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Surface Forces in Nanomechanical Systems: Living on the Edge. J Provine Stanford University 2012-01-11 Fermilab Colloquium. Outline. Scaling in the micro/nanometer range Introduction to several surface effects Nanoelectromechanical Switches Application As a nanoprobe

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surface forces in nanomechanical systems living on the edge

Surface Forces in Nanomechanical Systems: Living on the Edge

J ProvineStanford University

2012-01-11

Fermilab Colloquium

outline
Outline
  • Scaling in the micro/nanometer range
  • Introduction to several surface effects
  • Nanoelectromechanical Switches
    • Application
    • As a nanoprobe
    • Device design for probing surface forces
  • Conclusion
outline1
Outline
  • Scaling in the micro/nanometer range
  • Introduction to several surface effects
  • Nanoelectromechanical Switches
    • Application
    • As a nanoprobe
    • Device design for probing surface forces
  • Conclusion
a few quick words on scaling
A few quick words on scaling
  • We live in the m-cm world (100to 10-2m)
  • MicroElectroMechanical Systems (MEMS) and CMOS electronics circa 1990 1µm (10-6m)
  • Current CMOS, thin film optical coatings, NEMS 10nm (10-8m)
  • Carbon Nanotubes, atomic layer deposition coatings, self assembled monolayers 1nm (10-9m)
  • Lattice constant of Si 5.4A (10-10m)
  • Fermilab…
the dominance of surface effects
The Dominance of Surface Effects

Volume

4/3  r3

Surface Area

6  r2

Surface Area:Volume

1/r

As the size of an object shrinks, the surface affects become more dominant because the object is becoming “all surface.”

outline2
Outline
  • Scaling in the micro/nanometer range
  • Introduction to several surface effects
  • Nanoelectromechanical Switches
    • Application
    • As a nanoprobe
    • Device design for probing surface forces
  • Conclusion
some surface effects in nanodevices
Some surface effects in nanodevices
  • Photonics effects
  • Adhesion (geckos)
  • Nourredine smith wear/friction
  • Casimir Force
surface effects in photonics
Surface Effects in Photonics

1. Make any material a good optical material

2. Get at the unique optical properties of specific materials

Various unique optical material properties can be explored and exploited now because of great materials understanding.

Polariton Modes

Kerr Effect

Birefringence

Photoelectric transduction

  • New ways to get excellent optical performance from a wide range of materials.
  • Photonic Crystal and Subwavelength Grating design for allows a very wide range of materials to provide desired performance.
pcs come in many flavors
Excellent test bed for some deep physics experiments (QED, surface physics, etc.)

Telecom and Photonic circuits.

Slow light.

PCs come in many flavors

Lin, et al, 2003

Kuchinsky, et al, 2002

broadband reflector applications
Broadband Reflector Applications
  • High temperature, high power handling.
  • CMOS compatible and integrable processing.

M.C.Y. Huang, Y. Zhou,

and C. Chang-Hasnain,

Feb. 2007

I. Jung, S. Kim, O. Solgaard, Trans. 2007

monolithic si photonic crystal slab
Monolithic Si Photonic Crystal Slab

Monolithic photonic crystal

Slab photonic crystal

Dielectric stack (DBR)

materials for pc
Materials for PC

20nm (2%) Increase

20nm (5%)

Increase

  • Extensive testing has been done for particular materials (Si, poly-Si, SiN, SiO2)
  • But the key is ANY DIELECTRIC can be used to design PCs.
  • Strong wavelength dependent guided or reflected modes can be created in materials to suit specific applications.

