Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

MEMS/NEMS and BioMEMS/BioNEMS 

Materials and Devices and Biomimetics 

Prof. Bharat Bhushan 

Ohio Eminent Scholar and Howard D. Winbigler Professor 

and Director NLBB 

Bhushan.2@osu.edu 

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 

© B. Bhushan 

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Outline 

• Background 

Definition of MEMS/NEMS and characteristic dimensions 

Examples of MEMS/NEMS and BioMEMS/bioNEMS with nanotribology 

and nanomechanics issues 

 

Biomimetics – Lessons from Nature 

• Experimental 

Atomic force/Friction force microscope (AFM/FFM) 

• Tribological Studies of Si and Related Materials 

Virgin, treated/coated silicon; polysilicon films and SiC film 

• Bioadhesion Studies 

Surface modification approaches to improve bioadhesion 

• Device Level Studies 

Nanotribological characterization of digital micromirror devices (DMD) 

• Hierarchical Nanostructures for Superhydrophobicity, self cleaning and low 

adhesion (Lotus Effect) 


Background 

Definition of MEMS/NEMS and characteristic dimensions 

MEMS - characteristic length less than 1 mm, 

larger than 100 nm 

NEMS - less than 100 nm 

Human hair 

50-100 μm 

500 nm 

DMD 

12 μm 

Quantum-dots transistor 

300 nm 

Red blood cell 

8 μm 

Molecular gear 

10 nm-100 nm 

SWNT chemical sensor 

2 nm 

C atom 

0.16 nm 

DNA 

2.5 nm 

0.1 1 10 100 1000 10000 100000 

Size (nm) 

Characteristic dimensions in perspective 

B. Bhushan, Springer Handbook of Nanotechnology, Springer, 2 nd ed. (2007) 


Examples of MEMS/NEMS and BioMEMS/NEMS 

shuttle 

springs 

gears and pin joint 

Microgear unit can be driven at speeds up 

to 250,000 RPM. Various sliding comp. are 

shown after wear test for 600k cycles at 

1.8% RH (Tanner et al., 2000) 

Microengine driven by electrostatically-actuated 

comb drive 

Sandia Summit Technologies (www.mems.sandia.gov) 


Stuck comb drive

Microfabricated commercial MEMS components 

5 


The generating points of friction and wear due to interaction of 

a biomolecular layer on a synthetic microdevice with tissue 

(Bhushan, Lee et al., 2006) 


6

Need to address nanotribology and nanomechanics issues 

• The nanotribology and nanomechanics problems can drastically 

compromise device performance and reliability. To solve these 

problems, there is a need to develop a fundamental understanding 

of adhesion, friction/stiction, wear and the role of surface 

contamination and environment in MEMS/NEMS and 

BioMEMS/NEMS. This can be done by studying 

 

 

 

 

 

Approach 

Nanotribology and nanomechanics of MEMS/NEMS materials 

Lubricant methods for MEMS/NEMS 

Bioadhesion Studies 

Development of superhydrophobic surfaces 

Device level studies 

• Use an AFM/FFM for imaging and to study adhesion, friction, scratch and 

wear properties of materials and lubricants, which better simulates 

MEMS/NEMS and BioMEMS/BioNEMS contacts 

• Develop and employ techniques to measure tribological phenomena in 

devices 

B. Bhushan et al., Nature 374, 607 (1995); B. Bhushan, Handbook of Micro/Nanotribology, second ed., CRC Press, 1999; 

B. Bhushan, Introduction to Tribology, Wiley, NY, 2002; B. Bhushan, Springer Handbook of Nanotechnology, 2 nd ed., 2007; 

B. Bhushan, Nanotribology and Nanomechanics – An Introduction, Springer, 2005. 


Lessons From Nature (Biomimetics) 

Biomimetics 

• Biomimetics means mimicking biology or nature. It is derived from a 

Greek word “biomimesis.” Other words used include bionics, biomimicry 

and biognosis. 

• Biomimetics involves taking ideas from nature and implementing them in 

an application. 

• Nature has gone through evolution over 3.8 billion years. It has evolved 

objects with high performance using commonly found materials. 

• Biological materials have hierarchical structure, made of commonly 

found materials. 

