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This
project exploits the concept of change in the oscillating frequency and
modulating the drain current of MOS integrated cantilever structure, caused by
the binding of an analyte to the cantilever. This requires design and
development of high sensitivity, high resolution innovative functionalized
cantilever, which is a real technological challenge. The toughest landmark of
the project will be the integration of MEMS structure with CMOS process leading
to the development high resolution high sensitivity device for early diagnostic
of deadly diseases. This research proposal is a step towards conceptualizing
the design, fabrication and testing of MEMS integrated CMOS system on chip Soc
capable of performing real time bio-moleular analysis, and early diagnostic of
deadly diseases.

In
the present research project we plan is to design and develop a high
resolution, high sensitivity MEMS and CMOS integrated system on chip. These
CMOS based MEMS micro-array will be capable of bio-molecular sensing in
attogram range for an early diagnostics of toxins, hormones, proteins,
bacteria, and DNA strands etc. The SoC planned to be developed in this project
will also be capable of performing the real time analysis of reaction of an
antibody to its antigen.

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Out
of several emerging techniques for sensing, diagnostics and measuring the
bio-molecular concentration, the micro-cantilever detection paradigm has
attracted considerable attention in recent years. Ion-Sensitive Field Effect
Transistor ISFET and frequency shift of micro-cantilever are used to detect the
label-free bio-molecules. However, life time of the ISFET is limited due to
fast degradation of gate oxide in the presence 
of the bio-molecules, whereas the micro-cantilever requires bulky
circuits to detect the electrical signal that consumes high power. An
MOSFET-embedded micro-cantilever for measuring deflection caused by the binding
of bio-molecules has been proposed by Shekhawat et. al. This approach relies on
the stress induced in the channel region of the MOSFET embedded cantilever due
to bending of the cantilever. The stress caused by the binding of bio-molecules
to immobilized cantilever modulates the output drain current leading to
detection of diverse bio-molecular or chemical recognition events or measuring
the activity of a biochemical in an organism. However, such a scheme has a
severe drawback of poor sensitivity and resolution and attogram range
resolution cannot be achieved.

A
better approach of modulating the channel of MOSFET and its output drain
current could be changing the gate voltage by using the sensitized layer coated
cantilever to sense the bio-molecule or bio-chemical reaction, which is
referred as static property. In addition, it is proposed to combine the dynamic
property obtained from the change in the frequency of the oscillating
cantilever along with the static content providing another degree of freedom in
the sensing technique. In this process the gate of the MOSFET and the
micro-cantilever are to be integrated with the chosen chemical sensing layer.
To reduce the power consumption and enhance the life-time of sensing devices,
an integrated approach of micro-cantilever embedded MOSFET is proposed to be
developed in the present research project. The static property accounting for
the change in operating point and drain current of the MOS structure, and
dynamic property derived from the change in oscillating frequency of the
cantilever will be used to obtain high resolution and sensitivity.

Operation
of the proposed Project

Here, we propose the use of 2D
microcantilever arrays with geometrically configured metal-oxide semiconductor
field-effect transistors (MOSFETs) embedded in the high-stress region of the
microcantilevers to measure deflections induced by biomolecular binding.

The
two arrays of MosFET MEMS, each have been considered; one with receptor layer,
and the other one without receptor layer to be used as a reference. When
the target molecules attach to their functionalized surface, the surface stress
distribution on the surface is changed causing deflections in the cantilever.
During adsorption of target molecules onto the functionalized cantilever surface,
biochemical reactions occur which reduces the free energy of the cantilever
surface. The reduction in free energy of one side of cantilever is balanced by increase
in strain energy of the other side, producing deflection in the cantilever. The
deflections may be upward or downward depending on the type of molecules involved
and are linearly proportional to the target analyte solution concentration. It
means that higher deflections manifest higher sensitivity in the cantilever biosensor.

When a microcantilever bends as a
result of adsorption-induced surface stress, the modulation of the channel
current underneath the gate region results from altered channel mobility of the
transistor due to increased channel resistance. As fixed biased voltages are applied
on the gate and source-drain region of the transistor, any change in channel
mobility will result in change in the drain current of the transistor.

Because
MOSFETs and contact pads are passivated with a thin coating of silicon nitride,
they are inherently protected from any environmental influence; thus, their
performance is not compromised by contact with gases or corrosive liquids such
as saline solution. The MOSFET-embedded microcantilever detection approach is
illustrated in Fig. 1

The
output of these two MOSFET are passed through a differential stage. Using the
differential stage leads to the cancellation of noise, and hence improves SNR.
The frequency shift can be obtained through correlating the output of the .differential
stage corresponding to sensing array with that of the reference one.

This
output of differential unit is then passed to microcontroller which has two functionalities.
Firstly it will Display the result on screen, so user can understand the result.
Secondly it will connect to Lab/Hospital server, so a detailed report can be
generated

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