST technical staff and conducted research on crystalline structures, assembly mechanisms, and phase transitions of alkanethiol molecular monolayers on noble metal surfaces.
Robin M. Walton received a PhD in Chemical Engineering from the University of Michigan in 1997. She was a National Research Council Post-doctoral Associate at the National Institute of Science and Technology from 1997–1999. She is currently, a senior research scientist at Corning Incorporated. Her research interests include chemical microsensors, biosensors, and planar lightwave circuits.
John S. Suehle received his PhD degree in Electrical Engineering from the University of Maryland, College Park, in 1988. In 1981, he received a Graduate Research Fellowship with the National Institute of Standards and Technology (NIST), Gaithersburg, MD. Since 1982, he has been working in the Semiconductor Electronics Division at NIST where he is leader of the Dielectric Reliability Metrology project. Dr. Suehle has over 16 years experience in research investigating the failure and wear-out mechanisms of semiconductor devices. He is also involved in developing CMOS-compatible micro-electro-mechanical-systems (MEMS) devices for integrated sensor systems. Dr. Suehle is a senior member of IEEE and a member of Eta Kappa Nu.
Balaji Panchapakesan received a BS in Metallurgy & Materials science from Regional Engineering College in India. He is currently, a PhD student at the MEMS Laboratory in the Department of Mechanical Engineering at the University of Maryland, College Park. His current research interests include design, fabrication, and characterization of microsystems for MEMS based gas microsensor applications. His PhD work has involved development of new techniques for making nanostructured gas sensing materials that are fully compatible with the batch fabricated micromachined structures.
Donald L. DeVoe is an Assistant Professor of Mechanical Engineering at the University of Maryland, College Park. Dr. DeVoe received his PhD in Mechanical Engineering from the University of California, Berkeley. In 1997, Dr. DeVoe joined the Department of Mechanical Engineering at the University of Maryland, where he has a joint appointment with the Institute for Systems Research. He is a founding Director of the Center for Micro Engineering at the University of Maryland, where his interests include novel silicon microfabrication technologies, bioMEMS, and thin film piezoelectric microsystems. Dr. DeVoe received the 1999 NSF Presidential Early Career Award for his work in micromechanism technology. He serves on the Executive Committee for the MEMS subdivision of the American Society of Mechanical Engineers.
- 1
Current address: Science and Technology Division, Corning Incorporated, Corning, NY 14831.