幻灯片 1 - KOCW
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Transcript 幻灯片 1 - KOCW
Homework:
Resemble the case of trapezoid cross section in Page 47-48, try to calculate
the moment of inertia of a “T”-shaped cross-sectional beam
a1
b1
b2
a2
Review of important formulas for
bending stress and strain of a beam
Uniform acceleration
How about a double-clamped beam
with self-weight loading?
Analysis and design rule of the beam bending problem
Cantilever can be used not only for mechanical sensors
and probes, but also for bio/chemical sensors
1.1. How Cantilever as a Sensing Platform?
Cantilever-mass micromachining structures have been long-period
used in MEMS inertial sensors: Accelerometers and Gyroscopes, etc.
Comb damper
Seismic mass
Bending cantilever
beam
a
Mass legs
Piezoresistor embedded
axial beams
Reference
resistors
S. Huang, Xinxin Li, Transducers’03
Xinxin Li, M. Bao, Transducers’99
• In an inertial sensor, the spring deformation is
forced by a seismic mass, i.e. a bulk effect
• In a bio/chemical sensing cantilever, the seismic
mass is no use but surface effect becomes to work
Antibodies
with
bacteria
What causes this change?
Different sensing mechanism for bio/chemicals
Two sensing interfaces: both contribute to sensitivity/selectivity in different ways
Bio/Chemical
Physical
Enzymatic
Microbial / Cell
Immunological
DNA
Organic
…
Analyte
Recognizing
materials
Informatics
Electrochemical:
Amperometer, Potentiometer, ISFET, …
Thermal:
Calorimeters, DSC…
Mass or Mechanical:
SAW, QCM, Cantilever, …
Signal
Processing
Circuit
Optical:
Interferometer, Spectrometer, SPR, …
…
Transducers
Circuit
Signal
Science, 1997 by IBM Zurich reported that self-assembly of SAM on
Au surface generates nano-mechanical surface-stress that was
measured by a micro-cantilever and signal read out by an AFM
photonic detector.
Although studies have tried to find the origin of surface-stress
generation, the molecule-level mechanism on the self-assembly
induced surface-stress is still ambiguous.
During the chemical sensing experiment in last section, using
ammonia to replace the tri-methylamine vapor in the experiment
results in no significant frequency-shift measured. Though their
chemical principles are similar, apparently the size of the ammonia
molecule is much smaller than that of the tri-methylamine.
Thus, the mechanism of surface-stress generation during specific
molecules binding on a solid surface is strongly dependent of the
molecule size or other principles.
1.2. Why Cantilever Promising for
Bio/Chemical Detection?
(1) Static cantilever for specific-reaction-induced surface-stress sensing
Single DNA hybridization recognized
Sub-nanometer bending is self-sensed
“Translating Bio-molecular
Recognition into Nano-mechanics”
Science 288 (2000) by IBM
P. Li, Xinxin Li, APL 2000
Proxi-Lever with thiol-SAM of 6MNA on Au
surface for 20ppt-resoluble trace TNT detection
-
-
O
CO
O
CO
O
CO
O
CO
O
CO
O
-
-
SiO2 surface
Au surface
S
S
S
S
S
S
Si
Sens. cant.
O
O
Si
O
O
O
Si
CF2
CF2
F2C
F2C
CF2
CF2
F2C
F2C
CF2
CF2
F2C
F2C
CF2
CF2
F2C
F2C
CF3
CF3
O
Si
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
Si
O
O
CF3
CF3
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
Si O
O
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
Si
O
Ref. Cant.
O
O
O
O
O
S
CF3
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF2
Si
CF2
CF2
F 2C
F2C
CF2
CF2
F 2C
F2C
CF2
CF2
F 2C
F2C
CF2
CF2
F 2C
F2C
CF3
CF3
O
Si
Si
CF2
CF2
F2C
F2C
CF2
CF2
F2C
F2C
CF2
CF2
F2C
F2C
CF2
CF2
F2C
F2C
CF3
CF3
SiO2 surface
O
O
O
O
Si
CF2
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF3
O
O
Si
CF2
F2C
CF2
F2C
CF2
F2C
CF2
F2C
CF3
O
100
CF3
SiO2 surface w/o FAS-17 modification
Response voltage (V)
-
-
CO
-
CO
O
Cu2+ Cu2+ Cu2+ Cu2+ Cu2+ Cu2+
SiO2 surface modifed with FAS-17
80
95%
60
74%
40
51%
20
33%
11%
0
0
5
10
15
20
25
Time (min)
P. Li, Xinxin Li, et al, APL 2006 and JMM 2007
Siloxane-head bi-layer modified on SiO2
surface for long life-time TNT detection
2
Sensing Canti.
quad-cantilever sensor
-2
-4
-6
-8
-10
-12
0
5
10
15
20
25
30
Time(min)
after 140 days
the 1st-time test
Response Voltage (V)
Sensing Canti.
Respone Voltage(V)
0
0
0
-5
-5
-10
-10
-15
-15
0.
-20
0
5
10
Time (min)
-20
0
5
10
15
Time (min)
How to design the static cantilever for
specific-reaction induced surface-stress
Stoney’s equation:
3L (1 )
z
s
2
Et
2
When the cantilever is bent by uniformly distributed
loading surface stressσs, the free-end bending moment
is M=Δσst/2, where w is the cantilever width.
the radius of the deflective cantilever, R, can be expressed as
1
M
s whn
R EIeff ( EI )eff
( EI ) eff
and
.
Ei
wi (
(t i3 / 12 t i (hi hn ) 2 ))
1 i
hn (i Ei hi t i ) /(i Ei ti )
The bending stress at the piezoresistive layer
can be expressed is
1
Esi ( hn ht )
R
where Esi is Young’s module of silicon, ht is the distance between the upper
surface of the cantilever
and the piezoresistor layer.
Esi hn (hn ht )
s
( EI )eff
represents the mechanical sensitivity of the piezoresistive cantilever
How to know the surface-stress value induced by
a certain specific molecule binding? Only be
experimental results? Is there and design model?
By now no people in the world knows it in details?
You can try and publish the results in Science or
Nature
Key points for micro-nano compatible cantilevers:
Top down
Combination
Bottom up
Atomic behavior
Seamless
coupling
Continuum mechanism
Informatics
Bio-molecule
Nano
BNI
Fusion
Road map for recent work
Bio-Nano Binding
Nano-Micro Coupling
Bio-Nano-Informatics
(BNI) Fusion
In farther future … …
“There's plenty of room at the bottom”
(R. P. Feynman)