• It is estimated that the 100 largest biomimetic products had generated 

$1.5 billion over 2005-08. The annual sales are expected to continue to 

increase dramatically. 

M. Nosonovsky and B. Bhushan (2008), Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, 

and Biomimetics, Springer-Verlag, Heidelberg, Germany; B. Bhushan (2007), Springer Handbook of Nanotechnology, second ed., 

Springer-Verlag, Heidelberg, Germany; B. Bhushan, Phil. Trans. R. Soc. A 367, 1445-1486 (2009). 


8

Montage of some 

examples from nature. 

B. Bhushan, Phil. Trans. R. Soc. A 367, 1445-1486 (2009).). 


9

Experimental 

Atomic force/Friction force microscope (AFM/FFM) 

• At most interfaces of technological relevance, contact occurs at 

numerous asperities. It is of importance to investigate a single 

asperity contact in the fundamental tribological studies. 

Engineering Interface 

Tip - based microscope allows 

simulation of a single asperity contact 

• Nanotribological studies are needed 

To develop fundamental understanding of interfacial phenomena 

on a small scale 

 

To study interfacial i phenomena in micro- or nanostructures t and 

performance of ultra-thin films used in MEMS/NEMS 

components 


Tribological Studies of Si and Related Materials 

Macroscale friction and wear performance of silicon 

and effect of ion implantation 

Reciprocating sliding tests against an alumina ball at 1 N load. 

V refers to virgin silicon. S and P correspond to doped single-crystal 

and polycrystalline silicon. Ion energy used was 200 keV. 

B. K. Gupta, B. Bhushan et al., ASME J. Tribol. 115, 392 (1993); B. K. Gupta, B. Bhushan et al., Tribol. Trans. 37, 601 (1994) 


Scratch, wear and nanoindentation of virgin 

and treated/coated silicon 

Microscale scratch tests using a diamond tip in an AFM 

B. Bhushan and V. N. Koinkar, J. Appl. Phys. 75, 5741 (1994) 


Friction, scratch, wear and nanoindentation of 

polysilicon films and SiC film 

• Polysilicon films, undoped and doped are commonly used as 

MEMS materials 

• Silicon-based MEMS devices lack high-temperature capabilities 

with respect to both mechanical and electrical properties 

Density 

Hardness 

Elastic 

Fracture 

Thermal 

Coeff. of 

Melting Band- 

(kg/m 3 ) (GPa) modulus toughness conductivity thermal point gap 

(GPa) (MPa m 1/2 ) (W/m K) expansion ( ο C) (eV) 

(x 10 -6 / ο C) 

• SiC is being gpursued as a material for high-temperature 

microsensor and microactuator applications based on its 

successful use in high-power devices 

Sample 

β-SiC 3210 23.5-26.5 440 4.6 85-260 4.5 - 6 2830 2.3 

Si(100) 2330 9-10 130 0.95 155 2 – 4.5 1410 1.1 

Selected bulk properties of 3C SiC and Si(100) 


AFM 3D maps and average 2D profiles of 

scratch marks on various samples 

B. Bhushan, Tribology Issues and Opportunities in MEMS, Kluwer, 1998; S. Sundararajan and B. Bhushan, Wear 217, 251 (1998) 


Summary of tribological studies of MEMS/NEMS materials 

• Tribological properties of silicon are inadequate 

• Ion implantation ti and oxidation of silicon improve the 

tribological properties of silicon 

• SiC exhibits significantly better tribological properties than 

silicon-based materials and is a good candidate for 

MEMS/NEMS devices 


Bioadhesion Studies 

• Study surface modification approaches - nanopatterning and 

chemical linker method to improve adhesion of biomolecules on 

silicon based surfaces. 

B. Bhushan et al., Acta Biomaterialia 1, 327 (2005) ; ibid 2, 39 (2006); S. C. Lee et al., J. Vac. Sci. Technol. B 23, 1856 (2005) ; 

D. Tokachichu and B. Bhushan, IEEE Trans. Nanotech. 5, 228 (2006); E. Eteshola et al., J. Royal Soc. Interf. 5, 123 (2008); B. 