Polysilicon thickness change

Air gap thickness change

10nm (3%)

Increase

0.2 (5%) Increase

Refractive index change

Hole radius

slide13

PC Fiber Tip Sensor Applications

  • Biological, chemical, and mechanical sensors (such as accelerometers) at the end of an optical fiber can be useful for control and security applications
  • The small size (125 µm diameter) enables them to penetrate tissue or veins for medical applications
  • PCs at the tip of fibers can be used both for free-space and inline applications as a reflector, polarizer and filter
fiber tip assembly
Fiber Tip Assembly

Pt weld of PC

Direct weld of PC

Utilize direct weld of PC with ion beam as opposed to Pt weld to study impact of weld technique.

slide15

Broadband source

Power meter

3dB coupler

Optical spectrum analyzer

Fiber

PC

Water/Solvent

Index Sensing Experiment

Index Sensing Experiment

Experimental data

slide16

Refractive Index Sensing

Isopropanol concentration increase in increments of 30ml in DI Water of 150ml

Refractive index calculated from volume concentration

  • Responsivity = DR.I./Dl = 0.04768 [nm-1]
  • Sensitivity ≈ 4.8 x10-5 [pm-1]
    • Using an optical system (tunable laser, OSA) with picometer resolution
    • Comparable to FBG refractive index sensors [W. Liang, A. Yariv et al, APL 2005]

IEEE Nanophotonics 2009.

slide17

Temperature Sensing Experiment

Temperature Sensing Experiment

Experimental data

slide18

Temperature Sensing

Temperature measurement taken while cooling from 80°C to room temperature

  • Responsivity = Dtemp/Dl = 16.0858 [°C/nm]
  • Sensitivity ≈ 0.016 [°C/pm]
    • Using an optical system (tunable laser, OSA) with picometer resolution
    • Almost an order better sensitivity than a FBG temperature sensor [A. D. Kersey et al., Fiber Grating Sensors Invited Paper, JLT 1997]

LEOS annual meeting 2009

impact applications

[blog.mlive.com]

[Onur Kilic]

[www.cnconveyorbelt.com]

[www.tommcmahon.net]

[www.blueparrotevents.coml]

[www.reuk.co.uk]

[www.gallagher.com]

[newswhitehouse.com]

[www.af.mil]

Impact & Applications
  • Harsh environments
  • High voltage, high power machinery
  • High temperature
  • Motion/Vibration/Explosion detection
  • Acoustic sensing
  • Gyro/Acceleration
  • Bio/chemical detection
  • Biological/chemical agents
  • Fluid, Gas sensing
    • Structural Health monitoring
  • Combustion chambers, Turbines
  • Aircraft, wind turbines, bridges, dams, oil wells, pipelines
  • Smart structures: Integrated fiber-optic sensors (aging, vibrations)
accessing a particular optical property in a novel material sic
Accessing a particular optical property in a novel material: SiC

Spitzer, et al, Phys Rev., 1959.

SiC coating

The optical properties of SiC have also been studied for a long time. Recently the interest has expanded because of the extremely strong mid-IR Phonon Polariton resonance.

Si beam

1m

device fabrication
Device Fabrication

SiO2

SiC

LPCVD SiC @ 800C

LPCVD SiO2 for hard mask

Bulk Si

Transfer photolithographic mask through SiO2 and SiC by RIE

RIE of SiC is HBr/HCl

Bulk Si

Release membrane

by XeF2 etch

Remove hard mask

with HF dip

80

sidewall

extraordinary transmission
Extraordinary Transmission

Polariton Gap

t = 4m

a = 10.4m

d = 5.6m

Hole Array

Patterned Film

Unpatterned

Film

a

d

t

Theroretical simulation with FD3D Finite Difference Time Domain code.

