Download EEE 488 Senior Design Group 12

Hybrid Molecular MOSFET
Chemical Sensor
12.11.02
- Group Members: Robert Anderson,
Fesaha Gebrehiwot, Stephanie Padilla, and
Ari Vogel
- Project Advisor: Dr. Trevor Thornton
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 Applications
The HM-FET has a wide range of envisioned applications.
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DNA decoder
Crime scene investigation
Medical applications
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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. Experimental
pH Sensor (150nm, W/L=1/6.2, Vd =100mV)
1.00E-06
-7
-6
-5
-4
-3
-2
Log Drain Current [A]
-8
-1
0
1.00E-07
1.00E-08
1.00E-09
Substrate Voltage [V]
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
-6.35
0
1
2
3
4
5
Threshold Voltage [V]
-6.4
-6.45
-6.5
-6.55
-6.6
-6.65
pH Level
Hybrid Molecular-Semiconductor
Chemical Sensor
6
7
8
Experimental (From B. Reddy)
1.00E-05
1.00E-06
1.00E-07
1.00E-08
1.00E-09
Baseline
PH 4
1.00E-10
PH 2
PH 1
1.00E-11
Threshold
1.00E-12
1.00E-13
-15
-10
-5
0
Hybrid Molecular-Semiconductor
Chemical Sensor
5
10