Poster Presentation Final

Detection of DNA Hybridization with a BioFET Sensor Acknowledgments Stanford EE REU 2008 Nishi Group Michael Chu Mentor: Kosar Parizi Faculty: Professor Yoshio Nishi Stanford University Electrical Engineering Objective The primary motivation for a Bio-Field Effect Transistor is the ability to function as a real-time and massively parallel sensor. We sought to design a BioFET device capable of detecting the hybridization of DNA. We particularly emphasize the implementation of a back bias to improve sensitivity. We also consider the effects of changing doping concentrations and patterns. Methods We used Sentaurus Structure Editor to integrate device components into a mesh. We used Sentaurus Device to run the simulation. We used TecPlot to verify the successful simulation of the doping types, as shown below. We see both npn and npp+ configurations. Figure 3. Shift of V G when charge density changes Figure 4. Our BioFET Figure 6. Two simulated doping patterns Results Shown below are the results of our simulations. Let’s compare the curves when V D = 1V. For PPP, the current at the threshold of 1 V is 7 x 10 -10 A. For PPP+, the current at .75 V is 1.6 x 10 -8 A. The improvement in sensitivity is determined by the difference in sub-threshold slopes of the curves. So slope PPP+ / slope PPP = 30.5 ≈ 30 times more sensitive ! Figure 7. Comparison of IV curves for different devices. Conclusions & Future Work Using simulations, we have determined that the doping configuration which would allow the greatest device sensitivity is PPP+. We will check P+ on the source (P+PP+) as one more test. Therefore, we can now begin fabrication of such a device and measure its IV characteristics. References T. Sakata et al., Jap. J. of App. Phys., Vol 44, No. 4B, 2005, pp. 2854-2859 D. Kim et al. Biosensors and Bioelectronics. Vol 20, 2004, pp 69-74 J. Fritz et al. PNAS. Vol. 99, 2002, pp 14142-14146. J. Hahm et al. Nano Letters. Vol 4. No.1. 2004. pp. 51-54. Background In the rapidly thriving industry of medical devices, a BioFET can be implemented for the detection and identification of diseases such as cancer. The key fundamental concept with this device is that the gate bias is controlled by the negatively charged DNA. Hybridization increases this negative charge which is changed into an electrical signal via the field effect. Hypothetical IV G Curves for a: MOSFET BIOFET --- At a ref V G --- Funct. Surface --- DNA Immob. --- Hybrid. Of DNA PDMS Microfluidic Channel --- At a ref VG --- Funct. Surface --- DNA Immob. --- Hybrid. Of DNA N-P-N N-P-N N-P-P+ N-P-P+ ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],50 nm Figure 5. Electrode Schematic Note the specific gate region defined by the aqueous solution conducting a voltage from the solution electrode Solution Electrode Aqueous Solution (conductive) Gate Source Body Drain I D V G V t Increase in P doping Figure 2. Effect of doping concentration on current for a double sided gate device. The threshold voltage is directly related to the thickness of the silicon Between the two doping patterns we change the doping type of the drain. Not shown here is PPP+, the configuration with the best sensitivity. Double Sided Gate Structure Map of Device Doping Source | Bulk | Drain 50 um Figure 1. Generic BioFET Note the similarities to the conventional MOSFET (Sakata et al.) I D V G ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

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