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Interaction Between CMOS Nonvolatile Charges and Molecules in Solution

Zengtao Liu, Gen Pei, Yumin Shen, and Edwin Kan*

School of Electrical and Computer Engineering, Cornell University,
Ithaca, NY 14853 USA

This is an abstract for a presentation given at the
10th Foresight Conference on Molecular Nanotechnology

 

Reliable and sensitive functional interface between integrated electronic devices and ions/molecules in solution is the key missing link for sensing and actuation in biomedical device applications. It can be observed that electrostatic forces are not only the basic forces in chemical covalent, ionic and hydrogen bonds, but also the main driving forces for carriers in semiconductor electronic and MEMS devices. Electrostatic forces obtained from applied potential difference are always attractive, except in fringing cases [1]. This will severely limit the device design for interaction with polar molecules. On the other hand, for electronic device structures that can generate, retain and reset nonvolatile charges in the floating gate, there are many more degrees of freedom in design. An illustrative device design modified from a conventional EEPROM cell is shown in the attached figure, and the measured IV characteristics are also shown. First, the interaction force can be either attractive or repulsive [2,3], controlled by the polarity of the nonvolatile charges in the floating gate. Also, since no direct current is necessary, isolation and contamination control can be achieved in a straightforward manner. Furthermore, the extension of the floating gate separates the structure in contact with the solution and the actual sensing transistor, which enables the use of aggressive FET design for ultimate sensitivity. In comparison with the nano-wire FET structure for similar sensing purposes [4], the new device provides much easier operations, more accuracy and larger dynamic range. As shown in the figure, either the threshold voltage shift can be used for large signal, or the channel current in the different-pair setup can be used for extremely minute traces of polar molecules. Multiple floating-gate extension structures with electrostatic (capacitive) coupling are also the base structure for translinear circuits and neuron MOSFET [5], which can allow further built-in analog functions with minimal number of devices. The proposed polar molecular sensors also exceed in many aspects in comparison with conventional MEMS-based chemical sensors [6].

References:

  1. W. C. Tang, M. G. Lim, and R. T. Howe, "Electrostatically balanced comb drive for controlled levitation," Tech. Dig., IEEE Solid-State Sensor and Actuator Workshop, pp. 23, 1990.
  2. Z. Liu, M. Kim, N. Shen and E. C. Kan, "Novel Electrostatic Repulsion Forces in MEMS Applications by Nonvolatile Charge Injection, " The 15th IEEE Robotics and Automation Society Conference on Micro Electro Mechanical Systems (MEMS), Las Vegas, NV, Jan. 22-24, 2002.
  3. E. C. Kan, Z. Liu, P. Wang, M. Kim, Y. N. Shen and G. Pei, "Si Fleas: Technology Demonstration of Functional Modules in Submillimeter Autonomous Microsystems", Invited talk, Ninth Foresight Conference on Molecular Nanotechnology, Santa Clara, CA, Nov. 9-11, 2001.
  4. C. Lieber, Science, August 17, 2001; vol. 293, pp. 1289-1292.
  5. J. M. Rabaey, Digital Integrated Circuits, Chapter 10, Prentice Hall, 1996.
  6. G. T. A. Kovacs, Micromachined Transducers Sourcebook, McGraw-Hill, 1998.

Abstract in Microsoft Word® format 141,126 bytes


*Corresponding Address:
Edwin Kan
School of Electrical and Computer Engineering, Cornell University
404 Phillips Hall, Ithaca, NY 14853 USA
Phone: 607-255-3998 Fax: 607-254-4565
Email: kan@ece.cornell.edu
Web: http://people.ece.cornell.edu/kan



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