Thesis proposals related to MEMS Alberto Corigliano

www.stru.polimi.it/mems

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

2 Research subjects which can be related to MS theses

1. MEMS reliability

2. MEMS modelling

3. Resonant accelerometers 4. Lorentz force based magnetometer 5. Technology related activity

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

3

6. Theoretical study and numerical modelling of solid damping

(thermoelastic + other solid damping phenomena also for

piezoelectric actuators)

7. Theoretical study and numerical modelling of van der Waals and

Casimir forces

8. Analytical & numerical models of dielectric accelerometers

9. Modelling, simulation and design of micro-pumps for drug delivery

10. Modelling, simulation and design of piezoelectric mems and energy

harvesters

Research subjects which can be related to MS theses

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

4 1. MEMS reliability

Objective: To deeply investigate issues related to micromechanical components

reliability (mechanical effects, rupture, spontaneous adhesion) Main achievements:

1.1 Experimental mechanical characterization of polysilicon through on-chip test methodology (elastic stiffness, tensile strength, Weibull approach, fracture, fatigue,…)

1.2 Experimental set-up for on chip testing with lock-in methodology 1.3 Theoretical, experimental and numerical study of spontaneous adhesion

phenomena in MEMS (stiction) 1.4 Study and modelling of moisture absorption in microsystems

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

1.1 Reliability - Experimental mechanical characterization of polysilicon through on-chip test methodology (elastic stiffness, tensile strength, fracture, fatigue, Weibull approach…)

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- Electrostatic actuators for tensile, bending, fracture and fatigue tests

- Electro-thermo-mechanical actuator for tensile tests

- Test structures for spontaneous adhesion detection

CV

Contact area SN

Contact area DX

020406080

100120140160

0 2 4 6 8

V force

C - o

ffset

[fF]

V pullinV pull out Hysteresis

amplitude

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

1.2 Reliability - Experimental set-up for on chip testing with lock-in methodology

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actuation voltage

sensing test signal

constrained moving

Vin(t)

Laboratory set-up for the execution of on-chip testing. Applied to fracture and fatigue tests, resonant accelerometer characterization

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

-1

-0.5

0

0.5

1

-0.02 -0.015 -0.01 -0.005 0

Displacement (µm)

Forc

e ( µ

m)

1.3 Reliability - Theoretical, experimental and numerical study of spontaneous adhesion phenomena in MEMS (stiction)

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detaching energy

meso-scale model for computing the detaching energy

FEM elastic-plastic analyses with adhesive contact

results

the adhesive contact model includes:

capillary attraction

depends on: • relative humidity • temperature • surface gap • shape of asperities

“dispersion” forces (Van der Waals, Casimir) depend on: • material features • surface gap • surface geometry

AFM measurements of surface roughness

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

8 2. MEMS modelling

Objective: To performe specific modelling activity for MEMS Main achievements:

2.1 Numerical modelling and simulation of fluid damping in MEMS at varying pressure

2.2 Numerical simulation of electrostatic problems: precise evaluation of capacitance and electrostatic force for complex geometries

2.3 Numerical modelling and simulation of accidental drop impacts

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

2.1 MEMS modelling - Numerical modelling and simulation of fluid damping in MEMS at varying pressure

9

Q e o ct o de a p ess o

10

100

1000

10000

100000

0.0001 0.001 0.01 0.1 1 10 100 1000Pressure [mbar]

Qua

lity

fact

or Q

Q (fit)Q (-3dB)

Example: damping regimes

fluid damping, rarefied regime: BGK model

solid/surface damping: e.g. thermoelasticity

Precise evaluation of quality factor Q at varying pressure. Applied to microphone and gyroscope

( )My by Ky F t+ + =

Q

Roszhart, 1990

F [µ

N]

b/b 0

fluid damping, continuum regime: Navier-Stokes

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

2.2 MEMS modelling - -Numerical simulation of electrostatic problems

Precise evaluation of capacitance and electrostatic force for complex geometries Applied to design of accelerometers and test device for stiction problems

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[V]