Bhushan et al., J. Royal Soc. Interf. 5(in press) 


Sample preparation 

STA: Streptavidin 

t APTES:Aminopropyltriethoxysilane 

NHS: N-hydroxysuccinimido 

BSA: Bovine serum albumin 


Schematic representation of deposition of streptavidin (STA) by chemical 

linker method 


Adhesion measurements in PBS with functionalized tips 

Patterned silica surface exhibits higher adhesion compared to 

unpatterned silica surface. Biotin coated surface exhibits even higher 

adhesion. 


Device Level Studies 

Device level studies - digital micromirror devices (DMD) 

AFM images of the arrays which were 

removed by ultrasonic method 


Surface height 

ht 

The stuck mirror can be identified and removed by AFM. 

“Hard” stuck micromirror 

H. Liu and B. Bhushan, Ultramicroscopy 100, 391 (2004) 


The adhesive force of FP larger than no FP region on the landing site. 

Roughness and adhesion of landing sites 


Weak bonds exist 

close to the 

uncovered sites 

Wear could initiate if 

contact occurs at the 

defects sites 

PFDA delaminated 

from the interface 

Formation of high energy surface 

increases the water adsorption, 

which in turn leads to large adhesion 

Assembled 

molecules 

Defects 

in PFDA 

Uncovered 

sites 

Residual Molecular 

head groups 

fragments 

Water 

molecule 

Mechanisms for Wear and Stiction 


The “soft” stuck micromirror (S) contains the debris at the edges 

“Soft” Stuck Micromirror 

H. Liu and B. Bhushan, J. Vac. Sci. Technol. A 22, 1388 (2004) 


“Soft” stuck mechanisms 


H. Liu and B. Bhushan, Nanotechnology 15, 1246 (2004) 


Hiearchical Nanostructures for Superhydrophobicity, 

self-cleaning and low adhesion 

One of the crucial property p in wet 

environments is non-wetting or 

superhydrophobicity and self cleaning. 

These surfaces are of interest in various 

applications, e.g., self cleaning windows, 

windshields, exterior paints for buildings, 

navigation-ships and utensils, roof tiles, 

textiles and reduction of drag in fluid flow, 

e. g. in micro/nanochannels. Also, 

superhydrophobic surface can be used for 

energy conservation and energy 

conversion such as in the development elopment of 

a microscale capillary engine. 

Reduction of wetting is also important in 

reducing meniscus formation, 

consequently reducing stiction. 

SEM of Lotus leaf showing bump structure. 

Various natural surfaces, including various 

leaves, e. g. Lotus, are known to be 

superhydrophobic, due to high roughness 

and the presence of a wax coating 

(Neinhuis and Barthlott, 1997) 

NY Times, 1/27/05; ABCNEWS.com, 1/26/05; Z. Burton and B. Bhushan, Ultramicroscopy 106, 709 (2006); B. Bhushan and Y. C. Jung, 

Nanotechnology 17, 2758 (2006); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008) 


Rolling off liquid droplet over superhydrophobic Lotus leaf 

with self cleaning ability 


Roughness optimization model for superhydrophobic and self 

cleaning surfaces 

Complete wetting 

Composite interface 

In fluid flow, another property of 

interest is contact angle 

hysteresis (θ H ) 

α : Tilt angle 

Cassie-Baxter equation: 

cosθ 

= R f cosθ 

− f 

Droplet of liquid in contact with 

f 

SL 0 LA 

a smooth and rough surface 

Wenzel’s equation: 

cos 

θ 

= R 

cos 

θ 

R f o 

θ 

H 

= θ 

adv 

− θ 

rec 

R 

≈ 

f 

1− 

f 

LA 

2( R 

(cosθθ 

f 

rec0 

cosθ 

for high contact angle 

(θ 180°) 

0 

− cosθθ 

f 

f 

= Rf 

cos θ0 − fLA( Rf 

cosθ0 

+ 1) Increase in f LA and reduction 

http://lotus-shower.isunet.edu/the_lotus_effect.htm 

+ 1) 

in R f decrease θ H 

M. Nosonovsky and B. Bhushan, Microsyst. Tech. 11, 535 (2005); ibid, 231 (2006); Microelectronic Eng. 84, 387 (2007); Ultramicroscopy 107, 969 

(2007); Nano Letters 7, 2633 (2007); J. Phys.: Condens. Matter 20, 225009 (2008); US Patent pending (2005); Y.C. Jung and B. Bhushan, 

Nanotechnology 17, 4970 (2006); B. Bhushan and Y.C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008) 


adv0 

)

Structure t of ideal hierarchical surface 

• Based on the modeling and observations made on leaf surfaces, hierarchical 

surface is needed d to develop composite interface with high h stability. 

