Hybrid Molecular-Semiconductor Chemical Sensor

12.11.02

- Group Members: Robert Anderson, Fesaha Gebrehiwot, Stephanie Padilla, and Ari Vogel

- Project Advisor: Dr. Trevor Thornton

Hybrid Molecular MOSFET Chemical Sensor

Hybrid Molecular-Semiconductor Chemical Sensor

Abstract

This project aims to develop a Hybrid Molecular MOSFET chemical sensor that is highly integrated, inexpensive, and versatile. The sensor consists of a polarizable molecular monolayer that adheres to an underlying CMOS-compatible integrated circuit. The molecular monolayers are designed in such a way that their physical structure changes after exposure to the chemical of interest. The change in physical structure leads to a change in their electrical polarization, which is detected by a sensitive transistor immediately below the monolayer. A simple pH sensor was realized in order to demonstrate the working principles of the HM-FET.

Hybrid Molecular-Semiconductor Chemical Sensor

Theory

The HM-FET chemical sensor is based on a fully depleted Silicon-on-Insulator (SOI) MOSFET. Due to the buried oxide in an SOI structure, the substrate voltage can be used in place of a conventional gate voltage. This allows the active surface to be free of any metal contacts. The channel is 150nm thick, and therefore the threshold voltage of the device can easily be controlled by the charge accumulated on the surface of the device. As the charge increases at the surface, additional carriers are available to allow greater current flow. Also, the native oxide of the silicon channel can be used as a bonding film for attaching the monolayer to the device.

Hybrid Molecular-Semiconductor Chemical Sensor

Hybrid Molecular-Semiconductor Chemical Sensor

Sensor ApplicationsThe HM-FET has a wide range of envisioned applications.

 

          DNA decoder

                        Crime scene investigation

                        Medical applications

 

          Chemical sensor

                        Planetary exploration

                        Detection of harmful natural gases

                        Detection of biological or chemical agents

                        pH sensor

Hybrid Molecular-Semiconductor Chemical Sensor

Conclusion

From the experimental and simulated results, a working pH sensor was constructed. The pH sensor demonstrates the working principles of an HM-FET by observing shifts in the threshold voltage when a charge is present at the surface of the device. The diverse applications of the HM-FET along with their benefits are evident, and therefore the team recommends that this design project be further pursued. The HM-FET can be used to make the world a safer and more educated place, and the technology is very close to being available to the public.

Hybrid Molecular-Semiconductor Chemical Sensor

Hybrid Molecular-Semiconductor Chemical Sensor

Atlas Device Model

Hybrid Molecular-Semiconductor Chemical Sensor

Matched Simulated vs. ExperimentalpH Sensor (150nm, W/L=1/6.2, Vd=100mV)

1.00E-09

1.00E-08

1.00E-07

1.00E-06

-8 -7 -6 -5 -4 -3 -2 -1 0

Substrate Voltage [V]

Lo

g D

rain

Cu

rren

t [A

]

pH4 q1=1.5, q2=2.6, int1=1e10, int2=9e10 pH2

q1=1.57, q2=2.6, int1=1e10, int1=9e10 DI-H20 q1=1.43, q2=2.6, int1=1e10, int2=9e10

Hybrid Molecular-Semiconductor Chemical Sensor

Linear Relationship Vth

pH Level vs. Threshold Voltage

-6.65

-6.6

-6.55

-6.5

-6.45

-6.4

-6.35

0 1 2 3 4 5 6 7 8

pH Level

Th

resh

old

Vo

ltag

e [V

]

Hybrid Molecular-Semiconductor Chemical Sensor

Experimental (From B. Reddy)

1.00E-13

1.00E-12

1.00E-11

1.00E-10

1.00E-09

1.00E-08

1.00E-07

1.00E-06

1.00E-05

-15 -10 -5 0 5 10

Baseline

PH 4

PH 2

PH 1

Threshold