V = V0

V = 0 symmetry

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

2.3 MEMS modelling - Numerical modeling and simulation of accidental drop impacts

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- Large scale FE numerical simulations - Simplified procedure for a top-down approach with decoupled responses. - Assessment of safety against accidental drop - Simulation of fracture processes in polycrystals - Applied to design of accelerometers and microphone

DIE

SENSOR

PACKAGE

MICROSCALE

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

12 3. Resonant accelerometers

Objective: to develop a 3-axis resonant accelerometer in order to explore new

approach to shrink devices. Main achievements:

3.1 Analytical & numerical models and design of 1axis and 2axis resonant accelerometers (patent pending for 1axis, 2axis and z-axis)

3.2 Experimental activity on resonant accelerometers

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

3.1 Resonant accelerometers - Analytical & numerical models and design of 1axis and 2axis resonant accelerometers (patent pending for 1 and 2axis)

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Design of new devices

2

0 1 rr

r

N hf f

EIγ= +

- Resonant accelerometer detects the external acceleration by measuring the frequency variation of a resonating beam.

F=ma m

resonator

resonator length

spring

0fffNmaFa resonatorextext −=→→=→ ∆variationfrequency resonator in force axialforce inertialonaccelerati external →→→

resonator inertia

a

0

2

4

6

8

10

12

14

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

New geometry

Nr /F Optimal position of resonator

position

resonators

springs

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

3.2 Resonant accelerometers - Experimental activity on resonant accelerometers

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0 g

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

15 4. Lorentz force based magnetometers

Objective: to study and develop Lorentz force based magnetometer in Thelma process

Main achievements:

5.1 Study and development of Lorentz force magnetometers 5.2 Development of coupled electro-mechanical models for the simulation of

sensing in magnetic fields (new, in progress)

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

16 4.1 magnetometers - Study and development of Lorentz force magnetometers

Magnetometer with 2 couples of differential parallel plates capacitors

Magnetometer with 16 couples of differential parallel plates capacitors

Design of various devices on kit part ck391

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

17 5. Technology related activities:

Objective: to help new technology development with dedicated simulation activity Main expected achievements (new, in progress):

5.1 Study and modelling of the moulding process 5.2 Study and modelling of the metal bonding process 5.3 Improvement of the etching process

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

18 5.2 Technology related activities - Study and modelling of the metal bonding process

Finite Element modelling of the thermo-compression phase, shape optimization AFM and spectral examination of

metal-bonded surfaces

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

6. Theoretical study and numerical modelling of solid damping (thermoelastic damping) Theoretical study and computational models for the correct evaluation of thermoelastic damping in MEMS. Possible applications to resonators, resonant accelerometers, gyroscopes…

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FEM-based discretization of thermoelastic problem

1.E+03

1.E+04

1.E+05

1.E+06

0.1 1 10f/f0

Q

QTED theoryQTED EFQTED exp

1st mode2nd mode

3rd mode

E 150GPa ρ 2330 kg/m3 ν 0.2 C 700 J/(kg · K) α 2.6·10-6 1/K k 148 W/(m · K)

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

7. Theoretical study and numerical modelling of van der Waals and Casimir forces

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• “retarded regime” of van der Waals forces (polarization of nearby molecules is “retarded”)

• relevant for separations ranging from 20÷50 nm to 300÷400 nm • attractive pressure for perfectly conductive infinite parallel surfaces:

• may become repulsive, depending on material properties and on surface geometry • Experimental test on Casimir force

2

4240cq

Dπ

=

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

9. Modelling and simulation of micro-pumps for drug delivery (design of parts in kit part 2010, possible patent, possible future EU FP/ project with ST)

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Emptying:

elastic recovery

Filling:

voltage is applied

Electro-mechanical static simulations Pull-in simulation: unstable regime Electrostatic-fluid-structure dynamic simulation Design of prototype produced with process for pressure sensors

Alberto Corigliano - Micro Electro Mechanical Systems (MEMS)

10. Modelling, simulation and design of piezoelectric mems and energy harvesters

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Figure from Roundy et al. (2005)