• Proposed transition criteria can be used to calculate geometrical parameters for 

a given droplet radius. For example, , for a droplet on the order of 1 mm or 

larger, a value of H on the order of 30 μm, D on the order of 15 μm and P on the 

order of 130 μm is optimum. 

• Nanoasperities should have a small pitch to handle nanodroplets, less than 1 

mm down to few nm radius. The values of h on the order of 10 nm, d on the 

order of 100 nm can be easily fabricated. 


Fabrication and characterization of hierarchical surface 

Fabrication of microstructure 

• Microstructure 

Replication of Lotus leaf and micropatterned silicon surface using 

an epoxy resin and then cover with the wax material 

B. Bhushan et al., Soft Matter 4, 1799 (2008); Appl. Phys. Lett. 93, 093101 (2008); Ultramicroscopy (in press); Langmuir 25, 1659-1666 (2009); 

Koch et al., Soft Matter 5, 1386-1393 (2009) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Fabrication of nanostructure and hierarchical structure 

Recrystallization of wax tubules 

• Nanostructure 

Self assembly of the Lotus wax deposited by thermal evaporation 

• Expose to a solvent in vapor phase for the mobility of wax molecules 

• Hierarchical structure 

Lotus and micropatterned epoxy replicas and covered with the tubules of Lotus wax 

B. Bhushan et al., Soft Matter 4, 1799 (2008); Appl. Phys. Lett. 93, 093101 (2008); Ultramicroscopy (in press); Langmuir 25, 1659-1666 (2009); 

Koch et al., Soft Matter 5, 1386-1393 (2009) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Static contact angle, contact angle hysteresis, tilt angle and adhesive force on 

various structures 

• Nano- and hierarchical structures with tubular wax led to high static contact 

angle of 167º and 173º and low hysteresis angle on the order of 6º and 1º. 

• Compared to a Lotus leaf, hierarchical structure showed higher static 

contact angle and lower contact angle hysteresis. 

B. Bhushan, Y. C. Jung, A. Niemietz, and K. Koch, Langmuir (in press) 


Self-cleaning efficiency of various surfaces 

• As the impact pressure of the droplet is zero or low, most of particles on 

nanostructure were removed by water droplets, resulting from geometrical scale 

effects. 

• As the impact pressure of the droplet is high, h all particles which h are sitting at the 

bottom of the cavities between the pillars on hierarchical structure were removed by 

the water droplets. 


Summary of nanotribology of bioadhesion and device level studies as 

well as hierarchical surfaces 

• Bioadhesion studies 

Adhesion between silica surfaces and biomolecules using chemical linker 

method is stronger than by direct adsorption 

• Device level studies 

Wear of the SAMs lubricant at the defects region can lead to the increase of 

surface energy which causes the increase of adhesion and lead to “hard” 

stiction. 

Micromirror sidewall contamination particles could cause micromirror “soft” 

stiction. 

• Hierarchical surfaces 

Optimum roughness distribution can be used to generate superhydrophobic 

surfaces. 


Acknowledgements 

• Financial support has been provided by the National Science Foundation 

(Contract No. ECS-0301056 ), the Nanotechnology Initiative of the National 

Institute of Standards and Technology in conjunction with Nanotribology 

Research Program (Contract No. 60 NANB1D0071), and Texas Instruments, 

Intel Corp and Nanochip Inc. 

• Polysilicon and SiC work was performed in collaboration with Prof. M. 

Mehregany and Dr. C. A. Zorman at Case Western Reserve University 

• The BioMEMS/BioNEMS studies were carried out in collaboration with Prof. 

S. C. Lee of OSU Medical School and Prof. D. Hansford of Biomedical Eng. 

• DMD chips were supplied by Dr. S. Joshua Jacobs of Texas Instruments

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

Create successful ePaper yourself

Delete template?

Save as template?