Micro-Electro-Mechanical Systems

-The Future Technology, but Today’s choice

Presented by… Vinayak HegdeGuide: Mrs. Priti M

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AIM OF MY PRESENTATION

To familiarize what the MEMS TECHNOLOGY is all about

To explain about Microfabrication Process.

Applications of the MEMS in various fields.

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Outline of My PresentationIntroductionHistorical Background

(MEMS Evolution)

Preparation Process of MEMS(Fabrication Process)

Applications of MEMS(Fields where MEMS Used)

Interrelationship between MEMS and Nano(Future Scope of MEMS)

Conclusion

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Introduction

What is MEMS Technology?MEMS technology is based on a number of tools and

methodologies, which are used to form small structures with dimensions in the micrometer scale

MEMS fabrication approach that conveys the advantages of miniaturization, multiple components, and microelectronics to the design and construction of integrated Electromechanical systems

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Introduction Conti…What are MEMS?

• Micro - Small size, microfabricated structures

• Electro - Electrical signal /control ( In / Out )

• Mechanical - Mechanical functionality (Out/ In )

• Systems - Structures, Devices, Systems controlsWhat is the size of MEMS?

They range in size from the sub micron level to the millimeter level, and there can be any number, from a few to millions, in a particular system.

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MEMS Scaling

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Building Blocks In MEMS

How MEMS are prepared? There are three basic building blocks in MEMS technology.

1. Deposition: The ability to deposit thin films of material on a substrate.

2. Lithography: To apply a patterned mask on top of

the films by photolithograpic imaging.

3. Etching: To etch the films selectively to the mask.

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MEMS Deposition TechnologyMEMS deposition technology can be classified in two groups:

1. Depositions that happen because of a chemical reaction: Chemical Vapor Deposition (CVD) Electrodeposition Epitaxy Thermal oxidation

2. Depositions that happen because of a physical reaction: Physical Vapor Deposition (PVD) Casting

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MEMS Lithography Technology

MEMS lithography technology can be classified in two groups:1. Pattern Transfer2. Lithographic Module

a. Dehydration bake and HMDS primeb. Resist spin/spray and Soft bakec. Alignment, Exposured. Post exposure bake and Hard bakee. Descum

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MEMS Etching Technology

There are two classes of etching process:

1. Wet etching: The material is dissolved when immersed in a chemical solution.

2. Dry etching: The material is sputtered or dissolved using reactive ions or a vapor phase etchant.

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Microfabrication Process

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PhotolithographyClean wafer : to remove particles on the surface as well as any traces of organic, ionic,

and metallic impuritiesDehydration bake: to drive off the absorbed water on the surface Coating

Coat wafer with adhesion promoting filmCoat with photoresist

Soft bake : to drive off excess solvent and to promote adhesionExposurePost exposure bake: to suppress standing wave-effectDevelop, Clean, Dry Hard bake: to harden the PR and improve adhesion to the substrate

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Photolithography

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Additive ProcessesOxidation

Thermal Oxidation of Silicon is done in a furnace in wet or dry conditions

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Additive Processes

Doping

Dopants : N type (Phosphorous, Arsenic), P type (Boron)

Doping Methods1. Diffusion

Dopants are diffused thermally into the substrate in furnace at 950 – 1280 0C.

It is governed by Fick’s Laws of Diffusion.

Dopant ions bombarded into targeting substrate by high energy.

Ion implantation are able to place any ion at any depth in sample.

2. Ion Implantation

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Additive ProcessesPhysical Vapor Deposition (PVD)

1. EvaporationDeposition is achieved by evaporation or sublimation of heated metal onto substrate.

2. SputteringSputtering is achieved by accelerated inert ion by DC drive in plasma through potential gradient to bombard metallic target.

Then the targeting material is sputtered away and deposited onto substrate placed on anode.

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Additive ProcessesPhysical Vapor Deposition (PVD)

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Additive ProcessesChemical Vapor Deposition (CVD)

Materials deposited: Polysilicon, silicon nitride, silicon oxide, silicon carbide etc.