extraordinary transmission1
Extraordinary Transmission

Polariton Gap

Polariton Gap

Hole Array

Patterned Film

Unpatterned

Film

t = 4m

a = 10.4m

d = 5.6m

t = 1.5m

Polycrystalline SiC

Experimental Data from FTIR

Unpatterned

Film

slide24

Extraordinary Transmission

Polariton Gap

Polariton Gap

Hole Array

Patterned Film

d=5.6m

Unpatterned

Film

t = 4m

a = 10.4m

d = 5.6m

t = 1.5m a = 10m

Polycrystalline SiC

Experimental Data from FTIR

Unpatterned

Film

slide25

Extraordinary Transmission

Polariton Gap

Polariton Gap

Hole Array

Patterned Film

d=5.6m

d=3.9m

Unpatterned

Film

t = 4m

a = 10.4m

d = 5.6m

t = 1.5m a = 10m

Polycrystalline SiC

Experimental Data from FTIR

Unpatterned

Film

Provine, et al, OMEMS 2007

slide26

Reflection Spectra

t = 1.5m a = 10m

Polycrystalline SiC

Experimental Data from FTIR

d=3.1m

d=3.9m

d=4.8m

d=5.6m

ongoing experiments a true meta material
Ongoing Experiments: A True Meta-Material
  • Selective metal surface coatings. (Catrysse and Fan, Physical Review B, 2007)
adhesion at the nanoscale
Adhesion at the Nanoscale

Work between Autumn Lab (Lewis & Clark) &

Kenny Lab (Stanford)

casimir force in metals
Casimir Force in Metals
  • Uncharged metals (equipotential) will still attract.
  • Purely a quantum & geometrical effect.
  • Hotly debated and studied because of the relation to the cosmical constant.
  • At the nanoscale starts to have appreciable forces.

Valid at 0 K and vacuum.

casimir effect in pt nanobeams
Casimir effect in Ptnanobeams

Nanobeam constructed from a single sheet of evaporated Pt (equipotential).

Slices are made with ion beam and then released from unlying Si with XeF2.

Crystal orientation makes this a challenging study.

outline3
Outline
  • Scaling in the micro/nanometer range
  • Introduction to several surface effects
  • Nanoelectromechanical Switches
    • Application
    • As a nanoprobe
    • Device design for probing surface forces
  • Conclusion
application a downside of scaling
Application: a downside of scaling
  • As modern CMOS electronics scales to smaller and smaller devices, the power consumption rising rapidly.
  • Because of the ubiquitous computing ongoing (and being proposed) the amount of energy going to servers and even personal computing is becoming appreciable.

E. J. Nowak, IBM J. Res & Dev. 2002

a solution back to the future
A Solution: Back to the Future
  • Mechanical computing can be an answer to this issue because it can deliver zero off-state power consumption.
  • Additional benefits:
    • Radiation hard operation
    • Lower thermal dependence
  • Is this a CMOS killer? NO
  • But it can have many applications and certainly help with energy consumption. (see for instance Chen et al FPGA 2010.)

Babbage Analytical Engine c 1877

examples of nem switches metallic structures
Examples of NEM Switches:Metallic Structures

Vertically actuated W

Colorado, Boulder

Laterally actuated Ru

Sandia National Labs

Vertically actuated Ni

KAIST

examples of nem switches conducting ceramics
Examples of NEM SwitchesConducting Ceramics

Laterally actuated TiN

Stanford

Vertically actuated TiN

KAIST

examples of nem switches semiconducting structures
Examples of NEM Switches:Semiconducting Structures

Vertically actuated W coated SiGe

California, Berkeley

Vertically actuated poly-Si

KAIST

arbitrary nem logic design methodologies
Arbitrary NEM Logic Design Methodologies
  • Only 6T relays required for all 3 generations
  • Our lateral 6T elemental logic block
  • New elemental block allows new design methodologies

G

the logic element 6t relay
The Logic Element: 6T Relay

Source 1

Gate 1

Isolation

Beam

Drain

Source 2

Gate 2

=Insulating Layer

(eg, Hafnium Oxide)

=Mold Layer

(eg, Polysilicon)

=Conductive Layer

(eg, TiN or Pt)

y device process flow
Y-Device Process Flow

AA’ BB’

(a) Deposit 1um polysilicon on 1.5um oxide.

Oxide

Substrate

(b) Pattern polysilicon

(mask 1).

y device process flow1
Y-Device Process Flow

AA’ BB’

(c) Deposit 20nm HfO2 via ALD.

(d) Blanket etch of HfO2.

y device process flow2
Y-Device Process Flow

AA’ BB’

(e) Deposit 20nm Pt or TiN via ALD.

(f) Etch Pt or TiN and pattern pads (mask 2).

y device process flow3
Y-Device Process Flow

AA’ BB’

(g) Pt or TiN wet etch for sidewall isolation (mask 3).

