Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences


UC Berkeley


2008 Research Summary

WetFET Fluidic Gate-Dielectric Transistor for Sensor Applications (WetFET)

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Donovan Lee, Xin Sun, Helen Tran and Tsu-Jae King Liu

The sensitivity of a MOSFET's performance to variations in gate dielectric properties is well known. This sensitivity lends itself perfectly to the MOSFET's utilization as a sensor. Modern biosensors employ gaps with dimensions on the nanometer scale, with their sidewalls functionalized to bind to particular target molecules (such as DNA). Changes in the electrical properties of a nanogap can be detected via resistance or capacitance measurement. Since a modern MOSFET has gate dielectric thickness in the range of nanometers, it is ideal for adaptation as a nanogap sensor. Furthermore, the use of a MOSFET to sense changes within a nanogap that constitutes a portion of the gate dielectric offers the advantage of signal amplification--a feature unique to transductive sensors (not found in 2-terminal sensors).

The WetFET is a fluidic gate-dielectric transistor with intended applications in chemical/biological sensing [1]. Process development and a proof of concept have been successfully conducted and the current phase of the project involves the encapsulation of the sensor element in a nanofluidic chamber. Additional applications based on the WetFET CMOS modification have been developed and explored [2] for high-performance CMOS.

Figure 1
Figure 1: The WetFET sensor is created by invoking a simple post-CMOS device modification which clears the underside of the gate and inserts fluid into the resultant nanogap.

D. Lee, X. Sun, E. Quevy, R. T. Howe, and T.-J. King, "WetFET--Novel Fluidic Gate-Dielectric Transistor for Sensor Applications," IEEE VLSI-TSA Meeting Technical Digest, 2007, pp. 124-125.
D. Lee, T. Seidel, J. Dalton, and T.-J. King Liu, "ALD Refill of Nanometer-Scale Gaps with High-k Dielectric for Advanced CMOS Technologies," Electrochemical and Solid-State Letters, Vol 10, Issue 9, 2007, pp. H257-H259.