How does CVD Work?Gaseous reactants are introduced into chamber at elevated temperatures.Reactant reacts and deposits onto substrate

Types of CVDLPCVD (Low Pressure CVD), PECVD (Plasma Enhanced CVD)

Salient FeaturesCVD results depend on pressure, gas, and temperatureCan be diffusion or reaction limitedVaries from film composition, deposition rate and electrical and mechanical properties

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Subtractive ProcessesDry Etching

Dry Chemical EtchingHF Etching

HF is a powerful etchant and hence, highly dangerous.

XeF2 Etching

2XeF2+Si→2Xe+SiF4 Isotropic etching (typically 1-3µm/min) Does not attack aluminum, silicon dioxide, and silicon nitride

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Subtractive Processes

Reaction MechanismProduce reactive species in gas-phase Reactive species diffuse to the solidAdsorption, and diffuse over the surface Reaction Desorption Diffusion

Dry Etching

Plasma Etching

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Subtractive Processes

Dry Etching

Deep Reactive Ion Etching (DRIE) A very high-aspect-ratio silicon etch method

DRIE Etched Pillars

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Subtractive Processes

Wet Etching

Isotropic Wet Etching

Isotropic etchants etch in all directions at nearly the same rate.

Commonly use chemical for Silicon is HNA (HF/HNO3/Acetic Acid) This results in a finite amount of undercutting

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Subtractive Processes

Wet Etching

Anisotropic Wet Etching

Anisotropic etchants etch much faster in one direction than in another.

Etchants are generally Alkali Hydroxides (KOH, NaOH, CeOH

Reaction :Silicon (s) + Water + Hydroxide Ions → Silicates + Hydrogen

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Metal Patterning

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Surface Micromachining

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MEMS Packaging

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Example: An insulin pump fabricated by classic MEMS technology

1. Pumping membrane 2. Pumping chamber

3. Inlet 4. Outlet

5. Large mesa 6. Upper glass plate

7. Bottom glass plate 8. patterned thin layer (for improved fluidics)

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MEMS Applications Micro-engines –Micro Reactors, Vibrating Wheel

Inertial Sensors –Virtual Reality Systems

Accelerometers –Airbag Accelerometer

Pressure Sensors –Air Pressure Sensors

Optical MEMS –Pill Camera

Fluidic MEMS -Cartridges for Printers

Bio MEMS -Blood Pressure Sensors

MEMS Memory Units -Flash Memory

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iPod Touch: Techno Sensitiveness

The two key elements of a

MEMS are: MEMS sensor, the silicon

mechanical element which senses the motion;

Interface chip, the IC which converts the motion measured by the sensor into an analog or digital signal.

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An implantable blood pressure sensor developed by

CardioMEMS

Bio MEMS Application

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MEMS Memory [Nanochip]

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MEMS driven Storage DevicesTB to PB device capacitiesMassively parallel data transfer

ratesVery fast file access times Improved reliability Smaller size and weight Device costs less than today's

devicesExcellent fit for applications to

enterprise

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Future of Magnetic Storage

HAMR-Heat Assisted Magnetic Recording or TAR -Thermally Assisted Recording

SOMA-Self Organized Magnetic Assemblies; a form of directed patterned media.

Super high coercivity storage layers (such as FePt) with stable grain sizes averaging < 2nm.

Super servos for (coarse/fine) tracking and flying height control.

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Advantages and Disadvantages

Minimize energy and materials use in manufacturing

Cost/performance advantages Improved reproducibility Improved accuracy and

reliability Increased selectivity and

sensitivity

Farm establishment requires huge investments

Micro-components are Costly compare to macro-components

Design includes very much complex procedures

Prior knowledge is needed to integrate MEMS devices

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ConclusionThe medical, wireless technology, biotechnology, computer, automotive and aerospace industries are only a few that will benefit greatly from MEMS.

This enabling technology promises to create entirely new categories of products

MEMS will be the indispensable factor for advancing technology in the 21st century

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References for MEMSIEEE Explore http://ieeexplore.ieee.org/Xplore/DynWel.jspPDF Files http://www.scribd.com/mems/

Introduction to Microengineering http://www.dbanks.demon.co.uk/ueng/MEMS Clearinghouse http://www.memsnet.org/MEMS Exchange http://www.mems-exchange.org/

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