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Surface Micromachining Piezoresistive Pressure Sensor

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by

Suzy Tan

on 10 February 2015

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Transcript of Surface Micromachining Piezoresistive Pressure Sensor

(ET0909)
MEMS and Microsystems:
Surface Micromachining Piezoresistive Pressure Sensor

Content

Background information
Concept
Design
Implementation
Background Information
Concept (1)
Design
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?
Implementation
How is the device going to be fabricated?
Sketch of Surface Micromachined Piezoresistive Pressure Sensor, with parts identfied.
Suzy
Jun Hong
Samuel
Jing Han

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

Conceive
Why do we need the device?
What are its uses?
How does it work?
Design
How does the device look like?
What are its dimensions?
Implementation
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?
Example:
Airbags
in a motor vehicle.

Inventions
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.
Examples
Concept (2)
Benefits
-
Low-cost
sensor fabrication opportunities

-
Mature
processing technology

-
Different pressure levels can be achieved
according to the application

-
Various sensitivies
can be obtained

-
Protect and save
lives
How does it work?
When the piezoresistors are
stressed
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.

Method
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
Dimensions
Conclusion
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
Full transcript