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Surface Micromachining Piezoresistive Pressure Sensor

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Suzy Tan

on 10 February 2015

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Transcript of Surface Micromachining Piezoresistive Pressure Sensor

MEMS and Microsystems:
Surface Micromachining Piezoresistive Pressure Sensor


Background information
Background Information
Concept (1)
How would the design look like?
Based on the chip of 1cm x 1cm, what would be the dimensions of the various components in the MEMS device?
How is the device going to be fabricated?
Sketch of Surface Micromachined Piezoresistive Pressure Sensor, with parts identfied.
Jun Hong
Jing Han

Sophia Sun, Graduate of DEEE. She is working in
DenseLight Semiconductor
as Engineering Assistant.
Deals with the
Design and Manufacture of MEMS devices
Research on
Surface Micromachined Piezoresistive Pressure Sensor

Why do we need the device?
What are its uses?
How does it work?
How does the device look like?
What are its dimensions?
How would the device be fabricated?

What methods of fabrications would be used?

What other factors are important in the fabrication of pressure sensor?
Why is there a need for the device?
in a motor vehicle.

draw a line between safety and danger

There is
a need
for the air-bag in the car
to be activated in case of accident

It can
help saving lives
in traffic accidents, which happens in many places.
Concept (2)
sensor fabrication opportunities

processing technology

Different pressure levels can be achieved
according to the application

Various sensitivies
can be obtained

Protect and save
How does it work?
When the piezoresistors are
causing its
resistance to change

The change of
resistance will exhibit a change
in the output voltage which
sends a signal
to a device, whether it be a
microactuator or a recorder.
Theory of Design
The design
requires several dimensions from calculations
of the various componments.

Several formula were used
to calculate
the important
values and dimensions
that are
required for the pressure sensor
Such as:
Junction depth of the piezoresistors
Resistance of the piezoresistors
Maximum stress of the pressure plate
Maximum deflection of the pressure plate
Thank You!
Nв = 7 x 10^15cm^-3
N(x) = Nmax e –(x-Rp) ^2 / 2▵Rp^2 , where Nmax = Q / √2(▵Rp)
Phosp = n-type
Use 100 keV
Rp = 13.5nm = 135 x 10^-7cm
▵Rp = 53.5nm = 535 x 10^-7cm
Assuming Nmax = 10^20cm^-3
7 x 10^15cm^-3 = 10^20 e –(x-Rp) ^2 / 2▵Rp^2 , when N(x) = Nв
In[7 x 10^15/10^20] = -(x-Rp) ^2/ 2▵Rp^2
-(9.57) = -(x-Rp) ^2/ 2▵Rp^2
(x-Rp) ^2 = (2)(9.57)(53.5 x 10^-7)^2
x-Rp = 23.40 x 10^-6
x = 23.40 x 10^-6 + 135 x 10^-7
= 0.369 x 10^-4
= 0.369µm
Junction depth
Resistance = PL / A
= (2) x (500 x 10^- 4) /
(500 x 10^- 4) x
(0.369 x 10^- 4)
= 54.2kΩ
Resistance, R₁ = 54.2kΩ
Where R₁ = R₂ = R₃ = R₄, when not under stress.
Resistance of Piezoresistor
Finding the maximum deflection,
ω(max) = 0.0138pa^4 / Eh^3
= (0.0138) x (10 x 10^6)
x (1000 x 10^-6)^ 4
/ (1.6 x 10^11)
x (50 x 10^-6)^3
= 6.9µm
Maximum stress of Pressure Plate
Finding the maximum stress,
σ(max) = 0.308pa^2 / h^2
= (0.308) x (10 x 10^6) x
(1000 x 10^-6)^2 / (50 x 10^-6)^2
= 1232000000 Pa
= 1232 MPa
Maximum deflection of Pressure Plate
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