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Advanced Sensors

Subprojects and Devices:
Polymer Tactile Sensors
Hot Wire Anemometry
Biologically Inspired Sensors
Polymer Deposition Monitoring
Sensors Slide Show

Project Overview:

A continuing major thrust in our research group is the development of low-cost, high performance micro sensors using highly efficient microfabrication technology and, in certain cases, new materials. MEMS technology offers many advantages in sensor applications including miniaturized sizes, high response speed (mechanical and thermal), and arrayed sensor capabilities. It is also possible to directly integrated micromechanical elements with microelectronics for local signal processing, resulting in lower the signal-to-noise ratios and detection limits.

The low cost aspect of integrated sensors is a strong driver in our research. To address this challenge, novel materials and fabrication processes are needed. Silicon, a common material for micromachining, is brittle and not the most ideal material for many physical sensors. In addition, silicon substrates are expensive and non-conformal. Hence, an important effort in our group is to develop polymer based microfabrication technology and create sensors that do not use silicon. This lowers cost and increases mechanical robustness as polymers are generally more durable than silicon or silicon-based thin films such as silicon nitride and silicon dioxide. Beneficial uses of our sensors can be found in robotics, automotive, and military applications.

Polymer Tactile Sensors:

Tactile sensors are important devices within the robotics industry. Advanced tactile sensors with high spatial resolution can be efficiently fabricated using micromachining technology. The use of polymers results in sensors that are conformal, inexpensive, and robust. We have used LCP and polyimide to produce individual sensors and sensor arrays that act as "smart skin." The fabrication process results in sensors with high spatial resolution and sensitivity.

Images:

1. A polymer tactile sensor

Related Papers:

1. J. Engel, J. Chen, B. Flachsbart, J.C. Selby, M.A. Shannon, C. Liu, "Development of Polyimide-based Flexible Tactile Sensing Skin," Materials Research Society Fall Meeting, Boston, MA, 2-6 December 2002.

Hot Wire Anemometry:

We have developed hot-wire anemometers (HWAs) that are fabricated with high yield and low cost, and can be easily packaged for boundary flow studies. The sensor is elevated above the substrate using magnetic assembly and has a time constant of less than 50 microseconds. The nature of the fabrication process allows for the production of large arrays of sensors in localized areas on flexible substrates.

Images:

1. An SEM micrograph of a triple point HWA

Related Papers:

1. J. Chen, J. Zou and C. Liu, "A Surface Micromachined, Out-of-Plane Anemometer," Proceedings of MEMS 02, Las Vegas, NV, 2002.

Biologically Inspired Sensors:

Biological systems have developed over billions of years and offer excellent examples of highly sensitive, versatile, and robust sensors. A classical example of a biological sensor is the haircell, a mechanoreceptor. Haircells are used for many biological functions including invertebrate hearing and equilibrium, insect flow sensing, fish lateral line flow sensing, and insect priopreceptors. We have developed an artificial MEMS haircell sensor. The sensor consists of a horizontal cantilever beam with a vertical cilium attached at its free end. Any mechanically induced displacement to the vertical cilium causes the horizontal beam to bend, resulting in an electrical output via a piezoresistive element embedded at the base of the horizontal cantilever.

Images:

1. An SEM micrograph of a single haircell sensor

Related Papers:

1. Z. Fan, J. Chen, J. Zou, D. Bullen, C. Liu, F. Delcomyn, "Design and Fabrication of Artificial Lateral-Line Flow Sensors," Journal of Micromechanics and Microengineering, Vol. 12, No. 5, pp. 655-661, September 2002
2. Z. Fan, J. Chen, J. Zou, J. Li, C. Liu, F. Delcomyn, "Development of Artificial Lateral-Line Flow Sensors," Proceedings of the Solid-state Sensors and Actuators Workshop, Hilton Head Island, June 2002.
3. J. Li, Z. Fan, J. Chen, J. Zou, C. Liu, "High Yield Microfabrication Process for Biomimetic Artificial Haircell Sensors," Smart Electronics, MEMS, and Nanotechnology Conference (4700), SPIE's 9th Annual International Symposium on Smart Structures and Materials, 17-21 March 2002, San Diego, CA.

Polymer Deposition Monitoring:

Parylene is an important polymer used in microfluidic MEMS applications. It is useful since it can be conformally deposited from a vapor at room temperature in a vacuum. Unfortunately, current deposition systems do not allow for the monitoring of film thickness. We have designed and fabricated a Parylene thickness monitor that uses heat transfer across a gap of known dimensions to calibrate the deposition process.

Images:

1. An optical micrograph of a parylene deposition sensor

Related Papers:

1. W. Sutomo, X. Wang, D. Bullen, S. Braden, C. Liu, "Development of An End-Point Detector for Parylene Deposition Process," Journal of Microelectromechanical Systems, in press.