(h) Release in 49% HF followed by CPD.

y device switching properties
Y-Device Switching Properties

Current Flow

(Source to Drain)

No Beam Current

[S. Lee et al., Transducers 2011]

ald platinum coated relay
ALD Platinum Coated Relay
  • Large pull-out variation!
  • Adhesion force variations: asperity deformation

Single device,

multiple cycles

other issues
Other issues
  • Desired improvement in
    • Total Lifetime
    • Uniformity between devices (same chip)
    • Uniformity between devices (different wafers)
  • Concerns
    • Fabrication tolerance
    • Adhesion forces
    • Contact Resistance
nem relays with improved contact properties
NEM Relays with improved contact properties

Controlling the contact mechanism and apparent contact area:

Flexible Contact Surface

Existing designs

Before pull-in

After pull-in

Point contact

Overdrive voltage

surface-surface contact

Point-surface contact mechanism with limited asperity-asperity contact

Flexible surface-surface contact

nem relays with improved contact properties1
NEM Relays with improved contact properties

Mechanically robust designs with large overdrive voltage:

nem relays with small footprint
NEM Relays with Small Footprint

Using the coating as the main structural material:

200nm process and 50nm coating:

Electrode length: 5µm

Beam length : 5µm

Source-gate gap: 100nm

TiN coating: 50nm

nem relays 6t relays
NEM Relays: 6T Relays

6T relays are sensitive to fabrication tolerances:

500nm process and 20nm coating:

Beam length: 21um

Gate length: 19um

Coating thickness: 20nm

Beam-gate gap: 560nm

Source-drain gap: 460nm

Source-drain tol.: 10nm (2%)

FEM simulations:

First contact : 23V

Second contact: > 37V

V = 37V

Result: Extensive overdrive often necessary.

nem relays new designs 6t
NEM Relays: New Designs (6T)

Relays with flexible source-drain:

FEM Simulations:

Displacements (V = 5V)

nem relays new designs 6t1
NEM Relays: New Designs (6T)

Relays with flexible source-drain:

FEM Simulations:

Contact pressure (V = 5V)

Result: Overdrive minimized for relay.

nem relays new designs 6t2
NEM Relays: New Designs (6T)

Relays with flexible source-drain:

FEM Simulations:

switch vs nanoprobe
Switch vs. Nanoprobe
  • While the switching application is important and interesting, surface affects mean that simultaneously:
    • We need to understand surface forces more accurately to optimize our switches
    • The switches can operate as excellent nanoprobes to determine what is happening.
      • Different materials
      • Different ambient conditions
      • Different designs to isolate particular material properties
nem relays reliability
NEM Relays: Reliability

Material and surface characterization:

Young’s modulus

Structural and air damping

Force

Displacement

nem relays reliability1
NEM Relays: Reliability

Material and surface characterization:

Fracture stress

Adhesion force/Young’s modulus/Initial stress

nem relays reliability2
NEM Relays: Reliability

Material and surface characterization: Adhesion

Minimum gap

Stiction to substrate

Stiction to side walls

Maximum length

outline4
Outline
  • Scaling in the micro/nanometer range
  • Introduction to several surface effects
  • Nanoelectromechanical Switches
    • Application
    • As a nanoprobe
    • Device design for probing surface forces
  • Conclusion
take home messages
Take Home Messages
  • In general, nanofabrication has “grown up” to the point we can make almost anything.
    • Lots of materials
    • A wide ranges of sizes (mm to A)
  • While this opens up a wide range of new applications, it just as quickly allows (necessitates?) new science to be explored.
acknowledgements
Acknowledgements
  • NEMS Logic Team (in particular Kamran Shavazipur)
  • Stanford
    • Roger Howe Group
    • Philip Wong Group
    • Olav Solgaard Group
  • UC Berkeley
    • RoyaMaboudian Group
    • Tsu-Jae King Liu Group
  • Center for Interfacial Engineering of MEMS (CIEMS)
  • DARPA and NSF for funding